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Effect of debond growth on stress-intensity factors in a cracked orthotropic sheet stiffened by a semi-infinite orthotropic sheet

NASA Technical Reports Server (NTRS)

Bigelow, C. A.

1986-01-01

Stress-intensity factors are determined for a cracked infinite sheet adhesively bonded to a stringer, and debonding of the adhesive layer is predicted. The stringer is modeled as a semi-infinite sheet. Adhesive nonlinearity is also included. Both the sheet and stringer are treated as homogeneous, orthotropic materials. A set of integral equations is formulated and solved to obtain the adhesive shear stresses and crack-tip stress-intensity factors. Adhesive debonding is predicted using a rupture criterion based on the combined adhesive stresses. When the crack is not under the stringer, the debond extends along the edge of the stringer. When the crack tip is beneath the stringer, the debond grows to the end of the crack, then along the edge of the stringer. Stress levels required for debond initiation decrease as the crack tip is moved beneath the stringer. With a nonlinear adhesive, the debond initiates at higher applied stress levels than in linear adhesive cases. Compared with the linear adhesive solution, modeling a nonlinear adhesive causes the stress-intensity factor to increase when the bond is assumed to remain intact but causes the stress-intensity factor to decrease when debonding is included.

Proteomic and metabolomic analyses of soybean root tips under flooding stress.

PubMed

Komatsu, Setsuko; Nakamura, Takuji; Sugimoto, Yurie; Sakamoto, Kazunori

2014-01-01

Flooding is one of the serious problems for soybean plants because it inhibits growth. Proteomic and metabolomic techniques were used to determine whether proteins and metabolites are altered in the root tips of soybeans under flooding stress. Two-day-old soybean plants were flooded for 2 days, and proteins and metabolites were extracted from root tips. Flooding-responsive proteins were identified using two-dimensional- or SDS-polyacrylamide gel electrophoresis- based proteomics techniques. Using both techniques, 172 proteins increased and 105 proteins decreased in abundance in the root tips of flood-stressed soybean. The abundance of methionine synthase, heat shock cognate protein, urease, and phosphoenol pyruvate carboxylase was significantly increased by flooding stress. Furthermore, 73 flooding-responsive metabolites were identified using capillary electrophoresis-mass spectrometry. The levels of gamma-aminobutyric acid, glycine, NADH2, and phosphoenol pyruvate were increased by flooding stress. Taken together, these results suggest that synthesis of phosphoenol pyruvate by way of oxaloacetate produced in the tricarboxylic acid cycle is activated in soybean root tips in response to flooding stress, and that flooding stress also leads to modulation of the urea cycle in the root tips.

Abscisic acid accumulation modulates auxin transport in the root tip to enhance proton secretion for maintaining root growth under moderate water stress.

PubMed

Xu, Weifeng; Jia, Liguo; Shi, Weiming; Liang, Jiansheng; Zhou, Feng; Li, Qianfeng; Zhang, Jianhua

2013-01-01

Maintenance of root growth is essential for plant adaptation to soil drying. Here, we tested the hypothesis that auxin transport is involved in mediating ABA's modulation by activating proton secretion in the root tip to maintain root growth under moderate water stress. Rice and Arabidopsis plants were raised under a hydroponic system and subjected to moderate water stress (-0.47 MPa) with polyethylene glycol (PEG). ABA accumulation, auxin transport and plasma membrane H(+)-ATPase activity at the root tip were monitored in addition to the primary root elongation and root hair density. We found that moderate water stress increases ABA accumulation and auxin transport in the root apex. Additionally, ABA modulation is involved in the regulation of auxin transport in the root tip. The transported auxin activates the plasma membrane H(+)-ATPase to release more protons along the root tip in its adaption to moderate water stress. The proton secretion in the root tip is essential in maintaining or promoting primary root elongation and root hair development under moderate water stress. These results suggest that ABA accumulation modulates auxin transport in the root tip, which enhances proton secretion for maintaining root growth under moderate water stress. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.

Modeling the Temperature Rise at the Tip of a Fast Crack

DTIC Science & Technology

1989-08-01

plastic deformation in the plastic zone, the strain rate and the temperature dependence of the flow stress have been incorporated in the determination ...of dislocation generation in the plastic zone. The stress field 1 associated with a moving elastic crack tip is used to determine the increment of...yield stress and the crack tip stress field for a given mode of the applied stress. The fracture toughness of several materials, determined

Reductions in maize root-tip elongation by salt and osmotic stress do not correlate with apoplastic O2*- levels.

PubMed

Bustos, Dolores; Lascano, Ramiro; Villasuso, Ana Laura; Machado, Estela; Senn, María Eugenia; Córdoba, Alicia; Taleisnik, Edith

2008-10-01

Experimental evidence in the literature suggests that O(2)(*-) produced in the elongation zone of roots and leaves by plasma membrane NADPH oxidase activity is required for growth. This study explores whether growth changes along the root tip induced by hyperosmotic treatments in Zea mays are associated with the distribution of apoplastic O(2)(*-). Stress treatments were imposed using 150 mm NaCl or 300 mM sorbitol. Root elongation rates and the spatial distribution of growth rates in the root tip were measured. Apoplastic O(2)(*-) was determined using nitro blue tetrazolium, and H(2)O(2) was determined using 2', 7'-dichlorofluorescin. In non-stressed plants, the distribution of accelerating growth and highest O(2)(*-) levels coincided along the root tip. Salt and osmotic stress of the same intensity had similar inhibitory effects on root elongation, but O(2)(*-) levels increased in sorbitol-treated roots and decreased in NaCl-treated roots. The lack of association between apoplastic O(2)(*-) levels and root growth inhibition under hyper-osmotic stress leads us to hypothesize that under those conditions the role of apoplastic O(2)(*-) may be to participate in signalling processes, that convey information on the nature of the substrate that the growing root is exploring.

The effect of crack blunting on the competition between dislocation nucleation and cleavage

NASA Astrophysics Data System (ADS)

Fischer, Lisa L.; Beltz, Glenn E.

2001-03-01

To better understand the ductile versus brittle fracture behavior of crystalline materials, attention should be directed towards physically realistic crack geometries. Currently, continuum models of ductile versus brittle behavior are typically based on the analysis of a pre-existing sharp crack in order to use analytical solutions for the stress fields around the crack tip. This paper examines the effects of crack blunting on the competition between dislocation nucleation and atomic decohesion using continuum methods. We accomplish this by assuming that the crack geometry is elliptical, which has the primary advantage that the stress fields are available in closed form. These stress field solutions are then used to calculate the thresholds for dislocation nucleation and atomic decohesion. A Peierls-type framework is used to obtain the thresholds for dislocation nucleation, in which the region of the slip plane ahead of the crack develops a distribution of slip discontinuity prior to nucleation. This slip distribution increases as the applied load is increased until an instability is reached and the governing integral equation can no longer be solved. These calculations are carried out for various crack tip geometries to ascertain the effects of crack tip blunting. The thresholds for atomic decohesion are calculated using a cohesive zone model, in which the region of the crack front develops a distribution of opening displacement prior to atomic decohesion. Again, loading of the elliptical crack tip eventually results in an instability, which marks the onset of crack advance. These calculations are carried out for various crack tip geometries. The results of these separate calculations are presented as the critical energy release rates versus the crack tip radius of curvature for a given crack length. The two threshold curves are compared simultaneously to determine which failure mode is energetically more likely at various crack tip curvatures. From these comparisons, four possible types of material fracture behavior are identified: intrinsically brittle, quasi-brittle, intrinsically ductile, and quasi-ductile. Finally, real material examples are discussed.

Droplet Breakup in Expansion-contraction Microchannels

PubMed Central

Zhu, Pingan; Kong, Tiantian; Lei, Leyan; Tian, Xiaowei; Kang, Zhanxiao; Wang, Liqiu

2016-01-01

We investigate the influences of expansion-contraction microchannels on droplet breakup in capillary microfluidic devices. With variations in channel dimension, local shear stresses at the injection nozzle and focusing orifice vary, significantly impacting flow behavior including droplet breakup locations and breakup modes. We observe transition of droplet breakup location from focusing orifice to injection nozzle, and three distinct types of recently-reported tip-multi-breaking modes. By balancing local shear stresses and interfacial tension effects, we determine the critical condition for breakup location transition, and characterize the tip-multi-breaking mode quantitatively. In addition, we identify the mechanism responsible for the periodic oscillation of inner fluid tip in tip-multi-breaking mode. Our results offer fundamental understanding of two-phase flow behaviors in expansion-contraction microstructures, and would benefit droplet generation, manipulation and design of microfluidic devices. PMID:26899018

Mapping the cyclic plastic zone to elucidate the mechanisms of crack tip deformation in bulk metallic glasses

NASA Astrophysics Data System (ADS)

Scudino, S.; Shahid, R. N.; Escher, B.; Stoica, M.; Li, B. S.; Kruzic, J. J.

2017-02-01

Developing damage-tolerant bulk metallic glasses (BMGs) requires knowledge of the physical mechanisms governing crack propagation. While fractography suggests that fatigue crack propagation occurs in an incremental manner, conclusive evidence of alternating crack tip blunting and resharpening is lacking. By mapping the strain fields in both the monotonic and cyclic plastic zones, it is shown that the characteristic compressive stresses required to resharpen the crack tip are developed in a BMG upon unloading. This result confirms the mechanism of fatigue crack propagation in BMGs. Broader implications of these findings are that the effect of shear banding is rather diffuse and plastic deformation ahead of a stress concentration, such as a crack tip, appears to extend well beyond the extent of visible shear bands on the sample surface.

[Effects of chlorobenzene stress on seedling growth and cell division of Vicia faba].

PubMed

Liu, Wan; Zhou, Qixing; Li, Peijun; Sun, Tieheng; Tai, Peidong; Xu, Huaxia; Zhang, Chungui; Zhang, Hairong

2003-04-01

Effects of 1, 2, 4-trichlorobenzene (TCB) stress on seedling growth, cell division and chromosomal aberration frequency of root-tip cells of Vicia faba were studied. The results indicated that the growth of the root length and mitotic index of root tip cells were successively decreased and even stopped with the increase of TCB concentrations and treatment duration. Numerical and structural chromosomal aberrations at metaphase and anaphase of root-tip cells in Vicia faba seedlings were produced by 50-300 micrograms.g-1 TCB treatment for 12-96 h. The percentage of c-mitosis, chromosomal bridge and chromosomal asymmetry array in root tip cells exposed to 50-100 micrograms.g-1 TCB for 12-24 h was up to 1.0-10.3%. The percentage of chromosomal stickness (S), chromosomal stickiness + chromosomal breakage (S + B), chromosomal stickness + chromosomal ring (S + R), chromosomal stickiness + chromosomal asymmetry array (S + A) and chromosomal stickness + chromosomal bridge (S + Be) in root tip cells reached 47.9-88.9%, and 18.1-29.6% for different kinds of chromosomal breakage at 300 micrograms.g-1 TCB for 12-96 h. Thus, the chromosomal aberration of root tip cells in Vicia faba seedlings could be used as a sensitive biomarker of monitoring soil contaminated with TCB.

Ellipsometry-like analysis of polarization state for micro cracks using stress-induced light scattering method

NASA Astrophysics Data System (ADS)

Sakata, Yoshitaro; Terasaki, Nao; Sakai, Kazufumi; Nonaka, Kazuhiro

2016-03-01

Fine polishing techniques, such as chemical mechanical polishing (CMP), are important to glass substrate manufacturing. When these techniques involve mechanical interaction in the form of friction between the abrasive and the substrate surface during polishing, latent flaws may form on the product. Fine polishing induced latent flaws in glass substrates may become obvious during a subsequent cleaning process if the glass surface is eroded away by chemical interaction with a cleaning liquid. Thus, latent flaws reduce product yield. A novel technique (the stress-induced light scattering method; SILSM) which was combined with light scattering method and stress effects was proposed for inspecting surface to detect polishing induced latent flaws. This method is able to distinguish between latent flaws and tiny particles on the surface. In this method, an actuator deforms a sample inducing stress effects around the tip of a latent flaw caused by the deformation, which in turn changes the refractive index of the material around the tip of the latent flaw because of the photoelastic effect. A CCD camera detects this changed refractive index as variations in light-scattering intensity. In this study, the changes in reflection coefficients and polarization states after application of stress to a glass substrate were calculated and evaluated qualitatively using Jones matrix-like ellipsometry. As the results, it was shown that change in the polarization states around the tip of latent flaw were evaluated between before and after applied stress, qualitatively.

Three Dimensional Numerical Simulation and Characterization of Crack Growth in the Weld Region of a Friction Stir Welded Structure

NASA Technical Reports Server (NTRS)

Seshadri, Banavara R.; Smith, Stephen W.; Newman, John A.

2013-01-01

Friction stir welding (FSW) fabrication technology is being adopted in aerospace applications. The use of this technology can reduce production cost, lead-times, reduce structural weight and need for fasteners and lap joints, which are typically the primary locations of crack initiation and multi-site fatigue damage in aerospace structures. FSW is a solid state welding process that is well-suited for joining aluminum alloy components; however, the process introduces residual stresses (both tensile and compressive) in joined components. The propagation of fatigue cracks in a residual stress field and the resulting redistribution of the residual stress field and its effect on crack closure have to be estimated. To insure the safe insertion of complex integral structures, an accurate understanding of the fatigue crack growth behavior and the complex crack path process must be understood. A life prediction methodology for fatigue crack growth through the weld under the influence of residual stresses in aluminum alloy structures fabricated using FSW will be detailed. The effects and significance of the magnitude of residual stress at a crack tip on the estimated crack tip driving force are highlighted. The location of the crack tip relative to the FSW and the effect of microstructure on fatigue crack growth are considered. A damage tolerant life prediction methodology accounting for microstructural variation in the weld zone and residual stress field will lead to the design of lighter and more reliable aerospace structures

Crack Turning Mechanics of Composite Wing Skin Panels

NASA Technical Reports Server (NTRS)

Yuan, F. G.; Reeder, James R. (Technical Monitor)

2001-01-01

The safety of future composite wing skin integral stiffener panels requires a full understanding of failure mechanisms of these damage tolerance critical structures under both in-plane and bending loads. Of primary interest is to derive mathematical models using fracture mechanics in anisotropic cracked plate structures, to assess the crack turning mechanisms, and thereby to enhance the residual strength in the integral stiffener composite structures. The use of fracture mechanics to assess the failure behavior in a cracked structure requires the identification of critical fracture parameters which govern the severity of stress and deformation field ahead of the flaw, and which can be evaluated using information obtained from the flaw tip. In the three-year grant, the crack-tip fields under plane deformation, crack-tip fields for anisotropic plates and anisotropic shells have been obtained. In addition, methods for determining the stress intensity factors, energy release rate, and the T-stresses have been proposed and verified. The research accomplishments can be summarized as follows: (1) Under plane deformation in anisotropic solids, the asymptotic crack-tip fields have been obtained using Stroh formalism; (2) The T-stress and the coefficient of the second term for sigma(sub y), g(sub 32), have been obtained using path-independent integral, the J-integral and Betti's reciprocal theorem together with auxiliary fields; (3) With experimental data performed by NASA, analyses indicated that the mode-I critical stress intensity factor K(sub Q) provides a satisfactory characterization of fracture initiation for a given laminate thickness, provided the failure is fiber-dominated and crack extends in a self-similar manner; (4) The high constraint specimens, especially for CT specimens, due to large T-stress and large magnitude of negative g(sub 32) term may be expected to inhibit the crack extension in the same plane and promote crack turning; (5) Crack turning out of crack plane in generally anisotropic solids under plane deformation has been studied; (6) The role of T-stress and the higher-order term of sigma(sub y) on the crack turning and stability of the kinked crack has been quantified; (7) Asymptotic crack-tip fields including the effect of transverse shear deformation (Reissner plate theory) in an anisotropic plate under bending, twisting moments, and transverse shear loads has been presented; (8) The expression of the path-independent J-integral in terms of the generalized stress and strain has been derived; (9) Asymptotic crack-tip fields including the effect of transverse shear deformation (Reissner shallow shell theory) in a general anisotropic shell has been developed; (10) The Stroh formalism was used to characterize the crack tip fields in shells up to the second term and the energy release rate was expressed in a very compact form.

Laser and acoustic lens for lithotripsy

DOEpatents

Visuri, Steven R.; Makarewicz, Anthony J.; London, Richard A.; Benett, William J.; Krulevitch, Peter; Da Silva, Luiz B.

2002-01-01

An acoustic focusing device whose acoustic waves are generated by laser radiation through an optical fiber. The acoustic energy is capable of efficient destruction of renal and biliary calculi and deliverable to the site of the calculi via an endoscopic procedure. The device includes a transducer tip attached to the distal end of an optical fiber through which laser energy is directed. The transducer tip encapsulates an exogenous absorbing dye. Under proper irradiation conditions (high absorbed energy density, short pulse duration) a stress wave is produced via thermoelastic expansion of the absorber for the destruction of the calculi. The transducer tip can be configured into an acoustic lens such that the transmitted acoustic wave is shaped or focused. Also, compressive stress waves can be reflected off a high density/low density interface to invert the compressive wave into a tensile stress wave, and tensile stresses may be more effective in some instances in disrupting material as most materials are weaker in tension than compression. Estimations indicate that stress amplitudes provided by this device can be magnified more than 100 times, greatly improving the efficiency of optical energy for targeted material destruction.

Effect of tip radius on the incipient plasticity of chromium studied by nanoindentation

DOE PAGES

Wu, Dong; Morris, James R.; Nieh, T. G.

2014-10-01

The onset of plasticity in Cr was investigated by nanoindentation using indenters with tip radii ranging from 60 to 759 nm. The stress for incipient plasticity was found to increase with decreasing tip radius. We find that the cumulative pop-in probability on load could be described successfully by a combined model over the full range of tip radius, indicating that the incipient plasticity might be triggered either by the homogeneous nucleation of dislocation or by the activation of existing dislocations underneath the indenter.

Analysis of stiffness and stress in I-bar clasps.

PubMed

Sato, Y; Tsuga, K; Abe, Y; Asahara, S; Akagawa, Y

2001-06-01

An I-bar clasp is one of the most popular direct retainers for distal-extension removable partial dentures. However, no adequate information is available on the shape associated with biomechanics. This study aimed (1) to establish a three-dimensional (3D) finite-element modelling method of I-bar clasps, and (2) to clarify the effect of the shape on the stress and stiffness of I-bar clasps. 3D computer models of I-bar clasps were created with vertical and horizontal straight sections connected with a curved section with six parameters: thickness of the clasp tip (T), width of the clasp tip (W), radius of the curvature (R), horizontal distance between the base and the vertical axis (H), vertical dimension between the tip and the horizontal axis (V), taper (change of width per unit length along the axis)(Tp). Stress decreased as T, W, R and Tp increased, and as V decreased. Stiffness (which is proportional to retention) increased as T, W, R and Tp increased, and as H and V decreased. In both stress and stiffness, the effects of T and Tp were especially large. From the results, a systematic formula between the clasp shape and the stiffness was derived.

Measurement of Kirchhoff's stress intensity factors in bending plates

NASA Astrophysics Data System (ADS)

Bäcker, D.; Kuna, M.; Häusler, C.

2014-03-01

A measurement method of the stress intensity factors defined by KIRCHHOFF's theory for a crack in a bending plate is shown. For this purpose, a thin piezoelectric polyvinylidene fluoride film (PVDF) is attached to the surface of the cracked plate. The measured electrical voltages are coupled with the load type and the crack tip position relative to the sensor film. Stress intensity factors and the crack tip position can be determined by solving the non-linear inverse problem based on the measured signals. To guarantee solvability of the problem, more measuring electrodes on the film have to be taken in to account. To the developed sensor concept the KIRCHHOFF's plate theory has been applied. In order to connect the electrical signals and the stress intensity factors the stresses near the crack tip have to be written in eigenfunctions (see WILLIAMS [1]). The presented method was verified by means of the example of a straight crack of the length 2a in an infinite isotropic plate under all- side bending. It was found that the positioning of the electrodes is delimited by two radii. On one hand, the measurement points should not be too close to the crack tip. In this area, the Kirchhoff's plate theory cannot be used effectively. On the other hand, the measuring electrodes should be placed at a smaller distance to each other and not too far from the crack tip regarding the convergence radius of the WILLIAMS series expansion. Test calculations on a straight crack in an infinite isotropic plate showed the general applicability of the measurement method.

The effect of broken stringers on the stress intensity factor for a uniformly stiffened sheet containing a crack

NASA Technical Reports Server (NTRS)

Poe, C. C., Jr.

1973-01-01

A linear elastic stress analysis was made of a centrally cracked sheet stiffened by riveted, uniformly spaced and sized stringers. The stress intensity factor for the sheet and the load concentration factor for the most highly loaded stringer were determined for various numbers of broken stringers. A broken stringer causes the stress intensity factor to be very high when the crack tip is near the broken stringer, but causes little effect when the crack tip extends beyond several intact stringers. A broken stringer also causes an increase in the load concentration factor of the adjacent stringers. The calculated residual strengths and fatigue-crack-growth lives of a stiffened aluminum sheet with a broken stringer were only slightly less than a sheet with all intact stringers, and were still much higher than those of an unstiffened sheet.

Descriptions of crack growth behaviors in glass-ZrO2 bilayers under thermal residual stresses.

PubMed

Belli, Renan; Wendler, Michael; Zorzin, José I; Petschelt, Anselm; Tanaka, Carina B; Meira, Josete; Lohbauer, Ulrich

2016-09-01

This study was intended to separate residual stresses arising from the mismatch in coefficients of thermal expansion between glass and zirconia (ZrO2) from those stresses arising solely from the cooling process. Slow crack growth experimentes were undertaken to demonstrate how cracks grow in different residual stress fields. Aluminosilicate glass discs were sintered onto ZrO2 to form glass-ZrO2 bilayers. Glass discs were allowed to bond to the ZrO2 substrate during sintering or prevented from bonding by means of coating the ZrO2 with a thin boron nitrade coating. Residual stress gradients on "bonded" and "unbonded" bilayers were assessed using birefringence measurements. Unbonded glass discs were further tested under biaxial flexure in dynamic fatigue conditions in order to evaluate the effect of residual stress on the slow crack growth behavior. When fast-ccoling was induced, residual tensile stresses on the glass increased significantly on the side toward the ZrO2 substrate. By allowing the bond between glass and ZrO2, those tensile stresses observed in unbonded specimens are overwhelmed by the contraction mismatch stresses between the ZrO2 substrate and the glassy overlayer. Specimens containing residual tensile stresses on the bending surface showed a time-dependent strength increase in relation to stress-free annealed samples in the dynamic biaxial bending test, with this effect being dependent on the magnitude of the residual tensile stress. The phenomenon observed is explained here on the basis of the water toughening effect, in which water diffuses into the glass promoting local swelling. An additional residual tensile stress at the crack tip adds an applied-stress-independent (Kres) term to the total tip stress intensity factor (Ktip), increasing the stress-enhanced diffusion and the shielding of the crack tip through swelling of the crack faces. Residual stresses in the glass influence the crack growth behavior of veneered-ZrO2 bilayered dental prostheses. The role of water in crack growth might be of higher complexity when residual stresses are present in the glass layer. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effects of External Hydrogen on Hydrogen Transportation and Distribution Around the Fatigue Crack Tip in Type 304 Stainless Steel

NASA Astrophysics Data System (ADS)

Chen, Xingyang; Zhou, Chengshuang; Cai, Xiao; Zheng, Jinyang; Zhang, Lin

2017-10-01

The effects of external hydrogen on hydrogen transportation and distribution around the fatigue crack tip in type 304 stainless steel were investigated by using hydrogen microprint technique (HMT) and thermal desorption spectrometry. HMT results show that some silver particles induced by hydrogen release are located near the fatigue crack and more silver particles are concentrated around the crack tip, which indicates that hydrogen accumulates in the vicinity of the crack tip during the crack growth in hydrogen gas environment. Along with the crack propagation, strain-induced α' martensite forms around the crack tip and promotes hydrogen invasion into the matrix, which will cause the crack initiation and propagation at the austenite/ α' martensite interface. In addition, the hydrogen content in the vicinity of the crack tip is higher than that at the crack edge far away from the crack tip, which is related to the stress state and strain-induced α' martensite.

Evaluation of crack-tip stress fields on microstructural-scale fracture in Al-Al2O3 interpenetrating network composites

Treesearch

Robert J. Moon; Mark Hoffman; Jurgen Rödel; Shigemi Tochino; Giuseppe Pezzotti

2009-01-01

The influence of local microstructure on the fracture process at the crack tip in a ceramic–metal composite was assessed by comparing the measured stress at a microstructural level and analogous finite element modelling (FEM). Fluorescence microprobe spectroscopy was used to investigate the influence of near-crack-tip stress fields on the resulting crack propagation at...

The effect of vertical bracket positioning on torque and the resultant stress in the periodontal ligament--a finite element study.

PubMed

Sardarian, Ahmadreza; Danaei, Shahla Momeni; Shahidi, Shoaleh; Boushehri, Sahar Ghodsi; Geramy, Allahyar

2014-01-01

The ideal built-in tip and torque values of the straight wire appliance reduce the need for wire bending and hence reduce chair time. The vertical position of the bracket on the tooth surface can alter the torque exerted on the tooth. This is a result of the altered surface curvature observed at each vertical position. To further clarify the role of vertical bracket positioning on the applied torque and the resultant stresses in the periodontal ligament (PDL), we designed a mandibular first premolar using finite element modeling. Cone beam computed tomography of 52 patients (83 lower first premolars) was selected to be included in the study. Curvature was measured for points along the labial surface with increasing distances (0.5 mm increments) from the cusp tip by calculating the angle between tangents drawn from these points and the axis joining the cusp tip and the root apex. The mean values for each distance were calculated, and a finite element model was designed incorporating these mean values. The resultant stress and hydrostatic pressure in the PDL were calculated using finite element analysis. The labial surface of the mandibular first premolar demonstrated a 26.39° change from 2.5 to 6 mm from the cusp tip. The maximum Von-Mises stress and hydrostatic pressure in the PDL were observed at the root apex for all of the bracket positions, and these values demonstrated, respectively, a change of up to 0.059 and 0.186 MPa between two successive points. It can be concluded that the variation in the vertical position of the bracket can have an important effect on the torque and subsequently on the stresses and pressures in the PDL.

A statistical approach for generating synthetic tip stress data from limited CPT soundings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basalams, M.K.

CPT tip stress data obtained from a Uranium mill tailings impoundment are treated as time series. A statistical class of models that was developed to model time series is explored to investigate its applicability in modeling the tip stress series. These models were developed by Box and Jenkins (1970) and are known as Autoregressive Moving Average (ARMA) models. This research demonstrates how to apply the ARMA models to tip stress series. Generation of synthetic tip stress series that preserve the main statistical characteristics of the measured series is also investigated. Multiple regression analysis is used to model the regional variationmore » of the ARMA model parameters as well as the regional variation of the mean and the standard deviation of the measured tip stress series. The reliability of the generated series is investigated from a geotechnical point of view as well as from a statistical point of view. Estimation of the total settlement using the measured and the generated series subjected to the same loading condition are performed. The variation of friction angle with depth of the impoundment materials is also investigated. This research shows that these series can be modeled by the Box and Jenkins ARMA models. A third degree Autoregressive model AR(3) is selected to represent these series. A theoretical double exponential density function is fitted to the AR(3) model residuals. Synthetic tip stress series are generated at nearby locations. The generated series are shown to be reliable in estimating the total settlement and the friction angle variation with depth for this particular site.« less

Identification of a novel promoter from banana aquaporin family gene (MaTIP1;2) which responses to drought and salt-stress in transgenic Arabidopsis thaliana.

PubMed

Song, Shun; Xu, Yi; Huang, Dongmei; Miao, Hongxia; Liu, Juhua; Jia, Caihong; Hu, Wei; Valarezo, Ana Valeria; Xu, Biyu; Jin, Zhiqiang

2018-07-01

Drought and salt stresses often affect plant growth and crop yields. Identification of promoters involved in drought and salt stress responses is of great significance for genetic improvement of crop resistance. Our previous studies showed that aquaporin can respond to drought and salt stresses, but its promoter has not yet been reported in plants. In the present study, cis-acting elements of MaAQP family member promoters were systematically analyzed in banana. Expression of MaTIP1; 2 was induced by drought and salt stresses but not sensitive to cold stress, waterlogging stress, or mechanical damage, and its promoter contained five stress-related cis-acting elements. The MaTIP1; 2 promoter (841 bp upstream of translation initiation site) from banana (Musa acuminata L. AAA group cv. Brazilian) was isolated through genome walking polymerase chain reaction, and found to contain a TATA Box, CAAT box, ABRE element, CCGTCC box, CGTCA motif, and TCA element. Transformation of the MaTIP1; 2 promoter into Arabidopsis to assess its function indicated that it responds to both drought and salt stress treatments. These results suggest that MaTIP1; 2 utilization may improve drought and salt stresses resistance of the transgenic plants by promoting banana aquaporin expression. Copyright © 2018 Elsevier Masson SAS. All rights reserved.

The effects of ion implantation on the beaks of orthodontic pliers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mizrahi, E.; Cleaton-Jones, P.E.; Luyckz, S.

1991-06-01

The surface of stainless steel may be hardened by bombarding the material with a stream of nitrogen ions generated by a nuclear accelerator. In the present study this technique was used to determine the hardening effect of ion implantation on the beaks of stainless steel orthodontic pliers. Ten orthodontic pliers (Dentarum 003 094) were divided into two equal groups, designated control and experimental. The beaks of the experimental pliers were subjected to ion implantation, after which the tips of the beaks of all the pliers were stressed in an apparatus attached to an Instron testing machine. A cyclical load ofmore » 500 N was applied to the handles of the pliers, while a 0.9 mm (0.036 inch) round, stainless steel wire was held between the tips of the beaks. The effect of the stress was assessed by measurement with a traveling microscope of the gap produced between the tips of the beaks. Measurements were taken before loading and after 20, 40, 60, and 80 cycles. Statistical analysis of variance and the two-sample t tests indicated that there was a significant increase in the size of the gap as the pliers were stressed from 0 to 80 cycles (p less than 0.001). Furthermore, the mean gap was significantly greater in the control group than in the experimental group (p less than 0.001). This study suggests that ion implantation increases the hardness of the tips of the beaks of orthodontic pliers.« less

Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy

PubMed Central

Withers, P. J.

2015-01-01

To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored. PMID:25624521

Redistribution of Welding Residual Stresses of Crack Tip Opening Displacement Specimen by Local Compression.

PubMed

Kim, Young-Gon; Song, Kuk-Hyun; Lee, Dong-Hoon; Joo, Sung-Min

2018-03-01

The demand of crack tip opening displacement (CTOD) test which evaluates fracture toughness of a cracked material is very important to ensure the stability of structure under severe service environment. The validity of the CTOD test result is judged using several criterions of the specification standards. One of them is the artificially generated fatigue pre-crack length inside the specimen. For acceptable CTOD test results, fatigue pre-crack must have a reasonable sharp crack front. The propagation of fatigue crack started from the tip of the machined notch, which might have propagated irregularly due to residual stress field. To overcome this problem, test codes suggest local compression method, reversed bending method and stepwise high-R ratio method to reduce the disparity of residual stress distribution inside the specimen. In this paper, the relation between the degree of local compression and distribution of welding residual stress has been analyzed by finite element analyses in order to determine the amount of effective local compression of the test piece. Analysis results show that initial welding residual stress is dramatically varied three-dimensionally while cutting, notch machining and local compressing due to the change of internal restraint force. From the simulation result, the authors find that there is an optimum amount of local compression to modify regularly for generating fatigue pre-crack propagation. In the case of 0.5% compressions of the model width is the most effective for uniforming residual stress distribution.

Influence of Crack-Tip Configurations on the Fracture Response of 0.04-Inch Thick 2024-T3 Aluminum Alloy Sheet

NASA Technical Reports Server (NTRS)

Johnston, William M.; Newman, James C. (Technical Monitor)

2002-01-01

A series of fracture tests were conducted on Middle-crack tension M(T) and compact tension C(T) specimens to determine the effects of specimen type, specimen width, notch tip sharpness and buckling on the fracture behavior of cracked thin sheet (0.04 inch thick) 2024-T3 aluminum alloy material. A series of M(T) specimens were tested with three notch tip configurations: (1) a fatigue pre-cracked notch, (2) a 0.010-inch-diameter wire electrical discharge machined (EDM) notch, and (3) a EDM notch sharpened with a razor blade. The test procedures are discussed and the experimental results for failure stress, load vs. crack extension and the material stress-strain response are reported.

Novel Regulation of Aquaporins during Osmotic Stress1

PubMed Central

Vera-Estrella, Rosario; Barkla, Bronwyn J.; Bohnert, Hans J.; Pantoja, Omar

2004-01-01

Aquaporin protein regulation and redistribution in response to osmotic stress was investigated. Ice plant (Mesembryanthemum crystallinum) McTIP1;2 (McMIPF) mediated water flux when expressed in Xenopus leavis oocytes. Mannitol-induced water imbalance resulted in increased protein amounts in tonoplast fractions and a shift in protein distribution to other membrane fractions, suggesting aquaporin relocalization. Indirect immunofluorescence labeling also supports a change in membrane distribution for McTIP1;2 and the appearance of a unique compartment where McTIP1;2 is expressed. Mannitol-induced redistribution of McTIP1;2 was arrested by pretreatment with brefeldin A, wortmannin, and cytochalasin D, inhibitors of vesicle trafficking-related processes. Evidence suggests a role for glycosylation and involvement of a cAMP-dependent signaling pathway in McTIP1;2 redistribution. McTIP1;2 redistribution to endosomal compartments may be part of a homeostatic process to restore and maintain cellular osmolarity under osmotic-stress conditions. PMID:15299122

Novel regulation of aquaporins during osmotic stress.

PubMed

Vera-Estrella, Rosario; Barkla, Bronwyn J; Bohnert, Hans J; Pantoja, Omar

2004-08-01

Aquaporin protein regulation and redistribution in response to osmotic stress was investigated. Ice plant (Mesembryanthemum crystallinum) McTIP1;2 (McMIPF) mediated water flux when expressed in Xenopus leavis oocytes. Mannitol-induced water imbalance resulted in increased protein amounts in tonoplast fractions and a shift in protein distribution to other membrane fractions, suggesting aquaporin relocalization. Indirect immunofluorescence labeling also supports a change in membrane distribution for McTIP1;2 and the appearance of a unique compartment where McTIP1;2 is expressed. Mannitol-induced redistribution of McTIP1;2 was arrested by pretreatment with brefeldin A, wortmannin, and cytochalasin D, inhibitors of vesicle trafficking-related processes. Evidence suggests a role for glycosylation and involvement of a cAMP-dependent signaling pathway in McTIP1;2 redistribution. McTIP1;2 redistribution to endosomal compartments may be part of a homeostatic process to restore and maintain cellular osmolarity under osmotic-stress conditions.

Toughness-Dominated Regime of Hydraulic Fracturing in Cohesionless Materials

NASA Astrophysics Data System (ADS)

Germanovich, L. N.; Hurt, R. S.; Ayoub, J.; Norman, W. D.

2011-12-01

This work examines the mechanisms of hydraulic fracturing in cohesionless particulate materials with geotechnical, geological, and petroleum applications. For this purpose, experimental techniques have been developed, and used to quantify the initiation and propagation of hydraulic fractures in saturated particulate materials. The fracturing liquid is injected into particulate materials, which are practically cohesionless. The liquid flow is localized in thin self-propagating crack-like conduits. By analogy we call them 'cracks' or 'hydraulic fractures.' When a fracture propagates in a solid, new surfaces are created by breaking material bonds. Consequently, the material is in tension at the fracture tip. Because the particulate material is already 'fractured,' no new surface is created and no fracturing process per se is involved. Therefore, the conventional fracture mechanics principles cannot be directly applied. Based on the laboratory observations, performed on three particulate materials (Georgia Red Clay, silica flour, and fine sand, and their mixtures), this work offers physical concepts to explain the observed phenomena. The goal is to determine the controlling parameters of fracture behavior and to quantify their effects. An important conclusion of our work is that all parts of the cohesionless particulate material (including the tip zone of hydraulic fracture) are likely to be in compression. The compressive stress state is an important characteristic of hydraulic fracturing in particulate materials with low, or no, cohesion (such as were used in our experiments). At present, two kinematic mechanisms of fracture propagation, consistent with the compressive stress regime, can be offered. The first mechanism is based on shear bands propagating ahead of the tip of an open fracture. The second is based on the tensile strain ahead of the fracture tip and reduction of the effective stresses to zero within the leak-off zone. Scaling indicates that in our experiments, there is a high pressure gradient in the leak-off zone in the direction normal to the fracture. Fluid pressure does not decrease considerably along the fracture, however, due to the relatively wide fracture aperture. This suggests that hydraulically induced fractures in unconsolidated materials may be considered to be within the toughness-dominated regime of hydraulic fracturing. Our results indicate that the primary influence on peak or initiation pressure comes from the remote stresses. However, fracture morphology changes significantly with other chosen parameters (stress, flow rate, rheology and permeability). Additionally, an important characteristic feature of fractures in our experiments is the frequent bluntness of the fracture tip, which suggests that plastic deformation at the fracture tip is important. Modeling shows that large openings at the fracture tip correspond to relatively large 'effective' fracture (surface) energy, which can be orders of magnitude greater than for typical (solid) rocks.

Identification and validation of reference genes for quantification of target gene expression with quantitative real-time PCR for tall fescue under four abiotic stresses.

PubMed

Yang, Zhimin; Chen, Yu; Hu, Baoyun; Tan, Zhiqun; Huang, Bingru

2015-01-01

Tall fescue (Festuca arundinacea Schreb.) is widely utilized as a major forage and turfgrass species in the temperate regions of the world and is a valuable plant material for studying molecular mechanisms of grass stress tolerance due to its superior drought and heat tolerance among cool-season species. Selection of suitable reference genes for quantification of target gene expression is important for the discovery of molecular mechanisms underlying improved growth traits and stress tolerance. The stability of nine potential reference genes (ACT, TUB, EF1a, GAPDH, SAND, CACS, F-box, PEPKR1 and TIP41) was evaluated using four programs, GeNorm, NormFinder, BestKeeper, and RefFinder. The combinations of SAND and TUB or TIP41 and TUB were most stably expressed in salt-treated roots or leaves. The combinations of GAPDH with TIP41 or TUB were stable in roots and leaves under drought stress. TIP41 and PEPKR1 exhibited stable expression in cold-treated roots, and the combination of F-box, TIP41 and TUB was also stable in cold-treated leaves. CACS and TUB were the two most stable reference genes in heat-stressed roots. TIP41 combined with TUB and ACT was stably expressed in heat-stressed leaves. Finally, quantitative real-time polymerase chain reaction (qRT-PCR) assays of the target gene FaWRKY1 using the identified most stable reference genes confirmed the reliability of selected reference genes. The selection of suitable reference genes in tall fescue will allow for more accurate identification of stress-tolerance genes and molecular mechanisms conferring stress tolerance in this stress-tolerant species.

The crack problem in bonded nonhomogeneous materials

NASA Technical Reports Server (NTRS)

Erdogan, Fazil; Kaya, A. C.; Joseph, P. F.

1988-01-01

The plane elasticity problem for two bonded half planes containing a crack perpendicular to the interface was considered. The effect of very steep variations in the material properties near the diffusion plane on the singular behavior of the stresses and stress intensity factors were studied. The two materials were thus, assumed to have the shear moduli mu(o) and mu(o) exp (Beta x), x=0 being the diffusion plane. Of particular interest was the examination of the nature of stress singularity near a crack tip terminating at the interface where the shear modulus has a discontinuous derivative. The results show that, unlike the crack problem in piecewise homogeneous materials for which the singularity is of the form r/alpha, 0 less than alpha less than 1, in this problem the stresses have a standard square-root singularity regardless of the location of the crack tip. The nonhomogeneity constant Beta has, however, considerable influence on the stress intensity factors.

The crack problem in bonded nonhomogeneous materials

NASA Technical Reports Server (NTRS)

Erdogan, F.; Joseph, P. F.; Kaya, A. C.

1991-01-01

The plane elasticity problem for two bonded half planes containing a crack perpendicular to the interface was considered. The effect of very steep variations in the material properties near the diffusion plane on the singular behavior of the stresses and stress intensity factors were studied. The two materials were thus, assumed to have the shear moduli mu(o) and mu(o) exp (Beta x), x=0 being the diffusion plane. Of particular interest was the examination of the nature of stress singularity near a crack tip termination at the interface where the shear modulus has a discontinuous derivative. The results show that, unlike the crack problem in piecewise homogeneous materials for which the singularity is of the form r/alpha, 0 less than alpha less than 1, in this problem the stresses have a standard square-root singularity regardless of the location of the crack tip. The nonhomogeneity constant Beta has, however, considerable influence on the stress intensity factors.

Investigation of the stress distribution around a mode 1 crack with a novel strain gradient theory

NASA Astrophysics Data System (ADS)

Lederer, M.; Khatibi, G.

2017-01-01

Stress concentrations at the tip of a sharp crack have extensively been investigated in the past century. According to the calculations of Inglis, the stress ahead of a mode 1 crack shows the characteristics of a singularity. This solution is exact in the framework of linear elastic fracture mechanics (LEFM). From the viewpoint of multiscale modelling, however, it is evident that the stress at the tip of a stable crack cannot be infinite, because the strengths of atomic bonds are finite. In order to prevent the problem of this singularity, a new version of strain gradient elasticity is employed here. This theory is implemented in the commercial FEM code ABAQUS through user subroutine UEL. Convergence of the model is proved through consecutive mesh refinement. In consequence, the stresses ahead of a mode 1 crack become finite. Furthermore, the model predicts a size effect in the sense “smaller is stronger”.

Dynamic fields near a crack tip growing in an elastic-perfectly-plastic solid

NASA Technical Reports Server (NTRS)

Nemat-Nasser, S.; Gao, Y. C.

1983-01-01

A full asymptotic solution is presented for the fields in the neighborhood of the tip of a steadily advancing crack in an incompressible elastic-perfectly-plastic solid. There are four findings for mode I crack growth in the plane strain condition. The first is that the entire crack tip in steady crack growth is surrounded by a plastic region and that no elastic unloading is predicted by the complete dynamic asymptotic solution. The second is that, in contrast to the quasi-static solution, the dynamic solution yields strain fields with a logarithmic singularity everywhere near the crack tip. The third is that whereas the stress field varies throughout the entire crack tip neighborhood, it does not exhibit behavior that can be approximated by a constant field followed by an essentially centered-fan field and then by another constant field, especially for small crack growth speeds. The fourth finding is that there are two shock fronts emanating from the crack tip across which certain stress and strain components undergo jump discontinuities. After reviewing the mode III steady-state crack growth, it is concluded that ductile fracture criteria for nonstationary cracks must be based on solutions that include the inertia effects and that for this purpose quasi-static solutions may be inadequate.

The generalized fracture criteria based on the multi-parameter representation of the crack tip stress field

NASA Astrophysics Data System (ADS)

Stepanova, L. V.

2017-12-01

The paper is devoted to the multi-parameter asymptotic description of the stress field near the crack tip of a finite crack in an infinite isotropic elastic plane medium subject to 1) tensile stress; 2) in-plane shear; 3) mixed mode loading for a wide range of mode-mixity situations (Mode I and Mode II). The multi-parameter series expansion of stress tensor components containing higher-order terms is obtained. All the coefficients of the multiparameter series expansion of the stress field are given. The main focus is on the discussion of the influence of considering the higher-order terms of the Williams expansion. The analysis of the higher-order terms in the stress field is performed. It is shown that the larger the distance from the crack tip, the more terms it is necessary to keep in the asymptotic series expansion. Therefore, it can be concluded that several more higher-order terms of the Williams expansion should be used for the stress field description when the distance from the crack tip is not small enough. The crack propagation direction angle is calculated. Two fracture criteria, the maximum tangential stress criterion and the strain energy density criterion, are used. The multi-parameter form of the two commonly used fracture criteria is introduced and tested. Thirty and more terms of the Williams series expansion for the near-crack-tip stress field enable the angle to be calculated more precisely.

Stress corrosion-controlled rates of mode I fracture propagation in calcareous bedrock

NASA Astrophysics Data System (ADS)

Voigtlaender, Anne; Leith, Kerry; Krautblatter, Michael

2014-05-01

Surface bedrock on natural rock slopes is subject to constant and cyclic environmental stresses (wind, water, wave, ice, seismic or gravitational). Studies indicate that these stresses range up to several hundred kPa, generally too low to cause macroscopic changes in intact rock, although clear evidence of fracture generation, crack propagation and weathering of bedrock illustrates the effect of environmental stresses at the Earth's surface. We suggest that material degradation and its extent, is likely to be controlled by the rate of stress corrosion cracking (SCC). Stress corrosion is a fluid-material reaction, where fluids preferentially react with strained atomic bonds at the tip of developing fractures. Stress corrosion in ferrous and siliceous materials is often accepted as the fracture propagation and degradation rate-controlling process where materials are subject to stresses and fluids. Although evidence for chemical weathering in propagating bedrock fractures is clear in natural environments, the physical system and quantification of stress corrosion in natural rocks is yet to be addressed. Here, we present preliminary data on the relationship between stresses at levels commonly present on natural rock slopes, and material damage resulting from stress corrosion under constant or cyclic tensile loading. We undertake single notch three-point bending tests (SNBT) on fresh calcareous bedrock specimens (1100x100x100mm) over a two-month period. Two beams containing an artificial notch are stressed to 75% of their ultimate strength, and a constant supply of weak acid is applied at the notch tip to enhance chemical reactions. A third, unloaded, beam is also exposed to weak acid in order to elucidate the contribution of stress corrosion cracking to the material degradation. Stresses at the tip of propagating cracks affect the kinetics of the chemical reaction in the specimen exposed to both loading and corrosion, leading to an increase in degradation, and greater stress relaxation. These changes in material properties are monitored using strain gauges, acoustic emission sensors, changes in P-wave velocity, and records of time to failure where appropriate. Our preliminary studies indicate changes in material properties are concentrated in the region of predicted tensile stress intensification. Reactions seem to favourably occur at the stressed bonds around the crack tip. The rate of chemical dissolution and further propagation of the fracture at the notch tip appears to be enhanced by the level of stress applied to the specimen. This provides the foundation for a suite of repeated experiments in which we plan to test corrosion-controlled rates of degradation across a range of loading conditions. The improved understanding into micro-mechanical controls, will contribute to the assessment of rock fall production rates and erosion processes in natural environments as well as natural building stones.

Tip cap for a turbine rotor blade

DOEpatents

Kimmel, Keith D

2014-03-25

A turbine rotor blade with a spar and shell construction, and a tip cap that includes a row of lugs extending from a bottom side that form dovetail grooves that engage with similar shaped lugs and grooves on a tip end of the spar to secure the tip cap to the spar against radial displacement. The lug on the trailing edge end of the tip cap is aligned perpendicular to a chordwise line of the blade in the trailing edge region in order to minimize stress due to the lugs wanting to bend under high centrifugal loads. A two piece tip cap with lugs at different angles will reduce the bending stress even more.

Numerical calculation and experimental research on crack arrest by detour effect and joule heating of high pulsed current in remanufacturing

NASA Astrophysics Data System (ADS)

Yu, Jing; Zhang, Hongchao; Deng, Dewei; Hao, Shengzhi; Iqbal, Asif

2014-07-01

The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is developed. According to finite element theory, the finite element(FE) model of the cracked rectangular specimen is established firstly. Then, based on electro-thermo-structure coupled theory, the distributions of current density, temperature field, and stress field are calculated for the instant of energizing. Furthermore, the simulation results are verified by some corresponding experiments performed on high pulsed current discharge device of type HCPD-I. Morphology and microstructure around the crack tip before and after electro pulsing treatment are observed by optical microscope(OM) and scanning electron microscope(SEM), and then the diameters of fusion zone and heat affected zone(HAZ) are measured in order to contrast with numerical calculation results. Element distribution, nano-indentation hardness and residual stress in the vicinity of the crack tip are surveyed by energy dispersive spectrometer(EDS), scanning probe microscopy(SPM) and X-ray stress gauge, respectively. The results show that the obvious partition and refined grain around the crack tip can be observed due to the violent temperature change. The contents of carbon and oxygen in fusion zone and HAZ are higher than those in matrix, and however the hardness around the crack tip decreases. Large residual compressive stress is induced in the vicinity of the crack tip and it has the same order of magnitude for measured results and numerical calculation results that is 100 MPa. The relational curves between discharge energies and diameters of the fusion zone and HAZ are obtained by experiments. The difference of diameter of fusion zone between measured and calculated results is less than 18.3%. Numerical calculation is very useful to define the experimental parameters. An effective method to prevent further extension of the crack is presented and can provide a reference for the compressor rotor blade remanufacturing.

Gel-free/label-free proteomic analysis of root tip of soybean over time under flooding and drought stresses.

PubMed

Wang, Xin; Oh, MyeongWon; Sakata, Katsumi; Komatsu, Setsuko

2016-01-01

Growth in the early stage of soybean is markedly inhibited under flooding and drought stresses. To explore the responsive mechanisms of soybean, temporal protein profiles of root tip under flooding and drought stresses were analyzed using gel-free/label-free proteomic technique. Root tip was analyzed because it was the most sensitive organ against flooding, and it was beneficial to root penetration under drought. UDP glucose: glycoprotein glucosyltransferase was decreased and increased in soybean root under flooding and drought, respectively. Temporal protein profiles indicated that fermentation and protein synthesis/degradation were essential in root tip under flooding and drought, respectively. In silico protein-protein interaction analysis revealed that the inductive and suppressive interactions between S-adenosylmethionine synthetase family protein and B-S glucosidase 44 under flooding and drought, respectively, which are related to carbohydrate metabolism. Furthermore, biotin/lipoyl attachment domain containing protein and Class II aminoacyl tRNA/biotin synthetases superfamily protein were repressed in the root tip during time-course stresses. These results suggest that biotin and biotinylation might be involved in energy management to cope with flooding and drought in early stage of soybean-root tip. Copyright © 2015 Elsevier B.V. All rights reserved.

Phosphoproteomics reveals the effect of ethylene in soybean root under flooding stress.

PubMed

Yin, Xiaojian; Sakata, Katsumi; Komatsu, Setsuko

2014-12-05

Flooding has severe negative effects on soybean growth. To explore the flooding-responsive mechanisms in early-stage soybean, a phosphoproteomic approach was used. Two-day-old soybean plants were treated without or with flooding for 3, 6, 12, and 24 h, and root tip proteins were then extracted and analyzed at each time point. After 3 h of flooding exposure, the fresh weight of soybeans increased, whereas the ATP content of soybean root tips decreased. Using a gel-free proteomic technique, a total of 114 phosphoproteins were identified in the root tip samples, and 34 of the phosphoproteins were significantly changed with respect to phosphorylation status after 3 h of flooding stress. Among these phosphoproteins, eukaryotic translation initiation factors were dephosphorylated, whereas several protein synthesis-related proteins were phosphorylated. The mRNA expression levels of sucrose phosphate synthase 1F and eukaryotic translation initiation factor 4 G were down-regulated, whereas UDP-glucose 6-dehydrogenase mRNA expression was up-regulated during growth but down-regulated under flooding stress. Furthermore, bioinformatic protein interaction analysis of flooding-responsive proteins based on temporal phosphorylation patterns indicated that eukaryotic translation initiation factor 4 G was located in the center of the network during flooding. Soybean eukaryotic translation initiation factor 4 G has homology to programmed cell death 4 protein and is implicated in ethylene signaling. The weight of soybeans was increased with treatment by an ethylene-releasing agent under flooding condition, but it was decreased when plants were exposed to an ethylene receptor antagonist. These results suggest that the ethylene signaling pathway plays an important role, via the protein phosphorylation, in mechanisms of plant tolerance to the initial stages of flooding stress in soybean root tips.

Nuclear Proteomics Reveals the Role of Protein Synthesis and Chromatin Structure in Root Tip of Soybean during the Initial Stage of Flooding Stress.

PubMed

Yin, Xiaojian; Komatsu, Setsuko

2016-07-01

To identify the upstream events controlling the regulation of flooding-responsive proteins in soybean, proteomic analysis of nuclear proteins in root tip was performed. By using nuclear fractions, which were highly enriched, a total of 365 nuclear proteins were changed in soybean root tip at initial stage of flooding stress. Four exon-junction complex-related proteins and NOP1/NOP56, which function in upstream of 60S preribosome biogenesis, were decreased in flooded soybean. Furthermore, proteomic analysis of crude protein extract revealed that the protein translation was suppressed by continuous flooding stress. Seventeen chromatin structure-related nuclear proteins were decreased in response to flooding stress. Out of them, histone H3 was clearly decreased with protein abundance and mRNA expression levels at the initial flooding stress. Additionally, a number of protein synthesis-, RNA-, and DNA-related nuclear proteins were decreased in a time-dependent manner. mRNA expressions of genes encoding the significantly changed flooding-responsive nuclear proteins were inhibited by the transcriptional inhibitor, actinomycin D. These results suggest that protein translation is suppressed through inhibition of preribosome biogenesis- and mRNA processing-related proteins in nuclei of soybean root tip at initial flooding stress. In addition, flooding stress may regulate histone variants with gene expression in root tip.

Intracellular Ca(2+) and K(+) concentration in Brassica oleracea leaf induces differential expression of transporter and stress-related genes.

PubMed

Lee, Jeongyeo; Kim, Jungeun; Choi, Jae-Pil; Lee, MiYe; Kim, Min Keun; Lee, Young Han; Hur, Yoonkang; Nou, Ill-Sup; Park, Sang Un; Min, Sung Ran; Kim, HyeRan

2016-03-09

One of the most important members of the genus Brassica, cabbage, requires a relatively high level of calcium for normal growth (Plant Cell Environ 7: 397-405, 1984; Plant Physiol 60: 854-856, 1977). Localized Ca(2+) deficiency in cabbage leaves causes tip-burn, bringing about serious economic losses (Euphytica 9:203-208, 1960; Ann Bot 43:363-372, 1979; Sci Hortic 14:131-138, 1981). Although it has been known that the occurrence of tip-burn is related to Ca(2+) deficiency, there is limited information on the underlying mechanisms of tip-burn or the relationship between Ca(2+) and tip-burn incidence. To obtain more information on the genetic control of tip-burn symptoms, we focused on the identification of genes differentially expressed in response to increasing intracellular Ca(2+) and K(+) concentrations in B. oleracea lines derived from tip-burn susceptible, tip-burn resistant cabbages (B. oleracea var. capitata), and kale (B. oleracea var. acephala). We compared the levels of major macronutrient cations, including Ca(2+) and K(+), in three leaf segments, the leaf apex (LA), middle of leaf (LM), and leaf base (LB), of tip-burn susceptible, tip-burn resistant cabbages, and kale. Ca(2+) and K(+) concentrations were highest in kale, followed by tip-burn resistant and then tip-burn susceptible cabbages. These cations generally accumulated to a greater extent in the LB than in the LA. Transcriptome analysis identified 58,096 loci as putative non-redundant genes in the three leaf segments of the three B. oleracea lines and showed significant changes in expression of 27,876 loci based on Ca(2+) and K(+) levels. Among these, 1844 loci were identified as tip-burn related phenotype-specific genes. Tip-burn resistant cabbage and kale-specific genes were largely related to stress and transport activity based on GO annotation. Tip-burn resistant cabbage and kale plants showed phenotypes clearly indicative of heat-shock, freezing, and drought stress tolerance compared to tip-burn susceptible cabbages, demonstrating a correlation between intracellular Ca(2+) and K(+) concentrations and tolerance of abiotic stress with differential gene expression. We selected 165 genes that were up- or down-regulated in response to increasing Ca(2+) and K(+) concentrations in the three leaf segments of the three plant lines. Gene ontology enrichment analysis indicated that these genes participated in regulatory metabolic processes or stress responses. Our results indicate that the genes involved in regulatory metabolic processes or stress responses were differentially expressed in response to increasing Ca(2+) and K(+) concentrations in the B. oleracea leaf. Our transcriptome data and the genes identified may serve as a starting point for understanding the mechanisms underlying essential macronutrient deficiencies in plants, as well as the features of tip-burn in cabbage and other Brassica species.

3D printed, bio-inspired prototypes and analytical models for structured suture interfaces with geometrically-tuned deformation and failure behavior

NASA Astrophysics Data System (ADS)

Lin, Erica; Li, Yaning; Ortiz, Christine; Boyce, Mary C.

2014-12-01

Geometrically structured interfaces in nature possess enhanced, and often surprising, mechanical properties, and provide inspiration for materials design. This paper investigates the mechanics of deformation and failure mechanisms of suture interface designs through analytical models and experiments on 3D printed polymer physical prototypes. Suture waveforms with generalized trapezoidal geometries (trapezoidal, rectangular, anti-trapezoidal, and triangular) are studied and characterized by several important geometric parameters: the presence or absence of a bonded tip region, the tip angle, and the geometry. It is shown that a wide range (in some cases as great as an order of magnitude) in stiffness, strength, and toughness is achievable dependent on tip bonding, tip angle, and geometry. Suture interfaces with a bonded tip region exhibit a higher initial stiffness due to the greater load bearing by the skeletal teeth, a double peak in the stress-strain curve corresponding to the failure of the bonded tip and the failure of the slanted interface region or tooth, respectively, and an additional failure and toughening mechanism due to the failure of the bonded tip. Anti-trapezoidal geometries promote the greatest amplification of properties for suture interfaces with a bonded tip due the large tip interface area. The tip angle and geometry govern the stress distributions in the teeth and the ratio of normal to shear stresses in the interfacial layers, which together determine the failure mechanism of the interface and/or the teeth. Rectangular suture interfaces fail by simple shearing of the interfaces. Trapezoidal and triangular suture interfaces fail by a combination of shear and tensile normal stresses in the interface, leading to plastic deformation, cavitation events, and subsequent stretching of interface ligaments with mostly elastic deformation in the teeth. Anti-trapezoidal suture interfaces with small tip angles have high stress concentrations in the teeth and fail catastrophically by tooth failure, whereas larger tip angles exhibit a shear failure of the interfaces. Therefore, larger tip angles and trapezoidal or triangular geometries promote graceful failure, and smaller tip angles and anti-trapezoidal geometries promote more brittle-like failure. This dependence is reminiscent of biological systems, which exhibit a range of failure behaviors with limited materials and varied geometry. Triangular geometries uniquely exhibit uniform stress distributions in its teeth and promote the greatest amplification of mechanical properties. In both the bonded and unbonded cases, the predictions from the presented analytical models and experimental results on 3D printed prototypes show excellent agreement. This validates the analytical models and allows for the models to be used as a tool for the design of new materials and interfaces with tailored mechanical behavior.

Hypersonic research engine project. Phase 2: Aerothermodynamic integration model development

NASA Technical Reports Server (NTRS)

Jilly, L. F. (Editor)

1970-01-01

The analytical effort was directed towards (1) completing the design of the combustor exit instrumentation assembly, (2) analyzing the coolant flow distribution of the cowl leading edge tip section, (3) determining effects of purge gas pressure on AIM performance analysis, and (4) analyzing heat transfer and associated stress problems related to the cowl leading edge tip section and the nozzle shroud assembly for test conditions.

Shadowing effects on multi-step Langmuir probe array on HL-2A tokamak

NASA Astrophysics Data System (ADS)

Ke, R.; Xu, M.; Nie, L.; Gao, Z.; Wu, Y.; Yuan, B.; Chen, J.; Song, X.; Yan, L.; Duan, X.

2018-05-01

Multi-step Langmuir probe arrays have been designed and installed on the HL-2A tokamak [1]–[2] to study the turbulent transport in the edge plasma, especially for the measurement of poloidal momentum flux, Reynolds stress Rs. However, except the probe tips on the top step, all other tips on lower steps are shadowed by graphite skeleton. It is necessary to estimate the shadowing effects on equilibrium and fluctuation measurement. In this paper, comparison of shadowed tips to unshadowed ones is presented. The results show that shadowing can strongly reduce the ion and electron effective collection area. However, its effect is negligible for the turbulence intensity and coherence measurement, confirming that the multi-step LP array is proper for the turbulent transport measurement.

Improved method for determining the stress relaxation at the crack tip

NASA Astrophysics Data System (ADS)

Grinevich, A. V.; Erasov, V. S.; Avtaev, V. V.

2017-10-01

A technique is suggested to determine the stress relaxation at the crack tip during tests of a specimen of a new type at a constant crack opening fixed by a stay bolt. The shape and geometry of the specimen make it possible to set the load and to determine the crack closure force after long-term exposure using the force transducer of a tensile-testing machine. The stress relaxation at the crack tip is determined in a V95pchT2 alloy specimen at elevated temperatures.

[Mechanism of the dentino-enamel junction on the resist-crack propagation of human teeth by the finite element method].

PubMed

Jingjing, Zheng; Tiezhou, Hou; Hong, Tao; Xueyan, Guo; Cui, Wu

2014-10-01

This study aims to identify the crack tip stress intensity factor of the propagation process, crack propagation path, and the changes in the shape of the crack tip by the finite element method. The finite element model of dentino-enamel junction was established with ANSYS software, and the length of the initial crack in the single edge was set to 0.1 mm. The lower end of the sample was fixed. The tensile load of 1 MPa with frequency of 5 Hz was applied to the upper end. The stress intensity factor, deflection angle, and changes in the shape of the crack tip in the crack propagation were calculated by ANSYS. The stress intensity factor suddenly and continuously decreased in dentino-enamel junction as the crack extended. A large skewed angle appeared, and the stress on crack tip was reduced. The dentino-enamel junction on human teeth may resist crack propagation through stress reduction.

Visualizing In Situ Microstructure Dependent Crack Tip Stress Distribution in IN-617 Using Nano-mechanical Raman Spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Yang; Mohanty, Debapriya P.; Tomar, Vikas

2016-11-01

Inconel 617 (IN-617) is a solid solution alloy, which is widely used in applications that require high-temperature component operation due to its high-temperature stability and strength as well as strong resistance to oxidation and carburization. The current work focuses on in situ measurements of stress distribution under 3-point bending at elevated temperature in IN-617. A nanomechanical Raman spectroscopy measurement platform was designed and built based on a combination of a customized open Raman spectroscopy (NMRS) system incorporating a motorized scanning and imaging system with a nanomechanical loading platform. Based on the scanning of the crack tip notch area using the NMRS notch tip, stress distribution under applied load with micron-scale resolution for analyzed microstructures is predicted. A finite element method-based formulation to predict crack tip stresses is presented and validated using the presented experimental data.

Fatigue crack growth with single overload - Measurement and modeling

NASA Technical Reports Server (NTRS)

Davidson, D. L.; Hudak, S. J., Jr.; Dexter, R. J.

1987-01-01

This paper compares experiments with an analytical model of fatigue crack growth under variable amplitude. The stereoimaging technique was used to measure displacements near the tips of fatigue cracks undergoing simple variations in load amplitude-single overloads and overload/underload combinations. Measured displacements were used to compute strains, and stresses were determined from the strains. Local values of crack driving force (Delta-K effective) were determined using both locally measured opening loads and crack tip opening displacements. Experimental results were compared with simulations made for the same load variation conditions using Newman's FAST-2 model. Residual stresses caused by overloads, crack opening loads, and growth retardation periods were compared.

A stiffness derivative finite element technique for determination of crack tip stress intensity factors

NASA Technical Reports Server (NTRS)

Parks, D. M.

1974-01-01

A finite element technique for determination of elastic crack tip stress intensity factors is presented. The method, based on the energy release rate, requires no special crack tip elements. Further, the solution for only a single crack length is required, and the crack is 'advanced' by moving nodal points rather than by removing nodal tractions at the crack tip and performing a second analysis. The promising straightforward extension of the method to general three-dimensional crack configurations is presented and contrasted with the practical impossibility of conventional energy methods.

Consequences of Fluid Lag in Three-Dimensional Hydraulic Fractures

NASA Astrophysics Data System (ADS)

Advani (Deceased), S. H.; Lee, T. S.; Dean, R. H.; Pak, C. K.; Avasthi, J. M.

1997-04-01

Research investigations on three-dimensional (3-D) rectangular hydraulic fracture configurations with varying degrees of fluid lag are reported. This paper demonstrates that a 3-D fracture model coupled with fluid lag (a small region of reduced pressure) at the fracture tip can predict very large excess pressure measurements for hydraulic fracture processes. Predictions of fracture propagation based on critical stress intensity factors are extremely sensitive to the pressure profile at the tip of a propagating fracture. This strong sensitivity to the pressure profile at the tip of a hydraulic fracture is more strongly pronounced in 3-D models versus 2-D models because 3-D fractures are clamped at the top and bottom, and pressures in the 3-D fractures that are far removed from the fracture tip have little effect on the stress intensity factor at the fracture tip. This rationale for the excess pressure mechanism is in marked contrast to the crack tip process damage zone assumptions and attendant high rock fracture toughness value hypotheses advanced in the literature. A comparison with field data is presented to illustrate the proposed fracture fluid pressure sensitivity phenomenon. This paper does not attempt to calculate the length of the fluid lag region in a propagating fracture but instead attempts to show that the pressure profile at the tip of the propagating fracture plays a major role in fracture propagation, and this role is magnified in 3-D models. Int. J. Numer. Anal. Meth. Geomech., vol. 21, 229-240 (1997).

Aluminum-induced cell death of barley-root border cells is correlated with peroxidase- and oxalate oxidase-mediated hydrogen peroxide production.

PubMed

Tamás, L; Budíková, S; Huttová, J; Mistrík, I; Simonovicová, M; Siroká, B

2005-06-01

The function of root border cells (RBC) during aluminum (Al) stress and the involvement of oxalate oxidase, peroxidase and H(2)O(2) generation in Al toxicity were studied in barley roots. Our results suggest that RBC effectively protect the barley root tip from Al relative to the situation in roots cultivated in hydroponics where RBC are not sustained in the area surrounding the root tip. The removal of RBC from Al-treated roots increased root growth inhibition, Al and Evans blue uptake, inhibition of RBC production, the level of dead RBC, peroxidase and oxalate oxidase activity and the production of H(2)O(2). Our results suggest that even though RBC actively produce active oxygen species during Al stress, their role in the protection of root tips against Al toxicity is to chelate Al in their dead cell body.

Dynamic steady-state analysis of crack propagation in rubber-like solids using an extended finite element method

NASA Astrophysics Data System (ADS)

Kroon, Martin

2012-01-01

In the present study, a computational framework for studying high-speed crack growth in rubber-like solids under conditions of plane stress and steady-state is proposed. Effects of inertia, viscoelasticity and finite strains are included. The main purpose of the study is to examine the contribution of viscoelastic dissipation to the total work of fracture required to propagate a crack in a rubber-like solid. The computational framework builds upon a previous work by the present author (Kroon in Int J Fract 169:49-60, 2011). The model was fully able to predict experimental results in terms of the local surface energy at the crack tip and the total energy release rate at different crack speeds. The predicted distributions of stress and dissipation around the propagating crack tip are presented. The predicted crack tip profiles also agree qualitatively with experimental findings.

Rock Fracture Toughness Under Mode II Loading: A Theoretical Model Based on Local Strain Energy Density

NASA Astrophysics Data System (ADS)

Rashidi Moghaddam, M.; Ayatollahi, M. R.; Berto, F.

2018-01-01

The values of mode II fracture toughness reported in the literature for several rocks are studied theoretically by using a modified criterion based on strain energy density averaged over a control volume around the crack tip. The modified criterion takes into account the effect of T-stress in addition to the singular terms of stresses/strains. The experimental results are related to mode II fracture tests performed on the semicircular bend and Brazilian disk specimens. There are good agreements between theoretical predictions using the generalized averaged strain energy density criterion and the experimental results. The theoretical results reveal that the value of mode II fracture toughness is affected by the size of control volume around the crack tip and also the magnitude and sign of T-stress.

Thermal Analysis by Numerical Methods of Debonding Effects near the Crack Tip under Composite Repairs

NASA Astrophysics Data System (ADS)

Tsamasphyros, G. J.; Kanderakis, G. N.; Marioli-Riga, Z. P.

2003-05-01

Composite patch repair of metallic structures has become a rapidly grown technology in the aerospace field due to the demand for significant increases in the useful life of both military and civilian aircraft. This has led to significant advances overall in the repair technology of cracked metallic structures. Adhesively bonded composite reinforcements offer remarkable advantages such as mechanical efficiency, repair time, cost reduction, high structural integrity, repair inspectability, damage tolerance to further causes of future strains, anticorrosion and antifretting properties. However, because of the different nature and properties of the materials that form a repair (metals, composites, adhesives), side-effects may occur: debonding due to high stress concentration in the vicinity of the crack, thermal residual stresses because of different thermal expansion coefficients of the adherents, etc. In this paper a three-dimensional finite elements analysis of the area around a patch repaired crack of a typical aircraft fuselage is performed, taking into account both the properties and the geometry of the involved materials. Examined in this case are 2024-T3 aluminum alloy as base material, FM-73 as the adhesive system and F4/5521 boron/epoxy prepreg as the patch material. Through the thickness stresses near the crack tip and along the patch edges with and without temperature effects are calculated and debonding near the crack tip is examined. Finally, the calculated results are compared with existing theories.

Pulverization provides a mechanism for the nucleation of earthquakes at low stress on strong faults

USGS Publications Warehouse

Felzer, Karen R.

2014-01-01

An earthquake occurs when rock that has been deformed under stress rebounds elastically along a fault plane (Gilbert, 1884; Reid, 1911), radiating seismic waves through the surrounding earth. Rupture along the entire fault surface does not spontaneously occur at the same time, however. Rather the rupture starts in one tiny area, the rupture nucleation zone, and spreads sequentially along the fault. Like a row of dominoes, one bit of rebounding fault triggers the next. This triggering is understood to occur because of the large dynamic stresses at the tip of an active seismic rupture. The importance of these crack tip stresses is a central question in earthquake physics. The crack tip stresses are minimally important, for example, in the time predictable earthquake model (Shimazaki and Nakata, 1980), which holds that prior to rupture stresses are comparable to fault strength in many locations on the future rupture plane, with bits of variation. The stress/strength ratio is highest at some point, which is where the earthquake nucleates. This model does not require any special conditions or processes at the nucleation site; the whole fault is essentially ready for rupture at the same time. The fault tip stresses ensure that the rupture occurs as a single rapid earthquake, but the fact that fault tip stresses are high is not particularly relevant since the stress at most points does not need to be raised by much. Under this model it should technically be possible to forecast earthquakes based on the stress-renewaql concept, or estimates of when the fault as a whole will reach the critical stress level, a practice used in official hazard mapping (Field, 2008). This model also indicates that physical precursors may be present and detectable, since stresses are unusually high over a significant area before a large earthquake.

The noncontinuum crack tip deformation behavior of surface microcracks

NASA Astrophysics Data System (ADS)

Morris, W. L.

1980-07-01

The crack tip opening displacement (CTOD) of small surface fatigue cracks (lengths of the grain size) in Al 2219-T851 depends upon the location of a crack relative to the grain boundaries. Both CTOD and crack tip closure stress are greatest when the crack tip is a large distance from the next grain boundary in the direction of crack propagation. Contrary to behavioral trends predicted by continuum fracture mechanics, crack length has no detectable effect on the contribution of plastic deformation to CTOD. It is apparent from these observations that the region of significant plastic deformation is confined by the grain boundaries, resulting in a plastic zone size that is insensitive to crack length and to external load.

HIV-1 Tat targets Tip60 to impair the apoptotic cell response to genotoxic stresses

PubMed Central

Col, Edwige; Caron, Cécile; Chable-Bessia, Christine; Legube, Gaelle; Gazzeri, Sylvie; Komatsu, Yasuhiko; Yoshida, Minoru; Benkirane, Monsef; Trouche, Didier; Khochbin, Saadi

2005-01-01

HIV-1 transactivator Tat uses cellular acetylation signalling by targeting several cellular histone acetyltransferases (HAT) to optimize its various functions. Although Tip60 was the first HAT identified to interact with Tat, the biological significance of this interaction has remained obscure. We had previously shown that Tat represses Tip60 HAT activity. Here, a new mechanism of Tip60 neutralization by Tat is described, where Tip60 is identified as a substrate for the newly reported p300/CBP-associated E4-type ubiquitin-ligase activity, and Tat uses this mechanism to induce the polyubiquitination and degradation of Tip60. Tip60 targeting by Tat results in a dramatic impairment of the Tip60-dependent apoptotic cell response to DNA damage. These data reveal yet unknown strategies developed by HIV-1 to increase cell resistance to genotoxic stresses and show a role of Tat as a modulator of cellular protein ubiquitination. PMID:16001085

Cytotoxicity of aluminum oxide nanoparticles on Allium cepa root tip--effects of oxidative stress generation and biouptake.

PubMed

Rajeshwari, A; Kavitha, S; Alex, Sruthi Ann; Kumar, Deepak; Mukherjee, Anita; Chandrasekaran, Natarajan; Mukherjee, Amitava

2015-07-01

The commercial usage of Al2O3 nanoparticles (Al2O3 NPs) has gone up significantly in the recent times, enhancing the risk of environmental contamination with these agents and their consequent adverse effects on living systems. The current study has been designed to evaluate the cytogenetic potential of Al2O3 NPs in Allium cepa (root tip cells) at a range of exposure concentrations (0.01, 0.1, 1, 10, and 100 μg/mL), their uptake/internalization profile, and the oxidative stress generated. We noted a dose-dependent decrease in the mitotic index (42 to 28 %) and an increase in the number of chromosomal aberrations. Various chromosomal aberrations, e.g. sticky, multipolar and laggard chromosomes, chromosomal breaks, and the formation of binucleate cells, were observed by optical, fluorescence, and confocal laser scanning microscopy. FT-IR analysis demonstrated the surface chemical interaction between the nanoparticles and root tip cells. The biouptake of Al2O3 in particulate form led to reactive oxygen species generation, which in turn probably contributed to the induction of chromosomal aberrations.

Origin of bias-stress induced instability in organic thin-film transistors with semiconducting small-molecule/insulating polymer blend channel.

PubMed

Park, Ji Hoon; Lee, Young Tack; Lee, Hee Sung; Lee, Jun Young; Lee, Kimoon; Lee, Gyu Baek; Han, Jiwon; Kim, Tae Woong; Im, Seongil

2013-03-13

The stabilities of a blending type organic thin-film transistor with phase-separated TIPS-pentacene channel layer were characterized under the conditions of negative-bias-stress (NBS) and positive-bias-stress (PBS). During NBS, threshold voltage (Vth) shifts noticeably. NBS-imposed devices revealed interfacial trap density-of-states (DOS) at 1.56 and 1.66 eV, whereas initial device showed the DOS at only 1.56 eV, as measured by photoexcited charge-collection spectroscopy (PECCS) method. Possible origin of this newly created defect is related to ester group in PMMA, which induces some hole traps at the TIPS-pentacene/i-PMMA interface. PBS-imposed device showed little Vth shift but visible off-current increase as "back-channel" effect, which is attributed to the water molecules trapped on the TFT surface.

Nasal tip support: A finite element analysis of the role of the caudal septum during tip depression

PubMed Central

Manuel, Cyrus T.; Leary, Ryan; Protsenko, Dmitriy E.; Wong, Brian J.F.

2014-01-01

Objective/Hypothesis Although minor and major tip support mechanisms have been described in detail, no quantitative models exist to provide support for the relative contributions of the structural properties of the major alar cartilage, the fibrous attachments to surrounding structures, and the rigid support structures in an objective manner. Study Design The finite element method was used to compute the stress distribution in the nose during simple tip compression, and then identify the specific anatomic structures that resist deformation and thus contribute to “tip support”. Additionally, the impact of caudal septal resection on nasal tip support was examined. Method The computer models consisted of three tissue components with anatomically correct geometries for skin and bone derived from CT data. Septum, upper lateral cartilages, and major alar cartilages were fitted within the model using 3D CAD software. 5mm nasal tip compression was performed on the models with caudal septal resection (3mm and 5 mm) and without resection to simulate palpation, then the resulting spatial distribution of stress and displacement was calculated. Results The von Mises stress in the normal model was primarily concentrated along medial crural angle. As caudal septum length was reduced, stress was redistributed to adjacent soft tissue and bone, resulting in less force acting on the septum. In all models, displacement was greatest near the intermediate crura. Conclusions These models are the first step in the comprehensive mechanical analysis of nasal tip dynamics. Our model supports the concept of the caudal septum and major alar cartilage as providing the majority of critical load-bearing support. Level of Evidence N/A PMID:23878007

Determination of Stress Intensity Factor Distributions for "Interface" Cracks in Incompressible, Dissimilar Materials

NASA Technical Reports Server (NTRS)

Smith, C. W.

1997-01-01

The present study was undertaken in order to develop test methods and procedures for measuring the variation of the stress intensity factor through the thickness in bimaterial specimens containing cracks within and parallel to the bond line using the frozen stress photoelastic method. Since stress freezing materials are incompressible above critical temperature, and since thick plates are to be employed which tend to produce a state of plane strain near the crack tip, the interface near tip fracture equations reduce to the classic form for homogeneous materials. Moreover, zero thickness interfaces do not exist when materials are bonded together. It was decided early on that it would be important to insure a uniform straight and accurate crack tip region through the thickness of the body to reduce scatter in the SIF distribution through the thickness. It was also observed that rubberlike materials which were desired to be modeled exhibited significant tip blunting prior to crack extension and that some blunting of the tip would provide a more realistic model. It should be noted that, in normal stress freezing photoelastic work, it is considered good practice to avoid utilizing data near bond lines in photoelastic models due to the bond line stresses which inevitably develop when two parts are bonded together. Thus, the present study involves certain exploratory aspects in deviating from standard practice in stress freezing work. With the above ideas in mind, several different test methods were investigated and are described in the following sections and appendices. The geometry selected for the program was a thick, edge cracked specimen containing a bond line.

Measurement and modeling of temperature-dependent hydrogen embrittlement of chromium-molybdenum steel to enable fitness-for-service life prediction

NASA Astrophysics Data System (ADS)

Al-Rumaih, Abdullah M.

Thick-wall vessels in petrochemical applications, fabricated from 2.25Cr-1Mo steel, operate in pressurized H2 at elevated temperature for more than 20 years. There is a concern regarding the interactive effects of temper-embrittlement and hydrogen-embrittlement on fitness-for-service during startup/shutdown near ambient temperatures. The database of degraded material properties is inadequate to enable accurate assessment. Specifically, H loss from small fracture mechanics specimens was substantial during either long-term or elevated temperature experiments. In addition, the influence of temperature on H-embrittlement of Cr-Mo steel is not fundamentally understood. The objectives of this research are to (1) design a novel laboratory method to retain H in small fracture mechanics specimens, (2) characterize the temperature dependent internal hydrogen embrittlement (IHE) of Cr-Mo weld metal using the developed method, and (3) model H distribution near a stressed crack tip in a H-trap laden bainitic microstructure to fundamentally understand the temperature dependent IHE. The new slotted CT specimen approach, with 3.0 wppm total H produced on the slot surface from acidified thiosulfate charging, quantitatively characterized the temperature dependent threshold stress intensity (KIH and K TH) and kinetics (da/dtRISE and da/dtHOLD) of IHE in Cr-Mo weld metal during both rising and slowly falling K loading. IHE was produced successfully and damage was more severe during rising K loading due to the role of crack tip plasticity in H cracking of low to moderate strength steel. The critical temperature at which embrittlement ceased is in the range 45°C < Tc ≤ 60°C for the weld metal and H content studied. This method provides a useful new tool to generate fracture mechanics based fitness-for-service data. A three-dimensional finite element diffusion model, that accounts for the effect of crack tip plasticity and trapping on H transport, established K, dK/dt and temperature dependencies of H distributed about the stressed crack tip in the slotted and standard CT specimens. The slot approach provides higher H levels for long times and/or elevated temperatures, and solves the problem of H loss during testing. The diffusion model was used to understand temperature dependent ME Stress field interaction energy (EH) vs. temperature at the blunted crack tip for Cr-Mo steel is lower than the estimated binding energies (EB) for the various surrounding reversible trap sites; indicating with probability calculations that H is unlikely to repartition from these traps to the stress field. Hydrogen transport to the fracture process zone (FPZ) from the surrounding bulk is by diffusion, enhanced by a plasticity-related mechanism. Interfaces and boundaries within the FPZ in the dilated region at the crack tip are the sites that form the interconnected H-fracture path. Trapped H concentration in these fracture sites critically governs the temperature dependent IHE, with negligible effect of temperature (≤100°C) on the crack tip stress field. The measured KIH for subcritical H cracking under rising K decreases systematically with increasing H trapped in the FPZ, as established by diffusion modeling for a variety of H cracking and temperature conditions. Diffusion model predictions of the critical trapped H concentration indicate that the Tc at which IHE is eliminated from Cr-Mo weld metal should be ≥110°C for a thick-wall hydroprocessing vessel with total-peak H of ≈4.0 wppm.

Insights on the development, kinetics, and variation of photoinhibition using chlorophyll fluorescence imaging of a chilled, variegated leaf.

PubMed

Hogewoning, Sander W; Harbinson, Jeremy

2007-01-01

The effect of chilling on photosystem II (PSII) efficiency was studied in the variegated leaves of Calathea makoyana, in order to gain insight into the causes of chilling-induced photoinhibition. Additionally, a relationship was revealed between (chilling) stress and variation in photosynthesis. Chilling treatments (5 degrees C and 10 degrees C) were performed for different durations (1-7 d) under a moderate irradiance (120 micromol m-2 s-1). The individual leaves were divided into a shaded zone and two illuminated, chilled zones. The leaf tip and sometimes the leaf base were not chilled. Measurements of the dark-adapted Fv/Fm were made on the different leaf zones at the end of the chilling treatment, and then for several days thereafter to monitor recovery. Chilling up to 7 d in the dark did not affect PSII efficiency and visual appearance, whereas chilling in the light caused severe photoinhibition, sometimes followed by leaf necrosis. Photoinhibition increased with the duration of the chilling period, whereas, remarkably, chilling temperature had no effect. In the unchilled leaf tip, photoinhibition also occurred, whereas in the unchilled leaf base it did not. Whatever the leaf zone, photoinhibition became permanent if the mean value dropped below 0.4, although chlorosis and necrosis were associated solely with chilled illuminated tissue. Starch accumulated in the unchilled leaf tip, in contrast to the adjacent chilled irradiated zone. This suggests that photoinhibition was due to a secondary effect in the unchilled leaf tip (sink limitation), whereas it was a direct effect of chilling and irradiance in the chilled illuminated zones. The PSII efficiency and its coefficient of variation showed a unique negative linearity across all leaf zones and different tissue types. The slope of this curve was steeper for chilled leaves than it was for healthy, non-stressed leaves, suggesting that the coefficient of variation may be an important tool for assessing stress in leaves.

Theoretical aspects of fracture mechanics

NASA Astrophysics Data System (ADS)

Atkinson, C.; Craster, R. V.

1995-03-01

In this review we try to cover various topics in fracture mechanics in which mathematical analysis can be used both to aid numerical methods and cast light on key features of the stress field. The dominant singular near crack tip stress field can often be parametrized in terms of three parameters K(sub I), K(sub II) and K(sub III) designating three fracture modes each having an angular variation entirely specified for the stress tensor and displacement vector. These results and contact zone models for removing the interpenetration anomaly are described. Generalizations of the above results to viscoelastic media are described. For homogeneous media with constant Poisson's ratio the angular variation of singular crack tip stresses and displacements are shown to be the same for all time and the same inverse square root singularity as occurs in the elastic medium case is found (this being true for a time varying Poisson ratio too). Only the stress intensity factor varies through time dependence of loads and relaxation properties of the medium. For cracks against bimaterial interfaces both the stress singularity and angular form evolve with time as a function of the time dependent properties of the bimaterial. Similar behavior is identified for sharp notches in viscoelastic plates. The near crack tip behavior in material with non-linear stress strain laws is also identified and stress singularities classified in terms of the hardening exponent for power law hardening materials. Again for interface cracks the near crack tip behavior requires careful analysis and it is shown that more than one singular term may be present in the near crack tip stress field. A variety of theory and applications is presented for inhomogeneous elastic media, coupled thermoelasticity etc. Methods based on reciprocal theorems and dual functions which can also aid in getting awkward singular stress behavior from numerical solutions are also reviewed. Finally theoretical calculations of fiber reinforced and particulate composite toughening mechanisms are briefly reviewed.

Incubation of Fear Is Regulated by TIP39 Peptide Signaling in the Medial Nucleus of the Amygdala

PubMed Central

Tsuda, Mumeko C.; Yeung, Ho-Man; Kuo, Jonathan

2015-01-01

Fear-related psychopathologies such as post-traumatic stress disorder are characterized by impaired extinction of fearful memories. Recent behavioral evidence suggests that the neuropeptide tuberoinfundibular peptide of 39 residues (TIP39), via its receptor, the parathyroid hormone 2 receptor (PTH2R), modulates fear memory. Here we examined the anatomical and cellular localization of TIP39 signaling that contributes to the increase in fear memory over time following a traumatic event, called fear memory incubation. Contextual freezing, a behavioral sign of fear memory, was significantly greater in PTH2R knock-out than wild-type male mice 2 and 4 weeks after a 2 s 1.5 mA footshock. PTH2R knock-out mice had significantly reduced c-Fos activation in the medial amygdala (MeA) following both footshock and fear recall, but had normal activation in the hypothalamic paraventricular nucleus and the amygdalar central nucleus compared with wild-type. We therefore investigated the contribution of MeA TIP39 signaling to fear incubation. Similar to the effect of global TIP39 signaling loss, blockade of TIP39 signaling in the MeA by lentivirus-mediated expression of a secreted PTH2R antagonist augmented fear incubation. Ablation of MeA PTH2R-expressing neurons also strengthened the fear incubation effect. Using the designer receptor exclusively activated by designer drug pharmacogenetic approach, transient inhibition of MeA PTH2R-expressing neurons before or immediately after the footshock, but not at the time of fear recall, enhanced fear incubation. Collectively, the findings demonstrate that TIP39 signaling within the MeA at the time of an aversive event regulates the increase over time in fear associated with the event context. SIGNIFICANCE STATEMENT Fear-related psychopathologies such as post-traumatic stress disorder (PTSD) are characterized by excessive responses to trauma-associated cues. Fear responses can increase over time without additional cue exposure or stress. This work shows that modulatory processes within the medial nucleus of the amygdala near the time of a traumatic event influence the strength of fear responses that occur much later. The modulatory processes include signaling by the neuropeptide TIP39 and neurons that express its receptor. These findings will help in the understanding of why traumatic events sometimes have severe psychological consequences. One implication is that targeting neuromodulation in the medial amygdala could potentially help prevent development of PTSD. PMID:26338326

Incubation of Fear Is Regulated by TIP39 Peptide Signaling in the Medial Nucleus of the Amygdala.

PubMed

Tsuda, Mumeko C; Yeung, Ho-Man; Kuo, Jonathan; Usdin, Ted B

2015-09-02

Fear-related psychopathologies such as post-traumatic stress disorder are characterized by impaired extinction of fearful memories. Recent behavioral evidence suggests that the neuropeptide tuberoinfundibular peptide of 39 residues (TIP39), via its receptor, the parathyroid hormone 2 receptor (PTH2R), modulates fear memory. Here we examined the anatomical and cellular localization of TIP39 signaling that contributes to the increase in fear memory over time following a traumatic event, called fear memory incubation. Contextual freezing, a behavioral sign of fear memory, was significantly greater in PTH2R knock-out than wild-type male mice 2 and 4 weeks after a 2 s 1.5 mA footshock. PTH2R knock-out mice had significantly reduced c-Fos activation in the medial amygdala (MeA) following both footshock and fear recall, but had normal activation in the hypothalamic paraventricular nucleus and the amygdalar central nucleus compared with wild-type. We therefore investigated the contribution of MeA TIP39 signaling to fear incubation. Similar to the effect of global TIP39 signaling loss, blockade of TIP39 signaling in the MeA by lentivirus-mediated expression of a secreted PTH2R antagonist augmented fear incubation. Ablation of MeA PTH2R-expressing neurons also strengthened the fear incubation effect. Using the designer receptor exclusively activated by designer drug pharmacogenetic approach, transient inhibition of MeA PTH2R-expressing neurons before or immediately after the footshock, but not at the time of fear recall, enhanced fear incubation. Collectively, the findings demonstrate that TIP39 signaling within the MeA at the time of an aversive event regulates the increase over time in fear associated with the event context. Fear-related psychopathologies such as post-traumatic stress disorder (PTSD) are characterized by excessive responses to trauma-associated cues. Fear responses can increase over time without additional cue exposure or stress. This work shows that modulatory processes within the medial nucleus of the amygdala near the time of a traumatic event influence the strength of fear responses that occur much later. The modulatory processes include signaling by the neuropeptide TIP39 and neurons that express its receptor. These findings will help in the understanding of why traumatic events sometimes have severe psychological consequences. One implication is that targeting neuromodulation in the medial amygdala could potentially help prevent development of PTSD. Copyright © 2015 the authors 0270-6474/15/3512152-10$15.00/0.

Thermodynamic analysis on the role of hydrogen in anodic stress corrosion cracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiao, L.; Mao, X.

1995-11-01

A synergistic effect of hydrogen and stress on a corrosion rate was analyzed with thermodynamics. The results showed that an interaction of stress and hydrogen could increase the corrosion rate remarkably. Stress corrosion cracking (SCC) of austenitic stainless steel (ASS) was investigated in boiling chloride solution to confirm the analysis. Hydrogen could be introduced into the specimen concentrated at the crack tip during SCC in boiling LiCl solution (143 C). The concentrating factor is about 3 which is consistent with calculated results according to stress induced diffusion.

Experimental and analytical study of ceramic-coated turbine-tip shroud seals for small turbine engines

NASA Technical Reports Server (NTRS)

Biesiadny, T. J.; Mcdonald, G. E.; Hendricks, R. C.; Little, J. K.; Robinson, R. A.; Klann, G. A.; Lassow, E. S.

1985-01-01

The results of an experimental and analytical evaluation of ceramic turbine tip shrouds within a small turbine engine operating environment are presented. The ceramic shrouds were subjected to 1001 cycles between idle and high power and steady-state conditions for a total of 57.8 engine hr. Posttest engine inspection revealed mud-flat surface cracking, which was attributed to microcracking under tension with crack penetration to the ceramic and bond coat interface. Sections and micrographs tend to corroborate the thesis. The engine test data provided input to a thermomechanical analysis to predict temperature and stress profiles throughout the ceramic gas-path seal. The analysis predicts cyclic thermal stresses large enough to cause the seal to fail. These stresses are, however, mitigated by inelastic behavior of the shroud materials and by the microfracturing that tensile stresses produce. Microfracturing enhances shroud longevity during early life but provides the failure mechanism during life but provides the failure mechanism during extended life when coupled with the time dependent inelastic materials effects.

A note on the effect of bending stiffness of stringers attached to a plate with a crack

NASA Technical Reports Server (NTRS)

Arin, K.

1974-01-01

An infinite stringer partially bonded to a plate through a layer of adhesive is considered. The stringer had bending as well as longitudinal stiffness. The effect of the stringer's bending rigidity on the stress intensity factor at the tip of the crack is illustrated. Shear stress distribution between the plate and the stringer and the stress intensity factors are obtained from the solution of a system of Fredholm integral equations. The continuity of displacements along the line of bond is represented by the equations.

Comparison of TVT and TOT on urethral mobility and surgical outcomes in stress urinary incontinence with hypermobile urethra.

PubMed

Cavkaytar, Sabri; Kokanalı, Mahmut Kuntay; Guzel, Ali Irfan; Ozer, Irfan; Aksakal, Orhan Seyfi; Doganay, Melike

2015-07-01

To compare the change of urethral mobility after midurethral sling procedures in stress urinary incontinence with hypermobile urethra and assess these findings with surgical outcomes. 141 women who agreed to undergo midurethral sling operations due to stress urinary incontinence with hypermobile urethra were enrolled in this non-randomized prospective observational study. Preoperatively, urethral mobility was measured by Q tip test. All women were asked to complete Urogenital Distress Inventory Short Form (UDI-6) and Incontinence Impact Questionnaire Short Form (IIQ-7) to assess the quality of life. Six months postoperatively, Q tip test and quality of life assessment were repeated. The primary surgical outcomes were classified as cure, improvement and failure. Transient urinary obstruction, de novo urgency, voiding dysfunction were secondary surgical outcomes. Of 141 women, 50 (35. 5%) women underwent TOT, 91 (64.5%) underwent TVT. In both TOT and TVT groups, postoperative Q tip test values, IIQ-7 and UDI-6 scores were statistically reduced when compared with preoperative values. Postoperative Q tip test value in TVT group was significantly smaller than in TOT group [25°(15-45°) and 20° (15-45°), respectively]. When we compared the Q-tip test value, IIQ-7 and UDI-6 scores changes, there were no statistically significant changes between the groups. Postoperative urethral mobility was more frequent in TOT group than in TVT group (40% vs 23.1%, respectively). Postoperative primary and secondary outcomes were similar in both groups. Although midurethral slings decrease the urethtal hypermobility, postoperative mobility status of urethra does not effect surgical outcomes of midurethral slings in women with preoperative urethral hypermobility. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Determination of Fracture Parameters for Multiple Cracks of Laminated Composite Finite Plate

NASA Astrophysics Data System (ADS)

Srivastava, Amit Kumar; Arora, P. K.; Srivastava, Sharad Chandra; Kumar, Harish; Lohumi, M. K.

2018-04-01

A predictive method for estimation of stress state at zone of crack tip and assessment of remaining component lifetime depend on the stress intensity factor (SIF). This paper discusses the numerical approach for prediction of first ply failure load (FL), progressive failure load, SIF and critical SIF for multiple cracks configurations of laminated composite finite plate using finite element method (FEM). The Hashin and Chang failure criterion are incorporated in ABAQUS using subroutine approach user defined field variables (USDFLD) for prediction of progressive fracture response of laminated composite finite plate, which is not directly available in the software. A tensile experiment on laminated composite finite plate with stress concentration is performed to validate the numerically predicted subroutine results, shows excellent agreement. The typical results are presented to examine effect of changing the crack tip distance (S), crack offset distance (H), and stacking fiber angle (θ) on FL, and SIF .

Corrosion fatigue crack propagation in metals

NASA Technical Reports Server (NTRS)

Gangloff, Richard P.

1990-01-01

This review assesses fracture mechanics data and mechanistic models for corrosion fatigue crack propagation in structural alloys exposed to ambient temperature gases and electrolytes. Extensive stress intensity-crack growth rate data exist for ferrous, aluminum and nickel based alloys in a variety of environments. Interactive variables (viz., stress intensity range, mean stress, alloy composition and microstructure, loading frequency, temperature, gas pressure and electrode potential) strongly affect crack growth kinetics and complicate fatigue control. Mechanistic models to predict crack growth rates were formulated by coupling crack tip mechanics with occluded crack chemistry, and from both the hydrogen embrittlement and anodic dissolution/film rupture perspectives. Research is required to better define: (1) environmental effects near threshold and on crack closure; (2) damage tolerant life prediction codes and the validity of similitude; (3) the behavior of microcrack; (4) probes and improved models of crack tip damage; and (5) the cracking performance of advanced alloys and composites.

The crack problem in a specially orthotropic shell with double curvature

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1983-01-01

The crack problem of a shallow shell with two nonzero curvatures is considered. It is assumed that the crack lies in one of the principal planes of curvature and the shell is under Mode I loading condition. The material is assumed to be specially orthotropic. After giving the general formulation of the problem the asymptotic behavior of the stress state around the crack tip is examined. The analysis is based on Reissner's transverse shear theory. Thus, as in the bending of cracked plates, the asymptotic results are shown to be consistent with that obtained from the plane elasticity solution of crack problems. Rather extensive numerical results are obtained which show the effect of material orthotropy on the stress intensity factors in cylindrical and spherical shells and in shells with double curvature. Other results include the stress intensity factors in isotropic toroidal shells with positive or negative curvature ratio, the distribution of the membrane stress resultant outside the crack, and the influence of the material orthotropy on the angular distribution of the stresses around the crack tip. Previously announced in STAR as N83-16782

The crack problem in a specially orthotropic shell with double curvature

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1982-01-01

The crack problem of a shallow shell with two nonzero curvatures is considered. It is assumed that the crack lies in one of the principal planes of curvature and the shell is under Mode I loading condition. The material is assumed to be specially orthotropic. After giving the general formulation of the problem the asymptotic behavior of the stress state around the crack tip is examined. The analysis is based on Reissner's transverse shear theory. Thus, as in the bending of cracked plates, the asymptotic results are shown to be consistent with that obtained from the plane elasticity solution of crack problems. Rather extensive numerical results are obtained which show the effect of material orthotropy on the stress intensity factors in cylindrical and spherical shells and in shells with double curvature. Other results include the stress intensity factors in isotropic toroidal shells with positive or negative curvature ratio, the distribution of the membrane stress resultant outside the crack, and the influence of the material orthotropy on the angular distribution of the stresses around the crack tip.

[Finite element analysis of mechanical characteristics during retracting mandibular incisors through sliding mechanics].

PubMed

Gu, Yong-Jia; Wu, Yan-Ping; Gao, Mei-Qin; Yao, Ning; Chen, Wen-Jing

2008-10-01

To analyze the mechanical characteristic changes of teeth and arch under different loading direction during retracting mandibular incisors through implant, simulating clinical loading system. Three- dimensional finite element model, including brackets, archwire, crampable hooks and implants, was reconstructed. The force direction was determined by connecting the points in crampable hook and the center point of implant, and the force point and force direction were changed with the adjustment of the height of crampable hook and the height of implant. Then three-dimensional movement trend of teeth, stress distribution in periodontal membrane and the largest displacement of archwire nodes in each group were calculated and analyzed. SPSS13.0 software package was used for statistical analysis. It was found that the height of implant and the height of crampable hook were correlated with the movement of teeth and stress distribution in periodontal membrane (P<0.01). The movement trend of teeth in the condition of different height of implant and different height of crampable hook was illustrated as follows:(1)with the height increase of crampable hook, the movement trend of the central and lateral incisors varied from mesial lingual tipping to mesial labial tipping. However, canines tipped distally and lingually; the second premolars tipped mesially and lingually, and the first molar roots tipped distally and buccally with decreasing tipping angle. (2) The largest stress distribution in the whole arch was located in the labial apical one-third area of the lateral incisors, while that of canines and the first molars was located in the alveolar ridges and root bifurcations. These findings indicate that the different movement trend during retracting anterior teeth can be achieved through the adjustment of the height of crampable hook, and implant, anchorage can effectively control anterior movement of the posterior teeth. Supported by Research Fund of Bureau of Science and Technology of Nantong City (Grant No. S40023).

Desiccation and osmotic stress increase the abundance of mRNA of the tonoplast aquaporin BobTIP26-1 in cauliflower cells.

PubMed

Barrieu, F; Marty-Mazars, D; Thomas, D; Chaumont, F; Charbonnier, M; Marty, F

1999-07-01

Changes in vacuolar structure and the expression at the RNA level of a tonoplast aquaporin (BobTIP26-1) were examined in cauliflower (Brassicaoleracea L. var. botrytis) under water-stress conditions. Gradual drying out of slices of cauliflower floret tissue caused its collapse, with a shrinkage in tissue and cell volumes and an apparent vesiculation of the central vacuole, whereas osmotic stress resulted in plasmolysis with a collapse of the cytoplasm and the central vacuole within. Osmotic stress caused a rapid and substantial increase in BobTIP26 mRNA in slices of floret tissue. Exposure of tissue slices to a regime of desiccation showed a slower but equally large rise in BobTIP26 mRNA followed by a rapid decline upon rehydration. In situ hybridization showed that BobTIP26-2 mRNA is expressed most highly in meristematic and expanding cells of the cauliflower florets and that desiccation strongly increased the expression in those cells and in differentiated cells near the xylem vessels. These data indicate that under water-deficit conditions, expression of the tonoplast aquaporin gene in cauliflower is subject to a precise regulation that can be correlated with important cytological changes in the cells.

On Generating Fatigue Crack Growth Thresholds

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Newman, James, Jr.; Forman, Royce G.

2003-01-01

The fatigue crack growth threshold, defining crack growth as either very slow or nonexistent, has been traditionally determined with standardized load reduction methodologies. These experimental procedures can induce load history effects that result in crack closure. This history can affect the crack driving force, i.e. during the unloading process the crack will close first at some point along the wake or blunt at the crack tip, reducing the effective load at the crack tip. One way to reduce the effects of load history is to propagate a crack under constant amplitude loading. As a crack propagates under constant amplitude loading, the stress intensity factor range, Delta K, will increase, as will the crack growth rate. da/dN. A fatigue crack growth threshold test procedure is experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R. The authors have chosen to study a ductile aluminum alloy where the plastic deformations generated during testing may be of the magnitude to impact the crack opening.

On stress field near a stationary crack tip

NASA Technical Reports Server (NTRS)

Nemat-Nasser, S.; Obata, M.

1984-01-01

It is well known that the stress and elastic-plastic deformation fields near a crack tip have important roles in the corresponding fracture process. For elastic-perfectly-plastic solids, different solutions are given in the literature. In this work several of these solutions are examined and compared for Mode I (tension), Mode II (shear), and mixed Modes I and II loading conditions in plane strain. By consideration of the dynamic solution, it is shown that the assumption that the material is yielding all around a crack tip may not be reasonable in all cases. By admitting the existence of some elastic sectors, continuous stress fields are obtained even for mixed Modes I and II.

Finite element solutions for crack-tip behavior in small-scale yielding

NASA Technical Reports Server (NTRS)

Tracey, D. M.

1976-01-01

The subject considered is the stress and deformation fields in a cracked elastic-plastic power law hardening material under plane strain tensile loading. An incremental plasticity finite element formulation is developed for accurate analysis of the complete field problem including the extensively deformed near tip region, the elastic-plastic region, and the remote elastic region. The formulation has general applicability and was used to solve the small scale yielding problem for a set of material hardening exponents. Distributions of stress, strain, and crack opening displacement at the crack tip and through the elastic-plastic zone are presented as a function of the elastic stress intensity factor and material properties.

Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedman, E.

1998-11-25

Marty brittle fracture evaluation procedures include plasticity corrections to elastically computed stress intensity factors. These corrections, which are based on the existence of a plastic zone in the vicinity of the crack tip, can overestimate the plasticity effect for a crack embedded in a stress concentration region in which the elastically computed stress exceeds the yield strength of the material in a localized zone. The interactions between the crack, which acts to relieve the high stresses driving the crack, plasticity effects in the stress concentration region, and the nature and source of the loading are examined by formulating explicit flawmore » finite element models for a crack emanating from the root of a notch located in a panel subject to an applied tensile stress. The results of these calculations provide conditions under which a crack-tip plasticity correction based on the Irwin plastic zone size overestimates the plasticity effect. A failure assessment diagram (FAD) curve is used to characterize the effect of plasticity on the crack driving force and to define a less restrictive plasticity correction for cracks at notch roots when load-controlled boundary conditions are imposed. The explicit flaw finite element results also demonstrate that stress intensity factors associated with load-controlled boundary conditions, such as those inherent in the ASME Boiler and Pressure Vessel Code as well as in most handbooks of stress intensity factors, can be much higher than those associated with displacement-controlled conditions, such as those that produce residual or thermal stresses. Under certain conditions, the inclusion of plasticity effects for cracks loaded by displacement-controlled boundary conditions reduces the crack driving force thus justifying the elimination of a plasticity correction for such loadings. The results of this study form the basis for removing unnecessary conservatism from flaw evaluation procedures that utilize plasticity corrections.« less

The Effect of Low Oxygen Stress on Phytophthora cinnamomi Infection and Disease of Cork Oak Roots

Treesearch

Karel A. Jacobs; James D. MacDonald; Alison M. Berry; Laurence R. Costello

1997-01-01

The incidence and severity of Phytophthora cinnamomi Rands root disease was quantified in cork oak (Quercus suber L.) roots subjected to low oxygen (hypoxia) stress. Seedling root tips were inoculated with mycelial plugs of the fungus and incubated in ≤1, 3-4, or 21 percent oxygen for 5 days. Ninety-four percent of roots...

The Dynamics of Miscible Fluids: A Space Flight Experiment (MIDAS)

NASA Technical Reports Server (NTRS)

Maxworthy, T.; Meiburg, E.; Balasubramaniam, R.; Rashidnia, N.; Lauver, R.

2001-01-01

We propose a space flight experiment to study the dynamics of miscible interfaces. A less viscous fluid displaces one of higher viscosity within a tube. The two fluids are miscible in all proportions. An intruding "finger" forms that occupies a fraction of the tube. As time progresses diffusion at the interface combined with flow induced straining between the two fluids modifies the concentration and velocity distributions within the whole tube. Also, under such circumstances it has been proposed that the interfacial stresses could depend on the local concentration gradients (Korteweg stresses) and that the divergence of the velocity need not be zero, even though the flow is incompressible. We have obtained reasonable agreement for the tip velocity between numerical simulations (that ignored the Korteweg stress and divergence effects) and physical experiments only at high Peelet Numbers. However at moderate to low Pe agreement was poor. As one possibility we attributed this lack of agreement to the disregard of these effects. We propose a space experiment to measure the finger shape, tip velocity, and the velocity and concentration fields. From intercomparisons between the experiment and the calculations we can then extract values for the coefficients of the Korteweg stress terms and confirm or deny the importance of these stresses.

The Dynamics of Miscible Fluids: A Space Flight Experiment (MIDAS)

NASA Technical Reports Server (NTRS)

Maxworthy, T.; Meiburg, E.; Balasubramaniam, R.; Rashidnia, N.; Lauver, R.

2001-01-01

We propose a space flight experiment to study the dynamics of miscible interfaces. A less viscous fluid displaces one of higher viscosity within a tube. The two fluids are miscible in all proportions. An intruding "finger" forms that occupies a fraction of the tube. As time progresses diffusion at the interface combined with flow induced straining between the two fluids modifies the concentration and velocity distributions within the whole tube. Also, under such circumstances it has been proposed that the interfacial stresses could depend on the local concentration gradients (Korteweg stresses) and that the divergence of the velocity need not be zero, even though the flow is incompressible. We have obtained reasonable agreement for the tip velocity between numerical simulations (that ignored the Korteweg stress and divergence effects) and physical experiments only at high Peclet Numbers. However at moderate to low Pe agreement was poor. As one possibility we attributed this lack of agreement to the disregard of these effects. We propose a space experiment to measure the finger shape, tip velocity, and the velocity and concentration fields. From intercomparisons between the experiment and the calculations we can then extract values for the coefficients of the Korteweg stress terms and confirm or deny the importance of these stresses.

Mechanical improvement of metal reinforcement rings for a finite ring-shaped superconducting bulk

NASA Astrophysics Data System (ADS)

Huang, Chen-Guang; Zhou, You-He

2018-03-01

As a key technique, reinforcement of type-II superconducting bulks with metal rings can efficiently improve their mechanical properties to enhance the maximum trapped field. In this paper, we study the magnetostrictive and fracture behaviors of a finite superconducting ring bulk reinforced by three typical reinforcing structures composed of metal rings during the magnetizing process by means of the minimization of magnetic energy and the finite element method. After a field-dependent critical current density is adopted, the magnetostriction, pinning-induced stress, and crack tip stress intensity factor are calculated considering the demagnetization effects. The results show that the mechanical properties of the ring bulk are strongly dependent on the reinforcing structure and the material and geometrical parameters of the metal rings. Introducing the metal ring can significantly reduce the hoop stress, and the reduction effect by internal reinforcement is much improved relative to external reinforcement. By comparison, bilateral reinforcement seems to be the best candidate structure. Only when the metal rings have particular Young's modulus and radial thickness will they contribute to improve the mechanical properties the most. In addition, if an edge crack is pre-existing in the ring bulk, the presence of metal rings can effectively avoid crack propagation since it reduces the crack tip stress intensity factor by nearly one order of magnitude.

Numerical Analysis of Crack Tip Plasticity and History Effects under Mixed Mode Conditions

NASA Astrophysics Data System (ADS)

Lopez-Crespo, Pablo; Pommier, Sylvie

The plastic behaviour in the crack tip region has a strong influence on the fatigue life of engineering components. In general, residual stresses developed as a consequence of the plasticity being constrained around the crack tip have a significant role on both the direction of crack propagation and the propagation rate. Finite element methods (FEM) are commonly employed in order to model plasticity. However, if millions of cycles need to be modelled to predict the fatigue behaviour of a component, the method becomes computationally too expensive. By employing a multiscale approach, very precise analyses computed by FEM can be brought to a global scale. The data generated using the FEM enables us to identify a global cyclic elastic-plastic model for the crack tip region. Once this model is identified, it can be employed directly, with no need of additional FEM computations, resulting in fast computations. This is done by partitioning local displacement fields computed by FEM into intensity factors (global data) and spatial fields. A Karhunen-Loeve algorithm developed for image processing was employed for this purpose. In addition, the partitioning is done such as to distinguish into elastic and plastic components. Each of them is further divided into opening mode and shear mode parts. The plastic flow direction was determined with the above approach on a centre cracked panel subjected to a wide range of mixed-mode loading conditions. It was found to agree well with the maximum tangential stress criterion developed by Erdogan and Sih, provided that the loading direction is corrected for residual stresses. In this approach, residual stresses are measured at the global scale through internal intensity factors.

Injector tip for an internal combustion engine

DOEpatents

Shyu, Tsu Pin; Ye, Wen

2003-05-20

This invention relates to a the tip structure of a fuel injector as used in a internal combustion engine. Internal combustion engines using Homogeneous Charge Compression Ignition (HCCI) technology require a tip structure that directs fuel spray in a downward direction. This requirement necessitates a tip design that is capable of withstanding mechanical stresses associated with the design.

Coping with Terrorism--Helping Children with Special Needs: Tips for School Personnel and Parents.

ERIC Educational Resources Information Center

Communication Disorders Quarterly, 2002

2002-01-01

This article offers suggestions to help children with disabilities cope with terrorism. It stresses recognition of triggers and cues to anticipate rather than react to stress and offers tips for specific populations including autism; cognitive limitations; learning disabilities; visual, hearing or physical limitations; and severe emotional…

Stress Intensity Factor Plasticity Correction for Flaws in Stress Concentration Regions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedman, E.; Wilson, W.K.

2000-02-01

Plasticity corrections to elastically computed stress intensity factors are often included in brittle fracture evaluation procedures. These corrections are based on the existence of a plastic zone in the vicinity of the crack tip. Such a plastic zone correction is included in the flaw evaluation procedure of Appendix A to Section XI of the ASME Boiler and Pressure Vessel Code. Plasticity effects from the results of elastic and elastic-plastic explicit flaw finite element analyses are examined for various size cracks emanating from the root of a notch in a panel and for cracks located at fillet fadii. The results ofmore » these caluclations provide conditions under which the crack-tip plastic zone correction based on the Irwin plastic zone size overestimates the plasticity effect for crack-like flaws embedded in stress concentration regions in which the elastically computed stress exceeds the yield strength of the material. A failure assessment diagram (FAD) curve is employed to graphically c haracterize the effect of plasticity on the crack driving force. The Option 1 FAD curve of the Level 3 advanced fracture assessment procedure of British Standard PD 6493:1991, adjusted for stress concentration effects by a term that is a function of the applied load and the ratio of the local radius of curvature at the flaw location to the flaw depth, provides a satisfactory bound to all the FAD curves derived from the explicit flaw finite element calculations. The adjusted FAD curve is a less restrictive plasticity correction than the plastic zone correction of Section XI for flaws embedded in plastic zones at geometric stress concentrators. This enables unnecessary conservatism to be removed from flaw evaluation procedures that utilize plasticity corrections.« less

Caring for yourself during times of organizational change.

PubMed

Cook, C A; Buck, E A

1999-09-01

Mergers, acquisitions, and other organizational changes in the health care system pose many challenges and stresses for nursing leaders. Although considerable effort is expended helping staff adjust to change, nurse managers and executives often neglect their own vulnerability to occupational stress. The personal and organizational costs of managerial burnout are high, sometimes resulting in physical illness, mental exhaustion, and decreased productivity. This article emphasizes the importance of prevention through the recognition of potential or actual signs of organizational stress. Handy tips are provided on effective ways to cope with the stress of organizational change.

Effects of water on the strength of Zerodur

NASA Technical Reports Server (NTRS)

Tucker, Dennis S.; Setzer, Andrew

1991-01-01

An experimental design matrix was constructed to determine the effects of time and temperature water soak on the strength of Zerodur glass-ceramic. It was found that strength does increase in a nonlinear manner which is consistent with existing theories of crack tip blunting and residual stress reduction.

Interactive effects of juvenile defoliation, light conditions, and interspecific competition on growth and ectomycorrhizal colonization of Fagus sylvatica and Pinus sylvestris seedlings.

PubMed

Trocha, Lidia K; Weiser, Ewa; Robakowski, Piotr

2016-01-01

Seedlings of forest tree species are exposed to a number of abiotic (organ loss or damage, light shortage) and biotic (interspecific competition) stress factors, which may lead to an inhibition of growth and reproduction and, eventually, to plant death. Growth of the host and its mycorrhizal symbiont is often closely linked, and hence, host damage may negatively affect the symbiont. We designed a pot experiment to study the response of light-demanding Pinus sylvestris and shade-tolerant Fagus sylvatica seedlings to a set of abiotic and biotic stresses and subsequent effects on ectomycorrhizal (ECM) root tip colonization, seedling biomass, and leaf nitrogen content. The light regime had a more pronounced effect on ECM colonization than did juvenile damage. The interspecific competition resulted in higher ECM root tip abundance for Pinus, but this effect was insignificant in Fagus. Low light and interspecific competition resulted in lower seedling biomass compared to high light, and the effect of the latter was partially masked by high light. Leaf nitrogen responded differently in Fagus and Pinus when they grew in interspecific competition. Our results indicated that for both light-demanding (Pinus) and shade-tolerant (Fagus) species, the light environment was a major factor affecting seedling growth and ECM root tip abundance. The light conditions favorable for the growth of seedlings may to some extent compensate for the harmful effects of juvenile organ loss or damage and interspecific competition.

Root Tip Shape Governs Root Elongation Rate under Increased Soil Strength1[OPEN

PubMed Central

Kirchgessner, Norbert; Walter, Achim

2017-01-01

Increased soil strength due to soil compaction or soil drying is a major limitation to root growth and crop productivity. Roots need to exert higher penetration force, resulting in increased penetration stress when elongating in soils of greater strength. This study aimed to quantify how the genotypic diversity of root tip geometry and root diameter influences root elongation under different levels of soil strength and to determine the extent to which roots adjust to increased soil strength. Fourteen wheat (Triticum aestivum) varieties were grown in soil columns packed to three bulk densities representing low, moderate, and high soil strength. Under moderate and high soil strength, smaller root tip radius-to-length ratio was correlated with higher genotypic root elongation rate, whereas root diameter was not related to genotypic root elongation. Based on cavity expansion theory, it was found that smaller root tip radius-to-length ratio reduced penetration stress, thus enabling higher root elongation rates in soils with greater strength. Furthermore, it was observed that roots could only partially adjust to increased soil strength. Root thickening was bounded by a maximum diameter, and root tips did not become more acute in response to increased soil strength. The obtained results demonstrated that root tip geometry is a pivotal trait governing root penetration stress and root elongation rate in soils of greater strength. Hence, root tip shape needs to be taken into account when selecting for crop varieties that may tolerate high soil strength. PMID:28600344

Nanoindentation cannot accurately predict the tensile strength of graphene or other 2D materials

NASA Astrophysics Data System (ADS)

Han, Jihoon; Pugno, Nicola M.; Ryu, Seunghwa

2015-09-01

Due to the difficulty of performing uniaxial tensile testing, the strengths of graphene and its grain boundaries have been measured in experiments by nanoindentation testing. From a series of molecular dynamics simulations, we find that the strength measured in uniaxial simulation and the strength estimated from the nanoindentation fracture force can differ significantly. Fracture in tensile loading occurs simultaneously with the onset of crack nucleation near 5-7 defects, while the graphene sheets often sustain the indentation loads after the crack initiation because the sharply concentrated stress near the tip does not give rise to enough driving force for further crack propagation. Due to the concentrated stress, strength estimation is sensitive to the indenter tip position along the grain boundaries. Also, it approaches the strength of pristine graphene if the tip is located slightly away from the grain boundary line. Our findings reveal the limitations of nanoindentation testing in quantifying the strength of graphene, and show that the loading-mode-specific failure mechanism must be taken into account in designing reliable devices from graphene and other technologically important 2D materials.Due to the difficulty of performing uniaxial tensile testing, the strengths of graphene and its grain boundaries have been measured in experiments by nanoindentation testing. From a series of molecular dynamics simulations, we find that the strength measured in uniaxial simulation and the strength estimated from the nanoindentation fracture force can differ significantly. Fracture in tensile loading occurs simultaneously with the onset of crack nucleation near 5-7 defects, while the graphene sheets often sustain the indentation loads after the crack initiation because the sharply concentrated stress near the tip does not give rise to enough driving force for further crack propagation. Due to the concentrated stress, strength estimation is sensitive to the indenter tip position along the grain boundaries. Also, it approaches the strength of pristine graphene if the tip is located slightly away from the grain boundary line. Our findings reveal the limitations of nanoindentation testing in quantifying the strength of graphene, and show that the loading-mode-specific failure mechanism must be taken into account in designing reliable devices from graphene and other technologically important 2D materials. Electronic ESI (ESI) available: Modelling of polycrystalline graphene, verification of loading speed, biaxial tensile simulations, comparison of stress distribution, size effects of indenter radius, force-deflection curves, and stability analysis of crack propagation. See DOI: 10.1039/c5nr04134a

Role of sulphur atoms on stress relaxation and crack propagation in monolayer MoS2

NASA Astrophysics Data System (ADS)

Wang, Baoming; Islam, Zahabul; Zhang, Kehao; Wang, Ke; Robinson, Joshua; Haque, Aman

2017-09-01

We present in-situ transmission electron microscopy of crack propagation in a freestanding monolayer MoS2 and molecular dynamic analysis of the underlying mechanisms. Chemical vapor deposited monolayer MoS2 was transferred from sapphire substrate using interfacial etching for defect and contamination minimization. Atomic resolution imaging shows crack tip atoms sustaining 14.5% strain before bond breaking, while the stress field decays at unprecedented rate of 2.15 GPa Å-1. Crack propagation is seen mostly in the zig-zag direction in both model and experiment, suggesting that the mechanics of fracture is not brittle. Our computational model captures the mechanics of the experimental observations on crack propagation in MoS2. While molybdenum atoms carry most of the mechanical load, we show that the sliding motion of weakly bonded sulphur atoms mediate crack tip stress relaxation, which helps the tip sustain very high, localized stress levels.

Measurement and analysis of critical crack tip processes during fatigue crack growth

NASA Technical Reports Server (NTRS)

Davidson, D. L.; Hudak, S. J.; Dexter, R. J.

1985-01-01

The mechanics of fatigue crack growth under constant-amplitudes and variable-amplitude loading were examined. Critical loading histories involving relatively simple overload and overload/underload cycles were studied to provide a basic understanding of the underlying physical processes controlling crack growth. The material used for this study was 7091-T7E69, a powder metallurgy aluminum alloy. Local crack-tip parameters were measured at various times before, during, and after the overloads, these include crack-tip opening loads and displacements, and crack-tip strain fields. The latter were useed, in combination with the materials cyclic and monotonic stress-strain properties, to compute crack-tip residual stresses. The experimental results are also compared with analytical predictions obtained using the FAST-2 computer code. The sensitivity of the analytical model to constant-amplitude fatigue crack growth rate properties and to through-thickness constrain are studied.

On the measurement of the crack tip stress field as a means of determining Delta K(sub eff) under conditions of fatigue crack closure

NASA Technical Reports Server (NTRS)

Wallhead, Ian R.; Edwards, Lyndon; Poole, Peter

1994-01-01

The optical method of caustics has been successfully extended to enable stress intensity factors as low as 1MPa square root of m to be determined accurately for central fatigue cracks in 2024-T3 aluminium alloy test panels. The feasibility of using this technique to study crack closure, and to determine the effective stress intensity factor range, Delta K(sub eff), has been investigated. Comparisons have been made between the measured values of stress intensity factor, K(sub caus), and corresponding theoretical values, K(sub theo), for a range of fatigue cracks grown under different loading conditions. The values of K(sub caus) and K(sub theo) were in good agreement at maximum stress, where the cracks are fully open, while K(sub caus) exceeded K(sub theo) at minimum stress, due to crack closure. However, the levels of crack closure and values of Delta K(sub eff) obtained could not account for the variations of crack growth rate with loading conditions. It is concluded that the values of Delta K(sub eff), based on caustic measurements in a 1/square root of r stress field well outside the plastic zone, do not fully reflect local conditions which control crack tip behavior.

Experimental study of thermodynamics propagation fatigue crack in metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vshivkov, A., E-mail: vshivkov.a@icmm.ru; Iziumova, A., E-mail: fedorova@icmm.ru; Plekhov, O., E-mail: poa@icmm.ru

This work is devoted to the development of an experimental method for studying the energy balance during cyclic deformation and fracture. The studies were conducted on 304 stainless steel AISE samples. The investigation of the fatigue crack propagation was carried out on flat samples with stress concentrators. The stress concentrator was three central holes. The heat flux sensor was developed based on the Seebeck effect. This sensor was used for measuring the heat dissipation power in the examined samples during the fatigue tests. The measurements showed that the rate of fatigue crack growth depends on the heat flux at themore » crack tip and there are two propagation mode of fatigue crack with different link between the propagation mode and heat flux from crack tip.« less

Stress corrosion cracking of titanium alloys

NASA Technical Reports Server (NTRS)

May, R. C.; Beck, F. H.; Fontana, M. G.

1971-01-01

Experiments were conducted to study (1) the basic electrochemical behavior of titanium in acid chloride solutions and (2) the response of the metal to dynamic straining in the same evironment. The aim of this group of experiments was to simulate, as nearly as possible, the actual conditions which exist at the tip of a crack. One of the foremost theories proposed to explain the propagation of stress corrosion cracks is a hydrogen embrittlement theory involving the precipitation of embrittling titanium hydrides inside the metal near the crack tip. An initial survey of the basic electrochemical literature indicated that surface hydrides play a critical role in the electrochemistry of titanium in acid solutions. A comprehensive analysis of the effect of surface films, particularly hydrides, on the electrochemical behavior of titanium in these solution is presented.

Corrosion Product Film-Induced Stress Facilitates Stress Corrosion Cracking

PubMed Central

Wang, Wenwen; Zhang, Zhiliang; Ren, Xuechong; Guan, Yongjun; Su, Yanjing

2015-01-01

Finite element analyses were conducted to clarify the role of corrosion product films (CPFs) in stress corrosion cracking (SCC). Flat and U-shaped edge-notched specimens were investigated in terms of the CPF-induced stress in the metallic substrate and the stress in the CPF. For a U-shaped edge-notched specimen, the stress field in front of the notch tip is affected by the Young’s modulus of the CPF and the CPF thickness and notch geometry. The CPF-induced tensile stress in the metallic substrate is superimposed on the applied load to increase the crack tip strain and facilitate localized plasticity deformation. In addition, the stress in the CPF surface contributes to the rupture of the CPFs. The results provide physical insights into the role of CPFs in SCC. PMID:26066367

Analysis and Support Initiative for Structural Technology (ASIST) Delivery Order 0016: USAF Damage Tolerant Design Handbook: Guidelines For the Analysis and Design of Damage Tolerant Aircraft Structures

DTIC Science & Technology

2002-11-01

hand crack tip (point B) and with angular displacement from the x-axis. As the stress element is moved closer to the crack tip, the stresses are...on the methods of obtaining the required relationships are presented by Broek [1974]. The necessary relationships for Vσ, VF, Vp and Vst ...4.5.18. Geometrical and Displacement Parameters Relative to the Crack Tip 4.5.21 Vσ + VF + Vp = Vst (4.5.15) substituting the expressions 4.5.6

Aluminium-induced reduction of plant growth in alfalfa (Medicago sativa) is mediated by interrupting auxin transport and accumulation in roots.

PubMed

Wang, Shengyin; Ren, Xiaoyan; Huang, Bingru; Wang, Ge; Zhou, Peng; An, Yuan

2016-07-20

The objective of this study was to investigate Al(3+)-induced IAA transport, distribution, and the relation of these two processes to Al(3+)-inhibition of root growth in alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or 100 μM AlCl3 and were foliar sprayed with water or 6 mg L(-1) IAA. Aluminium stress resulted in disordered arrangement of cells, deformed cell shapes, altered cell structure, and a shorter length of the meristematic zone in root tips. Aluminium stress significantly decreased the IAA concentration in apical buds and root tips. The distribution of IAA fluorescence signals in root tips was disturbed, and the IAA transportation from shoot base to root tip was inhibited. The highest intensity of fluorescence signals was detected in the apical meristematic zone. Exogenous application of IAA markedly alleviated the Al(3+)-induced inhibition of root growth by increasing IAA accumulation and recovering the damaged cell structure in root tips. In addition, Al(3+) stress up-regulated expression of AUX1 and PIN2 genes. These results indicate that Al(3+)-induced reduction of root growth could be associated with the inhibitions of IAA synthesis in apical buds and IAA transportation in roots, as well as the imbalance of IAA distribution in root tips.

Aluminium-induced reduction of plant growth in alfalfa (Medicago sativa) is mediated by interrupting auxin transport and accumulation in roots

PubMed Central

Wang, Shengyin; Ren, Xiaoyan; Huang, Bingru; Wang, Ge; Zhou, Peng; An, Yuan

2016-01-01

The objective of this study was to investigate Al3+-induced IAA transport, distribution, and the relation of these two processes to Al3+-inhibition of root growth in alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or 100 μM AlCl3 and were foliar sprayed with water or 6 mg L−1 IAA. Aluminium stress resulted in disordered arrangement of cells, deformed cell shapes, altered cell structure, and a shorter length of the meristematic zone in root tips. Aluminium stress significantly decreased the IAA concentration in apical buds and root tips. The distribution of IAA fluorescence signals in root tips was disturbed, and the IAA transportation from shoot base to root tip was inhibited. The highest intensity of fluorescence signals was detected in the apical meristematic zone. Exogenous application of IAA markedly alleviated the Al3+-induced inhibition of root growth by increasing IAA accumulation and recovering the damaged cell structure in root tips. In addition, Al3+ stress up-regulated expression of AUX1 and PIN2 genes. These results indicate that Al3+-induced reduction of root growth could be associated with the inhibitions of IAA synthesis in apical buds and IAA transportation in roots, as well as the imbalance of IAA distribution in root tips. PMID:27435109

dK/da effects on the SCC growth rates of nickel base alloys in high-temperature water

NASA Astrophysics Data System (ADS)

Chen, Kai; Wang, Jiamei; Du, Donghai; Andresen, Peter L.; Zhang, Lefu

2018-05-01

The effect of dK/da on crack growth behavior of nickel base alloys has been studied by conducting stress corrosion cracking tests under positive and negative dK/da loading conditions on Alloys 690, 600 and X-750 in high temperature water. Results indicate that positive dK/da accelerates the SCC growth rates, and the accelerating effect increases with dK/da and the initial CGR. The FRI model was found to underestimate the dK/da effect by ∼100X, especially for strain hardening materials, and this underscores the need for improved insight and models for crack tip strain rate. The effect of crack tip strain rate and dK/dt in particular can explain the dK/da accelerating effect.

Analysis of initial changes in the proteins of soybean root tip under flooding stress using gel-free and gel-based proteomic techniques.

PubMed

Yin, Xiaojian; Sakata, Katsumi; Nanjo, Yohei; Komatsu, Setsuko

2014-06-25

Flooding has a severe negative effect on soybean cultivation in the early stages of growth. To obtain a better understanding of the response mechanisms of soybean to flooding stress, initial changes in root tip proteins under flooding were analyzed using two proteomic techniques. Two-day-old soybeans were treated with flooding for 3, 6, 12, and 24h. The weight of soybeans increased during the first 3h of flooding, but root elongation was not observed. Using gel-based and gel-free proteomic techniques, 115 proteins were identified in root tips, of which 9 proteins were commonly detected by both methods. The 71 proteins identified by the gel-free proteomics were analyzed by a hierarchical clustering method based on induction levels during the flooding, and the proteins were divided into 5 clusters. Additional interaction analysis of the proteins revealed that ten proteins belonging to cluster I formed the center of a protein interaction network. mRNA expression analysis of these ten proteins showed that citrate lyase and heat shock protein 70 were down-regulated, whereas calreticulin was up-regulated in initial phase of flooding. These results suggest that flooding stress to soybean induces calcium-related signal transduction, which might play important roles in the early responses to flooding. Flooding has a severe negative effect on soybean cultivation, particularly in the early stages of growth. To better understand the response mechanisms of soybean to the early stages of flooding stress, two proteomic techniques were used. Two-day-old soybeans were treated without or with flooding for 3, 6, 12, and 24h. The fresh weight of soybeans increased during the first 3h of flooding stress, but the growth then slowed and no root elongation was observed. Using gel-based and gel-free proteomic techniques, 115 proteins were identified in root tips, of which 9 proteins were commonly detected by both methods. The 71 proteins identified by the gel-free proteomics were analyzed by a hierarchical clustering method based on induction levels during the flooding stress, and 5 protein clusters were recognized. Protein interaction analysis revealed that ten proteins belonging to cluster I formed the center of a protein interaction network. mRNA expression analysis of these ten proteins showed that citrate lyase and heat shock protein 70 were down-regulated in response to flooding stress, whereas calreticulin was up-regulated. These results suggest that flooding stress to soybean induces calcium-related signal transduction, which might play important roles in the early responses to flooding. Copyright © 2014 Elsevier B.V. All rights reserved.

Consider Workplace Needs When Purchasing Office Furniture.

ERIC Educational Resources Information Center

Burton, Bob

1999-01-01

Examines furniture-buying tips, involving workplace-needs assessment, that can help make the organization's workplace more effective. Stresses the importance of planning, tying the furniture purchasing into the strategic business, considering alternatives to furniture ownership, evaluating employee health and safety, and understanding any added…

You're Not Alone in Facing These Board-Related Bugaboos.

ERIC Educational Resources Information Center

Van Loozen, Luann F.

1982-01-01

School board service can have detrimental effects on members' personal lives. The most frequent and pervasive problems faced by board members are lack of time, loneliness, stress, alienation from community life, abuse, and fatigue. Problem-solving tips are offered. (Author/MLF)

Gel-Free/Label-Free Proteomic Analysis of Endoplasmic Reticulum Proteins in Soybean Root Tips under Flooding and Drought Stresses.

PubMed

Wang, Xin; Komatsu, Setsuko

2016-07-01

Soybean is a widely cultivated crop; however, it is sensitive to flooding and drought stresses. The adverse environmental cues cause the endoplasmic reticulum (ER) stress due to accumulation of unfolded or misfolded proteins. To investigate the mechanisms in response to flooding and drought stresses, ER proteomics was performed in soybean root tips. The enzyme activity of NADH cytochrome c reductase was two-fold higher in the ER than other fractions, indicating that the ER was isolated with high purity. Protein abundance of ribosomal proteins was decreased under both stresses compared to control condition; however, the percentage of increased ribosomes was two-fold higher in flooding compared to drought. The ER proteins related to protein glycosylation and signaling were in response to both stresses. Compared to control condition, calnexin was decreased under both stresses; however, protein disulfide isomerase-like proteins and heat shock proteins were markedly decreased under flooding and drought conditions, respectively. Furthermore, fewer glycoproteins and higher levels of cytosolic calcium were identified under both stresses compared to control condition. These results suggest that reduced accumulation of glycoproteins in response to both stresses might be due to dysfunction of protein folding through calnexin/calreticulin cycle. Additionally, the increased cytosolic calcium levels induced by flooding and drought stresses might disturb the ER environment for proper protein folding in soybean root tips.

Transverse shear effects on the stress-intensity factor for a circumferentially cracked, specially orthotropic cylindrical shell

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1977-01-01

The problem of a cylindrical shell containing a circumferential through crack is considered by taking into account the effect of transverse shear deformations. The formulation is given for a specially orthotropic material within the confines of a linearized shallow shell theory. The particular theory used permits the consideration of all five boundary conditions regarding moment and stress resultants on the crack surface. Consequently, aside from multiplicative constants representing the stress intensity factors, the membrane and bending components of the asymptotic stress fields near the crack tip are found to be identical. The stress intensity factors are calculated separately for a cylinder under a uniform membrane load, and that under a uniform bending moment. Sample results showing the nature of the out-of-plane crack surface displacement and the effect of the Poisson's ratio are presented.

Elastic-plastic Crack Growth Along Ductile/Ductile Interfaces

NASA Astrophysics Data System (ADS)

Drugan, W. J.

An analytical study is performed of the stress and deformation fields near the tip of a crack that grows quasi-statically along an interface between two generally dissimilar ductile materials. The materials are modeled as homogeneous, isotropic, incompressible, elastic-ideally plastic Prandtl-Reuss-Mises, and the analysis is carried out within a small-displacement-gradient formulation. The case of anti-plane shear deformations is considered first. We derive near-tip solutions for the full range of the ratio of the two materials' yield stresses, and show that a near-tip family of solutions exists for each set of material properties; the implication is that far-field loading and geometrical conditions determine which specific near-tip solution governs in a particular problem. As a by-product of this analysis, we derive a new solution family for anti-plane shear crack growth in homogeneous material, one limiting member of which is the familiar Chitaley and McClintock (1971) solution. We also analyze the case of plane strain crack growth under applied tensile loading. Here, we account for curvature of inter-sector boundaries, in an attempt to obtain a complete set of solutions. When the material properties are identical, the solution family of Drugan and Chen (1989) for homogeneous material crack growth, which has an undetermined parameter in the near-tip field, is recovered. As the ratio of the two materials' yield strengths, ĸ, deviates from unity, the near-tip solution structure is found to change, but the near-tip fields are shown to continue to possess a free parameter for a substantial range of ĸ. Below this range, a second solution structure develops for which the near-tip free parameter has a restricted range of freedom. Finally, a third near-tip solution structure develops for sufficiently low ĸ, for which there are no free parameters. The implications of these results appear to be that as the plastic yield strength mismatch of the two materials becomes larger, far-field loading and geometry have increasingly weaker effects on the leading-order near-tip fields, until finally a mismatch level is reached beyond which far-field conditions no longer affect the leading-order fields. However, conclusions are complicated by the fact that the analysis also implies the radius of validity of the leading-order fields to decrease continuously with increasing yield strength mismatch (beyond a certain level), so that below some ¯k value, it will become necessary to retain more than one term to describe the physical near-tip fields. Although not specifically explored here, our analysis also allows comparison of the effects of changing elastic and plastic properties of the two materials on crack growth propensity, so that perhaps this analysis could assist in the optimization of interfacial fracture properties.

Patterns and perspectives in applied fracture mechanics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Merkle, J.G.

1994-12-31

This lecture begins with a overview of applied fracture mechanics pertinent to safety of pressure vessels. It then progresses to a chronological panorama of experimental and analytical results. To be useful and dependable in safety analysis of real structures, new analysis developments must be physically realistic, which means that they must accurately describe physical cause and effect. Consequently, before mathematical modeling can begin, cause and effect must be established from experimental data. This can be difficult and time consuming, but worth the effort. Accordingly, the theme of this paper is that the search for patterns is constant and vital. Thismore » theme is illustrated by the development of small, single-specimen, fracture toughness testing techniques. It is also illustrated by the development, based on two different published large-strain, elastic-plastic, three-dimensional finite-element analyses, of a hypothesis concerning three-dimensional loss of constraint. When a generalization of Irwin`s thickness-normalized plastic-zone parameter, reaches a value close to 2{pi}, the through-thickness contraction strain at the apex of the near-tip logarithmic-spiral slip-line region becomes the dominant negative strain accommodating crack opening. Because slip lines passing from the midplane to the stress-free side surfaces do not have to curve, once these slip lines are established, stresses near the crack tip are only elevated by strain hardening and constraint becomes significantly relaxed. This hypothesis, based on published three-dimensional elastic-plastic analyses, provides a potentially valuable means for gaining additional insight into constraint effects on fracture toughness by considering the roles played by the plastic strains as well as the stresses that develop near a crack tip.« less

The interaction of fatigue cracks with a residual stress field using thermoelastic stress analysis and synchrotron X-ray diffraction experiments

PubMed Central

Amjad, Khurram; Asquith, David; Sebastian, Christopher M.; Wang, Wei-Chung

2017-01-01

This article presents an experimental study on the fatigue behaviour of cracks emanating from cold-expanded holes utilizing thermoelastic stress analysis (TSA) and synchrotron X-ray diffraction (SXRD) techniques with the aim of resolving the long-standing ambiguity in the literature regarding potential relaxation, or modification, of beneficial compressive residual stresses as a result of fatigue crack propagation. The crack growth rates are found to be substantially lower as the crack tip moved through the residual stress zone induced by cold expansion. The TSA results demonstrated that the crack tip plastic zones were reduced in size by the presence of the residual compressive stresses induced by cold expansion. The crack tip plastic zones were found to be insignificant in size in comparison to the residual stress zone resulting from cold expansion, which implied that they were unlikely to have had a notable impact on the surrounding residual stresses induced by cold expansion. The residual stress distributions measured along the direction of crack growth, using SXRD, showed no signs of any significant stress relaxation or redistribution, which validates the conclusions drawn from the TSA data. Fractographic analysis qualitatively confirmed the influence on crack initiation of the residual stresses induced by the cold expansion. It was found that the application of single compressive overload caused a relaxation, or reduction in the residual stresses, which has wider implications for improving the fatigue life. PMID:29291095

Crack Growth Prediction Methodology for Multi-Site Damage: Layered Analysis and Growth During Plasticity

NASA Technical Reports Server (NTRS)

James, Mark Anthony

1999-01-01

A finite element program has been developed to perform quasi-static, elastic-plastic crack growth simulations. The model provides a general framework for mixed-mode I/II elastic-plastic fracture analysis using small strain assumptions and plane stress, plane strain, and axisymmetric finite elements. Cracks are modeled explicitly in the mesh. As the cracks propagate, automatic remeshing algorithms delete the mesh local to the crack tip, extend the crack, and build a new mesh around the new tip. State variable mapping algorithms transfer stresses and displacements from the old mesh to the new mesh. The von Mises material model is implemented in the context of a non-linear Newton solution scheme. The fracture criterion is the critical crack tip opening displacement, and crack direction is predicted by the maximum tensile stress criterion at the crack tip. The implementation can accommodate multiple curving and interacting cracks. An additional fracture algorithm based on nodal release can be used to simulate fracture along a horizontal plane of symmetry. A core of plane strain elements can be used with the nodal release algorithm to simulate the triaxial state of stress near the crack tip. Verification and validation studies compare analysis results with experimental data and published three-dimensional analysis results. Fracture predictions using nodal release for compact tension, middle-crack tension, and multi-site damage test specimens produced accurate results for residual strength and link-up loads. Curving crack predictions using remeshing/mapping were compared with experimental data for an Arcan mixed-mode specimen. Loading angles from 0 degrees to 90 degrees were analyzed. The maximum tensile stress criterion was able to predict the crack direction and path for all loading angles in which the material failed in tension. Residual strength was also accurately predicted for these cases.

Thermomechanical coupling and dynamic strain ageing in ductile fracture

NASA Astrophysics Data System (ADS)

Delafosse, David

1995-01-01

This work is concerned with plastic deformation at the tip of a ductile tearing crack during propagation. Two kinds of effects are investigated: the thermomechanical coupling at the tip of a mobile ductile crack, and the influence of Dynamic Strain Aging (DSA) on ductile fracture. Three alloys are studied: a nickel based superalloy (N18), a soft carbon steel, and an Al-Li light alloy (2091). The experimental study of the thermo mechanical coupling effects by means of infrared thermography stresses the importance of plastic dissipation in the energy balance of ductile fracture. Numerical simulations involving plastic deformation as the only dissipation mechanism account for the main part of the measured heating. The effects of DSA on ductile tearing are investigated in the 2091 Al-Li alloy. Based on the strain rate/temperature dependence predicted by the standard model of DSA, an experimental procedure is set up for this purpose. Three main effects are evidenced. A maximum in tearing resistance is shown to be associated with the minimum of strain rate sensitivity. Through a simple model, this peak in tearing resistance is attributed to an increase in plastic dissipation as the strain rate sensitivity is decreased. Heterogenous plastic deformation is observed in the crack tip plastic zone. Comparison with uniaxial testing allows us to identify the observed strain heterogeneities as Portevin-Le Chatelier instabilities in the crack tip plastic zone. We perform a simplified numerical analysis of the effect of strain localization on crack tip screening. Finally, small crack propagation instabilities appear at temperatures slightly above that of the tearing resistance peak. These are interpreted as resulting from a positive feed-back between the local heating at the tip of a moving crack and the decrease in tearing resistance with increasing temperature.

Determination of Stress Coefficient Terms in Cracked Solids for Monoclinic Materials with Plane Symmetry at x3 = 0

NASA Technical Reports Server (NTRS)

Yuan, F. G.

1998-01-01

Determination of all the coefficients in the crack tip field expansion for monoclinic materials under two-dimensional deformation is presented in this report. For monoclinic materials with a plane of material symmetry at x(sub 3) = 0, the in-plane deformation is decoupled from the anti-plane deformation. In the case of in-plane deformation, utilizing conservation laws of elasticity and Betti's reciprocal theorem, together with selected auxiliary fields, T-stress and third-order stress coefficients near the crack tip are evaluated first from path-independent line integrals. To determine the T-stress terms using the J-integral and Betti's reciprocal work theorem, auxiliary fields under a concentrated force and moment acting at the crack tip are used respectively. Through the use of Stroh formalism in anisotropic elasticity, analytical expressions for all the coefficients including the stress intensity factors are derived in a compact form that has surprisingly simple structure in terms of the Barnett-Lothe tensors, L. The solution forms for degenerated materials, orthotropic, and isotropic materials are presented.

Cyclic plasticity models and application in fatigue analysis

NASA Technical Reports Server (NTRS)

Kalev, I.

1981-01-01

An analytical procedure for prediction of the cyclic plasticity effects on both the structural fatigue life to crack initiation and the rate of crack growth is presented. The crack initiation criterion is based on the Coffin-Manson formulae extended for multiaxial stress state and for inclusion of the mean stress effect. This criterion is also applied for the accumulated damage ahead of the existing crack tip which is assumed to be related to the crack growth rate. Three cyclic plasticity models, based on the concept of combination of several yield surfaces, are employed for computing the crack growth rate of a crack plane stress panel under several cyclic loading conditions.

Crack problems for bonded nonhomogeneous materials under antiplane shear loading

NASA Technical Reports Server (NTRS)

Erdogan, F.

1984-01-01

The singular nature of the crack tip stress field in a nonhomogeneous medium with a shear modulus with a discontinuous derivative was investigated. The simplest possible loading and geometry, the antiplane shear loading of two bonded half spaces in which the crack is perpendicular to the interface is considered. It is shown that the square root singularity of the crack tip stress field is unaffected by the discontinuity in the derivative of the shear modulus. The problem is solved for a finite crack and results for the stress intensity factors are presented.

Teaching Young Children about AIDS.

ERIC Educational Resources Information Center

Schonfeld, David J.; Quackenbush, Marcia

2000-01-01

AIDS is a genuine concern for young schoolchildren, as a significant number begin having unprotected sex before completing elementary school. The most effective sex-education programs stress delaying the age of first intercourse and adopting safe sexual practices. Principals' supportive behaviors and prevention education tips are discussed. (MLH)

Comprehensive Structural Dynamic Analysis of the SSME/AT Fuel Pump First-Stage Turbine Blade

NASA Technical Reports Server (NTRS)

Brown, A. M.

1998-01-01

A detailed structural dynamic analysis of the Pratt & Whitney high-pressure fuel pump first-stage turbine blades has been performed to identify the cause of the tip cracking found in the turbomachinery in November 1997. The analysis was also used to help evaluate potential fixes for the problem. Many of the methods available in structural dynamics were applied, including modal displacement and stress analysis, frequency and transient response to tip loading from the first-stage Blade Outer Gas Seals (BOGS), fourier analysis, and shock spectra analysis of the transient response. The primary findings were that the BOGS tip loading is impulsive in nature, thereby exciting many modes of the blade that exhibit high stress at the tip cracking location. Therefore, a proposed BOGS count change would not help the situation because a clearly identifiable resonance situation does not exist. The recommendations for the resolution of the problem are to maintain the existing BOGS count, eliminate the stress concentration in the blade due to its geometric design, and reduce the applied load on the blade by adding shiplaps in the BOGS.

Effect of Crack Tip Stress Concentration Factor on Fracture Resistance in Vacuum Environment

DTIC Science & Technology

2015-01-20

indicate: (1) in all alloys, the fracture resistance is highest for blunt-notches (smaller Kt), and is lowest for fatigue -sharpened precracked...paths are transgranular and the fracture mode is ductile void coalescence in all cases, irrespective of the stress concentration factor. 20-01-2015...because of corrosion and/or various loading conditions such as fatigue , fretting, abrasion, etc. Also, the geometry of the structure may cause an

Achilles Tendonitis

MedlinePlus

... almost impossible. Achilles tendonitis is a very common running injury. But it can also affect basketball players, dancers, ... Proximal Biceps Tendonitis Safety Tips: Basketball Safety Tips: Running Repetitive Stress Injuries Sports and Exercise Safety Dealing With Sports Injuries ...

Actual light deflections in regions of crack tips and their influence on measurements in photomechanics

NASA Astrophysics Data System (ADS)

Hecker, Friedrich W.; Pindera, Jerzy T.; Wen, Baicheng

Crack-tip photomechanics procedures are based on certain simplifying assumptions that are seldom discussed. In a recent paper the theoretical bases of the shadow optical methods of caustics have been analysed and tested using the results obtained by three analytical-experimental procedures, namely classical strain gage techniques, isodynes, and strain-gradient index method. It has been concluded that the straing-radient index method appears to be a suitable tool for analysis of stress states near crack tips and notches and, in particular, for testing the predictive power of the pertinent singular solutions of the linear elastic fracture mechanics and the ranges of their applicability. In the present paper, a more detailed analysis of all results obtained in light deflection experiments allows to quantify the contribution of both involved effects and to determine the distortion of the faces of the investigated plates along their crack planes. The ability of the strain-gradient light bending method to analyse some features of the three-dimensional stress-state is reported. Finally, the presented experimental evidence allows to draw conclusions related to limits of applicability of certain photomechanical measurements near crack tips. An extensive summary of this paper is published in the Proceedings of the Second International Conference on Photomechanics and Speckle Metrology, Vol. 1554A, part of SPIE's 1991 International Symposium on Optical Applied Science and Engineering, 22-26 July 1991, San Diego, CA, USA. 1

The Effect of Freezing on the Dynamics of Dike Propagation

NASA Astrophysics Data System (ADS)

Tait, S.; Taisne, B.

2007-12-01

When magma-filled cracks propagate close to the Earth's surface, host rock temperature is well below the magma solidus. Solidification and substantial increase in magma viscosity can occur, are most pronounced near the propagating tip and can slow or arrest the progress of the dike. Quantitative analysis is required to predict whether a given dike will reach the surface to erupt and the duration of the precursor sequence. This challenging physical problem mixes elasticity, fracture mechanics, heat transfer and fluid flow with strong rheologic gradients due to cooling. We describe the propagation behaviour of such a hydraulic fracture using a laboratory experimental system of a crack fed by a constant flux of paraffin wax from a source reservoir propagating through gelatin below the solidus of the wax. The most novel behaviour is an intermittent regime in which cracks periodically stop advancing due to solidification, then swell at constant length while enhancing the elastic deformation in the surrounding solid before propagation resumes. We present a physical model of this system, based on different balances between driving and resistive forces: the former are elastic stress and liquid buoyancy, the latter are fracture resistance at the tip and viscous resistance. The fracture is represented as a head, behind the propagating tip, connected to the source by a narrow tail. Freezing of liquid close to the tip is assumed to enhance fracture resistance according to a cooling law, and propagation is assumed to occur only when the stress exerted by the liquid is enough to overcome fracture resistance. Our theoretical model reproduces intermittent propagation with precise behaviour depending on the controlling stress balances, and provides a tool to analyse natural systems.

Lifestyle-induced metabolic inflexibility and accelerated ageing syndrome: insulin resistance, friend or foe?

PubMed Central

Nunn, Alistair VW; Bell, Jimmy D; Guy, Geoffrey W

2009-01-01

The metabolic syndrome may have its origins in thriftiness, insulin resistance and one of the most ancient of all signalling systems, redox. Thriftiness results from an evolutionarily-driven propensity to minimise energy expenditure. This has to be balanced with the need to resist the oxidative stress from cellular signalling and pathogen resistance, giving rise to something we call 'redox-thriftiness'. This is based on the notion that mitochondria may be able to both amplify membrane-derived redox growth signals as well as negatively regulate them, resulting in an increased ATP/ROS ratio. We suggest that 'redox-thriftiness' leads to insulin resistance, which has the effect of both protecting the individual cell from excessive growth/inflammatory stress, while ensuring energy is channelled to the brain, the immune system, and for storage. We also suggest that fine tuning of redox-thriftiness is achieved by hormetic (mild stress) signals that stimulate mitochondrial biogenesis and resistance to oxidative stress, which improves metabolic flexibility. However, in a non-hormetic environment with excessive calories, the protective nature of this system may lead to escalating insulin resistance and rising oxidative stress due to metabolic inflexibility and mitochondrial overload. Thus, the mitochondrially-associated resistance to oxidative stress (and metabolic flexibility) may determine insulin resistance. Genetically and environmentally determined mitochondrial function may define a 'tipping point' where protective insulin resistance tips over to inflammatory insulin resistance. Many hormetic factors may induce mild mitochondrial stress and biogenesis, including exercise, fasting, temperature extremes, unsaturated fats, polyphenols, alcohol, and even metformin and statins. Without hormesis, a proposed redox-thriftiness tipping point might lead to a feed forward insulin resistance cycle in the presence of excess calories. We therefore suggest that as oxidative stress determines functional longevity, a rather more descriptive term for the metabolic syndrome is the 'lifestyle-induced metabolic inflexibility and accelerated ageing syndrome'. Ultimately, thriftiness is good for us as long as we have hormetic stimuli; unfortunately, mankind is attempting to remove all hormetic (stressful) stimuli from his environment. PMID:19371409

The initiation, propagation, and effect of matrix microcracks in cross-ply and related laminates

NASA Technical Reports Server (NTRS)

Nairn, John A.; Hu, Shoufeng; Liu, Siulie; Bark, Jong

1991-01-01

Recently, a variational mechanics approach was used to determine the thermoelastic stress state in cracked laminates. Described here is a generalization of the variational mechanics techniques to handle other cross-ply laminates, related laminates, and to account for delaminations emanating from microcrack tips. Microcracking experiments on Hercules 3501-6/AS4 carbon fiber/epoxy laminates show a staggered cracking pattern. These results can be explained by the variational mechanics analysis. The analysis of delaminations emanating from microcrack tips has resulted in predictions about the structural and material variables controlling competition between microcracking and delamination failure modes.

Determination of Villous Rigidity in the Distal Ileum of the Possum (Trichosurus vulpecula)

PubMed Central

Lim, Yuen Feung; Lentle, Roger G.; Janssen, Patrick W. M.; Williams, Martin A. K.; de Loubens, Clément; Mansel, Bradley W.; Chambers, Paul

2014-01-01

We investigated the passive mechanical properties of villi in ex vivo preparations of sections of the wall of the distal ileum from the brushtail possum (Trichosurus vulpecula) by using a flow cell to impose physiological and supra-physiological levels of shear stress on the tips of villi. We directly determined the stress applied from the magnitude of the local velocities in the stress inducing flow and additionally mapped the patterns of flow around isolated villi by tracking the trajectories of introduced 3 µm microbeads with bright field micro particle image velocimetry (mPIV). Ileal villi were relatively rigid along their entire length (mean 550 µm), and exhibited no noticeable bending even at flow rates that exceeded calculated normal physiological shear stress (>0.5 mPa). However, movement of villus tips indicated that the whole rigid structure of a villus could pivot about the base, likely from laxity at the point of union of the villous shaft with the underlying mucosa. Flow moved upward toward the tip on the upper portions of isolated villi on the surface facing the flow and downward toward the base on the downstream surface. The fluid in sites at distances greater than 150 µm below the villous tips was virtually stagnant indicating that significant convective mixing in the lower intervillous spaces was unlikely. Together the findings indicate that mixing and absorption is likely to be confined to the tips of villi under conditions where the villi and intestinal wall are immobile and is unlikely to be greatly augmented by passive bending of the shafts of villi. PMID:24956476

Crack Tip Dislocation Nucleation in FCC Solids

NASA Astrophysics Data System (ADS)

Knap, J.; Sieradzki, K.

1999-02-01

We present results of molecular dynamic simulations aimed at examining crack tip dislocation emission in fcc solids. The results are analyzed in terms of recent continuum formulations of this problem. In mode II, Au, Pd, and Pt displayed a new unanticipated mechanism of crack tip dislocation emission involving the creation of a pair of Shockley partials on a slip plane one plane below the crack plane. In mode I, for all the materials examined, Rice's continuum formulation [J. Mech. Phys. Solids 40, 239 (1992)] underestimated the stress intensity for dislocation emission by almost a factor of 2. Surface stress corrections to the emission criterion brought the agreement between continuum predictions and simulations to within 20%.

Mixed-mode crack tip loading and crack deflection in 1D quasicrystals

NASA Astrophysics Data System (ADS)

Wang, Zhibin; Scheel, Johannes; Ricoeur, Andreas

2016-12-01

Quasicrystals (QC) are a new class of materials besides crystals and amorphous solids and have aroused much attention of researchers since they were discovered. This paper presents a generalized fracture theory including the J-integral and crack closure integrals, relations between J1, J2 and the stress intensity factors as well as the implementation of the near-tip stress and displacement solutions of 1D QC. Different crack deflection criteria, i.e. the J-integral and maximum circumferential stress criteria, are investigated for mixed-mode loading conditions accounting for phonon-phason coupling. One focus is on the influence of phason stress intensity factors on crack deflection angles.

Investigation of grain-scale microstructural variability in tantalum using crystal plasticity-finite element simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Hojun; Dingreville, Rémi; Deibler, Lisa A.

In this research, a crystal plasticity-finite element (CP-FE) model is used to investigate the effects of microstructural variability at a notch tip in tantalum single crystals and polycrystals. It is shown that at the macroscopic scale, the mechanical response of single crystals is sensitive to the crystallographic orientation while the response of polycrystals shows relatively small susceptibility to it. However, at the microscopic scale, the local stress and strain fields in the vicinity of the crack tip are completely determined by the local crystallographic orientation at the crack tip for both single and polycrystalline specimens with similar mechanical field distributions.more » Variability in the local metrics used (maximum von Mises stress and equivalent plastic strain at 3% deformation) for 100 different realizations of polycrystals fluctuates by up to a factor of 2–7 depending on the local crystallographic texture. Comparison with experimental data shows that the CP model captures variability in stress–strain response of polycrystals that can be attributed to the grain-scale microstructural variability. In conclusion, this work provides a convenient approach to investigate fluctuations in the mechanical behavior of polycrystalline materials induced by grain morphology and crystallographic orientations.« less

Stretching of Single Polymer Chains Using the Atomic Force Microscope

NASA Astrophysics Data System (ADS)

Ortiz, C.; van der Vegte, E. W.; van Swieten, E.; Robillard, G. T.; Hadziioannou, G.

1998-03-01

A variety of macroscopic phenomenon involve "nanoscale" polymer deformation including rubber elasticity, shear yielding, strain hardening, stress relaxation, fracture, and flow. With the advent of new and improved experimental techniques, such as the atomic force microscope (AFM), the probing of physical properties of polymers has reached finer and finer scales. The development of mixed self-assembling monolayer techniques and the chemical functionalization of AFM probe tips has allowed for mechanical experiments on single polymer chains of molecular dimensions. In our experiments, mixed monolayers are prepared in which end-functionalized, flexible polymer chains of thiol-terminated poly(methacrylic acid) are covalently bonded, isolated, and randomly distributed on gold substrates. The coils are then imaged, tethered to a gold-coated AFM tip, and stretched between the tip and the substrate in a conventional force / distance experiment. An increase in the attractive force due to entropic, elastic resistance to stretching, as well as fracture of the polymer chain is observed. The effect of chain stiffness, topological constraints, strain rate, mechanical hysteresis, and stress relaxation were investigated. Force modulation techniques were also employed in order to image the viscoelastic character of the polymer chains. Parallel work includes similar studies of biological systems such as wheat gluten proteins and polypeptides.

Investigation of grain-scale microstructural variability in tantalum using crystal plasticity-finite element simulations

DOE PAGES

Lim, Hojun; Dingreville, Rémi; Deibler, Lisa A.; ...

2016-02-27

In this research, a crystal plasticity-finite element (CP-FE) model is used to investigate the effects of microstructural variability at a notch tip in tantalum single crystals and polycrystals. It is shown that at the macroscopic scale, the mechanical response of single crystals is sensitive to the crystallographic orientation while the response of polycrystals shows relatively small susceptibility to it. However, at the microscopic scale, the local stress and strain fields in the vicinity of the crack tip are completely determined by the local crystallographic orientation at the crack tip for both single and polycrystalline specimens with similar mechanical field distributions.more » Variability in the local metrics used (maximum von Mises stress and equivalent plastic strain at 3% deformation) for 100 different realizations of polycrystals fluctuates by up to a factor of 2–7 depending on the local crystallographic texture. Comparison with experimental data shows that the CP model captures variability in stress–strain response of polycrystals that can be attributed to the grain-scale microstructural variability. In conclusion, this work provides a convenient approach to investigate fluctuations in the mechanical behavior of polycrystalline materials induced by grain morphology and crystallographic orientations.« less

Blade Tip Rubbing Stress Prediction

NASA Technical Reports Server (NTRS)

Davis, Gary A.; Clough, Ray C.

1991-01-01

An analytical model was constructed to predict the magnitude of stresses produced by rubbing a turbine blade against its tip seal. This model used a linearized approach to the problem, after a parametric study, found that the nonlinear effects were of insignificant magnitude. The important input parameters to the model were: the arc through which rubbing occurs, the turbine rotor speed, normal force exerted on the blade, and the rubbing coefficient of friction. Since it is not possible to exactly specify some of these parameters, values were entered into the model which bracket likely values. The form of the forcing function was another variable which was impossible to specify precisely, but the assumption of a half-sine wave with a period equal to the duration of the rub was taken as a realistic assumption. The analytical model predicted resonances between harmonics of the forcing function decomposition and known harmonics of the blade. Thus, it seemed probable that blade tip rubbing could be at least a contributor to the blade-cracking phenomenon. A full-scale, full-speed test conducted on the space shuttle main engine high pressure fuel turbopump Whirligig tester was conducted at speeds between 33,000 and 28,000 RPM to confirm analytical predictions.

Crack problems for bonded nonhomogeneous materials under antiplane shear loading

NASA Technical Reports Server (NTRS)

Erdogan, F.

1985-01-01

The singular nature of the crack tip stress field in a nonhomogeneous medium having a shear modulus with a discontinuous derivative was investigated. The problem is considered for the simplest possible loading and geometry, namely the antiplane shear loading of two bonded half spaces in which the crack is perpendicular to the interface. It is shown that the square-root singularity of the crack tip stress field is unaffected by the discontinuity in the derivative of the shear modulus. The problem is solved for a finite crack and extensive results are given for the stress intensity factors.

The crack problem for bonded nonhomogeneous materials under antiplane shear loading

NASA Technical Reports Server (NTRS)

Erdogan, F.

1985-01-01

The singular nature of the crack tip stress field in a nonhomogeneous medium having a shear modulus with a discontinuous derivative was investigated. The problem is considered for the simplest possible loading and geometry, namely the antiplane shear loading of two bonded half spaces in which the crack is perpendicular to the interface. It is shown that the square-root singularity of the crack tip stress field is unaffected by the discontinuity in the derivative of the shear modulus. The problem is solved for a finite crack and extensive results are given for the stress intensity factors.

Effects of Residual Impurities on Hydrogen Assisted Cracking in High Strength Steels. Part II.

DTIC Science & Technology

1982-06-01

source of hydrogen is the corrosion reaction of steel with aqueous hydrogen sulfide solutions encountered either in the production of crude oil and...autoradiography technique, it has been shown that in Armco iron and in maraging steel of hydrogen is trapped at prior austenite grain boundaries. Tritium...also play a deleterious role in hydrogen-induced cracking. In these ultra-high strength steels , the crack-tip stress level and the concomitant stress

Enhanced Drought Stress Tolerance by the Arbuscular Mycorrhizal Symbiosis in a Drought-Sensitive Maize Cultivar Is Related to a Broader and Differential Regulation of Host Plant Aquaporins than in a Drought-Tolerant Cultivar

PubMed Central

Quiroga, Gabriela; Erice, Gorka; Aroca, Ricardo; Chaumont, François; Ruiz-Lozano, Juan M.

2017-01-01

The arbuscular mycorrhizal (AM) symbiosis has been shown to improve maize tolerance to different drought stress scenarios by regulating a wide range of host plants aquaporins. The objective of this study was to highlight the differences in aquaporin regulation by comparing the effects of the AM symbiosis on root aquaporin gene expression and plant physiology in two maize cultivars with contrasting drought sensitivity. This information would help to identify key aquaporin genes involved in the enhanced drought tolerance by the AM symbiosis. Results showed that when plants were subjected to drought stress the AM symbiosis induced a higher improvement of physiological parameters in drought-sensitive plants than in drought-tolerant plants. These include efficiency of photosystem II, membrane stability, accumulation of soluble sugars and plant biomass production. Thus, drought-sensitive plants obtained higher physiological benefit from the AM symbiosis. In addition, the genes ZmPIP1;1, ZmPIP1;3, ZmPIP1;4, ZmPIP1;6, ZmPIP2;2, ZmPIP2;4, ZmTIP1;1, and ZmTIP2;3 were down-regulated by the AM symbiosis in the drought-sensitive cultivar and only ZmTIP4;1 was up-regulated. In contrast, in the drought-tolerant cultivar only three of the studied aquaporin genes (ZmPIP1;6, ZmPIP2;2, and ZmTIP4;1) were regulated by the AM symbiosis, resulting induced. Results in the drought-sensitive cultivar are in line with the hypothesis that down-regulation of aquaporins under water deprivation could be a way to minimize water loss, and the AM symbiosis could be helping the plant in this regulation. Indeed, during drought stress episodes, water conservation is critical for plant survival and productivity, and is achieved by an efficient uptake and stringently regulated water loss, in which aquaporins participate. Moreover, the broader and contrasting regulation of these aquaporins by the AM symbiosis in the drought-sensitive than the drought-tolerant cultivar suggests a role of these aquaporins in water homeostasis or in the transport of other solutes of physiological importance in both cultivars under drought stress conditions, which may be important for the AM-induced tolerance to drought stress. PMID:28674550

Exercise for Stress and Anxiety

MedlinePlus

... Breadcrumb Learn From Us Managing Anxiety Exercise for Stress and Anxiety The physical benefits of exercise — improving ... University Press, 2011) Fitness Tips: Stay Healthy, Manage Stress The most recent federal guidelines for adults recommend ...

Physiological and molecular analysis of the interaction between aluminium toxicity and drought stress in common bean (Phaseolus vulgaris)

PubMed Central

Yang, Zhong-Bao; Eticha, Dejene; Albacete, Alfonso; Rao, Idupulapati Madhusudana; Roitsch, Thomas; Horst, Walter Johannes

2012-01-01

Aluminium (Al) toxicity and drought are two major factors limiting common bean (Phaseolus vulgaris) production in the tropics. Short-term effects of Al toxicity and drought stress on root growth in acid, Al-toxic soil were studied, with special emphasis on Al–drought interaction in the root apex. Root elongation was inhibited by both Al and drought. Combined stresses resulted in a more severe inhibition of root elongation than either stress alone. This result was different from the alleviation of Al toxicity by osmotic stress (–0.60 MPa polyethylene glycol) in hydroponics. However, drought reduced the impact of Al on the root tip, as indicated by the reduction of Al-induced callose formation and MATE expression. Combined Al and drought stress enhanced up-regulation of ACCO expression and synthesis of zeatin riboside, reduced drought-enhanced abscisic acid (ABA) concentration, and expression of NCED involved in ABA biosynthesis and the transcription factors bZIP and MYB, thus affecting the regulation of ABA-dependent genes (SUS, PvLEA18, KS-DHN, and LTP) in root tips. The results provide circumstantial evidence that in soil, drought alleviates Al injury, but Al renders the root apex more drought-sensitive, particularly by impacting the gene regulatory network involved in ABA signal transduction and cross-talk with other phytohormones necessary for maintaining root growth under drought. PMID:22371077

Nonlinear interaction of strong S-waves with the rupture front in the shallow subsurface

NASA Astrophysics Data System (ADS)

Sleep, N. H.

2017-12-01

Shallow deformation in moderate to large earthquakes is sometimes distributed rather than being concentrated on a single fault plane. Strong high-frequency S-waves interact with the rupture front to produce this effect. For strike-slip faults, the rupture propagation velocity is a fraction of the S-wave velocity. The rupture propagation vector refracts essentially vertically in the low (S-wave) velocity shallow subsurface. So does the propagation direction of S-waves. The shallow rupture front is essentially mode 3 near the surface. Strong S-waves arrive before the rupture front. They continue to arrive for several seconds in a large event. There are simple scaling relationships. The dynamic Coulomb stress ratio of horizontal stress on horizontal planes from S-waves is the normalized acceleration in g's. For fractured rock and gravel, frictional failure occurs when the normalized acceleration exceeds the effective coefficient of friction. Acceleration tends to saturate at that level as the anelastic strain rate increases rapidly with stress. For muddy materials, failure begins at a low normalized acceleration but increases slowly with dynamic stress. Dynamic accelerations sometimes exceed 1 g. In both cases, the rupture tip finds the shallow subsurface already in nonlinear failure down to a few to tens of meters depth. The material does not distinguish between S-wave and rupture tip stresses. Both stresses add to the stress invariant and hence to the anelastic strain rate tensor. Surface anelastic strain from fault slip is thus distributed laterally over a distance scaling to the depth of nonlinearity from S-waves. The environs of the fault anelastically accommodate the fault slip at depth. This process differs from blind faults where the shallow coseismic strain is mostly elastic and interseismic anelastic processes accommodate the long-term shallow deformation.

Sleep Tips: 7 Steps to Better Sleep

MedlinePlus

... turn every night. Consider simple tips for better sleep, from setting a sleep schedule to including physical activity in your daily ... factors that can interfere with a good night's sleep — from work stress and family responsibilities to unexpected ...

Effect of punch tip geometry and embossment on the punch tip adherence of a model ibuprofen formulation.

PubMed

Roberts, Matthew; Ford, James L; MacLeod, Graeme S; Fell, John T; Smith, George W; Rowe, Philip H; Dyas, A Mark

2004-07-01

The sticking of a model ibuprofen-lactose formulation with respect to compaction force, punch tip geometry and punch tip embossment was assessed. Compaction was performed at 10, 25 or 40 kN using an instrumented single-punch tablet press. Three sets of 'normal' concave punches were used to evaluate the influence of punch curvature and diameter. The punches were 10, 11 and 12 mm in diameter, respectively. The 10-mm punch was embossed with a letter 'A' logo to assess the influence of an embossment on sticking. Flat-faced punches (12.5 mm) were used for comparison with the concave tooling. Surface profiles (Taylor Hobson Talysurf 120) of the upper punch faces were obtained to evaluate the surface quality of the tooling used. Following compaction, ibuprofen attached to the upper punch face was quantified by spectroscopy. Increasing punch curvature from flat-faced punches to concave decreased sticking. Altering punch diameter of the concave punches had no effect on sticking when expressed as microg mm(-2). The embossed letter 'A' logo increased sticking considerably owing to the probable concentration of shear stresses at the lateral faces of the embossed logo.

A Finite Element Study on Crack Tip Deformation.

DTIC Science & Technology

1976-08-01

REPOPINUMDER • TNOR(.) CONTRACT OR GRANT NUMSER(.) ______ ~~~ ~~~ /I. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMEN T. PROJECT . TASKJ AREA ...that the bulk of the strain measurements agree well with the results of the plane stress calculations except in the small area close to the crack tip...that the bulk of the strain measurements agree veil with the results of the plane stress calcula- tions except in the small area cloae to the crack

Finite element analysis on preferable I-bar clasp shape.

PubMed

Sato, Y; Tsuga, K; Abe, Y; Asahara, S; Akagawa, Y

2001-05-01

An I-bar clasp is one of the most popular direct retainers for distal-extension removable partial dentures. However, no adequate information is available on preferable shape as determined by biomechanics. This study aimed (1) to investigate, by finite element analysis (FEA), the dimensions and stress of I-bar clasps having the same stiffness, and (2) to estimate a mechanically preferable clasp design. Three-dimensional FEA models of I-bar clasps were created with vertical and horizontal straight sections connected by a curved section characterized by six parameters: thickness of the clasp tip, width of the clasp tip, radius of the curvature, horizontal distance between the base and the vertical axis, vertical dimension between the tip and the horizontal axis, and taper (change of width per unit length along the axis). Stress was calculated with a concentrated load of 5 N applied 2 mm from the tip of the clasp in the buccal direction. A thinner and wider clasp having an taper of 0.020-0.023 and radius of curvature of 2.75-3.00 showed less stress. The results suggest that such a shape might be the preferable I-bar clasp shape as biomechanical viewpoint.

A Parametric Study for the Design of an Optimized Ultrasonic Percussive Planetary Drill Tool.

PubMed

Li, Xuan; Harkness, Patrick; Worrall, Kevin; Timoney, Ryan; Lucas, Margaret

2017-03-01

Traditional rotary drilling for planetary rock sampling, in situ analysis, and sample return are challenging because the axial force and holding torque requirements are not necessarily compatible with lightweight spacecraft architectures in low-gravity environments. This paper seeks to optimize an ultrasonic percussive drill tool to achieve rock penetration with lower reacted force requirements, with a strategic view toward building an ultrasonic planetary core drill (UPCD) device. The UPCD is a descendant of the ultrasonic/sonic driller/corer technique. In these concepts, a transducer and horn (typically resonant at around 20 kHz) are used to excite a toroidal free mass that oscillates chaotically between the horn tip and drill base at lower frequencies (generally between 10 Hz and 1 kHz). This creates a series of stress pulses that is transferred through the drill bit to the rock surface, and while the stress at the drill-bit tip/rock interface exceeds the compressive strength of the rock, it causes fractures that result in fragmentation of the rock. This facilitates augering and downward progress. In order to ensure that the drill-bit tip delivers the greatest effective impulse (the time integral of the drill-bit tip/rock pressure curve exceeding the strength of the rock), parameters such as the spring rates and the mass of the free mass, the drill bit and transducer have been varied and compared in both computer simulation and practical experiment. The most interesting findings and those of particular relevance to deep drilling indicate that increasing the mass of the drill bit has a limited (or even positive) influence on the rate of effective impulse delivered.

Probing viscoelastic surfaces with bimodal tapping-mode atomic force microscopy: Underlying physics and observables for a standard linear solid model.

PubMed

Solares, Santiago D

2014-01-01

This paper presents computational simulations of single-mode and bimodal atomic force microscopy (AFM) with particular focus on the viscoelastic interactions occurring during tip-sample impact. The surface is modeled by using a standard linear solid model, which is the simplest system that can reproduce creep compliance and stress relaxation, which are fundamental behaviors exhibited by viscoelastic surfaces. The relaxation of the surface in combination with the complexities of bimodal tip-sample impacts gives rise to unique dynamic behaviors that have important consequences with regards to the acquisition of quantitative relationships between the sample properties and the AFM observables. The physics of the tip-sample interactions and its effect on the observables are illustrated and discussed, and a brief research outlook on viscoelasticity measurement with intermittent-contact AFM is provided.

Rhodamine B induces long nucleoplasmic bridges and other nuclear anomalies in Allium cepa root tip cells.

PubMed

Tan, Dehong; Bai, Bing; Jiang, Donghua; Shi, Lin; Cheng, Shunchang; Tao, Dongbing; Ji, Shujuan

2014-03-01

The cytogenetic toxicity of rhodamine B on root tip cells of Allium cepa was investigated. A. cepa were cultured in water (negative control), 10 ppm methyl methanesulfonate (positive control), and three concentrations of rhodamine B (200, 100, and 50 ppm) for 7 days. Rhodamine B inhibited mitotic activity; increased nuclear anomalies, including micronuclei, nuclear buds, and bridged nuclei; and induced oxidative stress in A. cepa root tissues. Furthermore, a substantial amount of long nucleoplasmic bridges were entangled together, and some nuclei were simultaneously linked to several other nuclei and to nuclear buds with nucleoplasmic bridges in rhodamine B-treated cells. In conclusion, rhodamine B induced cytogenetic effects in A. cepa root tip cells, which suggests that the A. cepa root is an ideal model system for detecting cellular interactions.

Modeling the Interactions Between Multiple Crack Closure Mechanisms at Threshold

NASA Technical Reports Server (NTRS)

Newman, John A.; Riddell, William T.; Piascik, Robert S.

2003-01-01

A fatigue crack closure model is developed that includes interactions between the three closure mechanisms most likely to occur at threshold; plasticity, roughness, and oxide. This model, herein referred to as the CROP model (for Closure, Roughness, Oxide, and Plasticity), also includes the effects of out-of plane cracking and multi-axial loading. These features make the CROP closure model uniquely suited for, but not limited to, threshold applications. Rough cracks are idealized here as two-dimensional sawtooths, whose geometry induces mixed-mode crack- tip stresses. Continuum mechanics and crack-tip dislocation concepts are combined to relate crack face displacements to crack-tip loads. Geometric criteria are used to determine closure loads from crack-face displacements. Finite element results, used to verify model predictions, provide critical information about the locations where crack closure occurs.

Comninou contact zones for a crack parallel to an interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joseph, P.F.; Gadi, K.S.; Erdogen, F.

One of the interesting features in studying the state of stress in elastic solids near singular points, is the so called complex singularity that gives rise to an apparent local oscillatory behavior in the stress and displacement fields. The region in which this occurs is very small, much smaller than any plastic zone would be, and therefore the oscillations can be ignored in practical applications. Nevertheless, it is a matter of interesting theoretical investigation. The Comninou model of a small contact zone near the crack tip appears to correct for this anomaly within the framework of the linear theory. Thismore » model seems to make sense out of a {open_quotes}solution{close_quotes} that violates the boundary conditions. Erdogan and Joseph, showed (to themselves anyway) that the Comninou model actually has a physical basis. They considered a crack parallel to an interface where the order of the singularity is always real. With great care in solving the singular integral equations, it was shown that as the crack approaches the interface, a pinching effect is observed at the crack tip. This pinching effect proves that in the limit as the crack approaches the interface, the correct way to handle the problem is to consider crack surface contact. In this way, the issue of {open_quotes}oscillations{close_quotes} is never encountered for the interface crack problem. In the present study, the value of h/a that corresponds to crack closure (zero value of the stress intensity factor) will be determined for a given material pair for tensile loading. An asymptotic numerical method for the solution of singular integral equations making use of is used to obtain this result. Results for the crack opening displacement near the tip of the crack and the behavior of the stress intensity factor for cracks very close to the interface are presented. Among other interesting issues to be discussed, this solution shows that the semi-infinite crack parallel to an interface is closed.« less

Experimental and Finite Element Modeling of Near-Threshold Fatigue Crack Growth for the K-Decreasing Test Method

NASA Technical Reports Server (NTRS)

Smith, Stephen W.; Seshadri, Banavara R.; Newman, John A.

2015-01-01

The experimental methods to determine near-threshold fatigue crack growth rate data are prescribed in ASTM standard E647. To produce near-threshold data at a constant stress ratio (R), the applied stress-intensity factor (K) is decreased as the crack grows based on a specified K-gradient. Consequently, as the fatigue crack growth rate threshold is approached and the crack tip opening displacement decreases, remote crack wake contact may occur due to the plastically deformed crack wake surfaces and shield the growing crack tip resulting in a reduced crack tip driving force and non-representative crack growth rate data. If such data are used to life a component, the evaluation could yield highly non-conservative predictions. Although this anomalous behavior has been shown to be affected by K-gradient, starting K level, residual stresses, environmental assisted cracking, specimen geometry, and material type, the specifications within the standard to avoid this effect are limited to a maximum fatigue crack growth rate and a suggestion for the K-gradient value. This paper provides parallel experimental and computational simulations for the K-decreasing method for two materials (an aluminum alloy, AA 2024-T3 and a titanium alloy, Ti 6-2-2-2-2) to aid in establishing clear understanding of appropriate testing requirements. These simulations investigate the effect of K-gradient, the maximum value of stress-intensity factor applied, and material type. A material independent term is developed to guide in the selection of appropriate test conditions for most engineering alloys. With the use of such a term, near-threshold fatigue crack growth rate tests can be performed at accelerated rates, near-threshold data can be acquired in days instead of weeks without having to establish testing criteria through trial and error, and these data can be acquired for most engineering materials, even those that are produced in relatively small product forms.

Roughness-Dominated Hydraulic Fracture Propagation

NASA Astrophysics Data System (ADS)

Garagash, D.

2015-12-01

Current understanding suggests that the energy to propagate a hydraulic fracture is defined by the viscous fluid pressure drop along the fracture channel, while the energy dissipation in the immediate vicinity of the fracture front (i.e. fracture toughness) is negligible. This status quo relies on the assumption of Poiseuille flow in the fracture, which transmissivity varies as cube of the aperture. We re-evaluate this assumption in the vicinity of the fracture tip, where the aperture roughness and/or branching of the fracture path may lead to very significant deviations from the cubic law. Existing relationships suggest rough fracture transmissivity power laws ~ wr with 4.5 ≤ r ≤ 6, when aperture w is smaller than the roughness. Solving for the tip region of a steadily propagating hydraulic fracture with the "rough fracture" transmissivity, we are able to show (a) larger energy dissipation than predicted by the Poiseuille flow model; (b) localization of the fluid pressure drop into the low-transmissivity, rough tip region; and (c) emergence of potentially preeminent "toughness-dominated" fracture propagation regime where most of the energy is dissipated at the tip and can be described in the context of classical fracture mechanics by invoking the effective fracture toughness dependent upon the details of the pressure drop in the rough tip. We establish that the ratio of the roughness scale wc to the viscous aperture scale wμ = μVE / σ02, controls the pressure drop localization. (Here V - propagation speed, μ - fluid viscosity, E - rock modulus, and σ0 - in-situ stress). For a range of industrial fracturing fluids (from slick-water to linear gels) and treatment conditions, wc/wμ is large, suggesting a fully-localized pressure drop and energy dissipation. The latter is adequately described by the effective toughness - a function of the propagation velocity, confining stress and material parameters, which estimated values are much larger than the "dry" rock fracture toughness measured in the lab. Using the effective, velocity-dependent fracture toughness to predict the evolution of a penny-shape fracture, we are able to show how/when the classical viscosity-dominated and toughness-dominated solutions based upon the Poiseuille law and the "dry", laboratory fracture toughness values, respectively, may become inadequate.

Characterization of the TIP4P-Ew water model: vapor pressure and boiling point.

PubMed

Horn, Hans W; Swope, William C; Pitera, Jed W

2005-11-15

The liquid-vapor-phase equilibrium properties of the previously developed TIP4P-Ew water model have been studied using thermodynamic integration free-energy simulation techniques in the temperature range of 274-400 K. We stress that free-energy results from simulations need to be corrected in order to be compared to the experiment. This is due to the fact that the thermodynamic end states accessible through simulations correspond to fictitious substances (classical rigid liquids and classical rigid ideal gases) while experiments operate on real substances (liquids and real gases, with quantum effects). After applying analytical corrections the vapor pressure curve obtained from simulated free-energy changes is in excellent agreement with the experimental vapor pressure curve. The boiling point of TIP4P-Ew water under ambient pressure is found to be at 370.3+/-1.9 K, about 7 K higher than the boiling point of TIP4P water (363.7+/-5.1 K; from simulations that employ finite range treatment of electrostatic and Lennard-Jones interactions). This is in contrast to the approximately +15 K by which the temperature of the density maximum and the melting temperature of TIP4P-Ew are shifted relative to TIP4P, indicating that the temperature range over which the liquid phase of TIP4P-Ew is stable is narrower than that of TIP4P and resembles more that of real water. The quality of the vapor pressure results highlights the success of TIP4P-Ew in describing the energetic and entropic aspects of intermolecular interactions in liquid water.

Fluid Production Induced Stress Analysis Surrounding an Elliptic Fracture

NASA Astrophysics Data System (ADS)

Pandit, Harshad Rajendra

Hydraulic fracturing is an effective technique used in well stimulation to increase petroleum well production. A combination of multi-stage hydraulic fracturing and horizontal drilling has led to the recent boom in shale gas production which has changed the energy landscape of North America. During the fracking process, highly pressurized mixture of water and proppants (sand and chemicals) is injected into to a crack, which fractures the surrounding rock structure and proppants help in keeping the fracture open. Over a longer period, however, these fractures tend to close due to the difference between the compressive stress exerted by the reservoir on the fracture and the fluid pressure inside the fracture. During production, fluid pressure inside the fracture is reduced further which can accelerate the closure of a fracture. In this thesis, we study the stress distribution around a hydraulic fracture caused by fluid production. It is shown that fluid flow can induce a very high hoop stress near the fracture tip. As the pressure gradient increases stress concentration increases. If a fracture is very thin, the flow induced stress along the fracture decreases, but the stress concentration at the fracture tip increases and become unbounded for an infinitely thin fracture. The result from the present study can be used for studying the fracture closure problem, and ultimately this in turn can lead to the development of better proppants so that prolific well production can be sustained for a long period of time.

Genome-wide identification and characterization of aquaporin gene family in common bean (Phaseolus vulgaris L.).

PubMed

Ariani, Andrea; Gepts, Paul

2015-10-01

Plant aquaporins are a large and diverse family of water channel proteins that are essential for several physiological processes in living organisms. Numerous studies have linked plant aquaporins with a plethora of processes, such as nutrient acquisition, CO2 transport, plant growth and development, and response to abiotic stresses. However, little is known about this protein family in common bean. Here, we present a genome-wide identification of the aquaporin gene family in common bean (Phaseolus vulgaris L.), a legume crop essential for human nutrition. We identified 41 full-length coding aquaporin sequences in the common bean genome, divided by phylogenetic analysis into five sub-families (PIPs, TIPs, NIPs, SIPs and XIPs). Residues determining substrate specificity of aquaporins (i.e., NPA motifs and ar/R selectivity filter) seem conserved between common bean and other plant species, allowing inference of substrate specificity for these proteins. Thanks to the availability of RNA-sequencing datasets, expression levels in different organs and in leaves of wild and domesticated bean accessions were evaluated. Three aquaporins (PvTIP1;1, PvPIP2;4 and PvPIP1;2) have the overall highest mean expressions, with PvTIP1;1 having the highest expression among all aquaporins. We performed an EST database mining to identify drought-responsive aquaporins in common bean. This analysis showed a significant increase in expression for PvTIP1;1 in drought stress conditions compared to well-watered environments. The pivotal role suggested for PvTIP1;1 in regulating water homeostasis and drought stress response in the common bean should be verified by further field experimentation under drought stress.

Thermal characterization of phacoemulsification probes operated in axial and torsional modes.

PubMed

Zacharias, Jaime

2015-01-01

To analyze temperature increases and identify potential sources of heat generated when sleeved and sleeveless phacoemulsification probes were operated in axial and torsional modes using the Infiniti Vision System with the Ozil torsional handpiece. Phacodynamics Laboratory, Pasteur Ophthalmic Clinic, Santiago, Chile. Experimental study. Two computer-controlled thermal transfer systems were developed to evaluate the contribution of internal metal stress and tip-to-sleeve friction on heat generation during phacoemulsification using axial and torsional ultrasound modalities. Both systems incorporated infrared thermal imaging and used a black-body film to accurately capture temperature measurements. Axial mode was consistently associated with greater temperature increases than torsional mode whether tips were operated with or without sleeves. In tests involving bare tips, axial mode and torsional mode peaked at 51.7°C and 34.2°C, respectively. In an example using sleeved tips in which a 30.0 g load was applied for 1 second, temperatures for axial mode reached 45°C and for torsional mode, 38°C. Friction between the sleeved probe and the incisional wall contributed more significantly to the temperature increase than internal metal stress regardless of the mode used. In all experiments, the temperature increase observed with axial mode was greater than that observed with torsional mode, even when conditions such as power or amplitude and flow rate were varied. Tip-to-sleeve friction was a more dominant source of phaco probe heating than internal metal stress. The temperature increase due to internal metal stress was greater with axial mode than with torsional mode. Dr. Zacharias received research funding from Alcon Laboratories, Inc., to conduct this study. He has no financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Cracks in Complex Bodies: Covariance of Tip Balances

NASA Astrophysics Data System (ADS)

Mariano, Paolo Maria

2008-04-01

In complex bodies, actions due to substructural changes alter (in some cases drastically) the force driving the tip of macroscopic cracks in quasi-static and dynamic growth, and must be represented directly. Here it is proven that tip balances of standard and substructural interactions are covariant. In fact, the former balance follows from the Lagrangian density’s requirement of invariance with respect to the action of the group of diffeomorphisms of the ambient space to itself, the latter balance accrues from an analogous invariance with respect to the action of a Lie group over the manifold of substructural shapes. The evolution equation of the crack tip can be obtained by exploiting invariance with respect to relabeling the material elements in the reference place. The analysis is developed by first focusing on general complex bodies that admit metastable states with substructural dissipation of viscous-like type inside each material element. Then we account for gradient dissipative effects that induce nonconservative stresses; the covariance of tip balances in simple bodies follows as a corollary. When body actions and boundary data of Dirichlet type are absent, the standard variational description of quasi-static crack growth is simply extended to the case of complex materials.

Tips for Survivors of a Traumatic Event: Managing Your Stress

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... for Survivors of a Traumatic Event Managing Your Stress Know When to Get Help Sometimes things become ... anger, or desires revenge; or shows signs of stress (listed on this page) for several days or ...

The Evolution of Stress Intensity Factors and the Propagation of Cracks in Elastic Media

NASA Astrophysics Data System (ADS)

Friedman, Avner; Hu, Bei; Velazquez, Juan J. L.

When a crack Γs propagates in an elastic medium the stress intensity factors evolve with the tip x(s) of Γs. In this paper we derive formulae which describe the evolution of these stress intensity factors for a homogeneous isotropic elastic medium under plane strain conditions. Denoting by ψ=ψ(x,s) the stress potential (ψ is biharmonic and has zero traction along the crack Γs) and by κ(s) the curvature of the crack at the tip x(s), we prove that the stress intensity factors A1(s), A2(s), as functions of s, satisfy: where , are stress intensity factors of the tangential derivative of in the polar coordinate system at x(s) with θ=0 in the direction of the crack at x(s). The case of antiplane shearing is also briefly considered; in this case ψ is harmonic.

Stress regime in the Philippine Sea slab beneath Kanto, Japan

NASA Astrophysics Data System (ADS)

Nakajima, Junichi; Hasegawa, Akira; Hirose, Fuyuki

2011-08-01

We determine the focal mechanisms of earthquakes within the Philippine Sea slab beneath the Tokyo metropolitan area, and perform stress tensor inversions to investigate the detailed stress field within the slab. The results show a characteristic spatial variation in earthquake-generating stress. Slab stress in northeastern part of the PHS slab is characterized by down-dip tension (DDT), except for the uppermost tip of the seismic portion of the slab where down-dip compression (DDC) stress is dominant. We interpret that DDT is caused by the net slab pull and DDC is attributable to local resistance to subduction at the tip of the slab. In southwestern part of the PHS slab, σ1 and σ3 are generally rotated oblique to the dip of the slab, suggesting that earthquakes occur under stress conditions of neither DDC nor DDT. The rotations in σ1 and σ3 may be related to stress accumulation by the slip deficit along the asperity of the 1923 Kanto earthquake (M7.9).

Micro-mechanical analysis of damage growth and fracture in discontinuous fiber reinforced metal matrix composites

NASA Technical Reports Server (NTRS)

Goree, James G.; Richardson, David E.

1990-01-01

The near-crack-tip stresses in any planar coupon of arbitrary geometry subjected to mode 1 loading may be equated to those in an infinite center-cracked panel subjected to the appropriate equivalent remote biaxial stresses (ERBS). Since this process can be done for all such mode 1 coupons, attention may be focused on the behavior of the equivalent infinite cracked panel. To calculate the ERBS, the constant term in the series expansion of the crack-tip stress must be retained. It is proposed that the ERBS may be used quantitatively to explain different fracture phenomena such as crack branching.

Electrochemical model of local corrosion at the tip of a loaded crack

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreikiv, O.E.; Tym`yak, N.I.

1994-07-01

A model of electrochemical processes near a crack tip in a stressed metal subjected to corrosion with hydrogen depolarization is suggested. It is shown that, in order to describe the kinetics of hydrogenation of the prefracture area, it is necessary to take into account the type of passivation layer on the newly formed metal surface near the crack tip and the mechanism of its formation.

A pharmacokinetic-pharmacodynamic model for intrathecal baclofen in patients with severe spasticity.

PubMed

Heetla, H W; Proost, J H; Molmans, B H; Staal, M J; van Laar, T

2016-01-01

Intrathecal baclofen (ITB) has proven to be an effective and safe treatment for severe spasticity. However, although ITB is used extensively, clinical decisions are based on very scarce pharmacokinetic-pharmacodynamic (PKPD) data. The aim of this study was to measure baclofen CSF concentrations and clinical effects after administration of various ITB boluses in patients with spasticity and to create a PKPD model for ITB. Twelve patients with severe spasticity received four different bolus doses of ITB (0, 25, 50, 75 μg and an optional dose of 100 μg), administered via a catheter with the tip at thoracic level (Th) 10. After each bolus, 10 CSF samples were taken at fixed time intervals, using a catheter with the tip located at Th12. Clinical effect was assessed by measuring spasticity with the Modified Ashworth Scale (MAS). These data were used to develop a PKPD model. All patients achieved an adequate spasmolytic effect with ITB doses varying from 50 to 100 μg. No serious side effects were observed. CSF baclofen concentrations, as well as the clinical effects, correlated significantly with ITB doses. The PK model predicted a steep spinal concentration gradient of ITB along the spinal axis. The clinical effect could be predicted using a delayed-effect model. ITB is an effective and safe therapy with, however, a steep concentration gradient along the spinal axis. This means that the administered baclofen is staying mainly around the catheter tip, which stresses the importance to position the ITB catheter tip closely to the targeted spinal level. © 2015 The British Pharmacological Society.

Numerical investigation on the prefabricated crack propagation of FV520B stainless steel

NASA Astrophysics Data System (ADS)

Pan, Juyi; Qin, Ming; Chen, Songying

FV520B is a common stainless steel for manufacturing centrifugal compressor impeller and shaft. The internal metal flaw destroys the continuity of the material matrix, resulting in the crack propagation fracture of the component, which seriously reduces the service life of the equipment. In this paper, Abaqus software was used to simulate the prefabricated crack propagation of FV520B specimen with unilateral gap. The results of static crack propagation simulation results show that the maximum value of stress-strain located at the tip of the crack and symmetrical distributed like a butterfly along the prefabricated crack direction, the maximum stress is 1990 MPa and the maximum strain is 9.489 × 10-3. The Mises stress and stress intensity factor KI increases with the increase of the expansion step, the critical value of crack initiation is reached at the 6th extension step. The dynamic crack propagation simulation shows that the crack propagation path is perpendicular to the load loading direction. Similarly, the maximum Mises stress located at the crack tip and is symmetrically distributed along the crack propagation direction. The critical stress range of the crack propagation is 23.3-43.4 MPa. The maximum value of stress-strain curve located at the 8th extension step, that is, the crack initiation point, the maximum stress is 55.22 MPa, and the maximum strain is 2.26 × 10-4. On the crack tip, the stress changed as 32.24-40.16 MPa, the strain is at 1.292 × 10-4-1.897 × 10-4.

Finite element techniques applied to cracks interacting with selected singularities

NASA Technical Reports Server (NTRS)

Conway, J. C.

1975-01-01

The finite-element method for computing the extensional stress-intensity factor for cracks approaching selected singularities of varied geometry is described. Stress-intensity factors are generated using both displacement and J-integral techniques, and numerical results are compared to those obtained experimentally in a photoelastic investigation. The selected singularities considered are a colinear crack, a circular penetration, and a notched circular penetration. Results indicate that singularities greatly influence the crack-tip stress-intensity factor as the crack approaches the singularity. In addition, the degree of influence can be regulated by varying the overall geometry of the singularity. Local changes in singularity geometry have little effect on the stress-intensity factor for the cases investigated.

Tips for Chronic Pain

MedlinePlus

... Don’t let stress compound your pain. • Stress is the result of the way you react to the world, and heightened stress equals heightened pain. Learn relaxation techniques or seek help in reducing your stress level. Get enough sleep. • Practice good sleep habits and get adequate sleep on a ...

The Dynamics of Miscible Interfaces: Simulations

NASA Technical Reports Server (NTRS)

Meiburg, Eckart

2002-01-01

The goal of this experimental/computational investigation (joint with Prof Maxworthy at USC) has been to study the dynamics of miscible interfaces, both from a scientific and a practical point of view, and to prepare a related experiment to be flown on the International Space Station. In order to address these effects, we have focused experimental and computational investigations on miscible displacements in cylindrical capillary tubes, as well as in Hele-Shaw cells. Regarding the flow in a capillary tube, the question was addressed as to whether Korteweg stresses and/or divergence effects can potentially account for discrepancies observed between conventional Stokes flow simulations and experiments for miscible flows in capillary tubes. An estimate of the vorticity and streamfunction fields induced by the Kortewegs stresses was derived, which shows these stresses to result in the formation of a vortex ring structure near the tip of the concentration front. Through this mechanism the propagation velocity of the concentration front is reduced, in agreement with the experimental observations. Divergence effects, on the other hand, were seen to be very small, and they have a negligible influence on the tip velocity. As a result, it can be concluded that they are not responsible for the discrepancies between experiments and conventional Stokes simulations. A further part of our investigation focussed on the development of high-accuracy three-dimensional spectral element simulation techniques for miscible flows in capillary tubes, including the effects of variable density and viscosity. Towards this end, the conservation equations are treated in cylindrical coordinates.

New theory for Mode I crack-tip dislocation emission

NASA Astrophysics Data System (ADS)

Andric, Predrag; Curtin, W. A.

2017-09-01

A material is intrinsically ductile under Mode I loading when the critical stress intensity KIe for dislocation emission is lower than the critical stress intensity KIc for cleavage. KIe is usually evaluated using the approximate Rice theory, which predicts a dependence on the elastic constants and the unstable stacking fault energy γusf for slip along the plane of dislocation emission. Here, atomistic simulations across a wide range of fcc metals show that KIe is systematically larger (10-30%) than predicted. However, the critical (crack tip) shear displacement is up to 40% smaller than predicted. The discrepancy arises because Mode I emission is accompanied by the formation of a surface step that is not considered in the Rice theory. A new theory for Mode I emission is presented based on the ideas that (i) the stress resisting step formation at the crack tip creates "lattice trapping" against dislocation emission such that (ii) emission is due to a mechanical instability at the crack tip. The new theory is formulated using a Peierls-type model, naturally includes the energy to form the step, and reduces to the Rice theory (no trapping) when the step energy is small. The new theory predicts a higher KIe at a smaller critical shear displacement, rationalizing deviations of simulations from the Rice theory. Specific predictions of KIe for the simulated materials, usually requiring use of the measured critical crack tip shear displacement due to complex material non-linearity, show very good agreement with simulations. An analytic model involving only γusf, the surface energy γs, and anisotropic elastic constants is shown to be quite accurate, serves as a replacement for the analytical Rice theory, and is used to understand differences between Rice theory and simulation in recent literature. The new theory highlights the role of surface steps created by dislocation emission in Mode I, which has implications not only for intrinsic ductility but also for crack tip twinning and fracture due to chemical interactions at the crack tip.

Dynamic Negative Compressibility of Few-Layer Graphene, h-BN, and MoS2

NASA Astrophysics Data System (ADS)

Neves, Bernardo; Barboza, Ana Paula; Chacham, Helio; Oliveira, Camilla; Fernandes, Thales; Martins Ferreira, Erlon; Archanjo, Braulio; Batista, Ronaldo; Oliveira, Alan

2013-03-01

We report a novel mechanical response of few-layer graphene, h-BN, and MoS2 to the simultaneous compression and shear by an atomic force microscope (AFM) tip. The response is characterized by the vertical expansion of these two-dimensional (2D) layered materials upon compression. Such effect is proportional to the applied load, leading to vertical strain values (opposite to the applied force) of up to 150%. The effect is null in the absence of shear, increases with tip velocity, and is anisotropic. It also has similar magnitudes in these solid lubricant materials (few-layer graphene, h-BN, and MoS2), but it is absent in single-layer graphene and in few-layer mica and Bi2Se3. We propose a physical mechanism for the effect where the combined compressive and shear stresses from the tip induce dynamical wrinkling on the upper material layers, leading to the observed flake thickening. The new effect (and, therefore, the proposed wrinkling) is reversible in the three materials where it is observed.[2] Financial support from CNPq, Fapemig, Rede Nacional de Pesquisa em Nanotubos de Carbono and INCT-Nano-Carbono

Extruded upper first molar intrusion: Comparison between unilateral and bilateral miniscrew anchorage.

PubMed

Sugii, Mari Miura; Barreto, Bruno de Castro Ferreira; Francisco Vieira-Júnior, Waldemir; Simone, Katia Regina Izola; Bacchi, Ataís; Caldas, Ricardo Armini

2018-01-01

The aim of his study was to evaluate the stress on tooth and alveolar bone caused by orthodontic intrusion forces in a supraerupted upper molar, by using a three-dimensional Finite Element Method (FEM). A superior maxillary segment was modeled in the software SolidWorks 2010 (SolidWorks Corporation, Waltham, MA, USA) containing: cortical and cancellous bone, supraerupted first molar, periodontal tissue and orthodontic components. A finite element model has simulated intrusion forces of 4N onto a tooth, directed to different mini-screw locations. Three different intrusion mechanics vectors were simulated: anchoring on a buccal mini-implant; anchoring on a palatal mini-implant and the association of both anchorage systems. All analyses were performed considering the minimum principal stress and total deformation. Qualitative analyses exhibited stress distribution by color maps. Quantitative analysis was performed with a specific software for reading and solving numerical equations (ANSYS Workbench 14, Ansys, Canonsburg, Pennsylvania, USA). Intrusion forces applied from both sides (buccal and palatal) resulted in a more homogeneous stress distribution; no high peak of stress was detected and it has allowed a vertical resultant movement. Buccal or palatal single-sided forces resulted in concentrated stress zones with higher values and tooth tipping to respective force side. Unilateral forces promoted higher stress in root apex and higher dental tipping. The bilateral forces promoted better distribution without evidence of dental tipping. Bilateral intrusion technique suggested lower probability of root apex resorption.

Stress-intensity factors for a thick-walled cylinder containing an annular imbedded or external or internal surface crack

NASA Technical Reports Server (NTRS)

Erdol, R.; Erdogan, F.

1976-01-01

The elastostatic axisymmetric problem for a long thick-walled cylinder containing a ring-shaped internal or edge crack is considered. Using the standard transform technique the problem is formulated in terms of an integral equation which has a simple Cauchy kernel for the internal crack and a generalized Cauchy kernel for the edge crack as the dominant part. As examples the uniform axial load and the steady-state thermal stress problems have been solved and the related stress intensity factors have been calculated. Among other findings the results show that in the cylinder under uniform axial stress containing an internal crack the stress intensity factor at the inner tip is always greater than that at the outer tip for equal net ligament thicknesses and in the cylinder with an edge crack which is under a state of thermal stress the stress intensity factor is a decreasing function of the crack depth, tending to zero as the crack depth approaches the wall thickness.

Bending and shear stresses developed by the instantaneous arrest of the root of a cantilever beam rotating with constant angular velocity about a transverse axis through the root

NASA Technical Reports Server (NTRS)

Stowell, Elbridge Z; Schwartz, Edward B; Houbolt, John C

1945-01-01

A theoretical investigation was made of the behavior of a cantilever beam in rotational motion about a transverse axis through the root determining the stresses, the deflections, and the accelerations that occur in the beam as a result of the arrest of motion. The equations for bending and shear stress reveal that, at a given percentage of the distance from root to tip and at a given trip velocity, the bending stresses for a particular mode are independent of the length of the beam and the shear stresses vary inversely with the length. When examined with respect to a given angular velocity instead of a given tip velocity, the equations reveal that the bending stress is proportional to the length of the beam whereas the shear stress is independent of the length. Sufficient experimental verification of the theory has previously been given in connection with another problem of the same type.

Genome duplication improves rice root resistance to salt stress

PubMed Central

2014-01-01

Background Salinity is a stressful environmental factor that limits the productivity of crop plants, and roots form the major interface between plants and various abiotic stresses. Rice is a salt-sensitive crop and its polyploid shows advantages in terms of stress resistance. The objective of this study was to investigate the effects of genome duplication on rice root resistance to salt stress. Results Both diploid rice (HN2026-2x and Nipponbare-2x) and their corresponding tetraploid rice (HN2026-4x and Nipponbare-4x) were cultured in half-strength Murashige and Skoog medium with 150 mM NaCl for 3 and 5 days. Accumulations of proline, soluble sugar, malondialdehyde (MDA), Na+ content, H+ (proton) flux at root tips, and the microstructure and ultrastructure in rice roots were examined. We found that tetraploid rice showed less root growth inhibition, accumulated higher proline content and lower MDA content, and exhibited a higher frequency of normal epidermal cells than diploid rice. In addition, a protective gap appeared between the cortex and pericycle cells in tetraploid rice. Next, ultrastructural analysis showed that genome duplication improved membrane, organelle, and nuclei stability. Furthermore, Na+ in tetraploid rice roots significantly decreased while root tip H+ efflux in tetraploid rice significantly increased. Conclusions Our results suggest that genome duplication improves root resistance to salt stress, and that enhanced proton transport to the root surface may play a role in reducing Na+ entrance into the roots. PMID:25184027

Near-tip dual-length scale mechanics of mode-I cracking in laminate brittle matrix composites

NASA Technical Reports Server (NTRS)

Ballarini, R.; Islam, S.; Charalambides, P. G.

1992-01-01

This paper presents the preliminary results of an on-going study of the near-tip mechanics of mode-I cracking in brittle matrix composite laminates. A finite element model is developed within the context of two competing characteristic lengths present in the composite: the microstructural length (the thickness of the layers) and a macro-length (crack-length, uncracked ligament size, etc.). For various values of the parameters which describe the ratio of these lengths and the constituent properties, the stresses ahead of a crack perpendicular to the laminates are compared with those predicted by assuming the composite is homogeneous orthotropic. The results can be used to determine the conditions for which homogenization can provide a sufficiently accurate description of the stresses in the vicinity of the crack-tip.

Linear least squares approach for evaluating crack tip fracture parameters using isochromatic and isoclinic data from digital photoelasticity

NASA Astrophysics Data System (ADS)

Patil, Prataprao; Vyasarayani, C. P.; Ramji, M.

2017-06-01

In this work, digital photoelasticity technique is used to estimate the crack tip fracture parameters for different crack configurations. Conventionally, only isochromatic data surrounding the crack tip is used for SIF estimation, but with the advent of digital photoelasticity, pixel-wise availability of both isoclinic and isochromatic data could be exploited for SIF estimation in a novel way. A linear least square approach is proposed to estimate the mixed-mode crack tip fracture parameters by solving the multi-parameter stress field equation. The stress intensity factor (SIF) is extracted from those estimated fracture parameters. The isochromatic and isoclinic data around the crack tip is estimated using the ten-step phase shifting technique. To get the unwrapped data, the adaptive quality guided phase unwrapping algorithm (AQGPU) has been used. The mixed mode fracture parameters, especially SIF are estimated for specimen configurations like single edge notch (SEN), center crack and straight crack ahead of inclusion using the proposed algorithm. The experimental SIF values estimated using the proposed method are compared with analytical/finite element analysis (FEA) results, and are found to be in good agreement.

Cell-Biological Studies of Osmotic Shock Response in Streptomyces spp.

PubMed

Fuchino, Katsuya; Flärdh, Klas; Dyson, Paul; Ausmees, Nora

2017-01-01

Most bacteria are likely to face osmotic challenges, but there is yet much to learn about how such environmental changes affect the architecture of bacterial cells. Here, we report a cell-biological study in model organisms of the genus Streptomyces, which are actinobacteria that grow in a highly polarized fashion to form branching hyphae. The characteristic apical growth of Streptomyces hyphae is orchestrated by protein assemblies, called polarisomes, which contain coiled-coil proteins DivIVA and Scy, and recruit cell wall synthesis complexes and the stress-bearing cytoskeleton of FilP to the tip regions of the hyphae. We monitored cell growth and cell-architectural changes by time-lapse microscopy in osmotic upshift experiments. Hyperosmotic shock caused arrest of growth, loss of turgor, and hypercondensation of chromosomes. The recovery period was protracted, presumably due to the dehydrated state of the cytoplasm, before hyphae could restore their turgor and start to grow again. In most hyphae, this regrowth did not take place at the original hyphal tips. Instead, cell polarity was reprogrammed, and polarisomes were redistributed to new sites, leading to the emergence of multiple lateral branches from which growth occurred. Factors known to regulate the branching pattern of Streptomyces hyphae, such as the serine/threonine kinase AfsK and Scy, were not involved in reprogramming of cell polarity, indicating that different mechanisms may act under different environmental conditions to control hyphal branching. Our observations of hyphal morphology during the stress response indicate that turgor and sufficient hydration of cytoplasm are required for Streptomyces tip growth. Polar growth is an intricate manner of growth for accomplishing a complicated morphology, employed by a wide range of organisms across the kingdoms of life. The tip extension of Streptomyces hyphae is one of the most pronounced examples of polar growth among bacteria. The expansion of the cell wall by tip extension is thought to be facilitated by the turgor pressure, but it was unknown how external osmotic change influences Streptomyces tip growth. We report here that severe hyperosmotic stress causes cessation of growth, followed by reprogramming of cell polarity and rearrangement of growth zones to promote lateral hyphal branching. This phenomenon may represent a strategy of hyphal organisms to avoid osmotic stress encountered by the growing hyphal tip. Copyright © 2016 American Society for Microbiology.

Stressed Oxidation of C/SiC Composites

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Brewer, David N.; Eckel, Andrew J.; Cawley, James D.

1997-01-01

Constant load, stressed oxidation testing was performed on T-300 C/SiC composites with a SiC seal coat. Test conditions included temperatures ranging from 350 C to 1500 C at stresses of 69 MPa and 172 MPa (10 and 25 ksi). The coupon subjected to stressed oxidation at 550 C/69 MPa for 25 hours had a room temperature residual strength one-half that of the as-received coupons. The coupon tested at the higher stress and all coupons tested at higher temperatures failed in less than 25 hr. Microstructural analysis of the fracture surfaces, using SEM (scanning electron microscopy), revealed the formation of reduced cross-sectional fibers with pointed tips. Analysis of composite cross-sections show pathways for oxygen ingress. The discussion will focus on fiber/matrix interphase oxidation and debonding as well as the formation and implications of the fiber tip morphology.

A theory for the fracture of thin plates subjected to bending and twisting moments

NASA Technical Reports Server (NTRS)

Hui, C. Y.; Zehnder, Alan T.

1993-01-01

Stress fields near the tip of a through crack in an elastic plate under bending and twisting moments are reviewed assuming both Kirchhoff and Reissner plate theories. The crack tip displacement and rotation fields based on the Reissner theory are calculated. These results are used to calculate the J-integral (energy release rate) for both Kirchhoff and Reissner plate theories. Invoking Simmonds and Duva's (1981) result that the value of the J-integral based on either theory is the same for thin plates, a universal relationship between the Kirchhoff theory stress intensity factors and the Reissner theory stress intensity factors is obtained for thin plates. Calculation of Kirchhoff theory stress intensity factors from finite elements based on energy release rate is illustrated. It is proposed that, for thin plates, fracture toughness and crack growth rates be correlated with the Kirchhoff theory stress intensity factors.

Characterization of Residual Stress Effects on Fatigue Crack Growth of a Friction Stir Welded Aluminum Alloy

NASA Technical Reports Server (NTRS)

Newman, John A.; Smith, Stephen W.; Seshadri, Banavara R.; James, Mark A.; Brazill, Richard L.; Schultz, Robert W.; Donald, J. Keith; Blair, Amy

2015-01-01

An on-line compliance-based method to account for residual stress effects in stress-intensity factor and fatigue crack growth property determinations has been evaluated. Residual stress intensity factor results determined from specimens containing friction stir weld induced residual stresses are presented, and the on-line method results were found to be in excellent agreement with residual stress-intensity factor data obtained using the cut compliance method. Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress-intensity factor, can be used to determine the total crack-tip stress-intensity factor. Finite element, VCCT (virtual crack closure technique), and J-integral analysis methods have been used to characterize weld-induced residual stress using thermal expansion/contraction in the form of an equivalent delta T (change in local temperature during welding) to simulate the welding process. This equivalent delta T was established and applied to analyze different specimen configurations to predict residual stress distributions and associated residual stress-intensity factor values. The predictions were found to agree well with experimental results obtained using the crack- and cut-compliance methods.

[Effectivity and Safety of a Modified Tip Design in Torsional Phacoemulsification].

PubMed

Schmidt, Sabine; Hubich, Sophie; Vetter, Jan Markus; Wirbelauer, Christopher

2018-02-16

Torsional mode phacoemulsification results in more effective fragmentation of the nucleus due to a different movement of the phacotip. In this clinical study, we investigated the influence of a modified tip design and active fluidics on the efficacy of phacoemulsification and safety for the corneal endothelium. We conducted a prospective randomized 2 : 1 study in which 40 patients were operated on with the mini-flared Kelman Tip using the Infiniti ® System (group 1), and 20 patients were operated on with the Intrepid ® Balanced Tip and the Centurion ® System. We analyzed the intraoperative cumulative dissipated energy and also the density of the corneal endothelium measured with an endothelial microscope (CEM 530, Nidek) pre- and postoperatively. Both groups did not differ preoperatively in age, sex, axial length of the globe or corneal endothelium cell density nor cataract density (LOCS3). All surgeries were uneventful. The cumulative dissipated energy in group 1 (mini-flared Kelman tip, Infiniti System) was 38% higher than in group 2 (balanced tip, Centurion System; p < 0.05). The endothelial cell loss was 8% in group 1 and 10.3% in group 2 (p > 0.05). The cell size (polymegathism) increased in both groups significantly with + 37 µm in group 1 (p < 0.05) und + 54 µm in group 2 (p < 0.05). There was no statistically significant difference between both groups (p > 0.05). The number of hexagonal cells (pleomorphism) and corneal thickness did not differ in both groups either pre- nor postoperatively. Compared to torsional phacoemulsification with a mini-flared Kelman Tip and gravity fluidics, torsional phacoemulsification with a modified tip design and active fluidics is 38% more effective regarding the cumulative dissipated energy. Endothelial cell loss occurs to a similar extend using both systems. The postoperative changes in cell size (polymegathism), number of hexagonal cells (pleomorphism) and corneal thickness (pachymetry) were similar among both systems. We conclude, that the intraoperative stress on the endothelium is equivalent with both systems used. Georg Thieme Verlag KG Stuttgart · New York.

Early Effects of Salinity on Water Transport in Arabidopsis Roots. Molecular and Cellular Features of Aquaporin Expression1

PubMed Central

Boursiac, Yann; Chen, Sheng; Luu, Doan-Trung; Sorieul, Mathias; van den Dries, Niels; Maurel, Christophe

2005-01-01

Aquaporins facilitate the uptake of soil water and mediate the regulation of root hydraulic conductivity (Lpr) in response to a large variety of environmental stresses. Here, we use Arabidopsis (Arabidopsis thaliana) plants to dissect the effects of salt on both Lpr and aquaporin expression and investigate possible molecular and cellular mechanisms of aquaporin regulation in plant roots under stress. Treatment of plants by 100 mm NaCl was perceived as an osmotic stimulus and induced a rapid (half-time, 45 min) and significant (70%) decrease in Lpr, which was maintained for at least 24 h. Macroarray experiments with gene-specific tags were performed to investigate the expression of all 35 genes of the Arabidopsis aquaporin family. Transcripts from 20 individual aquaporin genes, most of which encoded members of the plasma membrane intrinsic protein (PIP) and tonoplast intrinsic protein (TIP) subfamilies, were detected in nontreated roots. All PIP and TIP aquaporin transcripts with a strong expression signal showed a 60% to 75% decrease in their abundance between 2 and 4 h following exposure to salt. The use of antipeptide antibodies that cross-reacted with isoforms of specific aquaporin subclasses revealed that the abundance of PIP1s decreased by 40% as early as 30 min after salt exposure, whereas PIP2 and TIP1 homologs showed a 20% to 40% decrease in abundance after 6 h of treatment. Expression in transgenic plants of aquaporins fused to the green fluorescent protein revealed that the subcellular localization of TIP2;1 and PIP1 and PIP2 homologs was unchanged after 45 min of exposure to salt, whereas a TIP1;1-green fluorescent protein fusion was relocalized into intracellular spherical structures tentatively identified as intravacuolar invaginations. The appearance of intracellular structures containing PIP1 and PIP2 homologs was occasionally observed after 2 h of salt treatment. In conclusion, this work shows that exposure of roots to salt induces changes in aquaporin expression at multiple levels. These changes include a coordinated transcriptional down-regulation and subcellular relocalization of both PIPs and TIPs. These mechanisms may act in concert to regulate root water transport, mostly in the long term (≥6 h). PMID:16183846

Do mesoscale faults near the tip of an active strike-slip fault indicate regional or local stress?

NASA Astrophysics Data System (ADS)

Yamaji, Atsushi

2017-04-01

Fault-slip analysis is used in Japan after the Great Tohoku Earthquake (2011) to judge the stability of fractures in the foundations of nuclear power plants. In case a fault-slip datum from a fracture surface is explained by the present stress condition, the fracture is thought to have a risk to be activated as a fault. So, it is important to understand the relative significance of regional and local stresses. To answer the question whether mesoscale faults indicate regional or local stress, fault-slip data were collected from the walls of a trenching site of the Nojima Fault in central Japan—an active, dextral, strike-slip fault. The fault gave rise to the 1995 Kobe earthquake, which killed more than 6000 people. The trench was placed near the fault tip, which produced compressional and extensional local stress conditions on the sides of the fault near the tip. A segment of the fault, which ruptured the surface in 1995, bounded Cretaceous granite and latest Pliocene sediments in the trench. As a result, the stress inversion of the data from the mesoscale faults observed in the trench showed both the local stresses. The present WNW-ESE regional compression was found from the compressive side, but was not in the extensional side, probably because local extension surpassed the regional compression. Instead, the regional N-S compression of the Early Pleistocene was found from the extensional side. From this project, we got the lesson that fault-slip analysis reveals regional and local stresses, and that local stress sometimes masks regional one. This work was supported by a science project of "Drilling into Fault Damage Zone" (awarded to A. Lin) of the Secretariat of Nuclear Regulation Authority (Japan).

The Stress-responsive Gene ATF3 Mediates Dichotomous UV Responses by Regulating the Tip60 and p53 Proteins*

PubMed Central

Cui, Hongmei; Li, Xingyao; Han, Chunhua; Wang, Qi-En; Wang, Hongbo; Ding, Han-Fei; Zhang, Junran; Yan, Chunhong

2016-01-01

The response to UV irradiation is important for a cell to maintain its genetic integrity when challenged by environmental genotoxins. An immediate early response to UV irradiation is the rapid induction of activating transcription factor 3 (ATF3) expression. Although emerging evidence has linked ATF3 to stress pathways regulated by the tumor suppressor p53 and the histone acetyltransferase Tip60, the role of ATF3 in the UV response remains largely unclear. Here, we report that ATF3 mediated dichotomous UV responses. Although UV irradiation enhanced the binding of ATF3 to Tip60, knockdown of ATF3 expression decreased Tip60 stability, thereby impairing Tip60 induction by UV irradiation. In line with the role of Tip60 in mediating UV-induced apoptosis, ATF3 promoted the death of p53-defective cells in response to UV irradiation. However, ATF3 could also activate p53 and promote p53-mediated DNA repair, mainly through altering histone modifications that could facilitate recruitment of DNA repair proteins (such as DDB2) to damaged DNA sites. As a result, ATF3 rather protected the p53 wild-type cells from UV-induced apoptosis. Our results thus indicate that ATF3 regulates cell fates upon UV irradiation in a p53-dependent manner. PMID:26994140

Strain Profiling of Fatigue Crack Overload Effects Using Energy Dispersive X-Ray Diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Croft,M.; Zhong, Z.; Jisrawi, N.

In this paper, an assessment of commonly used assumptions associated with {Delta}K{sub eff} and their implications on FCG predictions in light of existing experimental and numerical data is presented. In particular, the following assumptions are examined: (1). {Delta}K{sub eff} fully describes cyclic stresses and strains at the crack-tip vicinity. (2). K{sub op} can be determined experimentally or numerically with certain accuracy. (3). Overload alters K{sub op} but not K{sub max} and associated s{sub max} at the crack-tip 'process zone'. (4). Contact of crack faces curtails the crack driving force in terms of {Delta}K{sub eff}. The analysis indicates that there ismore » insufficient support to justify the above assumptions. In contrary, the analysis demonstrates that a two-parameter fatigue crack driving force in terms of {Delta}K and K{sub max}, which accounts for both applied and the internal stresses should be used in FCG analyses and predictions.« less

Doesn't He Have Beautiful Blue Eyes? Tips for a Successful Parent-Teacher Conference.

ERIC Educational Resources Information Center

Strudler, Ruth

1993-01-01

Tips for successful parent-teacher conferences concerning children with special needs focus on preventing a conflict cycle and developing a cooperation cycle. Specific suggestions to reduce stress levels and involve parents positively are offered for preconference behaviors, conference behaviors, and postconference behaviors. (DB)

Material Constitutive Models for Creep and Rupture of SiC/SiC Ceramic-Matrix Composites (CMCs) Under Multiaxial Loading

NASA Astrophysics Data System (ADS)

Grujicic, Mica; Galgalikar, R.; Snipes, J. S.; Ramaswami, S.

2016-05-01

Material constitutive models for creep deformation and creep rupture of the SiC/SiC ceramic-matrix composites (CMCs) under general three-dimensional stress states have been developed and parameterized using one set of available experimental data for the effect of stress magnitude and temperature on the time-dependent creep deformation and rupture. To validate the models developed, another set of available experimental data was utilized for each model. The models were subsequently implemented in a user-material subroutine and coupled with a commercial finite element package in order to enable computational analysis of the performance and durability of CMC components used in high-temperature high-stress applications, such as those encountered in gas-turbine engines. In the last portion of the work, the problem of creep-controlled contact of a gas-turbine engine blade with the shroud is investigated computationally. It is assumed that the blade is made of the SiC/SiC CMC, and that the creep behavior of this material can be accounted for using the material constitutive models developed in the present work. The results clearly show that the blade-tip/shroud clearance decreases and ultimately becomes zero (the condition which must be avoided) as a function of time. In addition, the analysis revealed that if the blade is trimmed at its tip to enable additional creep deformation before blade-tip/shroud contact, creep-rupture conditions can develop in the region of the blade adjacent to its attachment to the high-rotational-speed hub.

Spherical nanoindentation study of the deformation micromechanisms of LiTaO{sub 3} single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anasori, B.; Barsoum, M. W.; Sickafus, K. E.

2011-07-15

Herein, spherical nanoindentation (NI) was used to investigate the room temperature deformation behavior of C-plane LiTaO{sub 3} single crystals loaded along the [0001] direction as a function of ion irradiation. When the NI load-displacement curves of 3 different nanoindenter radii (1.4 {mu}m, 5 {mu}m, and 21 {mu}m) were converted to NI stress-strain curves, good agreement between them was found. The surface first deforms elastically - with a Young's modulus of 205 {+-} 5 GPa, calculated from the stiffness versus contact radii curves and 207 {+-} 3 GPa measured using a Berkovich tip - and then plastically deforms at {approx_equal} 6more » GPa. Repeated loading into the same location results in large, reproducible, fully reversible, nested hysteresis loops attributed to the formation of incipient kink bands (IKBs). The latter are coaxial fully reversible dislocation loops that spontaneously shrink when the load is removed. The IKBs most probably nucleate within the (1012) twins that form near the surface. The sharper radii resulted in twin nucleation at lower stresses. The changes in the reversible loops' shape and areas can be related to the width of the twins that form. The latter were proportional to the nanoindenter tip radii and confirmed by scanning electron microscopy and by the fact that larger threshold stresses were needed for IKB nucleation with the smaller tip sizes. No effect of irradiation was observed on the NI response, presumably because of the mildness of the irradiation damage.« less

On size and geometry effects on the brittle fracture of ferritic and tempered martensitic steels

NASA Astrophysics Data System (ADS)

Odette, G. R.; Chao, B. L.; Lucas, G. E.

1992-09-01

A finite element computation of nonsingular crack tip fields was combined with a weakest link statistics model of cleavage fracture. Model predictions for three point bend specimens with various widths and crack depth to width ratios are qualitatively consistent with a number of trends observed in a 12 Cr martensitic stainless steel. The toughness “benefits” of small sizes and shallow cracks are primarily reflected in strain limits rather than net section stress capacities, which is significant to fusion structures subject to large secondary stresses.

Fatigue crack growth in unidirectional metal matrix composite

NASA Technical Reports Server (NTRS)

Ghosn, Louis J.; Telesman, Jack; Kantzos, Peter

1990-01-01

The weight function method was used to determine the effective stress intensity factor and the crack opening profile for a fatigue tested composite which exhibited fiber bridging. The bridging mechanism was modeled using two approaches; the crack closure approach and the shear lag approach. The numerically determined stress intensity factor values from both methods were compared and correlated with the experimentally obtained crack growth rates for SiC/Ti-15-3 (0)(sub 8) oriented composites. The near crack tip opening profile was also determined for both methods and compared with the experimentally obtained measurements.

Stress in School Administration: Coping Tips for Principals

ERIC Educational Resources Information Center

Sogunro, Olusegun Agboola

2012-01-01

With the need for rapid school reform amid changes in socioeconomic and political situations, evidence abounds that today's school principals operate in a stress-strained environment. Participants of this study identified at least a form of stress on the job. More than 96% claimed to have experienced work-related stress at a level they believed…

Tips for Disaster Responders: Preventing and Managing Stress

MedlinePlus

... are called upon to respond, as well as approaches you can apply to manage stress during your deployment. You can also download SAMHSA’s new Disaster Behavioral Health App and access resources specific to pre- and post-deployment (for responders, supervisors, and family members). Stress ...

Characterization and Regulation of Aquaporin Genes of Sorghum [Sorghum bicolor (L.) Moench] in Response to Waterlogging Stress

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kadam, Suhas; Abril, Alejandra; Dhanapal, Arun P.

Waterlogging is a significant environmental constraint to crop production, and a better understanding of plant responses is critical for the improvement of crop tolerance to waterlogged soils. Aquaporins (AQPs) are a class of channel-forming proteins that play an important role in water transport in plants. Our study aimed to examine the regulation of AQP genes under waterlogging stress and to characterize the genetic variability of AQP genes in sorghum (Sorghum bicolor). Transcriptional profiling of AQP genes in response to waterlogging stress in nodal root tips and nodal root basal regions of two tolerant and two sensitive sorghum genotypes at 18more » and 96 h after waterlogging stress imposition revealed significant gene-specific pattern with regard to genotype, root tissue sample, and time point. For some tissue sample and time point combinations, PIP2-6, PIP2-7, TIP2-2, TIP4-4, and TIP5-1 expression was differentially regulated in tolerant compared to sensitive genotypes. The differential response of these AQP genes suggests that they may play a tissue specific role in mitigating waterlogging stress. Genetic analysis of sorghum revealed that AQP genes were clustered into the same four subfamilies as in maize (Zea mays) and rice (Oryza sativa) and that residues determining the AQP channel specificity were largely conserved across species. Single nucleotide polymorphism (SNP) data from 50 sorghum accessions were used to build an AQP gene-based phylogeny of the haplotypes. Phylogenetic analysis based on single nucleotide polymorphisms of sorghum AQP genes placed the tolerant and sensitive genotypes used for the expression study in distinct groups. Expression analyses suggested that selected AQPs may play a pivotal role in sorghum tolerance to water logging stress. Furthermore experimentation is needed to verify their role and to leverage phylogenetic analyses and AQP expression data to improve water logging tolerance in sorghum.« less

Characterization and Regulation of Aquaporin Genes of Sorghum [Sorghum bicolor (L.) Moench] in Response to Waterlogging Stress

DOE PAGES

Kadam, Suhas; Abril, Alejandra; Dhanapal, Arun P.; ...

2017-05-30

Waterlogging is a significant environmental constraint to crop production, and a better understanding of plant responses is critical for the improvement of crop tolerance to waterlogged soils. Aquaporins (AQPs) are a class of channel-forming proteins that play an important role in water transport in plants. Our study aimed to examine the regulation of AQP genes under waterlogging stress and to characterize the genetic variability of AQP genes in sorghum (Sorghum bicolor). Transcriptional profiling of AQP genes in response to waterlogging stress in nodal root tips and nodal root basal regions of two tolerant and two sensitive sorghum genotypes at 18more » and 96 h after waterlogging stress imposition revealed significant gene-specific pattern with regard to genotype, root tissue sample, and time point. For some tissue sample and time point combinations, PIP2-6, PIP2-7, TIP2-2, TIP4-4, and TIP5-1 expression was differentially regulated in tolerant compared to sensitive genotypes. The differential response of these AQP genes suggests that they may play a tissue specific role in mitigating waterlogging stress. Genetic analysis of sorghum revealed that AQP genes were clustered into the same four subfamilies as in maize (Zea mays) and rice (Oryza sativa) and that residues determining the AQP channel specificity were largely conserved across species. Single nucleotide polymorphism (SNP) data from 50 sorghum accessions were used to build an AQP gene-based phylogeny of the haplotypes. Phylogenetic analysis based on single nucleotide polymorphisms of sorghum AQP genes placed the tolerant and sensitive genotypes used for the expression study in distinct groups. Expression analyses suggested that selected AQPs may play a pivotal role in sorghum tolerance to water logging stress. Furthermore experimentation is needed to verify their role and to leverage phylogenetic analyses and AQP expression data to improve water logging tolerance in sorghum.« less

Fractography applied to investigations of cores, outcrops, and fractured reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulander, B.

1995-11-01

Fractography focuses investigations on the topography of fracture surfaces. This topography is composed of fractographic features produced by changing stress magnitudes and directions along the advancing crack tip. Fractographic features commonly useful in core and outcrop analysis include the origin, twist hackle, inclusion hackle, and rib marks. These structures develop during brittle failure by Mode I loading at the crack tip and act together to form a hackle plume. Fractographic components throughout the plume record the dynamic history of fracture development. Components show, to the limit of visual scale, the principal stress directions, as well as relative stress magnitudes andmore » propagation velocities, that existed at the advancing fracture front. This information contributes to more meaningful conclusions in fracture investigations. In core studies, fractography aids identification of induced and natural fractures. Induced fractures and fractographic features show distinct geometry with that of the core and reflect the effects of the core boundary, in-situ stresses, drilling stresses, and rock anisotropies. Certain drilling- and coring-induced fractures possess orientations and fractographic features that suggest the direction of minimum in-situ stress and that this direction may change abruptly within the drilled volume of rock. Cored natural fractures generally originated away from the bit and possess fractographic features that bear no geometerical relationship to core parameters. Abrupt changes of natural fracture strike and development of twist hackle suggest locally complex paleostress distributions. A combined knowledge of in-situ stress and natural fracture trends is useful in predicting reservoir permeability. In outcrop, fractographic features, including abutting relationships between joints, more readily depict order of development, intrastratum distribution of fracturing stress, and size for joints in any set.« less

Tensile cracking of a brittle conformal coating on a rough substrate

DOE PAGES

Reedy, Jr., E. D.

2016-04-07

This note examines the effect of interfacial roughness on the initiation and growth of channel cracks in a brittle film. A conformal film with cusp-like surface flaws that replicate the substrate roughness is investigated. This type of surface flaw is relatively severe in the sense that stress diverges as the cusp-tip is approached (i.e., there is a power-law stress singularity). For the geometry and range of film properties considered, the analysis suggests that smoothing the substrate could substantially increase the film’s resistance to the formation of the through-the-thickness cracks that precede channel cracking. Furthermore, smoothing the substrate’s surface has amore » relatively modest effect on the film stress needed to propagate a channel crack.« less

The importance of the cellular stress response in the pathogenesis and treatment of type 2 diabetes.

PubMed

Hooper, Philip L; Balogh, Gabor; Rivas, Eric; Kavanagh, Kylie; Vigh, Laszlo

2014-07-01

Organisms have evolved to survive rigorous environments and are not prepared to thrive in a world of caloric excess and sedentary behavior. A realization that physical exercise (or lack of it) plays a pivotal role in both the pathogenesis and therapy of type 2 diabetes mellitus (t2DM) has led to the provocative concept of therapeutic exercise mimetics. A decade ago, we attempted to simulate the beneficial effects of exercise by treating t2DM patients with 3 weeks of daily hyperthermia, induced by hot tub immersion. The short-term intervention had remarkable success, with a 1 % drop in HbA1, a trend toward weight loss, and improvement in diabetic neuropathic symptoms. An explanation for the beneficial effects of exercise and hyperthermia centers upon their ability to induce the cellular stress response (the heat shock response) and restore cellular homeostasis. Impaired stress response precedes major metabolic defects associated with t2DM and may be a near seminal event in the pathogenesis of the disease, tipping the balance from health into disease. Heat shock protein inducers share metabolic pathways associated with exercise with activation of AMPK, PGC1-a, and sirtuins. Diabetic therapies that induce the stress response, whether via heat, bioactive compounds, or genetic manipulation, improve or prevent all of the morbidities and comorbidities associated with the disease. The agents reduce insulin resistance, inflammatory cytokines, visceral adiposity, and body weight while increasing mitochondrial activity, normalizing membrane structure and lipid composition, and preserving organ function. Therapies restoring the stress response can re-tip the balance from disease into health and address the multifaceted defects associated with the disease.

Thermo-mechanically coupled fracture analysis of shape memory alloys using the extended finite element method

NASA Astrophysics Data System (ADS)

Hatefi Ardakani, S.; Ahmadian, H.; Mohammadi, S.

2015-04-01

In this paper, the extended finite element method is used for fracture analysis of shape memory alloys for both cases of super elastic and shape memory effects. Heat generation during the forward and reverse phase transformations can lead to temperature variation in the material because of strong thermo-mechanical coupling, which significantly influences the SMA mechanical behavior. First, the stationary crack mode is studied and the effects of loading rate on material behavior in the crack tip are examined. Then, the crack propagation analysis is performed in the presence of an initial crack by adopting a weighted averaging criterion, where the direction of crack propagation is determined by weighted averaging of effective stresses at all the integration points in the vicinity of the crack tip. Finally, several numerical examples are analyzed and the obtained results are compared with the available reference results.

Alteration of cell-wall porosity is involved in osmotic stress-induced enhancement of aluminium resistance in common bean (Phaseolus vulgaris L.)

PubMed Central

Yang, Zhong-Bao; Eticha, Dejene; Rao, Idupulapati Madhusudana; Horst, Walter Johannes

2010-01-01

Aluminium (Al) toxicity and drought are the two major abiotic stress factors limiting common bean production in the tropics. Using hydroponics, the short-term effects of combined Al toxicity and drought stress on root growth and Al uptake into the root apex were investigated. In the presence of Al stress, PEG 6000 (polyethylene glycol)-induced osmotic (drought) stress led to the amelioration of Al-induced inhibition of root elongation in the Al-sensitive genotype VAX 1. PEG 6000 (>> PEG 1000) treatment greatly decreased Al accumulation in the 1 cm root apices even when the roots were physically separated from the PEG solution using dialysis membrane tubes. Upon removal of PEG from the treatment solution, the root tips recovered from osmotic stress and the Al accumulation capacity was quickly restored. The PEG-induced reduction of Al accumulation was not due to a lower phytotoxic Al concentration in the treatment solution, reduced negativity of the root apoplast, or to enhanced citrate exudation. Also cell-wall (CW) material isolated from PEG-treated roots showed a low Al-binding capacity which, however, was restored after destroying the physical structure of the CW. The comparison of the Al3+, La3+, Sr2+, and Rb+ binding capacity of the intact root tips and the isolated CW revealed the specificity of the PEG 6000 effect for Al. This could be due to the higher hydrated ionic radius of Al3+ compared with other cations (Al3+ >> La3+ > Sr2+ > Rb+). In conclusion, the results provide circumstantial evidence that the osmotic stress-inhibited Al accumulation in root apices and thus reduced Al-induced inhibition of root elongation in the Al-sensitive genotype VAX 1 is related to the alteration of CW porosity resulting from PEG 6000-induced dehydration of the root apoplast. PMID:20511277

Numerical Optimization of the Position in Femoral Head of Proximal Locking Screws of Proximal Femoral Nail System; Biomechanical Study.

PubMed

Konya, Mehmet Nuri; Verim, Özgür

2017-09-29

Proximal femoral fracture rates are increasing due to osteoporosis and traffic accidents. Proximal femoral nails are routinely used in the treatment of these fractures in the proximal femur. To compare various combinations and to determine the ideal proximal lag screw position in pertrochanteric fractures (Arbeitsgemeinschaft für Osteosynthesefragen classification 31-A1) of the femur by using optimized finite element analysis. Biomechanical study. Computed tomography images of patients' right femurs were processed with Mimics. Afterwards a solid femur model was created with SolidWorks 2015 and transferred to ANSYS Workbench 16.0 for response surface optimization analysis which was carried out according to anterior-posterior (-10°0) and posterior-anterior directions of the femur neck significantly increased these stresses. The most suitable position of the proximal lag screw was confirmed as the middle of the femoral neck by using optimized finite element analysis.

Sub-10-micrometer toughening and crack tip toughness of dental enamel.

PubMed

Ang, Siang Fung; Schulz, Anja; Pacher Fernandes, Rodrigo; Schneider, Gerold A

2011-04-01

In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip's toughness (K(I0),K(III0)), the crack's closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine enamel was studied using atomic force microscopy (AFM). The mode I crack tip toughness K(I0) of cracks along enamel rod boundaries and across enamel rods exhibit a similar range of values: K(I0,Ir)=0.5-1.6MPa m(0.5) (based on Irwin's 'near-field' solution) and K(I0,cz)=0.8-1.5MPa m(0.5) (based on the cohesive zone solution of the Dugdale-Muskhelishvili (DM) crack model). The mode III crack tip toughness K(III0,Ir) was computed as 0.02-0.15MPa m(0.5). The crack-closure stress at the crack tip was computed as 163-770 MPa with a cohesive zone length and width 1.6-10.1μm and 24-44 nm utilizing the cohesive zone solution. Toughening elements were observed under AFM and SEM: crack bridging due to protein ligament and hydroxyapatite fibres (micro- and nanometer scale) as well as microcracks were identified. Crown Copyright © 2010. Published by Elsevier Ltd. All rights reserved.

Antioxidant and Anti-stress Compounds Improve Regrowth of Cryopreserved Rubus Shoot Tips

USDA-ARS?s Scientific Manuscript database

Regrowth of plants after cryopreservation varies and resulting regrowth ranges from poor to excellent. Oxidative stress is a potential cause of damage in plant tissues. Antioxidants and anti-stress compounds may improve regrowth by preventing or repairing the damage. Lipoic acid (LA), glutathione (...

A Continuum-Atomistic Analysis of Transgranular Crack Propagation in Aluminum

NASA Technical Reports Server (NTRS)

Yamakov, V.; Saether, E.; Glaessgen, E.

2009-01-01

A concurrent multiscale modeling methodology that embeds a molecular dynamics (MD) region within a finite element (FEM) domain is used to study plastic processes at a crack tip in a single crystal of aluminum. The case of mode I loading is studied. A transition from deformation twinning to full dislocation emission from the crack tip is found when the crack plane is rotated around the [111] crystallographic axis. When the crack plane normal coincides with the [112] twinning direction, the crack propagates through a twinning mechanism. When the crack plane normal coincides with the [011] slip direction, the crack propagates through the emission of full dislocations. In intermediate orientations, a transition from full dislocation emission to twinning is found to occur with an increase in the stress intensity at the crack tip. This finding confirms the suggestion that the very high strain rates, inherently present in MD simulations, which produce higher stress intensities at the crack tip, over-predict the tendency for deformation twinning compared to experiments. The present study, therefore, aims to develop a more realistic and accurate predictive modeling of fracture processes.

Sites of abscisic acid synthesis and metabolism in Ricinus communis L

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeevaart, J.A.D.

1977-05-01

The sites of abscisic acid (ABA) synthesis and metabolism in Ricinus communis L. were investigated by analyzing the levels of ABA and its two metabolites phaseic acid (PA) and dihydrophaseic acid (DPA) in the shoot tips, mature leaves, and phloem sap of stressed and nonstressed plants. Water stress increased the concentration of ABA, PA, and DPA in phloem exudate and also increased the levels of all three compounds in mature leaves and in shoot tips. The latter had a very high DPA content (18.7 ..mu..g/g fresh weight) even in plants not subjected to water stress. When young and mature leavesmore » were excised and allowed to wilt, the level of ABA increased in both, demonstrating that leaves at an early stage of development have the capacity to produce ABA. These results have been interpreted to mean that in mature leaves of nonstressed Ricinus plants, ABA is synthesized and metabolized, and that ABA itself, as well as its metabolites, are translocated in the phloem to the shoot tips (sinks). Since DPA, but not ABA, accumulates in the shoot tips, it follows that ABA is metabolized rapidly in the apical region. To what extent ABA present in young leaves of nonstressed plants is the consequence of synthesis in situ and of import from older leaves remains to be determined.« less

Living with Arthritis

MedlinePlus

... safety. If you want to: Avoid or reduce pain and stress on your joints. Consider these activity tips: An ... suggest ways to do them differently to avoid stress on your joints, pain, and reduced energy levels. Help you engage in ...

New Dad: Tips to Help Manage Stress

MedlinePlus

Healthy Lifestyle Infant and toddler health Becoming a new dad can bring joy — and stress. Find out ... your newborn. By Mayo Clinic Staff Becoming a new dad can be an exciting and overwhelming experience. ...

A Crack Closure Model and Its Application to Vibrothermography Nondestructive Evaluation

NASA Astrophysics Data System (ADS)

Schiefelbein, Bryan Edward

Vibrothermography nondestructive evaluation (NDE) is in the early stages of research and development, and there exists uncertainty in the fundamental mechanisms and processes by which heat generation occurs. Holland et al. have developed a set of tools which simulate and predict the outcome of a vibrothermography inspection by breaking the inspection into three distinct processes: vibrational excitation, heat generation, and thermal imaging. The stage of vibrothermography which is not well understood is the process by which vibrations are converted to heat at the crack surface. It has been shown that crack closure and closure state impact the resulting heat generation. Despite this, research into the link between partial crack closure and vibrothermography is limited. This work seeks to rectify this gap in knowledge by modeling the behavior of a partially closed crack in response to static external loading and a dynamic vibration. The residual strains left by the plastic wake during fatigue crack growth manifest themselves as contact stresses acting at the crack surface interface. In response to an applied load below the crack opening stress, the crack closure state will evolve, but the crack will remain partially closed. The crack closure model developed in this work is based in linear elastic fracture mechanics (LEFM) and describes the behavior of a partially closed crack in response to a tensile external load and non-uniform closure stress distribution. The model builds on work by Fleck to describe the effective length, crack opening displacement, and crack tip stress field for a partially closed crack. These quantities are solved for by first establishing an equilibrium condition which governs the effective or apparent length of the partially closed crack. The equilibrium condition states that, under any external or crack surface loading, the effective crack tip will be located where the effective stress intensity factor is zero. In LEFM, this is equivalent to saying that the effective crack tip is located where the stress singularity vanishes. If the closure stresses are unknown, the model provides an algorithm with which to solve for the distribution, given measurements of the effective crack length as a function of external load. Within literature, a number of heating mechanisms have been proposed as being dominant in vibrothermography. These include strain hysteresis, adhesion hysteresis, plastic flow, thermoelasticity, and sliding friction. Based on experimental observation and theory, this work eliminates strain hysteresis, thermoelasticity, and plastic flow as plausible heating mechanisms. This leaves friction and adhesion hysteresis as the only plausible mechanisms. Frictional heating is based on the classical Coulomb friction model, while adhesion hysteresis heating comes from irreversibility in surface adhesion. Adhesion hysteresis only satisfies the experimental observation that heating vanishes for high compressive loading if surface roughness and the instability of surface adhesion is considered. By understanding the fundamental behavior of a partially closed crack in response to non-uniform loading, and the link between crack surface motion and heat generation, we are one step closer to a fully predictive vibrothermography heat generation model. Future work is needed to extend the crack closure model to a two-dimensional semi-elliptical surface crack and better understand the distinction between frictional and adhesion heating.

Modelling of surface stresses and fracturing during dyke emplacement: Application to the 2009 episode at Harrat Lunayyir, Saudi Arabia

NASA Astrophysics Data System (ADS)

Al Shehri, Azizah; Gudmundsson, Agust

2018-05-01

Correct interpretation of surface stresses and deformation or displacement during volcanotectonic episodes is of fundamental importance for hazard assessment and dyke-path forecasting. Here we present new general numerical models on the local stresses induced by arrested dykes. In the models, the crustal segments hosting the dyke vary greatly in mechanical properties, from uniform or non-layered (elastic half-spaces) to highly anisotropic (layers with strong contrast in Young's modulus). The shallow parts of active volcanoes and volcanic zones are normally highly anisotropic and some with open contacts. The numerical results show that, for a given surface deformation, non-layered (half-space) models underestimate the dyke overpressure/thickness needed and overestimate the likely depth to the tip of the dyke. Also, as the mechanical contrast between the layers increases, so does the stress dissipation and associated reduction in surface stresses (and associated fracturing). In the absence of open contacts, the distance between the two dyke-induced tensile and shear stress peaks (and fractures, if any) at the surface is roughly twice the depth to the tip of the dyke. The width of a graben, if it forms, should therefore be roughly twice the depth to the tip of the associated arrested dyke. When applied to the 2009 episode at Harrat Lunayyir, the main results are as follows. The entire 3-7 km wide fracture zone/graben formed during the episode is far too wide to have been generated by induced stresses of a single, arrested dyke. The eastern part of the zone/graben may have been generated by the inferred, arrested dyke, but the western zone primarily by regional extensional loading. The dyke tip was arrested at only a few hundred metres below the surface, the estimated thickness of the uppermost part of the dyke being between about 6 and 12 m. For the inferred dyke length (strike dimension) of about 14 km, this yields a dyke length/thickness ratio between 2400 and 1200, similar to commonly measured ratios of regional dykes in the field.

Variations of a global constraint factor in cracked bodies under tension and bending loads

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Crews, J. H., Jr.; Bigelow, C. A.; Dawicke, D. S.

1994-01-01

Elastic-plastic finite-element analyses were used to calculate stresses and displacements around a crack in finite-thickness plates for an elastic-perfectly plastic material. Middle- and edge-crack specimens were analyzed under tension and bending loads. Specimens were 1.25 to 20 mm thick with various widths and crack lengths. A global constraint factor alpha(sub g), an averaged normal-stress to flow-stress ratio over the plastic region, was defined to simulate three-dimensional (3D) effects in two-dimensional (2D) models. For crack lengths and uncracked ligament lengths greater than four times the thickness, the global constraint factor was found to be nearly a unique function of a normalized stress-intensity factor (related to plastic-zone size to thickness ratio) from small- to large-scale yielding conditions for various specimen types and thickness. For crack length-to-thickness ratios less than four, the global constraint factor was specimen type, crack length and thickness dependent. Using a 2D strip-yield model and the global constraint factors, plastic-zone sizes and crack-tip displacements agreed reasonably well with the 3D analyses. For a thin sheet aluminum alloy, the critical crack-tip-opening angle during stable tearing was found to be independent of specimen type and crack length for crack length-to-thickness ratios greater than 4.

Edge delamination in angle-ply composite laminates, part 5

NASA Technical Reports Server (NTRS)

Wang, S. S.

1981-01-01

A theoretical method was developed for describing the edge delamination stress intensity characteristics in angle-ply composite laminates. The method is based on the theory of anisotropic elasticity. The edge delamination problem is formulated using Lekhnitskii's complex-variable stress potentials and an especially developed eigenfunction expansion method. The method predicts exact orders of the three-dimensional stress singularity in a delamination crack tip region. With the aid of boundary collocation, the method predicts the complete stress and displacement fields in a finite-dimensional, delaminated composite. Fracture mechanics parameters such as the mixed-mode stress intensity factors and associated energy release rates for edge delamination can be calculated explicity. Solutions are obtained for edge delaminated (theta/-theta theta/-theta) angle-ply composites under uniform axial extension. Effects of delamination lengths, fiber orientations, lamination and geometric variables are studied.

Ocimum sanctum leaf extract induces drought stress tolerance in rice

PubMed Central

Pandey, Veena; Ansari, M.W.; Tula, Suresh; Sahoo, R.K.; Bains, Gurdeep; Kumar, J.; Tuteja, Narendra; Shukla, Alok

2016-01-01

ABSTRACT Ocimum leaves are highly enriched in antioxidant components. Thus, its leaf extract, if applied in plants, is believed to efficiently scavenge ROS, thereby preventing oxidative damage under drought stress. Thus, the present study was performed in kharif 2013 and rabi 2014 season to evaluate the effect of aqueous leaf extract of Ocimum sanctum against drought stress in 2 rice genotype under glass house conditions. Here we show that various morpho- physiological (chlorophyll fluorescence, leaf rolling score, leaf tip burn, number of senesced leaves and total dry matter) and biochemical parameters (proline, malondialdehyde and superoxide dismutase content) were amended by Ocimum treatment in both the seasons. Application of Ocimum extract increased expression of dehydrin genes, while reducing expression of aquaporin genes in drought stressed rice plant. Thus, application of Ocimum leaf extract under drought stress can be suggested as a promising strategy to mitigate drought stress in economical, accessible and ecofriendly manner. PMID:26890603

Phytotoxic cyanamide affects maize (Zea mays) root growth and root tip function: from structure to gene expression.

PubMed

Soltys, Dorota; Rudzińska-Langwald, Anna; Kurek, Wojciech; Szajko, Katarzyna; Sliwinska, Elwira; Bogatek, Renata; Gniazdowska, Agnieszka

2014-05-01

Cyanamide (CA) is a phytotoxic compound produced by four Fabaceae species: hairy vetch, bird vetch, purple vetch and black locust. Its toxicity is due to complex activity that involves the modification of both cellular structures and physiological processes. To date, CA has been investigated mainly in dicot plants. The goal of this study was to investigate the effects of CA in the restriction of the root growth of maize (Zea mays), representing the monocot species. CA (3mM) reduced the number of border cells in the root tips of maize seedlings and degraded their protoplasts. However, CA did not induce any significant changes in the organelle structure of other root cells, apart from increased vacuolization. CA toxicity was also demonstrated by its effect on cell cycle activity, endoreduplication intensity, and modifications of cyclins CycA2, CycD2, and histone HisH3 gene expression. In contrast, the arrangement of microtubules was not altered by CA. Treatment of maize seedlings with CA did not completely arrest mitotic activity, although the frequency of dividing cells was reduced. Furthermore, prolonged CA treatment increased the proportion of endopolyploid cells in the root tip. Cytological malformations were accompanied by an induction of oxidative stress in root cells, which manifested as enhanced accumulation of H2O2. Exposure of maize seedlings to CA resulted in an increased concentration of auxin and stimulated ethylene emission. Taken together, these findings suggested that the inhibition of root growth by CA may be a consequence of stress-induced morphogenic responses. Copyright © 2014. Published by Elsevier GmbH.

The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulaganathan, Jaganathan, E-mail: jagan.ulaganathan@mail.utoronto.ca; Newman, Roger C., E-mail: roger.newman@utoronto.ca

2014-06-01

The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously withinmore » the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work. - Highlights: • Plastic strain localization has a complex relationship with SCC susceptibility. • Surface relief created by cold work creates its own granular strain localization. • Cold work promotes crack growth but several other factors are involved.« less

Space-saving tips to lower stress

NASA Astrophysics Data System (ADS)

Gordon, Vernita D.

2018-03-01

Understanding how some single cells evolved into multicellular life means figuring out how they overcome the stresses associated with crowding as they multiply. New insights from yeast suggest that changes in the shape of cells may provide an answer.

On the variation in crack-opening stresses at different locations in a three-dimensional body

NASA Technical Reports Server (NTRS)

Chermahini, R. G.; Blom, Anders F.

1990-01-01

Crack propagation and closure behavior of thin, and thick middle crack tension specimens under constant amplitude loading were investigated using a three dimensional elastic plastic finite element analysis of fatigue crack propagation and closure. In the thin specimens the crack front closed first on the exterior (free) surface and closed last in the interior during the unloading portion of cyclic loading; a load reduced displacement technique was used to determine crack opening stresses at specified locations in the plate from the displacements calculated after the seven cycle. All the locations were on the plate external surface and were located near the crack tip, behind the crack tip, at the centerline of the crack. With this technique, the opening stresses at the specified points were found to be 0.52, 0.42, and 0.39 times the maximum applied stress.

Structural optimization procedure of a composite wind turbine blade for reducing both material cost and blade weight

NASA Astrophysics Data System (ADS)

Hu, Weifei; Park, Dohyun; Choi, DongHoon

2013-12-01

A composite blade structure for a 2 MW horizontal axis wind turbine is optimally designed. Design requirements are simultaneously minimizing material cost and blade weight while satisfying the constraints on stress ratio, tip deflection, fatigue life and laminate layup requirements. The stress ratio and tip deflection under extreme gust loads and the fatigue life under a stochastic normal wind load are evaluated. A blade element wind load model is proposed to explain the wind pressure difference due to blade height change during rotor rotation. For fatigue life evaluation, the stress result of an implicit nonlinear dynamic analysis under a time-varying fluctuating wind is converted to the histograms of mean and amplitude of maximum stress ratio using the rainflow counting algorithm Miner's rule is employed to predict the fatigue life. After integrating and automating the whole analysis procedure an evolutionary algorithm is used to solve the discrete optimization problem.

Changes in transcript expression patterns as a result of cryoprotectant treatment and liquid nitrogen exposure in Arabidopsis shoot tips.

PubMed

Gross, Briana L; Henk, Adam D; Bonnart, Remi; Volk, Gayle M

2017-03-01

Transcripts related to abiotic stress, oxidation, and wounding were differentially expressed in Arabidopsis shoot tips in response to cryoprotectant and liquid nitrogen treatment. Cryopreservation methods have been implemented in genebanks as a strategy to back-up plant genetic resource collections that are vegetatively propagated. Cryopreservation is frequently performed using vitrification methods, whereby shoot tips are treated with cryoprotectant solutions, such as Plant Vitrification Solution 2 (PVS2) or Plant Vitrification Solution 3 (PVS3); these solutions remove and/or replace freezable water within the meristem cells. We used the model system Arabidopsis thaliana to identify suites of transcripts that are up- or downregulated in response to PVS2 and PVS3 treatment and liquid nitrogen (LN) exposure. Our results suggest that there are many changes in transcript expression in shoot tips as a result of cryoprotection and that these changes exceed the number detected as a result of LN exposure. In total, 180 transcripts showed significant changes in expression level unique to treatment with either the cryoprotectant or cryopreservation followed by recovery. Of these 180 transcripts, 67 were related to stress, defense, wounding, lipid, carbohydrate, abscisic acid, oxidation, temperature (cold/heat), or osmoregulation. The responses of five transcripts were confirmed using qPCR methods. The transcripts responding to PVS2 + LN suggest an oxidative response to this treatment, whereas the PVS3 + LN treatment invoked a more general metabolic response. This work shows that the choice of cryoprotectant can have a major influence on the patterns of transcript expression, presumably due to the level and extent of stress experienced by the shoot tip. As a result, there may be divergent responses of study systems to PVS2 and PVS3 treatments.

Stent and leaflet stresses in a 26-mm first-generation balloon-expandable transcatheter aortic valve.

PubMed

Xuan, Yue; Krishnan, Kapil; Ye, Jian; Dvir, Danny; Guccione, Julius M; Ge, Liang; Tseng, Elaine E

2017-05-01

Transcatheter aortic valve replacement is established therapy for high-risk and inoperable patients with severe aortic stenosis, but questions remain regarding long-term durability. Valve design influences durability. Increased leaflet stresses in surgical bioprostheses have been correlated with degeneration; however, transcatheter valve leaflet stresses are unknown. From 2007 to 2014, a majority of US patients received first-generation balloon-expandable transcatheter valves. Our goal was to determine stent and leaflet stresses in this valve design using finite element analyses. A 26-mm Sapien Transcatheter Heart Valve (Edwards Lifesciences, Inc, Irvine, Calif) underwent high-resolution microcomputed tomography scanning to develop precise 3-dimensional geometry of the leaflets, the stent, and the polyethylene terephthalate elements. The stent was modeled using 3-dimensional elements and the leaflets were modeled using shell elements. Stent material properties were based on stainless steel, whereas those for leaflets were obtained from surgical bioprostheses. Noncylindrical Sapien valve geometry was also simulated. Pressure loading to 80 mm Hg and 120 mm Hg was performed using ABAQUS finite element software (Dassault Systèmes, Waltham, Mass). At 80 mm Hg, maximum principal stresses on Sapien leaflets were 1.31 megaspascals (MPa). Peak leaflet stress was observed at commissural tips where leaflets connected to the stent. Maximum principal stresses for the stent were 188.91 MPa and located at stent tips where leaflet commissures were attached. Noncylindrical geometry increased peak principal leaflet stresses by 16%. Using exact geometry from high-resolution scans, the 26-mm Sapien Transcatheter Heart Valve showed that peak stresses for both stent and leaflets were present at commissural tips where leaflets were attached. These regions would be prone to leaflet degeneration. Understanding stresses in first-generation transcatheter valves allows comparison to future designs for relative durability. Copyright © 2017 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.

Crack Turning and Arrest Mechanisms for Integral Structure

NASA Technical Reports Server (NTRS)

Pettit, Richard; Ingraffea, Anthony

1999-01-01

In the course of several years of research efforts to predict crack turning and flapping in aircraft fuselage structures and other problems related to crack turning, the 2nd order maximum tangential stress theory has been identified as the theory most capable of predicting the observed test results. This theory requires knowledge of a material specific characteristic length, and also a computation of the stress intensity factors and the T-stress, or second order term in the asymptotic stress field in the vicinity of the crack tip. A characteristic length, r(sub c), is proposed for ductile materials pertaining to the onset of plastic instability, as opposed to the void spacing theories espoused by previous investigators. For the plane stress case, an approximate estimate of r(sub c), is obtained from the asymptotic field for strain hardening materials given by Hutchinson, Rice and Rosengren (HRR). A previous study using of high order finite element methods to calculate T-stresses by contour integrals resulted in extremely high accuracy values obtained for selected test specimen geometries, and a theoretical error estimation parameter was defined. In the present study, it is shown that a large portion of the error in finite element computations of both K and T are systematic, and can be corrected after the initial solution if the finite element implementation utilizes a similar crack tip discretization scheme for all problems. This scheme is applied for two-dimensional problems to a both a p-version finite element code, showing that sufficiently accurate values of both K(sub I) and T can be obtained with fairly low order elements if correction is used. T-stress correction coefficients are also developed for the singular crack tip rosette utilized in the adaptive mesh finite element code FRANC2D, and shown to reduce the error in the computed T-stress significantly. Stress intensity factor correction was not attempted for FRANC2D because it employs a highly accurate quarter-point scheme to obtain stress intensity factors.

A simplified field protocol for genetic sampling of birds using buccal swabs

USGS Publications Warehouse

Vilstrup, Julia T.; Mullins, Thomas D.; Miller, Mark P.; McDearman, Will; Walters, Jeffrey R.; Haig, Susan M.

2018-01-01

DNA sampling is an essential prerequisite for conducting population genetic studies. For many years, blood sampling has been the preferred method for obtaining DNA in birds because of their nucleated red blood cells. Nonetheless, use of buccal swabs has been gaining favor because they are less invasive yet still yield adequate amounts of DNA for amplifying mitochondrial and nuclear markers; however, buccal swab protocols often include steps (e.g., extended air-drying and storage under frozen conditions) not easily adapted to field settings. Furthermore, commercial extraction kits and swabs for buccal sampling can be expensive for large population studies. We therefore developed an efficient, cost-effective, and field-friendly protocol for sampling wild birds after comparing DNA yield among 3 inexpensive buccal swab types (2 with foam tips and 1 with a cotton tip). Extraction and amplification success was high (100% and 97.2% respectively) using inexpensive generic swabs. We found foam-tipped swabs provided higher DNA yields than cotton-tipped swabs. We further determined that omitting a drying step and storing swabs in Longmire buffer increased efficiency in the field while still yielding sufficient amounts of DNA for detailed population genetic studies using mitochondrial and nuclear markers. This new field protocol allows time- and cost-effective DNA sampling of juveniles or small-bodied birds for which drawing blood may cause excessive stress to birds and technicians alike.

Strength and Mechanics of Bonded Scarf Joints for Repair of Composite Materials

NASA Technical Reports Server (NTRS)

Pipes, R. B.; Adkins, D. W.

1982-01-01

Experimental and analytical investigations of scarf joints indicate that slight bluntness of adherend tips induces adhesive stress concentrations which significantly reduce joint strength, and the stress distribution through the adhesive thickness is non-uniform and has significant stress concentrations at the ends of the joint. The laminate stacking sequence can have important effects on the adhesive stress distribution. A significant improvement in joint strength is possible by increasing overlap at the expense of raising the repair slightly above the original surface. Although a surface grinder was used to make most experimental specimens, a hand held rotary bur can make a surprisingly good scarf. Scarf joints wit doublers on one side, such as might be used for repair, bend under tensile loads and may actually be weaker than joints without doublers.

[Stress analysis of femoral stems in cementless total hip arthroplasty by two-dimensional finite element method using boundary friction layer].

PubMed

Oomori, H; Imura, S; Gesso, H

1992-04-01

To develop stem design achieving primary fixation of stems and effective load transfer to the femur, we studied stress analysis of stems in cementless total hip arthroplasty by two-dimensional finite element method using boundary friction layer in stem-bone interface. The results of analyses of stem-bone interface stresses and von Mises stresses at the cortical bones indicated that ideal stem design features would be as follows: 1) Sufficient length, with the distal end extending beyond the isthmus region. 2) Maximum possible width, to contact the cortical bones in the isthmus region. 3) No collars but a lateral shoulder at the proximal portion. 4) A distal tip, to contact the cortical bones at the distal portion.

Effect of preheating on fatigue resistance of gears in spin induction coil hardening process

NASA Astrophysics Data System (ADS)

Kumar, Pawan; Aggarwal, M. L.

2018-02-01

Spin hardening inductors are typically used for fine-sized teeth gear geometry. With the proper selection of several design parameters, only the gear teeth can be case surface hardened without affecting the other surface of gear. Preheating may be done to reach an adapted high austenitizing temperature in the root circle to avoid overheating of the tooth tip during final heating. The effect of preheating of gear on control of compressive residual stresses and case hardening has been experimentally discussed in this paper. Present work is about analysing single frequency mode, preheat hardening treatment and compressive residual stresses field for hardening process of spur gear using spin hardening inductors.

Investigation of Three-Dimensional Stress Fields and Slip Systems for FCC Single Crystal Superalloy Notched Specimens

NASA Technical Reports Server (NTRS)

Arakere, Nagaraj K.; Magnan, Shannon; Ebrahimi, Fereshteh; Ferroro, Luis

2004-01-01

Metals and their alloys, except for a few intermetallics, are inherently ductile, i.e. plastic deformation precedes fracture in these materials. Therefore, resistance to fracture is directly related to the development of the plastic zone at the crack tip. Recent studies indicate that the fracture toughness of single crystals depends on the crystallographic orientation of the notch as well as the loading direction. In general, the dependence of crack propagation resistance on crystallographic orientation arises from the anisotropy of (i) elastic constants, (ii) plastic deformation (or slip), and (iii) the weakest fracture planes (e.g. cleavage planes). Because of the triaxial stress state at the notch tips, many slip systems that otherwise would not be activated during uniaxial testing, become operational. The plastic zone formation in single crystals has been tackled theoretically by Rice and his co-workers and only limited experimental work has been conducted in this area. The study of the stresses and strains in the vicinity of a FCC single crystal notch tip is of relatively recent origin. We present experimental and numerical investigation of 3D stress fields and evolution of slip sector boundaries near notches in FCC single crystal tension test specimens, and demonstrate that a 3D linear elastic finite element model that includes the effect of material anisotropy is shown to predict active slip planes and sectors accurately. The slip sector boundaries are shown to have complex curved shapes with several slip systems active simultaneously near the notch. Results are presented for surface and mid-plane of the specimens. The results demonstrate that accounting for 3D elastic anisotropy is very important for accurate prediction of slip activation near FCC single crystal notches loaded in tension. Results from the study will help establish guidelines for fatigue damage near single crystal notches.

Rock fracture processes in chemically reactive environments

NASA Astrophysics Data System (ADS)

Eichhubl, P.

2015-12-01

Rock fracture is traditionally viewed as a brittle process involving damage nucleation and growth in a zone ahead of a larger fracture, resulting in fracture propagation once a threshold loading stress is exceeded. It is now increasingly recognized that coupled chemical-mechanical processes influence fracture growth in wide range of subsurface conditions that include igneous, metamorphic, and geothermal systems, and diagenetically reactive sedimentary systems with possible applications to hydrocarbon extraction and CO2 sequestration. Fracture processes aided or driven by chemical change can affect the onset of fracture, fracture shape and branching characteristics, and fracture network geometry, thus influencing mechanical strength and flow properties of rock systems. We are investigating two fundamental modes of chemical-mechanical interactions associated with fracture growth: 1. Fracture propagation may be aided by chemical dissolution or hydration reactions at the fracture tip allowing fracture propagation under subcritical stress loading conditions. We are evaluating effects of environmental conditions on critical (fracture toughness KIc) and subcritical (subcritical index) fracture properties using double torsion fracture mechanics tests on shale and sandstone. Depending on rock composition, the presence of reactive aqueous fluids can increase or decrease KIc and/or subcritical index. 2. Fracture may be concurrent with distributed dissolution-precipitation reactions in the hostrock beyond the immediate vicinity of the fracture tip. Reconstructing the fracture opening history recorded in crack-seal fracture cement of deeply buried sandstone we find that fracture length growth and fracture opening can be decoupled, with a phase of initial length growth followed by a phase of dominant fracture opening. This suggests that mechanical crack-tip failure processes, possibly aided by chemical crack-tip weakening, and distributed solution-precipitation creep in the hostrock can independently affect fracture opening displacement and thus fracture aperture profiles and aperture distribution.

A note on the cracked plates reinforced by a line stiffener

NASA Technical Reports Server (NTRS)

Yahsi, O. S.; Erdogan, F.

1983-01-01

The problem of a cracked plate reinforced by a line stiffener is reconsidered. The original solution of this problem was given in the literature. Also, a variation of the problem with debonding between the plate and the stiffener near the cracked region was reported in the literature. However, the special case of the problem in which the crack tip terminates at the stiffener does not appear to have been studied. In practice, the solution may be necessary in order to assess the crack arrest effectiveness of the stiffener. The problem of a stiffened plate with a crack is reformulated, the asymptotic stress state near the crack tip terminating at the stiffener is examined, and numerical results are given for various stiffness constants.

Abiotic stresses modulate expression of major intrinsic proteins in barley (Hordeum vulgare).

PubMed

Ligaba, Ayalew; Katsuhara, Maki; Shibasaka, Mineo; Djira, Gemechis

2011-02-01

In one of the most important crops, barley (Hordeum vulgare L.), gene expression and physiological roles of most major intrinsic proteins (MIPs) remained to be elucidated. Here we studied expression of five tonoplast intrinsic protein isoforms (HvTIP1;2, HvTIP2;1, HvTIP2;2, HvTIP2;3 and HvTIP4;1), a NOD26-like intrinsic protein (HvNIP2;1) and a plasma membrane intrinsic protein (HvPIP2;1) by using the quantitative real-time RT-PCR. Five-day-old seedlings were exposed to abiotic stresses (salt, heavy metals and nutrient deficiency), abscisic acid (ABA) and gibberellic acid (GA) for 24 h. Treatment with 100 mM NaCl, 0.1 mM ABA and 1 mM GA differentially regulated gene expression in roots and shoots. Nitrogen and prolonged P-deficiency downregulated expression of most MIP genes in roots. Intriguingly, gene expression was restored to the values in the control three days after nutrient supply was resumed. Heavy metals (0.2 mM each of Cd, Cu, Zn and Cr) downregulated the transcript levels by 60-80% in roots, whereas 0.2 mM Hg upregulated expressions of most genes in roots. This was accompanied by a 45% decrease in the rate of transpiration. In order to study the physiological role of the MIPs, cDNA of three genes (HvTIP2;1, HvTIP2;3 and HvNIP2;1) have been cloned and heterologous expression was performed in Xenopus laevis oocytes. Osmotic water permeability was determined by a swelling assay. However, no water uptake activity was observed for the three proteins. Hence, the possible physiological role of the proteins is discussed. Copyright © 2010 Académie des sciences. Published by Elsevier SAS. All rights reserved.

The effect of transverse shear in a cracked plate under skew-symmetric loading

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1979-01-01

The problem of an elastic plate containing a through crack and subjected to twisting moments or transverse shear loads is considered. By using a bending theory which allows the satisfaction of the boundary conditions on the crack surface regarding the normal and the twisting moments and the transverse shear load separately, it is found that the resulting asymptotic stress field around the crack tip becomes identical to that given by the elasticity solutions of the plane strain and antiplane shear problems. The problem is solved for uniformly distributed or concentrated twisting moment or transverse shear load and the normalized Mode II and Mode III stress-intensity factors are tabulated. The results also include the effect of the Poisson's ratio and material orthotropy for specially orthotropic materials on the stress-intensity factors.

Creep deformation at crack tips in elastic-viscoplastic solids

NASA Astrophysics Data System (ADS)

Riedel, H.

1981-02-01

THE EVALUATION of crack growth tests under creep conditions must be based on the stress analysis of a cracked body taking into account elastic, plastic and creep deformation. In addition to the well-known analysis of a cracked body creeping in secondary (steady-state) creep, the stress field at the tip of a stationary crack is calculated for primary (strain-hardening) or tertiary (strain-softening) creep of the whole specimen. For the special hardening creep-law considered, a path-independent integral C∗h, can be defined which correlates the near-tip field to the applied load. It is also shown how, after sudden load application, creep strains develop in the initially elastic or, for a higher load level, plastic body. Characteristic times are derived to distinguish between short times when the creep-zones, in which creep strains are concentrated, are still small, and long times when the whole specimen creeps extensively in primary and finally in secondary and tertiary creep. Comparing the creep-zone sizes with the specimen dimensions or comparing the characteristic times with the test duration, one can decide which deformation mechanism prevails in the bulk of the specimen and which load parameter enters into the near-tip stress field and determines crack growth behavior. The governing load parameter is the stress intensity factor K 1 if the bulk of the specimen is predominantly elastic and it is the J-integral in a fully-plastic situation when large creep strains are still confined to a small zone. The C∗h-integral applies if the bulk of the specimen deforms in primary or tertiary creep, and C∗ is the relevant load parameter for predominantly secondary creep of the whole specimen.

Effects of Extremity Armor on Metabolic Cost and Gait Biomechanics

DTIC Science & Technology

2010-05-26

of prosthetics , orthotics, and exercise equipment could benefit from knowing the tipping point at which a mass on the limb begins to effect metabolic...measured. For this, you wear a nose clip and 4 breathe through a rubber mouthpiece and valve , similar to those found in scuba diving 5 equipment. The...32 33 Stress fractures , or breaks of bones in the foot and leg, have been associated with road 34 marching while carrying loads, especially

Fracture Mechanics of Thin, Cracked Plates Under Tension, Bending and Out-of-Plane Shear Loading

NASA Technical Reports Server (NTRS)

Zehnder, Alan T.; Hui, C. Y.; Potdar, Yogesh; Zucchini, Alberto

1999-01-01

Cracks in the skin of aircraft fuselages or other shell structures can be subjected to very complex stress states, resulting in mixed-mode fracture conditions. For example, a crack running along a stringer in a pressurized fuselage will be subject to the usual in-plane tension stresses (Mode-I) along with out-of-plane tearing stresses (Mode-III like). Crack growth and initiation in this case is correlated not only with the tensile or Mode-I stress intensity factor, K(sub I), but depends on a combination of parameters and on the history of crack growth. The stresses at the tip of a crack in a plate or shell are typically described in terms of either the small deflection Kirchhoff plate theory. However, real applications involve large deflections. We show, using the von-Karman theory, that the crack tip stress field derived on the basis of the small deflection theory is still valid for large deflections. We then give examples demonstrating the exact calculation of energy release rates and stress intensity factors for cracked plates loaded to large deflections. The crack tip fields calculated using the plate theories are an approximation to the actual three dimensional fields. Using three dimensional finite element analyses we have explored the relationship between the three dimensional elasticity theory and two dimensional plate theory results. The results show that for out-of-plane shear loading the three dimensional and Kirchhoff theory results coincide at distance greater than h/2 from the crack tip, where h/2 is the plate thickness. Inside this region, the distribution of stresses through the thickness can be very different from the plate theory predictions. We have also explored how the energy release rate varies as a function of crack length to plate thickness using the different theories. This is important in the implementation of fracture prediction methods using finite element analysis. Our experiments show that under certain conditions, during fatigue crack growth, the presence of out-of-plane shear loads induces a great deal of contact and friction on the crack surfaces, dramatically reducing crack growth rate. A series of experiments and a proposed computational approach for accounting for the friction is discussed.

Little Kids, Big Worries: Stress-Busting Tips for Early Childhood Classrooms

ERIC Educational Resources Information Center

Honig, Alice Sterling

2010-01-01

Research shows that stress in the crucial early years of a child's life can pose dramatic, lasting challenges to development, learning, and behavior. This is the practical book early childhood professionals need to recognize stress in young children--and intervene with proven relief strategies before pressures turn into big problems. Developed by…

Numerical study on air-structure coupling dynamic characteristics of the axial fan blade

NASA Astrophysics Data System (ADS)

Chen, Q. G.; Xie, B.; Li, F.; Gu, W. G.

2013-12-01

In order to understand the dynamic characteristics of the axial-flow fan blade due to the effect of rotating stress and the action of unsteady aerodynamic forces caused by the airflow, a numerical simulation method for air-structure coupling in an axial-flow fan with fixed rear guide blades was performed. The dynamic characteristics of an axial-flow fan rotating blade were studied by using the two-way air-structure coupling method. Based on the standard k-ε turbulence model, and using weak coupling method, the preceding six orders modal parameters of the rotating blade were obtained, and the distributions of stress and strain on the rotating blade were presented. The results show that the modal frequency from the first to the sixth order is 3Hz higher than the modal frequency without considering air-structure coupling interaction; the maximum stress and the maximum strain are all occurred in the vicinity of root area of the blade no matter the air-structure coupling is considered or not, thus, the blade root is the dangerous location subjected to fatigue break; the position of maximum deformation is at the blade tip, so the vibration of the blade tip is significant. This study can provide theoretical references for the further study on the strength analysis and mechanical optimal design.

Gravitational collapse of colloidal gels: Origins of the tipping point

NASA Astrophysics Data System (ADS)

Padmanabhan, Poornima; Zia, Roseanna

2016-11-01

Reversible colloidal gels are soft viscoelastic solids in which durable but reversible bonds permit on-demand transition from solidlike to liquidlike behavior; these O(kT) bonds also lead to ongoing coarsening and age stiffening, making their rheology inherently time dependent. To wit, such gels may remain stable for an extended time, but then suddenly collapse, sedimenting to the bottom of the container (or creaming to the top) and eliminating any intended functionality of the material. Although this phenomenon has been studied extensively in the experimental literature, the microscopic mechanism underlying the collapse is not well understood. Effects of gel age, interparticle attraction strength, and wall effects all have been shown to affect collapse behavior, but the microstructural transformations underlying the 'tipping point' remain murky. To study this behavior, we conduct large-scale dynamic simulation to model the structural and rheological evolution of colloidal gels subjected to various gravitational stresses, examining the detailed micromechanics in three temporal regimes: slow sedimentation prior to collapse; the tipping point leading to the onset of rapid collapse; and the subsequent compaction of the material as it approaches its final bed height. Acknowledgment for funding and support from the Office of Naval Research; the National Science Foundation; and NSF XSEDE.

Healing of Fatigue Crack in 1045 Steel by Using Eddy Current Treatment

PubMed Central

Yang, Chuan; Xu, Wenchen; Guo, Bin; Shan, Debin; Zhang, Jian

2016-01-01

In order to investigate the methods to heal fatigue cracks in metals, tubular specimens of 1045 steel with axial and radial fatigue cracks were treated under the eddy current. The optical microscope was employed to examine the change of fatigue cracks of specimens before and after the eddy current treatment. The results show that the fatigue cracks along the axial direction of the specimen could be healed effectively in the fatigue crack initiation zone and the crack tip zone under the eddy current treatment, and the healing could occur within a very short time. The voltage breakdown and the transient thermal compressive stress caused by the detouring of eddy current around the fatigue crack were the main factors contributing to the healing in the fatigue crack initiation zone and the crack tip zone, respectively. Eddy current treatment may be a novel and effective method for crack healing. PMID:28773761

Healing of Fatigue Crack in 1045 Steel by Using Eddy Current Treatment.

PubMed

Yang, Chuan; Xu, Wenchen; Guo, Bin; Shan, Debin; Zhang, Jian

2016-07-29

In order to investigate the methods to heal fatigue cracks in metals, tubular specimens of 1045 steel with axial and radial fatigue cracks were treated under the eddy current. The optical microscope was employed to examine the change of fatigue cracks of specimens before and after the eddy current treatment. The results show that the fatigue cracks along the axial direction of the specimen could be healed effectively in the fatigue crack initiation zone and the crack tip zone under the eddy current treatment, and the healing could occur within a very short time. The voltage breakdown and the transient thermal compressive stress caused by the detouring of eddy current around the fatigue crack were the main factors contributing to the healing in the fatigue crack initiation zone and the crack tip zone, respectively. Eddy current treatment may be a novel and effective method for crack healing.

Associations of Tipped and Untipped Service Work with Poor Mental Health in a Nationally Representative Cohort of Adolescents Followed into Adulthood.

PubMed

Andrea, Sarah B; Messer, Lynne C; Marino, Miguel; Boone-Heinonen, Janne

2018-06-11

Precarious work is concentrated in the service industry in the United States and is a risk factor for poor mental health. Service occupations in which workers receive tips are potentially more precarious due to unstable schedule, income, and lack of benefits. We tested hypotheses that individuals working in tipped service occupations have greater odds of experiencing poor mental health (self-reported depression, sleep problems, and/or greater perceived stress) relative to individuals in untipped service and non-service occupations using cross-sectional data from the National Longitudinal study of Adolescent to Adult Health dataset (Wave IV:2007-2008; age 24-33 years). To improve comparability of occupation types, propensity-scores were computed as a function of childhood factors, then used to construct a sample of 2,815 women and 2,586 men. In gender-stratified multivariable regression, women in tipped service had greater odds of reporting depression diagnosis or symptoms relative to women in non-service work (Odds Ratio:1.61; 95% Confidence Interval:1.11,2.34). Associations of similar magnitude for sleep problems and perceived stress were observed among women, but were not significant; all associations were close to the null among men. Further research is necessary to understand the factors that underlie differences in poor mental health in tipped and untipped service versus non-service workers.

Near-field nano-Raman imaging of Si device structures

NASA Astrophysics Data System (ADS)

Atesang, Jacob; Geer, Robert

2005-05-01

Apertureless-based, near-field Raman imaging holds the potential for nanoscale stress metrology in emerging Si devices. Preliminary application of near-field Raman imaging on Si device structures has demonstrated the potential for stress measurements. However, detailed investigations have not been published regarding the effect of tip radius on observed near-field enhancement. Such investigations are important to understand the fundamental limits regarding the signal-to-noise ratio of the measurement and the spatial resolution that can potentially be achieved before wide application to semiconductor metrology can be considered. Investigations are presented into near-field enhancement of Raman scattering from Si device structures using a modified near-field optical microscope (NSOM). The nano-Raman system utilizes an off-axis (45°) backscattering NSOM geometry with free-space collection optics. The spectroscopic configuration utilizes a single-bounce spectrometer incorporating a holographic notch filter assembly utilized as a secondary beam-splitter for an apertureless backscattering collection geometry. Near-field enhancement is observed for both Al- and Ag-coated probes. An inverse square power-law relationship is observed between near-field enhancement factor and tip radius.

Evaluation of a self-equilibrium cutting strategy for the contour method of residual stress measurement

DOE PAGES

Muránsky, Ondrej; Hamelin, Cory J.; Hosseinzadeh, F.; ...

2017-04-06

An assessment of cutting-induced plasticity (CIP) is performed, by finite element (FE) prediction of the plastic strain accumulation along the cut tip when the EDM wire sections the NeT TG4 weld benchmark specimen along two cutting directions. The first direction corresponds to a conventional (C) cutting strategy, whereby the EDM wire cuts through the thickness of the weld specimen and travels in a direction transverse to the weld. The second direction corresponds to a self-equilibrating cutting (SE) strategy, whereby the EDM wire cuts across the transverse direction of the weld specimens and travels through the thickness of the plate. Themore » cutting thus progresses simultaneously through the compression-tension-compression regions of present weld residual stress (WRS) field. This type of cutting strategy is believed to minimize the CIP by minimising residual stress redistribution during cutting, due to stress equilibration across the sectioned material. The simulated cutting procedures are conducted under a range of clamping conditions to assess whether mechanical restraint has a primary or secondary influence on CIP accumulation. Both predictions of CIP and the resultant back-calculated WRS demonstrate that (i) mechanical restraint is the primary variable influencing CIP development, and (ii) under no circumstance does a self-equilibrating cutting strategy perform significantly better than a conventional cutting approach. Furthermore, the reason that self-equilibrating cuts are not effective is illustrated by calculating the Mode I (K I) stress intensity factor (SIF) along the cut tip, and correlating trends in K I to CIP development.« less

Evaluation of a self-equilibrium cutting strategy for the contour method of residual stress measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muránsky, Ondrej; Hamelin, Cory J.; Hosseinzadeh, F.

An assessment of cutting-induced plasticity (CIP) is performed, by finite element (FE) prediction of the plastic strain accumulation along the cut tip when the EDM wire sections the NeT TG4 weld benchmark specimen along two cutting directions. The first direction corresponds to a conventional (C) cutting strategy, whereby the EDM wire cuts through the thickness of the weld specimen and travels in a direction transverse to the weld. The second direction corresponds to a self-equilibrating cutting (SE) strategy, whereby the EDM wire cuts across the transverse direction of the weld specimens and travels through the thickness of the plate. Themore » cutting thus progresses simultaneously through the compression-tension-compression regions of present weld residual stress (WRS) field. This type of cutting strategy is believed to minimize the CIP by minimising residual stress redistribution during cutting, due to stress equilibration across the sectioned material. The simulated cutting procedures are conducted under a range of clamping conditions to assess whether mechanical restraint has a primary or secondary influence on CIP accumulation. Both predictions of CIP and the resultant back-calculated WRS demonstrate that (i) mechanical restraint is the primary variable influencing CIP development, and (ii) under no circumstance does a self-equilibrating cutting strategy perform significantly better than a conventional cutting approach. Furthermore, the reason that self-equilibrating cuts are not effective is illustrated by calculating the Mode I (K I) stress intensity factor (SIF) along the cut tip, and correlating trends in K I to CIP development.« less

Tensile stress stimulates microtubule outgrowth in living cells

NASA Technical Reports Server (NTRS)

Kaverina, Irina; Krylyshkina, Olga; Beningo, Karen; Anderson, Kurt; Wang, Yu-Li; Small, J. Victor

2002-01-01

Cell motility is driven by the sum of asymmetric traction forces exerted on the substrate through adhesion foci that interface with the actin cytoskeleton. Establishment of this asymmetry involves microtubules, which exert a destabilising effect on adhesion foci via targeting events. Here, we demonstrate the existence of a mechano-sensing mechanism that signals microtubule polymerisation and guidance of the microtubules towards adhesion sites under increased stress. Stress was applied either by manipulating the body of cells moving on glass with a microneedle or by stretching a flexible substrate that cells were migrating on. We propose a model for this mechano-sensing phenomenon whereby microtubule polymerisation is stimulated and guided through the interaction of a microtubule tip complex with actin filaments under tension.

Crack tip field and fatigue crack growth in general yielding and low cycle fatigue

NASA Technical Reports Server (NTRS)

Minzhong, Z.; Liu, H. W.

1984-01-01

Fatigue life consists of crack nucleation and crack propagation periods. Fatigue crack nucleation period is shorter relative to the propagation period at higher stresses. Crack nucleation period of low cycle fatigue might even be shortened by material and fabrication defects and by environmental attack. In these cases, fatigue life is largely crack propagation period. The characteristic crack tip field was studied by the finite element method, and the crack tip field is related to the far field parameters: the deformation work density, and the product of applied stress and applied strain. The cyclic carck growth rates in specimens in general yielding as measured by Solomon are analyzed in terms of J-integral. A generalized crack behavior in terms of delta is developed. The relations between J and the far field parameters and the relation for the general cyclic crack growth behavior are used to analyze fatigue lives of specimens under general-yielding cyclic-load. Fatigue life is related to the applied stress and strain ranges, the deformation work density, crack nucleus size, fracture toughness, fatigue crack growth threshold, Young's modulus, and the cyclic yield stress and strain. The fatigue lives of two aluminum alloys correlate well with the deformation work density as depicted by the derived theory. The general relation is reduced to Coffin-Manson low cycle fatigue law in the high strain region.

Effects of sodium chloride salinity on ecophysiological and biochemical parameters of oak seedlings (Quercus robur L.) from use of de-icing salts for winter road maintenance.

PubMed

Laffray, Xavier; Alaoui-Sehmer, Laurence; Bourioug, Mohamed; Bourgeade, Pascale; Alaoui-Sossé, Badr; Aleya, Lotfi

2018-04-04

Salt is widely used to melt snow on roads especially in mountain regions. Whether as rock salt or aerosols, spread or sprayed over road surfaces, salt may result in increased salt concentrations in soils, which, in turn, affect natural vegetation, especially tree seedlings already subjected to various other types of abiotic stress. The authors investigated the effects of salt treatment-related stress on seedling growth and certain biochemical parameters in Quercus robur to determine ion concentrations in root tips. Seedlings growing in a quartz sand/vermiculite mixture were subjected to NaCl concentrations of 0, 50, or 100 mM for 5 weeks. The results showed that high NaCl concentrations caused a marked reduction in total leaf biomass 55 and 75% for 50 and 100 mM treatments, respectively, in dry weight of stems (84%) and roots (175%) for 100 mM treatment and modified root architecture, whereas no changes appeared in leaf number. A non-significant decrease in relative water content, with changes in ion balance was recorded. Comparison of stressed to control plants show an increase in sodium (3.5-8-fold), potassium (0.6-fold), and chloride (9.5-14-fold) concentrations in the root tips while the K + /Na + ratio decreased. In taproots, no significant biochemical differences were observed between the salt-treated and the control plants for acid invertase activity, reducing sugars, sucrose, or soluble protein contents. The significance of ion and sugar accumulations in relation to osmotic adjustment and the ability of oak seedlings to cope with salt stress are discussed.

Lateral Tip Control Effects in CD-AFM Metrology: The Large Tip Limit.

PubMed

Dixson, Ronald G; Orji, Ndubuisi G; Goldband, Ryan S

2016-01-25

Sidewall sensing in critical dimension atomic force microscopes (CD-AFMs) usually involves continuous lateral dithering of the tip or the use of a control algorithm and fast response piezo actuator to position the tip in a manner that resembles touch-triggering of coordinate measuring machine (CMM) probes. All methods of tip position control, however, induce an effective tip width that may deviate from the actual geometrical tip width. Understanding the influence and dependence of the effective tip width on the dither settings and lateral stiffness of the tip can improve the measurement accuracy and uncertainty estimation for CD-AFM measurements. Since CD-AFM typically uses tips that range from 15 nm to 850 nm in geometrical width, the behavior of effective tip width throughout this range should be understood. The National Institute of Standards and Technology (NIST) has been investigating the dependence of effective tip width on the dither settings and lateral stiffness of the tip, as well as the possibility of material effects due to sample composition. For tip widths of 130 nm and lower, which also have lower lateral stiffness, the response of the effective tip width to lateral dither is greater than for larger tips. However, we have concluded that these effects will not generally result in a residual bias, provided that the tip calibration and sample measurement are performed under the same conditions. To validate that our prior conclusions about the dependence of effective tip width on lateral stiffness are valid for large CD-tips, we recently performed experiments using a very large non-CD tip with an etched plateau of approximately 2 μm width. The effective lateral stiffness of these tips is at least 20 times greater than typical CD-AFM tips, and these results supported our prior conclusions about the expected behavior for larger tips. The bottom-line importance of these latest observations is that we can now reasonably conclude that a dither slope of 3 nm/V is the baseline response due to the induced motion of the cantilever base.

Lateral Tip Control Effects in CD-AFM Metrology: The Large Tip Limit

PubMed Central

Dixson, Ronald G.; Orji, Ndubuisi G.; Goldband, Ryan S.

2016-01-01

Sidewall sensing in critical dimension atomic force microscopes (CD-AFMs) usually involves continuous lateral dithering of the tip or the use of a control algorithm and fast response piezo actuator to position the tip in a manner that resembles touch-triggering of coordinate measuring machine (CMM) probes. All methods of tip position control, however, induce an effective tip width that may deviate from the actual geometrical tip width. Understanding the influence and dependence of the effective tip width on the dither settings and lateral stiffness of the tip can improve the measurement accuracy and uncertainty estimation for CD-AFM measurements. Since CD-AFM typically uses tips that range from 15 nm to 850 nm in geometrical width, the behavior of effective tip width throughout this range should be understood. The National Institute of Standards and Technology (NIST) has been investigating the dependence of effective tip width on the dither settings and lateral stiffness of the tip, as well as the possibility of material effects due to sample composition. For tip widths of 130 nm and lower, which also have lower lateral stiffness, the response of the effective tip width to lateral dither is greater than for larger tips. However, we have concluded that these effects will not generally result in a residual bias, provided that the tip calibration and sample measurement are performed under the same conditions. To validate that our prior conclusions about the dependence of effective tip width on lateral stiffness are valid for large CD-tips, we recently performed experiments using a very large non-CD tip with an etched plateau of approximately 2 μm width. The effective lateral stiffness of these tips is at least 20 times greater than typical CD-AFM tips, and these results supported our prior conclusions about the expected behavior for larger tips. The bottom-line importance of these latest observations is that we can now reasonably conclude that a dither slope of 3 nm/V is the baseline response due to the induced motion of the cantilever base. PMID:27087883

Interface crack in a nonhomogeneous elastic medium

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1988-01-01

The linear elasticity problem for an interface crack between two bonded half planes is reconsidered. It is assumed that one of the half planes is homogeneous and the second is nonhomogeneous in such a way that the elastic properties are continuous throughout the plane and have discontinuous derivatives along the interface. The problem is formulated in terms of a system of integral equations and the asymptotic behavior of the stress state near the crack tip is determined. The results lead to the conclusion that the singular behavior of stresses in the nonhomogeneous medium is identical to that in a homogeneous material provided the spacial distribution of material properties is continuous near and at the crack tip. The problem is solved for various values of the nonhomogeneity parameter and for four different sets of crack surface tractions, and the corresponding stress intensity factors are tabulated.

Kerr microscopy studies of the effects of bending stress on galfenola)

NASA Astrophysics Data System (ADS)

Raghunath, Ganesh; Marana, Michael; Na, Suok-Min; Flatau, Alison

2014-05-01

This work deals with using a magneto-optic Kerr effect (MOKE) microscope to optically analyze the evolution of magnetic domains in a rolled and Goss textured galfenol (Fe81Ga19 + 1.0% NbC) sample when subjected to a bending stress. The initial magnetization state of the cantilevered sample was fixed along its length by a 0.3 T permanent magnet. The magnetic state was monitored with the MOKE microscope as a tip load was applied to bend the sample. The magnetic state of galfenol depends on its magneto-elastic properties. A finite element model that incorporates an energy based formulation of magnetostriction [W. D. Armstrong, J. Magn. Magn. Mater. 263(1-2), 208-218 (2003)] was used to investigate the stresses in the sample and the corresponding change in the magnetic induction as bending occurred. A qualitative comparison with the domain pictures is presented, and the experimental micromagnetic behavior results are shown to correlate well to the macro scale bending stress and magnetization results obtained in the FEM simulations.

Development of a plasma sprayed ceramic gas path seal for high pressure turbine application

NASA Technical Reports Server (NTRS)

Shiembob, L. T.

1978-01-01

Development of the plasma sprayed graded, layered ZRO2/CoCrAlY seal system for gas turbine engine blade tip seal applications up to 1589 K (2400 F) surface temperature was continued. The effect of changing ZRO2/CoCrAlY ratios in the intermediate layers on thermal stresses was evaluated analytically with the goal of identifying the materials combinations which would minimize thermal stresses in the seal system. Three methods of inducing compressive residual stresses in the sprayed seal materials to offset tensile thermal stresses were analyzed. The most promising method, thermal prestraining, was selected based upon potential, feasibility and complexity considerations. The plasma spray equipment was modified to heat, control and monitor the substrate temperature during spraying. Specimens were fabricated and experimentally evaluated to: (1) substantiate the capability of the thermal prestrain method to develop compressive residual stresses in the sprayed structure and (2) define the effect of spraying on a heated substate on abradability, erosion and thermal shock characteristics of the seal system. Thermal stress analysis, including residual stresses and material properties variations, was performed and correlated with thermal shock test results. Seal system performance was assessed and recommendations for further development were made.

Cytogenetic evaluation of gold nanorods using Allium cepa test.

PubMed

Rajeshwari, A; Roy, Barsha; Chandrasekaran, Natarajan; Mukherjee, Amitava

2016-12-01

The current study reveals the impact of gold nanorods (NRs) capped with CTAB (cetyltrimethylammonium bromide) or PEG (polyethylene glycol) on Allium cepa. The morphology and surface charge of CTAB- and PEG-capped gold NRs were characterized by electron microscopic and zeta potential analyses. The chromosomal aberrations like clumped chromosome, chromosomal break, chromosomal bridge, diagonal anaphase, disturbed metaphase, laggard chromosome, and sticky chromosome were observed in the root tip cells exposed to different concentrations (0.1, 1, and 10 μg/mL) of CTAB- and PEG-capped gold NRs. We found that both CTAB- and PEG-capped gold NRs were able to induce toxicity in the plant system after 4-h interaction. At a maximum concentration of 10 μg/mL, the mitotic index reduction induced by CTAB-capped gold NRs was 40-fold higher than that induced by PEG-capped gold NRs. The toxicity of gold NRs was further confirmed by lipid peroxidation and oxidative stress analyses. The unbound CTAB also contributed to the toxicity in root tip cells, while PEG alone shows less toxicity to the cells. The vehicle control CTAB contributed to the toxic effects in root tip cells, while PEG alone did not show any toxicity to the cells. The results revealed that even though both the particles have adverse effects on A. cepa, there was a significant difference in the mitotic index and oxidative stress generation in root cells exposed to CTAB-capped gold NRs. Thus, this study concludes that the surface polymerization of gold NRs by PEG can reduce the toxicity of CTAB-capped gold NRs. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

High Bypass Turbofan Component Development. Phase II. Fan Detail Design.

DTIC Science & Technology

1979-12-01

Vane metal angles ........ ..................... ... 18 22 Vane conical airfoil sections ..... ............... ... 19 23 Principal blade stresses at...31.25 deg. The number of rotor airfoils is 20 while the stator has 42 vanes . The number of vanes and the vane - blade spacing were consequences of...effect of radius change are accounted for. Figure 16 shows the blade hub, mean, and tip conical airfoil sections in engine orientation. For

Study of the Effects of Metallurgical Factors on the Growth of Fatigue Microcracks.

DTIC Science & Technology

1987-11-25

polycrystalline) yield stress. 8. The resulting model, predicated on the notion of orientation-dependent microplastic grains, predicts quantitatively the entire...Figure 5. Predicted crack growth curves for small cracks propagating from a microplastic grain into elastic-plastic, contiguous grains; Ao is defined as...or the crack tip opening *displacement, 6. Figure 5. Predicted crack growth curves for small cracks propagating from a microplastic grain into

Tree diversity mitigates defoliation after a drought-induced tipping point.

PubMed

Sousa-Silva, Rita; Verheyen, Kris; Ponette, Quentin; Bay, Elodie; Sioen, Geert; Titeux, Hugues; Van de Peer, Thomas; Van Meerbeek, Koenraad; Muys, Bart

2018-05-26

Understanding the processes that underlie drought-related tree vitality loss is essential for anticipating future forest dynamics, and for developing management plans aiming at increasing the resilience of forests to climate change. Forest vitality has been continuously monitored in Europe since the acid rain alert in the 1980s, and the intensive monitoring plots of ICP Forests offer the opportunity to investigate the effects of air pollution and climate change on forest condition. By making use of over 100 long-term monitoring plots, where crown defoliation has been assessed extensively since 1990, we discovered a progressive shift from a negative to a positive effect of species richness on forest health. The observed tipping point in the balance of net interactions, from competition to facilitation, has never been reported from real ecosystems outside experimental conditions; and the strong temporal consistency of our observations with increasing drought stress emphasizes its climate change relevance. Furthermore, we show that higher species diversity has reduced the severity of defoliation in the long term. Our results confirm the greater resilience of diverse forests to future climate change-induced stress. More generally, they add to an accumulating body of evidence on the large potential of tree species mixtures to face manifold disturbances in a changing world. © 2018 John Wiley & Sons Ltd.

Deterministic blade row interactions in a centrifugal compressor stage

NASA Technical Reports Server (NTRS)

Kirtley, K. R.; Beach, T. A.

1991-01-01

The three-dimensional viscous flow in a low speed centrifugal compressor stage is simulated using an average passage Navier-Stokes analysis. The impeller discharge flow is of the jet/wake type with low momentum fluid in the shroud-pressure side corner coincident with the tip leakage vortex. This nonuniformity introduces periodic unsteadiness in the vane frame of reference. The effect of such deterministic unsteadiness on the time-mean is included in the analysis through the average passage stress, which allows the analysis of blade row interactions. The magnitude of the divergence of the deterministic unsteady stress is of the order of the divergence of the Reynolds stress over most of the span, from the impeller trailing edge to the vane throat. Although the potential effects on the blade trailing edge from the diffuser vane are small, strong secondary flows generated by the impeller degrade the performance of the diffuser vanes.

Elimination of strength degrading effects caused by surface microdefect: A prevention achieved by silicon nanotexturing to avoid catastrophic brittle fracture

NASA Astrophysics Data System (ADS)

Kashyap, Kunal; Kumar, Amarendra; Huang, Chuan-Torng; Lin, Yu-Yun; Hou, Max T.; Andrew Yeh, J.

2015-06-01

The unavoidable occurrence of microdefects in silicon wafers increase the probability of catastrophic fracture of silicon-based devices, thus highlighting the need for a strengthening mechanism to minimize fractures resulting from defects. In this study, a novel mechanism for manufacturing silicon wafers was engineered based on nanoscale reinforcement through surface nanotexturing. Because of nanotexturing, different defect depths synthetically emulated as V-notches, demonstrated a bending strength enhancement by factors of 2.5, 3.2, and 6 for 2-, 7-, and 14-μm-deep V-notches, respectively. A very large increase in the number of fragments observed during silicon fracturing was also indicative of the strengthening effect. Nanotextures surrounding the V-notch reduced the stress concentration factor at the notch tip and saturated as the nanotexture depth approached 1.5 times the V-notch depth. The stress reduction at the V-notch tip measured by micro-Raman spectroscopy revealed that nanotextures reduced the effective depth of the defect. Therefore, the nanotextured samples were able to sustain a larger fracture force. The enhancement in Weibull modulus, along with an increase in bending strength in the nanotextured samples compared to polished single-crystal silicon samples, demonstrated the reliability of the strengthening method. These results suggest that this method may be suitable for industrial implementation.

A note on the cracked plates reinforced by a line stiffener

NASA Technical Reports Server (NTRS)

Yahsi, O. S.; Erdogan, F.

1983-01-01

The problem of a cracked plate reinforced by a line stiffener is reconsidered. The original solution of this problem was given in the literature. Also, a variation of the problem with debonding between the plate and the stiffener near the cracked region was reported in the literature. However, the special case of the problem in which the crack tip terminates at the stiffener does not appear to have been studied. In practice, the solution may be necessary in order to assess the crack arrest effectiveness of the stiffener. The problem of a stiffened plate with a crack is reformulated, the asymptotic stress state near the crack tip terminating at the stiffener is examined, and numerical results are given for various stiffness constants. Previously announced in STAR as N83-21388

Controlled manipulation of oxygen vacancies using nanoscale flexoelectricity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Saikat; Wang, Bo; Cao, Ye

Oxygen vacancies, especially their distribution, are directly coupled to the electromagnetic properties of oxides and related emergent functionalities that have implications for device applications. Here using a homoepitaxial strontium titanate thin film, we demonstrate a controlled manipulation of the oxygen vacancy distribution using the mechanical force from a scanning probe microscope tip. By combining Kelvin probe force microscopy imaging and phase-field simulations, we show that oxygen vacancies can move under a stress-gradient-induced depolarisation field. When tailored, this nanoscale flexoelectric effect enables a controlled spatial modulation. In motion, the scanning probe tip thereby deterministically reconfigures the spatial distribution of vacancies. Finally,more » the ability to locally manipulate oxygen vacancies on-demand provides a tool for the exploration of mesoscale quantum phenomena and engineering multifunctional oxide devices.« less

A viewpoint on considering physiological principles to study stress resistance and resilience with aging.

PubMed

Miller, Benjamin F; Seals, Douglas R; Hamilton, Karyn L

2017-09-01

Adaptation to stress is identified as one of the seven pillars of aging research. Our viewpoint discusses the importance of the distinction between stress resistance and resilience, highlights how integration of physiological principles is critical for further understanding in vivo stress resistance and resilience, and advocates for the use of early warning signs to prevent a tipping point in stress resistance and resilience. Copyright © 2017 Elsevier B.V. All rights reserved.

Fatigue Behavior of a Third Generation PM Disk Superalloy

NASA Technical Reports Server (NTRS)

Gayda, John; Gabb, Timothy P.

2008-01-01

The fatigue behavior of a 3rd generation PM disk alloy, LSHR, was studied at 1300 F. Tensile, creep, and fatigue tests were run on smooth and notched (Kt = 2) bars under a variety of conditions. Analysis of smooth bar fatigue data, run under strain and load control with R ratios of 0 and -1, showed that a stress based Smith-Watson-Topper approach could collapse the data set. While the tensile and creep data showed substantial notch strengthening at 1300 F, the fatigue data showed a life deficit for the notch specimens. A viscoplastic finite element model, which accounted for stress relaxation at the notch tip, provided the best correlation between the notched and smooth bar behavior, although the fatigue data was not fully rationalized based on this simplified viscoplastic model of the stresses at the notch tip.Inclusion of a 90 sec dwell at peak load was found to dramatically decrease notch fatigue life. This result was shown to be consistent with a simple linear creep-fatigue damage rule, where creep damage dominated at low stresses and fatigue damage was more prevalent at higher stresses.

Main factors causing intergranular and quasi-cleavage fractures at hydrogen-induced cracking in tempered martensitic steels

NASA Astrophysics Data System (ADS)

Kurokawa, Ami; Doshida, Tomoki; Hagihara, Yukito; Suzuki, Hiroshi; Takai, Kenichi

2018-05-01

Though intergranular (IG) and quasi-cleavage (QC) fractures have been widely recognized as typical fracture modes of the hydrogen-induced cracking in high-strength steels, the main factor has been unclarified yet. In the present study, the hydrogen content dependence on the main factor causing hydrogen-induced cracking has been examined through the fracture mode transition from QC to IG at the crack initiation site in the tempered martensitic steels. Two kinds of tempered martensitic steels were prepared to change the cohesive force due to the different precipitation states of Fe3C on the prior γ grain boundaries. A high amount of Si (H-Si) steel has a small amount of Fe3C on the prior austenite grain boundaries. Whereas, a low amount of Si (L-Si) steel has a large amount of Fe3C sheets on the grain boundaries. The fracture modes and initiations were observed using FE-SEM (Field Emission-Scanning Electron Microscope). The crack initiation sites of the H-Si steel were QC fracture at the notch tip under various hydrogen contents. While the crack initiation of the L-Si steel change from QC fracture at the notch tip to QC and IG fractures from approximately 10 µm ahead of the notch tip as increasing in hydrogen content. For L-Si steels, two possibilities are considered that the QC or IG fracture occurred firstly, or the QC and IG fractures occurred simultaneously. Furthermore, the principal stress and equivalent plastic strain distributions near the notch tip were calculated with FEM (Finite Element Method) analysis. The plastic strain was the maximum at the notch tip and the principle stress was the maximum at approximately 10 µm from the notch tip. The position of the initiation of QC and IG fracture observed using FE-SEM corresponds to the position of maximum strain and stress obtained with FEM, respectively. These findings indicate that the main factors causing hydrogen-induced cracking are different between QC and IG fractures.

Application of computer assisted moire to the study of a crack tip

NASA Astrophysics Data System (ADS)

Sciammarella, C. A.; Albertazzi, A., Jr.; Mourikes, J.

The basic principles of computer assisted moire are discussed. The influence of the image sensor and its finite dimensions on the sampling theorem requirements is discussed. Criteria for the selection of grating pitch on the basis of the spatial bandwidth of the pattern to be observed and the requirements arising from sensitivity considerations are given. The method is used to analyze the strain field in the neighborhood of the crack tip of a standard ASTM compact tension specimen. From the displacements the strains are computed, and from the strains the stresses are obtained using the generalized Ramberg-Osgood stress strain relationship. The stresses are used to compute the values for the J-integral in several circuits surrounding the crack. Good agreement is obtained between the values of the stress intensity factors obtained by different methods. The plastic region surrounding the crack does not show a HRR field and thus the usual rationale to justify the J-integral methods must be re-evaluated.

Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

NASA Technical Reports Server (NTRS)

Chen, Q.; Liu, H. W.

1988-01-01

Fatigue crack growth tests were carried out on large-grain Al 7029 aluminum alloy and the finite element method was used to calculate the stress field near the tip of a zigzag crack. The resolved shear stresses on all 12 slip systems were computed, and the resolved shear stress intensity coefficient (RSSIC) was defined. The RSSIC was used to analyze the irregular crack path and was correlated with the rate of single-slip-plane shear crack growth. Fatigue crack growth was found to be caused primarily by shear decohesion at a crack tip. When the RSSIC on a single-slip system was much larger than all the others, the crack followed a single-slip plane. When the RSSICs on two conjugate slip systems were comparable, a crack grew in a zigzag manner on these planes and the macrocrack-plane bisected the two active slip planes. The maximum RSSIC on the most active slip system is proposed as a parameter to correlate with the shear fatigue crack growth rate in large crystals.

Crack-tip-opening angle measurements and crack tunneling under stable tearing in thin sheet 2024-T3 aluminum alloy

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Sutton, M. A.

1993-01-01

The stable tearing behavior of thin sheets 2024-T3 aluminum alloy was studied for middle crack tension specimens having initial cracks that were: flat cracks (low fatigue stress) and 45 degrees through-thickness slant cracks (high fatigue stress). The critical crack-tip-opening angle (CTOA) values during stable tearing were measured by two independent methods, optical microscopy and digital image correlation. Results from the two methods agreed well. The CTOA measurements and observations of the fracture surfaces showed that the initial stable tearing behavior of low and high fatigue stress tests is significantly different. The cracks in the low fatigue stress tests underwent a transition from flat-to-slant crack growth, during which the CTOA values were high and significant crack tunneling occurred. After crack growth equal to about the thickness, CTOA reached a constant value of 6 deg and after crack growth equal to about twice the thickness, crack tunneling stabilized. The initial high CTOA values, in the low fatigue crack tests, coincided with large three-dimensional crack front shape changes due to a variation in the through-thickness crack tip constraint. The cracks in the high fatigue stress tests reach the same constant CTOA value after crack growth equal to about the thickness, but produced only a slightly higher CTOA value during initial crack growth. For crack growth on the 45 degree slant, the crack front and local field variables are still highly three-dimensional. However, the constant CTOA values and stable crack front shape may allow the process to be approximated with two-dimensional models.

Effect of load, area of contact, and contact stress on the wear mechanisms of a bonded solid lubricant film

NASA Technical Reports Server (NTRS)

Fusaro, R. L.

1980-01-01

A pin on disk type of friction and wear apparatus was used to study the effect of load, contact stress and rider area of contact on the friction and wear properties of polyimide bonded graphite fluoride films. Different rider area contacts were obtained by initially generating flats (with areas of 0.0035, 0.0071, 0.0145, and 0.0240 cm) on 0.476-cm radius hemispherically tipped riders. Different projected contact stresses were obtained by applying loads of 2.5- to 58.8-N to the flats. Two film wear mechanisms were observed. The first was found to be a linear function of contact stress and was independent of rider area of contact. The second was found to increase exponentially as the stress increased. The second also appeared to be a function of rider contact area. Wear equations for each mechanism were empirically derived from the experimental data. In general, friction coefficients increased with increasing rider contact area and with sliding duration. This was related to the build up of thick rider transfer films.

Effect of load, area of contact, and contact stress on the tribological properties of polyimide bonded graphite fluoride films

NASA Technical Reports Server (NTRS)

Fusaro, R. L.

1981-01-01

A pin-on-disk type of friction and wear apparatus was used to study the effect of load, contact stress and rider area of contact on the friction and wear properties of polyimide-bonded graphite fluoride films. Different rider area contacts were obtained by initially generating flats (with areas of 0.0035, 0.0071, 0.0145, and 0.0240 cm) on 0.476-cm radius hemispherically-tipped riders. Different projected contact stresses were obtained by applying loads of 2.5-to 58.8-N to the flats. Two film wear mechanisms were observed. The first was found to be a linear function of contact stress and was independent of rider area of contact. The second was found to increase exponentially as the stress increased. The second also appeared to be a function of rider contact area. Wear equations for each mechanism were empirically derived from the experimental data. In general, friction coefficients increased with increasing rider contact area and with sliding duration. This was related to the build-up of thick rider transfer films.

Identification and characterization of microRNAs from in vitro-grown pear shoots infected with Apple stem grooving virus in response to high temperature using small RNA sequencing.

PubMed

Liu, Juan; Zhang, XueJiao; Zhang, FangPeng; Hong, Ni; Wang, GuoPing; Wang, Aiming; Wang, LiPing

2015-11-16

MicroRNAs (miRNAs) have functions in diverse biological processes such as growth, signal transduction, disease resistance, and stress responses in plants. Thermotherapy is an effective approach for elimination of viruses from fruit trees. However, the role of miRNAs in this process remains elusive. Previously, we showed that high temperature treatment reduces the titers of Apple stem grooving virus (ASGV) from the tips of in vitro-grown Pyrus pyrifolia plants. In this study, we identified high temperature-altered pear miRNAs using the next generation sequencing technology, and futher molecularly characterized miRNA-mediated regulaton of target gene expression in the meristem tip and base tissues of in vitro-grown, ASGV-infected pear shoots under different temperatures. Using in vitro-grown P. pyrifolia shoot meristem tips infected with ASGV, a total of 22,592,997 and 20,411,254 clean reads were obtained from Illumina high-throughput sequencing of small RNA libraries at 24 °C and 37 °C, respectively. We identified 149 conserved and 141 novel miRNAs. Seven conserved miRNAs and 77 novel miRNAs were differentially expressed at different temperatures. Target genes for differentially expressed known and novel miRNAs were predicted and functionally annotated. Gene Ontology (GO) analysis showed that high-ranking miRNA target genes were involved in metabolic processes, responses to stress, and signaling, indicating that these high temperature-responsive miRNAs have functions in diverse gene regulatory networks. Spatial expression patterns of the miRNAs and their target genes were found to be expressed in shoot tip and base tissues by qRT-PCR. In addition, high temperature reduced viral titers in the shoot meristem tip, while negatively regulated miRNA-mediated target genes related to resistance disease defense and hormone signal transduction pathway were up-regulated in the P. pyrifolia shoot tip in response to high temperature. These results suggested that miRNAs may have important functions in the high temperature-dependent decrease of ASGV titer in in vitro-grown pear shoots. This is the first report of miRNAs differentially expressed at 24 °C and 37 °C in the meristem tip of pear shoots infected with ASGV. The results of this study provide valuable information for further exploration of the function of high temperature-altered miRNAs in suppressing viral infections in pear and other fruit trees.

A linear least squares approach for evaluation of crack tip stress field parameters using DIC

NASA Astrophysics Data System (ADS)

Harilal, R.; Vyasarayani, C. P.; Ramji, M.

2015-12-01

In the present work, an experimental study is carried out to estimate the mixed-mode stress intensity factors (SIF) for different cracked specimen configurations using digital image correlation (DIC) technique. For the estimation of mixed-mode SIF's using DIC, a new algorithm is proposed for the extraction of crack tip location and coefficients in the multi-parameter displacement field equations. From those estimated coefficients, SIF could be extracted. The required displacement data surrounding the crack tip has been obtained using 2D-DIC technique. An open source 2D DIC software Ncorr is used for the displacement field extraction. The presented methodology has been used to extract mixed-mode SIF's for specimen configurations like single edge notch (SEN) specimen and centre slant crack (CSC) specimens made out of Al 2014-T6 alloy. The experimental results have been compared with the analytical values and they are found to be in good agreement, thereby confirming the accuracy of the algorithm being proposed.

Abscisic Acid Regulates Auxin Homeostasis in Rice Root Tips to Promote Root Hair Elongation

PubMed Central

Wang, Tao; Li, Chengxiang; Wu, Zhihua; Jia, Yancui; Wang, Hong; Sun, Shiyong; Mao, Chuanzao; Wang, Xuelu

2017-01-01

Abscisic acid (ABA) plays an essential role in root hair elongation in plants, but the regulatory mechanism remains to be elucidated. In this study, we found that exogenous ABA can promote rice root hair elongation. Transgenic rice overexpressing SAPK10 (Stress/ABA-activated protein kinase 10) had longer root hairs; rice plants overexpressing OsABIL2 (OsABI-Like 2) had attenuated ABA signaling and shorter root hairs, suggesting that the effect of ABA on root hair elongation depends on the conserved PYR/PP2C/SnRK2 ABA signaling module. Treatment of the DR5-GUS and OsPIN-GUS lines with ABA and an auxin efflux inhibitor showed that ABA-induced root hair elongation depends on polar auxin transport. To examine the transcriptional response to ABA, we divided rice root tips into three regions: short root hair, long root hair and root tip zones; and conducted RNA-seq analysis with or without ABA treatment. Examination of genes involved in auxin transport, biosynthesis and metabolism indicated that ABA promotes auxin biosynthesis and polar auxin transport in the root tip, which may lead to auxin accumulation in the long root hair zone. Our findings shed light on how ABA regulates root hair elongation through crosstalk with auxin biosynthesis and transport to orchestrate plant development. PMID:28702040

Thermal-Mechanical Response of Cracked Satin Weave CFRP Composites at Cryogenic Temperatures

NASA Astrophysics Data System (ADS)

Watanabe, S.; Shindo, Y.; Narita, F.; Takeda, T.

2008-03-01

This paper examines the thermal-mechanical response of satin weave carbon fiber reinforced polymer (CFRP) laminates with internal and/or edge cracks subjected to uniaxial tension load at cryogenic temperatures. Cracks are considered to occur in the transverse fiber bundles and extend through the entire thickness of the fiber bundles. Two-dimentional generalized plane strain finite element models are developed to study the effects of residual thermal stresses and cracks on the mechanical behavior of CFRP woven laminates. A detailed examination of the Young's modulus and stress distributions near the crack tip is carried out which provides insight into material behavior at cryogenic temperatures.

Hybrid-finite-element analysis of some nonlinear and 3-dimensional problems of engineering fracture mechanics

NASA Technical Reports Server (NTRS)

Atluri, S. N.; Nakagaki, M.; Kathiresan, K.

1980-01-01

In this paper, efficient numerical methods for the analysis of crack-closure effects on fatigue-crack-growth-rates, in plane stress situations, and for the solution of stress-intensity factors for arbitrary shaped surface flaws in pressure vessels, are presented. For the former problem, an elastic-plastic finite element procedure valid for the case of finite deformation gradients is developed and crack growth is simulated by the translation of near-crack-tip elements with embedded plastic singularities. For the latter problem, an embedded-elastic-singularity hybrid finite element method, which leads to a direct evaluation of K-factors, is employed.

The relative stress-corrosion-cracking susceptibility of candidate aluminum-lithium alloys for aerospace applications

NASA Technical Reports Server (NTRS)

Pizzo, P. P.

1982-01-01

Stress corrosion tests of Al-Li-Cu powder metallurgy alloys are described. Alloys investigated were Al-2.6% Li-1.4% and Al-2.6% Li-1.4% Cu-1.6% Mg. The base properties of the alloys were characterized. Process, heat treatment, and size/orientational effects on the tensile and fracture behavior were investigated. Metallurgical and electrochemical conditions are identified which provide reproducible and controlled parameters for stress corrosion evaluation. Preliminary stress corrosion test results are reported. Both Al-Li-Cu alloys appear more susceptible to stress corrosion crack initiation than 7075-T6 aluminum, with the magnesium bearing alloy being the most susceptible. Tests to determine the threshold stress intensity for the base and magnesium bearing alloys are underway. Twelve each, bolt loaded DCB type specimens are under test (120 days) and limited crack growth in these precracked specimens has been observed. General corrosion in the aqueous sodium chloride environment is thought to be obscuring results through crack tip blunting.

Managing Stress on the Job. P.R.I.D.E. People Retraining for Industry Excellence.

ERIC Educational Resources Information Center

Pollak, Ave

This workplace skills course on managing stress on the job is designed to provide an opportunity to develop the skills needed to meet the stress and reduce the "overload." Introductory material includes a course description, objectives, and course topics. The course consists of 24 sessions, each of which has these components: teacher tips,…

Experimental and Numerical Analysis of Fracture in 41Cr4 Steel - Issues of the Stationary Cracks

NASA Astrophysics Data System (ADS)

Graba, M.

2018-02-01

This paper analyzes the process of fracture in 41Cr4 steel on the basis of experimental and numerical data obtained for non-propagating cracks. The author's previous and latest experimental results were used to determine the apparent crack initiation moment and fracture toughness for the material under plane strain conditions. Numerical simulations were carried out to assess changes in the J-integral, the crack tip opening displacement, the size of the plastic region and the distribution of stresses around the crack tip. A complex numerical analysis based on the true stress-strain curve was performed to determine the behavior of 41Cr4 steel under increasing external loads.

Stressed Out in the Classroom.

ERIC Educational Resources Information Center

Black, Susan

2003-01-01

Many teachers feel overwhelmed about meeting the needs of students getting ready for tests, and about relations with principals. Four exceptionally high-stress factors that teachers admit carrying into their classrooms are money management, health, relationships, and care giving. A sidebar lists tips for administrators to help alleviate teachers'…

Effects of pressure angle and tip relief on the life of speed increasing gearbox: a case study.

PubMed

Shanmugasundaram, Sankar; Kumaresan, Manivarma; Muthusamy, Nataraj

2014-01-01

This paper examines failure of helical gear in speed increasing gearbox used in the wind turbine generator (WTG). In addition, an attempt has been made to get suitable gear micro-geometry such as pressure angle and tip relief to minimize the gear failure in the wind turbines. As the gear trains in the wind turbine gearbox is prearranged with higher speed ratio and the gearboxes experience shock load due to atmospheric turbulence, gust wind speed, non-synchronization of pitching, frequent grid drops and failure of braking, the gear failure occurs either in the intermediate or high speed stage pinion. KISS soft gear calculation software was used to determine the gear specifications and analysis is carried out in ANSYS software version.11.0 for the existing and the proposed gear to evaluate the performance of bending stress tooth deflection and stiffness. The main objective of this research study is to propose suitable gear micro-geometry that is tip relief and pressure angle blend for increasing tooth strength of the helical gear used in the wind turbine for trouble free operation.

Static and free-vibration analyses of cracks in thin-shell structures based on an isogeometric-meshfree coupling approach

NASA Astrophysics Data System (ADS)

Nguyen-Thanh, Nhon; Li, Weidong; Zhou, Kun

2018-03-01

This paper develops a coupling approach which integrates the meshfree method and isogeometric analysis (IGA) for static and free-vibration analyses of cracks in thin-shell structures. In this approach, the domain surrounding the cracks is represented by the meshfree method while the rest domain is meshed by IGA. The present approach is capable of preserving geometry exactness and high continuity of IGA. The local refinement is achieved by adding the nodes along the background cells in the meshfree domain. Moreover, the equivalent domain integral technique for three-dimensional problems is derived from the additional Kirchhoff-Love theory to compute the J-integral for the thin-shell model. The proposed approach is able to address the problems involving through-the-thickness cracks without using additional rotational degrees of freedom, which facilitates the enrichment strategy for crack tips. The crack tip enrichment effects and the stress distribution and displacements around the crack tips are investigated. Free vibrations of cracks in thin shells are also analyzed. Numerical examples are presented to demonstrate the accuracy and computational efficiency of the coupling approach.

Universal aspects of sonolubrication in amorphous and crystalline materials

NASA Astrophysics Data System (ADS)

Pfahl, V.; Ma, C.; Arnold, W.; Samwer, K.

2018-01-01

We studied sonolubricity, a phenomenon reducing the friction between two sliding surfaces by ultrasound. Friction force measurements were performed using an atomic force microscope (AFM) when the tip-surface contact was excited to out-of-plane oscillations by a transducer attached to the rear of the sample or by oscillating the AFM cantilever by the built-in piezoelectric element in the cantilever holder. Experiments were carried out near or at the first cantilever contact-resonance. We studied friction on crystalline and amorphous Pd77.5Cu6Si16.5 ribbons, on a silicon wafer at room temperature, and on a La0.6Sr0.4MnO3 (LSMO) thin film at different temperatures. Measurements were carried out varying the cantilever amplitude, the ultrasonic frequency, and the normal static load. The effect of sonolubrication is explained by the non-linear force-distance curve between the sample and the tip due to the local interaction potential. The reduction of friction in LSMO as a function temperature is due to the direct coupling of the tip's stress-field to the electrons.

Theoretical Model of the Effect of Crack Tip Blunting on the Ultimate Tensile Strength of Welds in 2219-T87 Aluminum

NASA Technical Reports Server (NTRS)

Beil, R. J.

1982-01-01

A theoretical model representing blunting of a crack tip radius through diffusion of vacancies is presented. The model serves as the basis for a computer program which calculates changes, due to successive weld heat passes, in the ultimate tensile strength of 2219-T81 aluminum. In order for the model to yield changes of the same order in the ultimate tensile strength as that observed experimentally, a crack tip radius of the order of .001 microns is required. Such sharp cracks could arise in the fusion zone of a weld from shrinkage cavities or decohered phase boundaries between dendrites and the eutectic phase, or, possibly, from plastic deformation due to thermal stresses encountered during the welding process. Microstructural observations up to X2000 (resolution of about .1 micron) did not, in the fusion zone, show structural details which changed significantly under the influence of a heat pass, with the exception of possible small changes in the configuration of the interdendritic eutectic and in porosity build-up in the remelt zone.

Hollow steel tips for reducing distal fiber burn-back during thulium fiber laser lithotripsy.

PubMed

Hutchens, Thomas C; Blackmon, Richard L; Irby, Pierce B; Fried, Nathaniel M

2013-07-01

The use of thulium fiber laser (TFL) as a potential alternative laser lithotripter to the clinical holmium:YAG laser is being studied. The TFL's Gaussian spatial beam profile provides efficient coupling of higher laser power into smaller core fibers without proximal fiber tip degradation. Smaller fiber diameters are more desirable, because they free up space in the single working channel of the ureteroscope for increased saline irrigation rates and allow maximum ureteroscope deflection. However, distal fiber tip degradation and "burn-back" increase as fiber diameter decreases due to both excessive temperatures and mechanical stress experienced during stone ablation. To eliminate fiber tip burn-back, the distal tip of a 150-μm core silica fiber was glued inside 1-cm-long steel tubing with fiber tip recessed 100, 250, 500, 1000, or 2000 μm inside the steel tubing to create the hollow-tip fiber. TFL pulse energy of 34 mJ with 500-μs pulse duration and 150-Hz pulse rate was delivered through the hollow-tip fibers in contact with human calcium oxalate monohydrate urinary stones during ex vivo studies. Significant fiber tip burn-back and degradation was observed for bare 150-μm core-diameter fibers. However, hollow steel tip fibers experienced minimal fiber burn-back without compromising stone ablation rates. A simple, robust, compact, and inexpensive hollow fiber tip design was characterized for minimizing distal fiber burn-back during the TFL lithotripsy. Although an increase in stone retropulsion was observed, potential integration of the hollow fiber tip into a stone basket may provide rapid stone vaporization, while minimizing retropulsion.

Teen Intervention Project--Cherokee (TIP-C).

PubMed

Lowe, John

2006-01-01

To test the feasibility of providing a cultural school-based substance abuse intervention for Cherokee adolescents and to examine the relationship between Cherokee self-reliance, substance abuse, and stress. A 10-week group intervention was implemented over a 3-year period for Cherokee adolescent substance abusers. Pre-intervention, immediate post-intervention, and 90-day post-intervention measures of Cherokee self-reliance, substance abuse, and stress were administered to 108 Cherokee adolescent high school students who participated in the intervention. Immediate and 90-day post-intervention substance abuse rates were significantly lower than pre-intervention rates. Cherokee self-reliance scores were significantly increased. Perceived stress scores were significantly lower immediately post-intervention but increased 90-day post-intervention. The Teen Intervention Project--Cherokee is an effective and culturally appropriate school-based intervention for Cherokee adolescent substance abusers.

Dependence of displacement-length scaling relations for fractures and deformation bands on the volumetric changes across them

USGS Publications Warehouse

Schultz, R.A.; Soliva, R.; Fossen, H.; Okubo, C.H.; Reeves, D.M.

2008-01-01

Displacement-length data from faults, joints, veins, igneous dikes, shear deformation bands, and compaction bands define two groups. The first group, having a power-law scaling relation with a slope of n = 1 and therefore a linear dependence of maximum displacement and discontinuity length (Dmax = ??L), comprises faults and shear (non-compactional or non-dilational) deformation bands. These shearing-mode structures, having shearing strains that predominate over volumetric strains across them, grow under conditions of constant driving stress, with the magnitude of near-tip stress on the same order as the rock's yield strength in shear. The second group, having a power-law scaling relation with a slope of n = 0.5 and therefore a dependence of maximum displacement on the square root of discontinuity length (Dmax = ??L0.5), comprises joints, veins, igneous dikes, cataclastic deformation bands, and compaction bands. These opening- and closing-mode structures grow under conditions of constant fracture toughness, implying significant amplification of near-tip stress within a zone of small-scale yielding at the discontinuity tip. Volumetric changes accommodated by grain fragmentation, and thus control of propagation by the rock's fracture toughness, are associated with scaling of predominantly dilational and compactional structures with an exponent of n = 0.5. ?? 2008 Elsevier Ltd.

Influence of adequate pelvic floor muscle contraction on the movement of the coccyx during pelvic floor muscle training.

PubMed

Fujisaki, Akiko; Shigeta, Miwa; Shimoinaba, Misa; Yoshimura, Yasukuni

2018-04-01

[Purpose] Pelvic floor muscle training is a first-line therapy for female stress urinary incontinence. Previous studies have suggested that the coccyx tip moves ventrally and cranially during pelvic floor muscle contraction. The study aimed to elucidate the influence of adequate pelvic floor muscle contraction on coccyx movement. [Subjects and Methods] Sixty-three females (57 patients with stress urinary incontinence and additional 6 healthy volunteers) were enrolled. Using magnetic resonance imaging, coccyx movement was evaluated during pelvic floor muscle contraction and strain. An adequate contraction was defined as a contraction with good Oxford grading scale [≥3] and without inadequate muscle substitution patterns. [Results] Inadequate muscle substitution patterns were observed in 33 participants (52.4%). No significant difference was observed in the movement of the coccyx tip in the ventrodorsal direction between females with and without inadequate muscle substitution patterns. However, a significant increase in the movement of the coccyx tip in the cranial direction was detected in the group without inadequate muscle substitution patterns. Compared to participants with inadequate pelvic floor muscle contraction, those who had adequate pelvic floor muscle contraction exhibited significantly increased cranial movement of the coccyx. [Conclusion] Adequate pelvic floor muscle contraction can produce cranial movement of the coccyx tip.

Determining cyclic corrosion cracking resistance for titanium alloys with allowance for electrochemical conditions at the fatigue corrosion crack tip

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panasyuk, V.V.; Ratich, L.V.; Petranyuk, I.Ya.

1994-08-01

Published data are examined on how various factors affect fatigue crack growth rates. Basic diagrams have been constructed for the cyclic cracking resistance in Ti-6Al-4V and Ti-6Al-2Sn alloys in air, distilled water, and 3.5% NaCl for use in working-life calculations. Appropriate heat treatment can produce two microstructures in a titanium alloy, one of which has the largest cyclic cracking resistance, while in the second, the cracks grow at the lowest rate. The cyclic corrosion cracking resistance for a titanium alloy should be determined in relation to the state of stress and strain and to the electrochemical conditions at the corrosionmore » fatigue crack tip, while the variations in fatigue crack growth rate for a given stress intensity factor in a corrosive medium are due to differing electrochemical conditions at the crack tip during the testing on different specimens. Basic diagrams can be derived for titanium alloys by using a physically sound methodology developed previously for steels, which is based on invariant diagrams for cyclic cracking resistance in air and in the corresponding medium, which can be constructed in relation to extremal working and electrochemical conditions at corrosion-fatigue crack tips.« less

Taking Care of Your Behavioral Health: Tips for Social Distancing, Quarantine, and Isolation

MedlinePlus

... REDUCE FINANCIAL STRESS If you’re unable to work during this time, you may experience stress related to your job status or financial situation. 2 Toll-Free: 1-877-SAMHSA-7 ... you are away from work. ƒ Contact the U.S. Department of Labor toll- free ...

Test Anxiety? Try a Stick of Gum...

ERIC Educational Resources Information Center

Wilmore, Elaine L.

American schools face pressure to increase their students' test scores. Research reports have shown American students to be particularly stressed over test taking partially because of other outside interests in their lives that also take up time. This paper offers tips to help students relieve stress arising from the testing situation. Students…

Toxicological Tipping Points and Cell Stress (SOT 2016 Symposium Discriminating between adaptation and adversity))

EPA Science Inventory

This symposium will bring together cutting-edge ideas on HCI as alternative testing paradigm for predictive toxicology and will focus on: 1) innovative tools for interrogating the molecular and cellular state of cells; 2) evaluating sentinel stress response pathways that can prof...

Behavior of Fatigue Crack Tip Opening in Air and Corrosive Atmosphere

NASA Astrophysics Data System (ADS)

Hayashi, Morihito; Toeda, Kazunori

In the study, a formula for predicting fatigue crack tip opening displacement is deduced firstly. And then, due to comparing actual crack growth rate with the deduced formula, the crack tip configuration factor is defined to figure out the crack tip opening configuration that is useful to clarify the behavior of fatigue crack tip formation apparently. Applying the concept, the crack growth of 7/3 brass and 6/4 brass is predicted from the formula, by replacing material properties such as plastic flow resistance, Young modulus, the Poisson ratio, and fatigue toughness, and fatigue test conditions such as the stress intensity factor range, the load ratio, and cycle frequency. Furthermore, the theoretically expected results are verified with the fatigue tests which were carried out on CT specimens under different load conditions of load ratio, cycle frequency, and cyclic peak load, in different environments of air or corrosive ammonia atmosphere, for various brasses. And by comparing and discussing the calculated crack growth rate with attained experimental results, the apparent configuration factor at the crack tip is determined. And through the attained factor which changes along with crack growth, the behaviors of fatigue crack tip formation under different test conditions have been found out.

Crack tip fracture toughness of base glasses for dental restoration glass-ceramics using crack opening displacements.

PubMed

Deubener, J; Höland, M; Höland, W; Janakiraman, N; Rheinberger, V M

2011-10-01

The critical stress intensity factor, also known as the crack tip toughness K(tip), was determined for three base glasses, which are used in the manufacture of glass-ceramics. The glasses included the base glass for a lithium disilicate glass-ceramic, the base glass for a fluoroapatite glass-ceramic and the base glass for a leucite glass-ceramic. These glass-ceramic are extensively used in the form of biomaterials in restorative dental medicine. The crack tip toughness was established by using crack opening displacement profiles under experimental conditions. The crack was produced by Vickers indentation. The crack tip toughness parameters determined for the three glass-ceramics differed quite significantly. The crack tip parameters of the lithium disilicate base glass and the leucite base glass were higher than that of the fluoroapatite base glass. This last material showed glass-in-glass phase separation. The discussion of the results clearly shows that the droplet glass phase is softer than the glass matrix. Therefore, the authors conclude that a direct relationship exists between the chemical nature of the glasses and the crack tip parameter. Copyright © 2011 Elsevier Ltd. All rights reserved.

Tonoplast-Bound Protein Kinase Phosphorylates Tonoplast Intrinsic Protein 1

PubMed Central

Johnson, Kenneth D.; Chrispeels, Maarten J.

1992-01-01

Tonoplast intrinsic protein (TIP) is a member of a family of putative membrane channels found in bacteria, animals, and plants. Plants have seed-specific, vegetative/reproductive organ-specific, and water-stress-induced forms of TIP. Here, we report that the seed-specific TIP is a phosphoprotein whose phosphorylation can be monitored in vivo by allowing bean cotyledons to take up [32P]orthophosphate and in vitro by incubating purified tonoplasts with γ-labeled [32P]ATP. Characterization of the in vitro phosphorylation of TIP indicates that a membrane-bound protein kinase phosphorylates TIP in a Ca2+-dependent manner. The capacity of the isolated tonoplast membranes to phosphorylate TIP declined markedly during seed germination, and this decline occurred well before the development-mediated decrease in TIP occurs. Phosphoamino acid analysis of purified, radiolabeled TIP showed that serine is the major, if not only, phosphorylated residue, and cyanogen bromide cleavage yielded a single radioactive peptide peak on a reverse-phase high-performance liquid chromatogram. Estimation of the molecular mass of the cyanogen bromide phosphopeptide by laser desorption mass spectroscopy led to its identification as the hydrophilic N-terminal domain of TIP. The putative phosphate-accepting serine residue occurs in a consensus phosphorylation site for serine/threonine protein kinases. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 PMID:16653198

Assessment of arsenic toxicity using Allium/Vicia root tip micronucleus assays.

PubMed

Wu, Lihua; Yi, Huilan; Yi, Min

2010-04-15

Arsenic is ubiquitous in the environment and is a potential human carcinogen. Its carcinogenicity has been demonstrated in several models. In this study, broad bean (Vicia faba L.) and common onion (Allium cepa L.), two plant species which are commonly used for detecting the genotoxic effects of environmental pollutants, were used to measure possible genotoxic effect of arsenite (0.3-30 mg/l). Present results showed that arsenite (As(III)) induced micronuclei (MN) formation in both Allium and Vicia root tips. MN frequency significantly increased in Vicia root cells exposed to 0.3-10 mg/l arsenite and in Allium root cells exposed to 1-30 mg/l arsenite, which indicated that Vicia root tip cells are more sensitive to arsenite than Allium. Mitotic index (MI) decreased in a concentration-dependent manner and showed significant differences in Vicia/Allium roots among treatments and the control, after exposure to 1-30 mg/l arsenite for at least 4 h. In the present study, MN frequency was positively associated with lipid peroxidation, which indicated that arsenite exposure can induce oxidative stress, cytotoxicity and genotoxicity in plant cells. The results also suggested that Vicia/Allium root micronucleus (MN) assays are simple, efficient and reproducible methods for the genotoxicity monitoring of arsenic water contamination. 2009 Elsevier B.V. All rights reserved.

Generating Fatigue Crack Growth Thresholds with Constant Amplitude Loads

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Newman, James C., J.; Forman, Royce G.

2002-01-01

The fatigue crack growth threshold, defining crack growth as either very slow or nonexistent, has been traditionally determined with standardized load reduction methodologies. Some experimental procedures tend to induce load history effects that result in remote crack closure from plasticity. This history can affect the crack driving force, i.e. during the unloading process the crack will close first at some point along the wake, reducing the effective load at the crack tip. One way to reduce the effects of load history is to propagate a crack under constant amplitude loading. As a crack propagates under constant amplitude loading, the stress intensity factor, K, will increase, as will the crack growth rate, da/dN. A fatigue crack growth threshold test procedure is developed and experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R.

Aging of XLPE cable insulation under combined electrical and mechanical stresses

DOE Office of Scientific and Technical Information (OSTI.GOV)

David, E.; Parpal, J.L.; Crine, J.P.

1996-12-31

Extruded crosslinked polyethylene (XLPE) insulation is widely used in high-voltage cables since it presents such attractive features as excellent dielectric properties and good thermomechanical behavior. However, its performance is affected by long-term degradation when it is subjected to the various thermal, mechanical and environmental stresses occurring in service in combination with electrical stress. The synergetic effect of superposed electrical and other stresses remains to be fully clarified. In particular, a fairly high level of mechanical stresses can be present in the insulation volume, originating from residual internal stresses created during the cooling process in the fabrication, external forces when cablesmore » are bent sharply, or thermomechanical stresses caused by differential thermal expansion between the conductor and the insulating material. In order to investigate the influence of the superposition of mechanical and electrical stresses, various measurements were conducted on XLPE and LDPE specimens in tip-plane and plane-plane geometries. Experimental data of time-to-breakdown, breakdown field and tree length are presented as a function of the magnitude of the stresses. In all cases, superposition of the mechanical stress was found to reduce the dielectric strength of the material.« less

Hyper- and viscoelastic modeling of needle and brain tissue interaction.

PubMed

Lehocky, Craig A; Yixing Shi; Riviere, Cameron N

2014-01-01

Deep needle insertion into brain is important for both diagnostic and therapeutic clinical interventions. We have developed an automated system for robotically steering flexible needles within the brain to improve targeting accuracy. In this work, we have developed a finite element needle-tissue interaction model that allows for the investigation of safe parameters for needle steering. The tissue model implemented contains both hyperelastic and viscoelastic properties to simulate the instantaneous and time-dependent responses of brain tissue. Several needle models were developed with varying parameters to study the effects of the parameters on tissue stress, strain and strain rate during needle insertion and rotation. The parameters varied include needle radius, bevel angle, bevel tip fillet radius, insertion speed, and rotation speed. The results will guide the design of safe needle tips and control systems for intracerebral needle steering.

Stable tearing behavior of a thin-sheet material with multiple cracks

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Newman, J. C., Jr.; Sutton, M. A.; Amstutz, B. E.

1994-01-01

Fracture tests were conducted on 2.3mm thick, 305mm wide sheets of 2024-T3 aluminum alloy with 1-5 collinear cracks. The cracks were introduced (crack history) into the specimens by three methods: (1) saw cutting; (2) fatigue precracking at a low stress range; and (3) fatigue precracking at a high stress range. For the single crack tests, the initial crack history influenced the stress required for the onset of stable crack growth and the first 10mm of crack growth. The effect on failure stress was about 4 percent or less. For the multiple crack tests, the initial crack history was shown to cause differences of more than 20 percent in the link-up stress and 13 percent in failure stress. An elastic-plastic finite element analysis employing the Crack Tip Opening Angle (CTOA) fracture criterion was used to predict the fracture behavior of the single and multiple crack tests. The numerical predictions were within 7 percent of the observed link-up and failure stress in all the tests.

Statolith positioning by microfilaments in Chara rhizoids and protonemata

NASA Astrophysics Data System (ADS)

Hodick, Dieter; Buchen, Brigitte; Sievers, Andreas

The rhizoids of the green alga Chara are tip-growing cells with a precise positive gravitropism. In rhizoids growing downwards the statoliths never sediment upon the cell wall at the very tip but keep a minimal distance of approximately 10 μm from the cell vertex. It has been argued that this position is attained by a force acting upon the statoliths in the basal direction and that this force is generated by an interaction between actin microfilaments and myosin on the statolith membrane. This hypothesis received experimental support from (1) effects of the actin-attacking drug cytochalasin, (2) experiments under microgravity conditions, and (3) clinostat experiments. Using video-microscopy it is now shown that this basipetal force also acts on statoliths during sedimentation. As a result, many statoliths in Chara rhizoids do not simply fall along the plumb line while sedimenting during gravistimulation, but move basipetally. This statolith movement is compared to the ones occurring in the unicellular Chara protonemata during gravistimulation. Dark-grown protonemata morphologically closely resemble the rhizoids but respond negatively gravitropic. In contrast to the rhizoids a gravistimulation of the protonemata induces a transport of statoliths towards the tip. This transport is mainly along the cell axis and not parallel to the gravity vector. It is stressed that the sedimentation of statoliths in Chara rhizoids and protonemata as well as in gravity sensing cells in mosses and higher plants is accompanied by statolith movements based on interactions with the cytoskeleton. In tip-growing cells these movements direct the statoliths to a definite region of the cell where they can sediment and elicit a gravitropic curvature. In the statocytes of higher plants the interactions of the statoliths with the cytoskeleton probably do not serve primarily to move the statoliths but to transduce mechanical stresses from the sedimenting statoliths to the plasma membrane.

Statolith positioning by microfilaments in Chara rhizoids and protonemata.

PubMed

Hodick, D; Buchen, B; Sievers, A

1998-01-01

The rhizoids of the green alga Chara are tip-growing cells with a precise positive gravitropism. In rhizoids growing downwards the statoliths never sediment upon the cell wall at the very tip but keep a minimal distance of approximately 10 micrometers from the cell vertex. It has been argued that this position is attained by a force acting upon the statoliths in the basal direction and that this force is generated by an interaction between actin microfilaments and myosin on the statolith membrane. This hypothesis received experimental support from (1) effects of the actin-attacking drug cytochalasin, (2) experiments under microgravity conditions, and (3) clinostat experiments. Using video-microscopy it is now shown that this basipetal force also acts on statoliths during sedimentation. As a result, many statoliths in Chara rhizoids do not simply fall along the plumb line while sedimenting during gravistimulation, but move basipetally. This statolith movement is compared to the ones occurring in the unicellular Chara protonemata during gravistimulation. Dark-grown protonemata morphologically closely resemble the rhizoids but respond negatively gravitropic. In contrast to the rhizoids a gravistimulation of the protonemata induces a transport of statoliths towards the tip. This transport is mainly along the cell axis and not parallel to the gravity vector. It is stressed that the sedimentation of statoliths in Chara rhizoids and protonemata as well as in gravity sensing cells in mosses and higher plants is accompanied by statolith movements based on interactions with the cytoskeleton. In tip-growing cells these movements direct the statoliths to a definite region of the cell where they can sediment and elicit a gravitropic curvature. In the statocytes of higher plants the interactions of the statoliths with the cytoskeleton probably do not serve primarily to move the statoliths but to transduce mechanical stresses from the sedimenting statoliths to the plasma membrane.

Selection and Validation of Appropriate Reference Genes for Quantitative Real-Time PCR Analysis of Gene Expression in Lycoris aurea

PubMed Central

Ma, Rui; Xu, Sheng; Zhao, Yucheng; Xia, Bing; Wang, Ren

2016-01-01

Lycoris aurea (L' Hér.) Herb, a perennial grass species, produces a unique variety of pharmacologically active Amaryllidaceae alkaloids. However, the key enzymes and their expression pattern involved in the biosynthesis of Amaryllidaceae alkaloids (especially for galanthamine) are far from being fully understood. Quantitative real-time polymerase chain reaction (qRT-PCR), a commonly used method for quantifying gene expression, requires stable reference genes to normalize its data. In this study, to choose the appropriate reference genes under different experimental conditions, 14 genes including YLS8 (mitosis protein YLS8), CYP2 (Cyclophilin 2), CYP 1 (Cyclophilin 1), TIP41 (TIP41-like protein), EXP2 (Expressed protein 2), PTBP1 (Polypyrimidine tract-binding protein 1), EXP1 (Expressed protein 1), PP2A (Serine/threonine-protein phosphatase 2A), β-TUB (β-tubulin), α-TUB (α-tubulin), EF1-α (Elongation factor 1-α), UBC (Ubiquitin-conjugating enzyme), ACT (Actin) and GAPDH (Glyceraldehyde 3-phosphate dehydrogenase) were selected from the transcriptome datasets of L. aurea. And then, expressions of these genes were assessed by qRT-PCR in various tissues and the roots under different treatments. The expression stability of the 14 candidates was analyzed by three commonly used software programs (geNorm, NormFinder, and BestKeeper), and their results were further integrated into a comprehensive ranking based on the geometric mean. The results show the relatively stable genes for each subset as follows: (1) EXP1 and TIP41 for all samples; (2) UBC and EXP1 for NaCl stress; (3) PTBP1 and EXP1 for heat stress, polyethylene glycol (PEG) stress and ABA treatment; (4) UBC and CYP2 for cold stress; (5) PTBP1 and PP2A for sodium nitroprusside (SNP) treatment; (6) CYP1 and TIP41 for methyl jasmonate (MeJA) treatment; and (7) EXP1 and TIP41 for various tissues. The reliability of these results was further enhanced through comparison between part qRT-PCR result and RNA sequencing (RNA-seq) data. In summary, our results identified appropriate reference genes for qRT-PCR in L. aurea, and will facilitate gene expression studies under these conditions. PMID:27200013

Acoustic emission studies for characterization of fatigue crack growth behavior in HSLA steel

NASA Astrophysics Data System (ADS)

Kumar, Jalaj; Ahmad, S.; Mukhopadhyay, C. K.; Jayakumar, T.; Kumar, Vikas

2016-01-01

High strength low alloy (HSLA) steels are a group of low carbon steels and used in oil and gas pipelines, automotive components, offshore structures and shipbuilding. Fatigue crack growth (FCG) characteristics of a HSLA steel have been studied at two different stress ratios (R = 0.3 and 0.5). Acoustic emission (AE) signals generated during the FCG tests have been used to understand the FCG processes. The AE signals were captured by mounting two piezoelectric sensors on compact tension specimens in liner location configuration. The AE generated in stage II of the linear Paris region of FCG has been attributed to the presence of two sub-stages with two different slopes. The AE generated at higher values of stress intensity factor is found to be useful to identify the transition from stage II to stage III of the FCG. AE location analysis has provided support for increased damage at the crack tip for higher stress ratio. The peak stress intensity (Kmax) values at the crack tip have shown good correlation with the transitions from stage IIa to stage IIb and stage II to stage III of the FCG for the two stress ratios.

Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

NASA Technical Reports Server (NTRS)

Chen, QI; Liu, Hao-Wen

1988-01-01

Fatigue crack growth in large grain Al alloy was studied. Fatigue crack growth is caused primarily by shear decohesion due to dislocation motion in the crack tip region. The crack paths in the large crystals are very irregular and zigzag. The crack planes are often inclined to the loading axis both in the inplane direction and the thickness direction. The stress intensity factors of such inclined cracks are approximated from the two dimensional finite element calculations. The plastic deformation in a large crystal is highly anisotropic, and dislocation motion in such crystals are driven by the resolved shear stress. The resolved shear stress intensity coefficient in a crack solid, RSSIC, is defined, and the coefficients for the slip systems at a crack tip are evaluated from the calculated stress intensity factors. The orientations of the crack planes are closely related to the slip planes with the high RSSIC values. If a single slip system has a much higher RSSIC than all the others, the crack will follow the slip plane, and the slip plane becomes the crack plane. If two or more slip systems have a high RSSIC, the crack plane is the result of the decohesion processes on these active slip planes.

Computational modelling of flow and tip variations of aortic cannulae in cardiopulmonary bypass procedure

NASA Astrophysics Data System (ADS)

Thomas, Siti A.; Empaling, Shirly; Darlis, Nofrizalidris; Osman, Kahar; Dillon, Jeswant; Taib, Ishkrizat; Khudzari, Ahmad Zahran Md

2017-09-01

Aortic cannulation has been the gold standard for maintaining cardiovascular function during open heart surgery while being connected onto the heart lung machine. These cannulation produces high velocity outflow which may lead to adverse effect on patient condition, especially sandblasting effect on aorta wall and blood cells damage. This paper reports a novel design that was able to decrease high velocity outflow. There were three design factors of that was investigated. The design factors consist of the cannula type, the flow rate, and the cannula tip design which result in 12 variations. The cannulae type used were the spiral flow inducing cannula and the standard cannula. The flow rates are varied from three to five litres per minute (lpm). Parameters for each cannula variation included maximum velocity within the aorta, pressure drop, wall shear stress (WSS) area exceeding 15 Pa, and impinging velocity on the aorta wall were evaluated. Based on the result, spiral flow inducing cannulae is proposed as a better alternatives due to its ability to reduce outflow velocity. Meanwhile, the pressure drop of all variations are less than the limit of 100 mmHg, although standard cannulae yielded better result. All cannulae show low reading of wall shear stress which decrease the possibilities for atherogenesis formation. In conclusion, as far as velocity is concerned, spiral flow is better compared to standard flow across all cannulae variations.

Single versus successive pop-in modes in nanoindentation tests of single crystals

DOE PAGES

Xia, Yuzhi; Gao, Yanfei; Pharr, George M.; ...

2016-05-24

From recent nanoindentation experiments, two types of pop-in modes have been identified: a single pop-in with a large displacement excursion, or a number of pop-ins with comparable and small displacement excursions. Theoretical analyses are developed here to study the roles played by indenter tip radius, pre-existing defect density, heterogeneous nucleation source type, and lattice resistance on the pop-in modes. The evolution of dislocation structures in earlier pop-ins provides input to modeling a stochastic, heterogeneous mechanism that may be responsible for the subsequent pop-ins. It is found that when the first pop-in occurs near theoretical shear stress, the pop-in mode ismore » determined by the lattice resistance and tip radius. When the first pop-in occurs at low shear stress, whether the successive pop-in mode occurs depends on how the heterogeneous dislocation nucleation source density increases as compared to the increase of the total dislocation density. Lastly, the above transitions are found to correlate well with the ratio of indenter tip radius to the mean spacing of dislocation nucleation sources.« less

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE PAGES

Gao, Yanfei

2015-11-30

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Yanfei

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Single-shot pressure-sensitive paint lifetime measurements on fast rotating blades using an optimized double-shutter technique

NASA Astrophysics Data System (ADS)

Weiss, Armin; Geisler, Reinhard; Schwermer, Till; Yorita, Daisuke; Henne, Ulrich; Klein, Christian; Raffel, Markus

2017-09-01

A pressure-sensitive paint (PSP) system is presented to measure global surface pressures on fast rotating blades. It is dedicated to solve the problem of blurred image data employing the single-shot lifetime method. The efficient blur reduction capability of an optimized double-shutter imaging technique is demonstrated omitting error-prone post-processing or laborious de-rotation setups. The system is applied on Mach-scaled DSA-9A helicopter blades in climb at various collective pitch settings and blade tip Mach and chord Reynolds numbers (M_{ {tip}} = 0.29-0.57; Re_{ {tip}} = 4.63-9.26 × 10^5). Temperature effects in the PSP are corrected by a theoretical approximation validated against measured temperatures using temperature-sensitive paint (TSP) on a separate blade. Ensemble-averaged PSP results are comparable to pressure-tap data on the same blade to within 250 Pa. Resulting pressure maps on the blade suction side reveal spatially high resolved flow features such as the leading edge suction peak, footprints of blade-tip vortices and evidence of laminar-turbulent boundary-layer (BL) transition. The findings are validated by a separately conducted BL transition measurement by means of TSP and numerical simulations using a 2D coupled Euler/boundary-layer code. Moreover, the principal ability of the single-shot technique to capture unsteady flow phenomena is stressed revealing three-dimensional pressure fluctuations at stall.

Effect of Measured Welding Residual Stresses on Crack Growth

NASA Technical Reports Server (NTRS)

Hampton, Roy W.; Nelson, Drew; Doty, Laura W. (Technical Monitor)

1998-01-01

Welding residual stresses in thin plate A516-70 steel and 2219-T87 aluminum butt weldments were measured by the strain-gage hole drilling and X-ray diffraction methods. The residual stress data were used to construct 3D strain fields which were modeled as thermally induced strains. These 3D strain fields were then analyzed with the WARP31) FEM fracture analysis code in order to predict their effect on fatigue and on fracture. For analyses of fatigue crack advance and subsequent verification testing, fatigue crack growth increments were simulated by successive saw-cuts and incremental loading to generate, as a function of crack length, effects on crack growth of the interaction between residual stresses and load induced stresses. The specimen experimental response was characterized and compared to the WARM linear elastic and elastic-plastic fracture mechanics analysis predictions. To perform the fracture analysis, the plate material's crack tearing resistance was determined by tests of thin plate M(T) specimens. Fracture analyses of these specimen were performed using WARP31D to determine the critical Crack Tip Opening Angle [CTOA] of each material. These critical CTOA values were used to predict crack tearing and fracture in the weldments. To verify the fracture predictions, weldment M(T) specimen were tested in monotonic loading to fracture while characterizing the fracture process.

Genome-Wide Characterization and Expression Analysis of Major Intrinsic Proteins during Abiotic and Biotic Stresses in Sweet Orange (Citrus sinensis L. Osb.)

PubMed Central

de Paula Santos Martins, Cristina; Pedrosa, Andresa Muniz; Du, Dongliang; Gonçalves, Luana Pereira; Yu, Qibin; Gmitter, Frederick G.; Costa, Marcio Gilberto Cardoso

2015-01-01

The family of aquaporins (AQPs), or major intrinsic proteins (MIPs), includes integral membrane proteins that function as transmembrane channels for water and other small molecules of physiological significance. MIPs are classified into five subfamilies in higher plants, including plasma membrane (PIPs), tonoplast (TIPs), NOD26-like (NIPs), small basic (SIPs) and unclassified X (XIPs) intrinsic proteins. This study reports a genome-wide survey of MIP encoding genes in sweet orange (Citrus sinensis L. Osb.), the most widely cultivated Citrus spp. A total of 34 different genes encoding C. sinensis MIPs (CsMIPs) were identified and assigned into five subfamilies (CsPIPs, CsTIPs, CsNIPs, CsSIPs and CsXIPs) based on sequence analysis and also on their phylogenetic relationships with clearly classified MIPs of Arabidopsis thaliana. Analysis of key amino acid residues allowed the assessment of the substrate specificity of each CsMIP. Gene structure analysis revealed that the CsMIPs possess an exon-intron organization that is highly conserved within each subfamily. CsMIP loci were precisely mapped on every sweet orange chromosome, indicating a wide distribution of the gene family in the sweet orange genome. Investigation of their expression patterns in different tissues and upon drought and salt stress treatments, as well as with ‘Candidatus Liberibacter asiaticus’ infection, revealed a tissue-specific and coordinated regulation of the different CsMIP isoforms, consistent with the organization of the stress-responsive cis-acting regulatory elements observed in their promoter regions. A special role in regulating the flow of water and nutrients is proposed for CsTIPs and CsXIPs during drought stress, and for most CsMIPs during salt stress and the development of HLB disease. These results provide a valuable reference for further exploration of the CsMIPs functions and applications to the genetic improvement of both abiotic and biotic stress tolerance in citrus. PMID:26397813

Genome-Wide Characterization and Expression Analysis of Major Intrinsic Proteins during Abiotic and Biotic Stresses in Sweet Orange (Citrus sinensis L. Osb.).

PubMed

Martins, Cristina de Paula Santos; Pedrosa, Andresa Muniz; Du, Dongliang; Gonçalves, Luana Pereira; Yu, Qibin; Gmitter, Frederick G; Costa, Marcio Gilberto Cardoso

2015-01-01

The family of aquaporins (AQPs), or major intrinsic proteins (MIPs), includes integral membrane proteins that function as transmembrane channels for water and other small molecules of physiological significance. MIPs are classified into five subfamilies in higher plants, including plasma membrane (PIPs), tonoplast (TIPs), NOD26-like (NIPs), small basic (SIPs) and unclassified X (XIPs) intrinsic proteins. This study reports a genome-wide survey of MIP encoding genes in sweet orange (Citrus sinensis L. Osb.), the most widely cultivated Citrus spp. A total of 34 different genes encoding C. sinensis MIPs (CsMIPs) were identified and assigned into five subfamilies (CsPIPs, CsTIPs, CsNIPs, CsSIPs and CsXIPs) based on sequence analysis and also on their phylogenetic relationships with clearly classified MIPs of Arabidopsis thaliana. Analysis of key amino acid residues allowed the assessment of the substrate specificity of each CsMIP. Gene structure analysis revealed that the CsMIPs possess an exon-intron organization that is highly conserved within each subfamily. CsMIP loci were precisely mapped on every sweet orange chromosome, indicating a wide distribution of the gene family in the sweet orange genome. Investigation of their expression patterns in different tissues and upon drought and salt stress treatments, as well as with 'Candidatus Liberibacter asiaticus' infection, revealed a tissue-specific and coordinated regulation of the different CsMIP isoforms, consistent with the organization of the stress-responsive cis-acting regulatory elements observed in their promoter regions. A special role in regulating the flow of water and nutrients is proposed for CsTIPs and CsXIPs during drought stress, and for most CsMIPs during salt stress and the development of HLB disease. These results provide a valuable reference for further exploration of the CsMIPs functions and applications to the genetic improvement of both abiotic and biotic stress tolerance in citrus.

An Intergenic Region Shared by At4g35985 and At4g35987 in Arabidopsis thaliana Is a Tissue Specific and Stress Inducible Bidirectional Promoter Analyzed in Transgenic Arabidopsis and Tobacco Plants

PubMed Central

Banerjee, Joydeep; Sahoo, Dipak Kumar; Dey, Nrisingha; Houtz, Robert L.; Maiti, Indu Bhushan

2013-01-01

On chromosome 4 in the Arabidopsis genome, two neighboring genes (calmodulin methyl transferase At4g35987 and senescence associated gene At4g35985) are located in a head-to-head divergent orientation sharing a putative bidirectional promoter. This 1258 bp intergenic region contains a number of environmental stress responsive and tissue specific cis-regulatory elements. Transcript analysis of At4g35985 and At4g35987 genes by quantitative real time PCR showed tissue specific and stress inducible expression profiles. We tested the bidirectional promoter-function of the intergenic region shared by the divergent genes At4g35985 and At4g35987 using two reporter genes (GFP and GUS) in both orientations in transient tobacco protoplast and Agro-infiltration assays, as well as in stably transformed transgenic Arabidopsis and tobacco plants. In transient assays with GFP and GUS reporter genes the At4g35985 promoter (P85) showed stronger expression (about 3.5 fold) compared to the At4g35987 promoter (P87). The tissue specific as well as stress responsive functional nature of the bidirectional promoter was evaluated in independent transgenic Arabidopsis and tobacco lines. Expression of P85 activity was detected in the midrib of leaves, leaf trichomes, apical meristemic regions, throughout the root, lateral roots and flowers. The expression of P87 was observed in leaf-tip, hydathodes, apical meristem, root tips, emerging lateral root tips, root stele region and in floral tissues. The bidirectional promoter in both orientations shows differential up-regulation (2.5 to 3 fold) under salt stress. Use of such regulatory elements of bidirectional promoters showing spatial and stress inducible promoter-functions in heterologous system might be an important tool for plant biotechnology and gene stacking applications. PMID:24260266

Study of mechanical behavior of AFM silicon tips under mechanical load

NASA Astrophysics Data System (ADS)

Kopycinska-Mueller, M.; Gluch, J.; Köhler, B.

2016-11-01

In this paper we address critical issues concerning calibration of AFM based methods used for nanoscale mechanical characterization of materials. It has been shown that calibration approaches based on macroscopic models for contact mechanics may yield excellent results in terms of the indentation modulus of the sample, but fail to provide a comprehensive and actual information concerning the tip-sample contact radius or the mechanical properties of the tip. Explanations for the severely reduced indentation modulus of the tip included the inadequacies of the models used for calculations of the tip-sample contact stiffness, discrepancies in the actual and ideal shape of the tip, presence of the amorphous silicon phase within the silicon tip, as well as negligence of the actual size of the stress field created in the tip during elastic interactions. To clarify these issues, we investigated the influence of the mechanical load applied to four AFM silicon tips on their crystalline state by exposing them to systematically increasing loads, evaluating the character of the tip-sample interactions via the load-unload stiffness curves, and assessing the state of the tips from HR-TEM images. The results presented in this paper were obtained in a series of relatively simple and basic atomic force acoustic microscopy (AFAM) experiments. The novel combination of TEM imaging of the AFM tips with the analysis of the load-unload stiffness curves gave us a detailed insight into their mechanical behavior under load conditions. We were able to identify the limits for the elastic interactions, as well as the hallmarks for phase transformation and dislocation formation and movement. The comparison of the physical dimensions of the AFM tips, geometry parameters determined from the values of the contact stiffness, and the information on the crystalline state of the tips allowed us a better understanding of the nanoscale contact.

RNA-seq for gene identification and transcript profiling in relation to root growth of bermudagrass (Cynodon dactylon) under salinity stress.

PubMed

Hu, Longxing; Li, Huiying; Chen, Liang; Lou, Yanhong; Amombo, Erick; Fu, Jinmin

2015-08-04

Soil salinity is one of the most significant abiotic stresses affecting plant shoots and roots growth. The adjustment of root architecture to spatio-temporal heterogeneity in salinity is particularly critical for plant growth and survival. Bermudagrass (Cynodon dactylon) is a widely used turf and forage perennial grass with a high degree of salinity tolerance. Salinity appears to stimulate the growth of roots and decrease their mortality in tolerant bermudagrass. To estimate a broad spectrum of genes related to root elongation affected by salt stress and the molecular mechanisms that control the positive response of root architecture to salinity, we analyzed the transcriptome of bermudagrass root tips in response to salinity. RNA-sequencing was performed in root tips of two bermudagrass genotypes contrasting in salt tolerance. A total of 237,850,130 high quality clean reads were generated and 250,359 transcripts were assembled with an average length of 1115 bp. Totally, 103,324 unigenes obtained with 53,765 unigenes (52 %) successfully annotated in databases. Bioinformatics analysis indicated that major transcription factor (TF) families linked to stress responses and growth regulation (MYB, bHLH, WRKY) were differentially expressed in root tips of bermudagrass under salinity. In addition, genes related to cell wall loosening and stiffening (xyloglucan endotransglucosylase/hydrolases, peroxidases) were identified. RNA-seq analysis identified candidate genes encoding TFs involved in the regulation of lignin synthesis, reactive oxygen species (ROS) homeostasis controlled by peroxidases, and the regulation of phytohormone signaling that promote cell wall loosening and therefore root growth under salinity.

Crack curving in a ductile pressurized fuselage

NASA Astrophysics Data System (ADS)

Lam, Paul W.

Moire interferometry was used to study crack tip displacement fields of a biaxially loaded cruciform type 0.8mm thick 2024-T3 aluminum specimen with various tearstrap reinforcement configurations: Unreinforced, Bonded, Bonded+Riveted, and Machined Pad-up. A program was developed using the commercially available code Matlab to derive strain, stress, and integral parameters from the experimental displacements. An FEM model of the crack tip area, with experimental displacements as boundary conditions, was used to validate FEM calculations of crack tip parameters. The results indicate that T*-integral parameter reaches a value of approximately 120 MPa-m0.5 during stable crack propagation which agrees with previously published values for straight cracks in the same material. The approximate computation method employed in this study uses a partial contour around the crack tip that neglects the contribution from the portion behind the crack tip where there is significant unloading. Strain distributions around the crack tip were obtained from experimental displacements and indicate that Maximum Principal Strain or Equivalent Strain can predict the direction of crack propagation, and is generally comparable with predictions using the Erdogan-Sih and Kosai-Ramulu-Kobayashi criteria. The biaxial tests to failure showed that the Machined Pad-up specimen carried the highest load, with the Bonded specimen next, at 78% of the Machined Pad-up value. The Bonded+Riveted specimen carried a lower load than the Bonded, at 67% of the Machined Pad-up value, which was the same as that carried by the Unreinforced specimen. The tearstraps of the bonded specimens remained intact after the specimen failed while the integrally machined reinforcement broke with the specimen. FEM studies were also made of skin flapping in typical Narrow and Wide-body fuselage sections, both containing the same crack path from a full-scale fatigue test of a Narrow-body fuselage. Results indicate that the magnitude of CTOA and CTOD depends on the structural geometry, and including plasticity increases the crack tip displacements. An estimate of the strain in the skin flaps at the crack tip may indicate the tendency for flapping. Out-of-plane effects become significant as the crack propagates and curves.

Influences of semiconductor morphology on the mechanical fatigue behavior of flexible organic electronics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Young-Joo; Yeon, Han-Wool; Shin, Hae-A-Seul

2013-12-09

The influence of crystalline morphology on the mechanical fatigue of organic semiconductors (OSCs) was investigated using 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as a crystalline OSC and poly(triarylamine) (PTAA) as an amorphous OSC. During cyclic bending, resistances of the OSCs were monitored using the transmission-line method on a metal-semiconductor-metal structure. The resistance of the TIPS-pentacene increased under fatigue damage in tensile-stress mode, but no such degradation was observed in the PTAA. Both OSCs were stable under compressive bending fatigue. The formation of intergranular cracks at the domain boundaries of the TIPS-pentacene was responsible for the degradation of its electrical properties under tensile bending fatigue.

Response of Main Maize Varieties to Water Stress and Comprehensive Evaluation in Hebei Province

NASA Astrophysics Data System (ADS)

Yue, Haiwang; Chen, Shuping; Bu, Junzhou; Wei, Jianwei; Peng, Haicheng; Li, Yuan; Li, Chunjie; Xie, Junliang

2018-01-01

Drought is a serious threat to maize production in Hebei province. Planting drought resistant maize varieties is an effective measure to solve drought in arid and less rain areas. Drought resistance in maize is controlled by many genes, and multiple indexes should be used for comprehensive evaluation (Campos H et al.2004). In the arid rain shed, using 34 maize varieties to promote crop production compared to the drought resistance test. The experiment was conducted with two treatments of drought stress (irrigation only at seedling stage) and normal irrigation, and 12 agronomic traits related to drought resistance of maize were determined. The results showed that drought had significant effects on maize yield and main agronomic characters. Under drought stress, plant height, ear length, bare tip, ear row number, row grains, 1000-kernel weight, ASI index can be used as identification index of drought resistance of maize in different period. The results indicated that the variety with strong drought resistance is Zhongdi175, the worst drought resistance is Woyu964.

Investigation of translaminar fracture in fibrereinforced composite laminates---applicability of linear elastic fracture mechanics and cohesive-zone model

NASA Astrophysics Data System (ADS)

Hou, Fang

With the extensive application of fiber-reinforced composite laminates in industry, research on the fracture mechanisms of this type of materials have drawn more and more attentions. A variety of fracture theories and models have been developed. Among them, the linear elastic fracture mechanics (LEFM) and cohesive-zone model (CZM) are two widely-accepted fracture models, which have already shown applicability in the fracture analysis of fiber-reinforced composite laminates. However, there remain challenges which prevent further applications of the two fracture models, such as the experimental measurement of fracture resistance. This dissertation primarily focused on the study of the applicability of LEFM and CZM for the fracture analysis of translaminar fracture in fibre-reinforced composite laminates. The research for each fracture model consisted of two sections: the analytical characterization of crack-tip fields and the experimental measurement of fracture resistance parameters. In the study of LEFM, an experimental investigation based on full-field crack-tip displacement measurements was carried out as a way to characterize the subcritical and steady-state crack advances in translaminar fracture of fiber-reinforced composite laminates. Here, the fiber-reinforced composite laminates were approximated as anisotropic solids. The experimental investigation relied on the LEFM theory with a modification with respect to the material anisotropy. Firstly, the full-field crack-tip displacement fields were measured by Digital Image Correlation (DIC). Then two methods, separately based on the stress intensity approach and the energy approach, were developed to measure the crack-tip field parameters from crack-tip displacement fields. The studied crack-tip field parameters included the stress intensity factor, energy release rate and effective crack length. Moreover, the crack-growth resistance curves (R-curves) were constructed with the measured crack-tip field parameters. In addition, an error analysis was carried out with an emphasis on the influence of out-of-plane rotation of specimen. In the study of CZM, two analytical inverse methods, namely the field projection method (FPM) and the separable nonlinear least-squares method, were developed for the extraction of cohesive fracture properties from crack-tip full-field displacements. Firstly, analytical characterizations of the elastic fields around a crack-tip cohesive zone and the cohesive variables within the cohesive zone were derived in terms of an eigenfunction expansion. Then both of the inverse methods were developed based on the analytical characterization. With the analytical inverse methods, the cohesive-zone law (CZL), cohesive-zone size and position can be inversely computed from the cohesive-crack-tip displacement fields. In the study, comprehensive numerical tests were carried out to investigate the applicability and robustness of two inverse methods. From the numerical tests, it was found that the field projection method was very sensitive to noise and thus had limited applicability in practice. On the other hand, the separable nonlinear least-squares method was found to be more noise-resistant and less ill-conditioned. Subsequently, the applicability of separable nonlinear least-squares method was validated with the same translaminar fracture experiment for the study of LEFM. Eventually, it was found that the experimental measurements of R-curves and CZL showed a great agreement, in both of the fracture energy and the predicted load carrying capability. It thus demonstrated the validity of present research for the translaminar fracture of fiber-reinforced composite laminates.

Internet-based early intervention to prevent posttraumatic stress disorder in injury patients: randomized controlled trial.

PubMed

Mouthaan, Joanne; Sijbrandij, Marit; de Vries, Giel-Jan; Reitsma, Johannes B; van de Schoot, Rens; Goslings, J Carel; Luitse, Jan S K; Bakker, Fred C; Gersons, Berthold P R; Olff, Miranda

2013-08-13

Posttraumatic stress disorder (PTSD) develops in 10-20% of injury patients. We developed a novel, self-guided Internet-based intervention (called Trauma TIPS) based on techniques from cognitive behavioral therapy (CBT) to prevent the onset of PTSD symptoms. To determine whether Trauma TIPS is effective in preventing the onset of PTSD symptoms in injury patients. Adult, level 1 trauma center patients were randomly assigned to receive the fully automated Trauma TIPS Internet intervention (n=151) or to receive no early intervention (n=149). Trauma TIPS consisted of psychoeducation, in vivo exposure, and stress management techniques. Both groups were free to use care as usual (nonprotocolized talks with hospital staff). PTSD symptom severity was assessed at 1, 3, 6, and 12 months post injury with a clinical interview (Clinician-Administered PTSD Scale) by blinded trained interviewers and self-report instrument (Impact of Event Scale-Revised). Secondary outcomes were acute anxiety and arousal (assessed online), self-reported depressive and anxiety symptoms (Hospital Anxiety and Depression Scale), and mental health care utilization. Intervention usage was documented. The mean number of intervention logins was 1.7, SD 2.5, median 1, interquartile range (IQR) 1-2. Thirty-four patients in the intervention group did not log in (22.5%), 63 (41.7%) logged in once, and 54 (35.8%) logged in multiple times (mean 3.6, SD 3.5, median 3, IQR 2-4). On clinician-assessed and self-reported PTSD symptoms, both the intervention and control group showed a significant decrease over time (P<.001) without significant differences in trend. PTSD at 12 months was diagnosed in 4.7% of controls and 4.4% of intervention group patients. There were no group differences on anxiety or depressive symptoms over time. Post hoc analyses using latent growth mixture modeling showed a significant decrease in PTSD symptoms in a subgroup of patients with severe initial symptoms (n=20) (P<.001). Our results do not support the efficacy of the Trauma TIPS Internet-based early intervention in the prevention of PTSD symptoms for an unselected population of injury patients. Moreover, uptake was relatively low since one-fifth of individuals did not log in to the intervention. Future research should therefore focus on innovative strategies to increase intervention usage, for example, adding gameplay, embedding it in a blended care context, and targeting high-risk individuals who are more likely to benefit from the intervention. International Standard Randomized Controlled Trial Number (ISRCTN): 57754429; http://www.controlled-trials.com/ISRCTN57754429 (Archived by WebCite at http://webcitation.org/6FeJtJJyD).

The effects of micro-implant assisted rapid palatal expansion (MARPE) on the nasomaxillary complex--a finite element method (FEM) analysis.

PubMed

MacGinnis, Matt; Chu, Howard; Youssef, George; Wu, Kimberley W; Machado, Andre Wilson; Moon, Won

2014-08-29

Orthodontic palatal expansion appliances have been widely used with satisfactory and, most often, predictable clinical results. Recently, clinicians have successfully utilized micro-implants with palatal expander designs to work as anchors to the palate to achieve more efficient skeletal expansion and to decrease undesired dental effects. The purpose of the study was to use finite element method (FEM) to determine the stress distribution and displacement within the craniofacial complex when simulated conventional and micro-implant-assisted rapid palatal expansion (MARPE) expansion forces are applied to the maxilla. The simulated stress distribution produced within the palate and maxillary buttresses in addition to the displacement and rotation of the maxilla could then be analyzed to determine if micro-implants aid in skeletal expansion. A three-dimensional (3D) mesh model of the cranium with associated maxillary sutures was developed using computed tomography (CT) images and Mimics modeling software. To compare transverse expansion stresses in rapid palatal expansion (RPE) and MARPE, expansion forces were distributed to differing points on the maxilla and evaluated with ANSYS simulation software. The stresses distributed from forces applied to the maxillary teeth are distributed mainly along the trajectories of the three maxillary buttresses. In comparison, the MARPE showed tension and compression directed to the palate, while showing less rotation, and tipping of the maxillary complex. In addition, the conventional hyrax displayed a rotation of the maxilla around the teeth as opposed to the midpalatal suture of the MARPE. This data suggests that the MARPE causes the maxilla to bend laterally, while preventing unwanted rotation of the complex. In conclusion, the MARPE may be beneficial for hyperdivergent patients, or those that have already experienced closure of the midpalatal suture, who require palatal expansion and would worsen from buccal tipping of the teeth or maxillary complex.

Electrohydrodynamic and flow induced tip-streaming

NASA Astrophysics Data System (ADS)

Collins, Robert

2008-11-01

A liquid subjected to a strong electric field emits thin fluid jets from conical structures (Taylor cones) that form at its surface. Such behavior has both practical and fundamental implications, e.g. for raindrops in thunderclouds and in electrospray mass spectrometry. Theoretical analysis of the temporal development of such electrohydrodynamic (EHD) tip- streaming phenomena has been elusive given the large disparity in length scales between the macroscopic drops/films and the microscopic (nanoscopic) jets. Here, simulation and experiment are used to investigate the mechanisms of EHD tip-streaming from a film of finite conductivity. In the simulations, the full Taylor-Melcher leaky-dielectric model, which accounts for charge relaxation, is solved. Simulations show that tip- streaming does not occur for perfectly conducting or perfectly insulating liquids. Scaling laws for sizes of drops produced from the breakup of the thin jets is developed. Further, simulations demonstrate the critical role played by electrically induced surface shear stresses in the inception of tip-streaming. This invites a comparison to flow focusing, i.e. tip-streaming induced by co-flowing two fluids. The latter phenomenon is also investigated by simulation. In collaboration with Ronald Suryo, Exxon-Mobil; and Jeremy Jones, Michael Harris, and Osman Basaran, Purdue University.

Aspergillus oryzae AoSO is a novel component of stress granules upon heat stress in filamentous fungi.

PubMed

Huang, Hsiang-Ting; Maruyama, Jun-ichi; Kitamoto, Katsuhiko

2013-01-01

Stress granules are a type of cytoplasmic messenger ribonucleoprotein (mRNP) granule formed in response to the inhibition of translation initiation, which typically occurs when cells are exposed to stress. Stress granules are conserved in eukaryotes; however, in filamentous fungi, including Aspergillus oryzae, stress granules have not yet been defined. For this reason, here we investigated the formation and localization of stress granules in A. oryzae cells exposed to various stresses using an EGFP fusion protein of AoPab1, a homolog of Saccharomyces cerevisiae Pab1p, as a stress granule marker. Localization analysis showed that AoPab1 was evenly distributed throughout the cytoplasm under normal growth conditions, and accumulated as cytoplasmic foci mainly at the hyphal tip in response to stress. AoSO, a homolog of Neurospora crassa SO, which is necessary for hyphal fusion, colocalized with stress granules in cells exposed to heat stress. The formation of cytoplasmic foci of AoSO was blocked by treatment with cycloheximide, a known inhibitor of stress granule formation. Deletion of the Aoso gene had effects on the formation and localization of stress granules in response to heat stress. Our results suggest that AoSO is a novel component of stress granules specific to filamentous fungi. The authors would specially like to thank Hiroyuki Nakano and Kei Saeki for generously providing experimental and insightful opinions.

Alignment mechanism of carbon nanofibers produced by plasma-enhanced chemical-vapor deposition

NASA Astrophysics Data System (ADS)

Merkulov, Vladimir I.; Melechko, Anatoli V.; Guillorn, Michael A.; Lowndes, Douglas H.; Simpson, Michael L.

2001-10-01

We report experimental evidence showing a direct correlation between the alignment of carbon nanofibers (CNFs) prepared by plasma-enhanced chemical-vapor deposition and the location of the catalyst particle during CNF growth. In particular, we find that CNFs that have a catalyst particle at the tip (i.e., growth proceeds from the tip) align along the electric-field lines, whereas CNFs with the particle at the base (i.e., growth proceeds from the base) grow in random orientations. We propose a model that explains the alignment process as a result of a feedback mechanism associated with a nonuniform stress (part tensile, part compressive) that is created across the interface of the catalyst particle with the CNF due to electrostatic forces. Furthermore, we propose that the alignment seen recently in some dense CNF films is due to a crowding effect and is not directly the result of electrostatic forces.

The stress intensity factor for the double cantilever beam

NASA Technical Reports Server (NTRS)

Fichter, W. B.

1983-01-01

Fourier transforms and the Wiener-Hopf technique are used in conjunction with plane elastostatics to examine the singular crack tip stress field in the double cantilever beam (DCB) specimen. In place of the Dirac delta function, a family of functions which duplicates the important features of the concentrated forces without introducing unmanageable mathematical complexities is used as a loading function. With terms of order h-squared/a-squared retained in the series expansion, the dimensionless stress intensity factor is found to be K (h to the 1/2)/P = 12 to the 1/2 (a/h + 0.6728 + 0.0377 h-squared/a-squared), in which P is the magnitude of the concentrated forces per unit thickness, a is the distance from the crack tip to the points of load application, and h is the height of each cantilever beam. The result is similar to that obtained by Gross and Srawley by fitting a line to discrete results from their boundary collocation analysis.

Dynamic ductile fracture of a central crack

NASA Technical Reports Server (NTRS)

Tsai, Y. M.

1976-01-01

A central crack, symmetrically growing at a constant speed in a two dimensional ductile material subject to uniform tension at infinity, is investigated using the integral transform methods. The crack is assumed to be the Dugdale crack, and the finite stress condition at the crack tip is satisfied during the propagation of the crack. Exact expressions of solution are obtained for the finite stress condition at the crack tip, the crack shape, the crack opening displacement, and the energy release rate. All those expressions are written as the product of explicit dimensional quantities and a nondimensional dynamic correction function. The expressions reduce to the associated static results when the crack speed tends to zero, and the nondimensional dynamic correction functions were calculated for various values of the parameter involved.

Dynamic contact forces on leukocyte microvilli and their penetration of the endothelial glycocalyx.

PubMed Central

Zhao, Y; Chien, S; Weinbaum, S

2001-01-01

We develop a theoretical model to examine the combined effect of gravity and microvillus length heterogeneity on tip contact force (F(m)(z)) during free rolling in vitro, including the initiation of L-, P-, and E-selectin tethers and the threshold behavior at low shear. F (m)(z) grows nonlinearly with shear. At shear stress of 1 dyn/cm(2), F(m)(z) is one to two orders of magnitude greater than the 0.1 pN force for gravitational settling without flow. At shear stresses > 0.2 dyn/cm(2) only the longest microvilli contact the substrate; hence at the shear threshold (0.4 dyn/cm(2) for L-selectin), only 5% of microvilli can initiate tethering interaction. The characteristic time for tip contact is surprisingly short, typically 0.1-1 ms. This model is then applied in vivo to explore the free-rolling interaction of leukocyte microvilli with endothelial glycocalyx and the necessary conditions for glycocalyx penetration to initiate cell rolling. The model predicts that for arteriolar capillaries even the longest microvilli cannot initiate rolling, except in regions of low shear or flow reversal. In postcapillary venules, where shear stress is approximately 2 dyn/cm(2), tethering interactions are highly likely, provided that there are some relatively long microvilli. Once tethering is initiated, rolling tends to ensue because F(m)(z) and contact duration will both increase substantially to facilitate glycocalyx penetration by the shorter microvilli. PMID:11222278

Damage tolerance of pressurized graphite/epoxy tape cylinders under uniaxial and biaxial loading. M.S. Thesis

NASA Technical Reports Server (NTRS)

Priest, Stacy Marie

1993-01-01

The damage tolerance behavior of internally pressurized, axially slit, graphite/epoxy tape cylinders was investigated. Specifically, the effects of axial stress, structural anisotropy, and subcritical damage were considered. In addition, the limitations of a methodology which uses coupon fracture data to predict cylinder failure were explored. This predictive methodology was previously shown to be valid for quasi-isotropic fabric and tape cylinders but invalid for structurally anisotropic (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders. The effects of axial stress and structural anisotropy were assessed by testing tape cylinders with (90/0/+/-45)(sub s), (+/-45/90)(sub s), and (+/-45/0)(sub s) layups in a uniaxial test apparatus, specially designed and built for this work, and comparing the results to previous tests conducted in biaxial loading. Structural anisotropy effects were also investigated by testing cylinders with the quasi-isotropic (0/+/-45/90)(sub s) layup which is a stacking sequence variation of the previously tested (90/0/+/-45)(sub s) layup with higher D(sub 16) and D(sub 26) terms but comparable D(sub 16) and D(sub 26) to D(sub 11) ratios. All cylinders tested and used for comparison are made from AS4/3501-6 graphite/epoxy tape and have a diameter of 305 mm. Cylinder slit lengths range from 12.7 to 50.8 mm. Failure pressures are lower for the uniaxially loaded cylinders in all cases. The smallest percent failure pressure decreases are observed for the (+/-45/90)(sub s) cylinders, while the greatest such decreases are observed for the (+/-45/0)(sub s) cylinders. The relative effects of the axial stress on the cylinder failure pressures do not correlate with the degree of structural coupling. The predictive methodology is not applicable for uniaxially loaded (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders, may be applicable for uniaxially loaded (90/0/+/-45)(sub s) cylinders, and is applicable for the biaxially loaded (90/0/+/-45)(sub s) and (0/+/-45/90)(sub s) cylinders. This indicates that the ratios of D(sub 16) and D(sub 26) to D(sub 11), as opposed to the absolute magnitudes of D(sub 16) and D(sub 26), may be important in the failure of these cylinders and in the applicability of the methodology. Discontinuities observed in the slit tip hoop strains for all the cylinders tested indicate that subcritical damage can play an important role in the failure of tape cylinders. This role varies with layup and loading condition and is likely coupled to the effects of structural anisotropy. Biaxial failure pressures may exceed the uniaxial values because the axial stress contributes to the formation of 0 deg ply splitting (accompanied by delamination) or similar stress-mitigating subcritical damage. The failure behavior of similar cylinders can also vary as a result of differences in the role of subcritical damage as observed for the case of a biaxially loaded (90/0/+/-45)(sub s) cylinder with a 12.7 mm slit. For this case, the methodology is valid when the initial coupon and cylinder fracture modes agree. However, the methodology underpredicts the failure pressure of the cylinder when a circumferential fracture path, suggestive of a 0 deg ply split, occurs at one slit tip. Thus, the failure behavior of some tape cylinders may be highly sensitive to the initial subcritical damage mechanism. Finite element analyses are recommended to determine how structural anisotropy and axial stress modify the slit tip stress states in cylinders from those found in flat plates since similarity of these stress states is a fundamental assumption of the current predictive methodology.

Role of Slip Mode on Stress Corrosion Cracking Behavior

NASA Astrophysics Data System (ADS)

Vasudevan, A. K.; Sadananda, K.

2011-02-01

In this article, we examine the effect of aging treatment and the role of planarity of slip on stress corrosion cracking (SCC) behavior in precipitation-hardened alloys. With aging, the slip mode can change from a planar slip in the underage (UA) to a wavy slip in the overage (OA) region. This, in turn, results in sharpening the crack tip in the UA compared to blunting in the OA condition. We propose that the planar slip enhances the stress concentration effects by making the alloys more susceptible to SCC. In addition, the planarity of slip enhances plateau velocities, reduces thresholds for SCC, and reduces component life. We show that the effect of slip planarity is somewhat similar to the effects of mechanically induced stress concentrations such as due to the presence of sharp notches. Aging treatment also causes variations in the matrix and grain boundary (GB) microstructures, along with typical mechanical and SCC properties. These properties include yield stress, work hardening rate, fracture toughness K IC , thresholds K Iscc, and steady-state plateau velocity ( da/ dt). The SCC data for a wide range of ductile alloys including 7050, 7075, 5083, 5456 Al, MAR M steels, and solid solution copper-base alloys are collected from the literature. Our assertion is that slip mode and the resulting stress concentration are important factors in SCC behavior. This is further supported by similar observations in many other systems including some steels, Al alloys, and Cu alloys.

Hygrothermal Effects in Continuous Fibre Reinforced Composites. Part 4. Mechanical Properties 2 - Fatigue and Time-Dependent Properties (Effets Hygrothermiques dans les Composites a Renfort de Fibre Continu. Partie 4. Proprietes Mecaniques 2 - Fatigue et Proprietes Dependant du Temps)

DTIC Science & Technology

1983-09-01

reduction of stress intensity at a crack tip due to Lreep was responsible for increasing the fatigue life during the "slow- fast " L .sts. As creep is clearly...Aeronautical Establishment Structures and Materials Laboratory SPONSORING AGENCY/AGENCE DE SUBVENTION 8 DATE FILE/DOSSIER LAB. ORDER PAGES FIGS/ DIAGRAMMES

Crack turning in integrally stiffened aircraft structures

NASA Astrophysics Data System (ADS)

Pettit, Richard Glen

Current emphasis in the aircraft industry toward reducing manufacturing cost has created a renewed interest in integrally stiffened structures. Crack turning has been identified as an approach to improve the damage tolerance and fail-safety of this class of structures. A desired behavior is for skin cracks to turn before reaching a stiffener, instead of growing straight through. A crack in a pressurized fuselage encounters high T-stress as it nears the stiffener---a condition favorable to crack turning. Also, the tear resistance of aluminum alloys typically varies with crack orientation, a form of anisotropy that can influence the crack path. The present work addresses these issues with a study of crack turning in two-dimensions, including the effects of both T-stress and fracture anisotropy. Both effects are shown to have relation to the process zone size, an interaction that is central to this study. Following an introduction to the problem, the T-stress effect is studied for a slightly curved semi-infinite crack with a cohesive process zone, yielding a closed form expression for the future crack path in an infinite medium. For a given initial crack tip curvature and tensile T-stress, the crack path instability is found to increase with process zone size. Fracture orthotropy is treated using a simple function to interpolate between the two principal fracture resistance values in two-dimensions. An extension to three-dimensions interpolates between the six principal values of fracture resistance. Also discussed is the transition between mode I and mode II fracture in metals. For isotropic materials, there is evidence that the crack seeks out a direction of either local symmetry (pure mode I) or local asymmetry (pure mode II) growth. For orthotropic materials the favored states are not pure modal, and have mode mixity that is a function of crack orientation. Drawing upon these principles, two crack turning prediction approaches are extended to include fracture resistance orthotropy---a second-order linear elastic method with a characteristic length parameter to incorporate T-stress/process-zone effects, and an elastic-plastic method that uses the Crack Tip Opening Displacement (CTOD) to determine the failure response. Together with a novel method for obtaining enhanced accuracy T-stress calculations, these methods are incorporated into an adaptive-mesh, finite-element fracture simulation code. A total of 43 fracture tests using symmetrically and asymmetrically loaded double cantilever beam specimens were run to develop crack turning parameters and compare predicted and observed crack paths.

Redesigned rotor for a highly loaded, 1800 ft/sec tip speed compressor fan stage 1: Aerodynamic and mechanical design

NASA Technical Reports Server (NTRS)

Halle, J. E.; Ruschak, J. T.

1975-01-01

A highly loaded, high tip-speed fan rotor was designed with multiple-circular-arc airfoil sections as a replacement for a marginally successful rotor which had precompression airfoil sections. The substitution of airfoil sections was the only aerodynamic change. Structural design of the redesigned rotor blade was guided by successful experience with the original blade. Calculated stress levels and stability parameters for the redesigned rotor are within limits demonstrated in tests of the original rotor.

Continuum Mechanics at the Atomic Scale.

DTIC Science & Technology

1977-01-01

an infinite hoop stress at the tip of the crack (Figure 9 ). Because of this singularity a perfectly good criterion of brittle fracture, the maximum...for brittle fracture, we will arrive at the Griffith criterion with the extra benefit that the Griffith constant is now fully determined. As a result...crack tip. From (5.9) it now follows that 2 2 2toZ - [a/2 C (v)] t = C (5.10) 0c Alas, this is the Griffith fracture criterion for brittle fracture with

A review on how meditation could be used to comfort the terminally ill.

PubMed

Ball, Michael Stephen; Vernon, Bryan

2015-10-01

Our objective was to review how meditation could comfort the terminally ill. Our methodology was a literature search, which included books, journals, papers in collections, and online databases. The main search engines employed were Google Scholar and the Durham University Library. The main databases consulted were the Christian Meditation Centre, Project Meditation, and Stress-Related Facts and Well-Being at Monash. We were specifically interested in data acquired from clinical and nonclinical trials. The arguments needed to be based on qualitative and quantitative scientific data. Papers were published between 1985 and 2014. We then subdivided the review into three subcategories: physical, emotional, and self-awareness. When reviewing each category, we put our results into tabular form. In each table, we noted the percentage of terminally ill patients (TIPs) and non-terminally ill patients (NTIPs), and whether meditation had comforted them. Our review demonstrated that there are many areas that have yet to be researched. First, very little work has been done on how meditation affects the physical health of TIPs, including such variables as blood pressure, chronic pain, and sleeping patterns. However, no research has been done on heart disease, hypertension, depression, among others. Second, virtually no research has been conducted on how meditation affects the mental health of TIPs. Notably neglected areas include anxiety, compliance, depression, and stress. Third, no research has been done on whether meditation increases self-awareness in TIPs. In each of these cases, most NTIPs reacted positively; however, no research has been done on why TIPs reacted differently. Our results demonstrate the need for further research on how meditation affects terminally ill patients. In turn, this would enrich the debate on whether meditation should be prescribed for the dying.

Internal hydrogen-induced subcritical crack growth in austenitic stainless steels

NASA Astrophysics Data System (ADS)

Huang, J. H.; Altstetter, C. J.

1991-11-01

The effects of small amounts of dissolved hydrogen on crack propagation were determined for two austenitic stainless steel alloys, AISI 301 and 310S. In order to have a uniform distribution of hydrogen in the alloys, they were cathodically charged at high temperature in a molten salt electrolyte. Sustained load tests were performed on fatigue precracked specimens in air at 0 ‡C, 25 ‡C, and 50 ‡C with hydrogen contents up to 41 wt ppm. The electrical potential drop method with optical calibration was used to continuously monitor the crack position. Log crack velocity vs stress intensity curves had definite thresholds for subcritical crack growth (SCG), but stage II was not always clearly delineated. In the unstable austenitic steel, AISI 301, the threshold stress intensity decreased with increasing hydrogen content or increasing temperature, but beyond about 10 wt ppm, it became insensitive to hydrogen concentration. At higher concentrations, stage II became less distinct. In the stable stainless steel, subcritical crack growth was observed only for a specimen containing 41 wt ppm hydrogen. Fractographic features were correlated with stress intensity, hydrogen content, and temperature. The fracture mode changed with temperature and hydrogen content. For unstable austenitic steel, low temperature and high hydrogen content favored intergranular fracture while microvoid coalescence dominated at a low hydrogen content. The interpretation of these phenomena is based on the tendency for stress-induced phase transformation, the different hydrogen diffusivity and solubility in ferrite and austenite, and outgassing from the crack tip. After comparing the embrittlement due to internal hydrogen with that in external hydrogen, it is concluded that the critical hydrogen distribution for the onset of subcritical crack growth is reached at a location that is very near the crack tip.

2D simulation of active species and ozone production in a multi-tip DC air corona discharge

NASA Astrophysics Data System (ADS)

Meziane, M.; Eichwald, O.; Sarrette, J. P.; Ducasse, O.; Yousfi, M.

2011-11-01

The present paper shows for the first time in the literature a complete 2D simulation of the ozone production in a DC positive multi-tip to plane corona discharge reactor crossed by a dry air flow at atmospheric pressure. The simulation is undertaken until 1 ms and involves tens of successive discharge and post-discharge phases. The air flow is stressed by several monofilament corona discharges generated by a maximum of four anodic tips distributed along the reactor. The nonstationary hydrodynamics model for reactive gas mixture is solved using the commercial FLUENT software. During each discharge phase, thermal and vibrational energies as well as densities of radical and metastable excited species are locally injected as source terms in the gas medium surrounding each tip. The chosen chemical model involves 10 neutral species reacting following 24 reactions. The obtained results allow us to follow the cartography of the temperature and the ozone production inside the corona reactor as a function of the number of high voltage anodic tips.

Determination of stress intensity factors for interface cracks under mixed-mode loading

NASA Technical Reports Server (NTRS)

Naik, Rajiv A.; Crews, John H., Jr.

1992-01-01

A simple technique was developed using conventional finite element analysis to determine stress intensity factors, K1 and K2, for interface cracks under mixed-mode loading. This technique involves the calculation of crack tip stresses using non-singular finite elements. These stresses are then combined and used in a linear regression procedure to calculate K1 and K2. The technique was demonstrated by calculating three different bimaterial combinations. For the normal loading case, the K's were within 2.6 percent of an exact solution. The normalized K's under shear loading were shown to be related to the normalized K's under normal loading. Based on these relations, a simple equation was derived for calculating K1 and K2 for mixed-mode loading from knowledge of the K's under normal loading. The equation was verified by computing the K's for a mixed-mode case with equal and normal shear loading. The correlation between exact and finite element solutions is within 3.7 percent. This study provides a simple procedure to compute K2/K1 ratio which has been used to characterize the stress state at the crack tip for various combinations of materials and loadings. Tests conducted over a range of K2/K1 ratios could be used to fully characterize interface fracture toughness.

Gear crack propagation investigations

NASA Technical Reports Server (NTRS)

Lewicki, David G.; Ballarini, Roberto

1996-01-01

Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture ANalysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modeling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gages in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.

Micromechanisms of Monotonic and Cyclic Subcritical Crack Growth in Advanced High Melting Point Low-Ductility Intermetallics

DTIC Science & Technology

1991-05-01

next generation of hk,- s-performance jet engines will require markedly stiffer materials, operating at higher stress levels anw. :apable of...the crack tip, and fatigue-crack propagation is observed at stress -intensity levels as low as 6 MPa&m, far below those required to initiate cracking...The next generation of high-performance jet engines will require markedly stiffer materials, operating at higher stress levels and capable of

Critical Issues in Hydrogen Assisted Cracking of Structural Alloys

DTIC Science & Technology

2006-01-01

does not precipitate ? Does the HEAC mechanism explain environment-assisted (stress corrosion ) crack growth in high strength alloys stressed in moist...superalloys were cracked in high pressure (100-200 M~a) H2, while maraging and tempered-martensitic steels were cracked in low pressure (-100 kPa) H2...of IRAC in ultra-high strength AerMet®l00 steel demonstrates the role of crack tip stress in promoting H accumulation and embrittlement. The cracking

Dispersive aortic cannulas reduce aortic wall shear stress affecting atherosclerotic plaque embolization.

PubMed

Assmann, Alexander; Gül, Fethi; Benim, Ali Cemal; Joos, Franz; Akhyari, Payam; Lichtenberg, Artur

2015-03-01

Neurologic complications during on-pump cardiovascular surgery are often induced by mobilization of atherosclerotic plaques, which is directly related to enhanced wall shear stress. In the present study, we numerically evaluated the impact of dispersive aortic cannulas on aortic blood flow characteristics, with special regard to the resulting wall shear stress profiles. An idealized numerical model of the human aorta and its branches was created and used to model straight as well as bent dispersive aortic cannulas with meshlike tips inserted in the distal ascending aorta. Standard cannulas with straight beveled or bent tips served as controls. Using a recently optimized computing method, simulations of pulsatile and nonpulsatile extracorporeal circulation were performed. Dispersive aortic cannulas reduced the maximum and average aortic wall shear stress values to approximately 50% of those with control cannulas, while the difference in local values was even larger. Moreover, under pulsatile circulation, dispersive cannulas shortened the time period during which wall shear stress values were increased. The turbulent kinetic energy was also diminished by utilizing dispersive cannulas, reducing the risk of hemolysis. In summary, dispersive aortic cannulas decrease aortic wall shear stress and turbulence during extracorporeal circulation and may therefore reduce the risk of endothelial and blood cell damage as well as that of neurologic complications caused by atherosclerotic plaque mobilization. Copyright © 2014 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Stress intensity factors in a reinforced thick-walled cylinder

NASA Technical Reports Server (NTRS)

Tang, R.; Erdogan, F.

1984-01-01

An elastic thick-walled cylinder containing a radial crack is considered. It is assumed that the cylinder is reinforced by an elastic membrane on its inner surface. The model is intended to simulate pressure vessels with cladding. The formulation of the problem is reduced to a singular integral equation. Various special cases including that of a crack terminating at the cylinder-reinforcement interface are investigated and numerical examples are given. Results indicate that in the case of the crack touching the interface the crack surface displacement derivative is finite and consequently the stress state around the corresponding crack tip is bounded; and generally, for realistic values of the stiffness parameter, the effect of the reinforcement is not very significant.

Analysis of drought-tolerant sugar beet (Beta vulgaris L.) mutants induced with gamma radiation using SDS-PAGE and ISSR markers.

PubMed

Sen, Ayse; Alikamanoglu, Sema

2012-01-01

Drought is one of the major environmental stresses which greatly affect the plant growth and productivity. In the present study, various doses (0-75Gy) of gamma rays were applied to investigate the effect of radiation on shoot tip explants. It was observed that the regeneration rates and plant fresh weights decreased significantly with an increase in radiation dose. The optimal irradiation doses for mutation induction were determined at 15 and 20Gy. Afterwards, the induction of somatic mutation in sugar beet (Beta vulgaris L.) was investigated by irradiation of shoot tips with 15 and 20Gy gamma rays. Irradiated shoot tips were sub-cultured and M(1)V(1)-M(1)V(3) generations were obtained. Mutants tolerant to drought stress were selected on MS medium, supplemented with 10 and 20gl(-1) PEG6000. Of the M(1)V(3) plantlets, drought-tolerant mutants were selected. Leaf soluble proteins obtained from the control and drought-tolerant mutants were analyzed by SDS-PAGE. A total of 22 protein bands were determined and 2 of them were observed to be drought-tolerant mutants except the control. Polymorphism was also detected among the control and drought-tolerant mutants by DNA fingerprinting using ISSR markers. A total of 106 PCR fragments were amplified with 19 ISSR primers and 91 of them were polymorphic. The dendrograms were separated into two main clusters. First cluster included M8 mutant plant, which was applied 20Gy gamma radiation and regenerated on selective culture media containing 10gl(-1) PEG6000 concentration, and the second cluster was further divided into five sub-clusters. Copyright © 2012 Elsevier B.V. All rights reserved.

Global expression pattern comparison between low phosphorus insensitive 4 and WT Arabidopsis reveals an important role of reactive oxygen species and jasmonic acid in the root tip response to phosphate starvation

PubMed Central

Chacón-López, Alejandra; Ibarra-Laclette, Enrique; Sánchez-Calderón, Lenin; Gutiérrez-Alanís, Dolores

2011-01-01

Plants are exposed to several biotic and abiotic stresses. A common environmental stress that plants have to face both in natural and agricultural ecosystems that impacts both its growth and development is low phosphate (Pi) availability. There has been an important progress in the knowledge of the molecular mechanisms by which plants cope with Pi deficiency. However, the mechanisms that mediate alterations in the architecture of the Arabidopsis root system responses to Pi starvation are still largely unknown. One of the most conspicuous developmental effects of low Pi on the Arabidopsis root system is the inhibition of primary root growth that is accompanied by loss of root meristematic activity. To identify signalling pathways potentially involved in the Arabidpsis root meristem response to Pi-deprivation, here we report the global gene expression analysis of the root tip of wild type and low phosphorus insensitive4 (lpi4) mutant grown under Pi limiting conditions. Differential gene expression analysis and physiological experiments show that changes in the redox status, probably mediated by jasmonic acid and ethylene, play an important role in the primary root meristem exhaustion process triggered by Pi-starvation. PMID:21368582

Choking and Strangulation Prevention Tips

MedlinePlus

... away from children. These include magnets found in construction sets, children's toys or stress-relieving adult desk ... with Us Donate Join Our Mailing List Global Road Safety Sponsors Recalls Media Center Blog Videos Newsletter ...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, John Zhiqiang

A gas turbine has buckets rotatable about an axis, the buckets having angel wing seals. The seals have outer and inner surfaces, at least one of which, and preferably both, extend non-linearly between root radii and the tip of the seal body. The profiles are determined in a manner to minimize the weight of the seal bodies, while maintaining the stresses below predetermined maximum or allowable stresses.

Mode 1 stress intensity factors for round compact specimens

NASA Technical Reports Server (NTRS)

Gross, B.

1976-01-01

The mode 1 stress intensity factors were computed for round compact specimens by the boundary collocation method. Results are presented for ratios A sub T/R sub 0 in the range 0.3 to 0.8, where A sub t is the distance from the specimen center to the crack tip for a specimen of diameter 2R sub 0.

Study of the toughening mechanisms in bone and biomimetic hydroxyapatite materials using Raman microprobe spectroscopy.

PubMed

Pezzotti, Giuseppe; Sakakura, Seiji

2003-05-01

A Raman microprobe spectroscopy characterization of microscopic fracture mechanisms is presented for a natural hydroxyapatite material (cortical bovine femur) and two synthetic hydroxyapatite-based materials with biomimetic structures-a hydroxyapatite skeleton interpenetrated with a metallic (silver) or a polymeric (nylon-6) phase. In both the natural and synthetic materials, a conspicuous amount of toughening arose from a microscopic crack-bridging mechanism operated by elasto-plastic stretching of unbroken second-phase ligaments along the crack wake. This mechanism led to a rising R-curve behavior. An additional micromechanism, responsible for stress relaxation at the crack tip, was recognized in the natural bone material and was partly mimicked in the hydroxyapatite/silver composite. This crack-tip mechanism conspicuously enhanced the cortical bone material resistance to fracture initiation. A piezo-spectroscopic technique, based on a microprobe measurement of 980 cm(-1) Raman line of hydroxyapatite, enabled us to quantitatively assess in situ the microscopic stress fields developed during fracture both at the crack tip and along the crack wake. Using the Raman piezo-spectroscopy technique, toughening mechanisms were assessed quantitatively and rationally related to the macroscopic fracture characteristics of hydroxyapatite-based materials. Copyright 2003 Wiley Periodicals, Inc.

Investigating ultraflexible freestanding graphene by scanning tunneling microscopy and spectroscopy

NASA Astrophysics Data System (ADS)

Breitwieser, R.; Hu, Yu-Cheng; Chao, Yen Cheng; Tzeng, Yi Ren; Liou, Sz-Chian; Lin, Keng Ching; Chen, Chih Wei; Pai, Woei Wu

2017-08-01

A strictly two-dimensional (2D) material such as freestanding graphene (FSG) is rarely investigated at the atomic scale by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). A basic difficulty in probing FSG by STM and STS is the mechanical instability when a highly compliant 2D atomic layer interacts with a proximal tip. Here we report a detailed method to conduct reliable STM and STS on FSG with atomic precision. We found that FSG is intrinsically rippled and exhibits a nonlinear strain-stress relation under applied normal forces; it shows a very soft region of bending strain and stiffer regions of in-plane tensile strain once the nanoscale ripples of FSG are eliminated. The elimination of the nanoripples can be controlled by tip-induced pulling or pushing force through the so-called closed-loop Z-V STS mode which can monitor the FSG deformation. A key factor for controllable STM and STS measurements is to select tunneling set points to place FSG in metastable configurations, as determined from stress-strain (i.e., Z-V) response. Atomic imaging and electronic states thus measured must be interpreted by considering the dynamical deformation of FSG as tunneling parameters, and therefore tip-FSG forces, are varied.

Nitric Oxide Inhibits Al-Induced Programmed Cell Death in Root Tips of Peanut (Arachis hypogaea L.) by Affecting Physiological Properties of Antioxidants Systems and Cell Wall

PubMed Central

Pan, Chun-Liu; Yao, Shao-Chang; Xiong, Wei-Jiao; Luo, Shu-Zhen; Wang, Ya-Lun; Wang, Ai-Qin; Xiao, Dong; Zhan, Jie; He, Long-Fei

2017-01-01

It has been reported that nitric oxide (NO) is a negative regulator of aluminum (Al)-induced programmed cell death (PCD) in peanut root tips. However, the inhibiting mechanism of NO on Al-induced PCD is unclear. In order to investigate the mechanism by which NO inhibits Al-induced PCD, the effects of co-treatment Al with the exogenous NO donor or the NO-specific scavenger on peanut root tips, the physiological properties of antioxidants systems and cell wall (CW) in root tip cells of NO inhibiting Al-induced PCD were studied with two peanut cultivars. The results showed that Al exposure induced endogenous NO accumulation, and endogenous NO burst increased antioxidant enzyme activity in response to Al stress. The addition of NO donor sodium nitroprusside (SNP) relieved Al-induced root elongation inhibition, cell death and Al adsorption in CW, as well as oxidative damage and ROS accumulation. Furthermore, co-treatment with the exogenous NO donor decreased MDA content, LOX activity and pectin methylesterase (PME) activity, increased xyloglucan endotransglucosylase (XET) activity and relative expression of the xyloglucan endotransglucosylase/hydrolase (XTH-32) gene. Taken together, exogenous NO alleviated Al-induced PCD by inhibiting Al adsorption in CW, enhancing antioxidant defense and reducing peroxidation of membrane lipids, alleviating the inhibition of Al on root elongation by maintaining the extensibility of CW, decreasing PME activity, and increasing XET activity and relative XTH-32 expression of CW. PMID:29311970

Nitric Oxide Inhibits Al-Induced Programmed Cell Death in Root Tips of Peanut (Arachis hypogaea L.) by Affecting Physiological Properties of Antioxidants Systems and Cell Wall.

PubMed

Pan, Chun-Liu; Yao, Shao-Chang; Xiong, Wei-Jiao; Luo, Shu-Zhen; Wang, Ya-Lun; Wang, Ai-Qin; Xiao, Dong; Zhan, Jie; He, Long-Fei

2017-01-01

It has been reported that nitric oxide (NO) is a negative regulator of aluminum (Al)-induced programmed cell death (PCD) in peanut root tips. However, the inhibiting mechanism of NO on Al-induced PCD is unclear. In order to investigate the mechanism by which NO inhibits Al-induced PCD, the effects of co-treatment Al with the exogenous NO donor or the NO-specific scavenger on peanut root tips, the physiological properties of antioxidants systems and cell wall (CW) in root tip cells of NO inhibiting Al-induced PCD were studied with two peanut cultivars. The results showed that Al exposure induced endogenous NO accumulation, and endogenous NO burst increased antioxidant enzyme activity in response to Al stress. The addition of NO donor sodium nitroprusside (SNP) relieved Al-induced root elongation inhibition, cell death and Al adsorption in CW, as well as oxidative damage and ROS accumulation. Furthermore, co-treatment with the exogenous NO donor decreased MDA content, LOX activity and pectin methylesterase (PME) activity, increased xyloglucan endotransglucosylase (XET) activity and relative expression of the xyloglucan endotransglucosylase/hydrolase ( XTH-32 ) gene. Taken together, exogenous NO alleviated Al-induced PCD by inhibiting Al adsorption in CW, enhancing antioxidant defense and reducing peroxidation of membrane lipids, alleviating the inhibition of Al on root elongation by maintaining the extensibility of CW, decreasing PME activity, and increasing XET activity and relative XTH-32 expression of CW.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Y.J.; Sohn, G.H.; Kim, Y.J.

Typical LBB (Leak-Before-Break) analysis is performed for the highest stress location for each different type of material in the high energy pipe line. In most cases, the highest stress occurs at the nozzle and pipe interface location at the terminal end. The standard finite element analysis approach to calculate J-Integral values at the crack tip utilizes symmetry conditions when modeling near the nozzle as well as away from the nozzle region to minimize the model size and simplify the calculation of J-integral values at the crack tip. A factor of two is typically applied to the J-integral value to accountmore » for symmetric conditions. This simplified analysis can lead to conservative results especially for small diameter pipes where the asymmetry of the nozzle-pipe interface is ignored. The stiffness of the residual piping system and non-symmetries of geometry along with different material for the nozzle, safe end and pipe are usually omitted in current LBB methodology. In this paper, the effects of non-symmetries due to geometry and material at the pipe-nozzle interface are presented. Various LBB analyses are performed for a small diameter piping system to evaluate the effect a nozzle has on the J-integral calculation, crack opening area and crack stability. In addition, material differences between the nozzle and pipe are evaluated. Comparison is made between a pipe model and a nozzle-pipe interface model, and a LBB PED (Piping Evaluation Diagram) curve is developed to summarize the results for use by piping designers.« less

Stresses around a miniscrew. 3-D analysis with the finite element method (FEM).

PubMed

Geramy, Allahyar

2009-11-01

Miniscrews used for absolute anchorage may induce stresses in the surrounding tissues that are dependent on their proximity to the miniscrew. To determine the stresses in the buccal walls of the sockets of lower molars adjacent to a miniscrew under load when the position and angulation of the miniscrew are changed. Five 3-D FEM models containing the first and second lower molars, their periodontal ligaments and the surrounding spongy and cortical bone, were modelled in SolidWorks 2006 (SolidWorks, Concord, MA, USA) and transferred to the ANSYS Workbench (ANSYS Inc., Southpointe, Canonsburg, PA, U.S.A.). A tensile force of 2 N, decomposed in 3-D space, was applied to a miniscrew inserted between the lower first and second molars. The von Mises (equivalent) stresses along the buccal walls of the sockets of the first and second molars were derived following changes in miniscrew position and angulation. No direct force was applied to the molars. When the miniscrew was inserted at right angles to the bone and midway between the molars the stress in the crestal area was 0.093 MPa. This stress increased proportionally in the first molar socket as the miniscrew was moved towards the first molar and declined when the miniscrew was tipped towards the second molar. Stresses also decreased in the crestal area of the second molar as the miniscrew was moved towards the first molar, but increased when it was tipped towards the second molar. A 30-55 per cent increase in crestal stress in the first molar socket was detected. Stress occurred in the tissues surrounding a miniscrew subjected to a force vector. Changes in the position or angulation of a miniscrew can affect the stress in the socket walls of adjacent teeth.

Ergonomic factors related to drop-off detection with the long cane: effects of cane tips and techniques.

PubMed

Kim, Dae Shik; Emerson, Robert S Wall; Curtis, Amy B

2010-06-01

This study examined the effect of cane tips and cane techniques on drop-off detection with the long cane. Blind pedestrians depend on a long cane to detect drop-offs. Missing a drop-off may result in falls or collision with moving vehicles in the street. Although cane tips appear to affect a cane user's ability to detect drop-offs, few experimental studies have examined such effect. A repeated-measures design with block randomization was used for the study. Participants were 17 adults who were legally blind and had no other disabilities. Participants attempted to detect the drop-offs of varied depths using different cane tips and cane techniques. Drop-off detection rates were similar between the marshmallow tip (77.0%) and the marshmallow roller tip (79.4%) when both tips were used with the constant contact technique, p = .294. However, participants detected drop-offs at a significantly higher percentage when they used the constant contact technique with the marshmallow roller tip (79.4%) than when they used the two-point touch technique with the marshmallow tip (63.2%), p < .001. The constant contact technique used with a marshmallow roller tip (perceived as a less advantageous tip) was more effective than the two-point touch technique used with a marshmallow tip (perceived as a more advantageous tip) in detecting drop-offs. The findings of the study may help cane users and orientation and mobility specialists select appropriate cane techniques and cane tips in accordance with the cane user's characteristics and the nature of the travel environment.

Modeling the growth and interaction of stylolite networks, using the discrete element method for pressure solution

NASA Astrophysics Data System (ADS)

Makedonska, N.; Sparks, D. W.; Aharonov, E.

2012-12-01

Pressure solution (also termed chemical compaction) is considered the most important ductile deformation mechanism operating in the Earth's upper crust. This mechanism is a major player in a variety of geological processes, including evolution of sedimentary basins, hydrocarbon reservoirs, aquifers, earthquake recurrence cycles, and fault healing. Pressure solution in massive rocks often localizes into solution seams or stylolites. Field observations of stylolites often show elastic/brittle interactions in regions between pressure solution features, including and shear fractures, veins and pull-apart features. To understand these interactions, we use a grain-scale model based on the Discrete Element Method that allows granular dissolution at stressed contacts between grains. The new model captures both the slow chemical compaction process and the more abrupt brittle fracturing and sliding between grains. We simulate a sample of rock as a collection of particles, each representing either a grain or a unit of rock, bonded to each other with breakable cement. We apply external stresses to this sample, and calculate elastic and frictional interactions between the grains. Dissolution is modeled by an irreversible penetration of contacting grains into each other at a rate that depends on the contact stress and an adjustable rate constant. Experiments have shown that dissolution rates at grain contacts are greatly enhanced when there is a mineralogical contrast. Therefore, we dissolution rate constant can be increased to account for an amount of impurities (e.g. clay in a quartz or calcite sandstone) that can accumulate on dissolving contacts. This approach allows large compaction and shear strains within the rock, while allowing examination of local grain-scale heterogeneity. For example, we will describe the effect of pressure solution on the distribution of contact forces magnitudes and orientations. Contact forces in elastic granular packings are inherently heteregeneous, but stress-dependent dissolution tends to equalize them. We apply our model to the simulation of stylolite networks, particularly the interaction of stylolite tips. The stress concentrations from these tips are transmitted through the intervening rock, which can cause elastic strain, brittle damage and frictional sliding. Our model shows that grain rearrangement and compaction rate depend on the surface friction coefficient of grains. Simulation results show the development of shear zones between stylolites, and a high porosity process zone at the tips of stylolites. These features, which have been observed in field studies, are modeled and predicted for the first time. This modeling tool holds a promise to provide many new insights regarding the coupling between pressure solution and brittle deformation, i.e. between mechanical and chemical compaction.

Numerical investigation of tip clearance effects on the performance of ducted propeller

NASA Astrophysics Data System (ADS)

Ding, Yongle; Song, Baowei; Wang, Peng

2015-09-01

Tip clearance loss is a limitation of the improvement of turbomachine performance. Previous studies show the Tip clearance loss is generated by the leakage flow through the tip clearance, and is roughly linearly proportional to the gap size. This study investigates the tip clearance effects on the performance of ducted propeller. The investigation was carried out by solving the Navier-Stokes equations with the commercial Computational Fluid Dynamic (CFD) code CFX14.5. These simulations were carried out to determine the underlying mechanisms of the tip clearance effects. The calculations were performed at three different chosen advance ratios. Simulation results showed that the tip loss slope was not linearly at high advance due to the reversed pressure at the leading edge. Three type of vortical structures were observed in the tip clearance at different clearance size.

Numerical 3D flow simulation of ultrasonic horns with attached cavitation structures and assessment of flow aggressiveness and cavitation erosion sensitive wall zones.

PubMed

Mottyll, Stephan; Skoda, Romuald

2016-07-01

As a contribution to a better understanding of cavitation erosion mechanisms, a compressible inviscid finite volume flow solver with barotropic homogeneous liquid-vapor mixture cavitation model is applied to ultrasonic horn set-ups with and without stationary specimen, that exhibit attached cavitation at the horn tip. Void collapses and shock waves, which are closely related to cavitation erosion, are resolved. The computational results are compared to hydrophone, shadowgraphy and erosion test data. At the horn tip, vapor volume and topology, subharmonic oscillation frequency as well as the amplitude of propagating pressure waves are in good agreement with experimental data. For the evaluation of flow aggressiveness and the assessment of erosion sensitive wall zones, statistical analyses of wall loads and of the multiplicity of distinct collapses in wall-adjacent flow regions are applied to the horn tip and the stationary specimen. An a posteriori projection of load collectives, i.e. cumulative collapse rate vs. collapse pressure, onto a reference grid eliminates the grid dependency effectively for attached cavitation at the horn tip, whereas a significant grid dependency remains at the stationary specimen. The load collectives show an exponential decrease towards higher collapse pressures. Erosion sensitive wall zones are well predicted for both, horn tip and stationary specimen, and load profiles are in good qualitative agreement with measured topography profiles of eroded duplex stainless steel samples after long-term runs. For the considered amplitude and gap width according to ASTM G32-10 standard, the analysis of load collectives reveals that the distinctive erosive ring shape at the horn tip can be attributed to frequent breakdown and re-development of a small portion of the tip-attached cavity. This partial breakdown of the attached cavity repeats at each driving cycle and is associated with relatively moderate collapse peak pressures, whereas the stationary specimen is rather unfrequently stressed at the end of each subharmonic oscillation cycle by the violent collapse of the complete cavity. Copyright © 2016 Elsevier B.V. All rights reserved.

A novel tracking tool for the analysis of plant-root tip movements.

PubMed

Russino, A; Ascrizzi, A; Popova, L; Tonazzini, A; Mancuso, S; Mazzolai, B

2013-06-01

The growth process of roots consists of many activities, such as exploring the soil volume, mining minerals, avoiding obstacles and taking up water to fulfil the plant's primary functions, that are performed differently, depending on environmental conditions. Root movements are strictly related to a root decision strategy, which helps plants to survive under stressful conditions by optimizing energy consumption. In this work, we present a novel image-analysis tool to study the kinematics of the root tip (apex), named analyser for root tip tracks (ARTT). The software implementation combines a segmentation algorithm with additional software imaging filters in order to realize a 2D tip detection. The resulting paths, or tracks, arise from the sampled tip positions through the acquired images during the growth. ARTT allows work with no markers and deals autonomously with new emerging root tips, as well as handling a massive number of data relying on minimum user interaction. Consequently, ARTT can be used for a wide range of applications and for the study of kinematics in different plant species. In particular, the study of the root growth and behaviour could lead to the definition of novel principles for the penetration and/or control paradigms for soil exploration and monitoring tasks. The software capabilities were demonstrated by experimental trials performed with Zea mays and Oryza sativa.

CPT-based probabilistic and deterministic assessment of in situ seismic soil liquefaction potential

USGS Publications Warehouse

Moss, R.E.S.; Seed, R.B.; Kayen, R.E.; Stewart, J.P.; Der Kiureghian, A.; Cetin, K.O.

2006-01-01

This paper presents a complete methodology for both probabilistic and deterministic assessment of seismic soil liquefaction triggering potential based on the cone penetration test (CPT). A comprehensive worldwide set of CPT-based liquefaction field case histories were compiled and back analyzed, and the data then used to develop probabilistic triggering correlations. Issues investigated in this study include improved normalization of CPT resistance measurements for the influence of effective overburden stress, and adjustment to CPT tip resistance for the potential influence of "thin" liquefiable layers. The effects of soil type and soil character (i.e., "fines" adjustment) for the new correlations are based on a combination of CPT tip and sleeve resistance. To quantify probability for performancebased engineering applications, Bayesian "regression" methods were used, and the uncertainties of all variables comprising both the seismic demand and the liquefaction resistance were estimated and included in the analysis. The resulting correlations were developed using a Bayesian framework and are presented in both probabilistic and deterministic formats. The results are compared to previous probabilistic and deterministic correlations. ?? 2006 ASCE.

Bacterial cooperative organization under antibiotic stress

NASA Astrophysics Data System (ADS)

Ben-Jacob, Eshel; Cohen, Inon; Golding, Ido; Gutnick, David L.; Tcherpakov, Marianna; Helbing, Dirk; Ron, Ilan G.

2000-07-01

Bacteria have developed sophisticated modes of cooperative behavior to cope with unfavorable environmental conditions. Here we report the effect of antibiotic stress on the colonial development of Paenibacillus dendritiformis and P. vortex. We focus on the effect of co-trimoxazole on the colonial organization of P. dendritiformis. We find that the exposure to non-lethal concentrations of antibiotic leads to dramatic changes in the colonial growth patterns. Branching, tip-splitting patterns are affected by reduction in the colonial fractal dimension from Df=2.0 to 1.7, appearance of pronounced weak chirality and pronounced radial orientation of the growth. We combine the experimental observations with numerical studies of both discrete and continuous generic models to reveal the causes for the modifications in the patterns. We conclude that the bacteria adjust their chemotactic signaling together with variations in the bacteria length and increase in the metabolic load.

Newborn Care: 10 Tips for Stressed-Out Parents

MedlinePlus

... of Pediatrics Textbook of Pediatric Care. Elk Grove Village, Ill.: American Academy of Pediatrics; 2009:840. Jana ... From Birth to Reality. 3rd ed. Elk Grove Village, Ill.: American Academy of Pediatrics; 2015. Sept. 29, ...

Memory Loss: 7 Tips to Improve Your Memory

MedlinePlus

... Volunteer at a local school or community organization. Social interaction helps ward off depression and stress, both of ... most healthy adults, the Department of Health and Human Services recommends at least 150 minutes a week ...

Ergonomic Factors Related to Drop-Off Detection With the Long Cane: Effects of Cane Tips and Techniques

PubMed Central

Kim, Dae Shik; Wall Emerson, Robert S.; Curtis, Amy B.

2010-01-01

Objective This study examined the effect of cane tips and cane techniques on drop-off detection with the long cane. Background Blind pedestrians depend on a long cane to detect drop-offs. Missing a drop-off may result in falls or collision with moving vehicles in the street. Although cane tips appear to affect a cane user’s ability to detect drop-offs, few experimental studies have examined such effect. Method A repeated-measures design with block randomization was used for the study. Participants were 17 adults who were legally blind and had no other disabilities. Participants attempted to detect the drop-offs of varied depths using different cane tips and cane techniques. Results Drop-off detection rates were similar between the marshmallow tip (77.0%) and the marshmallow roller tip (79.4%) when both tips were used with the constant contact technique, p = .294. However, participants detected drop-offs at a significantly higher percentage when they used the constant contact technique with the marshmallow roller tip (79.4%) than when they used the two-point touch technique with the marshmallow tip (63.2%), p < .001. Conclusion The constant contact technique used with a marshmallow roller tip (perceived as a less advantageous tip) was more effective than the two-point touch technique used with a marshmallow tip (perceived as a more advantageous tip) in detecting drop-offs. Application The findings of the study may help cane users and orientation and mobility specialists select appropriate cane techniques and cane tips in accordance with the cane user’s characteristics and the nature of the travel environment. PMID:21077566

Controlling Hydrogen Embrittlement in Ultra-High Strength Steels

DTIC Science & Technology

2006-06-01

this tempering temperature, (5) finely distributed, partly coherent M2C (where M = 75 at.% Cr, 13 Fe and 12 Mo) in martensite , averaging 2 nm...states in a complex precipitation hardened martensitic microstructure and is susceptible to severe hydrogen embrittlement (HE) at threshold stress...repartitions to interstitial sites proximate to the highly stressed crack tip and, subsequently, may retrap at martensitic lath interfaces to produce substantial

Child Welfare, Juvenile Justice, Mental Health, and Education Providers' Conceptualizations of Trauma-Informed Practice.

PubMed

Donisch, Katelyn; Bray, Chris; Gewirtz, Abigail

2016-05-01

This study systematically examined child-service providers' conceptualizations of trauma-informed practice (TIP) across service systems, including child welfare, juvenile justice, mental health, and education. Eleven focus groups and nine individual interviews were conducted, totaling 126 child-service providers. Conventional content analysis was used to analyze the qualitative data with interrater reliability analyses indicating near perfect agreement between coders. Qualitative analysis revealed that child-service providers identified traumatic stress as an important common theme among children and families served as well as the interest in TIP in their service systems. At the same time, child-service providers generally felt knowledgeable about what they define TIP to be, although they articulated wide variations in the degree to which they are taught skills and strategies to respond to their traumatized clients. The results of this study suggest a need for a common lexicon and metric with which to advance TIP within and across child-service systems. © The Author(s) 2016.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, J.K.; Yoo, M.H.

The aspect of elastic strain for a deformation twin with a pure shear strain is studied through Eshelby's inclusion theory. Beta-Sn, TiO[sub 2], and TiAl of tetragonal structures are considered. As the aspect ratio of a twin approaches zero, its elastic strain energy vanishes since the stress components coupled with the twin shear strain vanish, suggesting that the twin habit plane cannot be determined solely from the shear energy viewpoint, for any twin mode would provide a vanishingly small strain energy for a thin twin. The application of Johnson and Cahn's shape bifurcation theory predicts that the transition from amore » circular to an elliptic shape would occur when the linear dimension of a lenticular twin is only in the order of 10 nm, indicating that most twins with a substantial aspect ratio should be influenced by growth kinetics. Under an applied stress. The extreme condition of the free energy change usually occurs when the resolved shear stress becomes extreme in the direction of the twin shear strain, thus following the relationship of Schmid's law. The analysis of the matrix stress field immediately outside a twin plate shows a biomodal stress distribution around the lateral tip of the lenticular plate. The locations of stress concentrations depend on both the twin aspect ratio and the elastic anisotropy. The locations of stress concentrations depend on both the twin aspect ratio and the elastic anisotropy. As the twin aspect ratio approaches zero, however, the two exterior stress concentrations merge together at the lateral tip of the lenticular plate, yielding a maximum stress value in the order of [mu]g, where [mu] and g are shear modulus and twin shear strain, respectively.« less

A New Optical Technique for Rapid Determination of Creep and Fatigue Thresholds at High Temperature.

DTIC Science & Technology

1984-04-01

measurements, made far away from the crack tip, produced much smoother and more sensible results. Measurements by Macha et al (16) agree very well with...dependent upon the measurement positin. It becomes independent of position far enough away from the tip; this is consistent with the results of Macha , et...D. E. Macha , W. N. Sharpe, Jr., and A. P. ’ral(11, ’.., "A Laser Interferometry Method for ,xp.rim,-rit;a1 Stress Intensity Factor Calibration", AST

Experimental Study of Tip Vortex Flow from a Periodically Pitched Airfoil Section

NASA Technical Reports Server (NTRS)

Zaman, Khairul; Fagan, Amy; Mankbadi, Mina

2016-01-01

An experimental investigation of tip vortex flow from a NACA0012 airfoil, pitched periodically at various frequencies, is conducted in a low-speed wind tunnel. Initially, data for stationary airfoil held fixed at various angles-of-attack are gathered. Flow visualization pictures as well as detailed cross-sectional properties areobtained at various streamwise locations using hot-wire anemometry. Data include mean velocity, streamwise vorticity as well as various turbulent stresses. Preliminary data are also acquired for periodically pitched airfoil. These results are briefly presented in this extended abstract.

The mechanics of delamination in fiber-reinforced composite materials. Part 2: Delamination behavior and fracture mechanics parameters

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1983-01-01

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extenstion. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined.

Bending and Shear Stresses Developed by the Instantaneous Arrest of the Root of a Moving Cantilever Beam

NASA Technical Reports Server (NTRS)

Stowell, Elbridge, Z; Schwartz, Edward B; Houbolt, John C

1945-01-01

A theoretical and experimental investigation has been made of the behavior of a cantilever beam in transverse motion when its root is suddenly brought to rest. Equations are given for determining the stresses, the deflections, and the accelerations that arise in the beam as a result of the impact. The theoretical equations, which have been confirmed experimentally, reveal that, at a given percentage of the distance from root to tip, the bending stresses for a particular mode are independent of the length of the beam, whereas the shear stresses vary inversely with the length.

Effect of tip flange on tip leakage flow of small axial flow fans

NASA Astrophysics Data System (ADS)

Zhang, Li; Jin, Yingzi; Jin, Yuzhen

2014-02-01

Aerodynamic performance of an axial flow fan is closely related to its tip clearance leakage flow. In this paper, the hot-wire anemometer is used to measure the three dimensional mean velocity near the blade tips. Moreover, the filtered N-S equations with finite volume method and RNG k-ɛ turbulence model are adopted to carry out the steady simulation calculation of several fans that differ only in tip flange shape and number. The large eddy simulation and the FW-H noise models are adopted to carry out the unsteady numerical calculation and aerodynamic noise prediction. The results of simulation calculation agree roughly with that of tests, which proves the numerical calculation method is feasible.The effects of tip flange shapes and numbers on the blade tip vortex structure and the characteristics are analyzed. The results show that tip flange of the fan has a certain influence on the characteristics of the fan. The maximum efficiencies for the fans with tip flanges are shifted towards partial flow with respect to the design point of the datum fan. Furthermore, the noise characteristics for the fans with tip flanges have become more deteriorated than that for the datum fan. Tip flange contributes to forming tip vortex shedding and the effect of the half-cylinder tip flange on tip vortex shedding is obvious. There is a distinct relationship between the characteristics of the fan and tip vortex shedding. The research results provide the profitable reference for the internal flow mechanism of the performance optimization of small axial flow fans.

Williams Element with Generalized Degrees of Freedom for Fracture Analysis of Multiple-Cracked Beam

NASA Astrophysics Data System (ADS)

Xu, Hua; Wei, Quyang; Yang, Lufeng

2017-10-01

In this paper, the method of finite element with generalized degrees of freedom (FEDOFs) is used to calculate the stress intensity factor (SIF) of multiple cracked beam and analysed the effect of minor cracks on the main crack SIF in different cases. Williams element is insensitive to the size of singular region. So that calculation efficiency is highly improved. Examples analysis validates that the SIF near the crack tip can be obtained directly though FEDOFs. And the result is well consistent with ANSYS solution and has a satisfied accuracy.

Compendium of CARDEROCKDIV Articles Published in Navy Domestic Technology Transfer Fact Sheet, January 1990 through December 1992

DTIC Science & Technology

1992-12-01

longer in the Gulf of Mexico and the patrol, in such areas as th(. Florida Straits have learned what Yucatan Peninsula and from naval Ii means to look down...same performed on conventional deep - containing shallow cracks aW/W < J value have markedly different crack specimens The increa-ed 02, are commonly...the Jc values ’for characterization of the crack-tip atW ratio effects on the measured corresponding deep -crack spec- stress field Moreover, these

The effect of pre-stress cycles on fatigue crack growth - An analysis of crack growth mechanism. [in Al alloy plates

NASA Technical Reports Server (NTRS)

Kang, T. S.; Liu, H. W.

1974-01-01

Cyclic prestress increases subsequent fatigue crack growth rate in 2024-T351 aluminum alloy. This increase in growth rate, caused by the prestress, and the increased rate, caused by temper embrittlement as observed by Ritchie and Knott (1973), cannot be explained by the crack tip blunting model alone. Each fatigue crack increment consists of two components, a brittle and a ductile component. They are controlled by the ductility of the material and its cyclic yield strength, respectively.

Effects of cloning and root-tip size on observations of fungal ITS sequences from Picea glauca roots

Treesearch

Daniel L. Lindner; Mark T. Banik

2009-01-01

To better understand the effects of cloning on observations of fungal ITS sequences from Picea glauca (white spruce) roots two techniques were compared: (i) direct sequencing of fungal ITS regions from individual root tips without cloning and (ii) cloning and sequencing of fungal ITS regions from individual root tips. Effect of root tip size was...

An Experimental Characterization of Tip Leakage Flows and Corresponding Effects on Multistage Compressor Performance

NASA Astrophysics Data System (ADS)

Berdanier, Reid Adam

The effect of rotor tip clearances in turbomachinery applications has been a primary research interest for nearly 80 years. Over that time, studies have shown increased tip clearance in axial flow compressors typically has a detrimental effect on overall pressure rise capability, isentropic efficiency, and stall margin. With modern engine designs trending toward decreased core sizes to increase propulsive efficiency (by increasing bypass ratio) or additional compression stages to increase thermal efficiency by increasing the overall pressure ratio, blade heights in the rear stages of the high pressure compressor are expected to decrease. These rear stages typically feature smaller blade aspect ratios, for which endwall flows are more important, and the rotor tip clearance height represents a larger fraction of blade span. As a result, data sets collected with large relative rotor tip clearance heights are necessary to facilitate these future small core design goals. This research seeks to characterize rotor tip leakage flows for three tip clearance heights in the Purdue three-stage axial compressor facility (1.5%, 3.0%, and 4.0% as a percentage of overall annulus height). The multistage environment of this compressor provides the unique opportunity to examine tip leakage flow effects due to stage matching, stator-rotor interactions, and rotor-rotor interactions. The important tip leakage flow effects which develop as a result of these interactions are absent for previous studies which have been conducted using single-stage machines or isolated rotors. A series of compressor performance maps comprise points at four corrected speeds for each of the three rotor tip clearance heights. Steady total pressure and total temperature measurements highlight the effects of tip leakage flows on radial profiles and wake shapes throughout the compressor. These data also evaluate tip clearance effects on efficiency, stall margin, and peak pressure rise capability. An emphasis of measurements collected at these part-speed and off-design conditions provides a unique data set for calibrating computational models and predictive algorithms. Further investigations with detailed steady total pressure traverses provide additional insight to tip leakage flow effects on stator performance. A series of data on the 100% corrected speedline further characterize the tip leakage flow using time-resolved measurements from a combination of instrumentation techniques. An array of high-frequency-response piezoresistive pressure transducers installed over the rotors allows quantification of tip leakage flow trajectories. These data, along with measurements from a fast-response total pressure probe downstream of the rotors, evaluate the development of tip leakage flows and assess the corresponding effects of upstream stator wakes. Finally, thermal anemometry measurements collected using the single slanted hot-wire technique evaluate three-dimensional velocity components throughout the compressor. These data facilitate calculations of several flow metrics, including a blockage parameter and phase-locked streamwise vorticity.

Analysis on composition and inclusions of ballpoint pen tip steel

NASA Astrophysics Data System (ADS)

Yang, Qian-kun; Shen, Ping; Zhang, Dong; Wu, Yan-xin; Fu, Jian-xun

2018-04-01

Ballpoint pen tip steel, a super free-cutting stainless steel, exhibits excellent corrosion resistance and good machining properties. In this study, inductively coupled plasma spectroscopy, metallographic microscopy, and scanning electron microscopy were used to determine the elemental contents in five ballpoint pen tips and their components, morphologies, and inclusion distributions. The results showed that the steels were all S-Pb-Te super free-cutting ferritic stainless steel. The free-cutting phases in the steels were mainly MnS, Pb, and small amounts of PbTe. MnS inclusions were in the form of chain distributions, and the aspect ratio of each size inclusion in the chain was small. The stress concentration effect could substantially reduce the cutting force when the material was machined. Some of the Pb was distributed evenly in the steel matrix as fine particles (1-2 μm), and the rest of the Pb was distributed at the middle or at both ends of the MnS inclusions. The Pb plays a role in lubrication and melting embrittlement, which substantially increases the cutting performance. PbTe was also usually distributed in the middle and at both ends of the MnS inclusions, and Te could convert the sulfides into spindles, thereby improving the cutting performance of the steel.

Drought response transcriptomes are altered in poplar with reduced tonoplast sucrose transporter expression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Liang-Jiao; Frost, Christopher J.; Tsai, Chung-Jui

Transgenic Populus tremula x alba (717-1B4) plants with reduced expression of a tonoplast sucrose efflux transporter, PtaSUT4, exhibit reduced shoot growth compared to wild type (WT) under sustained mild drought. The present study was undertaken to determine whether SUT4-RNAi directly or indirectly altered poplar predisposition and/or response to changes in soil water availability. While sucrose and hexose levels were constitutively elevated in shoot organs, expression responses to drought were most altered in the root tips of SUT4-RNAi plants. Prior to any drought treatment, constitutively elevated transcript levels of abscisic acid biosynthetic genes and bark/vegetative storage proteins suggested altered metabolism inmore » root tips of RNAi plants. Stronger drought-stimulation of stress-inducible genes encoding late-embryogenesis-abundant proteins in transgenic roots was consistent with increased vulnerability to soil drying. Transcript evidence suggested an RNAi effect on intercellular water trafficking by aquaporins in stem xylem during soil drying and recovery. Co-expression network analysis predicted altered integration of abscisic acid sensing/signaling with ethylene and jasmonate sensing/signaling in RNAi compared to WT roots. The overall conclusion is that steepened shoot-root sugar gradient in RNAi plants increased sensitivity of root tips to decreasing soil water availability.« less

Drought response transcriptomes are altered in poplar with reduced tonoplast sucrose transporter expression

DOE PAGES

Xue, Liang-Jiao; Frost, Christopher J.; Tsai, Chung-Jui; ...

2016-09-19

Transgenic Populus tremula x alba (717-1B4) plants with reduced expression of a tonoplast sucrose efflux transporter, PtaSUT4, exhibit reduced shoot growth compared to wild type (WT) under sustained mild drought. The present study was undertaken to determine whether SUT4-RNAi directly or indirectly altered poplar predisposition and/or response to changes in soil water availability. While sucrose and hexose levels were constitutively elevated in shoot organs, expression responses to drought were most altered in the root tips of SUT4-RNAi plants. Prior to any drought treatment, constitutively elevated transcript levels of abscisic acid biosynthetic genes and bark/vegetative storage proteins suggested altered metabolism inmore » root tips of RNAi plants. Stronger drought-stimulation of stress-inducible genes encoding late-embryogenesis-abundant proteins in transgenic roots was consistent with increased vulnerability to soil drying. Transcript evidence suggested an RNAi effect on intercellular water trafficking by aquaporins in stem xylem during soil drying and recovery. Co-expression network analysis predicted altered integration of abscisic acid sensing/signaling with ethylene and jasmonate sensing/signaling in RNAi compared to WT roots. The overall conclusion is that steepened shoot-root sugar gradient in RNAi plants increased sensitivity of root tips to decreasing soil water availability.« less

Research on fatigue cracking growth parameters in asphaltic mixtures using computed tomography

NASA Astrophysics Data System (ADS)

Braz, D.; Lopes, R. T.; Motta, L. M. G.

2004-01-01

Distress of asphalt concrete pavement due to repeated bending from traffic loads has been a well-recognized problem in Brazil. If it is assumed that fatigue cracking growth is governed by the conditions at the crack tip, and that the crack tip conditions can be characterized by the stress intensity factor, then fatigue cracking growth as a function of stress intensity range Δ K can be determined. Computed tomography technique is used to detect crack evolution in asphaltic mixtures which were submitted to fatigue tests. Fatigue tests under conditions of controlled stress were carried out using diametral compression equipment and repeat loading. The aim of this work is imaging several specimens at different stages of the fatigue tests. In preliminary studies it was noted that the trajectory of a crack was influenced by the existence of voids in the originally unloaded specimens. Cracks would first be observed in the central region of a specimen, propagating in the direction of the extremities. Analyzing the graphics, that represent the fatigue cracking growth (d c/d N) as a function of stress intensity factor (Δ K), it is noticed that the curve has practically shown the same behavior for all specimens at the same level of the static tension rupture stress. The experimental values obtained for the constants A and n (of the Paris-Erdogan Law) present good agreement with the results obtained by Liang and Zhou.

Fe65 is required for Tip60-directed histone H4 acetylation at DNA strand breaks

PubMed Central

Stante, Maria; Minopoli, Giuseppina; Passaro, Fabiana; Raia, Maddalena; Vecchio, Luigi Del; Russo, Tommaso

2009-01-01

Fe65 is a binding partner of the Alzheimer's β-amyloid precursor protein APP. The possible involvement of this protein in the cellular response to DNA damage was suggested by the observation that Fe65 null mice are more sensitive to genotoxic stress than WT counterpart. Fe65 associated with chromatin under basal conditions and its involvement in DNA damage repair requires this association. A known partner of Fe65 is the histone acetyltransferase Tip60. Considering the crucial role of Tip60 in DNA repair, we explored the hypothesis that the phenotype of Fe65 null cells depended on its interaction with Tip60. We demonstrated that Fe65 knockdown impaired recruitment of Tip60-TRRAP complex to DNA double strand breaks and decreased histone H4 acetylation. Accordingly, the efficiency of DNA repair was decreased upon Fe65 suppression. To explore whether APP has a role in this mechanism, we analyzed a Fe65 mutant unable to bind to APP. This mutant failed to rescue the phenotypes of Fe65 null cells; furthermore, APP/APLP2 suppression results in the impairment of recruitment of Tip60-TRRAP complex to DNA double strand breaks, decreased histone H4 acetylation and repair efficiency. On these bases, we propose that Fe65 and its interaction with APP play an important role in the response to DNA damage by assisting the recruitment of Tip60-TRRAP to DNA damage sites. PMID:19282473

Effect of cold work on the stress corrosion cracking behavior of Alloy 690 in supercritical water environment

NASA Astrophysics Data System (ADS)

Chen, Kai; Du, Donghai; Gao, Wenhua; Guo, Xianglong; Zhang, Lefu; Andresen, Peter L.

2018-01-01

The stress corrosion cracking (SCC) behavior of Alloy 690 with 0, 20% and 30% cold work (CW) was studied in supercritical water (SCW) environment with an emphasis on CW and creep on the CGRs (CGR). SCC and creep CGRs increased with %CW, which correlated hardness very well. Microscopic characterization of the crack tip and fracture surface showed obvious cavity-like features, which is clear evidence of creep attack. The creep CGRs in inert gas were comparable to the SCC CGRs in SCW, indicating that creep is a major factor in crack growth. Increasing level of CW was found to increase the creep susceptibility, and high activation energies for creep crack growth were observed between 500 °C and 550 °C.

Interaction of a penny-shaped crack and an external circular crack in a transversely isotropic composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, Y.M.

1998-12-31

The interaction of a penny-shaped crack and an external circular crack in a transversely isotropic composite is investigated using the techniques of Hankel transform and multiplying factors. The boundary conditions of the problem have three different parts. The stress intensity factors at the inner and the outer crack tips are obtained in exact expressions as the products of a dimensional quantity and nondimensional functions. The presence of a penny-shaped crack is shown to have a strong effect on the magnitude of the stress intensity of the external circular crack. The crack surface displacement is also obtained and evaluated numerically formore » different values of the ratio of the inner crack radius to the external crack radius.« less

Quantifying uncertainties in the structural response of SSME blades

NASA Technical Reports Server (NTRS)

Nagpal, Vinod K.

1987-01-01

To quantify the uncertainties associated with the geometry and material properties of a Space Shuttle Main Engine (SSME) turbopump blade, a computer code known as STAEBL was used. A finite element model of the blade used 80 triangular shell elements with 55 nodes and five degrees of freedom per node. The whole study was simulated on the computer and no real experiments were conducted. The structural response has been evaluated in terms of three variables which are natural frequencies, root (maximum) stress, and blade tip displacements. The results of the study indicate that only the geometric uncertainties have significant effects on the response. Uncertainties in material properties have insignificant effects.

Flow-induced vibration testing of replacement thermowell designs

NASA Astrophysics Data System (ADS)

Haslinger, K. H.

2003-09-01

Inconel 600 Primary Water Stress Corrosion Cracking (PWSCC) in Nuclear Pressurized Water Reactors (PWRs) has necessitated the repair/replacement of various small bore nozzles. These repairs/replacements must be designed to avoid unwanted vibrations. So, to this end, new RTD-Thermowell-Nozzle replacement designs were developed and subjected to flow testing over a velocity range from 9.14 to 33.53m/s (30-110ft/s), and temperatures ranging from 121°C to 316°C (250-600°F). The replacement nozzles are welded on the pipe OD, rather than on the pipe ID. A split, tapered ferrule is used to support the nozzle tip inside the pipe bore. This maintains high thermowell tip-resonance frequencies with the objective of avoiding self-excitation from vortex shedding that is believed to have caused failures in an earlier design during initial, precritical plant startup testing. The flow testing was complicated by the small size of the thermowell tips (5.08mm or 0.2in ID), which necessitated use of a complement of low temperature and high temperature instrumentation. Since the high temperature device had an internal resonance (750Hz) within the frequency range of interest (0-2500Hz), adequate sensor correlations had to be derived from low temperature tests. The current nozzle/thermowell design was tested concurrently with two slight variations of the replacement design. The acceleration signals were acquired during incremental and continuous flow sweeps, nominally at 5kHz sampling rates and for time domain processing as high as 25kHz. Whereas vortex-shedding frequencies were predicted to prevail between 400 and 1500Hz, no such response was observed at these frequencies. Rather, the thermowell tips responded due to turbulent buffeting with a peak response that was related directly to flow velocity. Lift direction response was always larger than drag direction response. The thermowell tips also responded at their natural tip frequencies in a narrow band random fashion. At the higher flow rates, one replacement design experienced an instability mode leading to high tip stresses. Although this instability did not repeat, this particular design was eliminated from consideration. The second replacement design performed almost identically to the current in-plant design. The experimental data were used to extract forcing functions and thermowell responses that were used as input into the design calculations.

Multi-Scale Effects in the Strength of Ceramics

PubMed Central

Cook, Robert F.

2016-01-01

Multiple length-scale effects are demonstrated in indentation-strength measurements of a range of ceramic materials under inert and reactive conditions. Meso-scale effects associated with flaw disruption by lateral cracking at large indentation loads are shown to increase strengths above the ideal indentation response. Micro-scale effects associated with toughening by microstructural restraints at small indentation loads are shown to decrease strengths below the ideal response. A combined meso-micro-scale analysis is developed that describes ceramic inert strength behaviors over the complete indentation flaw size range. Nano-scale effects associated with chemical equilibria and crack velocity thresholds are shown to lead to invariant minimum strengths at slow applied stressing rates under reactive conditions. A combined meso-micro-nano-scale analysis is developed that describes the full range of reactive and inert strength behaviors as a function of indentation load and applied stressing rate. Applications of the multi-scale analysis are demonstrated for materials design, materials selection, toughness determination, crack velocity determination, bond-rupture parameter determination, and prediction of reactive strengths. The measurements and analysis provide strong support for the existence of sharp crack tips in ceramics such that the nano-scale mechanisms of discrete bond rupture are separate from the larger scale crack driving force mechanics characterized by continuum-based stress-intensity factors. PMID:27563150

Calculation of stress intensity factors in an isotropic multicracked plate: Part 2: Symbolic/numeric implementation

NASA Technical Reports Server (NTRS)

Arnold, S. M.; Binienda, W. K.; Tan, H. Q.; Xu, M. H.

1992-01-01

Analytical derivations of stress intensity factors (SIF's) of a multicracked plate can be complex and tedious. Recent advances, however, in intelligent application of symbolic computation can overcome these difficulties and provide the means to rigorously and efficiently analyze this class of problems. Here, the symbolic algorithm required to implement the methodology described in Part 1 is presented. The special problem-oriented symbolic functions to derive the fundamental kernels are described, and the associated automatically generated FORTRAN subroutines are given. As a result, a symbolic/FORTRAN package named SYMFRAC, capable of providing accurate SIF's at each crack tip, was developed and validated. Simple illustrative examples using SYMFRAC show the potential of the present approach for predicting the macrocrack propagation path due to existing microcracks in the vicinity of a macrocrack tip, when the influence of the microcrack's location, orientation, size, and interaction are taken into account.

Growth rate models for short surface cracks in AI 2219-T851

NASA Astrophysics Data System (ADS)

Morris, W. L.; James, M. R.; Buck, O.

1981-01-01

Rates of fatigue propagation of short Mode I surface cracks in Al 2219-T851 are measured as a function of crack length and of the location of the surface crack tips relative to the grain boundaries. The measured rates are then compared to values predicted from crack growth models. The crack growth rate is modeled with an underlying assumption that slip responsible for early propagation does not extend in significant amounts beyond the next grain boundary in the direction of crack propagation. Two models that contain this assumption are combined: 1) cessation of propagation into a new grain until a mature plastic zone is developed; 2) retardation of propagation by crack closure stress, with closure stress calculated from the location of a crack tip relative to the grain boundary. The transition from short to long crack growth behavior is also discussed.

Proteomic Analysis of Calcium Effects on Soybean Root Tip under Flooding and Drought Stresses.

PubMed

Wang, Xin; Komatsu, Setsuko

2017-08-01

Flooding and drought are disadvantageous environmental conditions that induce cytosolic calcium in soybean. To explore the effects of flooding- and drought-induced increases in calcium, a gel-free/label-free proteomic analysis was performed. Cytosolic calcium was decreased by blocking calcium channels in the endoplasmic reticulum (ER) and plasma membrane under both stresses. Calnexin, protein disulfide isomerase, heat shock proteins and thioredoxin were predominantly affected as the ER proteins in response to calcium, and ER-associated degradation-related proteins of HCP-like superfamily protein were up-regulated under stress exposure and then down-regulated. Glycolysis, fermentation, the tricarboxylic acid cycle and amino acid metabolism were mainly induced as the types of cellular metabolism in response to calcium under both stresses. Pyruvate decarboxylase was increased and decreased under flooding and drought, respectively, and was further decreased by the reduction of cytosolic calcium; however, it was recovered by exogenous calcium under both stresses. Furthermore, pyruvate decarboxylase activity was increased under flooding, but decreased under drought. These results suggest that calcium is involved in protein folding in the ER, and ER-associated degradation might alleviate ER stress during the early stage of both stresses. Furthermore, calcium appears to modify energy metabolism, and pyruvate decarboxylase may be a key enzyme in this process under flooding and drought. © The Author 2017. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Biochemical and molecular changes in response to aluminium-stress in highbush blueberry (Vaccinium corymbosum L.).

PubMed

Inostroza-Blancheteau, Claudio; Reyes-Díaz, Marjorie; Aquea, Felipe; Nunes-Nesi, Adriano; Alberdi, Miren; Arce-Johnson, Patricio

2011-09-01

Aluminium (Al) stress is an important factor limiting crop yields in acid soils. Despite this, very little is known about the mechanisms of resistance to this stress in woody plants. To understand the mechanisms of Al-toxicity and response in blueberries, we compared the impact of Al-stress in Al-resistant and Al-sensitive genotypes using Vaccinium corymbosum L. (Ericaceae) as a plant model. We investigated the effect of Al-stress on the physiological performance, oxidative metabolism and expression of genes that encode antioxidant enzymes in two V. corymbosum cultivars maintained hydroponically with AlCl(3) (0 and 100 μM). Microscopic analyses of Al-treated root tips suggested a higher degree of Al-induced morphological injury in Bluegold (sensitive genotype) compared to Brigitta (resistant genotype). Furthermore, the results indicated that Brigitta had a greater ability to control oxidative stress under Al-toxicity, as reflected by enhancement of several antioxidative and physiological properties (radical scavenging activity: RSA, superoxide dismutase: SOD and catalase: CAT; maximum quantum yield: Fv/Fm, effective quantum yield: ФPSII, electron transport rate: ETR and non-photochemical quenching: NPQ). Finally, we analyzed the expression of genes homologous to GST and ALDH, which were identified in a global expression analysis. In the resistant genotype, the expression of these genes in response to Al-stress was greater in leaves than in roots. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

Mechanical Evolution and Dynamics of Decollement Slip in Contractional Systems: Correlating Macro- and Micro-Scale Processes in Particle Dynamics Simulation

NASA Astrophysics Data System (ADS)

Morgan, J. K.

2014-12-01

Particle-based numerical simulations allow detailed investigations of small-scale processes and mechanisms associated with fault initiation and slip, which emerge naturally in such models. This study investigates the evolving mechanical conditions and associated micro-mechanisms during transient slip on a weak decollement propagating beneath a growing contractional wedge (e.g., accretionary prism, fold and thrust belt). The models serve as analogs of the seismic cycle, although lacking full earthquake dynamics. Nonetheless, the mechanical evolution of both decollement and upper plate can be monitored, and correlated with the particle-scale physical and contact properties, providing insights into changes that accompany such stick-slip behavior. In this study, particle assemblages consolidated under gravity and bonded to impart cohesion, are pushed at a constant velocity above a weak, unbonded decollement surface. Forward propagation of decollement slip occurs in discrete pulses, modulated by heterogeneous stress conditions (e.g., roughness, contact bridging) along the fault. Passage of decollement slip resets the stress along this horizon, producing distinct patterns: shear stress is enhanced in front of the slipped decollement due to local contact bridging and fault locking; shear stress minima occur immediately above the tip, denoting local stress release and contact reorganization following slip; more mature portions of the fault exhibit intermediate shear stress, reflecting more stable contact force distributions and magnitudes. This pattern of shear stress pre-conditions the decollement for future slip events, which must overcome the high stresses at the fault tip. Long-term slip along the basal decollement induces upper plate contraction. When upper plate stresses reach critical strength conditions, new thrust faults break through the upper plate, relieving stresses and accommodating horizontal shortening. Decollement activity retreats back to the newly formed thrust fault. The cessation of upper plate fault slip causes gradual increases in upper plate stresses, rebuilding shear stresses along the decollement and enabling renewed pulses of decollement slip. Thus, upper plate deformation occurs out of phase with decollement propagation.

Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

NASA Astrophysics Data System (ADS)

Ranjan, Srikant

2005-11-01

Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the resolved shear stress on primary slip planes. The maximum value of Krss and DeltaKrss was found to determine the crack growth direction and the fatigue crack growth rate respectively. The fatigue crack driving force parameter, DeltaK rss, forms an important multiaxial fatigue damage parameter that can be used to predict life in superalloy components.

Off-fault tip splay networks: a genetic and generic property of faults indicative of their long-term propagation, and a major component of off-fault damage

NASA Astrophysics Data System (ADS)

Perrin, C.; Manighetti, I.; Gaudemer, Y.

2015-12-01

Faults grow over the long-term by accumulating displacement and lengthening, i.e., propagating laterally. We use fault maps and fault propagation evidences available in literature to examine geometrical relations between parent faults and off-fault splays. The population includes 47 worldwide crustal faults with lengths from millimeters to thousands of kilometers and of different slip modes. We show that fault splays form adjacent to any propagating fault tip, whereas they are absent at non-propagating fault ends. Independent of parent fault length, slip mode, context, etc, tip splay networks have a similar fan shape widening in direction of long-term propagation, a similar relative length and width (~30 and ~10 % of parent fault length, respectively), and a similar range of mean angles to parent fault (10-20°). Tip splays more commonly develop on one side only of the parent fault. We infer that tip splay networks are a genetic and a generic property of faults indicative of their long-term propagation. We suggest that they represent the most recent damage off-the parent fault, formed during the most recent phase of fault lengthening. The scaling relation between parent fault length and width of tip splay network implies that damage zones enlarge as parent fault length increases. Elastic properties of host rocks might thus be modified at large distances away from a fault, up to 10% of its length. During an earthquake, a significant fraction of coseismic slip and stress is dissipated into the permanent damage zone that surrounds the causative fault. We infer that coseismic dissipation might occur away from a rupture zone as far as a distance of 10% of the length of its causative fault. Coseismic deformations and stress transfers might thus be significant in broad regions about principal rupture traces. This work has been published in Comptes Rendus Geoscience under doi:10.1016/j.crte.2015.05.002 (http://www.sciencedirect.com/science/article/pii/S1631071315000528).

Nitric Oxide Is Associated with Long-Term Zinc Tolerance in Solanum nigrum1[W

PubMed Central

Xu, Jin; Yin, Hengxia; Li, Yulong; Liu, Xiaojing

2010-01-01

Nitric oxide (NO) has been identified as a signal molecule that interplays with reactive oxygen species in response to heavy metal stresses. Roles of NO in regulating cadmium toxicity and iron deficiency have been proposed; however, the function of NO in zinc (Zn) tolerance in plants remains unclear. Here, we investigated NO accumulation and its role in plant Zn tolerance. Zn-induced NO production promoted an increase in reactive oxygen species accumulation in Solanum nigrum roots by modulating the expression and activity of antioxidative enzymes. Subsequently, programmed cell death (PCD) was observed in primary root tips. Inhibiting NO accumulation by 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (a specific NO scavenger) or NG-nitro-l-arginine-methyl ester (a NO synthase inhibitor) prevented the increase of superoxide radical and hydrogen peroxide as well as the subsequent cell death in the root tips, supporting the role of NO in Zn-induced PCD in the root tips. Zn-induced NO production affected the length of primary roots, the number of lateral roots, and root hair growth and thereby modulated root system architecture and activity. Investigation of metal contents in Zn-treated roots suggests that NO is required for metal (especially iron) uptake and homeostasis in plants exposed to excess Zn. Taken together, our results indicate that NO production and the subsequent PCD in root tips exposed to excess Zn are favorable for the S. nigrum seedling response to long-term Zn toxicity by modulating root system architecture and subsequent adaptation to Zn stress. PMID:20855519

Molecular-dynamics Simulation-based Cohesive Zone Representation of Intergranular Fracture Processes in Aluminum

NASA Technical Reports Server (NTRS)

Yamakov, Vesselin I.; Saether, Erik; Phillips, Dawn R.; Glaessgen, Edward H.

2006-01-01

A traction-displacement relationship that may be embedded into a cohesive zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics simulations. A molecular-dynamics model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element an atomistic analog to a continuum cohesive zone model element - the results from the molecular-dynamics simulation are recast to obtain an average continuum traction-displacement relationship to represent cohesive zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion. Keywords: Crack-tip plasticity; Cohesive zone model; Grain boundary decohesion; Intergranular fracture; Molecular-dynamics simulation

Proteomic and phosphoproteomic analysis of polyethylene glycol-induced osmotic stress in root tips of common bean (Phaseolus vulgaris L.)

PubMed Central

Horst, Walter Johannes

2013-01-01

Previous studies have shown that polyethylene glycol (PEG)-induced osmotic stress (OS) reduces cell-wall (CW) porosity and limits aluminium (Al) uptake by root tips of common bean (Phaseolus vulgaris L.). A subsequent transcriptomic study suggested that genes related to CW processes are involved in adjustment to OS. In this study, a proteomic and phosphoproteomic approach was applied to identify OS-induced protein regulation to further improve our understanding of how OS affects Al accumulation. Analysis of total soluble proteins in root tips indicated that, in total, 22 proteins were differentially regulated by OS; these proteins were functionally categorized. Seventy-seven per- cent of the total expressed proteins were involved in metabolic pathways, particularly of carbohydrate and amino acid metabolism. An analysis of the apoplastic proteome revealed that OS reduced the level of five proteins and increased that of seven proteins. Investigation of the total soluble phosphoproteome suggested that dehydrin responded to OS with an enhanced phosphorylation state without a change in abundance. A cellular immunolocalization analysis indicated that dehydrin was localized mainly in the CW. This suggests that dehydrin may play a major protective role in the OS-induced physical breakdown of the CW structure and thus maintenance of the reversibility of CW extensibility during recovery from OS. The proteomic and phosphoproteomic analyses provided novel insights into the complex mechanisms of OS-induced reduction of Al accumulation in the root tips of common bean and highlight a key role for modification of CW structure. PMID:24123251

Origin of anomalous inverse notch effect in bulk metallic glasses

NASA Astrophysics Data System (ADS)

Pan, J.; Zhou, H. F.; Wang, Z. T.; Li, Y.; Gao, H. J.

2015-11-01

Understanding notch-related failure is crucial for the design of reliable engineering structures. However, substantial controversies exist in the literature on the notch effect in bulk metallic glasses (BMGs), and the underlying physical mechanism responsible for the apparent confusion is still poorly understood. Here we investigate the physical origin of an inverse notch effect in a Zr-based metallic glass, where the tensile strength of the material is dramatically enhanced, rather than decreased (as expected from the stress concentration point of view), by introduction of a notch. Our experiments and molecular dynamics simulations show that the seemingly anomalous inverse notch effect is in fact caused by a transition in failure mechanism from shear banding at the notch tip to cavitation and void coalescence. Based on our theoretical analysis, the transition occurs as the stress triaxiality in the notched sample exceeds a material-dependent threshold value. Our results fill the gap in the current understanding of BMG strength and failure mechanism by resolving the conflicts on notch effects and may inspire re-interpretation of previous reports on BMG fracture toughness where pre-existing notches were routinely adopted.

Influence of Electrolyte Modulus on the Local Current Density at a Dendrite Tip on a Lithium Metal Electrode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harry, Katherine J.; Higa, Kenneth; Srinivasan, Venkat

Understanding and controlling the electrochemical deposition of lithium is imperative for the safe use of rechargeable batteries with a lithium metal anode. Solid block copolymer electrolyte membranes are known to enhance the stability of lithium metal anodes by mechanically suppressing the formation of lithium protrusions during battery charging. Time-resolved hard X-ray microtomography was used to monitor the internal structure of a symmetric lithium-polymer cell during galvanostatic polarization. The microtomography images were used to determine the local rate of lithium deposition, i.e. local current density, in the vicinity of a lithium globule growing through the electrolyte. Measurements of electrolyte displacement enabledmore » estimation of local stresses in the electrolyte. At early times, the current density was maximized at the globule tip, as expected from simple current distribution arguments. At later times, the current density was maximized at the globule perimeter. We show that this phenomenon is related to the local stress fields that arise as the electrolyte is deformed. The local current density, normalized for the radius of curvature, decreases with increasing compressive stresses at the lithium-polymer interface. To our knowledge, our study provides the first direct measurement showing the influence of local mechanical stresses on the deposition kinetics at lithium metal electrodes.« less

Influence of Electrolyte Modulus on the Local Current Density at a Dendrite Tip on a Lithium Metal Electrode

DOE PAGES

Harry, Katherine J.; Higa, Kenneth; Srinivasan, Venkat; ...

2016-08-10

Understanding and controlling the electrochemical deposition of lithium is imperative for the safe use of rechargeable batteries with a lithium metal anode. Solid block copolymer electrolyte membranes are known to enhance the stability of lithium metal anodes by mechanically suppressing the formation of lithium protrusions during battery charging. Time-resolved hard X-ray microtomography was used to monitor the internal structure of a symmetric lithium-polymer cell during galvanostatic polarization. The microtomography images were used to determine the local rate of lithium deposition, i.e. local current density, in the vicinity of a lithium globule growing through the electrolyte. Measurements of electrolyte displacement enabledmore » estimation of local stresses in the electrolyte. At early times, the current density was maximized at the globule tip, as expected from simple current distribution arguments. At later times, the current density was maximized at the globule perimeter. We show that this phenomenon is related to the local stress fields that arise as the electrolyte is deformed. The local current density, normalized for the radius of curvature, decreases with increasing compressive stresses at the lithium-polymer interface. To our knowledge, our study provides the first direct measurement showing the influence of local mechanical stresses on the deposition kinetics at lithium metal electrodes.« less

Influence of surrounding environment on subcritical crack growth in marble

NASA Astrophysics Data System (ADS)

Nara, Yoshitaka; Kashiwaya, Koki; Nishida, Yuki; , Toshinori, Ii

2017-06-01

Understanding subcritical crack growth in rock is essential for determining appropriate measures to ensure the long-term integrity of rock masses surrounding structures and for construction from rock material. In this study, subcritical crack growth in marble was investigated experimentally, focusing on the influence of the surrounding environment on the relationship between the crack velocity and stress intensity factor. The crack velocity increased with increasing temperature and/or relative humidity. In all cases, the crack velocity increased with increasing stress intensity factor. However, for Carrara marble (CM) in air, we observed a region in which the crack velocity still increased with temperature, but the increase in the crack velocity with increasing stress intensity factor was not significant. This is similar to Region II of subcritical crack growth observed in glass in air. Region II in glass is controlled by mass transport to the crack tip. In the case of rock, the transport of water to the crack tip is important. In general, Region II is not observed for subcritical crack growth in rock materials, because rocks contain water. Because the porosity of CM is very low, the amount of water contained in the marble is also very small. Therefore, our results imply that we observed Region II in CM. Because the crack velocity increased in both water and air with increasing temperature and humidity, we concluded that dry conditions at low temperature are desirable for the long-term integrity of a carbonate rock mass. Additionally, mass transport to the crack tip is an important process for subcritical crack growth in rock with low porosity.

The influence of tip shape on bending force during needle insertion

PubMed Central

van de Berg, Nick J.; de Jong, Tonke L.; van Gerwen, Dennis J.; Dankelman, Jenny; van den Dobbelsteen, John J.

2017-01-01

Steering of needles involves the planning and timely modifying of instrument-tissue force interactions to allow for controlled deflections during the insertion in tissue. In this work, the effect of tip shape on these forces was studied using 10 mm diameter needle tips. Six different tips were selected, including beveled and conical versions, with or without pre-bend or pre-curve. A six-degree-of-freedom force/torque sensor measured the loads during indentations in tissue simulants. The increased insertion (axial) and bending (radial) forces with insertion depth — the force-displacement slopes — were analyzed. Results showed that the ratio between radial and axial forces was not always proportional. This means that the tip load does not have a constant orientation, as is often assumed in mechanics-based steering models. For all tip types, the tip-load assumed a more radial orientation with increased axial load. This effect was larger for straight tips than for pre-bent or pre-curved tips. In addition, the force-displacement slopes were consistently higher for (1) increased tip angles, and for (2) beveled tips compared to conical tips. Needles with a bent or curved tip allow for an increased bending force and a decreased variability of the tip load vector orientation. PMID:28074939

Combined effects of thinning and decline on fine root dynamics in a Quercus robur L. forest adjoining the Italian Pre-Alps.

PubMed

Mosca, E; Montecchio, L; Barion, G; Dal Cortivo, C; Vamerali, T

2017-05-01

Oak decline is a complex phenomenon, characterized by symptoms of canopy transparency, bark cracks and root biomass reduction. Root health status is one of the first stress indicators, and root turnover is a key process in plant adaptation to unfavourable conditions. In this study, the combined effects of decline and thinning were evaluated on fine root dynamics in an oak forest adjoining the Italian Pre-Alps by comparison of acute declining trees with non-declining trees, both with and without thinning treatment of surrounding trees. Dynamics of volumetric root length density (RLD V ) and tip density (RTD V ), root tip density per unit length of root (RTD L ), diameter, branching index (BI) and mycorrhizal colonization were monitored by soil coring over 2 years as possible descriptors of decline. At the beginning of the experiment, the relationship between canopy transparency and root status was weak, declining trees having slightly lower RLD V (-20 %) and RTD V (-11 %). After a 1 year lag, during which the parameters were almost unaffected, BI and RLD V , together with tip density, tip vitality and mycorrhizal colonization, became the descriptors most representative of both decline class and thinning. Thinning of declining trees increased RLD V (+12 %) and RTD V (+32 %), but reduced tip mycorrhizal colonization and vitality over time compared with non-thinned trees, whereas the opposite occurred in healthy trees, together with a marked decrease in branching. After thinning, there was an initial reduction in the structure of the ectomycorrhizal community, although recovery occurred about 10 months later, regardless of decline severity. Decline causes losses of fine root length, and a moderate recovery can be achieved by thinning, allowing better soil exploration by oak roots. The close correlation between root vitality and mycorrhizal colonization and their deterioration after thinning indicates that decline does not benefit from reduced root competition, excluding the hypothesis of limited water and nutrient availability as a possible cause of the syndrome in this forest. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com

Combined effects of thinning and decline on fine root dynamics in a Quercus robur L. forest adjoining the Italian Pre-Alps

PubMed Central

Montecchio, L.; Barion, G.; Dal Cortivo, C.; Vamerali, T.

2017-01-01

Abstract Aims Oak decline is a complex phenomenon, characterized by symptoms of canopy transparency, bark cracks and root biomass reduction. Root health status is one of the first stress indicators, and root turnover is a key process in plant adaptation to unfavourable conditions. In this study, the combined effects of decline and thinning were evaluated on fine root dynamics in an oak forest adjoining the Italian Pre-Alps by comparison of acute declining trees with non-declining trees, both with and without thinning treatment of surrounding trees. Methods Dynamics of volumetric root length density (RLDV) and tip density (RTDV), root tip density per unit length of root (RTDL), diameter, branching index (BI) and mycorrhizal colonization were monitored by soil coring over 2 years as possible descriptors of decline. Key Results At the beginning of the experiment, the relationship between canopy transparency and root status was weak, declining trees having slightly lower RLDV (–20 %) and RTDV (–11 %). After a 1 year lag, during which the parameters were almost unaffected, BI and RLDV, together with tip density, tip vitality and mycorrhizal colonization, became the descriptors most representative of both decline class and thinning. Thinning of declining trees increased RLDV (+12 %) and RTDV (+32 %), but reduced tip mycorrhizal colonization and vitality over time compared with non-thinned trees, whereas the opposite occurred in healthy trees, together with a marked decrease in branching. After thinning, there was an initial reduction in the structure of the ectomycorrhizal community, although recovery occurred about 10 months later, regardless of decline severity. Conclusions Decline causes losses of fine root length, and a moderate recovery can be achieved by thinning, allowing better soil exploration by oak roots. The close correlation between root vitality and mycorrhizal colonization and their deterioration after thinning indicates that decline does not benefit from reduced root competition, excluding the hypothesis of limited water and nutrient availability as a possible cause of the syndrome in this forest. PMID:28334145

Nanostar probes for tip-enhanced spectroscopy

NASA Astrophysics Data System (ADS)

Kim, Woong; Kim, Nara; Park, Joon Won; Kim, Zee Hwan

2015-12-01

To overcome the current limit of tip-enhanced spectroscopy that is based on metallic nano-probes, we developed a new scanning probe with a metallic nanostar, a nanoparticle with sharp spikes. A Au nanoparticle of 5 nm was first attached to the end of a tip through DNA-DNA hybridization and mechanical pick-up. The nanoparticle was converted to a nanostar with a core diameter of ~70 nm and spike lengths between 50 nm and 80 nm through the reduction of Au3+ with ascorbic acid in the presence of Ag+. Fabrication yields of such tips exceeded 60%, and more than 80% of such tips showed a mechanical durability sufficient for use in scanning microscopy. Effectiveness of the new probes for tip-enhanced Raman scattering (TERS) and tip-enhanced fluorescence (TEF) was confirmed. The probes exhibited the necessary enhancement for TEF, and the tip-on and tip-off ratios varied between 5 and 100. This large tip-to-tip variability may arise from the uncontrolled orientation of the apexes of the spike with respect to the sample surface, which calls for further fabrication improvement. The result overall supports a new fabrication approach for the probe that is effective for tip-enhanced spectroscopy.To overcome the current limit of tip-enhanced spectroscopy that is based on metallic nano-probes, we developed a new scanning probe with a metallic nanostar, a nanoparticle with sharp spikes. A Au nanoparticle of 5 nm was first attached to the end of a tip through DNA-DNA hybridization and mechanical pick-up. The nanoparticle was converted to a nanostar with a core diameter of ~70 nm and spike lengths between 50 nm and 80 nm through the reduction of Au3+ with ascorbic acid in the presence of Ag+. Fabrication yields of such tips exceeded 60%, and more than 80% of such tips showed a mechanical durability sufficient for use in scanning microscopy. Effectiveness of the new probes for tip-enhanced Raman scattering (TERS) and tip-enhanced fluorescence (TEF) was confirmed. The probes exhibited the necessary enhancement for TEF, and the tip-on and tip-off ratios varied between 5 and 100. This large tip-to-tip variability may arise from the uncontrolled orientation of the apexes of the spike with respect to the sample surface, which calls for further fabrication improvement. The result overall supports a new fabrication approach for the probe that is effective for tip-enhanced spectroscopy. Electronic supplementary information (ESI) available: Illustrations of TERS and TEF experiments, information about the TEM images, scheme of surface preparation and peak assignments of TERS spectra. See DOI: 10.1039/c5nr06657c

Plasma treatment of fiber facets for increased (de)mating endurance in physical contact fiber connectors

NASA Astrophysics Data System (ADS)

Van Erps, Jürgen; Voss, Kevin; De Witte, Martijn; Radulescu, Radu; Beri, Stefano; Watté, Jan; Thienpont, Hugo

2016-04-01

It is known that cleaving an optical fiber introduces a number of irregularities and defects to the fiber's end-face, such as hackles and shockwaves. These defects can act as failure initiators when stress is applied to the end-face. Given the fiber's small diameter of 125 ffm, a large amount of mechanical stress can be expected to be applied on its end-face during the mating-demating cycle. In addition, a connector in a fiber-to-the-home (FTTH) network can be expected to be mated and demated more than 30 times during its lifetime for purposes such as testing, churning, or provisioning. For this reason, the performance of a connector that displays low optical loss when first installed can dramatically degrade after few mating-demating cycles and catastrophic connector failure due to end-face breakage is likely. We present plasma discharge shaping of cleaved fiber tips to strongly improve the endurance of the fibers to repeated mating-demating cycles. We quantify the dependency of the plasma-induced surface curvature of the fiber tip on the plasma duration and on the position of the fiber tip within the plasma cloud. Finally we present data showing the improved endurance of fibers that are exposed to plasma compared to conventional as-cleaved fibers.

The effect of an East Pacific Rise offset on the formation of secondary cracks ahead of the Cocos-Nazca Rift at the Galapagos Triple Junction

NASA Astrophysics Data System (ADS)

Smith, D. K.; Montesi, L. G.; Schouten, H.; Zhu, W.

2011-12-01

A succession of short-lived, E-W trending cracks at the Galapagos Triple Junction north and south of the Cocos-Nazca (C-N) Rift, has been explained by a simple crack interaction model. The locations of where the cracks initiate are controlled by tensile stresses generated at the East Pacific Rise (EPR) by two interacting cracks: One representing the north-south trending EPR, and the other the large, westward propagating C-N Rift, whose tip is separated from the EPR by a distance D. The model predicts symmetric cracking at the EPR north and south of the C-N Rift tip. Symmetry in the distribution of cracks north and south of the C-N Rift is observed and especially remarkable between 2.5 and 1.5 Ma when the rapid jumping of cracks toward the C-N Rift appears synchronous. The rapid jumping can be explained by decreasing D, which means that the tip of the C-N Rift was moving closer to the EPR. Symmetry of cracking breaks down at 1.5 Ma, however, with the establishment of the Dietz Deep Rift, the southern boundary of the Galapagos microplate. Symmetry of cracking also breaks down on older crust to the east between about 100 35'W and 100 45'W (about 2.6 Ma) where a rapid jumping of cracks toward the C-N Rift is observed in the south cracking region. There is no evidence of similar rapid jumping in the north cracking region. It could be simply that the response to changing the value of D is not always as predicted. It could also be that the shape of the EPR has not always been symmetric about the C-N Rift, as assumed in the model. Currently, an overlapping spreading center with a 15 km east-west offset between the limbs of the EPR has formed at 1 50'N. We assess the importance of the geometry of the EPR on the crack interaction model. The model has been modified to include a ridge offset similar to what is observed today. We find that the region of stress enhancement at the EPR (where cracks initiate) is subdued south of the C-N Rift tip because of the EPR offset. It is possible, therefore, that the asymmetry in cracking observed since about 1.5 Ma may be explained in part by the presence of a ridge offset south of the C-N Rift tip.

Ten Tips for Your Child's Success in School

MedlinePlus

... of stress. Learn Always Your child may be past the preschool years, but home education is still a critical part of his overall learning experience. “Some of the attitude recently is that it’s up to the schools ...

A Cost-Effectiveness Analysis of the First Federally Funded Antismoking Campaign

PubMed Central

Xu, Xin; Alexander, Robert L.; Simpson, Sean A.; Goates, Scott; Nonnemaker, James M.; Davis, Kevin C.; McAfee, Tim

2015-01-01

Background In 2012, CDC launched the first federally funded national mass media antismoking campaign. The Tips From Former Smokers (Tips) campaign resulted in a 12% relative increase in population-level quit attempts. Purpose Cost-effectiveness analysis was conducted in 2013 to evaluate Tips from a funding agency’s perspective. Methods Estimates of sustained cessations; premature deaths averted; undiscounted life years (LYs) saved; and quality-adjusted life years (QALYs) gained by Tips were estimated. Results Tips saved about 179,099 QALYs and prevented 17,109 premature deaths in the U.S. With the campaign cost of roughly $48 million, Tips spent approximately $480 per quitter, $2,819 per premature death averted, $393 per LY saved, and $268 per QALY gained. Conclusions Tips was not only successful at reducing smoking-attributable morbidity and mortality but also was a highly cost-effective mass media intervention. PMID:25498550

Creep crack-growth: A new path-independent integral (T sub c), and computational studies. Ph.D. Thesis Final Report

NASA Technical Reports Server (NTRS)

Stonesifer, R. B.; Atluri, S. N.

1982-01-01

The development of valid creep fracture criteria is considered. Two path-independent integral parameters which show some degree of promise are the C* and (Delta T)sub c integrals. The mathematical aspects of these parameters are reviewed by deriving generalized vector forms of the parameters using conservation laws which are valid for arbitrary, three dimensional, cracked bodies with crack surface tractions (or applied displacements), body forces, inertial effects, and large deformations. Two principal conclusions are that (Delta T)sub c has an energy rate interpretation whereas C* does not. The development and application of fracture criteria often involves the solution of boundary/initial value problems associated with deformation and stresses. The finite element method is used for this purpose. An efficient, small displacement, infinitesimal strain, displacement based finite element model is specialized to two dimensional plane stress and plane strain and to power law creep constitutive relations. A mesh shifting/remeshing procedure is used for simulating crack growth. The model is implemented with the quartz-point node technique and also with specially developed, conforming, crack-tip singularity elements which provide for the r to the n-(1+n) power strain singularity associated with the HRR crack-tip field. Comparisons are made with a variety of analytical solutions and alternate numerical solutions for a number of problems.

Aluminum stress signaling in plants

PubMed Central

Baluska, Frantisek; Matsumoto, Hideaki

2009-01-01

Aluminum (Al) toxicity is a major constraint for crop production in acidic soil worldwide. When the soil pH is lower than 5, Al3+ is released to the soil and enters into root tip cell ceases root development of plant. In acid soil with high mineral content, Al is the major cause of phytotoxicity. The target of Al toxicity is the root tip, in which Al exposure causes inhibition of cell elongation and cell division, leading to root stunting accompanied by reduced water and nutrient uptake. A variety of genes have been identified that are induced or repressed upon Al exposure. At tissue level, the distal part of the transition zone is the most sensitive to Al. At cellular and molecular level, many cell components are implicated in the Al toxicity including DNA in nucleus, numerous cytoplastic compounds, mitochondria, the plasma membrane and the cell wall. Although it is difficult to distinguish the primary targets from the secondary effects so far, understanding of the target sites of the Al toxicity is helpful for elucidating the mechanisms by which Al exerts its deleterious effects on root growth. To develop high tolerance against Al stress is the major goal of plant sciences. This review examines our current understanding of the Al signaling with the physiological, genetic and molecular approaches to improve the crop performance under the Al toxicity. New discoveries will open up new avenues of molecular/physiological inquiry that should greatly advance our understanding of Al tolerance mechanisms. Additionally, these breakthroughs will provide new molecular resources for improving the crop Al tolerance via molecular-assisted breeding and biotechnology. PMID:19820334

Study on bending behaviour of nickel–titanium rotary endodontic instruments by analytical and numerical analyses

PubMed Central

Tsao, C C; Liou, J U; Wen, P H; Peng, C C; Liu, T S

2013-01-01

Aim To develop analytical models and analyse the stress distribution and flexibility of nickel–titanium (NiTi) instruments subject to bending forces. Methodology The analytical method was used to analyse the behaviours of NiTi instruments under bending forces. Two NiTi instruments (RaCe and Mani NRT) with different cross-sections and geometries were considered. Analytical results were derived using Euler–Bernoulli nonlinear differential equations that took into account the screw pitch variation of these NiTi instruments. In addition, the nonlinear deformation analysis based on the analytical model and the finite element nonlinear analysis was carried out. Numerical results are obtained by carrying out a finite element method. Results According to analytical results, the maximum curvature of the instrument occurs near the instrument tip. Results of the finite element analysis revealed that the position of maximum von Mises stress was near the instrument tip. Therefore, the proposed analytical model can be used to predict the position of maximum curvature in the instrument where fracture may occur. Finally, results of analytical and numerical models were compatible. Conclusion The proposed analytical model was validated by numerical results in analysing bending deformation of NiTi instruments. The analytical model is useful in the design and analysis of instruments. The proposed theoretical model is effective in studying the flexibility of NiTi instruments. Compared with the finite element method, the analytical model can deal conveniently and effectively with the subject of bending behaviour of rotary NiTi endodontic instruments. PMID:23173762

Composition and Antioxidant Activity of Water-Soluble Polysaccharides from Tuber indicum

PubMed Central

Luo, Qiang; Zhang, Jie; Yan, Liang; Tang, Yuanlin; Ding, Xiang; Yang, Zhirong

2011-01-01

Abstract Crude water-soluble Chinese truffle Tuber indicum polysaccharide (TIP) was extracted from the fruiting bodies with water and then successively purified by DEAE–cellulose 52 and Sephadex G-100 column chromatography, yielding two major polysaccharide fractions: TIP1-1 and TIP2-1. High-performance gel permeation chromatography analysis showed that the average molecular sizes of TIP1-1 and TIP2-1 were approximately 1.75×104 Da and 5.73×103 Da, respectively. Monosaccharide component analysis by gas chromatography indicated that TIP1-1 was composed of mannose, glucose, galactose, and rhamannose in the respective molar ratio of 3.93:1.24:0.75:1.26 and that TIP2-1 contained mannose, glucose, and arabinose in the respective molar ratio of 5.27:1.44:0.43. The antioxidant activity analyses revealed that TIP1-1 and TIP2-1 possessed considerable antioxidant activity. Compared with TIP1-1, which has a higher molecular weight and contains no uronic acid, TIP2-1 exhibited a protective effect on PC12 cells injured by H2O2 and a higher scavenging activity against free radicals. The relative effects of the lower molecular size, the presence of uronic acid, and the antioxidant activity of TIP2-1 appear to be significant. Accordingly, the Chinese truffle T. indicum might serve as an effective antioxidative healthcare food and source of natural antioxidants. PMID:21877953

Why the chameleon has spiral-shaped muscle fibres in its tongue

PubMed Central

Leeuwen, J. L. van

1997-01-01

The intralingual accelerator muscle is the primary actuator for the remarkable ballistic tongue projection of the chameleon. At rest, this muscle envelopes the elongated entoglossal process, a cylindrically shaped bone with a tapering distal end. During tongue projection, the accelerator muscle elongates and slides forward along the entoglossal process until the entire muscle extends beyond the distal end of the process. The accelerator muscle fibres are arranged in transverse planes (small deviations are possible), and form (hitherto unexplained) spiral-shaped arcs from the peripheral to the internal boundary. To initiate tongue projection, the muscle fibres probably generate a high intramuscular pressure. The resulting negative pressure gradient (from base to tip) causes the muscle to elongate and to accelerate forward. Effective forward sliding is made possible by a lubricant and a relatively low normal stress exerted on the proximal cylindrical part of the entoglossal process. A relatively high normal stress is, however, probably required for an effective acceleration of muscle tissue over the tapered end of the process. For optimal performance, the fast extension movement should occur without significant (energy absorbing) torsional motion of the tongue. In addition, the tongue extension movement is aided by a close packing of the muscles fibres (required for a high power density) and a uniform strain and work output in every cross-section of the muscle. A quantitative model of the accelerator muscle was developed that predicts internal muscle fibre arrangements based on the functional requirements above and the physical principle of mechanical stability. The curved shapes and orientations of the muscle fibres typically found in the accelerator muscle were accurately predicted by the model. Furthermore, the model predicts that the reduction of the entoglossal radius towards the tip (and thus the internal radius of the muscle) tends to increase the normal stress on the entoglossal bone.

Study on the Effect of the Impact Location and the Type of Hammer Tip on the Frequency Response Function (FRF) in Experimental Modal Analysis of Rectangular Plates

NASA Astrophysics Data System (ADS)

Mali, K. D.; Singru, P. M.

2018-03-01

In this work effect of the impact location and the type of hammer tip on the frequency response function (FRF) is studied. Experimental modal analysis of rectangular plates is carried out for this purpose by using impact hammer, accelerometer and fast Fourier transform (FFT) analyzer. It is observed that the impulse hammer hit location has, no effect on the eigenfrequency, yet a difference in amplitude of the eigenfrequencies is obtained. The effect of the hammer tip on the pulse and the force spectrum is studied for three types of tips metal, plastic and rubber. A solid rectangular plate was excited by using these tips one by one in three different tests. It is observed that for present experimental set up plastic tip excites the useful frequency range.

A new aeroelastic model for composite rotor blades with straight and swept tips

NASA Technical Reports Server (NTRS)

Yuan, Kuo-An; Friedmann, Peretz P.; Venkatesan, Comandur

1992-01-01

An analytical model for predicting the aeroelastic behavior of composite rotor blades with straight and swept tips is presented. The blade is modeled by beam type finite elements along the elastic axis. A single finite element is used to model the swept tip. The nonlinear equations of motion for the finite element model are derived using Hamilton's principle and based on a moderate deflection theory and accounts for: arbitrary cross-sectional shape, pretwist, generally anisotropic material behavior, transverse shears and out-of-plane warping. Numerical results illustrating the effects of tip sweep, anhedral and composite ply orientation on blade aeroelastic behavior are presented. Tip sweep can induce aeroelastic instability by flap-twist coupling. Tip anhedral causes lag-torsion and flap-axial couplings, however, its effects on blade stability is less pronounced than the effect due to sweep. Composite ply orientation has a substantial effect on blade stability.

Three-dimensional stress intensity factor analysis of a surface crack in a high-speed bearing

NASA Technical Reports Server (NTRS)

Ballarini, Roberto; Hsu, Yingchun

1990-01-01

The boundary element method is applied to calculate the stress intensity factors of a surface crack in the rotating inner raceway of a high-speed roller bearing. The three-dimensional model consists of an axially stressed surface cracked plate subjected to a moving Hertzian contact loading. A multidomain formulation and singular crack-tip elements were employed to calculate the stress intensity factors accurately and efficiently for a wide range of configuration parameters. The results can provide the basis for crack growth calculations and fatigue life predictions of high-performance rolling element bearings that are used in aircraft engines.

Measurements of the Time-Averaged and Instantaneous Induced Velocities in the Wake of a Helicopter Rotor Hovering at High Tip Speeds

NASA Technical Reports Server (NTRS)

Heyson, Harry H.

1960-01-01

Measurements of the time-averaged induced velocities were obtained for rotor tip speeds as great as 1,100 feet per second (tip Mach number of 0.98) and measurements of the instantaneous induced velocities were obtained for rotor tip speeds as great as 900 feet per second. The results indicate that the small effects on the wake with increasing Mach number are primarily due to the changes in rotor-load distribution resulting from changes in Mach number rather than to compressibility effects on the wake itself. No effect of tip Mach number on the instantaneous velocities was observed. Under conditions for which the blade tip was operated at negative pitch angles, an erratic circulatory flow was observed.

Transverse cracking and stiffness reduction in composite laminates

NASA Technical Reports Server (NTRS)

Yuan, F. G.; Selek, M. C.

1993-01-01

A study of transverse cracking mechanism in composite laminates is presented using a singular hybrid finite element model. The model provides the global structural response as well as the precise local crack-tip stress fields. An elasticity basis for the problem is established by employing Lekhnitskii's complex variable potentials and method of eigenfunction expansion. Stress singularities associated with the transverse crack are obtained by decomposing the deformation into the symmetric and antisymmetric modes and proper boundary conditions. A singular hybrid element is thereby formulated based on the variational principle of a modified hybrid functional to incorporate local crack singularities. Axial stiffness reduction due to transverse cracking is studied. The results are shown to be in very good agreement with the existing experimental data. Comparison with simple shear lag analysis is also given. The effects of stress intensity factors and strain energy density on the increase of crack density are analyzed. The results reveal that the parameters approach definite limits when crack densities are saturated, an evidence of the existence of characteristic damage state.

When Your Parent Has Cancer

Cancer.gov

Help for teens whose mom or dad has cancer. Learn how families cope and find support when a parent has cancer. Tips to help you talk with your friends, deal with stress, and take care of your mind and body are also shared.

When Your Brother or Sister Has Cancer

Cancer.gov

Help when a brother or sister has cancer. Learn how families cope and find support when a sibling has cancer. Tips to help you talk with your friends, deal with stress, and take care of your mind and body are also shared.

Fractography of glasses and ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frechette, V.D.; Varner, J.R.

1988-01-01

This book collects papers on fracture mechanics in vitreous and ceramic materials. Topics include: crack branching in ceramics, fractographic determination of crack-tip stress intensity, fracture mechanisms of solid-state slab lasers, beta alumina failure in sodium-sulfur batteries, and fractography of glass.

Phytotoxicity of carbon nanotubes in soybean as determined by interactions with micronutrients

NASA Astrophysics Data System (ADS)

Zaytseva, Olga; Wang, Zhengrui; Neumann, Günter

2017-02-01

Carbon nanomaterials released into the environment exert extremely variable effects on living organisms. In this study, we used soybean ( Glycine max) to investigate early responses to seed exposure to multi-walled carbon nanotubes (MWCNTs, outer diameter 20-70 nm, inner diameter 5-10 nm, length of >2 μm). Soybean seeds were imbibed with deionised water (control) or MWCNT suspension (1000 mg L-1) and were analysed for MWCNT contamination using light microscopy. The seedlings vitality status was evaluated by staining with triphenyltetrazolium chloride and measurement of oxidative stress indicators in the root tissue. Micronutrient (Zn, Mn, Cu) availability in different seedling organs was assessed and the effects of antioxidants, and micronutrient supplementation was investigated. Oxidative stress induction by MWCNTs was detectable in radicle tips, coincided with MWCNTs accumulation and was reverted by external application of proline as antioxidant and micronutrients (Zn, Cu, Mn) as cofactors for various enzymes involved in oxidative stress defence. Accordingly, SOD activity increased after Zn supplementation. During germination, the MWCNT treatments reduced Zn translocation from the cotyledons to the seedling and MWCNTs exhibited adsorption potential for Zn and Cu, which may be involved in internal micronutrients immobilisation. This study demonstrates for the first time that MWCNT phytotoxicity is linked with oxidative stress-related disturbances of micronutrient homeostasis.

Dose-dependent response of Trichoderma harzianum in improving drought tolerance in rice genotypes.

PubMed

Pandey, Veena; Ansari, Mohammad W; Tula, Suresh; Yadav, Sandep; Sahoo, Ranjan K; Shukla, Nandini; Bains, Gurdeep; Badal, Shail; Chandra, Subhash; Gaur, A K; Kumar, Atul; Shukla, Alok; Kumar, J; Tuteja, Narendra

2016-05-01

This study demonstrates a dose-dependent response of Trichoderma harzianum Th-56 in improving drought tolerance in rice by modulating proline, SOD, lipid peroxidation product and DHN / AQU transcript level, and the growth attributes. In the present study, the effect of colonization of different doses of T. harzianum Th-56 strain in rice genotypes were evaluated under drought stress. The rice genotypes treated with increasing dose of T. harzianum strain Th-56 showed better drought tolerance as compared with untreated control plant. There was significant change in malondialdehyde, proline, higher superoxide dismutase level, plant height, total dry matter, relative chlorophyll content, leaf rolling, leaf tip burn, and the number of scorched/senesced leaves in T. harzianum Th-56 treated rice genotypes under drought stress. This was corroborated with altered expression of aquaporin and dehydrin genes in T. harzianum Th-56 treated rice genotypes. The present findings suggest that a dose of 30 g/L was the most effective in improving drought tolerance in rice, and its potential exploitation will contribute to the advancement of rice genotypes to sustain crop productivity under drought stress. Interaction studies of T. harzianum with three aromatic rice genotypes suggested that PSD-17 was highly benefitted from T. harzianum colonization under drought stress.

Micromechanisms of Crack Growth in Ceramics and Glasses in Corrosive Environments.

DTIC Science & Technology

1980-05-01

Resistance Mecanique du Verre et les Moyens de l’Amelioree, Union Scientifique Continentale du Verre , Charleroix, Belgium, (1962). 8. B. A. Proctor, I...exhibit similar types of delayed failure curves. Failure occurs most rapidly at high loads. Below a critical value of the load known as the stress...fracture for the three types of materials differ greatly. Polymers and metals have plastic zones at their crack tips, so that stress corrosion

Strengthening silicon carbide by quenching

NASA Technical Reports Server (NTRS)

Gruver, R. M.; Platts, D. R.; Kirchner, H. P.

1974-01-01

Quenching was used to form compressive surface layers in hot-pressed silicon carbide. The presence of the compressive stresses was verified by slotted rod tests. The slotted rod tip deflection was retained at temperatures to at least 1380 C, showing that the stresses are not relieved immediately at elevated temperatures. The flexural strength and impact resistance of specimens quenched from moderate temperatures (2000 C) were increased. Frequently, specimens quenched from higher temperatures were weakened by thermal shock damage.

Interactions between Polygonal Normal Faults and Larger Normal Faults, Offshore Nova Scotia, Canada

NASA Astrophysics Data System (ADS)

Pham, T. Q. H.; Withjack, M. O.; Hanafi, B. R.

2017-12-01

Polygonal faults, small normal faults with polygonal arrangements that form in fine-grained sedimentary rocks, can influence ground-water flow and hydrocarbon migration. Using well and 3D seismic-reflection data, we have examined the interactions between polygonal faults and larger normal faults on the passive margin of offshore Nova Scotia, Canada. The larger normal faults strike approximately E-W to NE-SW. Growth strata indicate that the larger normal faults were active in the Late Cretaceous (i.e., during the deposition of the Wyandot Formation) and during the Cenozoic. The polygonal faults were also active during the Cenozoic because they affect the top of the Wyandot Formation, a fine-grained carbonate sedimentary rock, and the overlying Cenozoic strata. Thus, the larger normal faults and the polygonal faults were both active during the Cenozoic. The polygonal faults far from the larger normal faults have a wide range of orientations. Near the larger normal faults, however, most polygonal faults have preferred orientations, either striking parallel or perpendicular to the larger normal faults. Some polygonal faults nucleated at the tip of a larger normal fault, propagated outward, and linked with a second larger normal fault. The strike of these polygonal faults changed as they propagated outward, ranging from parallel to the strike of the original larger normal fault to orthogonal to the strike of the second larger normal fault. These polygonal faults hard-linked the larger normal faults at and above the level of the Wyandot Formation but not below it. We argue that the larger normal faults created stress-enhancement and stress-reorientation zones for the polygonal faults. Numerous small, polygonal faults formed in the stress-enhancement zones near the tips of larger normal faults. Stress-reorientation zones surrounded the larger normal faults far from their tips. Fewer polygonal faults are present in these zones, and, more importantly, most polygonal faults in these zones were either parallel or perpendicular to the larger faults.

Structural Modifications of Fructans in Aloe barbadensis Miller (Aloe Vera) Grown under Water Stress

PubMed Central

Salinas, Carlos; Cardemil, Liliana

2016-01-01

Aloe barbadensis Miller (Aloe vera) has a Crassulaceae acid metabolism which grants the plant great tolerance to water restrictions. Carbohydrates such as acemannans and fructans are among the molecules responsible for tolerating water deficit in other plant species. Nevertheless, fructans, which are prebiotic compounds, have not been described nor studied in Aloe vera, whose leaf gel is known to possess beneficial pharmaceutical, nutritional and cosmetic properties. As Aloe vera is frequently cultivated in semi-arid conditions, like those found in northern Chile, we investigated the effect of water deficit on fructan composition and structure. For this, plants were subjected to different irrigation regimes of 100%, 75%, 50% and 25% field capacity (FC). There was a significant increase in the total sugars, soluble sugars and oligo and polyfructans in plants subjected to water deficit, compared to the control condition (100% FC) in both leaf tips and bases. The amounts of fructans were also greater in the bases compared to the leaf tips in all water treatments. Fructans also increase in degree of polymerization with increasing water deficit. Glycosidic linkage analyses by GC-MS, led to the conclusion that there are structural differences between the fructans present in the leaves of control plants with respect to plants irrigated with 50% and 25% FC. Therefore, in non-stressed plants, the inulin, neo-inulin and neo-levan type of fructans predominate, while in the most stressful conditions for the plant, Aloe vera also synthesizes fructans with a more branched structure, the neofructans. To our knowledge, the synthesis and the protective role of neo-fructans under extreme water deficit has not been previously reported. PMID:27454873

Structural Modifications of Fructans in Aloe barbadensis Miller (Aloe Vera) Grown under Water Stress.

PubMed

Salinas, Carlos; Handford, Michael; Pauly, Markus; Dupree, Paul; Cardemil, Liliana

2016-01-01

Aloe barbadensis Miller (Aloe vera) has a Crassulaceae acid metabolism which grants the plant great tolerance to water restrictions. Carbohydrates such as acemannans and fructans are among the molecules responsible for tolerating water deficit in other plant species. Nevertheless, fructans, which are prebiotic compounds, have not been described nor studied in Aloe vera, whose leaf gel is known to possess beneficial pharmaceutical, nutritional and cosmetic properties. As Aloe vera is frequently cultivated in semi-arid conditions, like those found in northern Chile, we investigated the effect of water deficit on fructan composition and structure. For this, plants were subjected to different irrigation regimes of 100%, 75%, 50% and 25% field capacity (FC). There was a significant increase in the total sugars, soluble sugars and oligo and polyfructans in plants subjected to water deficit, compared to the control condition (100% FC) in both leaf tips and bases. The amounts of fructans were also greater in the bases compared to the leaf tips in all water treatments. Fructans also increase in degree of polymerization with increasing water deficit. Glycosidic linkage analyses by GC-MS, led to the conclusion that there are structural differences between the fructans present in the leaves of control plants with respect to plants irrigated with 50% and 25% FC. Therefore, in non-stressed plants, the inulin, neo-inulin and neo-levan type of fructans predominate, while in the most stressful conditions for the plant, Aloe vera also synthesizes fructans with a more branched structure, the neofructans. To our knowledge, the synthesis and the protective role of neo-fructans under extreme water deficit has not been previously reported.

Stress wave focusing transducers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Visuri, S.R., LLNL

Conversion of laser radiation to mechanical energy is the fundamental process behind many medical laser procedures, particularly those involving tissue destruction and removal. Stress waves can be generated with laser radiation in several ways: creation of a plasma and subsequent launch of a shock wave, thermoelastic expansion of the target tissue, vapor bubble collapse, and ablation recoil. Thermoelastic generation of stress waves generally requires short laser pulse durations and high energy density. Thermoelastic stress waves can be formed when the laser pulse duration is shorter than the acoustic transit time of the material: {tau}{sub c} = d/c{sub s} where dmore » = absorption depth or spot diameter, whichever is smaller, and c{sub s} = sound speed in the material. The stress wave due to thermoelastic expansion travels at the sound speed (approximately 1500 m/s in tissue) and leaves the site of irradiation well before subsequent thermal events can be initiated. These stress waves, often evolving into shock waves, can be used to disrupt tissue. Shock waves are used in ophthalmology to perform intraocular microsurgery and photodisruptive procedures as well as in lithotripsy to fragment stones. We have explored a variety of transducers that can efficiently convert optical to mechanical energy. One such class of transducers allows a shock wave to be focused within a material such that the stress magnitude can be greatly increased compared to conventional geometries. Some transducer tips could be made to operate regardless of the absorption properties of the ambient media. The size and nature of the devices enable easy delivery, potentially minimally-invasive procedures, and precise tissue- targeting while limiting thermal loading. The transducer tips may have applications in lithotripsy, ophthalmology, drug delivery, and cardiology.« less

The crack problem for a nonhomogeneous plane

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1982-01-01

The plane elasticity problem for a nonhomogeneous medium containing a crack is considered. It is assumed that the Poisson's ratio of the medium is constant and the Young's modulus E varies exponentially with the coordinate parallel to the crack. First the half plane problem is formulated and the solution is given for arbitrary tractions along the boundary. Then the integral equation for the crack problem is derived. It is shown that the integral equation having the derivative of the crack surface displacement as the density function has a simple Cauchy type kernel. Hence, its solution and the stresses around the crack tips have the conventional square root singularity. The solution is given for various loading conditions. The results show that the effect of the Poisson's ratio and consequently that of the thickness constraint on the stress intensity factors are rather negligible.

The crack problem for a nonhomogeneous plane

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1983-01-01

The plane elasticity problem for a nonhomogeneous medium containing a crack is considered. It is assumed that the Poisson's ratio of the medium is constant and the Young's modulus E varies exponentially with the coordinate parallel to the crack. First the half plane problem is formulated and the solution is given for arbitrary tractions along the boundary. Then the integral equation for the crack problem is derived. It is shown that the integral equation having the derivative of the crack surface displacement as the density function has a simple Cauchy type kernel. Hence, its solution and the stresses around the crack tips have the conventional square root singularity. The solution is given for various loading conditions. The results show that the effect of the Poisson's ratio and consequently that of the thickness constraint on the stress intensity factors are rather negligible.

Advances in cleavage fracture modelling in steels: Micromechanical, numerical and multiscale aspects

NASA Astrophysics Data System (ADS)

Pineau, André; Tanguy, Benoît

2010-04-01

Brittle cleavage fracture remains one of the major concerns for structural integrity assessment. The main characteristics of this mode of failure in relation to the stress field ahead of a crack, tip are described in the introduction. The emphasis is laid on the physical origins of scatter and the size effect observed in ferritic steels. It is shown that cleavage fracture is controlled by physical events occurring at different scales: initiation at (sub)micrometric particles, propagation across grain boundaries (10-50 microns) and final fracture at centimetric scale. The two first scales are detailed in this paper. The statistical origin of cleavage is described quantitatively from both microstructural defects and stress-strain heterogeneities due to crystalline plasticity at the grain scale. Existing models are applied to the prediction of the variation of Charpy fracture toughness with temperature.

Tensile stress induced depolarization in [001]-poled transverse mode Pb(Zn{sub 1/3}Nb{sub 2/3})O{sub 3} -(6-7)%PbTiO{sub 3} single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shukla, Rahul; Department of Mechanical Engineering, National University of Singapore, Singapore 119260; Lim, Leong-Chew

2011-04-01

This paper investigates the effects of electrically induced and direct tensile stress on the deformation and dielectric properties of Pb(Zn{sub 1/3}Nb{sub 2/3})O{sub 3}-(6-7)%PbTiO{sub 3} single crystals of [110]{sup L}x[001]{sup T} cut by using a unimorph sample and a four-point-bend (FPB) sample, respectively. The results show a dip in tip displacement for the unimorph sample at sufficiently high electric field parallel to the poling field direction and a sudden rise in capacitance for the FPB sample at sufficiently high tensile stress in the [110] crystal direction, respectively. These phenomena are attributed to the tensile stress induced rhombohedral-to-orthorhombic phase transition and associatedmore » depolarization events in the crystal. For the said crystal cut, the obtained tensile depoling stress is in the range of 15-20 MPa. The present work furthermore shows that the occurrence of tensile stress-induced depolarization is possible even when the direction of the applied electric field is parallel to the poling field direction, as in the unimorph sample examined.« less

A three-dimensional gravity study of the 95.5°W propagating rift in the Galapagos spreading center

NASA Astrophysics Data System (ADS)

Phipps Morgan, Jason; Parmentier, E. M.

1987-01-01

Seafloor at the Galapagos 95.5°W propagating rift (PR) has a varied morphological expression that can be spatially correlated with the predicted kinematic history of the PR. A median valley-like depression occurs near the tip of the growing ridge axis. To test if this bathymetry is a dynamic feature supported by mantle or lithosphere strength or if it is due to isostatically compensated crustal thickness variations, we use three-dimensional gravity modelling to constrain the crustal structure in this region, from data collected by Hey in 1979 and 1982. The gravity anomaly at the PR tip depression suggests that the tip depression is not caused by crustal thinning. The data are consistent with a stress-supported PR tip depression caused by asthenospheric along-axis flow into the growing ridge axis (Phipps Morgan and Parmentier [1]). In contrast to the tip depression, seafloor in the sheared zone of material transferred through transform migration from the Cocos to Nazca plate is anomalously shallow and has a pronounced regional 300-400 m tilt towards the growing ridge axis over the 20 km width of the sheared zone. The gravity data also suggest that the sheared zone is not compensated by crustal thickening.

The mechanics of delamination in fiber-reinforced composite materials. II - The delamination behavior and fracture mechanics parameters

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1983-01-01

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extension. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined. Previously announced in STAR as N84-13222

Rene 95 brazed joint metallurgical program

NASA Technical Reports Server (NTRS)

Gay, C.; Givens, J.; Mastrorroco, S.; Sterman, A.

1972-01-01

This metallurgical program was specifically conducted for the establishment of material properties required for the design of the LF460 fan. The LF460 lift fan is an advanced 18:1 high thrust to weight single stage design. It has a turbine attached to the outer flowpath of the fan blade tip which minimizes the axial depth of the fan. Advanced lightweight attachment designs are employed in this concept to achieve minimum mass polar moments of inertia which are required for good aircraft flight response control. The design features which are unique to this advanced LF460 lift fan are the 0.010 inch thin Udimet 700 alloy integral tip turbine design, minimum weight braze attachment of the turbine to the fan blade, and the high strength and elevated temperature capability of the Rene'95 alloy for the fan blade. The data presented in this report show that the LF460 fan rotor design is feasible and that the design stresses and margins of safety were more than adequate. Prior to any production application, however, additional stress rupture/shear lap joints should be run in order to establish a firm 1200 F stress rupture curve for the CM50 braze metal.

High-Resolution Characterizations of Grain Boundary Damage and Stress Corrosion Cracks in Cold-Rolled Alloy 690

NASA Astrophysics Data System (ADS)

Bruemmer, S. M.; Olszta, M. J.; Toloczko, M. B.; Thomas, L. E.

Unidirectional cold rolling has been shown to promote intergranular stress corrosion cracking (IGSCC) in alloy 690 tested in PWR primary water. High-resolution scanning (SEM) and transmission electron microscopy (TEM) have been employed to investigate the microstructural reasons for this enhanced susceptibility in two stages, first examining grain boundary damage produced by cold rolling and second by characterization of stress corrosion crack tips. The degree of permanent grain boundary damage from cold rolling was found to depend directly on the initial IG precipitate distribution. Cold rolling to high levels of reduction was discovered to produce small IG voids and cracked carbides in alloys with a high density of grain boundary carbides. For the same degree of cold rolling, alloys with few IG carbides exhibited much less permanent damage. Although this difference in grain boundary damage appears to correlate with measured SCC growth rates, crack tip examinations reveal no interaction between the preexisting voids and cracked carbides with the propagation. In many cases, these features appeared to blunt propagation of IGSCC cracks. High-resolution characterizations are described for cold-rolled alloy 690 CRDM tubing and plate materials to gain insights into IGSCC mechanisms.

Development of a high hertz-stress contact for conventional batch production using a unique scribing technology

NASA Astrophysics Data System (ADS)

Bhuiyan, M. M. I.; Alamgir, T.; Bhuiyan, M.; Kajihara, M.

2013-12-01

Gradually the electronic devices are getting more compact dimension with respect to the width and thickness. As a result, the contacts are becoming thinner and which leads the contact to be loose and unstable contact. In comercial stamping methode, connector tip diameter should be more than 300μm due to its size limitation. Consequently, the connector contact resistance is becoming higher due to weak contact force. To overcome this problem there were few more basic research using MEMS and Electro Fine Forming (EFF) technology to make high Hertz-Stress Contact (5μm) due to the limitation in the commercial stamping process and the result was in satisfactory level. However, since the MEMS and EFF fabrication is costly therefore, a new method is introduced in this paper using the commercial Phosphor Bronze stamping method to reduce the production cost. Moreover, scribing method is used to make tip on the contact. Accordingly, more compact fine pitch contact is successfully fabricated and tested with 5μm High Hertz Stress without using the MEMS and EFF technology. Hence the manufactured contact resistance becomes less than 20mΩ ±5mΩ.

Experimentally validated 3D MD model for AFM-based tip-based nanomanufacturing

NASA Astrophysics Data System (ADS)

Promyoo, Rapeepan

In order to control AFM-based TBN to produce precise nano-geometry efficiently, there is a need to conduct a more focused study of the effects of different parameters, such as feed, speed, and depth of cut on the process performance and outcome. This is achieved by experimentally validating a MD simulation model of nanomachining, and using it to conduct parametric studies to guide AFM-based TBN. A 3D MD model with a larger domain size was developed and used to gain a unique insight into the nanoindentation and nanoscratching processes such as the effect of tip speed (e.g. effect of tip speed on indentation force above 10 nm of indentation depth). The model also supported a more comprehensive parametric study (than other published work) in terms of number of parameters and ranges of values investigated, as well as a more cost effective design of experiments. The model was also used to predict material properties at the nanoscale (e.g. hardness of gold predicted within 6% error). On the other hand, a comprehensive experimental parametric study was conducted to produce a database that is used to select proper machining conditions for guiding the fabrication of nanochannels (e.g. scratch rate = 0.996 Hz, trigger threshold = 1 V, for achieving a nanochannel depth = 50 nm for the case of gold device). Similar trends for the variation of indentation force with depth of cut, pattern of the material pile-up around the indentation mark or scratched groove were found. The parametric studies conducted using both MD model simulations and AFM experiments showed the following: Normal forces for both nanoindentation and nanoscratching increase as the depth of cut increases. The indentation depth increases with tip speed, but the depth of scratch decrease with increasing tip speed. The width and depth of scratched groove also depend on the scratch angle. The recommended scratch angle is at 90°. The surface roughness increases with step over, especially when the step over is larger than the tip radius. The depth of cut also increases as the step over decreases. Additional study is conducted using the MD model to understand the effect of crystal structure and defects in material when subjected to a stress. Several types of defects, including vacancies and Shockley partial dislocation loops, can be observed during the MD simulation for the case of gold, copper and aluminum. Finally, AFM-based TBN is used with photolithography to fabricate a nano-fluidic device for medical application. In fact, the photolithography process is used to create microchannels on top of a silicon wafer, and AFM-based TBN is applied to fabricate nanochannels between the microchannels that connect to the reservoirs. Fluid flow test was conducted on the devices to ensure that the nanochannel was open and the bonding sealed.

Vee-notch tool cuts specimens

NASA Technical Reports Server (NTRS)

Spier, R. A.

1970-01-01

Triangular cutting tool uses carbide tips for notching heat-treated or abrasive materials, and alloys subjected to high structural stresses. The tool is rigidly mounted in a slot of mating contour to prevent deflection during cutting of tensile specimens. No other expensive machine equipment is required.

Bi nanowire-based thermal biosensor for the detection of salivary cortisol using the Thomson effect

NASA Astrophysics Data System (ADS)

Lee, Seunghyun; Hyun Lee, Jung; Kim, MinGin; Kim, Jeongmin; Song, Min-Jung; Jung, Hyo-Il; Lee, Wooyoung

2013-09-01

We present a study of a thermal biosensor based on bismuth nanowire that is fabricated for the detection of the human stress hormone cortisol using the Thomson effect. The Bi nanowire was grown using the On-Film Formation of Nanowires (OFF-ON) method. The thermal device was fabricated using photolithography, and the sensing area was modified with immobilized anti-cortisol antibodies conjugated with protein G for the detection of cortisol. The voltages were measured with two probe tips during surface modification to investigate the biochemical reactions in the fabricated thermal biosensor. The Bi nanowire-based thermal biosensor exhibited low detection limit and good selectivity for the detection of cortisol.

Ultrathin strain-gated field effect transistor based on In-doped ZnO nanobelts

NASA Astrophysics Data System (ADS)

Zhang, Zheng; Du, Junli; Li, Bing; Zhang, Shuhao; Hong, Mengyu; Zhang, Xiaomei; Liao, Qingliang; Zhang, Yue

2017-08-01

In this work, we fabricated a strain-gated piezoelectric transistor based on single In-doped ZnO nanobelt with ±(0001) top/bottom polar surfaces. In the vertical structured transistor, the Pt tip of the AFM and Au film are used as source and drain electrode. The electrical transport performance of the transistor is gated by compressive strains. The working mechanism is attributed to the Schottky barrier height changed under the coupling effect of piezoresistive and piezoelectric. Uniquely, the transistor turns off under the compressive stress of 806 nN. The strain-gated transistor is likely to have important applications in high resolution mapping device and MEMS devices.

A simple method to prevent hard X-ray-induced preheating effects inside the cone tip in indirect-drive fast ignition implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Dongxiao; Shan, Lianqiang; Zhou, Weimin

During fast-ignition implosions, preheating of inside the cone tip caused by hard X-rays can strongly affect the generation and transport of hot electrons in the cone. Although indirect-drive implosions have a higher implosion symmetry, they cause stronger preheating effects than direct-drive implosions. To control the preheating of the cone tip, we propose the use of indirect-drive fast-ignition targets with thicker tips. Experiments carried out at the ShenGuang-III prototype laser facility confirmed that thicker tips are effective for controlling preheating. Moreover, these results were consistent with those of 1D radiation hydrodynamic simulations.

A combined piezoelectric composite actuator and its application to wing/blade tips

NASA Astrophysics Data System (ADS)

Ha, Kwangtae

A novel combined piezoelectric-composite actuator configuration is proposed and analytically modeled in this work. The actuator is a low complexity, active compliant mechanism obtained by coupling a modified star cross sectional configuration composite beam with a helicoidal bimorph piezoelectric actuator coiled around it. This novel actuator is a good candidate as a hinge tension-torsion bar actuator for a helicopter rotor blade flap or blade tip and mirror rotational positioning. In the wing tip case, the tip deflection angle is different only according to the aerodynamic moment depending on the hinge position of the actuator along the chord and applied voltage because there is no centrifugal force. For an active blade tip subject to incompressible flow and 2D quasi steady airloads, its twist angle is related not only to aerodynamic moment and applied voltage but also to coupling terms, such as the trapeze effect and the tennis racquet effect. Results show the benefit of hinge position aft of the aerodynamic center, such that the blade tip response is amplified by airloads. Contrary to this effect, results also show that the centrifugal effects and inertial effect cause an amplitude reduction in the response. Summation of these effects determines the overall blade tip response. The results for a certain hinge position of Xh=1.5% chord aft of the quarter chord point proves that the tip deflection target design range of beta ∈ [-2,+2] can be achieved for all pitch angle configurations chosen.

Effects of boundary layer forcing on wing-tip vortices

NASA Astrophysics Data System (ADS)

Shaw-Ward, Samantha

The nature of turbulence within wing-tip vortices has been a topic of research for decades, yet accurate measurements of Reynolds stresses within the core are inherently difficult due to the bulk motion wandering caused by initial and boundary conditions in wind tunnels. As a result, characterization of a vortex as laminar or turbulent is inconclusive and highly contradicting. This research uses several experimental techniques to study the effects of broadband turbulence, introduced within the wing boundary layer, on the development of wing-tip vortices. Two rectangular wings with a NACA 0012 profile were fabricated for the use of this research. One wing had a smooth finish and the other rough, introduced by P80 grade sandpaper. Force balance measurements showed a small reduction in wing performance due to surface roughness for both 2D and 3D configurations, although stall characteristics remained relatively unchanged. Seven-hole probes were purpose-built and used to assess the mean velocity profiles of the vortices five chord lengths downstream of the wing at multiple angles of attack. Above an incidence of 4 degrees, the vortices were nearly axisymmetric, and the wing roughness reduced both velocity gradients and peak velocity magnitudes within the vortex. Laser Doppler velocimetry was used to further assess the time-resolved vortex at an incidence of 5 degrees. Evidence of wake shedding frequencies and wing shear layer instabilities at higher frequencies were seen in power spectra within the vortex. Unlike the introduction of freestream turbulence, wing surface roughness did not appear to increase wandering amplitude. A new method for removing the effects of vortex wandering is proposed with the use of carefully selected high-pass filters. The filtered data revealed that the Reynolds stress profiles of the vortex produced by the smooth and rough wing were similar in shape, with a peak occurring away from the vortex centre but inside of the core. Single hot-wire measurements in the 2D wing wake revealed the potential origin of dominant length-scales observed in the vortex power spectra. At angles above 5 degrees, the 2D wing wake had both higher velocity deficits and higher levels of total wake kinetic energy for the rough wing as compared to the smooth wing.

Theory of buttressed marine ice sheet dynamics and its application to the assessment of tipping-point conditions

NASA Astrophysics Data System (ADS)

Pegler, S.

2017-12-01

Understanding the fate of the West Antarctic Ice Sheet is constrained by difficulties of resolving the buttressing effect of ice shelves and its dynamic response to grounding-line migration. This effect may be responsible for protecting a large majority of outlet glaciers in Antarctica against surging into the ocean. I present a theoretical methodology for assessing the positions and stability of grounding lines that incorporates closed-form, dynamic descriptions of ice-shelf buttressing and extensional (stretching) viscous stresses. The method is applied to assess the conditions for grounding-line tipping points. Such points are shown to produce abrupt `cliff-edge' transitions to runaway retreat, representing the so-called marine ice sheet instability. Depending on the bed profile, melt and calving rates, a tipping point can either lie very near to a local maximum in the bed topography or potentially far upstream of it, along a reverse bed. The model predictions for both wide and narrow embayments are validated by numerical simulations and laboratory experiments. A case study of Pine Island Glacier indicates the possibility for long-term stabilisation, with the analytical method affording an extensive exploration of scenarios. The theory also elucidates a mode of grounding-line migration controlled entirely by the determinants of the ice-shelf buttressing force, with a loss of sensitivity to basal conditions, contrasting with the conclusion from one-dimensional theory that the ice shelf is irrelevant. The results provide an interpretive framework for understanding grounding-line dynamics, its coupling with ice-shelf dynamics, an efficient exploration of parameter variation, and a complement to large-scale simulation.

Micromechanical testing of individual collagen fibrils.

PubMed

van der Rijt, Joost A J; van der Werf, Kees O; Bennink, Martin L; Dijkstra, Pieter J; Feijen, Jan

2006-09-15

A novel method based on AFM was used to attach individual collagen fibrils between a glass surface and the AFM tip, to allow force spectroscopy studies of these. The fibrils were deposited on glass substrates that are partly coated with Teflon AF. A modified AFM tip was used to accurately deposit epoxy glue droplets on either end of the collagen fibril that cross the glass-Teflon AF interface, as to such attach it with one end to the glass and the other end to the AFM tip. Single collagen fibrils have been mechanically tested in ambient conditions and were found to behave reversibly up to stresses of 90 MPa. Within this regime a Young's modulus of 2-7 GPa was obtained. In aqueous media, the collagen fibrils could be tested reversibly up to about 15 MPa, revealing Young's moduli ranging from 0.2 to at most 0.8 GPa.

Note: Microelectrode-shielding tip for scanning probe electron energy spectroscopy

NASA Astrophysics Data System (ADS)

Huang, Wei; Li, Zhean; Xu, Chunkai; Liu, Jian; Xu, Chunye; Chen, Xiangjun

2018-04-01

We report a novel microelectrode-shielding tip (ME tip) for scanning probe electron energy spectroscopy (SPEES). The shielding effect of this tip is studied through comparing the detection efficiency with the normal tip by both experiment and simulation. The results show that the backscattering count rate detected by the SPEES instrument using the normal tip begins to decrease as the tip approaches to the sample surface within 21 μm, while that using the ME tip only starts to drop off within 1 μm. This indicates that the electron energy spectra can be measured with the ME tip at a much closer tip-sample distance. Furthermore, it is also demonstrated that the ME tip can be used to obtain topography of the sample surface in situ simultaneously.

Computer-aided design of high-contact-ratio gears for minimum dynamic load and stress

NASA Technical Reports Server (NTRS)

Lin, Hsiang Hsi; Lee, Chinwai; Oswald, Fred B.; Townsend, Dennis P.

1990-01-01

A computer aided design procedure is presented for minimizing dynamic effects on high contact ratio gears by modification of the tooth profile. Both linear and parabolic tooth profile modifications of high contact ratio gears under various loading conditions are examined and compared. The effects of the total amount of modification and the length of the modification zone were systematically studied at various loads and speeds to find the optimum profile design for minimizing the dynamic load and the tooth bending stress. Parabolic profile modification is preferred over linear profile modification for high contact ratio gears because of its lower sensitivity to manufacturing errors. For parabolic modification, a greater amount of modification at the tooth tip and a longer modification zone are required. Design charts are presented for high contact ratio gears with various profile modifications operating under a range of loads. A procedure is illustrated for using the charts to find the optimum profile design.

New theory for crack-tip twinning in fcc metals

NASA Astrophysics Data System (ADS)

Andric, Predrag; Curtin, W. A.

2018-04-01

Dislocation emission from a crack tip is a necessary mechanism for crack tip blunting and toughening. In fcc metals under Mode I loading, a first partial dislocation is emitted, followed either by a trailing partial dislocation ("ductile" behaviour) or a twinning partial dislocation ("quasi-brittle"). The twinning tendency is usually estimated using the Tadmor and Hai extension of the Rice theory. Extensive molecular statics simulations reveal that the predictions of the critical stress intensity factor for crack tip twinning are always systematically lower (20-35%) than observed. Analyses of the energy change during nucleation reveal that twin partial emission is not accompanied by creation of a surface step while emission of the trailing partial creates a step. The absence of the step during twinning motivates a modified model for twinning nucleation that accounts for the fact that nucleation does not occur directly at the crack tip. Predictions of the modified theory are in excellent agreement with all simulations that show twinning. Emission of the trailing partial dislocation, including the step creation, is predicted using a model recently introduced to accurately predict the first partial emission and shows why twinning is preferred. A second mode of twinning is found wherein the crack first advances by cleavage and then emits the twinning partial at the new crack tip; this mode dominates for emission beyond the first twinning partial. These new theories resolve all the discrepancies between the Tadmor twinning analysis and simulations, and have various implications for fracture behaviour and transitions.

Identification and Validation of Reference Genes and Their Impact on Normalized Gene Expression Studies across Cultivated and Wild Cicer Species

PubMed Central

Reddy, Palakolanu Sudhakar; Sri Cindhuri, Katamreddy; Sivaji Ganesh, Adusumalli; Sharma, Kiran Kumar

2016-01-01

Quantitative Real-Time PCR (qPCR) is a preferred and reliable method for accurate quantification of gene expression to understand precise gene functions. A total of 25 candidate reference genes including traditional and new generation reference genes were selected and evaluated in a diverse set of chickpea samples. The samples used in this study included nine chickpea genotypes (Cicer spp.) comprising of cultivated and wild species, six abiotic stress treatments (drought, salinity, high vapor pressure deficit, abscisic acid, cold and heat shock), and five diverse tissues (leaf, root, flower, seedlings and seed). The geNorm, NormFinder and RefFinder algorithms used to identify stably expressed genes in four sample sets revealed stable expression of UCP and G6PD genes across genotypes, while TIP41 and CAC were highly stable under abiotic stress conditions. While PP2A and ABCT genes were ranked as best for different tissues, ABCT, UCP and CAC were most stable across all samples. This study demonstrated the usefulness of new generation reference genes for more accurate qPCR based gene expression quantification in cultivated as well as wild chickpea species. Validation of the best reference genes was carried out by studying their impact on normalization of aquaporin genes PIP1;4 and TIP3;1, in three contrasting chickpea genotypes under high vapor pressure deficit (VPD) treatment. The chickpea TIP3;1 gene got significantly up regulated under high VPD conditions with higher relative expression in the drought susceptible genotype, confirming the suitability of the selected reference genes for expression analysis. This is the first comprehensive study on the stability of the new generation reference genes for qPCR studies in chickpea across species, different tissues and abiotic stresses. PMID:26863232

Identification and Validation of Reference Genes and Their Impact on Normalized Gene Expression Studies across Cultivated and Wild Cicer Species.

PubMed

Reddy, Dumbala Srinivas; Bhatnagar-Mathur, Pooja; Reddy, Palakolanu Sudhakar; Sri Cindhuri, Katamreddy; Sivaji Ganesh, Adusumalli; Sharma, Kiran Kumar

2016-01-01

Quantitative Real-Time PCR (qPCR) is a preferred and reliable method for accurate quantification of gene expression to understand precise gene functions. A total of 25 candidate reference genes including traditional and new generation reference genes were selected and evaluated in a diverse set of chickpea samples. The samples used in this study included nine chickpea genotypes (Cicer spp.) comprising of cultivated and wild species, six abiotic stress treatments (drought, salinity, high vapor pressure deficit, abscisic acid, cold and heat shock), and five diverse tissues (leaf, root, flower, seedlings and seed). The geNorm, NormFinder and RefFinder algorithms used to identify stably expressed genes in four sample sets revealed stable expression of UCP and G6PD genes across genotypes, while TIP41 and CAC were highly stable under abiotic stress conditions. While PP2A and ABCT genes were ranked as best for different tissues, ABCT, UCP and CAC were most stable across all samples. This study demonstrated the usefulness of new generation reference genes for more accurate qPCR based gene expression quantification in cultivated as well as wild chickpea species. Validation of the best reference genes was carried out by studying their impact on normalization of aquaporin genes PIP1;4 and TIP3;1, in three contrasting chickpea genotypes under high vapor pressure deficit (VPD) treatment. The chickpea TIP3;1 gene got significantly up regulated under high VPD conditions with higher relative expression in the drought susceptible genotype, confirming the suitability of the selected reference genes for expression analysis. This is the first comprehensive study on the stability of the new generation reference genes for qPCR studies in chickpea across species, different tissues and abiotic stresses.

Computer-aided analysis of cutting processes for brittle materials

NASA Astrophysics Data System (ADS)

Ogorodnikov, A. I.; Tikhonov, I. N.

2017-12-01

This paper is focused on 3D computer simulation of cutting processes for brittle materials and silicon wafers. Computer-aided analysis of wafer scribing and dicing is carried out with the use of the ANSYS CAE (computer-aided engineering) software, and a parametric model of the processes is created by means of the internal ANSYS APDL programming language. Different types of tool tip geometry are analyzed to obtain internal stresses, such as a four-sided pyramid with an included angle of 120° and a tool inclination angle to the normal axis of 15°. The quality of the workpieces after cutting is studied by optical microscopy to verify the FE (finite-element) model. The disruption of the material structure during scribing occurs near the scratch and propagates into the wafer or over its surface at a short range. The deformation area along the scratch looks like a ragged band, but the stress width is rather low. The theory of cutting brittle semiconductor and optical materials is developed on the basis of the advanced theory of metal turning. The fall of stress intensity along the normal on the way from the tip point to the scribe line can be predicted using the developed theory and with the verified FE model. The crystal quality and dimensions of defects are determined by the mechanics of scratching, which depends on the shape of the diamond tip, the scratching direction, the velocity of the cutting tool and applied force loads. The disunity is a rate-sensitive process, and it depends on the cutting thickness. The application of numerical techniques, such as FE analysis, to cutting problems enhances understanding and promotes the further development of existing machining technologies.

Yeh-Stratton Criterion for Stress Concentrations on Fiber-Reinforced Composite Materials

NASA Technical Reports Server (NTRS)

Yeh, Hsien-Yang; Richards, W. Lance

1996-01-01

This study investigated the Yeh-Stratton Failure Criterion with the stress concentrations on fiber-reinforced composites materials under tensile stresses. The Yeh-Stratton Failure Criterion was developed from the initial yielding of materials based on macromechanics. To investigate this criterion, the influence of the materials anisotropic properties and far field loading on the composite materials with central hole and normal crack were studied. Special emphasis was placed on defining the crack tip stress fields and their applications. The study of Yeh-Stratton criterion for damage zone stress fields on fiber-reinforced composites under tensile loading was compared with several fracture criteria; Tsai-Wu Theory, Hoffman Theory, Fischer Theory, and Cowin Theory. Theoretical predictions from these criteria are examined using experimental results.

Quantification of in-contact probe-sample electrostatic forces with dynamic atomic force microscopy.

PubMed

Balke, Nina; Jesse, Stephen; Carmichael, Ben; Okatan, M Baris; Kravchenko, Ivan I; Kalinin, Sergei V; Tselev, Alexander

2017-01-04

Atomic force microscopy (AFM) methods utilizing resonant mechanical vibrations of cantilevers in contact with a sample surface have shown sensitivities as high as few picometers for detecting surface displacements. Such a high sensitivity is harnessed in several AFM imaging modes. Here, we demonstrate a cantilever-resonance-based method to quantify electrostatic forces on a probe in the probe-sample junction in the presence of a surface potential or when a bias voltage is applied to the AFM probe. We find that the electrostatic forces acting on the probe tip apex can produce signals equivalent to a few pm of surface displacement. In combination with modeling, the measurements of the force were used to access the strength of the electrical field at the probe tip apex in contact with a sample. We find an evidence that the electric field strength in the junction can reach ca. 1 V nm -1 at a bias voltage of a few volts and is limited by non-ideality of the tip-sample contact. This field is sufficiently strong to significantly influence material states and kinetic processes through charge injection, Maxwell stress, shifts of phase equilibria, and reduction of energy barriers for activated processes. Besides, the results provide a baseline for accounting for the effects of local electrostatic forces in electromechanical AFM measurements as well as offer additional means to probe ionic mobility and field-induced phenomena in solids.

Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

NASA Technical Reports Server (NTRS)

Bassani, J. L.; Erdogan, F.

1979-01-01

The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks is considered. For the semi-infinite crack the problem is solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses are calculated. For finite cracks the problem is reduced to a pair of integral equations. Numerical results are obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

NASA Technical Reports Server (NTRS)

Bassani, J. L.; Erdogan, F.

1978-01-01

The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks was considered. For the semi-infinite crack the problem was solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses were calculated. For finite cracks the problem was reduced to a pair of integral equations. Numerical results were obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

Surface Modification in Control SiO2 Fiber Fracture.

DTIC Science & Technology

1981-10-01

If your address has changed or if you wish to be removid from the RAMC mailing list, or if the addressee is no longer employed by your organization...crack arrest is developed in terms of a stress intensity factor evaluated at a short distance ahead of the crack tip [2]. 1.3 Stress Corrosion It is... evaluated the comrosition of silica films produced by electron beam evaporation had shown earlier that the deposits retained the stoichiometry of the

Transjugular intrahepatic portosystemic shunt: impact on systemic hemodynamics and renal and cardiac function in patients with cirrhosis.

PubMed

Busk, Troels M; Bendtsen, Flemming; Poulsen, Jørgen H; Clemmesen, Jens O; Larsen, Fin S; Goetze, Jens P; Iversen, Jens S; Jensen, Magnus T; Møgelvang, Rasmus; Pedersen, Erling B; Bech, Jesper N; Møller, Søren

2018-02-01

Transjugular intrahepatic portosystemic shunt (TIPS) alleviates portal hypertension and possibly increases central blood volume (CBV). Moreover, renal function often improves; however, its effects on cardiac function are unclear. The aims of our study were to examine the effects of TIPS on hemodynamics and renal and cardiac function in patients with cirrhosis. In 25 cirrhotic patients, we analyzed systemic, cardiac, and splanchnic hemodynamics by catheterization of the liver veins and right heart chambers before and 1 wk after TIPS. Additionally, we measured renal and cardiac markers and performed advanced echocardiography before, 1 wk after, and 4 mo after TIPS. CBV increased significantly after TIPS (+4.6%, P < 0.05). Cardiac output (CO) increased (+15.3%, P < 0.005) due to an increase in stroke volume (SV) (+11.1%, P < 0.005), whereas heart rate (HR) was initially unchanged. Cardiopulmonary pressures increased after TIPS, whereas copeptin, a marker of vasopressin, decreased (-18%, P < 0.005) and proatrial natriuretic peptide increased (+52%, P < 0.0005) 1 wk after TIPS and returned to baseline 4 mo after TIPS. Plasma neutrophil gelatinase-associated lipocalin, renin, aldosterone, and serum creatinine decreased after TIPS (-36%, P < 0.005; -65%, P < 0.05; -90%, P < 0.005; and -13%, P < 0.005, respectively). Echocardiography revealed subtle changes in cardiac function after TIPS, although these were within the normal range. TIPS increases CBV by increasing CO and SV, whereas HR is initially unaltered. These results indicate an inability to increase the heart rate in response to a hemodynamic challenge that only partially increases CBV after TIPS. These changes, however, are sufficient for improving renal function. NEW & NOTEWORTHY For the first time, we have combined advanced techniques to study the integrated effects of transjugular intrahepatic portosystemic shunt (TIPS) in cirrhosis. We showed that TIPS increases central blood volume (CBV) through improved cardiac inotropy. Advanced echocardiography demonstrated that myocardial function was unaffected by the dramatic increase in preload after TIPS. Finally, renal function improved due to the increase in CBV. Recognition of these physiological changes significantly contributes to our clinical understanding of TIPS.

Effect of Stress Ratio and Loading Frequency on the Corrosion Fatigue Behavior of Smooth Steel Wire in Different Solutions

PubMed Central

Wang, Songquan; Zhang, Dekun; Hu, Ningning; Zhang, Jialu

2016-01-01

In this work, the effects of loading condition and corrosion solution on the corrosion fatigue behavior of smooth steel wire were discussed. The results of polarization curves and weight loss curves showed that the corrosion of steel wire in acid solution was more severe than that in neutral and alkaline solutions. With the extension of immersion time in acid solution, the cathodic reaction of steel wire gradually changed from the reduction of hydrogen ion to the reduction of oxygen, but was always the reduction of hydrogen ion in neutral and alkaline solutions. The corrosion kinetic parameters and equivalent circuits of steel wires were also obtained by simulating the Nyquist diagrams. In corrosion fatigue test, the effect of stress ratio and loading frequency on the crack initiation mechanism was emphasized. The strong corrosivity of acid solution could accelerate the nucleation of crack tip. The initiation mechanism of crack under different conditions was summarized according to the side and fracture surface morphologies. For the crack initiation mechanism of anodic dissolution, the stronger the corrosivity of solution was, the more easily the fatigue crack source formed, while, for the crack initiation mechanism of deformation activation, the lower stress ratio and higher frequency would accelerate the generation of corrosion fatigue crack source. PMID:28773869

Allele compensation in tip60+/- mice rescues white adipose tissue function in vivo.

PubMed

Gao, Yuan; Hamers, Nicole; Rakhshandehroo, Maryam; Berger, Ruud; Lough, John; Kalkhoven, Eric

2014-01-01

Adipose tissue is a key regulator of energy homestasis. The amount of adipose tissue is largely determined by adipocyte differentiation (adipogenesis), a process that is regulated by the concerted actions of multiple transcription factors and cofactors. Based on in vitro studies in murine 3T3-L1 preadipocytes and human primary preadipocytes, the transcriptional cofactor and acetyltransferase Tip60 was recently identified as an essential adipogenic factor. We therefore investigated the role of Tip60 on adipocyte differentiation and function, and possible consequences on energy homeostasis, in vivo. Because homozygous inactivation results in early embryonic lethality, Tip60+/- mice were used. Heterozygous inactivation of Tip60 had no effect on body weight, despite slightly higher food intake by Tip60+/- mice. No major effects of heterozygous inactivation of Tip60 were observed on adipose tissue and liver, and Tip60+/- displayed normal glucose tolerance, both on a low fat and a high fat diet. While Tip60 mRNA was reduced to 50% in adipose tissue, the protein levels were unaltered, suggesting compensation by the intact allele. These findings indicate that the in vivo role of Tip60 in adipocyte differentiation and function cannot be properly addressed in Tip60+/- mice, but requires the generation of adipose tissue-specific knock out animals or specific knock-in mice.

Analysis on the stress corrosion crack inception based on pit shape and size of the FV520B tensile specimen

NASA Astrophysics Data System (ADS)

Xiang, Longhao; Pan, Juyi; Chen, Songying

2018-06-01

The influence of pit shape and size on local stress concentration in the tensile specimen and the stress corrosion cracks inception was studied by employing the element remove technique. The maximum stress located in the bottom of pit on FV520B tensile specimen. The location of maximum strain was near the mouth of the pit or the shoulder and plastic strain existed in this region. Stress concentration factor and plastic deformation on four different geometrical shape pits of hemisphere, semi-ellipsoid, bullet and butterfly were numerically investigated, respectively. The simulation results showed that butterfly pit got the biggest stress concentration factor. The plastic strain rate during pit growth was in the sensitivity range of stress corrosion cracks inception, indicating that stress corrosion cracks were more likely to nucleate near the pit tip or the shoulder.

Optical method of caustics applied in viscoelastic fracture analysis

NASA Astrophysics Data System (ADS)

Gao, Guiyun; Li, Zheng; Xu, Jie

2011-05-01

The optical method of caustics is developed here to study the fracture of viscoelastic materials. By adopting a distribution of viscoelastic stress fields near the crack tip, the method of caustics is used to determine the viscoelastic fracture parameters from the caustic patterns near the crack tip. Two viscoelastic materials are studied. These are PMMA and ternary composites of HDPE/POE-g-MA/CaCO 3. The transmitted and reflective methods of caustics are performed separately to investigate viscoelastic fracture behaviors. The stress intensity factors (SIFs) versus time is determined by a series of shadow spot patterns combined with viscoelastic parameters evaluated by creep tests. In order to understand the viscoelastic fracture mechanisms of HDPE/POE-g-MA/CaCO 3 composites, their fracture surfaces are observed by a Scanning Electron Microscope (SEM). The results indicate that the method of caustics can be used to characterize the fracture behaviors of viscoelastic materials and further to optimize the design of polymer composites.

The role of water channel proteins in facilitating recovery of leaf hydraulic conductance from water stress in Populus trichocarpa.

PubMed

Laur, Joan; Hacke, Uwe G

2014-01-01

Gas exchange is constrained by the whole-plant hydraulic conductance (Kplant). Leaves account for an important fraction of Kplant and may therefore represent a major determinant of plant productivity. Leaf hydraulic conductance (Kleaf) decreases with increasing water stress, which is due to xylem embolism in leaf veins and/or the properties of the extra-xylary pathway. Water flow through living tissues is facilitated and regulated by water channel proteins called aquaporins (AQPs). Here we assessed changes in the hydraulic conductance of Populus trichocarpa leaves during a dehydration-rewatering episode. While leaves were highly sensitive to drought, Kleaf recovered only 2 hours after plants were rewatered. Recovery of Kleaf was absent when excised leaves were bench-dried and subsequently xylem-perfused with a solution containing AQP inhibitors. We examined the expression patterns of 12 highly expressed AQP genes during a dehydration-rehydration episode to identify isoforms that may be involved in leaf hydraulic adjustments. Among the AQPs tested, several genes encoding tonoplast intrinsic proteins (TIPs) showed large increases in expression in rehydrated leaves, suggesting that TIPs contribute to reversing drought-induced reductions in Kleaf. TIPs were localized in xylem parenchyma, consistent with a role in facilitating water exchange between xylem vessels and adjacent living cells. Dye uptake experiments suggested that reversible embolism formation in minor leaf veins contributed to the observed changes in Kleaf.

Twelve Tips for Effective Electronic Presentation.

ERIC Educational Resources Information Center

Crosby, Joy

1994-01-01

Offers 12 tips for effective electronic presentation. This article is intended for readers who may be considering using electronic presentation for the first time. Offers reasons for its popularity and occasions when it may be used. The tips offer assistance in the design and presentation of electronic material. (LZ)

Determination of the Fracture Parameters in a Stiffened Composite Panel

NASA Technical Reports Server (NTRS)

Lin, Chung-Yi

2000-01-01

A modified J-integral, namely the equivalent domain integral, is derived for a three-dimensional anisotropic cracked solid to evaluate the stress intensity factor along the crack front using the finite element method. Based on the equivalent domain integral method with auxiliary fields, an interaction integral is also derived to extract the second fracture parameter, the T-stress, from the finite element results. The auxiliary fields are the two-dimensional plane strain solutions of monoclinic materials with the plane of symmetry at x(sub 3) = 0 under point loads applied at the crack tip. These solutions are expressed in a compact form based on the Stroh formalism. Both integrals can be implemented into a single numerical procedure to determine the distributions of stress intensity factor and T-stress components, T11, T13, and thus T33, along a three-dimensional crack front. The effects of plate thickness and crack length on the variation of the stress intensity factor and T-stresses through the thickness are investigated in detail for through-thickness center-cracked plates (isotropic and orthotropic) and orthotropic stiffened panels under pure mode-I loading conditions. For all the cases studied, T11 remains negative. For plates with the same dimensions, a larger size of crack yields larger magnitude of the normalized stress intensity factor and normalized T-stresses. The results in orthotropic stiffened panels exhibit an opposite trend in general. As expected, for the thicker panels, the fracture parameters evaluated through the thickness, except the region near the free surfaces, approach two-dimensional plane strain solutions. In summary, the numerical methods presented in this research demonstrate their high computational effectiveness and good numerical accuracy in extracting these fracture parameters from the finite element results in three-dimensional cracked solids.

Transient thermal stresses in a reinforced hollow disk or cylinder containing a radial crack

NASA Technical Reports Server (NTRS)

Tang, R.; Erdogan, F.

1983-01-01

The transient thermal stress problem in a hollow cylinder or a disk containing a radial crack is considered. It is assumed that the cylinder is reinforced on its inner boundary by a membrane which has thermoelastic constants different than those of the base material. The transient temperature, thermal stresses and the crack tip stress intensity factors are calculated in a cylinder which is subjected to a sudden change of temperature on the inside surface. The results are obtained for various dimensionless parameters and material constants. The special cases of the crack terminating at the cylinder-membrane interface and of the broken membrane are separately considered and some examples are given.

Transient thermal stresses in a reinforced hollow disk or cylinder containing a radial crack

NASA Technical Reports Server (NTRS)

Tang, R.; Erdogan, F.

1984-01-01

The transient thermal stress problem in a hollow cylinder or a disk containing a radial crack is considered. It is assumed that the cylinder is reinforced on its inner boundary by a membrane which has thermoelastic constants different than those of the base material. The transient temperature, thermal stresses and the crack tip stress intensity factors are calculated in a cylinder which is subjected to a sudden change of temperature on the inside surface. The results are obtained for various dimensionless parameters and material constants. The special cases of the crack terminating at the cylinder-membrane interface and of the broken membrane are separately considered and some examples are given.

Photoelastic Analysis of Cracked Thick Walled Cylinders

NASA Astrophysics Data System (ADS)

Pastramă, Ştefan Dan

2017-12-01

In this paper, the experimental determination of the stress intensity factor in thick walled cylinders subject to uniform internal pressure and having longitudinal non-penetrating cracks is presented. Photoelastic measurements were used together with the expressions of the stress field near the crack tip for Mode I crack extension and a specific methodology for stress intensity factor determination. Two types of longitudinal cracks - internal and external - were considered. Four plane models were manufactured and analyzed in a plane polariscope at different values of the applied internal pressure. The values of the normalized stress intensity factor were calculated and the results were compared to those reported by other authors. A good accuracy was noticed, showing the reliability of the experimental procedure.

Numerical analysis of the blade tip-timing signal of a fiber bundle sensor probe

NASA Astrophysics Data System (ADS)

Guo, Haotian; Duan, Fajie; Cheng, Zhonghai

2015-03-01

Blade tip-timing is the most effective method for online blade vibration measurement of large rotating machines like turbine engines. Fiber bundle sensors are utilized in tip-timing system to measure the arrival time of the blade. The model of the tip-timing signal of the fiber bundle sensor is established. Experiments are conducted and the results are in concordance with the model established. The rising speed of the tip-timing signal is analyzed. To minimize the tip-timing error, the effects of the clearance change between the sensor and the blade and the deflection of the tip surface are analyzed. Simulation results indicate that the variable gain amplifier, which amplifies the signals to a similar level, can eliminate the measurement error caused by the variation of the clearance between the sensor and blade. Increasing the clearance between the sensor and blade can reduce the measurement error introduced by deflection of the tip surface.

Static Tensile and Transient Dynamic Response of Cracked Aluminum Plate Repaired with Composite Patch - Numerical Study

NASA Astrophysics Data System (ADS)

Khalili, S. M. R.; Shariyat, M.; Mokhtari, M.

2014-06-01

In this study, the central cracked aluminum plates repaired with two sided composite patches are investigated numerically for their response to static tensile and transient dynamic loadings. Contour integral method is used to define and evaluate the stress intensity factors at the crack tips. The reinforcement for the composite patches is carbon fibers. The effect of adhesive thickness and patch thickness and configuration in tensile loading case and pre-tension, pre-compression and crack length effect on the evolution of the mode I stress intensity factor (SIF) (KI) of the repaired structure under transient dynamic loading case are examined. The results indicated that KI of the central cracked plate is reduced by 1/10 to 1/2 as a result of the bonded composite patch repair in tensile loading case. The crack length and the pre-loads are more effective in repaired structure in transient dynamic loading case in which, the 100 N pre-compression reduces the maximum KI for about 40 %, and the 100 N pre-tension reduces the maximum KI after loading period, by about 196 %.

Effect of microstructure on stress corrosion cracking of alloy 600 and alloy 690 in 40% NaOH

NASA Astrophysics Data System (ADS)

Kim, H. P.; Hwang, S. S.; Lim, Y. S.; Kuk, I. H.; Kim, J. S.

2001-02-01

Stress corrosion cracking (SCC) behaviors of Alloy 600, Alloy 690 and the Ni-10Cr-10Fe alloy have been studied using a C-ring in 40% NaOH solution at 315°C. The current density of Alloy 690 in polarization curves was higher at 200 mV above corrosion potential than that of Alloy 600. SCC resistance increased with Cr content for the chromium carbide free alloys, probably due to facilitation of SCC crack tip blunting with an increase in Cr content. Both thermally treated Alloy 600 and sensitized Alloy 600 have a comparable amount of intergranular carbide. But the former is more resistant to SCC than the latter, which might be attributed to the presence of the slight Cr depletion around the grain boundary in the former one. Sensitized Alloy 600 showed higher SCC resistance than the solution annealed one due to intergranular carbide in sensitized Alloy 600. This implies that the beneficial effect of intergranular carbide overrides the harmful effects of Cr depletion for sensitized Alloy 600. SCC resistance of Alloy 600 increased with grain size.

Effects of Double-Leakage Tip Clearance Flow on the Performance of a Compressor Stage with a Large Rotor Tip Gap

NASA Technical Reports Server (NTRS)

Hah, Chunill

2016-01-01

Effects of a large rotor tip gap on the performance of a one and half stage axial compressor are investigated in detail with a numerical simulation based on LES and available PIV data. The current paper studies the main flow physics, including why and how the loss generation is increased with the large rotor tip gap. The present study reveals that when the tip gap becomes large, tip clearance fluid goes over the tip clearance core vortex and enters into the next blade's tip gap, which is called double-leakage tip clearance flow. As the tip clearance flow enters into the adjacent blade's tip gap, a vortex rope with a lower pressure core is generated. This vortex rope breaks up the tip clearance core vortex of the adjacent blade, resulting in a large additional mixing. This double-leakage tip clearance flow occurs at all operating conditions, from design flow to near stall condition, with the large tip gap for the current compressor stage. The double-leakage tip clearance flow, its interaction with the tip clearance core vortex of the adjacent blade, and the resulting large mixing loss are the main flow mechanism of the large rotor tip gap in the compressor. When the tip clearance is smaller, flow near the end wall follows more closely with the main passage flow and this double-leakage tip clearance flow does not happen near the design flow condition for the current compressor stage. When the compressor with a large tip gap operates at near stall operation, a strong vortex rope is generated near the leading edge due to the double-leakage flow. Part of this vortex separates from the path of the tip clearance core vortex and travels from the suction side of the blade toward the pressure side of the blade. This vortex is generated periodically at near stall operation with a large tip gap. As the vortex travels from the suction side to the pressure side of the blade, a large fluctuation of local pressure forces blade vibration. Nonsynchronous blade vibration occurs due to this vortex as the frequency of this vortex generation is not the same as the rotor. The present investigation confirms that this vortex is a part of separated tip clearance vortex, which is caused by the double-leakage tip clearance flow.

Modeling the Interaction between AFM Tips and Pinned Surface Nanobubbles.

PubMed

Guo, Zhenjiang; Liu, Yawei; Xiao, Qianxiang; Schönherr, Holger; Zhang, Xianren

2016-01-26

Although the morphology of surface nanobubbles has been studied widely with different AFM modes, AFM images may not reflect the real shapes of the nanobubbles due to AFM tip-nanobubble interactions. In addition, the interplay between surface nanobubble deformation and induced capillary force has not been well understood in this context. In our work we used constraint lattice density functional theory to investigate the interaction between AFM tips and pinned surface nanobubbles systematically, especially concentrating on the effects of tip hydrophilicity and shape. For a hydrophilic tip contacting a nanobubble, its hydrophilic nature facilitates its departure from the bubble surface, displaying a weak and intermediate-range attraction. However, when the tip squeezes the nanobubble during the approach process, the nanobubble shows an elastic effect that prevents the tip from penetrating the bubble, leading to a strong nanobubble deformation and repulsive interactions. On the contrary, a hydrophobic tip can easily pierce the vapor-liquid interface of the nanobubble during the approach process, leading to the disappearance of the repulsive force. In the retraction process, however, the adhesion between the tip and the nanobubble leads to a much stronger lengthening effect on nanobubble deformation and a strong long-range attractive force. The trends of force evolution from our simulations agree qualitatively well with recent experimental AFM observations. This favorable agreement demonstrates that our model catches the main intergradient of tip-nanobubble interactions for pinned surface nanobubbles and may therefore provide important insight into how to design minimally invasive AFM experiments.

Crack problems involving nonhomogeneous interfacial regions in bonded materials

NASA Technical Reports Server (NTRS)

Erdogan, F.

1990-01-01

Consideration is given to two classes of fracture-related solid mechanics problems in which the model leads to some physically anomalous results. The first is the interface crack problem associated with the debonding process in which the corresponding elasticity solution predicts severe oscillations of stresses and the crack surface displacements vary near the crack tip. The second deals with crack intersecting the interface. The nature of the solutions around the crack tips arising from these problems is reviewed. The rationale for introducing a new interfacial zone model is discussed, its analytical consequences within the context of the two crack-problem classes are described, and some examples are presented.

Analytical design of an advanced radial turbine. [automobile engines

NASA Technical Reports Server (NTRS)

Large, G. D.; Finger, D. G.; Linder, C. G.

1981-01-01

The aerodynamic and mechanical potential of a single stage ceramic radial inflow turbine was evaluated for a high temperature single stage automotive engine. The aerodynamic analysis utilizes a turbine system optimization technique to evaluate both radial and nonradial rotor blading. Selected turbine rotor configurations were evaluated mechanically with three dimensional finite element techniques. Results indicate that exceptionally high rotor tip speeds (2300 ft/sec) and performance potential are feasible with radial bladed rotors if the projected ceramic material properties are realized. Nonradial rotors reduced tip speed requirements (at constant turbine efficiency) but resulted in a lower cumulative probability of success due to higher blade and disk stresses.

Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficiency in Axial Turbines

NASA Technical Reports Server (NTRS)

Ameri, A. A.; Steinthorsson, E.; Rigby, David L.

1998-01-01

Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E 3 first stage turbine, which represents a modem gas turbine blade were used for the analysis. Clearance heights of 0%, 1%, 1.5% and 3% of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess, however only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances.

The Effect of Negative Dihedral, Tip Droop, and Wing-tip Shape on the Low-speed Aerodynamic Characteristics of a Complete Model Having a 45 Degrees Sweptback Wing

NASA Technical Reports Server (NTRS)

Spearman, M Leroy; Becht, Robert E

1948-01-01

An investigation has been conducted in the Langley 300 MPH 7- by 10-foot tunnel to determine the effect of negative dihedral, tip droop, and wing-tip shape on the low-speed aerodynamic characteristics of a complete model having a 45 degrees sweptback wing. Longitudinal and lateral stability characteristics were obtained for the model with and without tail surfaces.

Effects of Microstructure on Tensile, Charpy Impact, and Crack Tip Opening Displacement Properties of Two API X80 Pipeline Steels

NASA Astrophysics Data System (ADS)

Shin, Sang Yong

2013-06-01

The effects of microstructure on tensile, Charpy impact, and crack tip opening displacement (CTOD) properties of two API X80 pipeline steels were investigated in this study. Two API X80 pipeline steels consisting of acicular ferrite and granular bainite, and a small amount of hard phases such as martensite and secondary phases have elongated grains along the rolling direction, so that they show different mechanical properties as the specimens' directions change. The 90 deg specimens have high tensile strength due to the low stress concentration on the fine hard phases and the high loads for the deformation of the elongated grains. In contrast, the 30 deg specimens have less elongated grains and larger hard phases such as martensite, with the size of about 3 μm, than the 90 deg specimens. Hence, the 30 deg specimens have low tensile strength because of the high stress concentration on the large hard phases and the low loads to deform grains. In the 90 deg specimen, brittle crack propagation surfaces are even since cracks propagate in a straight line along the elongated grain structure. In the 30 deg specimen, however, brittle crack propagation surfaces are uneven, and secondary cracks are observed, because of the zigzag brittle crack propagation path. In the CTOD properties, the 90 deg specimens have maximum forces of higher magnitude than the 30 deg specimens, because of the elongated grain structure. However, CTODs of the 90 deg specimens are lower than those of the 30 deg specimens because of the low plastic deformation areas by the elongated grains in the 90 deg specimens.

Effects of simulated acid rain on germination, seedling growth and oxidative metabolism of recalcitrant-seeded Trichilia dregeana grown in its natural seed bank.

PubMed

Ramlall, Chandika; Varghese, Boby; Ramdhani, Syd; Pammenter, Norman W; Bhatt, Arvind; Berjak, Patricia; Sershen

2015-01-01

Increased air pollution in a number of developing African countries, together with the reports of vegetation damage typically associated with acid precipitation in commercial forests in South Africa, has raised concerns over the potential impacts of acid rain on natural vegetation in these countries. Recalcitrant (i.e. desiccation sensitive) seeds of many indigenous African species, e.g. must germinate shortly after shedding and hence, may not be able to avoid exposure to acid rain in polluted areas. This study investigated the effects of simulated acid rain (rainwater with pH adjusted to pH 3.0 and 4.5 with 70:30, H2 SO4 :HNO3 ) on germination, seedling growth and oxidative metabolism in a recalcitrant-seeded African tree species Trichilia dregeana Sond., growing in its natural seed bank. The results suggest that acid rain did not compromise T. dregeana seed germination and seedling establishment significantly, relative to the control (non-acidified rainwater). However, pH 3.0 treated seedlings exhibited signs of stress typically associated with acid rain: leaf tip necrosis, abnormal bilobed leaf tips, leaf necrotic spots and chlorosis, reduced leaf chlorophyll concentration, increased stomatal density and indications of oxidative stress. This may explain why total and root biomass of pH 3.0 treated seedlings were significantly lower than the control. Acid rain also induced changes in the species composition and relative abundance of the different life forms emerging from T. dregeana's natural seed bank and in this way could indirectly impact on T. dregeana seedling establishment success. © 2014 Scandinavian Plant Physiology Society.

Micromechanics of shear localization in granular rocks - effect of temperature

NASA Astrophysics Data System (ADS)

Kanaya, T.; Hirth, G.

2017-12-01

We conducted detailed microscopy on porous sandstones deformed to varying axial strains in the low-temperature, brittle faulting regime and high-temperature, semibrittle faulting regime. This study is aimed to test the hypothsis that macroscopic faulting results from the interaction of distributed microfractures in granular rocks, and to assess how elevated temperature influences these shear loalization processes. We determined the ratio of fracture length vs. spacing for distributed microfractures (away from macroscopic faults) and compared it with fracture mechanics models of crack interaction. At low temperature, both tensile and shear microfractures obtain the critical geometry for crack-tip interaction. Both modes of microfractures occur at initial yielding and continue to lengthen with strain, in which many tensile microfractures propagate across grains. In contrast, at high temperature, only shear microfractures continue to lengthen with strain and reach the critical geometry; almost all tensile microfracutures arrest at grain boundaries. In addition, using the observed microfracture lengths and stresses, we determined the energy release rate (including interaction effects) for the longest shear microfractues characterized. These microfractures show length and stress consistent with Griffith criteria. At low temperature, shear fractures show energy release rate far greater than fracture energy, consistent with the observed dynamic failure. In contrast, at high temperature, shear microfractures show energy release rate similar to fracture energy, consistent with observed stable failire. Taken toghether, our resutls show that the linkage of shear microfracture is far more important for shear localization (macroscopic faulting) in granular rocks than in non-porous rocks. The interaction of both tentile and shear microfractures is important at low temperature, whereas that of teneile fracture is less improtant at high temperature. In addition, structure (desnity distirbution and orientation) of microfractures within the fault tip region is being investigated.

Efficacy of air/water syringe tip sterilization.

PubMed

Inger, M; Bennani, V; Farella, M; Bennani, F; Cannon, R D

2014-03-01

Dental procedures involve contact between instruments and the patient's tissues, blood or saliva. This study evaluated the efficacy of the standardized sterilization of non-disposable air/water syringe tips and corrosion and contaminant build-up in these tips. The bacterial contamination of single-use and multiple-use non-disposable air/water syringe tips after routine use and sterilization was compared to that of single-use disposable tips by microbial culturing on PCA and blood agar plates. The effect of flushing the syringe tips prior to sterilization was also measured. The amount of corrosion in single-use and multiple-use non-disposable syringes was measured by SEM and EDS analyses. Non-disposable syringe tips had significantly (p < 0.05) greater bacterial contamination than single-use disposable tips. There were no statistically different levels of contamination between flushed and non-flushed non-disposable syringes or between single-use and multiple-use non-disposable syringes. SEM and EDS analyses showed greater evidence of corrosion and contaminant build-up in multiple-use syringes compared to single-use non-disposable syringes. Sterilization of non-disposable air/water syringes is not completely effective and rinsing, or the number of uses, does not affect the effectiveness of sterilization. There may be a lower risk of cross-infection from the use of disposable air/water syringe tips, instead of non-disposable ones. © 2014 Australian Dental Association.

Influence of different sizes of composite femora on the biomechanical behavior of cementless hip prosthesis.

PubMed

Schmidutz, Florian; Woiczinski, Mathias; Kistler, Manuel; Schröder, Christian; Jansson, Volkmar; Fottner, Andreas

2017-01-01

For the biomechanical evaluation of cementless stems different sizes of composite femurs have been used in the literature. However, the impact of different specimen sizes on test results is unknown. To determine the potential effect of femur size the biomechanical properties of a conventional stem (CLS Spotorno) were examined in 3 different sizes (small, medium and large composite Sawbones®). Primary stability was tested under physiologically adapted dynamic loading conditions measuring 3-dimensional micromotions. For the small composite femur the dynamic load needed to be adapted since fractures occurred when reaching 1700N. Additionally, surface strain distribution was recorded before and after implantation to draw conclusions about the tendency for stress shielding. All tested sizes revealed similar micromotions only reaching a significant different level at one measurement point. The highest micromotions were observed at the tip of the stems exceeding the limit for osseous integration of 150μm. Regarding strain distribution the highest strain reduction after implantation was registered in all sizes at the level of the lesser trochanter. Specimen size seems to be a minor influence factor for biomechanical evaluation of cementless stems. However, the small composite femur is less suitable for biomechanical testing since this size failed under physiological adapted loads. For the CLS Spotorno osseous integration is unlikely at the tip of the stem and the tendency for stress shielding is the highest at the level of the lesser trochanter. Copyright © 2016 Elsevier Ltd. All rights reserved.

A study of fiber volume fraction effects in notched unidirectional SCS-6/Ti-15V-3Cr-3Al-3Sn composite. Ph.D. Thesis Final Report

NASA Technical Reports Server (NTRS)

Covey, Steven J.

1993-01-01

Notched unidirectional SCS-6/Ti-15-3 composite of three different fiber volume fractions (vf = 0.15, 0.37, and 0.41) was investigated for various room temperature microstructural and material properties including: fatigue crack initiation, fatigue crack growth, and fracture toughness. While the matrix hardness is similar for all fiber volume fractions, the fiber/matrix interfacial shear strength and matrix residual stress increases with fiber volume fraction. The composite fatigue crack initiation stress is shown to be matrix controlled and occurs when the net maximum matrix stress approaches the endurance limit stress of the matrix. A model is presented which includes residual stresses and presents the composite initiation stress as a function of fiber volume fraction. This model predicts a maximum composite initiation stress at vf approximately 0.15 which agrees with the experimental data. The applied composite stress levels were increased as necessary for continued crack growth. The applied Delta(K) values at crack arrest increase with fiber volume fraction by an amount better approximated using an energy based formulation rather than when scaled linear with modulus. After crack arrest, the crack growth rate exponents for vf37 and vf41 were much lower and toughness much higher, when compared to the unreinforced matrix, because of the bridged region which parades with the propagating fatigue crack. However, the vf15 material exhibited a higher crack growth rate exponent and lower toughness than the unreinforced matrix because once the bridged fibers nearest the crack mouth broke, the stress redistribution broke all bridged fibers, leaving an unbridged crack. Degraded, unbridged behavior is modeled using the residual stress state in the matrix ahead of the crack tip. Plastic zone sizes were directly measured using a metallographic technique and allow prediction of an effective matrix stress intensity which agrees with the fiber pressure model if residual stresses are considered. The sophisticated macro/micro finite element models of the 0.15 and 0.37 fiber volume fractions presented show good agreement with experimental data and the fiber pressure model when an estimated effective fiber/matrix debond length is used.

Fan-structure waves in shear ruptures

NASA Astrophysics Data System (ADS)

Tarasov, Boris

2016-04-01

This presentation introduces a recently identified shear rupture mechanism providing a paradoxical feature of hard rocks - the possibility of shear rupture propagation through the highly confined intact rock mass at shear stress levels significantly less than frictional strength. According to the fan-mechanism the shear rupture propagation is associated with consecutive creation of small slabs in the fracture tip which, due to rotation caused by shear displacement of the fracture interfaces, form a fan-structure representing the fracture head. The fan-head combines such unique features as: extremely low shear resistance (below the frictional strength), self-sustaining stress intensification in the rupture tip (providing easy formation of new slabs), and self-unbalancing conditions in the fan-head (making the failure process inevitably spontaneous and violent). An important feature of the fan-mechanism is the fact that for the initial formation of the fan-structure an enhanced local shear stress is required, however, after completion of the fan-structure it can propagate as a dynamic wave through intact rock mass at shear stresses below the frictional strength. Paradoxically low shear strength of pristine rocks provided by the fan-mechanism determines the correspondingly low transient strength of the lithosphere, which favours generation of new earthquake faults in the intact rock mass adjoining pre-existing faults in preference to frictional stick-slip instability along these faults. The new approach reveals an alternative role of pre-existing faults in earthquake activity: they represent local stress concentrates in pristine rock adjoining the fault where special conditions for the fan-mechanism nucleation are created, while further dynamic propagation of the new fault (earthquake) occurs at low field stresses even below the frictional strength.

A Formate Dehydrogenase Confers Tolerance to Aluminum and Low pH1[OPEN

PubMed Central

Gong, Yu Long; Fan, Wei; Xu, Jia Meng; Liu, Yu; Cao, Meng Jie; Wang, Ming-Hu

2016-01-01

Formate dehydrogenase (FDH) is involved in various higher plant abiotic stress responses. Here, we investigated the role of rice bean (Vigna umbellata) VuFDH in Al and low pH (H+) tolerance. Screening of various potential substrates for the VuFDH protein demonstrated that it functions as a formate dehydrogenase. Quantitative reverse transcription-PCR and histochemical analysis showed that the expression of VuFDH is induced in rice bean root tips by Al or H+ stresses. Fluorescence microscopic observation of VuFDH-GFP in transgenic Arabidopsis plants indicated that VuFDH is localized in the mitochondria. Accumulation of formate is induced by Al and H+ stress in rice bean root tips, and exogenous application of formate increases internal formate content that results in the inhibition of root elongation and induction of VuFDH expression, suggesting that formate accumulation is involved in both H+- and Al-induced root growth inhibition. Over-expression of VuFDH in tobacco (Nicotiana tabacum) results in decreased sensitivity to Al and H+ stress due to less production of formate in the transgenic tobacco lines under Al and H+ stresses. Moreover, NtMATE and NtALS3 expression showed no changes versus wild type in these over-expression lines, suggesting that herein known Al-resistant mechanisms are not involved. Thus, the increased Al tolerance of VuFDH over-expression lines is likely attributable to their decreased Al-induced formate production. Taken together, our findings advance understanding of higher plant Al toxicity mechanisms, and suggest a possible new route toward the improvement of plant performance in acidic soils, where Al toxicity and H+ stress coexist. PMID:27021188

Dancing in the Rain: Tips on Thriving as a Leader in Tough Times

ERIC Educational Resources Information Center

Murphy, Jerome T.

2011-01-01

Experiencing discomfort as a leader is part of the job. But discomfort does not have to turn to anguish. Leaders who learn a new way to respond to the stress and strain of leadership can enhance their performance and enrich their experience.