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Sample records for actual fiber stress

  1. Fiber Creep Evaluation by Stress Relaxation Measurements

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Dicarlo, James A.; Wagner, Timothy

    1991-01-01

    A simple bend stress relaxation (BSR) test has been used to measure the creep related properties of a chemically vapor-deposited SiC fiber. Time, temperature, and strain dependent BSR data were analyzed to ascertain the ability of the stress relaxation results to predict tensile creep as a function of the same parameters. The predictions compared very well to actual creep data obtained by axial measurements, indicating that the BSR test could be used for determining both creep and stress relaxation of polycrystalline ceramic fibers under tensile loading.

  2. Fiber networks amplify active stress.

    PubMed

    Ronceray, Pierre; Broedersz, Chase P; Lenz, Martin

    2016-03-15

    Large-scale force generation is essential for biological functions such as cell motility, embryonic development, and muscle contraction. In these processes, forces generated at the molecular level by motor proteins are transmitted by disordered fiber networks, resulting in large-scale active stresses. Although these fiber networks are well characterized macroscopically, this stress generation by microscopic active units is not well understood. Here we theoretically study force transmission in these networks. We find that collective fiber buckling in the vicinity of a local active unit results in a rectification of stress towards strongly amplified isotropic contraction. This stress amplification is reinforced by the networks' disordered nature, but saturates for high densities of active units. Our predictions are quantitatively consistent with experiments on reconstituted tissues and actomyosin networks and shed light on the role of the network microstructure in shaping active stresses in cells and tissue. PMID:26921325

  3. Fiber networks amplify active stress

    NASA Astrophysics Data System (ADS)

    Lenz, Martin; Ronceray, Pierre; Broedersz, Chase

    Large-scale force generation is essential for biological functions such as cell motility, embryonic development, and muscle contraction. In these processes, forces generated at the molecular level by motor proteins are transmitted by disordered fiber networks, resulting in large-scale active stresses. While fiber networks are well characterized macroscopically, this stress generation by microscopic active units is not well understood. I will present a comprehensive theoretical study of force transmission in these networks. I will show that the linear, small-force response of the networks is remarkably simple, as the macroscopic active stress depends only on the geometry of the force-exerting unit. In contrast, as non-linear buckling occurs around these units, local active forces are rectified towards isotropic contraction and strongly amplified. This stress amplification is reinforced by the networks' disordered nature, but saturates for high densities of active units. I will show that our predictions are quantitatively consistent with experiments on reconstituted tissues and actomyosin networks, and that they shed light on the role of the network microstructure in shaping active stresses in cells and tissue.

  4. Stress optic coefficient and stress profile in optical fibers.

    PubMed

    Lagakos, N; Mohr, R; El-Bayoumi, O H

    1981-07-01

    The stress optic coefficient and stress profile in optical fibers have been determined photoelastically using a polariscope having good reproducibility and high sensitivity. The results of the work presented in this paper indicate that the photoelastic behavior may be different in fibers and in bulk glasses. The photoelastically determined clad compression in strengthened fibers was found to correlate well with the strengthening observed in these fibers using tensile tests. PMID:20332937

  5. Isolation and Contraction of the Stress Fiber

    PubMed Central

    Katoh, Kazuo; Kano, Yumiko; Masuda, Michitaka; Onishi, Hirofumi; Fujiwara, Keigi

    1998-01-01

    Stress fibers were isolated from cultured human foreskin fibroblasts and bovine endothelial cells, and their contraction was demonstrated in vitro. Cells in culture dishes were first treated with a low-ionic-strength extraction solution and then further extracted using detergents. With gentle washes by pipetting, the nucleus and the apical part of cells were removed. The material on the culture dish was scraped, and the freed material was forced through a hypodermic needle and fractionated by sucrose gradient centrifugation. Isolated, free-floating stress fibers stained brightly with fluorescently labeled phalloidin. When stained with anti-α-actinin or anti-myosin, isolated stress fibers showed banded staining patterns. By electron microscopy, they consisted of bundles of microfilaments, and electron-dense areas were associated with them in a semiperiodic manner. By negative staining, isolated stress fibers often exhibited gentle twisting of microfilament bundles. Focal adhesion–associated proteins were also detected in the isolated stress fiber by both immunocytochemical and biochemical means. In the presence of Mg-ATP, isolated stress fibers shortened, on the average, to 23% of the initial length. The maximum velocity of shortening was several micrometers per second. Polystyrene beads on shortening isolated stress fibers rotated, indicating spiral contraction of stress fibers. Myosin regulatory light chain phosphorylation was detected in contracting stress fibers, and a myosin light chain kinase inhibitor, KT5926, inhibited isolated stress fiber contraction. Our study demonstrates that stress fibers can be isolated with no apparent loss of morphological features and that they are truly contractile organelle. PMID:9658180

  6. Axial residual stresses in boron fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1978-01-01

    The axial residual stress distribution as a function of radius was determined from the fiber surface to the core including the average residual stress in the core. Such measurements on boron on tungsten (B/W) fibers show that the residual stresses for 102, 142, 203, and 366 micron diameter fibers were similar, being compressive at the surface and changing monotonically to a region of tensile within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile stress of about 860 mn/sq.m and then decreases to a compressive stress near the tungsten boride core. Data were presented for 203 micron diameter B/W fibers that show annealing above 900 C reduces the residual stresses. A comparison between 102 micron diameter B/W and boron on carbon (b/C) shows that the residual stresses were similar in the outer regions of the fibers, but that large differences near and in the core were observed. The effects of these residual stresses on the fracture of boron fibers were discussed.

  7. Thermoelastic stresses in composite ceramic fibers

    SciTech Connect

    Filimonov, I.A.; Grigor`ev, Yu. M.

    1995-08-01

    A calculation of stress and deformation fields in ceramic fibers formed by the method of chemical vapor deposition onto a heated substrate is performed within the framework of linear elasticity theory. Optimum parameters for fibers with a homogeneous structure, a layered structure, and a gradient one are sought.

  8. Triboluminescent Fiber-Optic Sensors Measure Stresses

    NASA Technical Reports Server (NTRS)

    Rogowski, Robert S.

    1994-01-01

    Triboluminescence exploited in fiber-optic sensor system for measuring changes in pressures, strains, vibrations, and acoustic emissions, in structural members. Sensors embedded in members for in situ monitoring of condition of structure. System passive in sense no source of radiation required to interrogate optical fiber. Technique has potential for wide range of applications in which detection and measurement of structural stress required.

  9. Focal adhesions, stress fibers and mechanical tension

    PubMed Central

    Burridge, Keith; Guilluy, Christophe

    2016-01-01

    Stress fibers and focal adhesions are complex protein arrays that produce, transmit and sense mechanical tension. Evidence accumulated over many years led to the conclusion that mechanical tension generated within stress fibers contributes to the assembly of both stress fibers themselves and their associated focal adhesions. However, several lines of evidence have recently been presented against this model. Here we discuss the evidence for and against the role of mechanical tension in driving the assembly of these structures. We also consider how their assembly is influenced by the rigidity of the substratum to which cells are adhering. Finally, we discuss the recently identified connections between stress fibers and the nucleus, and the roles that these may play, both in cell migration and regulating nuclear function. PMID:26519907

  10. Longitudinal residual stresses in boron fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1976-01-01

    A method of measuring the longitudinal residual stress distribution in boron fibers is presented. The residual stresses in commercial CVD boron on tungsten fibers of 102, 142, and 203 microns (4, 5.6, and 8 mil) diameters were determined. Results for the three sizes show a compressive stress at the surface 800 to -1400 MN/sq m 120 to -200 ksi), changing monotonically to a region of tensile stress within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile 600 to 1000 MN/sq m(90 to 150 ksi) and then decreases to compressive near the tungsten boride core. The core itself is under a compressive stress of approximately -1300 MN/sq m (-190 ksi). The effects of surface removal on core residual stress and core-initiated fracture are discussed.

  11. Behaviour of a few mode fiber modal pattern under stress

    NASA Technical Reports Server (NTRS)

    Egalon, Claudio O.; Rogowski, Robert S.

    1991-01-01

    A numerical model was developed to calculate the interference pattern at the end of a multimode weakly guiding optical fiber under stress. Whenever an optical fiber is under stress, the modal phase in the interference term of the intensity formula changes. Plots of the simulated output of a stressed fiber are presented. For multimode fibers, very complicated patterns result. Under stress, lobes in the pattern are generated, displaced and power is exchanged among them.

  12. Monitoring Fiber Stress During Curing of Single Fiber Glass- and Graphite-Epoxy Composites

    NASA Technical Reports Server (NTRS)

    Madhukar, Madhu S.; Kosuri, Ranga P.; Bowles, Kenneth J.

    1994-01-01

    The difference in thermal expansion characteristics of epoxy matrices and graphite fibers can produce significant residual stresses in the fibers during curing of composite materials. Tests on single fiber glass-epoxy and graphite-epoxy composite specimens were conducted in which the glass and graphite fibers were preloaded in tension, and the epoxy matrix was cast around the fibers. The fiber tension was monitored while the matrix was placed around the fiber and subjected to the temperature-time curing cycle. Two mechanisms responsible for producing stress in embedded fibers were identified as matrix thermal expansion and contraction and matrix cure shrinkage. A simple analysis based on the change in fiber tension during the curing cycle was conducted to estimate the produced stresses. Experimental results on single fiber glass- and graphite-epoxy composites show that the fiber was subjected to significant tensile stresses when the temperature was raised from the first to the second dwell period. When initial fiber pretension is about 60 percent of the fiber failure load, these curing-induced stresses can cause tensile fracture of the embedded fiber.

  13. Oxidation induced stress-rupture of fiber bundles

    SciTech Connect

    Lara-Curzio, E.

    1997-03-01

    The effect of oxidation on the stress-rupture behavior of fiber bundles was modeled. It is shown that oxidation-induced fiber strength degradation results in the delayed failure of the associated fiber bundle and that the fiber bundle strength decreases with time as t{sup {minus}1/4}. It is also shown that the temperature dependence of the bundle loss of strength reflects the thermal dependence of the mechanism controlling the oxidation of the fibers. The effect of gauge length on the fiber bundle strength was also analyzed. Numerical examples are presented for the special case of Nicalon{trademark} fibers.

  14. An analysis of fiber-matrix interface failure stresses for a range of ply stress states

    NASA Technical Reports Server (NTRS)

    Crews, J. H.; Naik, R. A.; Lubowinski, S. J.

    1993-01-01

    A graphite/bismaleimide laminate was prepared without the usual fiber treatment and was tested over a wide range of stress states to measure its ply cracking strength. These tests were conducted using off-axis flexure specimens and produced fiber-matrix interface failure data over a correspondingly wide range of interface stress states. The absence of fiber treatment, weakened the fiber-matrix interfaces and allowed these tests to be conducted at load levels that did not yield the matrix. An elastic micromechanics computer code was used to calculate the fiber-matrix interface stresses at failure. Two different fiber-array models (square and diamond) were used in these calculations to analyze the effects of fiber arrangement as well as stress state on the critical interface stresses at failure. This study showed that both fiber-array models were needed to analyze interface stresses over the range of stress states. A linear equation provided a close fit to these critical stress combinations and, thereby, provided a fiber-matrix interface failure criterion. These results suggest that prediction procedures for laminate ply cracking can be based on micromechanics stress analyses and appropriate fiber-matrix interface failure criteria. However, typical structural laminates may require elastoplastic stress analysis procedures that account for matrix yielding, especially for shear-dominated ply stress states.

  15. Simultaneous Stretching and Contraction of Stress Fibers In Vivo

    PubMed Central

    Peterson, Lynda J.; Rajfur, Zenon; Maddox, Amy S.; Freel, Christopher D.; Chen, Yun; Edlund, Magnus; Otey, Carol; Burridge, Keith

    2004-01-01

    To study the dynamics of stress fiber components in cultured fibroblasts, we expressed α-actinin and the myosin II regulatory myosin light chain (MLC) as fusion proteins with green fluorescent protein. Myosin activation was stimulated by treatment with calyculin A, a serine/threonine phosphatase inhibitor that elevates MLC phosphorylation, or with LPA, another agent that ultimately stimulates phosphorylation of MLC via a RhoA-mediated pathway. The resulting contraction caused stress fiber shortening and allowed observation of changes in the spacing of stress fiber components. We have observed that stress fibers, unlike muscle myofibrils, do not contract uniformly along their lengths. Although peripheral regions shortened, more central regions stretched. We detected higher levels of MLC and phosphorylated MLC in the peripheral region of stress fibers. Fluorescence recovery after photobleaching revealed more rapid exchange of myosin and α-actinin in the middle of stress fibers, compared with the periphery. Surprisingly, the widths of the myosin and α-actinin bands in stress fibers also varied in different regions. In the periphery, the banding patterns for both proteins were shorter, whereas in central regions, where stretching occurred, the bands were wider. PMID:15133124

  16. Effects of stress and strain on scintillating and clear fibers

    SciTech Connect

    Chung, M.; Margulies, S.

    1995-08-01

    Among the improvements planned for the 1997--98 upgrade of the D0 detector at Fermilab are installation of a scintillating-fiber central tracker and a lead-scintillator central preshower counter read out with wave-shifting fibers. Because of space limitations, fibers in both systems may need to undergo bends with fairly small radii, and the resulting stresses and strains may cause light losses. This paper presents results of a study of the effects of deformation on fiber light transmission. Particular emphasis is placed on the new multiclad fibers developed by Kuraray.

  17. A Multimodular Tensegrity Model of an Actin Stress Fiber

    PubMed Central

    Luo, Yaozhi; Xu, Xian; Lele, Tanmay; Kumar, Sanjay; Ingber, Donald E.

    2008-01-01

    Stress fibers are contractile bundles in the cytoskeleton that stabilize cell structure by exerting traction forces on extracellular matrix. Individual stress fibers are molecular bundles composed of parallel actin and myosin filaments linked by various actin-binding proteins, which are organized end-on-end in a sarcomere-like pattern within an elongated three-dimensional network. While measurements of single stress fibers in living cells show that they behave like tensed viscoelastic fibers, precisely how this mechanical behavior arises from this complex supramolecular arrangement of protein components remains unclear. Here we show that computationally modeling a stress fiber as a multi-modular tensegrity network can predict several key behaviors of stress fibers measured in living cells, including viscoelastic retraction, fiber splaying after severing, non-uniform contraction, and elliptical strain of a puncture wound within the fiber. The tensegrity model also can explain how they simultaneously experience passive tension and generate active contraction forces; in contrast, a tensed cable net model predicts some, but not all, of these properties. Thus, tensegrity models may provide a useful link between molecular and cellular scale mechanical behaviors, and represent a new handle on multi-scale modeling of living materials. PMID:18632107

  18. Dynamics of Mechanical Signal Transmission through Prestressed Stress Fibers

    PubMed Central

    Hwang, Yongyun; Barakat, Abdul I.

    2012-01-01

    Transmission of mechanical stimuli through the actin cytoskeleton has been proposed as a mechanism for rapid long-distance mechanotransduction in cells; however, a quantitative understanding of the dynamics of this transmission and the physical factors governing it remains lacking. Two key features of the actin cytoskeleton are its viscoelastic nature and the presence of prestress due to actomyosin motor activity. We develop a model of mechanical signal transmission through prestressed viscoelastic actin stress fibers that directly connect the cell surface to the nucleus. The analysis considers both temporally stationary and oscillatory mechanical signals and accounts for cytosolic drag on the stress fibers. To elucidate the physical parameters that govern mechanical signal transmission, we initially focus on the highly simplified case of a single stress fiber. The results demonstrate that the dynamics of mechanical signal transmission depend on whether the applied force leads to transverse or axial motion of the stress fiber. For transverse motion, mechanical signal transmission is dominated by prestress while fiber elasticity has a negligible effect. Conversely, signal transmission for axial motion is mediated uniquely by elasticity due to the absence of a prestress restoring force. Mechanical signal transmission is significantly delayed by stress fiber material viscosity, while cytosolic damping becomes important only for longer stress fibers. Only transverse motion yields the rapid and long-distance mechanical signal transmission dynamics observed experimentally. For simple networks of stress fibers, mechanical signals are transmitted rapidly to the nucleus when the fibers are oriented largely orthogonal to the applied force, whereas the presence of fibers parallel to the applied force slows down mechanical signal transmission significantly. The present results suggest that cytoskeletal prestress mediates rapid mechanical signal transmission and allows

  19. Creep and stress relaxation modeling of polycrystalline ceramic fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, James A.; Morscher, Gregory N.

    1994-01-01

    A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading about 800 C, these fibers display creep related instabilities which can result in detrimental changes in composite dimensions, strength, and internal stress distributions. As a first step toward understanding these effects, this study examines the validity of a mechanism-based empirical model which describes primary stage tensile creep and stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied stress or strain. To verify these functional dependencies, a simple bend test is used to measure stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the Bend Stress Relaxation (BSR) test not only confirm the stress, time, and temperature dependencies predicted by the model, but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model tensile creep predictions based on the BSR test results with the literature data show good agreement, supporting both the predictive capability of the model and the use of the BSR text as a simple method for parameter determination for other fibers.

  20. Creep and stress relaxation modeling of polycrystalline ceramic fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, James A.; Morscher, Gregory N.

    1991-01-01

    A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading above 800 C, these fibers display creep-related instabilities which can result in detrimental changes in composite dimensions, strength, and internal stress distributions. As a first step toward understanding these effects, this study examines the validity of mechanistic-based empirical model which describes primary stage tensile creep and stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied stress or strain. To verify these functional dependencies, a simple bend test is used to measure stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the bend stress relaxation (BSR) test not only confirm the stress, time, and temperature dependencies predicted by the model but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model predictions and BSR test results with the literature tensile creep data show good agreement, supporting both the predictive capability of the model and the use of the BSR test as a simple method for parameter determination for other fibers.

  1. Efficient computational simulation of actin stress fiber remodeling.

    PubMed

    Ristori, T; Obbink-Huizer, C; Oomens, C W J; Baaijens, F P T; Loerakker, S

    2016-09-01

    Understanding collagen and stress fiber remodeling is essential for the development of engineered tissues with good functionality. These processes are complex, highly interrelated, and occur over different time scales. As a result, excessive computational costs are required to computationally predict the final organization of these fibers in response to dynamic mechanical conditions. In this study, an analytical approximation of a stress fiber remodeling evolution law was derived. A comparison of the developed technique with the direct numerical integration of the evolution law showed relatively small differences in results, and the proposed method is one to two orders of magnitude faster. PMID:26823159

  2. Core stress distribution of phase shifting multimode polymer optical fiber

    SciTech Connect

    Furukawa, Rei Matsuura, Motoharu; Nagata, Morio; Mishima, Kenji; Inoue, Azusa; Tagaya, Akihiro; Koike, Yasuhiro

    2013-11-18

    Poly-(methyl methacrylate-co-benzyl methacrylate) polarization-maintaining optical fibers are known for their high response to normal stress. In this report, responses to higher stress levels up to 0.45 MPa were investigated. The stress amplitude and direction in the fiber cross section were calculated and analyzed with a coincident mode-field obtained from the near-field pattern. The stress amplitude varies significantly in the horizontal direction and is considered to create multiple phases, explaining the measurement results. To investigate possible permanent deformation, the core yield point profile was analyzed. Although it largely exceeds the average applied stress, the calculated stress distribution indicates that the core could partially experience stress that exceeds the yield point.

  3. A constitutive law for continuous fiber reinforced brittle matrix composites with fiber fragmentation and stress recovery

    NASA Astrophysics Data System (ADS)

    Neumeister, Jonas M.

    1993-08-01

    THE TENSILE BEHAVIOR of a brittle matrix composite is studied for post matrix crack saturation conditions. Scatter of fiber strength following the Weibull distribution as well as the influence of the major microstructural variables is considered. The stress in a fiber is assumed to recover linearly around a failure due to a fiber-matrix interface behavior mainly ruled by friction. The constitutive behavior for such a composite is analysed. Results are given for a simplified and a refined approximate description and compared with an analysis resulting from the exact analytical theory of fiber fragmentation. It is shown that the stress-strain relation for the refined model excellently follows the exact solution and gives the location of the maximum to within 1% in both stress and strain; for most materials the agreement is even better. Also it is shown that all relations can be normalized to depend on only two variables; a stress reference and the Weibull exponent. For systems with low scatter in fiber strength the simplified model is sufficient to determine the stress maximum but not the postcritical behavior. In addition, the simplified model gives explicit analytical expressions for the maximum stress and corresponding strain. None of the models contain any volume dependence or statistical scatter, but the maximum stress given by the stress-strain relation constitutes an upper bound for the ultimate tensile strength of the composite.

  4. Effects of stress and strain on scintillating and clear fibers

    NASA Astrophysics Data System (ADS)

    Chung, Manho; Margulies, Seymour

    1994-09-01

    Among the improvements planned for the 1997 upgrade of the D0 detector at Fermilab are installation of a new scintillating-fiber central tracker and a new lead-scintillator preshower counter read out with wave-shifting fibers. Because of space limitations, fibers in both systems may need to undergo bends of fairly small radius, and the resulting stresses and strains may cause light losses. This paper presents interim results from a study of the effects of deformation on fiber light transmission. A variety of scintillating, wave-shifting, and clear fibers with diameters near 1 mm have been examined. Particular emphasis was placed on the new, multiclad fibers developed by Kuraray. Light loss was measured by injecting light into one end of a fiber sample and measuring the exiting light before, during, and after controlled deformation of the fiber. The deformations studied include bending, tensile elongation, compression, and torsion. Generally, except for severe bending or considerable compression, light loss was found to be less than a few percent. The effect of bending were investigated using single-turn and multiple-turn loops of various radii. Light loss was found to increase with decreasing radius, but little dependence on either core dopants or diameter was observed. Generally, the light loss, L, in an N-turn loop of radius r could be parameterized by the form L equals A(root)N/rn, where A is a constant and n is near 1.5. Kuraray multiclad fiber was found to be superior to single-clad fiber in that the former can be bent into single- turn loops with radii as small as 1 cm before introducing a light loss of 3%, while the latter produces this loss at a 2 cm radius. Tensile stress for forces up to 1.3 kg for 2-m-long fibers produced less than 1% light loss. On the other hand, compressive stress exerted over a 10-cm- long fiber section could cause a loss of 10%. Finally, a single observation of the effects of torsion indicated no change in light transmission for a

  5. Model of cellular mechanotransduction via actin stress fibers.

    PubMed

    Gouget, Cecile L M; Hwang, Yongyun; Barakat, Abdul I

    2016-04-01

    Mechanical stresses due to blood flow regulate vascular endothelial cell structure and function and play a key role in arterial physiology and pathology. In particular, the development of atherosclerosis has been shown to correlate with regions of disturbed blood flow where endothelial cells are round and have a randomly organized cytoskeleton. Thus, deciphering the relation between the mechanical environment, cell structure, and cell function is a key step toward understanding the early development of atherosclerosis. Recent experiments have demonstrated very rapid ([Formula: see text]100 ms) and long-distance ([Formula: see text]10 [Formula: see text]m) cellular mechanotransduction in which prestressed actin stress fibers play a critical role. Here, we develop a model of mechanical signal transmission within a cell by describing strains in a network of prestressed viscoelastic stress fibers following the application of a force to the cell surface. We find force transmission dynamics that are consistent with experimental results. We also show that the extent of stress fiber alignment and the direction of the applied force relative to this alignment are key determinants of the efficiency of mechanical signal transmission. These results are consistent with the link observed experimentally between cytoskeletal organization, mechanical stress, and cellular responsiveness to stress. Based on these results, we suggest that mechanical strain of actin stress fibers under force constitutes a key link in the mechanotransduction chain. PMID:26081725

  6. Actomyosin stress fiber mechanosensing in 2D and 3D

    PubMed Central

    Lee, Stacey; Kumar, Sanjay

    2016-01-01

    Mechanotransduction is the process through which cells survey the mechanical properties of their environment, convert these mechanical inputs into biochemical signals, and modulate their phenotype in response. These mechanical inputs, which may be encoded in the form of extracellular matrix stiffness, dimensionality, and adhesion, all strongly influence cell morphology, migration, and fate decisions. One mechanism through which cells on planar or pseudo-planar matrices exert tensile forces and interrogate microenvironmental mechanics is through stress fibers, which are bundles composed of actin filaments and, in most cases, non-muscle myosin II filaments. Stress fibers form a continuous structural network that is mechanically coupled to the extracellular matrix through focal adhesions. Furthermore, myosin-driven contractility plays a central role in the ability of stress fibers to sense matrix mechanics and generate tension. Here, we review the distinct roles that non-muscle myosin II plays in driving mechanosensing and focus specifically on motility. In a closely related discussion, we also describe stress fiber classification schemes and the differing roles of various myosin isoforms in each category. Finally, we briefly highlight recent studies exploring mechanosensing in three-dimensional environments, in which matrix content, structure, and mechanics are often tightly interrelated. Stress fibers and the myosin motors therein represent an intriguing and functionally important biological system in which mechanics, biochemistry, and architecture all converge.

  7. The influence of motion and stress on optical fibers

    NASA Astrophysics Data System (ADS)

    Murphy, Jeremy D.; Hill, Gary J.; MacQueen, Phillip J.; Taylor, Trey; Soukup, Ian; Moreira, Walter; Cornell, Mark E.; Good, John; Anderson, Seth; Fuller, Lindsay; Lee, Hanshin; Kelz, Andreas; Rafal, Marc; Rafferty, Tom; Tuttle, Sarah; Vattiat, Brian

    2012-09-01

    We report on extensive testing carried out on the optical fibers for the VIRUS instrument. The primary result of this work explores how 10+ years of simulated wear on a VIRUS fiber bundle affects both transmission and focal ratio degradation (FRD) of the optical fibers. During the accelerated lifetime tests we continuously monitored the fibers for signs of FRD. We find that transient FRD events were common during the portions of the tests when motion was at telescope slew rates, but dropped to negligible levels during rates of motion typical for science observation. Tests of fiber transmission and FRD conducted both before and after the lifetime tests reveal that while transmission values do not change over the 10+ years of simulated wear, a clear increase in FRD is seen in all 18 fibers tested. This increase in FRD is likely due to microfractures that develop over time from repeated flexure of the fiber bundle, and stands in contrast to the transient FRD events that stem from localized stress and subsequent modal diffusion of light within the fibers. There was no measurable wavelength dependence on the increase in FRD over 350 nm to 600 nm. We also report on bend radius tests conducted on individual fibers and find the 266 μm VIRUS fibers to be immune to bending-induced FRD at bend radii of R 10 cm. Below this bend radius FRD increases slightly with decreasing radius. Lastly, we give details of a degradation seen in the fiber bundle currently deployed on the Mitchell Spectrograph (formally VIRUS-P) at McDonald Observatory. The degradation is shown to be caused by a localized shear in a select number of optical fibers that leads to an explosive form of FRD. In a few fibers, the overall transmission loss through the instrument can exceed 80%. These results are important for the VIRUS instrument, and for both current and proposed instruments that make use of optical fibers, particularly when the fibers are in continual motion during an observation, or experience

  8. Failure mechanics of fiber composite notched charpy specimens. [stress analysis

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.

    1976-01-01

    A finite element stress analysis was performed to determine the stress variation in the vicinity of the notch and far field of fiber composites Charpy specimens (ASTM Standard). NASTRAN was used for the finite element analysis assuming linear behavior and equivalent static load. The unidirectional composites investigated ranged from Thornel 75 Epoxy to S-Glass/Epoxy with the fiber direction parallel to the long dimension of the specimen. The results indicate a biaxial stress state exists in (1) the notch vicinity which is dominated by transverse tensile and interlaminar shear and (2) near the load application point which is dominated by transverse compression and interlaminar shear. The results also lead to the postulation of hypotheses for the predominant failure modes, the fracture initiation, and the fracture process. Finally, the results indicate that the notched Charpy test specimen is not suitable for assessing the impact resistance of nonmetallic fiber composites directly.

  9. Stress-rupture behavior of small diameter polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, Hee Mann; Goldsby, Jon C.; Dicarlo, James A.

    1993-01-01

    Continuous length polycrystalline alumina fibers are candidates as reinforcement in high temperature composite materials. Interest therefore exists in characterizing the thermomechanical behavior of these materials, obtaining possible insights into underlying mechanisms, and understanding fiber performance under long term use. Results are reported on the time-temperature dependent strength behavior of Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Below 1000 C and 100 hours, Nextel 610 with the smaller grain size had a greater fast fracture and rupture strength than Fiber FP. The time exponents for stress-rupture of these fibers were found to decrease from approximately 13 at 900 C to below 3 near 1050 C, suggesting a transition from slow crack growth to creep rupture as the controlling fracture mechanism. For both fiber types, an effective activation energy of 690 kJ/mol was measured for rupture. This allowed stress-rupture predictions to be made for extended times at use temperatures below 1000 C.

  10. Characterization of Optical Fiber Strength Under Applied Tensile Stress and Bending Stress

    SciTech Connect

    P.E. Klingsporn

    2011-08-01

    Various types of tensile testing and bend radius tests were conducted on silica core/silica cladding optical fiber of different diameters with different protective buffer coatings, fabricated by different fiber manufacturers. The tensile tests were conducted to determine not only the average fiber strengths at failure, but also the distribution in fracture strengths, as well as the influence of buffer coating on fracture strength. The times-to-failure of fiber subjected to constant applied bending stresses of various magnitudes were measured to provide a database from which failure times of 20 years or more, and the corresponding minimum bend radius, could be extrapolated in a statistically meaningful way. The overall study was done to provide an understanding of optical fiber strength in tensile loading and in applied bending stress as related to applications of optical fiber in various potential coizfgurations for weapons and enhanced surveillance campaigns.

  11. Prediction of the Elastic-Plastic Stress/Strain Response for Injection-Molded Long-Fiber Thermoplastics

    SciTech Connect

    Nguyen, Ba N.; Kunc, Vlastimil; Phelps, Jay H; TuckerIII, Charles L.; Bapanapalli, Satish K

    2009-01-01

    This paper proposes a model to predict the elastic-plastic response of injection-molded long-fiber thermoplastics (LFTs). The model accounts for elastic fibers embedded in a thermoplastic resin that exhibits the elastic-plastic behavior obeying the Ramberg-Osgood relation and J-2 deformation theory of plasticity. It also accounts for fiber length and orientation distributions in the composite formed by the injection-molding process. Fiber orientation was predicted using an anisotropic rotary diffusion model recently developed for LFTs. An incremental procedure using Eshelby's equivalent inclusion method and the Mori-Tanaka assumption is proposed to compute the overall stress increment resulting from an overall strain increment for an aligned-fiber composite that contains the same fiber volume fraction and length distribution as the actual composite. The incremental response of the latter is then obtained from the solution for the aligned-fiber composite by averaging over all fiber orientations. Failure during incremental loading is predicted using the Van Hattum-Bernado model. The model is validated against the experimental stress-strain results obtained for long-glass-fiber/polypropylene specimens.

  12. Prediction of the Elastic-Plastic Stress/Strain Response for Injection-Molded Long-Fiber Thermoplastics

    SciTech Connect

    Nguyen, Ba Nghiep; Bapanapalli, Satish K.; Kunc, Vlastimil; Phelps, Jay; Tucker III, Charles L.

    2009-01-26

    This paper proposes a model to predict the elastic-plastic response of injection-molded long-fiber thermoplastics (LFTs). The model accounts for elastic fibers embedded in a thermoplastic resin that exhibits the elastic-plastic behavior obeying the Ramberg-Osgood relation and J-2 deformation theory of plasticity. It also accounts for fiber length and orientation distributions in the composite formed by the injection-molding process. Fiber orientation was predicted using the anisotropic rotary diffusion model recently developed by Phelps and Tucker for LFTs. An incremental procedure using the Eshelby’s equivalent inclusion method and the Mori-Tanaka model is proposed to compute the overall stress increment resulting from an overall strain increment for an aligned fiber composite that contains the same fiber volume fraction and length distribution as the actual composite. The incremental response of the later is then obtained from the solution for the aligned fiber composite that is averaged over all possible fiber orientations using the orientation averaging method. Failure during incremental loading is predicted using the Van Hattum-Bernado model. The elastic-plastic and strength prediction model for LFTs was validated against the experimental stress-strain results obtained for long glass fiber/polypropylene specimens.

  13. Stress analysis of carbon fiber embedded composite material of rubber

    SciTech Connect

    Watanabe, O.; Taya, M.

    1995-12-31

    Thermo-mechanical properties of a composite of rubber embedded by carbon fill has been studied from the viewpoint of developing an electric device. The objective of the present study is to show stress analysis of carbon fiber embedded composite material of rubber by using a mixed-type finite element method. Based on the condition o plane strain, the geometry of composite material is taken as the two types of orientation of carbon fiber, which are distributed regularly according the specified volume fraction along the horizontal and vertical directions in the base material of rubber. The loading condition is assumed to be the two types of axial and shearing deformations. Through the calculated results of equivalent and mean stress distributions and the load-deflection curve, effects of the geometry size, the carbon fiber orientation and the loading condition are clarified. The results for the typical axial deformation is compared with the experimental results.

  14. Rho-Kinase–Mediated Contraction of Isolated Stress Fibers

    PubMed Central

    Katoh, Kazuo; Kano, Yumiko; Amano, Mutsuki; Onishi, Hirofumi; Kaibuchi, Kozo; Fujiwara, Keigi

    2001-01-01

    It is widely accepted that actin filaments and the conventional double-headed myosin interact to generate force for many types of nonmuscle cell motility, and that this interaction occurs when the myosin regulatory light chain (MLC) is phosphorylated by MLC kinase (MLCK) together with calmodulin and Ca2+. However, recent studies indicate that Rho-kinase is also involved in regulating the smooth muscle and nonmuscle cell contractility. We have recently isolated reactivatable stress fibers from cultured cells and established them as a model system for actomyosin-based contraction in nonmuscle cells. Here, using isolated stress fibers, we show that Rho-kinase mediates MLC phosphorylation and their contraction in the absence of Ca2+. More rapid and extensive stress fiber contraction was induced by MLCK than was by Rho-kinase. When the activity of Rho-kinase but not MLCK was inhibited, cells not only lost their stress fibers and focal adhesions but also appeared to lose cytoplasmic tension. Our study suggests that actomyosin-based nonmuscle contractility is regulated by two kinase systems: the Ca2+-dependent MLCK and the Rho-kinase systems. We propose that Ca2+ is used to generate rapid contraction, whereas Rho-kinase plays a major role in maintaining sustained contraction in cells. PMID:11331307

  15. Stress transfer of a Kevlar 49 fiber pullout test studied by micro-Raman spectroscopy.

    PubMed

    Lei, Zhenkun; Wang, Quan; Qiu, Wei

    2013-06-01

    The interfacial stress transfer behavior of a Kevlar 49 aramid fiber-epoxy matrix was studied with fiber pullout tests, the fibers of which were stretched by a homemade microloading device. Raman spectra on the embedded fiber were recorded by micro-Raman spectroscopy, under different strain levels. Then, the fiber axial stress was obtained by the relationship between the stress and Raman shift of the aramid fiber. Experimental results revealed that the fiber axial stress increased significantly with the load. The shear stress concentration occurred at the fiber entry to the epoxy resin. Thus, interfacial friction stages exist in the debonded fiber segment, and the interfacial friction shear stress is constant within one stage. The experimental results are consistent with the theoretical model predictions. PMID:23735244

  16. The influence of the fiber drawing process on intrinsic stress and the resulting birefringence optimization of PM fibers

    NASA Astrophysics Data System (ADS)

    Just, Florian; Spittel, Ron; Bierlich, Jörg; Grimm, Stephan; Jäger, Matthias; Bartelt, Hartmut

    2015-04-01

    The propagation properties of optical fibers can be significantly influenced by intrinsic stress. These effects are often undesired but in some cases essential for certain applications, e.g. in polarization maintaining (PM) fibers. In this paper, we present systematic studies on the influence of the fiber drawing process on the generated stress and demonstrate an approach to significantly increase the stress induced birefringence of PM-fibers. It is shown that the thermal stress caused by the material composition is superimposed with the mechanical stress caused by the fiber fabrication process. This intrinsic stress has a strong effect on the optical and mechanical properties of the glass and thus influences the fiber stability and modal behavior. By applying a thermal annealing step, the mechanical stress due to the fiber drawing process can be canceled. It is shown that this annealing step compensates the stress reducing influence of the drawing process on the birefringence of PM-fibers with panda structure. The comparison of the intrinsic stress states after fabrication with the state after the additional high temperature annealing step clearly shows that it is possible to improve the overall birefringence of panda fibers using appropriate preparation steps.

  17. Stress-displacement relation of fiber for fiber-reinforced ceramic composites during (indentation) loading and unloading

    SciTech Connect

    Hsueh, C.; Ferber, M.K.; Becher, P.F. )

    1989-11-01

    The stress-displacement relation of the fiber is analyzed for fiber-reinforced ceramic composites during axial compressive loading (indentation) and unloading on the exposed end of an embedded fiber. An unbonded fiber/matrix interface subject to Coulomb friction and residual radial clamping stresses is considered in the present study. The results show that the stress-displacement curves during loading and unloading can be used to evaluate the magnitude of the clamping stress, the coefficient of friction, and the frictional stress distribution at the interface. Specifically, in the absence of Poisson's effect (i.e., when Poisson's ratio of the fiber is zero), the interfacial shear stress is constant, the loading curve is parabolic, and, after complete unloading, the residual fiber displacement equals half of the maximum fiber displacement at the peak loading stress. In the presence of Poisson's effect, the interfacial shear stress is not constant, and, after complete unloading, the residual fiber displacement is less than half of the maximum fiber displacement at the peak loading stress.

  18. Optical fiber sensor for measurement of concrete structure stress

    NASA Astrophysics Data System (ADS)

    Zangaro, Renato A.; Silveira, Landulfo, Jr.; Barreto da Silva, R.

    1994-09-01

    In this work we describe an optical sensor to determine the stress applied at a concrete structure. The optical sensor is a monomode fiber optic, that is embedded in the concrete. The principle of these sensors is based on photoelastic effect, that produces a birefringence in the optical fiber and induces a rotation on the polarization angle of the guided polarized light. The photoelastic effect is produced due to a controlled applied charge in the center of the concrete structure. The shift of polarization is analyzed by a polaroid analyzer.

  19. Lamination residual stresses in fiber composites

    NASA Technical Reports Server (NTRS)

    Daniel, I. M.; Liber, T.

    1975-01-01

    An experimental investigation was conducted to determine the magnitude of lamination residual stresses in angle-ply composites and to evaluate their effects on composite structural integrity. The materials investigated were boron/epoxy, boron/polyimide, graphite/low modulus epoxy, graphite/high modulus epoxy, graphite/polyimide and s-glass/epoxy. These materials were fully characterized. Static properties of laminates were also determined. Experimental techniques using embedded strain gages were developed and used to measure residual strains during curing. The extent of relaxation of lamination residual stresses was investigated. It was concluded that the degree of such relaxation is low. The behavior of angle-ply laminates subjected to thermal cycling, tensile load cycling, and combined thermal cycling with tensile load was investigated. In most cases these cycling programs did not have any measurable influence on residual strength and stiffness of the laminates. In the tensile load cycling tests, the graphite/polyimide shows the highest endurance with 10 million cycle runouts at loads up to 90 percent of the static strength.

  20. Increased molecular mobility in humid silk fibers under tensile stress

    NASA Astrophysics Data System (ADS)

    Seydel, Tilo; Knoll, Wiebke; Greving, Imke; Dicko, Cedric; Koza, Michael M.; Krasnov, Igor; Müller, Martin

    2011-01-01

    Silk fibers are semicrystalline nanocomposite protein fibers with an extraordinary mechanical toughness that changes with humidity. Diffusive or overdamped motion on a molecular level is absent in dry silkworm silk, but present in humid silk at ambient temperature. This microscopic diffusion distinctly depends on the externally applied macroscopic tensile force. Quasielastic and inelastic neutron-scattering data as a function of humidity and of tensile strain on humid silk fibers support the model that both the adsorbed water and parts of the amorphous polymers participate in diffusive motion and are affected by the tensile force. It is notable that the quasielastic linewidth of humid silk at 100% relative humidity increases significantly with the applied force. The effect of the tensile force is discussed in terms of an increasing alignment of the polymer chains in the amorphous fraction with increasing tensile stress which changes the geometrical restrictions of the diffusive motions.

  1. Possible translocation of actin and alpha-actinin along stress fibers.

    PubMed

    McKenna, N M; Wang, Y L

    1986-11-01

    We have employed fluorescent analogue cytochemistry and fluorescence photobleaching to study the mobility of actin and alpha-actin along stress fibers. Rhodamine-labeled actin or alpha-actinin microinjected into embryonic chick cardiac fibroblasts soon became incorporated into stress fibers. A pulse of a laser microbeam was used to photobleach small spots on the fluorescent stress fibers. Images of the bleached fiber were recorded with an intensified image processing system at 2-3 min intervals. The distance between the bleached spot and the terminus of the stress fiber, which remained stationary throughout the experiment, was then measured in the successive images. Movement of bleached spots was detected along stress fibers located in the apparently trailing processes of polygonal fibroblasts, and only occurred in one direction: away from the distal tip of the stress fiber. The rate of movement calculated for alpha-actinin-injected cells was 0.24 +/- 0.12 micron/min, for actin-injected cells, 0.29 +/- 0.11 micron/min. The rate did not seem to be affected by the location of the spot relative to the distal end of the stress fiber unless the spot was located within the most distal 5 microns of the stress fiber. Anti-myosin antibody staining indicated that stress fibers which demonstrated translocation were relatively depleted of myosin. The apparent translocation of proteins along stress fibers, possibly generated by stretching, may be related to the retraction of cell processes during locomotion. PMID:3758212

  2. Nonlinear stress-strain behavior of carbon nanotube fibers subject to slow sustained strain rate

    NASA Astrophysics Data System (ADS)

    Sun, Gengzhi; Wang, Dong; Pang, John H. L.; Liu, Jun; Zheng, Lianxi

    2013-09-01

    Nonlinear stress-strain behavior of carbon nanotube (CNT) fibers is studied based on the test data where fiber strength can be modeled by the Weibull distribution. CNT fibers spun from vertically aligned arrays are tensioned at slow sustained strain rate (0.00001 1/s) to study the tensile strength resulting from sliding-to-failure effects. A model is developed to estimate the Weibull modulus which characterizes the dispersion of fiber strengths in terms of the maximum sustained stress and failure strain of the fibers. The results show that the sliding indeed has great influence on the stress-strain relation of CNT fibers at low strain rate.

  3. Cyclic stretch-induced stress fiber dynamics - Dependence on strain rate, Rho-kinase and MLCK

    SciTech Connect

    Lee, Chin-Fu; Haase, Candice; Deguchi, Shinji; Kaunas, Roland

    2010-10-22

    Research highlights: {yields} Cyclic stretch induces stress fiber disassembly, reassembly and fusion perpendicular to the direction of stretch. {yields} Stress fiber disassembly and reorientation were not induced at low stretch frequency. {yields} Stretch caused actin fiber formation parallel to stretch in distinct locations in cells treated with Rho-kinase and MLCK inhibitors. -- Abstract: Stress fiber realignment is an important adaptive response to cyclic stretch for nonmuscle cells, but the mechanism by which such reorganization occurs is not known. By analyzing stress fiber dynamics using live cell microscopy, we revealed that stress fiber reorientation perpendicular to the direction of cyclic uniaxial stretching at 1 Hz did not involve disassembly of the stress fiber distal ends located at focal adhesion sites. Instead, these distal ends were often used to assemble new stress fibers oriented progressively further away from the direction of stretch. Stress fiber disassembly and reorientation were not induced when the frequency of stretch was decreased to 0.01 Hz, however. Treatment with the Rho-kinase inhibitor (Y27632) reduced stress fibers to thin fibers located in the cell periphery which bundled together to form thick fibers oriented parallel to the direction of stretching at 1 Hz. In contrast, these thin fibers remained diffuse in cells subjected to stretch at 0.01 Hz. Cyclic stretch at 1 Hz also induced actin fiber formation parallel to the direction of stretch in cells treated with the myosin light chain kinase (MLCK) inhibitor ML-7, but these fibers were located centrally rather than peripherally. These results shed new light on the mechanism by which stress fibers reorient in response to cyclic stretch in different regions of the actin cytoskeleton.

  4. Residual stresses in continuous graphite fiber Al metal matrix composites

    NASA Technical Reports Server (NTRS)

    Park, Hun Sub; Zong, Gui Sheng; Marcus, Harris L.

    1988-01-01

    The residual stresses in graphite fiber reinforced aluminum (Gr/Al) composites with various thermal histories are measured using X-ray diffraction (XRD) methods. The XRD stress analysis is based on the determination of lattice strains by precise measurements of the interplanar spacings in different directions of the sample. The sample is a plate consisting of two-ply P 100 Gr/Al 6061 precursor wires and Al 6061 overlayers. Prior to XRD measurement, the 6061 overlayers are electrochemically removed. In order to calibrate the relationship between stress magnitude and lattice spacing shift, samples of Al 6061 are loaded at varying stress levels in a three-point bend fixture, while the stresses are simultaneously determined by XRD and surface-attached strain gages. The stresses determined by XRD closely match those determined by the strain gages. Using these calibrations, the longitudinal residual stresses of P 100 Gr/Al 6061 composites are measured for various heat treatments, and the results are presented.

  5. Accelerated stress rupture lifetime assessment for fiber composites

    SciTech Connect

    Groves, S.E.; DeTeresa, S.J.; Sanchez, R.J.; Zocher, M.A.; Christensen, R.M.

    1997-02-01

    Objective was to develop a theoretical and experimental framework for predicting stress rupture lifetime for fiber polymer composites based on short-term accelerated testing. Originally a 3-year project, it was terminated after the first year, which included stress rupture experiments and viscoelastic material characterization. In principle, higher temperature, stress, and saturated environmental conditions are used to accelerate stress rupture. Two types of specimens were to be subjected to long-term and accelerated static tensile loading at various temperatures, loads in order to quantify both fiber and matrix dominated failures. Also, we were to apply state-of-the-art analytical and experimental characterization techniques developed under a previous DOE/DP CRADA for capturing and tracking incipient degradation mechanisms associated with mechanical performance. Focus was increase our confidence to design, analyze, and build long-term composite structures such as flywheels and hydrogen gas storage vessels; other applications include advanced conventional weapons, infrastructures, marine and offshore systems, and stockpile stewardship and surveillance. Capabilities developed under this project, though not completed or verified, are being applied to NIF, AVLIS, and SSMP programs.

  6. Theoretical Foundations of Yoga Meditation: A Contribution to Self-Actualization and Stress Management.

    ERIC Educational Resources Information Center

    Janowiak, John J.

    Recent evidence purporting that stress contributes to the development of disorders ranging from depression to cancer to general immunological dysfunction suggests that a concise understanding of stress and stress management techniques is needed in order to develop efficacious interventions. What is needed is an effective, easy-to-learn technique…

  7. Developing Fiber Specific Promoter-Reporter Transgenic Lines to Study the Effect of Abiotic Stresses on Fiber Development in Cotton

    PubMed Central

    Chen, Junping; Burke, John J.

    2015-01-01

    Cotton is one of the most important cash crops in US agricultural industry. Environmental stresses, such as drought, high temperature and combination of both, not only reduce the overall growth of cotton plants, but also greatly decrease cotton lint yield and fiber quality. The impact of environmental stresses on fiber development is poorly understood due to technical difficulties associated with the study of developing fiber tissues and lack of genetic materials to study fiber development. To address this important question and provide the need for scientific community, we have generated transgenic cotton lines harboring cotton fiber specific promoter (CFSP)-reporter constructs from six cotton fiber specific genes (Expansin, E6, Rac13, CelA1, LTP, and Fb late), representing genes that are expressed at different stages of fiber development. Individual CFSP::GUS or CFSP::GFP construct was introduced into Coker 312 via Agrobacterium mediated transformation. Transgenic cotton lines were evaluated phenotypically and screened for the presence of selectable marker, reporter gene expression, and insertion numbers. Quantitative analysis showed that the patterns of GUS reporter gene activity during fiber development in transgenic cotton lines were similar to those of the native genes. Greenhouse drought and heat stress study showed a correlation between the decrease in promoter activities and decrease in fiber length, increase in micronaire and changes in other fiber quality traits in transgenic lines grown under stressed condition. These newly developed materials provide new molecular tools for studying the effects of abiotic stresses on fiber development and may be used in study of cotton fiber development genes and eventually in the genetic manipulation of fiber quality. PMID:26030401

  8. Effect of stress on ultrasonic pulses in fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Hemann, J. H.; Baaklini, G. Y.

    1986-01-01

    An acoustical-ultrasonic technique was used to demonstrate relationships existing between changes in attenuation of stress waves and tensile stress on an eight ply 0 degree graphite-epoxy fiber reinforced composite. All tests were conducted in the linear range of the material for which no mechanical or macroscopic damage was evident. Changes in attenuation were measured as a function of tensile stress in the frequency domain and in the time domain. Stress wave propagation in these specimens was dispersive, i.e., the wave speed depends on frequency. Wave speeds varied from 267,400 cm/sec to 680,000 cm/sec as the frequency of the signal was varied from 150 kHz to 1.9 MHz which strongly suggests that flexural/lamb wave modes of propagation exist. The magnitude of the attenuation changes depended strongly on tensile stress. It was further observed that the wave speeds increased slightly for all tested frequencies as the stress was increased.

  9. Noninvasive detection of plant nutrient stress using fiber optic spectrophotometry

    NASA Astrophysics Data System (ADS)

    Chen, Jun-Wei; Asundi, Anand K.; Liew, Oi Wah; Boey, William S. L.

    2001-05-01

    In a previous paper, we described the use of fiber optic spectrophotometry as a non-destructive and sensitive method to detect early symptoms of plant nutrient deficiency. We report further developments of our work on Brassica chinensis var parachinensis (Bailey) showing reproducibility of our data collected at a different seasonal period. Plants at the mid-log growth phase were subjected to nutrient stress by transferring them to nitrate- and calcium- deficient nutrient solution in a standing aerated hydroponic system. After tracking changes in leaf reflectance by FOSpectr for nine days, the plants were returned to complete nutrient solution and their recovery was monitored for a further nine days. The responses of nutrient stressed plants were compared with those grown under complete nutrient solution over the 18-day trial period. We also compared the sensitivity of FOSpectr detection against plant growth measurements vis-a-vis average leaf number and leaf width and show that the former method gave an indication of nutrient stress much earlier than the latter. In addition, this work indicated that while normal and nutrient-stressed plants could not be distinguished within the first 7 days by tracking plant growth indicators, stressed plants did show a clear decline in average leaf number and leaf width in later stages of growth even after the plants were returned to complete nutrient solution. The results further reinforce the need for early detection of nutrient stress, as late remedial action could not reverse the loss in plant growth in later stages of plant development.

  10. Modeling of stress/strain behavior of fiber-reinforced ceramic matrix composites including stress redistribution

    NASA Technical Reports Server (NTRS)

    Mital, Subodh K.; Murthy, Pappu L. N.; Chamis, Christos C.

    1994-01-01

    A computational simulation procedure is presented for nonlinear analyses which incorporates microstress redistribution due to progressive fracture in ceramic matrix composites. This procedure facilitates an accurate simulation of the stress-strain behavior of ceramic matrix composites up to failure. The nonlinearity in the material behavior is accounted for at the constituent (fiber/matrix/interphase) level. This computational procedure is a part of recent upgrades to CEMCAN (Ceramic Matrix Composite Analyzer) computer code. The fiber substructuring technique in CEMCAN is used to monitor the damage initiation and progression as the load increases. The room-temperature tensile stress-strain curves for SiC fiber reinforced reaction-bonded silicon nitride (RBSN) matrix unidirectional and angle-ply laminates are simulated and compared with experimentally observed stress-strain behavior. Comparison between the predicted stress/strain behavior and experimental stress/strain curves is good. Collectively the results demonstrate that CEMCAN computer code provides the user with an effective computational tool to simulate the behavior of ceramic matrix composites.

  11. The tension mounts: Stress fibers as force-generating mechanotransducers

    PubMed Central

    Wittchen, Erika S.

    2013-01-01

    Stress fibers (SFs) are often the most prominent cytoskeletal structures in cells growing in tissue culture. Composed of actin filaments, myosin II, and many other proteins, SFs are force-generating and tension-bearing structures that respond to the surrounding physical environment. New work is shedding light on the mechanosensitive properties of SFs, including that these structures can respond to mechanical tension by rapid reinforcement and that there are mechanisms to repair strain-induced damage. Although SFs are superficially similar in organization to the sarcomeres of striated muscle, there are intriguing differences in their organization and behavior, indicating that much still needs to be learned about these structures. PMID:23295347

  12. Importance of residual stresses in the Brillouin gain spectrum of single mode optical fibers.

    PubMed

    Mamdem, Y Sikali; Burov, E; de Montmorillon, L-A; Jaouën, Y; Moreau, G; Gabet, R; Taillade, F

    2012-01-16

    Residual stresses inside optical fibers can impact significantly on Brillouin spectrum properties. We have analyzed the importance of internal stresses on the Brillouin Gain Spectrum (BGS) for a conventional G.652 fiber and compared modeling results to measurements. Then the residual internal stresses have been investigated for a set of trench-assisted fibers: fibers are coming from a single preform with different draw tensions. Numerical modeling based on measured internal stresses profiles are compared with corresponding BGS experimental results. Clearly, Brillouin spectrum is shifted linearly versus draw tension with a coefficient of -20MHz/100g and its linewidth increases. PMID:22274523

  13. Characterization of the stress and refractive-index distributions in optical fibers and fiber-based devices

    NASA Astrophysics Data System (ADS)

    Hutsel, Michael R.

    2011-07-01

    Optical fiber technology continues to advance rapidly as a result of the increasing demands on communication systems and the expanding use of fiber-based sensing. New optical fiber types and fiber-based communications components are required to permit higher data rates, an increased number of channels, and more flexible installation requirements. Fiber-based sensors are continually being developed for a broad range of sensing applications, including environmental, medical, structural, industrial, and military. As optical fibers and fiber-based devices continue to advance, the need to understand their fundamental physical properties increases. The residual-stress distribution (RSD) and the refractive-index distribution (RID) play fundamental roles in the operation and performance of optical fibers. Custom RIDs are used to tailor the transmission properties of fibers used for long-distance transmission and to enable fiber-based devices such as long-period fiber gratings (LPFGs). The introduction and modification of RSDs enable specialty fibers, such as polarization-maintaining fiber, and contribute to the operation of fiber-based devices. Furthermore, the RSD and the RID are inherently linked through the photoelastic effect. Therefore, both the RSD and the RID need to be characterized because these fundamental properties are coupled and affect the fabrication, operation, and performance of fibers and fiber-based devices. To characterize effectively the physical properties of optical fibers, the RSD and the RID must be measured without perturbing or destroying the optical fiber. Furthermore, the techniques used must not be limited in detecting small variations and asymmetries in all directions through the fiber. Finally, the RSD and the RID must be characterized concurrently without moving the fiber to enable the analysis of the relationship between the RSD and the RID. Although many techniques exist for characterizing the residual stress and the refractive index in

  14. Characterization of the stress and refractive-index distributions in optical fibers and fiber-based devices

    NASA Astrophysics Data System (ADS)

    Hutsel, Michael R.

    2011-07-01

    Optical fiber technology continues to advance rapidly as a result of the increasing demands on communication systems and the expanding use of fiber-based sensing. New optical fiber types and fiber-based communications components are required to permit higher data rates, an increased number of channels, and more flexible installation requirements. Fiber-based sensors are continually being developed for a broad range of sensing applications, including environmental, medical, structural, industrial, and military. As optical fibers and fiber-based devices continue to advance, the need to understand their fundamental physical properties increases. The residual-stress distribution (RSD) and the refractive-index distribution (RID) play fundamental roles in the operation and performance of optical fibers. Custom RIDs are used to tailor the transmission properties of fibers used for long-distance transmission and to enable fiber-based devices such as long-period fiber gratings (LPFGs). The introduction and modification of RSDs enable specialty fibers, such as polarization-maintaining fiber, and contribute to the operation of fiber-based devices. Furthermore, the RSD and the RID are inherently linked through the photoelastic effect. Therefore, both the RSD and the RID need to be characterized because these fundamental properties are coupled and affect the fabrication, operation, and performance of fibers and fiber-based devices. To characterize effectively the physical properties of optical fibers, the RSD and the RID must be measured without perturbing or destroying the optical fiber. Furthermore, the techniques used must not be limited in detecting small variations and asymmetries in all directions through the fiber. Finally, the RSD and the RID must be characterized concurrently without moving the fiber to enable the analysis of the relationship between the RSD and the RID. Although many techniques exist for characterizing the residual stress and the refractive index in

  15. Residual stress effects on the impact resistance and strength of fiber composites

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.

    1973-01-01

    Equations have been derived to predict degradation effects of microresidual stresses on impact resistance of unidirectional fiber composites. Equations also predict lamination residual stresses in multilayered angle ply composites.

  16. Evaluation of Water Stress Coefficient Methods to Estimate Actual Corn Evapotranspiration in Colorado

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Abstract for Kullberg Hydrology Days: Abstract. Increased competition for water resources is placing pressure on the agricultural sector to remain profitable while reducing water use. Remote sensing techniques have been developed to monitor crop water stress and produce information for evapotranspi...

  17. Thermal dependence of stress-induced birefringence in single mode optical fibers

    NASA Technical Reports Server (NTRS)

    Berthold, J. W., III; Thompson, L. B.

    1984-01-01

    Measurements of the change in stress-induced birefringence with temperature in single mode optical fibers are reported. The fibers examined include those with low residual stress birefringence that have circular and elliptical cores. A section of each fiber was placed under constant load with weights and heated inside a furnace. Polarized light was coupled into and out of the fiber ends outside the furnace. Two mutually perpendicular polarization components were analyzed and detected at the fiber output end. Changes in the detected signal levels were monitored as a function of the temperature of the single mode fiber stressed under constant load. Discussion of results and applications to localized stress measurements at high temperatures are presented.

  18. The actual scaling of a nominally third-order Reynolds stress

    SciTech Connect

    Krommes, J. A. Hammett, G. W.

    2014-05-15

    It is shown that a particular higher-order Reynolds stress arising from a term in the third-order gyrokinetic Hamiltonian is smaller than it nominally appears to be. However, it does not follow that all third-order terms are unimportant. The discussion is relevant to the ongoing debate about the importance of higher-order terms in the gyrokinetic theory of momentum transport.

  19. Analysis of stress distributions in metal-matrix composites with variations in fiber spacing

    NASA Astrophysics Data System (ADS)

    Yancey, Robert Neil

    1997-09-01

    Results of micromechanical and finite element analyses are presented to quantify the effects of fiber spacing in unidirectional metal-matrix composites (MMC's). Computed tomography (CT) data of unidirectional metal-matrix composite samples provide information on fiber locations for the analysis of the fiber distribution within the composite. Image processing methods are developed to extract fiber centers from the CT data. A micromechanical model, based on the Generalized Method of Cells (GMC), is developed to include interface and crack elements and model the stress variations in a representative unit cell containing two half fibers. The minimum, average, and maximum distance between fibers, as measured from the CT data, is used as input to the model. The model results show that the stress between fibers increases as they get closer together. The CT data are also processed to produce a rectangular grid of finite elements which model the composite cross-section and where the stiffness matrix for each element is based on the local fiber volume fraction. The finite element results show that in some cases, stresses in the composite can be as high as 56% greater than the average stress and thereby set up stress concentrations which can initiate yielding and/or damage at loads well below those that would be calculated using average stress considerations only.

  20. Simplified micromechanical equations for thermal residual stress analysis of coated fiber composites

    NASA Technical Reports Server (NTRS)

    Naik, Rajiv A.

    1992-01-01

    The fabrication of metal matrix composites poses unique problems to the materials engineer. The large thermal expansion coefficient mismatch between the fiber and matrix leads to high tensile residual stresses at the fiber/matrix interface which could lead to premature matrix cracking during cooldown. Fiber coating could be used to reduce thermal residual stresses. A simple closed-form analysis, based on a three-phase composite cylinder model, was developed to calculate thermal residual stresses in a fiber/interface/matrix system. Guidelines, in the form of simple equations, for the selection of appropriate material properties of the fiber coating, were also derived to minimize thermal residual stresses in the matrix during fabrication.

  1. Multi-Stress Monitoring System with Fiber-Optic Mandrels and Fiber Bragg Grating Sensors in a Sagnac Loop.

    PubMed

    Kim, Hyunjin; Sampath, Umesh; Song, Minho

    2015-01-01

    Fiber Bragg grating sensors are placed in a fiber-optic Sagnac loop to combine the grating temperature sensors and the fiber-optic mandrel acoustic emission sensors in single optical circuit. A wavelength-scanning fiber-optic laser is used as a common light source for both sensors. A fiber-optic attenuator is placed at a specific position in the Sagnac loop in order to separate buried Bragg wavelengths from the Sagnac interferometer output. The Bragg wavelength shifts are measured with scanning band-pass filter demodulation and the mandrel output is analyzed by applying a fast Fourier transform to the interference signal. This hybrid-scheme could greatly reduce the size and the complexity of optical circuitry and signal processing unit, making it suitable for low cost multi-stress monitoring of large scale power systems. PMID:26230700

  2. Multi-Stress Monitoring System with Fiber-Optic Mandrels and Fiber Bragg Grating Sensors in a Sagnac Loop

    PubMed Central

    Kim, Hyunjin; Sampath, Umesh; Song, Minho

    2015-01-01

    Fiber Bragg grating sensors are placed in a fiber-optic Sagnac loop to combine the grating temperature sensors and the fiber-optic mandrel acoustic emission sensors in single optical circuit. A wavelength-scanning fiber-optic laser is used as a common light source for both sensors. A fiber-optic attenuator is placed at a specific position in the Sagnac loop in order to separate buried Bragg wavelengths from the Sagnac interferometer output. The Bragg wavelength shifts are measured with scanning band-pass filter demodulation and the mandrel output is analyzed by applying a fast Fourier transform to the interference signal. This hybrid-scheme could greatly reduce the size and the complexity of optical circuitry and signal processing unit, making it suitable for low cost multi-stress monitoring of large scale power systems. PMID:26230700

  3. Nondestructive evaluation of residual stress in short-fiber reinforced plastics by x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Tanaka, Keisuke; Tokoro, Syouhei; Akiniwa, Yoshiaki; Egami, Noboru

    2014-06-01

    The X-ray diffraction method is used to measure the residual stress in injection-molded plates of short-fiber reinforced plastics (SFRP) made of crystalline thermoplastics, polyphenylene sulphide (PPS), reinforced by carbon fibers with 30 mass%. Based on the orientation of carbon fibers, injection molded plates can be modeled as three-layered lamella where the core layer is sandwiched by skin layers. The stress in the matrix in the skin layer was measured using Cr-Kα radiation with the sin2Ψ method. Since the X-ray penetration depth is shallow, the state of stresses measured by X-rays in FRP can be assumed to be plane stress. The X-ray measurement of stress in carbon fibers was not possible because of high texture. A new method was proposed to evaluate the macrostress in SFRP from the measurement of the matrix stress. According to micromechanics analysis of SFRP, the matrix stresses in the fiber direction, σ1m, and perpendicular to the fiber direction, σ2m, and shear stress τ12m can be expressed as the functions of the applied (macro-) stresses, σ1A, σ2A , τ12A as follows: σ1m = α11σ1A +α12σ2A, σ2m = α21σ1A + α22σ2A, τ12m = α66τ12A, where α11 ,α12, α21, α22, α66 are stress-partitioning coefficients. Using skin-layer strips cut parallel, perpendicular and 45° to the molding direction, the stress in the matrix was measured under the uniaxial applied stress and the stress-partitioning coefficients of the above equations were determined. Once these relations are established, the macrostress in SFRP can be determined from the measurements of the matrix stresses by X-rays.

  4. Stresses in a three-dimensional unidirectional composite containing broken fibers

    NASA Technical Reports Server (NTRS)

    Goree, J. G.; Gross, R. S.

    1980-01-01

    An approximate solution is developed for the determination of the interlaminar normal and shear stresses in the vicinity of a crack in a three dimensional composite containing unidirectional linearly elastic fibers in an infinite linearly elastic matrix. In order to reduce the complexity of the formulation, certain assumptions are made as to the physically significant stresses to be retained. These simplifications reduce the partial differential equations of elasticity to differential-difference equations which are tractable using Fourier transform techniques. This 'material modeling' approach is in contrast with solutions developed by considering each lamina as a homogeneous, orthotropic layer. The resulting solution does not contain the classical singular stress field for the fibers and the influence of broken fibers on unbroken fibers is felt by a change in stress concentration factors. The matrix stresses however, are unbounded as the fiber spacing vanishes and an equivalent fiber-matrix geometry is proposed which gives the correct singular behavior. The numerical solution is considered in detail and several specific examples are presented. The potential for damaged or debonded zones to be generated by an embedded crack is discussed, and stress concentration factors for fibers near the crack are given. Detailed comparisons are made between the present solution, the analogous two-dimensional problem, and corresponding shear-lag models.

  5. Arc-discharge effects on residual stress and refractive index in single-mode optical fibers.

    PubMed

    Wang, Pengfei; Jenkins, Micah H; Gaylord, Thomas K

    2016-03-20

    Arc-discharge effects on the residual stress and refractive index in single-mode optical fibers are investigated using a previously developed three-dimensional concurrent stress-index measurement method. Using commercial optical fibers and a commercial fusion splicer, the residual stress and refractive index perturbations caused by weak electrical arc discharges in single-mode fibers were measured. Refractive index changes greater than 10-4 and longitudinal perturbation lengths of less than 500 μm were shown to be possible. The subsequent prospects for arc-induced long-period fiber gratings are analyzed, and a typical transmission resonance is predicted to have a depth of 56 dB and a bandwidth of 0.08 nm at a wavelength of 1585 nm. The results of this investigation will be useful in modeling device performance and optimization of arc-induced long-period fiber grating fabrication. PMID:27140587

  6. Augmented stress fiber arrays after cytopharmacologic disassembly of microtubules

    SciTech Connect

    Godman, G.C.; Tannenbaum, J.; Brett, J.B.

    1986-03-01

    Disruption of microtubules (mt) of bovine aortic endothelial (BAE) cells, and normal and transformed fibroblasts, by exposure to 2.5 ..mu..M colchicine; 12 ..mu..M vinblastine; or 1 ..mu..M nocodazole, for 5 or 20 hrs results in aggregation of vimentin-intermediate filament (IF) and the development of markedly augmented stress fiber (SF) arrays. After disassembly of mt, confluent BAE, with circumferential marginal microfilament bands and few central SF, develop dense ribbon-like SF arrays, and spontaneously transformed fibroblasts (tHmf-e), which before treatment are apolar or epithelioid and have few or no SF, acquire extensive organized SF arrays. The axially oriented SF span the entire cell length and terminate in vinculin-containing adhesion plaques, polarizing these cells. The visible increase in SF associated actin is not accompanied by an increase either in actin synthesis (determined from electropherograms after pulse labeling with (/sup 35/S)methionine), or content (DNAse I assay for total cell actin). The reorganization of actin into SF and the development of vinculin adhesion plaques is independent of protein synthesis and occurs in the presence of cycloheximide (10 ..mu..g/ml). These results suggest a role for mt and IF in the regulation of the organizational state of the actin-based cytoskeleton.

  7. Dynamic changes in stress fiber expression in rat uterine vein endothelial cells associated with pregnancy.

    PubMed

    Sago, H; Sugimoto, K; Fujii, S; Iinuma, K; Yamashita, K; Kitagawa, M; Terashima, Y

    1993-09-01

    En face endothelial preparations of rat uterine vein were stained with rhodamine-phalloidin to investigate the dynamics of stress fiber expression during pregnancy. In prepregnant animals, somewhat plump, spindle-like endothelial cells of the uterine vein had only a few short stress fibers. With the progress of pregnancy, however, many long stress fibers appeared within the elongated endothelial cells. Within 2 hr after delivery, these stress fibers became dramatically decreased in number as the cells reverted from an elongated to a plump shape and returned to the prepregnancy level by 14 days postpartum. The uterine vein showed a significant increase in length during pregnancy and quickly shortened after delivery. Thus, expression of stress fibers in endothelial cells of the uterine vein seems to be related to the tension loaded on this vessel during its elongation in parallel with the marked growth of the uterine body during pregnancy. This study shows that stress fibers are dynamic structures that may serve to maintain endothelial cell integrity during the exertion of tensile stress on the vessel wall. PMID:8246817

  8. Optical fiber sensors and their application in monitoring stress build-up in dental resin cements

    NASA Astrophysics Data System (ADS)

    Ottevaere, H.; Tabak, M.; Fernandez Fernandez, A.; Berghmans, F.; Thienpont, H.

    2005-09-01

    The field of optical fiber sensing is highly diverse and this diversity is perceived as a great advantage over more conventional sensors in that an optical sensor can be tailored to measure any of a myriad of physical parameters. In this paper we present a niche application for optical fiber sensors in the domain of biophotonics, namely the monitoring of stress build-up during the curing process of dental resin cements. We discuss the origin of this stress build-up and the problems it can cause when treating patients. Optical fiber sensors aim at excelling in two kind of applications: firstly to perform quality control on batch produced dental cements and measure their total material shrinkage, secondly to monitor the hardening of the cement during in-vivo measurements resulting in the dynamic measurement of the shrinkage and to control the stress in a facing based restoration. We therefore investigated two types of optical fiber sensors as alternatives to conventional measurement techniques; namely polarimetric optical fiber sensors and fiber Bragg gratings written in polarization maintaining fibers. After discussing the results obtained with both optical fiber sensors, we will conclude with a critical assessment of the suitability of the two proposed sensing configurations for multi-parameter stress monitoring.

  9. Functional analyses of cotton (Gossypium hirsutum L.) immature fiber (im) mutant infer that fiber cell wall development is associated with stress responses

    PubMed Central

    2013-01-01

    Background Cotton fiber maturity is an important factor for determining the commercial value of cotton. How fiber cell wall development affects fiber maturity is not well understood. A comparison of fiber cross-sections showed that an immature fiber (im) mutant had lower fiber maturity than its near isogenic wild type, Texas marker-1 (TM-1). The availability of the im mutant and TM-1 provides a unique way to determine molecular mechanisms regulating cotton fiber maturity. Results Transcriptome analysis showed that the differentially expressed genes (DEGs) in the im mutant fibers grown under normal stress conditions were similar to those in wild type cotton fibers grown under severe stress conditions. The majority of these DEGs in the im mutant were related to stress responses and cellular respiration. Stress is known to reduce the activity of a classical respiration pathway responsible for energy production and reactive oxygen species (ROS) accumulation. Both energy productions and ROS levels in the im mutant fibers are expected to be reduced if the im mutant is associated with stress responses. In accord with the prediction, the transcriptome profiles of the im mutant showed the same alteration of transcriptional regulation that happened in energy deprived plants in which expressions of genes associated with cell growth processes were reduced whereas expressions of genes associated with recycling and transporting processes were elevated. We confirmed that ROS production in developing fibers from the im mutant was lower than that from the wild type. The lower production of ROS in the im mutant fibers might result from the elevated levels of alternative respiration induced by stress. Conclusion The low degree of fiber cell wall thickness of the im mutant fibers is associated with deregulation of the genes involved in stress responses and cellular respiration. The reduction of ROS levels and up-regulation of the genes involved in alternative respirations suggest that

  10. Stress-and-Strain Analysis Of Hot Metal/Fiber Composites

    NASA Technical Reports Server (NTRS)

    Hopkins, Dale A.; Chamis, Christos C.

    1988-01-01

    Macroscopic mechanical properties derived from micromechanics. Stress-and-strain equations developed to express microscopic and macroscopic mechanical properties of metals reinforced by unidirectional fibers, over range of temperatures. New equations reduce computational load by providing approximate, closed-form expressions for microscopic and pseudohomogeneous anisotropic properties of single ply reinforced by unidirectional fibers. Typical application is calculation of residual stress in newly manufactured article.

  11. Developing fiber specific promoter-reporter transgenic lines to study the effect of abiotic stresses on fiber development in cotton

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cotton is one of the most important cash crops in US agricultural industry. Environmental stresses, such as drought, high temperature and combination of both, not only reduce the overall growth of cotton plants, but also greatly decrease cotton lint yield and fiber quality. The impact of environment...

  12. In situ stress measurement of fiber reinforced composite in low temperature state by neutron diffraction

    NASA Astrophysics Data System (ADS)

    Nishida, Masayuki; Jing, Tian; Muslih, M. Refai; Doi, Taisei; Matsue, Tatsuya; Hanabusa, Takao

    2015-03-01

    The tungsten fiber reinforced titanium composite (W/Ti) was produced by the spot welding method. The internal stress alteration of the W/Ti composite was measured by the neutron diffractometer, DN1, which had been installed at beam port #6 in National Nuclear Energy Agency Indonesia. The two-dimensional detector and cryostat system were mounted on the DN1 diffractometer, and the residual stress alterations were measured by the in situ neutron stress measurement technique under the cooling cycles from 300 K to 10 K. Residual stresses in tungsten fiber were investigated at several temperatures. In the longitudinal fiber direction, the thermal residual stresses of tungsten fiber became a large compressive state and represented the maximum value is about -950 MPa. The calculated results of the simple elastic model agreed with the experimental results of the in situ thermal stress measurement qualitatively. It is assumed that the stresses in the fiber longitudinal direction are the dominant stresses in the W/Ti composite.

  13. Simplified micromechanical equations for thermal residual stress analysis of coated fiber composites

    NASA Technical Reports Server (NTRS)

    Naik, R. A.

    1991-01-01

    The fabrication of metal matrix composites poses unique problems to the materials engineer. The large thermal expansion coefficient (CTE) mismatch between the fiber and matrix leads to high tensile residual stresses at the fiber/matrix (F/M) interface which could lead to premature matrix cracking during cooldown. Fiber coatings could be used to reduce thermal residual stresses. A simple closed form analysis, based on a three phase composite cylinder model, was developed to calculate thermal residual stresses in a fiber/interphase/matrix system. Parametric studies showed that the tensile thermal residual stresses at the F/M interface were very sensitive to the CTE and thickness of the interphase layer. The modulus of the layer had only a moderate effect on tensile residual stresses. For a silicon carbide titanium aluminide composite, the tangential stresses were 20 to 30 pct. larger than the axial stresses, over a wide range of interphase layer properties, indicating a tendency to form radial matrix cracks during cooldown. Guidelines for the selection of appropriate material properties of the fiber coating were also derived in order to minimize thermal residual stresses in the matrix during fabrication.

  14. Shear stress sensing with Bragg grating-based sensors in microstructured optical fibers.

    PubMed

    Sulejmani, Sanne; Sonnenfeld, Camille; Geernaert, Thomas; Luyckx, Geert; Van Hemelrijck, Danny; Mergo, Pawel; Urbanczyk, Waclaw; Chah, Karima; Caucheteur, Christophe; Mégret, Patrice; Thienpont, Hugo; Berghmans, Francis

    2013-08-26

    We demonstrate shear stress sensing with a Bragg grating-based microstructured optical fiber sensor embedded in a single lap adhesive joint. We achieved an unprecedented shear stress sensitivity of 59.8 pm/MPa when the joint is loaded in tension. This corresponds to a shear strain sensitivity of 0.01 pm/µε. We verified these results with 2D and 3D finite element modeling. A comparative FEM study with conventional highly birefringent side-hole and bow-tie fibers shows that our dedicated fiber design yields a fourfold sensitivity improvement. PMID:24105585

  15. Nucleation and Crystallization as Induced by Bending Stress in Lithium Silicate Glass Fibers

    NASA Technical Reports Server (NTRS)

    Reis, Signo T.; Kim, Cheol W.; Brow, Richard K.; Ray, Chandra S.

    2003-01-01

    Glass Fibers of Li2O.2SiO2 (LS2) and Li2O.1.6SiO2 (LS1.6) compositions were heated near, but below, the glass transition temperature for different times while subjected to a constant bending stress of about 1.2 GPa. The nucleation density and the crystallization tendency estimated by differential thermal analysis (DTA) of a glass sample in the vicinity of the maximum of the bending stress increased relative to that of stress-free glass fibers. LS2 glass fibers were found more resistant to nucleation and crystallization than the Ls1.6 glass fibers. These results are discussed in regards to shear thinning effects on glass stability.

  16. Correlation of fiber composite tensile strength with the ultrasonic stress wave factor

    NASA Technical Reports Server (NTRS)

    Vary, A.; Lark, R. F.

    1978-01-01

    An ultrasonic-acoustic technique was used to indicate the strength variations of tensile specimens of a graphite-epoxy composite. A 'stress wave factor' was determined and its value was found to depend on variations of the fiber-resin bonding as well as fiber orientation. The fiber orientations studied were 0 deg (longitudinal), 10 deg (off-axis), 90 deg (transverse), (0 deg/+ or - 45 deg/0) symmetrical, and (+ or - 45 deg) symmetrical. The stress wave factor can indicate variations of the tensile and shear strengths of composite materials. The stress wave factor was also found to be sensitive to strength variations associated with microporosity and differences in fiber-resin ratio.

  17. Correlation of Fiber Composite Tensile Strength with the Ultrasonic Stress Wave Factor

    NASA Technical Reports Server (NTRS)

    Vary, A.; Lark, R. F.

    1978-01-01

    An ultrasonic-acoustic technique was used to indicate the strength variations of tensile specimens of a graphite-epoxy composite. A stress wave factor was determined and its value was found to depend on variations of the fiber-resin bonding as well as fiber orientation. The fiber orientations studied were 0 deg (longitudinal), 10 deg (off-axis), 90 deg (transverse), 0 deg + or - 45 deg/0 deg symmetrical, and + or - 45 deg] symmetrical. The stress wave factor can indicate variations of the tensile and shear strengths of composite materials. The stress wave factor was also found to be sensitive to strength variations associated with microporosity and differences in fiber-resin ratio.

  18. Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

    2004-01-01

    The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

  19. Stress-induced birefringence and fabrication of in-fiber polarization devices by controlled femtosecond laser irradiations.

    PubMed

    Yuan, Lei; Cheng, Baokai; Huang, Jie; Liu, Jie; Wang, Hanzheng; Lan, Xinwei; Xiao, Hai

    2016-01-25

    Optical birefringence was created in a single-mode fiber by introducing a series of symmetric cuboid stress rods on both sides of the fiber core along the fiber axis using a femtosecond laser. The stress-induced birefringence was estimated to be 2.4 × 10(-4) at the wavelength of 1550 nm. By adding the desired numbers of stressed rods, an in-fiber quarter waveplate was fabricated with a insertion loss of 0.19 dB. The stress-induced birefringence was further explored to fabricate in-fiber polarizers based on the polarization-dependent long-period fiber grating (LPFG) structure. A polarization extinction ratio of more than 20 dB was observed at the resonant wavelength of 1523.9 nm. The in-fiber polarization devices may be useful in optical communications and fiber optic sensing applications. PMID:26832490

  20. Stress-Rupture of New Tyranno Si-C-O-Zr Fiber Reinforced Minicomposites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.

    1999-01-01

    Minicomposites consisting of two varieties of Zr containing SiC-based fibers from Ube (Tyranno) with BN interphases and CVI SiC matrices were studied. The two fiber-types were the ZMI and ZE fiber-types that contain approximately 8 and 2% oxygen, respectively. The minicomposites were precracked and tested under constant load testing at temperatures ranging from 700 to 1200 C. The data were then compared to the rupture behavior of Hi- Nicalon (TM) fiber reinforced minicomposites tested under identical conditions. It was found that the Ube fiber-types had stress rupture life equivalent to Hi- Nicalon (TM) over the entire temperature range. A potential benefit of the ZMI fiber-type is that it offers rupture properties almost as good as Hi-Nicalon (TM) at the cost of ceramic grade Nicalon (TM).

  1. Bond stress-slip mechanisms in high-performance fiber-reinforced cement composites

    NASA Astrophysics Data System (ADS)

    Guerrero Z., Aydee Patricia

    This research covers integrated experimental and analytical investigations of the mechanisms that influence the fiber pull-out versus slip response of typical fibers used in the production of fiber reinforced cementitious composites, in order to improve their mechanical performance. The fibers investigated include smooth steel fibers, hooked steel fibers, Torex twisted steel fibers and PVA (polyvinyl alcohol) fibers. Torex is a newly developed steel fiber, of general polygonal shape, that is twisted along its longitudinal axis to improve the mechanical component of bond. PVA fibers, currently used as replacement for asbestos fibers, have good mechanical properties and are believed to develop an adhesive or chemical bond component with cement matrices. Matrix parameters investigated comprised four different additives (fly ash, metakaolin, PVA polymer and latex) and the fineness of the sand. The experimental program included two types of tests, a single fiber pull-out test and a tensile test on notched prisms, considered an indirect test to measure bond. The first test was used when the fiber diameter exceeded 200 microns. The second test was primarily carried out for PVA fibers with a diameter in the range of 11 to 50 microns. Closed-loop control was used in the notched prism tests where the rate of crack opening at the notch controlled the machine displacement. Also in these tests, three different volume fractions of fibers were investigated for each parameter in order to back-calculate the bond strength. The analytical program includes three parts: (1) a study to model the contribution of the hook to the mechanical component of bond in hooked steel fibers, (2) a study to back-calculate adhesive-frictional bond of fine PVA fibers from the stress versus crack opening response of notched tensile prisms, and (3) a study to model the effect of twisting on the mechanical contribution of bond in Torex steel fibers. This last model utilizes a finite element code (based on

  2. Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber

    NASA Technical Reports Server (NTRS)

    Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.

    1995-01-01

    Understanding the thermomechanical behavior (creep and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile creep data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

  3. High extensibility of stress fibers revealed by in vitro micromanipulation with fluorescence imaging

    SciTech Connect

    Matsui, Tsubasa S.; Sato, Masaaki; Deguchi, Shinji

    2013-05-10

    Highlights: •We isolate contractile stress fibers from vascular smooth muscle cells. •We measure the extensibility of individual stress fibers. •We present the first direct evidence that individual stress fibers are highly extensible. •We quantitatively determine the local strain along the length of stress fibers. •The high extensibility we found is beyond that explained by a conventional model. -- Abstract: Stress fibers (SFs), subcellular bundles of actin and myosin filaments, are physically connected at their ends to cell adhesions. The intracellular force transmitted via SFs plays an essential role in cell adhesion regulation and downstream signaling. However, biophysical properties intrinsic to individual SFs remain poorly understood partly because SFs are surrounded by other cytoplasmic components that restrict the deformation of the embedded materials. To characterize their inherent properties independent of other structural components, we isolated SFs from vascular smooth muscle cells and mechanically stretched them by in vitro manipulation while visualizing strain with fluorescent quantum dots attached along their length. SFs were elongated along their entire length, with the length being approximately 4-fold of the stress-free length. This surprisingly high extensibility was beyond that explained by the tandem connection of actin filaments and myosin II bipolar filaments present in SFs, thus suggesting the involvement of other structural components in their passive biophysical properties.

  4. Micromechanics analysis of space simulated thermal deformations and stresses in continuous fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Bowles, David E.

    1990-01-01

    Space simulated thermally induced deformations and stresses in continuous fiber reinforced composites were investigated with a micromechanics analysis. The investigation focused on two primary areas. First, available explicit expressions for predicting the effective coefficients of thermal expansion (CTEs) for a composite were compared with each other, and with a finite element (FE) analysis, developed specifically for this study. Analytical comparisons were made for a wide range of fiber/matrix systems, and predicted values were compared with experimental data. The second area of investigation focused on the determination of thermally induced stress fields in the individual constituents. Stresses predicted from the FE analysis were compared to those predicted from a closed-form solution to the composite cylinder (CC) model, for two carbon fiber/epoxy composites. A global-local formulation, combining laminated plate theory and FE analysis, was used to determine the stresses in multidirectional laminates. Thermally induced damage initiation predictions were also made.

  5. Research on the fiber Bragg grating sensor for the shock stress measurement

    PubMed Central

    Deng, Xiangyang; Chen, Guanghua; Peng, Qixian; Li, Zeren; Meng, Jianhua; Liu, Jun

    2011-01-01

    A fiber Bragg grating (FBG) sensor with an unbalanced Mach-Zehnder fiber interferometer for the shock stress measurement is proposed and demonstrated. An analysis relationship between the shock stress and the central reflection wavelength shift of the FBG is firstly derived. In this sensor, the optical path difference of the unbalanced Mach-Zehnder fiber interferometer is ∼3.1 mm and the length of the FBG is 2 mm. An arctangent function reduction method, which can avoid sine function's insensitive zone where the shock stress measurement has a reduced accuracy, is presented. A shock stress measurement of water driven by one stage gun (up to 1.4 GPa), with good theoretical accuracy (∼10%), is launched. PMID:22047282

  6. Fiber optic stress-independent helical torsion sensor.

    PubMed

    Fernandes, Luís A; Grenier, Jason R; Aitchison, J Stewart; Herman, Peter R

    2015-02-15

    Femtosecond laser-fabricated waveguides have been formed into helical paths throughout the cladding of single-mode optical fibers to demonstrate a strain-independent fiber torsion sensor. A comparison between a Bragg grating sensor and a Mach-Zehnder based on helical waveguides (HWs) showed a much weaker twist sensitivity of 1.5 pm/(rad/m) for the grating in contrast with a value of 261 pm/(rad/m) for the interferometer. The HW geometry provided an unambiguous determination of the rotational direction of the twist while facilitating a convenient and efficient means for optical coupling into the single-mode core of the fiber. The flexible three-dimensional writing by the femtosecond laser fabrication method enabled the direct inscription of compact and robust optical cladding devices without the need for combining or splicing multiple-fiber segments. PMID:25680174

  7. Dissecting Regional Variations in Stress Fiber Mechanics in Living Cells with Laser Nanosurgery

    SciTech Connect

    Tanner, Kandice; Boudreau, Aaron; Bissell, Mina J; Kumar, Sanjay

    2010-03-02

    The ability of a cell to distribute contractile stresses across the extracellular matrix in a spatially heterogeneous fashion underlies many cellular behaviors, including motility and tissue assembly. Here we investigate the biophysical basis of this phenomenon by using femtosecond laser nanosurgery to measure the viscoelastic recoil and cell-shape contributions of contractile stress fibers (SFs) located in specific compartments of living cells. Upon photodisruption and recoil, myosin light chain kinase-dependent SFs located along the cell periphery display much lower effective elasticities and higher plateau retraction distances than Rho-associated kinase-dependent SFs located in the cell center, with severing of peripheral fibers uniquely triggering a dramatic contraction of the entire cell within minutes of fiber irradiation. Image correlation spectroscopy reveals that when one population of SFs is pharmacologically dissipated, actin density flows toward the other population. Furthermore, dissipation of peripheral fibers reduces the elasticity and increases the plateau retraction distance of central fibers, and severing central fibers under these conditions triggers cellular contraction. Together, these findings show that SFs regulated by different myosin activators exhibit different mechanical properties and cell shape contributions. They also suggest that some fibers can absorb components and assume mechanical roles of other fibers to stabilize cell shape.

  8. Reduction of thermal stresses in continuous fiber reinforced metal matrix composites with interface layers

    NASA Technical Reports Server (NTRS)

    Jansson, S.; Leckie, F. A.

    1992-01-01

    The potential of using interface layer to reduce thermal stresses in the matrix of composites with a mismatch in coefficients of thermal expansion of fiber and matrix has been investigated. It was found that compliant layers, with properties of readily available materials, do not have the potential to reduce thermal stresses significantly. However, interface layers with high coefficient of thermal expansion can compensate for the mismatch and reduce thermal stresses in the matrix significantly.

  9. Reduction of thermal stresses in continuous fiber reinforced metal matrix composites with interface layers

    NASA Technical Reports Server (NTRS)

    Jansson, S.; Leckie, F. A.

    1990-01-01

    The potential of using an interface layer to reduce thermal stresses in the matrix of composites with a mismatch in coefficients of thermal expansion of fiber and matrix was investigated. It was found that compliant layers, with properties of readily available materials, do not have the potential to reduce thermal stresses significantly. However, interface layers with high coefficient of thermal expansion can compensate for the mismatch and reduce thermal stresses in the matrix significantly.

  10. Numerical analysis of residual stresses in preforms of stress applying part for PANDA-type polarization maintaining optical fibers in view of technological imperfections of the doped zone geometry

    NASA Astrophysics Data System (ADS)

    Trufanov, Aleksandr N.; Trufanov, Nikolay A.; Semenov, Nikita V.

    2016-09-01

    The experimental data analysis of the stress applying rod section geometry for the PANDA-type polarization maintaining optical fiber has been performed. The dependencies of the change in the radial dimensions of the preform and the doping boundary on the angular coordinate have been obtained. The original algorithm of experimental data statistic analysis, which enables determination of the specimens' characteristic form of section, has been described. The influence of actual doped zone geometry on the residual stress fields formed during the stress rod preform fabrication has been investigated. It has been established that the deviation of the boundary between pure silica and the doped zone from the circular shape results in dissymmetry and local concentrations of the residual stress fields along the section, which can cause preforms destruction at high degrees of doping. The observed geometry deviations of up to 10% lead to the increase of the maximum stress intensity value by over 20%.

  11. Relationship between cell stiffness and stress fiber amount, assessed by simultaneous atomic force microscopy and live-cell fluorescence imaging.

    PubMed

    Gavara, Núria; Chadwick, Richard S

    2016-06-01

    Actomyosin stress fibers, one of the main components of the cell's cytoskeleton, provide mechanical stability to adherent cells by applying and transmitting tensile forces onto the extracellular matrix (ECM) at the sites of cell-ECM adhesion. While it is widely accepted that changes in spatial and temporal distribution of stress fibers affect the cell's mechanical properties, there is no quantitative knowledge on how stress fiber amount and organization directly modulate cell stiffness. We address this key open question by combining atomic force microscopy with simultaneous fluorescence imaging of living cells, and combine for the first time reliable quantitative parameters obtained from both techniques. We show that the amount of myosin and (to a lesser extent) actin assembled in stress fibers directly modulates cell stiffness in adherent mouse fibroblasts (NIH3T3). In addition, the spatial distribution of stress fibers has a second-order modulatory effect. In particular, the presence of either fibers located in the cell periphery, aligned fibers or thicker fibers gives rise to reinforced cell stiffness. Our results provide basic and significant information that will help design optimal protocols to regulate the mechanical properties of adherent cells via pharmacological interventions that alter stress fiber assembly or via micropatterning techniques that restrict stress fiber spatial organization. PMID:26206449

  12. Self-Reported and Actual Use of Proactive and Reactive Classroom Management Strategies and Their Relationship with Teacher Stress and Student Behaviour

    ERIC Educational Resources Information Center

    Clunies-Ross, Penny; Little, Emma; Kienhuis, Mandy

    2008-01-01

    This study investigated the relationship between primary school teachers' self-reported and actual use of classroom management strategies, and examined how the use of proactive and reactive strategies is related to teacher stress and student behaviour. The total sample consisted of 97 teachers from primary schools within Melbourne. Teachers…

  13. Thermal Stress-Induced Depolarization Loss in Conventional and Panda-Shaped Photonic Crystal Fiber Lasers

    NASA Astrophysics Data System (ADS)

    Mousavi, Seyedeh Laleh; Sabaeian, Mohammad

    2016-07-01

    We report on the modeling of the depolarization loss in the conventional and panda-shaped photonic crystal fiber lasers (PCFLs) due to the self-heating of the fiber, which we call it thermal stress-induced depolarization loss (TSIDL). We first calculated the temperature distribution over the fiber cross sections and then calculated the thermal stresses/strains as a function of heat load per meter. Thermal stress-induced birefringence (TSIB), which is defined as |n x - n y |, in the core and cladding regions was calculated. Finally, TSIDL was calculated for the conventional and panda-shaped PCFLs as a function of fiber length and, respectively, saturated values of 22 and 25 % were obtained which were independent of heat load per meter. For panda-shaped PCFLs, prior to being saturated, an oscillating and damping behavior against the fiber length was seen where in some lengths reached 35 %. The results are close to an experimental value of 30 % reported for a pulsed PCFL (Limpert et al., Opt Express 12:1313-1319, 2004) where the authors reported a degree of polarization of 70 % (i.e., a depolarization of 30 %). The most important result of this work is a saturation behavior of TSIDL at long-enough lengths of the fiber laser which is independent of heat load per meter. To our knowledge, this the first report of TSIBL for PCFLs.

  14. Analysis of shear stress distribution in pushout process of fiber-reinforced ceramics

    SciTech Connect

    Honda, Kouichi; Kagawa, Yutaka

    1995-04-01

    The interfacial shear stress distribution of a thin specimen of SiC fiber-reinforced glass matrix composite (fiber volume fraction of 0.1, 0.5, and 0.7) during a fiber pushout process was subjected to finite element analysis using a three concentric axisymmetrical model which consisted of fiber, matrix, and composite. A stress criterion was used to determine interface debonding. Effects of thermally-induced stress and a post debond sliding process at the interface were also included in the analysis. The analytical result showed that shear stress near the specimen surface was introduced during the specimen preparation process. Before the interfacial debonding, the distribution of shear stress during the pushout test was affected by the existence of thermally-induced stress in the specimen. The interfacial shear debonding initiated {approximately}30 {mu}m below the pushing surface and the sliding at the debonded interface proceeded in the direction of both the pushing surface and back surface from the peak shear position; the debonding from the back surface initiated just before the complete debonding of the interface. The pushout load-displacement curve near the origin was straight, however, after the existence of interface sliding at the debonded interface, the curve exhibited non-linearity with the increase in applied load up to the complete debonding at the interface. This debonding process was essentially independent of the fiber volume fraction. The results indicate that the total of thermally-induced stress in the specimen and shear stress distribution generated by applied load are important for the initiation of debonding and the frictional sliding process of the thin specimen pushout test.

  15. Effect of Simultaneous Water Deficit Stress and Meloidogyne incognita Infection on Cotton Yield and Fiber Quality

    PubMed Central

    Davis, R. F.; Earl, H. J.; Timper, P.

    2014-01-01

    Both water deficit stress and Meloidogyne incognita infection can reduce cotton growth and yield, and drought can affect fiber quality, but the effect of nematodes on fiber quality is not well documented. To determine whether nematode parasitism affects fiber quality and whether the combined effects of nematode and drought stress on yield and quality are additive (independent effects), synergistic, or antagonistic, we conducted a study for 7 yr in a field infested with M. incognita. A split-plot design was used with the main plot factor as one of three irrigation treatments (low [nonirrigated], moderate irrigation, and high irrigation [water-replete]) and the subplot factor as 0 or 56 l/ha 1,3-dichloropropene. We prevented water deficit stress in plots designated as water-replete by supplementing rainfall with irrigation. Plots receiving moderate irrigation received half the water applied to the water-replete treatment. The severity of root galling was greater in nonfumigated plots and in plots receiving the least irrigation, but the amount of irrigation did not influence the effect of fumigation on root galling (no irrigation × fumigation interaction). The weights of lint and seed harvested were reduced in nonfumigated plots and also decreased as the level of irrigation decreased, but fumigation did not influence the effect of irrigation. Nematodes affected fiber quality by increasing micronaire readings but typically had little or no effect on percent lint, fiber length (measured by HVI), uniformity, strength, elongation, length (based on weight or number measured by AFIS), upper quartile length, or short fiber content (based on weight or number). Micronaire also was increased by water deficit stress, but the effects from nematodes and water stress were independent. We conclude that the detrimental effects caused to cotton yield and quality by nematode parasitism and water deficit stress are independent and therefore additive. PMID:24987162

  16. Effect of Simultaneous Water Deficit Stress and Meloidogyne incognita Infection on Cotton Yield and Fiber Quality.

    PubMed

    Davis, R F; Earl, H J; Timper, P

    2014-06-01

    Both water deficit stress and Meloidogyne incognita infection can reduce cotton growth and yield, and drought can affect fiber quality, but the effect of nematodes on fiber quality is not well documented. To determine whether nematode parasitism affects fiber quality and whether the combined effects of nematode and drought stress on yield and quality are additive (independent effects), synergistic, or antagonistic, we conducted a study for 7 yr in a field infested with M. incognita. A split-plot design was used with the main plot factor as one of three irrigation treatments (low [nonirrigated], moderate irrigation, and high irrigation [water-replete]) and the subplot factor as 0 or 56 l/ha 1,3-dichloropropene. We prevented water deficit stress in plots designated as water-replete by supplementing rainfall with irrigation. Plots receiving moderate irrigation received half the water applied to the water-replete treatment. The severity of root galling was greater in nonfumigated plots and in plots receiving the least irrigation, but the amount of irrigation did not influence the effect of fumigation on root galling (no irrigation × fumigation interaction). The weights of lint and seed harvested were reduced in nonfumigated plots and also decreased as the level of irrigation decreased, but fumigation did not influence the effect of irrigation. Nematodes affected fiber quality by increasing micronaire readings but typically had little or no effect on percent lint, fiber length (measured by HVI), uniformity, strength, elongation, length (based on weight or number measured by AFIS), upper quartile length, or short fiber content (based on weight or number). Micronaire also was increased by water deficit stress, but the effects from nematodes and water stress were independent. We conclude that the detrimental effects caused to cotton yield and quality by nematode parasitism and water deficit stress are independent and therefore additive. PMID:24987162

  17. Tensile Creep and Stress-rupture Behavior of Polymer Derived Sic Fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.; Dicarlo, J. A.

    1994-01-01

    Tensile creep and stress-rupture studies were conducted on polymer derived Nicalon, Hi-Nicalon, and SiC/BN-coated Nicalon SiC fibers. Test conditions were temperatures from 1200 to 1400 C, stresses from 100 to 1600 MPa, stress application times up to 200 hours, and air, argon, and vacuum test environments. For all fibers, creep occurred predominantly in the primary stage. Hi-Nicalon had much higher 0.2 and 1 percent creep strengths than as-produced as well as-coated Nicalon fibers. The stress-rupture strength of Hi-Nicalon up to 100 hours was also higher than that of the coated and as-produced Nicalon fibers. SiC/BN coating on Nicalon increased only the short-term low-temperature rupture strength. Limited testing in argon and vacuum suggests that for all fiber types, creep and rupture resistances are reduced in comparison to the results in air. Possible mechanisms for the observed behavior are discussed.

  18. Fiber-matrix interface effects in the presence of thermally induced residual stresses

    SciTech Connect

    Nimmer, R.P. )

    1990-01-01

    The mechanics of transversely loaded high-temperature composites with a thermally induced residual stress field and a vanishingly weak fiber-matrix interface strength was investigated using two analytical models. In particular, the effects of several physical properties defining the performance of the constituent fiber, matrix, and interface are examined relative to their effect on composite's behavior. Both models demonstrate that, if there is a thermally induced residual stress field in the composite, the initial transverse modulus for the composite will be the same regardless of whether there is a well-bonded or an unbonded interface. 10 refs.

  19. Closed-form analysis of fiber-matrix interface stresses under thermo-mechanical loadings

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Closed form techniques for calculating fiber matrix (FM) interface stresses, using repeating square and diamond regular arrays, were presented for a unidirectional composite under thermo-mechanical loadings. An Airy's stress function micromechanics approach from the literature, developed for calculating overall composite moduli, was extended in the present study to compute FM interface stresses for a unidirectional graphite/epoxy (AS4/3501-6) composite under thermal, longitudinal, transverse, transverse shear, and longitudinal shear loadings. Comparison with finite element results indicate excellent agreement of the FM interface stresses for the square array. Under thermal and longitudinal loading, the square array has the same FM peak stresses as the diamond array. The square array predicted higher stress concentrations under transverse normal and longitudinal shear loadings than the diamond array. Under transverse shear loading, the square array had a higher stress concentration while the diamond array had a higher radial stress concentration. Stress concentration factors under transverse shear and longitudinal shear loadings were very sensitive to fiber volume fraction. The present analysis provides a simple way to calculate accurate FM interface stresses for both the square and diamond array configurations.

  20. Evaluation of the Fiber Stress Distribution in Aramid/Epoxy Model Composite Using Micro-Raman Spectroscopy and FEM Analysis

    NASA Astrophysics Data System (ADS)

    Tanaka, Kazuto; Minoshima, Kohji; Yamada, Hideo

    A single-fiber pull-out model composite for an aramid/epoxy system was specially designed to measure the stress distribution of the aramid fiber embedded in the matrix using micro-Raman spectroscopy. The stress transfer length of the fiber obtained was about 400-500 μm, which was equal to the result of FEM analysis. Just after the initiation and propagation of the fiber/matrix interfacial debonding, the fiber was broken, and the fiber in the matrix had the axial tensile residual stress. The tensile residual axial stress showed the maximum at around the tip of the interfacial debonding. The stress was reduced after the specimen was kept in air at 80°C for 44h, and it became almost equal to zero after being immersed in deionized water at 80°C for 44h. This behavior agreed with the result of FEM analysis, in which the friction coefficient was introduced in the fiber/matrix interface. The axial residual stress was caused by the friction between the fiber and matrix, due to the compressive stress acting between the resin and the fiber, which was caused by the difference of the coefficient of thermal expansion.

  1. 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.

  2. Microsurgery-aided in-situ force probing reveals extensibility and viscoelastic properties of individual stress fibers

    PubMed Central

    Labouesse, Céline; Gabella, Chiara; Meister, Jean-Jacques; Vianay, Benoît; Verkhovsky, Alexander B.

    2016-01-01

    Actin-myosin filament bundles (stress fibers) are critical for tension generation and cell shape, but their mechanical properties are difficult to access. Here we propose a novel approach to probe individual peripheral stress fibers in living cells through a microsurgically generated opening in the cytoplasm. By applying large deformations with a soft cantilever we were able to fully characterize the mechanical response of the fibers and evaluate their tension, extensibility, elastic and viscous properties. PMID:27025817

  3. Matrix cracking initiation stress in fiber-reinforced ceramic-matrix composites

    SciTech Connect

    Kangutkar, P.B.

    1991-01-01

    One of the important design parameters in CMC's is the matrix cracking initiation stress (MCIS) which corresponds to the stress at which first matrix cracks are observed. Above the MCIS, the fibers will be exposed to the oxidizing environment which may degrade the mechanical property of the fibers and thus of the composite. In this thesis, a systematic study to explore the effects of matrix toughness and inherent strength, fiber diameter, stiffness and volume fraction, temperature and interfacial bonding on the MCIS was carried out. Composites were fabricated using three different matrices - borosilicate glass, aluminosilicate glass and polycrystalline zirconium silicate (or zircon), and two different reinforcing fibers - an SiC monofilament (140 {mu}m diameter) and an SiC yarn (16 {mu}m diameter). In-situ observations during 3-point bend test inside the SEM indicate that matrix cracking is a local phenomenon and occurs first in the matrix between widest spaced fibers. In all composites the MCIS was found to increase with fiber additions and scaled with the monolithic strength.

  4. The relationship between stress and temperature distribution during tension test of GFRP by fiber orientation variation

    NASA Astrophysics Data System (ADS)

    Kim, Jin-Woo; Lee, Seung-Chul

    2013-12-01

    This study was investigated what affect strength and temperature distribution by fiber orientation variation under tension test of GFRP. Temperature distribution was proposed through IR thermography camera. Lock-in method, which is one of technique in IR thermography camera to measure minute change in temperature, was utilized to monitor temperature distribution and change during crack propagation. At the maximum stress point, temperature was significantly increased. As shown previously, specimen with shorter fracture time showed abrupt increment of temperature at the maximum stress point. Specimen with longer fracture time displayed increment of temperature after the maximum stress point. In this study, tension strength of 0° direction of GFRP increased being proportional the fiber content and fiber orientation function as change from isotropy (J=0) to anisotropy (J=1). But, tensile strength of 90° direction by separation of fiber filament decreased when tensile load is imposed for width direction of reinforcement fiber length direction. And, method to analyze of temperature distribution via IR thermography camera was suggested. The correlation of the tension strength and the temperature distribution was investigated.

  5. Fiber

    MedlinePlus

    ... it can help with weight control. Fiber aids digestion and helps prevent constipation . It is sometimes used ... fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in ...

  6. Interplay between Solo and keratin filaments is crucial for mechanical force–induced stress fiber reinforcement

    PubMed Central

    Fujiwara, Sachiko; Ohashi, Kazumasa; Mashiko, Toshiya; Kondo, Hiroshi; Mizuno, Kensaku

    2016-01-01

    Mechanical force–induced cytoskeletal reorganization is essential for cell and tissue remodeling and homeostasis; however, the underlying cellular mechanisms remain elusive. Solo (ARHGEF40) is a RhoA-targeting guanine nucleotide exchange factor (GEF) involved in cyclical stretch–induced human endothelial cell reorientation and convergent extension cell movement in zebrafish gastrula. In this study, we show that Solo binds to keratin-8/keratin-18 (K8/K18) intermediate filaments through multiple sites. Solo overexpression promotes the formation of thick actin stress fibers and keratin bundles, whereas knockdown of Solo, expression of a GEF-inactive mutant of Solo, or inhibition of ROCK suppresses stress fiber formation and leads to disorganized keratin networks, indicating that the Solo-RhoA-ROCK pathway serves to precisely organize keratin networks, as well as to promote stress fibers. Of importance, knockdown of Solo or K18 or overexpression of GEF-inactive or deletion mutants of Solo suppresses tensile force–induced stress fiber reinforcement. Furthermore, knockdown of Solo or K18 suppresses tensile force-induced RhoA activation. These results strongly suggest that the interplay between Solo and K8/K18 filaments plays a crucial role in tensile force–induced RhoA activation and consequent actin cytoskeletal reinforcement. PMID:26823019

  7. Interplay between Solo and keratin filaments is crucial for mechanical force-induced stress fiber reinforcement.

    PubMed

    Fujiwara, Sachiko; Ohashi, Kazumasa; Mashiko, Toshiya; Kondo, Hiroshi; Mizuno, Kensaku

    2016-03-15

    Mechanical force-induced cytoskeletal reorganization is essential for cell and tissue remodeling and homeostasis; however, the underlying cellular mechanisms remain elusive. Solo (ARHGEF40) is a RhoA-targeting guanine nucleotide exchange factor (GEF) involved in cyclical stretch-induced human endothelial cell reorientation and convergent extension cell movement in zebrafish gastrula. In this study, we show that Solo binds to keratin-8/keratin-18 (K8/K18) intermediate filaments through multiple sites. Solo overexpression promotes the formation of thick actin stress fibers and keratin bundles, whereas knockdown of Solo, expression of a GEF-inactive mutant of Solo, or inhibition of ROCK suppresses stress fiber formation and leads to disorganized keratin networks, indicating that the Solo-RhoA-ROCK pathway serves to precisely organize keratin networks, as well as to promote stress fibers. Of importance, knockdown of Solo or K18 or overexpression of GEF-inactive or deletion mutants of Solo suppresses tensile force-induced stress fiber reinforcement. Furthermore, knockdown of Solo or K18 suppresses tensile force-induced RhoA activation. These results strongly suggest that the interplay between Solo and K8/K18 filaments plays a crucial role in tensile force-induced RhoA activation and consequent actin cytoskeletal reinforcement. PMID:26823019

  8. A model for cell density effect on stress fiber alignment and collective directional migration

    NASA Astrophysics Data System (ADS)

    Abeddoust, Mohammad; Shamloo, Amir

    2015-12-01

    In this study, numerical simulation of collective cell migration is presented in order to mimic the group migration of endothelial cells subjected to the concentration gradients of a biochemical factor. The developed 2D model incorporates basic elements of the cell, including both the cell membrane and the cell cytoskeleton, based on a viscoelastic cell mechanic model. Various cell processes—including cell random walk, cell-cell interactions, cell chemotaxis, and cellular cytoskeleton rearrangements—are considered and analyzed in our developed model. After validating the model by using available experimental data, the model is used to investigate various important parameters during collective cell chemotaxis, such as cell density, cytoskeleton organization, stress fiber reorientations, and intracellular forces. The results suggest that increasing the cell density causes the cell-cell interactions to affect the orientation of stress fibers throughout the cytoskeleton and makes the stress fibers more aligned in the direction of the imposed concentration gradient. This improved alignment of the stress fibers correlates with the intensification of the intracellular forces transferred in the gradient direction; this improves the cell group migration. Comparison of the obtained results with available experimental observations of collective chemotaxis of endothelial cells shows an interesting agreement.

  9. Fibers in the extracellular matrix enable long-range stress transmission between cells.

    PubMed

    Ma, Xiaoyue; Schickel, Maureen E; Stevenson, Mark D; Sarang-Sieminski, Alisha L; Gooch, Keith J; Ghadiali, Samir N; Hart, Richard T

    2013-04-01

    Cells can sense, signal, and organize via mechanical forces. The ability of cells to mechanically sense and respond to the presence of other cells over relatively long distances (e.g., ∼100 μm, or ∼10 cell-diameters) across extracellular matrix (ECM) has been attributed to the strain-hardening behavior of the ECM. In this study, we explore an alternative hypothesis: the fibrous nature of the ECM makes long-range stress transmission possible and provides an important mechanism for long-range cell-cell mechanical signaling. To test this hypothesis, confocal reflectance microscopy was used to develop image-based finite-element models of stress transmission within fibroblast-seeded collagen gels. Models that account for the gel's fibrous nature were compared with homogenous linear-elastic and strain-hardening models to investigate the mechanisms of stress propagation. Experimentally, cells were observed to compact the collagen gel and align collagen fibers between neighboring cells within 24 h. Finite-element analysis revealed that stresses generated by a centripetally contracting cell boundary are concentrated in the relatively stiff ECM fibers and are propagated farther in a fibrous matrix as compared to homogeneous linear elastic or strain-hardening materials. These results support the hypothesis that ECM fibers, especially aligned ones, play an important role in long-range stress transmission. PMID:23561517

  10. Fibers in the Extracellular Matrix Enable Long-Range Stress Transmission between Cells

    PubMed Central

    Ma, Xiaoyue; Schickel, Maureen E.; Stevenson, Mark D.; Sarang-Sieminski, Alisha L.; Gooch, Keith J.; Ghadiali, Samir N.; Hart, Richard T.

    2013-01-01

    Cells can sense, signal, and organize via mechanical forces. The ability of cells to mechanically sense and respond to the presence of other cells over relatively long distances (e.g., ∼100 μm, or ∼10 cell-diameters) across extracellular matrix (ECM) has been attributed to the strain-hardening behavior of the ECM. In this study, we explore an alternative hypothesis: the fibrous nature of the ECM makes long-range stress transmission possible and provides an important mechanism for long-range cell-cell mechanical signaling. To test this hypothesis, confocal reflectance microscopy was used to develop image-based finite-element models of stress transmission within fibroblast-seeded collagen gels. Models that account for the gel’s fibrous nature were compared with homogenous linear-elastic and strain-hardening models to investigate the mechanisms of stress propagation. Experimentally, cells were observed to compact the collagen gel and align collagen fibers between neighboring cells within 24 h. Finite-element analysis revealed that stresses generated by a centripetally contracting cell boundary are concentrated in the relatively stiff ECM fibers and are propagated farther in a fibrous matrix as compared to homogeneous linear elastic or strain-hardening materials. These results support the hypothesis that ECM fibers, especially aligned ones, play an important role in long-range stress transmission. PMID:23561517

  11. Fracture strength and stress distributions of pulpless premolars restored with fiber posts.

    PubMed

    Furuya, Yu; Huang, Shih-Hao; Takeda, Yuko; Fok, Alex; Hayashi, Mikako

    2014-01-01

    This study examined the effect of glass fiber posts on increasing the fracture resistance of endodontically treated teeth. Extracted upper premolars with two canals in a root were divided into three groups according to the number of posts they were restored with: none, one, or two. All teeth were endodontically treated, crown-sectioned, and restored with a composite core and a metallic crown. A static oblique load was applied to the restored tooth until fracture, and the fracture pattern was recorded. Stress distributions were examined by finite element analysis (FEA). Teeth with glass fiber post(s) showed significantly higher fracture loads compared with those without posts. In the premolars without posts, von Mises and maximum principal stresses were found on the root surface alone; in premolars restored with posts, stresses were distributed on both root and post surfaces. Risk of root dentin fracture was significantly lowest in teeth restored with two posts. PMID:25483385

  12. Smart carbon nanotube/fiber and PVA fiber-reinforced composites for stress sensing and chloride ion detection

    NASA Astrophysics Data System (ADS)

    Hoheneder, Joshua

    Fiber reinforced composites (FRC) with polyvinyl alcohol (PVA) fibers and carbon nanofibers (CNF) had an excellent flexural strength in excess of 18.5 MPa compared to reference samples of 15.8 MPa. It was found that the developed, depending on applied stress and exposure to chloride solutions, composites exhibit some electrical conductivity, from 4.20×10 -4 (Ω-1m-1 to 4.13×10 -4 Ω-1m-1. These dependences can be characterized by piezioresistive and chemoresistive coefficients demonstrating that the material possesses self-sensing capabilities. The sensitivity to stain and chloride solutions can be enhanced by incorporating small amounts of carbon nanofibers (CNF) or carbon nanotube (CNT) into composite structure. Conducted research has demonstrated a strong dependency of electrical properties of composite on crack formation in moist environments. The developed procedure is scalable for industrial application in concrete structures that require nondestructive stress monitoring, integrity under high service loads and stability in harsh environments.

  13. Effect of stress and temperature on the optical phonons of aramid fibers

    NASA Astrophysics Data System (ADS)

    Bollas, D.; Parthenios, J.; Galiotis, C.

    2006-03-01

    The wave-number dependence upon stress and/or strain and temperature of two adjacent optical phonons of aramid fibers has been investigated. The results showed that both phonons soften considerably under axial tension. Experiments at various temperatures under fixed strain conditions have demonstrated that one of the phonons (ν1=1611cm-1) is moderately anharmonic whereas the adjacent phonon (ν2=1648cm-1) exhibits harmonic behavior. By modeling the fibers as one-dimensional molecular wires very good agreement between experiment and theory is obtained for the phonon temperature dependence under isostress conditions.

  14. Intermediate Temperature Stress Rupture of Woven SiC Fiber, BN Interphase, SiC Matrix Composites in Air

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Levine, Stanley (Technical Monitor)

    2000-01-01

    Tensile stress-rupture experiments were performed on woven Hi-Nicalon reinforced SiC matrix composites with BN interphases in air. Modal acoustic emission (AE) was used to monitor the damage accumulation in the composites during the tests and microstructural analysis was performed to determine the amount of matrix cracking that occurred for each sample. Fiber fractograph), was also performed for individual fiber failures at the specimen fracture surface to determine the strengths at which fibers failed. The rupture strengths were significantly worse than what would have been expected front the inherent degradation of the fibers themselves when subjected to similar rupture conditions. At higher applied stresses the rate of rupture "?as larger than at lower applied stresses. It was observed that the change in rupture rate corresponded to the onset of through-thickness cracking in the composites themselves. The primary cause of the sen,ere degradation was the ease with which fibers would bond to one another at their closest separation distances, less than 100 nanometers, when exposed to the environment. The near fiber-to-fiber contact in the woven tows enabled premature fiber failure over large areas of matrix cracks due to the stress-concentrations created b), fibers bonded to one another after one or a few fibers fail. i.e. the loss of global load sharing. An@, improvement in fiber-to-fiber separation of this composite system should result in improved stress- rupture properties. A model was den,eloped in order to predict the rupture life-time for these composites based on the probabilistic nature of indin,idual fiber failure at temperature. the matrix cracking state during the rupture test, and the rate of oxidation into a matrix crack. Also incorporated into the model were estimates of the stress-concentration that would occur between the outer rim of fibers in a load-bearing bundle and the unbridged region of a matrix crack after Xia et al. For the lower stresses

  15. Stress and strength analysis of fiber reinforced plastic pipe tees with reinforcement

    SciTech Connect

    Wei, Z.; Widera, G.E.O.; Xue, M.

    1996-12-01

    In this paper, a stress and strength analysis of fiber reinforced plastic (FRP) pipe tees with reinforcement by use of 3-D finite element method is presented. Wilson`s incompatible elements and the 16-node 3-D element with relative degrees of freedom have been employed to carry out the analysis. The reliability of the program is also investigated. Two reinforcing methods, pad and compact reinforcement, are investigated. The fact that the properties and principal directions of the materials of the two intersecting pipes and the reinforcement are different has been taken into account in the analysis. The continuity of stress and strain fields at the intersecting surface of two different materials is considered in the post processing of the FEM results. The results show that the stress concentration in a FRP pipe intersection without reinforcement (r/R = 0.4--0.7) is significant. A reasonable design can be obtained by considering both stress fields and the orthotropic strength parameters of the materials. The in-plane shear stress may be the controlling factor because of the relatively low shear strength of most composites. Use of either reinforcing method does not change the location of the maximum tensile stress and the maximum shear stress, and both alleviate the stress concentration at the intersection. It is shown that the compact reinforcing method is more effective than the pad one. The larger the reinforcing area of the compact reinforcing method, the smaller the stress concentration factor, but the lower the rate of reduction.

  16. Internal Crack Propagation in a Continuously Cast Austenitic Stainless Steel Analyzed by Actual Residual Stress Tensor Distributions

    NASA Astrophysics Data System (ADS)

    Saito, Youichi; Tanaka, Shun-Ichiro

    2016-04-01

    Initiation, propagation, and termination of internal cracks in a continuously cast austenitic stainless steel has been investigated with emphasis on stress loading of the solidified shell during casting. Cracks were formed at the center of the slab, parallel to the width of the cast, and were observed near the narrow faces. Optimized two-dimensional X-ray diffraction method was employed to measure residual stress tensor distributions around the cracks in the as-cast slab with coarse and strongly preferentially oriented grains. The tensor distributions had a sharp peak, as high as 430 MPa, at the crack end neighboring the columnar grains. On the other hand, lower values were measured at the crack end neighboring the equiaxed grains, where the local temperatures were higher during solidification. The true residual stress distributions were determined by evaluating the longitudinal elastic constant for each measured position, resulting in more accurate stress values than before. Electron probe micro-analysis at the terminal crack position showed that Ni, Ti, and Si were concentrated at the boundaries of the equiaxed grains, where the tensile strength was estimated to be lower than at the primary grains. A model of the crack formation and engineering recommendations to reduce crack formation are proposed.

  17. Stressed-Oxidation Lifetime of Different SiC Fiber, CVI Matrix SiC Minicomposites in Air

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Martinez-Fernandez, Julian

    1998-01-01

    The stressed-oxidation lifetime properties of several minicomposites composed of single fiber tows with a CVI SiC matrix were compared. The minicomposites were made up of Nicalon(Tm) and Hi-Nicalon(Tm) SiC fibers with carbon or BN interphases. Constant load stress-rupture tests were performed between 600 and 13000 C in air for all of the minicomposite systems. Cyclic load testing was performed on the Hi-Nicalon minicomposite systems. The factors controlling the different lifetime behaviors: fiber rupture properties, interphase oxidation, fiber degradation, and fiber-matrix bonding, are discussed in light of different minicomposite constituents. All of the systems were subject to intermediate temperature embrittlement. The Hi-Nicalon fiber, BN interphase system, performed the best for constant load conditions. For cyclic load conditions, both the BN- interphase and C-interphase minicomposites displayed poor, but different failure behavior.

  18. Optical fiber fatigue behavior over very extended periods at low stress levels in the field and in laboratory tests

    NASA Astrophysics Data System (ADS)

    Stockton, David J.; Mayhew, Andi J.

    1999-12-01

    The reliability of optical fiber exposed to relatively high static strains (> 2%) has been extensively modelled and investigated by experiment. Fatigue `knees' have been demonstrated predicting the premature fracture of fiber particularly where elevated temperatures and relatively large volumes of water have been used to soak the samples. The cause has been attributed to simultaneous stress- assisted and stress-free corrosion of the fiber surface. In this paper we show that, a t more moderate strains (1 to 2%) and using a limited volume of water, there is evidence of a strength recovery caused either by a healing process or the observance of some form of lower strain threshold. The expected strength reduction of the fiber, from contemporary models is contrasted to that observed. The unusually high strength retention shown by the test fiber in water is shown to have important implications for optical cable design and for the bending of fiber within joint housings.

  19. Optical measurements on overhead optical fiber cables for stresses and damage identification

    NASA Astrophysics Data System (ADS)

    Ravet, Fabien L.; Heens, Bernard; Daniaux, D.; Froidure, Jean-Christophe; Blondel, Michel; Dascotte, M.; Lots, P.

    1998-12-01

    This paper concerns the characterization of various trunks of an OPGW based network. No strong fiber aging has been observed but combined OTDR and PMD measurements have pointed out strong cable clamping at suspension pylon. Large local losses have been measured at both 1.55 micrometers and 1.6 micrometers and stress induced birefringent behavior have been experienced. PMD temporal evolution has also been studied. A correlation between temperature variation and PMD evolution has been observed.

  20. Combined-load stress-strain relationship for advanced fiber composites

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sullivan, T. L.

    1975-01-01

    It was demonstrated experimentally that only one test specimen is required to determine the combined-load stress-strain relationships of a given fiber composite system. These relationships were determined using a thin angle-plied laminate tube and subjecting it to a number of combined-loading conditions. The measured data obtained are compared with theoretical predictions. Some important considerations associated with such a test are identified, and the significance of combined-load stress-strain relationships in certain practical designs are discussed.

  1. Calculation of Stress Intensity Factors for Interfacial Cracks in Fiber Metal Laminates

    NASA Technical Reports Server (NTRS)

    Wang, John T.

    2009-01-01

    Stress intensity factors for interfacial cracks in Fiber Metal Laminates (FML) are computed by using the displacement ratio method recently developed by Sun and Qian (1997, Int. J. Solids. Struct. 34, 2595-2609). Various FML configurations with single and multiple delaminations subjected to different loading conditions are investigated. The displacement ratio method requires the total energy release rate, bimaterial parameters, and relative crack surface displacements as input. Details of generating the energy release rates, defining bimaterial parameters with anisotropic elasticity, and selecting proper crack surface locations for obtaining relative crack surface displacements are discussed in the paper. Even though the individual energy release rates are nonconvergent, mesh-size-independent stress intensity factors can be obtained. This study also finds that the selection of reference length can affect the magnitudes and the mode mixity angles of the stress intensity factors; thus, it is important to report the reference length used with the calculated stress intensity factors.

  2. Stress generated by customized glass fiber posts and other types by photoelastic analysis.

    PubMed

    Bosso, Kátia; Gonini Júnior, Alcides; Guiraldo, Ricardo Danil; Berger, Sandrine Bittencourt; Lopes, Murilo Baena

    2015-01-01

    Endodontic posts are necessary to provide adequate retention and support when no sufficient remaining structure is available to retain the core. There are different materials and techniques to construct post-and-core, but there is no consensus about which one promotes better stress distribution on the remaining tooth structure. This study aimed to quantify and evaluate the distribution of stress in the root produced by customized glass fiber posts compared to different endodontic posts. Twenty-five simulated roots from photoelastic resin were made and divided into 5 groups: CPC, cast post-and-core; SP, screw post; CF, carbon fiber post; GF, glass fiber post; and CGF, customized glass fiber post. After cementing CPC and SP posts with zinc phosphate cement, and CF, GF and CGF posts with resin cement, resin cores were made for groups 2-5. Specimens were evaluated with vertical or 45° oblique loading. To analyze the fringes, the root was divided into 6 parts: palatal cervical, palatal middle, palatal apical, vestibular cervical, vestibular middle, and vestibular apical. The formed fringes were photographed and quantified. Data were recorded and subjected to two-way ANOVA and Tukey's test (5%). SP (1.95±0.60) showed higher stress (p<0.05) compared to the others (CPC-0.52±0.74; CF-0.50±0.75, GF-0.23±0.48 and CGF-0.45±0.83). All posts showed high stress in apical third (CPC-1.40±0.65; SP-2.30±0.44, CF-1.80±0.45, GF-1.20±0.45, CGF-1.70±1.03) Low stress was found in cervical third (CPC-0.20±0.45; CF-0.00±0.00, GF-0.00±0.00, CGF-0.00±0.00), except by SP (1.90±0.65), which showed statistical difference (p<0.05). Customized post showed high stress concentration at the root and conventional glass fiber posts showed more favorable biomechanical behavior. PMID:26200144

  3. Impact damage characterization in cross-plied carbon fiber/thermoplastic composites using thermoelastic stress analysis

    NASA Astrophysics Data System (ADS)

    Yoshida, T.; Uenoya, T.; Miyamoto, H.

    2012-04-01

    Carbon fiber (CF)-plastic composites are expected from the view point of light weighting vehicle structures. The CF/thermoset plastic laminates have low damage resistance to out-of-plane impact as a problem to be solved, because they behave as a low strength inter-laminar as compared with high-strength in fiber direction. Accordingly it is strongly desired to develop CF-composite materials based thermoplastics that have higher toughness than thermoset, for vehicle use. The present paper describes investigation of impact damages through thermoelastic stress analysis (TSA). Lowvelocity impact test using drop weight was conducted on stitched non-crimp-fabric CF/NY6 composite specimens. Stress distribution of the specimens under impact loading was monitored by a lock-in thermography system from the opposite side of the impact direction. The instrumentation system, which had a focal plane array detector, provided a succession of thermoelastic stress information as a sequence of TSA images at a high rate. The measured stress distribution agreed well with a theoretical. And also, selecting a contour feature of the stress distribution determined with a suitable level conformed approximately to the internal damage image that was processed from the TSA images obtained before and after impact.

  4. A Critique of a Phenomenological Fiber Breakage Model for Stress Rupture of Composite Materials

    NASA Technical Reports Server (NTRS)

    Reeder, James R.

    2010-01-01

    Stress rupture is not a critical failure mode for most composite structures, but there are a few applications where it can be critical. One application where stress rupture can be a critical design issue is in Composite Overwrapped Pressure Vessels (COPV's), where the composite material is highly and uniformly loaded for long periods of time and where very high reliability is required. COPV's are normally required to be proof loaded before being put into service to insure strength, but it is feared that the proof load may cause damage that reduces the stress rupture reliability. Recently, a fiber breakage model was proposed specifically to estimate a reduced reliability due to proof loading. The fiber breakage model attempts to model physics believed to occur at the microscopic scale, but validation of the model has not occurred. In this paper, the fiber breakage model is re-derived while highlighting assumptions that were made during the derivation. Some of the assumptions are examined to assess their effect on the final predicted reliability.

  5. Development of In-Fiber Reflective Bragg Gratings as Shear Stress Monitors in Aerodynamic Facilities

    NASA Technical Reports Server (NTRS)

    Parmar, Devendra S.; Sprinkle, Danny R.; Singh, Jag J.

    1998-01-01

    Bragg gratings centered at nominal wavelengths of 1290 nm and 1300 run were inscribed in a 9/125 microns germano-silicate optical fiber, using continuous wave frequency doubled Ar+ laser radiation at 244 nm. Such gratings have been used extensively as temperature and strain monitors in smart structures. They have, however, never been used for measuring aerodynamic shear stresses. As a test of their sensitivity as shear stress monitors, a Bragg fiber attached to a metal plate was subjected to laminar flows in a glass pipe. An easily measurable large flow-induced wavelength shift (Delta Lambda(sub B)) was observed in the Bragg reflected wavelength. Thereafter, the grating was calibrated by making one time, simultaneous measurements of Delta Lambda(sub B) and the coefficient of skin friction (C(sub f)) with a skin friction balance, as a function of flow rates in a subsonic wind tunnel. Onset of fan-induced transition in the tunnel flow provided a unique flow rate for correlating Delta Lambda(sub B) and (C(sub f) values needed for computing effective modulus of rigidity (N(sub eff)) of the fiber attached to the metal plate. This value Of N(sub eff) is expected to remain constant throughout the elastic stress range expected during the Bragg grating aerodynamic tests. It has been used for calculating the value of Cf at various tunnel speeds, on the basis of measured values of Bragg wavelength shifts at those speeds.

  6. Stress distribution of oval and circular fiber posts in amandibular premolar: a three-dimensional finite element analysis

    PubMed Central

    Kilic, Kerem; Esim, Emir; Aslan, Tugrul; Kilinc, Halil Ibrahim; Yildirim, Sahin

    2013-01-01

    PURPOSE The aim of the present study was to evaluate the effects of posts with different morphologies on stress distribution in an endodontically treated mandibular premolar by using finite element models (FEMs). MATERIALS AND METHODS A mandibular premolar was modeled using the ANSYS software program. Two models were created to represent circular and oval fiber posts in this tooth model. An oblique force of 300 N was applied at an angle of 45° to the occlusal plane and oriented toward the buccal side. von Mises stress was measured in three regions each for oval and circular fiber posts. RESULTS FEM analysis showed that the von Mises stress of the circular fiber post (426.81 MPa) was greater than that of the oval fiber post (346.34 MPa). The maximum distribution of von Mises stress was in the luting agent in both groups. Additionally, von Mises stresses accumulated in the coronal third of root dentin, close to the post space in both groups. CONCLUSION Oval fiber posts are preferable to circular fiber posts in oval-shaped canals given the stress distribution at the post-dentin interface. PMID:24353882

  7. In Healthy Young Men, a Short Exhaustive Exercise Alters the Oxidative Stress Only Slightly, Independent of the Actual Fitness

    PubMed Central

    Finkler, Maya; Hochman, Ayala; Pinchuk, Ilya; Lichtenberg, Dov

    2016-01-01

    The aim of the present study was to evaluate the apparent disagreement regarding the effect of a typical cycling progressive exercise, commonly used to assess VO2max, on the kinetics of ex vivo copper induced peroxidation of serum lipids. Thirty-two (32) healthy young men, aged 24–30 years, who do not smoke and do not take any food supplements, participated in the study. Blood was withdrawn from each participant at three time points (before the exercise and 5 minutes and one hour after exercise). Copper induced peroxidation of sera made of the blood samples was monitored by spectrophotometry. For comparison, we also assayed TBARS concentration and the activity of oxidation-related enzymes. The physical exercise resulted in a slight and reversible increase of TBARS and slight changes in the activities of the studied antioxidant enzymes and the lag preceding peroxidation did not change substantially. Most altered parameters returned to baseline level one hour after exercise. Notably, the exercise-induced changes in OS did not correlate with the physical fitness of the subjects, as evaluated in this study (VO2max = 30–60 mL/min/kg). We conclude that in healthy young fit men a short exhaustive exercise alters only slightly the OS, independent of the actual physical fitness. PMID:26989456

  8. An in-fiber Bragg grating sensor for contact force and stress measurements in articular joints

    NASA Astrophysics Data System (ADS)

    Dennison, Christopher R.; Wild, Peter M.; Wilson, David R.; Gilbart, Michael K.

    2010-11-01

    We present an in-fiber Bragg grating-based sensor (240 µm diameter) for contact force/stress measurements in articular joints. The contact force sensor and another Bragg grating-based pressure sensor (400 µm diameter) are used to conduct the first simultaneous measurements of contact force/stress and fluid pressure in intact cadaveric human hips. The contact force/stress sensor addresses limitations associated with stress-sensitive films, the current standard tools for contact measurements in joints, including cartilage modulus-dependent sensitivity of films and the necessity to remove biomechanically relevant anatomy to implant the films. Because stress-sensitive films require removal of anatomy, it has been impossible to validate the mechanical rationale underlying preventive or corrective surgeries, which repair these anatomies, by conducting simultaneous stress and pressure measurements in intact hips. Methods are presented to insert the Bragg grating-based sensors into the joint, while relevant anatomy is left largely intact. Sensor performance is predicted using numerical models and the predicted sensitivity is verified through experimental calibrations. Contact force/stress and pressure measurements in cadaveric joints exhibited repeatability. With further validation, the Bragg grating-based sensors could be used to study the currently unknown relationships between contact forces and pressures in both healthy and degenerated joints.

  9. Effects of stress ratio and fiber orientation on fatigue crack growth behavior in APAL

    SciTech Connect

    Oh, S.W.; Park, W.J.; Yoon, H.K.; Lee, K.G.; Cho, J.M.; Lee, K.B.

    1993-12-31

    A new hybrid composite (APAL; Aramid Patched Aluminum Alloy), consisting of 2024-T3 aluminum alloy plate sandwiched between aramid/epoxy prepregs (HK 285/RS 1222), was developed. Fatigue crack growth behavior was examined at stress ratios of R = 0.2, 0.5 using two kinds of APAL with different fiber orientation (0{degree}/90{degree} and {+-} 45{degree} for crack direction). The APAL showed superior fatigue crack growth resistance, which may be attributed to the crack bridging effect imposed by the intact fibers in the crack wave. The magnitude of crack bridging was estimated quantitatively and determined by a new technique on the basis of the compliances of 2024-T3 aluminum alloy and APAL specimens. The crack growth rate of the APAL specimens was reduced significantly as comparison to the monolithic aluminum alloy and was not adequately correlated with the conventional stress intensity factor range ({Delta}K). It was found that the crack growth rate was successfully correlated with the effective stress intensity factor range ( {Delta}K{sub eff} = K{sub br} {minus} K{sub cl}) allowing for the crack closure and the crack bridging. The relation between da/dN and {Delta}K{sub eff} was plotted within a narrow scatter band regardless at loading line of 2024-T3 aluminum alloy, two kinds of the APAL (APAL 0{degree}/90{degree}, APAL {+-} 45{degree}) and two kinds of stress ratios (R = 0.2, 0.5).

  10. Modeling for Fatigue Hysteresis Loops of Carbon Fiber-Reinforced Ceramic-Matrix Composites under Multiple Loading Stress Levels

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2015-12-01

    In this paper, the fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs) under multiple loading stress levels considering interface wear has been investigated using micromechanical approach. Under fatigue loading, the fiber/matrix interface shear stress decreases with the increase of cycle number due to interface wear. Upon increasing of fatigue peak stress, the interface debonded length would propagate along the fiber/matrix interface. The difference of interface shear stress existed in the new and original debonded region would affect the interface debonding and interface frictional slipping between the fiber and the matrix. Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading and subsequent reloading, the interface slip lengths, i.e., the interface debonded length, interface counter-slip length and interface new-slip length, are determined by fracture mechanics approach. The fatigue hysteresis loops models under multiple loading stress levels have been developed. The effects of single/multiple loading stress levels and different loading sequences on fatigue hysteresis loops have been investigated. The fatigue hysteresis loops of unidirectional C/SiC composite under multiple loading stress levels have been predicted.

  11. Three-dimensional finite element analysis of stress distribution in composite resin cores with fiber posts of varying diameters.

    PubMed

    Okamoto, Kazuhiko; Ino, Teruno; Iwase, Naoki; Shimizu, Eitaroh; Suzuki, Megumi; Satoh, Goh; Ohkawa, Shuji; Fujisawa, Masanori

    2008-01-01

    Using three-dimensional finite element analysis (3D-FEA), stress distributions in the remaining radicular tooth structure were investigated under the condition of varying diameters of fiber post for fiber post-reinforced composite resin cores (fiber post and core) in maxillary central incisors. Four 3D-FEA models were constructed: (1) fiber post (ø1.2, ø1.4, and ø1.6 mm) and composite resin core; and (2) gold-cast post and core. Maximum stresses in the tooth structure for fiber post and core were higher than that for gold-cast post and core. In the former models, stresses in the tooth structure as well as in the composite resin were slightly reduced with increase in fiber post diameter. These results thus suggested that to reduce stress in the remaining radicular tooth with a large coronal defect, it is recommended to accompany a composite resin core with a fiber post of a large diameter. PMID:18309611

  12. The Role of Stress Fibers in the Shape Determination Mechanism of Fish Keratocytes.

    PubMed

    Nakata, Takako; Okimura, Chika; Mizuno, Takafumi; Iwadate, Yoshiaki

    2016-01-19

    Crawling cells have characteristic shapes that are a function of their cell types. How their different shapes are determined is an interesting question. Fish epithelial keratocytes are an ideal material for investigating cell shape determination, because they maintain a nearly constant fan shape during their crawling locomotion. We compared the shape and related molecular mechanisms in keratocytes from different fish species to elucidate the key mechanisms that determine cell shape. Wide keratocytes from cichlids applied large traction forces at the rear due to large focal adhesions, and showed a spatially loose gradient associated with actin retrograde flow rate, whereas round keratocytes from black tetra applied low traction forces at the rear small focal adhesions and showed a spatially steep gradient of actin retrograde flow rate. Laser ablation of stress fibers (contractile fibers connected to rear focal adhesions) in wide keratocytes from cichlids increased the actin retrograde flow rate and led to slowed leading-edge extension near the ablated region. Thus, stress fibers might play an important role in the mechanism of maintaining cell shape by regulating the actin retrograde flow rate. PMID:26789770

  13. The effect of stress on ultrasonic pulses in fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Hemann, J. H.; Baaklini, G. Y.

    1983-01-01

    An acoustical-ultrasonic technique was used to demonstrate relationships existing between changes in attenuation of stress waves and tensile stress for an eight ply 0 degree graphite-epoxy fiber reinforced composite. All tests were conducted in the linear range of the material for which no mechanical or macroscopic damage was evident. Changes in attenuation were measured as a function of tensile stress in the frequency domain and in the time domain. Stress wave propagation in these specimens was dispersive, i.e., the wave speed depends on frequency. Wave speeds varied from 267 400 cm/sec to 680 000 cm/sec as the frequency of the signal was varied from 150 kHz to 1.9 MHz which strongly suggests that flexural/lamb wave modes of propagation exist. The magnitude of the attenuation changes depended strongly on tensile stress. It was further observed that the wave speeds increased slightly for all tested frequencies as the stress was increased.

  14. The mechanics of delamination in fiber-reinforced composite materials. I - Stress singularities and solution structure

    NASA Technical Reports Server (NTRS)

    Wang, S. S.; Choi, I.

    1983-01-01

    The fundamental mechanics of delamination in fiber composite laminates is studied. Mathematical formulation of the problem is based on laminate anisotropic elasticity theory and interlaminar fracture mechanics concepts. Stress singularities and complete solution structures associated with general composite delaminations are determined. For a fully open delamination with traction-free surfaces, oscillatory stress singularities always appear, leading to physically inadmissible field solutions. A refined model is introduced by considering a partially closed delamination with crack surfaces in finite-length contact. Stress singularities associated with a partially closed delamination having frictional crack-surface contact are determined, and are found to be different from the inverse square-root one of the frictionless-contact case. In the case of a delamination with very small area of crack closure, a simplified model having a square-root stress singularity is employed by taking the limit of the partially closed delamination. The possible presence of logarithmic-type stress singularity is examined; no logarithmic singularity of any kind is found in the composite delamination problem. Numerical examples of dominant stress singularities are shown for delaminations having crack-tip closure with different frictional coefficients between general (1) and (2) graphite-epoxy composites. Previously announced in STAR as N84-13221

  15. Stress- and polarization-induced stimulated Raman scattering in optical fiber

    NASA Astrophysics Data System (ADS)

    Tan, Yong; Cai, Hongxing; Sun, Xiuping; Gao, Xun; Zhang, Xihe

    2013-04-01

    In this letter, the dependence of stimulated Raman scattering spectra on external pressure levels of tens of kPa and the polarized pump light is investigated in optical fibers. The Raman peaks show blueshift under a lower external pressure because of the self-phase modulation. But under a higher external pressure, the Raman peaks begin to redshift, because the change of the inter-tetrahedral angle of the glassy AX2 systems plays a more important role. Moreover, the shifts of an elliptically polarized pump beam are smaller than the those of a linearly polarized pump beam under external pressure. These results could provide new applications for silica fibers as optical frequency generators or stress sensors.

  16. Stress Distribution in Roots Restored with Fiber Posts and An Experimental Dentin Post: 3D-FEA.

    PubMed

    Diana, Hugo Henrique; Oliveira, Juliana Santos; Ferro, Mariana Carolina de Lara; Silva-Sousa, Yara T Corrêa; Gomes, Érica Alves

    2016-04-01

    The aim of this study was to compare the stress distribution in radicular dentin of a maxillary canine restored with either a glass fiber post, carbon fiber post or an experimental dentin post using finite element analysis (3D-FEA). Three 3D virtual models of a maxillary canine restored with a metal-ceramic crown and glass fiber post (GFP), carbon fiber post (CFP), and experimental dentin post (DP) were obtained based on micro-CT images. A total of 180 N was applied on the lingual surface of the incisal third of each tooth at 45 degrees. The models were supported by the periodontal ligament fixed in three axes (x=y=z=0). The von Mises stress (VMS) of radicular dentin and the intracanal posts was calculated. The structures of all groups showed similar values (MPa) and distribution of maximum von Mises stress. Higher stress was found in the apical third of dentin while the posts presented homogeneous stress distribution along the axis. The fiber and dentin posts exhibited similar stress values and distribution. Thus, the experimental dentin post is a promising restorative material. PMID:27058388

  17. Viscoelastic Retraction of Single Living Stress Fibers and Its Impact on Cell Shape, Cytoskeletal Organization, and Extracellular Matrix Mechanics

    PubMed Central

    Kumar, Sanjay; Maxwell, Iva Z.; Heisterkamp, Alexander; Polte, Thomas R.; Lele, Tanmay P.; Salanga, Matthew; Mazur, Eric; Ingber, Donald E.

    2006-01-01

    Cells change their form and function by assembling actin stress fibers at their base and exerting traction forces on their extracellular matrix (ECM) adhesions. Individual stress fibers are thought to be actively tensed by the action of actomyosin motors and to function as elastic cables that structurally reinforce the basal portion of the cytoskeleton; however, these principles have not been directly tested in living cells, and their significance for overall cell shape control is poorly understood. Here we combine a laser nanoscissor, traction force microscopy, and fluorescence photobleaching methods to confirm that stress fibers in living cells behave as viscoelastic cables that are tensed through the action of actomyosin motors, to quantify their retraction kinetics in situ, and to explore their contribution to overall mechanical stability of the cell and interconnected ECM. These studies reveal that viscoelastic recoil of individual stress fibers after laser severing is partially slowed by inhibition of Rho-associated kinase and virtually abolished by direct inhibition of myosin light chain kinase. Importantly, cells cultured on stiff ECM substrates can tolerate disruption of multiple stress fibers with negligible overall change in cell shape, whereas disruption of a single stress fiber in cells anchored to compliant ECM substrates compromises the entire cellular force balance, induces cytoskeletal rearrangements, and produces ECM retraction many microns away from the site of incision; this results in large-scale changes of cell shape (> 5% elongation). In addition to revealing fundamental insight into the mechanical properties and cell shape contributions of individual stress fibers and confirming that the ECM is effectively a physical extension of the cell and cytoskeleton, the technologies described here offer a novel approach to spatially map the cytoskeletal mechanics of living cells on the nanoscale. PMID:16500961

  18. Cdc42 deficiency induces podocyte apoptosis by inhibiting the Nwasp/stress fibers/YAP pathway

    PubMed Central

    Huang, Z; Zhang, L; Chen, Y; Zhang, H; Zhang, Q; Li, R; Ma, J; Li, Z; Yu, C; Lai, Y; Lin, T; Zhao, X; Zhang, B; Ye, Z; Liu, S; Wang, W; Liang, X; Liao, R; Shi, W

    2016-01-01

    Podocyte apoptosis is a major mechanism that leads to proteinuria in many chronic kidney diseases. However, the concert mechanisms that cause podocyte apoptosis in these kidney diseases are not fully understood. The Rho family of small GTPases has been shown to be required in maintaining podocyte structure and function. Recent studies have indicated that podocyte-specific deletion of Cdc42 in vivo, but not of RhoA or Rac1, leads to congenital nephrotic syndrome and glomerulosclerosis. However, the underlying cellular events in podocyte controlled by Cdc42 remain unclear. Here, we assessed the cellular mechanisms by which Cdc42 regulates podocyte apoptosis. We found that the expression of Cdc42 and its activity were significantly decreased in high glucose-, lipopolysaccharide- or adriamycin-injured podocytes. Reduced Cdc42 expression in vitro and in vivo by small interfering RNA and selective Cdc42 inhibitor ML-141, respectively, caused podocyte apoptosis and proteinuria. Our results further demonstrated that insufficient Cdc42 or Nwasp, its downstream effector, could decrease the mRNA and protein expression of YAP, which had been regarded as an anti-apoptosis protein in podocyte. Moreover, our data indicated that the loss of stress fibers caused by Cdc42/Nwasp deficiency also decreased Yes-associated protein (YAP) mRNA and protein expression, and induced podocyte apoptosis. Podocyte apoptosis induced by Cdc42/Nwasp/stress fiber deficiency was significantly inhibited by overexpressing-active YAP. Thus, the Cdc42/Nwasp/stress fibers/YAP signal pathway may potentially play an important role in regulating podocyte apoptosis. Maintaining necessary Cdc42 would be one potent way to prevent proteinuria kidney diseases. PMID:26986510

  19. Relation between left ventricular cavity pressure and volume and systolic fiber stress and strain in the wall.

    PubMed Central

    Arts, T; Bovendeerd, P H; Prinzen, F W; Reneman, R S

    1991-01-01

    Pumping power as delivered by the heart is generated by the cells in the myocardial wall. In the present model study global left-ventricular pump function as expressed in terms of cavity pressure and volume is related to local wall tissue function as expressed in terms of myocardial fiber stress and strain. On the basis of earlier studies in our laboratory, it may be concluded that in the normal left ventricle muscle fiber stress and strain are homogeneously distributed. So, fiber stress and strain may be approximated by single values, being valid for the whole wall. When assuming rotational symmetry and homogeneity of mechanical load in the wall, the dimensionless ratio of muscle fiber stress (sigma f) to left-ventricular pressure (Plv) appears to depend mainly on the dimensionless ratio of cavity volume (Vlv) to wall volume (Vw) and is quite independent of other geometric parameters. A good (+/- 10%) and simple approximation of this relation is sigma f/Plv = 1 + 3 Vlv/Vw. Natural fiber strain is defined by ef = In (lf/lf,ref), where lf,ref indicates fiber length (lf) in a reference situation. Using the principle of conservation of energy for a change in ef, it holds delta ef = (1/3)delta In (1 + 3Vlv/Vw). PMID:2015392

  20. Investigation on Stress-Rupture Behavior of a Chopped-Glass-Fiber Composite for Automotive Durability Design Criteria

    SciTech Connect

    Ren, W

    2001-08-24

    Practical and inexpensive testing methods were developed to investigate stress-rupture properties of a polymeric composite with chopped glass fiber reinforcement for automotive applications. The material was tested in representative automotive environments to generate experimental data. The results indicate that environments have substantial effects on the stress-rupture behavior. The data were analyzed and developed into stress-rupture design criteria to address one of the durability aspects of the material for automotive structural applications.

  1. Fiber

    MedlinePlus

    ... broccoli, spinach, and artichokes legumes (split peas, soy, lentils, etc.) almonds Look for the fiber content of ... salsa, taco sauce, and cheese for dinner. Add lentils or whole-grain barley to your favorite soups. ...

  2. Fiber

    MedlinePlus

    ... short period of time can cause intestinal gas ( flatulence ), bloating , and abdominal cramps . This problem often goes ... 213. National Research Council. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and ...

  3. Dynamic stress analysis of smooth and notched fiber composite flexural specimens

    NASA Technical Reports Server (NTRS)

    Murthy, P. L. N.; Chamis, C. C.

    1984-01-01

    A detailed analysis of the dynamic stress field in smooth and notched fiber composite (Charpy-type) specimens is reported in this paper. The analysis is performed with the aid of the direct transient response analysis solution sequence of MSC/NASTRAN. Three unidirectional composites were chosen for the study. They are S-Glass/Epoxy, Kevlar/Epoxy and T-300/Epoxy composite systems. The specimens are subjected to an impact load which is modeled as a triangular impulse with a maximum of 2000 lb and a duration of 1 ms. The results are compared with those of static analysis of the specimens subjected to a peak load of 2000 lb. For the geometry and type of materials studied, the static analysis results gave close conservative estimates for the dynamic stresses. Another interesting inference from the study is that the impact induced effects are felt by S-Glass/Epoxy specimens sooner than Kevlar/Epoxy or T-300/Epoxy specimens.

  4. Dynamic stress analysis of smooth and notched fiber composite flexural specimens

    NASA Technical Reports Server (NTRS)

    Murthy, P. L. N.; Chamis, C. C.

    1986-01-01

    A detailed analysis of the dynamic stress field in smooth and notched fiber composite (Charpy-type) specimens is reported in this paper. The analysis is performed with the aid of the direct transient response analysis solution sequence of MSC/NASTRAN. Three unidirectional composites were chosen for the study. They are S-Glass/Epoxy, Kevlar/Epoxy and T-300/Epoxy composite systems. The specimens are subjected to an impact load which is modeled as a triangular impulse with a maximum of 2000 lb and a duration of 1 ms. The results are compared with those of static analysis of the specimens subjected to a peak load of 2000 lb. For the geometry and type of materials studied, the static analysis results gave close conservative estimates for the dynamic stresses. Another interesting inference from the study is that the impact induced effects are felt by S-Glass/Epoxy specimens sooner than Kevlar/Epoxy or T-300/Epoxy specimens.

  5. Fatigue surviving, fracture resistance, shear stress and finite element analysis of glass fiber posts with different diameters.

    PubMed

    Wandscher, Vinícius Felipe; Bergoli, César Dalmolin; de Oliveira, Ariele Freitas; Kaizer, Osvaldo Bazzan; Souto Borges, Alexandre Luiz; Limberguer, Inácio da Fontoura; Valandro, Luiz Felipe

    2015-03-01

    This study evaluated the shear stress presented in glass fiber posts with parallel fiber (0°) and different coronal diameters under fatigue, fracture resistance and FEA. 160 glass-fiber posts (N=160) with eight different coronal diameters were used (DT=double tapered, number of the post=coronal diameter and W=Wider - fiber post with coronal diameter wider than the conventional): DT1.4; DT1.8W; DT1.6; DT2W; DT1.8; DT2.2W; DT2; DT2.2. Eighty posts were submitted to mechanical cycling (3×10(6) cycles; inclination: 45°; load: 50N; frequency: 4Hz; temperature: 37°C) to assess the surviving under intermittent loading and other eighty posts were submitted to fracture resistance testing (resistance [N] and shear-stress [MPa] values were obtained). The eight posts types were 3D modeled (Rhinoceros 4.0) and the shear-stress (MPa) evaluated using FEA (Ansys 13.0). One-way ANOVA showed statistically differences to fracture resistance (DT2.2W and DT2.2 showed higher values) and shear stress values (DT1.4 showed lower values). Only the DT1.4 fiber posts failed after mechanical cycling. FEA showed similar values of shear stress between the groups and these values were similar to those obtained by shear stress testing. The failure analysis showed that 95% of specimens failed by shear. Posts with parallel fiber (0°) may suffer fractures when an oblique shear load is applied on the structure; except the thinner group, greater coronal diameters promoted the same shear stresses. PMID:25553557

  6. Method for Forming Fiber Reinforced Composite Bodies with Graded Composition and Stress Zones

    NASA Technical Reports Server (NTRS)

    Singh, Mrityunjay (Inventor); Levine, Stanley R. (Inventor); Smialek, James A. (Inventor)

    1999-01-01

    A near-net, complex shaped ceramic fiber reinforced silicon carbide based composite bodies with graded compositions and stress zones is disclosed. To provide the composite a fiber preform is first fabricated and an interphase is applied by chemical vapor infiltration, sol-gel or polymer processes. This first body is further infiltrated with a polymer mixture containing carbon, and/or silicon carbide, and additional oxide, carbide, or nitride phases forming a second body. One side of the second body is spray coated or infiltrated with slurries containing high thermal expansion and oxidation resistant. crack sealant phases and the other side of this second body is coated with low expansion phase materials to form a third body. This third body consisting of porous carbonaceous matrix surrounding the previously applied interphase materials, is then infiltrated with molten silicon or molten silicon-refractory metal alloys to form a fourth body. The resulting fourth body comprises dense composites consisting of fibers with the desired interphase which are surrounded by silicon carbide and other second phases materials at the outer and inner surfaces comprising material of silicon, germanium, refractory metal suicides, borides, carbides, oxides, and combinations thereof The resulting composite fourth body has different compositional patterns from one side to the other.

  7. Time-Dependent Stress Rupture Strength Degradation of Hi-Nicalon Fiber-Reinforced Silicon Carbide Composites at Intermediate Temperatures

    NASA Technical Reports Server (NTRS)

    Sullivan, Roy M.

    2016-01-01

    The stress rupture strength of silicon carbide fiber-reinforced silicon carbide composites with a boron nitride fiber coating decreases with time within the intermediate temperature range of 700 to 950 degree Celsius. Various theories have been proposed to explain the cause of the time-dependent stress rupture strength. The objective of this paper is to investigate the relative significance of the various theories for the time-dependent strength of silicon carbide fiber-reinforced silicon carbide composites. This is achieved through the development of a numerically based progressive failure analysis routine and through the application of the routine to simulate the composite stress rupture tests. The progressive failure routine is a time-marching routine with an iterative loop between a probability of fiber survival equation and a force equilibrium equation within each time step. Failure of the composite is assumed to initiate near a matrix crack and the progression of fiber failures occurs by global load sharing. The probability of survival equation is derived from consideration of the strength of ceramic fibers with randomly occurring and slow growing flaws as well as the mechanical interaction between the fibers and matrix near a matrix crack. The force equilibrium equation follows from the global load sharing presumption. The results of progressive failure analyses of the composite tests suggest that the relationship between time and stress-rupture strength is attributed almost entirely to the slow flaw growth within the fibers. Although other mechanisms may be present, they appear to have only a minor influence on the observed time-dependent behavior.

  8. Strain Measurement during Stress Rupture of Composite Over-Wrapped Pressure Vessel with Fiber Bragg Gratings Sensors

    NASA Technical Reports Server (NTRS)

    Banks, Curtis E.; Grant, Joseph; Russell, Sam; Arnett, Shawn

    2008-01-01

    Fiber optic Bragg gratings were used to measure strain fields during Stress Rupture (SSM) test of Kevlar Composite Over-Wrapped Pressure Vessels (COPV). The sensors were embedded under the over-wrapped attached to the liner released from the Kevlar and attached to the Kevlar released from the liner. Additional sensors (foil gages and fiber bragg gratings) were surface mounted on the COPY liner.

  9. Strain measurement during stress rupture of composite over-wrapped pressure vessel with fiber Bragg gratings sensors

    NASA Astrophysics Data System (ADS)

    Banks, Curtis E.; Grant, Joseph; Russell, Sam; Arnett, Shawn

    2008-03-01

    Fiber optic Bragg gratings were used to measure strain fields during Stress Rupture (SSM) test of Kevlar Composite Over-Wrapped Pressure Vessels (COPVs). The sensors were embedded under the over-wrapped attached to the liner released from the Kevlar and attached to the Kevlar released from the liner. Additional sensors (foil gages and fiber bragg gratings) were surface mounted on the COPV liner.

  10. WAXS studies of heat - mechanically modified amorphous PET fibers. Role of the tensile stress

    NASA Astrophysics Data System (ADS)

    Velev, V.; Popov, A.; Kyurkchiev, P.; Veleva, L.; Pencheva, M.

    2014-12-01

    The present work is devoted to the investigation of the structure developments in as- spun amorphous poly (ethylene terephthalate) (PET) filaments occurred as a result of heat mechanically modification. The degree of crystallinity of the untreated samples was 1,7 %. The thermal deformation experiments were carried out under isothermal conditions. PET yarn was annealed during 10 min at constant temperature of 80°C after which the sample is subjected to a well-defined constant tensile stress for 120 s at the same temperature. The mechanical load is gravitationally in the range from 0 MPa to 30 MPa and with increment step of 3 MPa. Using of wide angle X-ray scattering (WAXS) were investigated the structural rearrangements in the studied samples caused by the fibers treatments. Dependences between the strain force values and the running in the specimen's structure development are established. And in particular, it was found that a small increase of the tensile stress from 3 MPa to 6 MPa leads to a massive increase in the fibers degree of crystallinity with more than 33%.

  11. Characterization of Palladin, a Novel Protein Localized to Stress Fibers and Cell Adhesions

    PubMed Central

    Parast, Mana M.; Otey, Carol A.

    2000-01-01

    Here, we describe the identification of a novel phosphoprotein named palladin, which colocalizes with α-actinin in the stress fibers, focal adhesions, cell–cell junctions, and embryonic Z-lines. Palladin is expressed as a 90–92-kD doublet in fibroblasts and coimmunoprecipitates in a complex with α-actinin in fibroblast lysates. A cDNA encoding palladin was isolated by screening a mouse embryo library with mAbs. Palladin has a proline-rich region in the NH2-terminal half of the molecule and three tandem Ig C2 domains in the COOH-terminal half. In Northern and Western blots of chick and mouse tissues, multiple isoforms of palladin were detected. Palladin expression is ubiquitous in embryonic tissues, and is downregulated in certain adult tissues in the mouse. To probe the function of palladin in cultured cells, the Rcho-1 trophoblast model was used. Palladin expression was observed to increase in Rcho-1 cells when they began to assemble stress fibers. Antisense constructs were used to attenuate expression of palladin in Rcho-1 cells and fibroblasts, and disruption of the cytoskeleton was observed in both cell types. At longer times after antisense treatment, fibroblasts became fully rounded. These results suggest that palladin is required for the normal organization of the actin cytoskeleton and focal adhesions. PMID:10931874

  12. A versatile micro-mechanical tester for actin stress fibers isolated from cells.

    PubMed

    Matsui, Tsubasa S; Deguchi, Shinji; Sakamoto, Naoya; Ohashi, Toshiro; Sato, Masaaki

    2009-01-01

    Conventional atomic force microscopy is one of the major techniques to evaluate mechanical properties of cells and subcellular components. The use of a cantilever probe for sample manipulation within the vertical plane often makes absolute positioning of the probe, subject to thermal drift, difficult. In addition, the vertical test is unable to observe changes in the sample structure responsible for mechanical behavior detected by the probe. In the present study, an alternative mechanical tester was developed that incorporated a pair of micro-needles to manipulate a sample in a project plane, allowing acquisition of the accurate probe position and entire sample image. Using a vision-based feedback control, a micro-needle driven by a piezo actuator is moved to give user-defined displacements or forces to sample. To show its usefulness and versatility, three types of viscoelastic measurements on actin stress fibers isolated from smooth muscle cells were demonstrated: strain rate-controlled tensile tests, relaxation tests and creep tests. Fluorescence imaging of the stress fibers using Qdots over the course of the measurements, obtained through multiple image detectors, was also carried out. The technique described here is useful for examining the quantitative relationship between mechanical behavior and related structural changes of biomaterials. PMID:19940356

  13. ADF and Cofilin1 Control Actin Stress Fibers, Nuclear Integrity, and Cell Survival

    PubMed Central

    Kanellos, Georgios; Zhou, Jing; Patel, Hitesh; Ridgway, Rachel A.; Huels, David; Gurniak, Christine B.; Sandilands, Emma; Carragher, Neil O.; Sansom, Owen J.; Witke, Walter; Brunton, Valerie G.; Frame, Margaret C.

    2015-01-01

    Summary Genetic co-depletion of the actin-severing proteins ADF and CFL1 triggers catastrophic loss of adult homeostasis in multiple tissues. There is impaired cell-cell adhesion in skin keratinocytes with dysregulation of E-cadherin, hyperproliferation of differentiated cells, and ultimately apoptosis. Mechanistically, the primary consequence of depleting both ADF and CFL1 is uncontrolled accumulation of contractile actin stress fibers associated with enlarged focal adhesions at the plasma membrane, as well as reduced rates of membrane protrusions. This generates increased intracellular acto-myosin tension that promotes nuclear deformation and physical disruption of the nuclear lamina via the LINC complex that normally connects regulated actin filaments to the nuclear envelope. We therefore describe a pathway involving the actin-severing proteins ADF and CFL1 in regulating the dynamic turnover of contractile actin stress fibers, and this is vital to prevent the nucleus from being damaged by actin contractility, in turn preserving cell survival and tissue homeostasis. PMID:26655907

  14. Modeling of the cooling rate effect on the residual stress formation in the cantala fiber/recycled HDPE composites

    NASA Astrophysics Data System (ADS)

    Probotinanto, Yosafat C.; Raharjo, Wijang W.; Budiana, Eko P.

    2016-03-01

    Residual stress has great influence on the mechanical properties of polymer composites. Therefore, its formation during the manufacturing process needs to be investigated. The aim of this study is to investigate the influences of cooling rate on the residual stress distribution of the cantala/rHDPE composite by simulation. The simulation was done by using a SOLID227 element type of ANSYS. The cooling rates that used in this study are 0.5°C/minute, 1°C/minute, and 60°C/minute. The values of the residual stress correspond to the increasing of the cooling rate are 1171.31 kPa, 1171.42 kPa, 1172.36 kPa. In the radial direction, the residual stress was tensile inside the fibers, while in the longitudinal direction, the tensile residual stress occurred in the matrix zones and compressive in the fiber zones.

  15. Carbon fiber based composites stress analysis. Experimental and computer comparative studies

    NASA Astrophysics Data System (ADS)

    Sobek, M.; Baier, A.; Buchacz, A.; Grabowski, Ł.; Majzner, M.

    2015-11-01

    Composite materials used nowadays for the production of composites are the result of advanced research. This allows assuming that they are among the most elaborate tech products of our century. That fact is evidenced by the widespread use of them in the most demanding industries like aerospace and space industry. But the heterogeneous materials and their advantages have been known to mankind in ancient times and they have been used by nature for millions of years. Among the fibers used in the industry most commonly used are nylon, polyester, polypropylene, boron, metal, glass, carbon and aramid. Thanks to their physical properties last three fiber types deserve special attention. High strength to weight ratio allow the use of many industrial solutions. Composites based on carbon and glass fibers are widely used in the automotive. Aramid fibers ideal for the fashion industry where the fabric made from the fibers used to produce the protective clothing. In the paper presented issues of stress analysis of composite materials have been presented. The components of composite materials and principles of composition have been discussed. Particular attention was paid to the epoxy resins and the fabrics made from carbon fibers. The article also includes basic information about strain measurements performed on with a resistance strain gauge method. For the purpose of the laboratory tests a series of carbon - epoxy composite samples were made. For this purpose plain carbon textile was used with a weight of 200 g/mm2 and epoxy resin LG730. During laboratory strain tests described in the paper Tenmex's delta type strain gauge rosettes were used. They were arranged in specific locations on the surface of the samples. Data acquisition preceded using HBM measurement equipment, which included measuring amplifier and measuring head. Data acquisition was performed using the Easy Catman. In order to verify the results of laboratory tests numerical studies were carried out in a

  16. HIPPOCAMPAL MOSSY FIBER LEU-ENKEPHALIN IMMUNOREACTIVITY IN FEMALE RATS IS SIGNIFICANTLY ALTERED FOLLOWING BOTH ACUTE AND CHRONIC STRESS

    PubMed Central

    Pierce, Joseph P.; Kelter, David T.; McEwen, Bruce S.; Waters, Elizabeth M.; Milner, Teresa A.

    2013-01-01

    Research indicates that responses to stress are sexually dimorphic, particularly in regard to learning and memory processes: while males display impaired cognitive performance and hippocampal CA3 pyramidal cell dendritic remodeling following chronic stress, females exhibit enhanced performance and no remodeling. Leu-enkephalin, an endogenous opioid peptide found in the hippocampal mossy fiber pathway, plays a critical role in mediating synaptic plasticity at the mossy fiber-CA3 pyramidal cell synapse. Estrogen is known to influence the expression of leu-enkephalin in the mossy fibers of females, with leu-enkephalin levels being highest at proestrus and estrus, when estrogen levels are elevated. Since stress is also known to alter the expression of leu-enkephalin in various brain regions, this study was designed to determine whether acute or chronic stress had an effect on mossy fiber leu-enkephalin levels in females or males, through the application of correlated quantitative light and electron microscopic immunocytochemistry. Both acute and chronic stress eliminated the estrogen-dependence of leu-enkephalin levels across the estrous cycle in females, but had no effect on male levels. However, following acute stress leu-enkephalin levels in females were consistently lowered to values comparable to the lowest control values, while following chronic stress they were consistently elevated to values comparable to the highest control values. Ultrastructural changes in leu-enkephalin labeled dense core vesicles paralleled light microscopic observations, with acute stress inducing a decrease in leu-enkephalin labeled dense core vesicles, and chronic stress inducing an increase in leu-enkephalin labeled dense-core vesicles in females. These findings suggest that alterations in leu-enkephalin levels following stress could play an important role in the sex-specific responses that females display in learning processes, including those important in addiction. PMID:24275289

  17. Thermal stress modification in regenerated fiber Bragg grating via manipulation of glass transition temperature based on CO₂-laser annealing.

    PubMed

    Lai, Man-Hong; Lim, Kok-Sing; Gunawardena, Dinusha S; Yang, Hang-Zhou; Chong, Wu-Yi; Ahmad, Harith

    2015-03-01

    In this work, we have demonstrated thermal stress relaxation in regenerated fiber Bragg gratings (RFBGs) by using direct CO₂-laser annealing technique. After the isothermal annealing and slow cooling process, the Bragg wavelength of the RFBG has been red-shifted. This modification is reversible by re-annealing and rapid cooling. It is repeatable with different cooling process in the subsequent annealing treatments. This phenomenon can be attributed to the thermal stress modification in the fiber core by means of manipulation of glass transition temperature with different cooling rates. This finding in this investigation is important for accurate temperature measurement of RFBG in dynamic environment. PMID:25723423

  18. Effect of fabric structure and polymer matrix on flexural strength, interlaminar shear stress, and energy dissipation of glass fiber-reinforced polymer composites

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We report the effect of glass fiber structure and the epoxy polymer system on the flexural strength, interlaminar shear stress (ILSS), and energy absorption properties of glass fiber-reinforced polymer (GFRP) composites. Four different GFRP composites were fabricated from two glass fiber textiles of...

  19. Effects of Thermal Treatment on Tensile Creep and Stress-Rupture Behavior of Hi-Nicalon SiC Fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.; Dicarlo, J. A.

    1995-01-01

    Tensile creep and stress-rupture studies were conducted on Hi-Nicalon SiC fibers at 1200 and 1400 C in argon and air. Examined were as-received fibers as well as fibers annealed from 1400 to 1800 C for 1 hour in argon before testing. The creep and rupture results for these annealed fibers were compared to those of the as-received fibers to determine the effects of annealing temperature, test temperature, and test environment. Argon anneals up to 1500 C degrade room temperature strength of Hi-Nicalon fibers, but improve fiber creep resistance in argon or air by as much as 100% with no significant degradation in rupture strength. Argon anneals above 1500 C continue to improve fiber creep resistance when tested in argon, but significantly degrade creep resistance and rupture strength when tested in air. Decrease in creep resistance in air is greater at 1200 C than at 1400 C. Mechanisms are suggested for the observed behavior.

  20. Role of stress fibers and focal adhesions as a mediator for mechano-signal transduction in endothelial cells in situ

    PubMed Central

    Katoh, Kazuo; Kano, Yumiko; Ookawara, Shigeo

    2008-01-01

    Fluid shear stress is the mechanical force generated by the blood flow which is applied over the apical surface of endothelial cells in situ. The findings of a recent study suggest that stress fibers and its associated focal adhesions play roles in mechano-signal transduction mechanism. Stress fibers are present along the apical and the basal portion of the endothelial cells. Endothelial cells respond to fluid shear stress and change their morphological characteristics in both their cell shape and cytoskeletal organization. Atherosclerosis is a common disease of the arteries and it occurs in areas around the branching site of blood vessels where the cells are exposed to low fluid shear stress. The organization of stress fibers and focal adhesions are strongly influenced by shear stress, and therefore the generation of atherosclerotic lesions seem to be associated with the cytoskeletal components of endothelial cells. This review describes the possible role of the cytoskeleton as a mechano-transducer in endothelial cells in situ. PMID:19337541

  1. Method for automatic determination of soybean actual evapotranspiration under open top chambers (OTC) subjected to effects of water stress and air ozone concentration.

    PubMed

    Rana, Gianfranco; Katerji, Nader; Mastrorilli, Marcello

    2012-10-01

    The present study describes an operational method, based on the Katerji et al. (Eur J Agron 33:218-230, 2010) model, for determining the daily evapotranspiration (ET) for soybean inside open top chambers (OTCs). It includes two functions, calculated day par day, making it possible to separately take into account the effects of concentrations of air ozone and plant water stress. This last function was calibrated in function of the daily values of actual water reserve in the soil. The input variables of the method are (a) the diurnal values of global radiation and temperature, usually measured routinely in a standard weather station; (b) the daily values of the AOT40 index accumulated (accumulated ozone over a threshold of 40 ppb during daylight hours, when global radiation exceeds 50 Wm(-2)) determined inside the OTC; and (c) the actual water reserve in the soil, at the beginning of the trial. The ensemble of these input variables can be automatable; thus, the proposed method could be applied in routine. The ability of the method to take into account contrasting conditions of ozone air concentration and water stress was evaluated over three successive years, for 513 days, in ten crop growth cycles, excluding the days employed to calibrate the method. Tests were carried out in several chambers for each year and take into account the intra- and inter-year variability of ET measured inside the OTCs. On the daily scale, the slope of the linear regression between the ET measured by the soil water balance and that calculated by the proposed method, under different water conditions, are 0.98 and 1.05 for the filtered and unfiltered (or enriched) OTCs with root mean square error (RMSE) equal to 0.77 and 1.07 mm, respectively. On the seasonal scale, the mean difference between measured and calculated ET is equal to +5% and +11% for the filtered and unfiltered OTCs, respectively. The ability of the proposed method to estimate the daily and seasonal ET inside the OTCs is

  2. Effect of inelastic shear stress at the interfaces in the material with a unidirectional fibrous structure on the SIF for a crack in the fiber and the energy absorbed at fiber fracture.

    PubMed

    Borovik, Alexandra V; Borovik, Valery G

    2014-06-01

    The paper suggests considering the presence of inelastic shear mechanisms in the direction of the maximum tensile stress and the absence of these mechanisms in the other directions as the main feature of a structural material of biological origin. A "cracked fiber in tube" model is used for the study of the effect of interface cohesive strength on the stress intensity factor (SIF) for a crack in the fiber and on the energy absorbed under inelastic shear at the interface of fibers at their fracture. The values of the cohesive strength of the interface between the fibers and the distance between the cracks in the fiber at which the maximum energy is absorbed at material fracture at the stage of the crack growth in the fibers are obtained. This stage precedes the pullout process of the completely fractured fibers. PMID:24566378

  3. Portable polarimetric fiber stress sensor system for visco-elastic and biomimetic material analysis

    NASA Astrophysics Data System (ADS)

    Harrison, Mark C.; Armani, Andrea M.

    2015-05-01

    Non-destructive materials characterization methods have significantly changed our fundamental understanding of material behavior and have enabled predictive models to be developed. However, the majority of these efforts have focused on crystalline and metallic materials, and transitioning to biomaterials, such as tissue samples, is non-trivial, as there are strict sample handling requirements and environmental controls which prevent the use of conventional equipment. Additionally, the samples are smaller and more complex in composition. Therefore, more advanced sample analysis methods capable of operating in these environments are needed. In the present work, we demonstrate an all-fiber-based material analysis system based on optical polarimetry. Unlike previous polarimetric systems which relied on free-space components, our method combines an in-line polarizer, polarization-maintaining fiber, and a polarimeter to measure the arbitrary polarization state of the output, eliminating all free-space elements. Additionally, we develop a more generalized theoretical analysis which allows more information about the polarization state to be obtained via the polarimeter. We experimentally verify our system using a series of elastomer samples made from polydimethylsiloxane (PDMS), a commonly used biomimetic material. By adjusting the base:curing agent ratio of the PDMS, we controllably tune the Young's modulus of the samples to span over an order of magnitude. The measured results are in good agreement with those obtained using a conventional load-frame system. Our fiber-based polarimetric stress sensor shows promise for use as a simple research tool that is portable and suitable for a wide variety of applications.

  4. Mathematical modeling of the dynamic mechanical behavior of neighboring sarcomeres in actin stress fibers

    PubMed Central

    Chapin, L.M.; Edgar, L.T.; Blankman, E.; Beckerle, M.C.; Shiu, Y T

    2014-01-01

    Actin stress fibers (SFs) in live cells consist of series of dynamic individual sarcomeric units. Within a group of consecutive SF sarcomeres, individual sarcomeres can spontaneously shorten or lengthen without changing the overall length of this group, but the underlying mechanism is unclear. We used a computational model to test our hypothesis that this dynamic behavior is inherent to the heterogeneous mechanical properties of the sarcomeres and the cytoplasmic viscosity. Each sarcomere was modeled as a discrete element consisting of an elastic spring, a viscous dashpot and an active contractile unit all connected in parallel, and experiences forces as a result of actin filament elastic stiffness, myosin II contractility, internal viscoelasticity, or cytoplasmic drag. When all four types of forces are considered, the simulated dynamic behavior closely resembles the experimental observations, which include a low-frequency fluctuation in individual sarcomere length and compensatory lengthening and shortening of adjacent sarcomeres. Our results suggest that heterogeneous stiffness and viscoelasticity of actin fibers, heterogeneous myosin II contractility, and the cytoplasmic drag are sufficient to cause spontaneous fluctuations in SF sarcomere length. Our results shed new light to the dynamic behavior of SF and help design experiments to further our understanding of SF dynamics. PMID:25110525

  5. Image Analysis for the Quantitative Comparison of Stress Fibers and Focal Adhesions

    PubMed Central

    Elosegui-Artola, Alberto; Jorge-Peñas, Alvaro; Moreno-Arotzena, Oihana; Oregi, Amaia; Lasa, Marta; García-Aznar, José Manuel; De Juan-Pardo, Elena M.; Aldabe, Rafael

    2014-01-01

    Actin stress fibers (SFs) detect and transmit forces to the extracellular matrix through focal adhesions (FAs), and molecules in this pathway determine cellular behavior. Here, we designed two different computational tools to quantify actin SFs and the distribution of actin cytoskeletal proteins within a normalized cellular morphology. Moreover, a systematic cell response comparison between the control cells and those with impaired actin cytoskeleton polymerization was performed to demonstrate the reliability of the tools. Indeed, a variety of proteins that were present within the string beginning at the focal adhesions (vinculin) up to the actin SFs contraction (non-muscle myosin II (NMMII)) were analyzed. Finally, the software used allows for the quantification of the SFs based on the relative positions of FAs. Therefore, it provides a better insight into the cell mechanics and broadens the knowledge of the nature of SFs. PMID:25269086

  6. Implementation of thermal residual stresses in the analysis of fiber bridged matrix crack growth in titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Bakuckas, John G., Jr.; Johnson, W. Steven

    1994-01-01

    In this research, thermal residual stresses were incorporated in an analysis of fiber-bridged matrix cracks in unidirectional and cross-ply titanium matrix composites (TMC) containing center holes or center notches. Two TMC were investigated, namely, SCS-6/Timelal-21S laminates. Experimentally, matrix crack initiation and growth were monitored during tension-tension fatigue tests conducted at room temperature and at an elevated temperature of 200 C. Analytically, thermal residual stresses were included in a fiber bridging (FB) model. The local R-ratio and stress-intensity factor in the matrix due to thermal and mechanical loadings were calculated and used to evaluate the matrix crack growth behavior in the two materials studied. The frictional shear stress term, tau, assumed in this model was used as a curve-fitting parameter to matrix crack growth data. The scatter band in the values of tau used to fit the matrix crack growth data was significantly reduced when thermal residual stresses were included in the fiber bridging analysis. For a given material system, lay-up and temperature, a single value of tau was sufficient to analyze the crack growth data. It was revealed in this study that thermal residual stresses are an important factor overlooked in the original FB models.

  7. Fiber-based polarimetric stress sensor for measuring the Young's modulus of biomaterials

    NASA Astrophysics Data System (ADS)

    Harrison, Mark C.; Armani, Andrea M.

    2015-03-01

    Polarimetric optical fiber-based stress and pressure sensors have proven to be a robust tool for measuring and detecting changes in the Young's modulus (E) of materials in response to external stimuli, including the real-time monitoring of the structural integrity of bridges and buildings. These sensors typically work by using a pair of polarizers before and after the sensing region of the fiber, and often require precise alignment to achieve high sensitivity. The ability to perform similar measurements in natural and in engineered biomaterials could provide significant insights and enable research advancement and preventative healthcare. However, in order for this approach to be successful, it is necessary to reduce the complexity of the system by removing free-space components and the need for alignment. As the first step in this path, we have developed a new route for performing these measurements. By generalizing and expanding established theoretical analyses for these types of sensors, we have developed a predictive theoretical model. Additionally, by replacing the conventional free space components and polarization filters with a polarimeter, we have constructed a sensor system with higher sensitivity and which is semi-portable. In initial experiments, a series of polydimethylsiloxane (PDMS) samples with several base:curing agent ratios ranging from 5:1 up to 30:1 were prepared to simulate tissues with different stiffnesses. By simultaneously producing stress-strain curves using a load frame and monitoring the polarization change of light traveling through the samples, we verified the accuracy of our theoretical model.

  8. Cytotoxicity, oxidative stress and genotoxicity induced by glass fibers on human alveolar epithelial cell line A549.

    PubMed

    Rapisarda, Venerando; Loreto, Carla; Ledda, Caterina; Musumeci, Giuseppe; Bracci, Massimo; Santarelli, Lory; Renis, Marcella; Ferrante, Margherita; Cardile, Venera

    2015-04-01

    Man-made vitreous fibers have been widely used as insulation material as asbestos substitutes; however their morphology and composition raises concerns. In 1988 the International Agency for Research on Cancer classified fiberglass, rock wool, slag wool, and ceramic fibers as Group 2B, i.e. possibly carcinogenic to humans. In 2002 it reassigned fiberglass, rock and slag wool, and continuous glass filaments to Group 3, not classifiable as carcinogenic to humans. The aim of this study was to verify the cytotoxic and genotoxic effects and oxidative stress production induced by in vitro exposure of human alveolar epithelial cells A549 to glass fibers with a predominant diameter <3 μm (97%) and length >5 μm (93%). A549 cells were incubated with 5, 50, or 100 μg/ml (2.1, 21, and 42 μg/cm(2), respectively) of glass fibers for 72 h. Cytotoxicity and DNA damage were tested by the MTT and the Comet assay, respectively. Oxidative stress was determined by measuring inducible nitric oxide synthase (iNOS) expression by Western blotting, production of nitric oxide (NO) with Griess reagent, and concentration of reactive oxygen species by fluorescent quantitative analysis with 2',7'-dichlorofluorescein-diacetate (DCFH-DA). The results showed that glass fiber exposure significantly reduced cell viability and increased DNA damage and oxidative stress production in a concentration-dependent manner, demonstrating that glass fibers exert cytotoxic and genotoxic effects related to increased oxidative stress on the human alveolar cell line A549. PMID:25620604

  9. Thermal stress and Ca-independent contractile activation in mammalian skeletal muscle fibers at high temperatures.

    PubMed Central

    Ranatunga, K W

    1994-01-01

    Temperature dependence of the isometric tension was examined in chemically skinned, glycerinated, rabbit Psoas, muscle fibers immersed in relaxing solution (pH approximately 7.1 at 20 degrees C, pCa approximately 8, ionic strength 200 mM); the average rate of heating/cooling was 0.5-1 degree C/s. The resting tension increased reversibly with temperature (5-42 degrees C); the tension increase was slight in warming to approximately 25 degrees C (a linear thermal contraction, -alpha, of approximately 0.1%/degree C) but became more pronounced above approximately 30 degrees C (similar behavior was seen in intact rat muscle fibers). The extra tension rise at the high temperatures was depressed in acidic pH and in the presence of 10 mM inorganic phosphate; it was absent in rigor fibers in which the tension decreased with heating (a linear thermal expansion, alpha, of approximately 4 x 10(-5)/degree C). Below approximately 20 degrees C, the tension response after a approximately 1% length increase (complete < 0.5 ms) consisted of a fast decay (approximately 150.s-1 at 20 degrees C) and a slow decay (approximately 10.s-1) of tension. The rate of fast decay increased with temperature (Q10 approximately 2.4); at 35-40 degrees C, it was approximately 800.s-1, and it was followed by a delayed tension rise (stretch-activation) at 30-40.s-1. The linear rise of passive tension in warming to approximately 25 degrees C may be due to increase of thermal stress in titin (connectin)-myosin composite filament, whereas the extra tension above approximately 30 degrees C may arise from cycling cross-bridges; based on previous findings from regulated actomyosin in solution (Fuchs, 1975), it is suggested that heating reversibly inactivates the troponin-tropomyosin control mechanism and leads to Ca-independent thin filament activation at high temperatures. Additionally, we propose that the heating-induced increase of endo-sarcomeric stress within titin-myosin composite filament makes the

  10. Creep and Stress-strain Behavior After Creep from Sic Fiber Reinforced, Melt-infiltrated Sic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Pujar, Vijay

    2004-01-01

    Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated Si were subjected to creep at 1315 C for a number of different stress conditions, This study is aimed at understanding the time-dependent creep behavior of CMCs for desired use-conditions, and also more importantly, how the stress-strain response changes as a result of the time-temperature-stress history of the crept material. For the specimens that did not rupture, fast fracture experiments were performed at 1315 C or at room temperature immediately following tensile creep. In many cases, the stress-strain response and the resulting matrix cracking stress of the composite change due to stress-redistribution between composite constituents during tensile creep. The paper will discuss these results and its implications on applications of these materials for turbine engine components.

  11. Sialylation of vitronectin regulates stress fiber formation and cell spreading of dermal fibroblasts via a heparin-binding site.

    PubMed

    Miyamoto, Yasunori; Tanabe, Mio; Date, Kimie; Sakuda, Kanoko; Sano, Kotone; Ogawa, Haruko

    2016-04-01

    Vitronectin (VN) plays an important role in tissue regeneration. We previously reported that VN from partial hepatectomized (PH) rats results in a decrease of sialylation of VN and de-sialylation of VN decreases the cell spreading of hepatic stellate cells. In this study, we analyzed the mechanism how sialylation of VN regulates the properties of mouse primary cultured dermal fibroblasts (MDF) and a dermal fibroblast cell line, Swiss 3T3 cells. At first, we confirmed that VN from PH rats or de-sialylated VN also decreased cell spreading in MDF and Swiss 3T3 cells. The de-sialylation suppressed stress fiber formation in Swiss 3T3 cells. Next, we analyzed the effect of the de-sialylation of VN on stress fiber formation in Swiss 3T3 cells. RGD peptide, an inhibitor for a cell binding site of VN, did not affect the cell attachment of Swiss 3T3 cells on untreated VN but significantly decreased it on de-sialylated VN, suggesting that the de-sialylation attenuates the binding activity of an RGD-independent binding site in VN. To analyze a candidate RGD-independent binding site, an inhibition experiment of stress fiber formation for a heparin binding site was performed. The addition of heparin and treatment of cells with heparinase decreased stress fiber formation in Swiss 3T3 cells. Furthermore, de-sialylation increased the binding activity of VN to heparin, as detected by surface plasmon resonance (SPR). These results demonstrate that sialylation of VN glycans regulates stress fiber formation and cell spreading of dermal fibroblast cells via a heparin binding site. PMID:26979432

  12. Stress-intensity factors of r-cracks in fiber-reinforced composites under thermal and mechanical loading

    NASA Astrophysics Data System (ADS)

    Mueller, W. H.; Schmauder, S.

    1993-02-01

    The plane stress/plane strain problem of radial matrix cracking in fiber-reinforced composites, due to thermal mismatch and externally applied stress is solved numerically in the framework of linear elasticity, using Erdogan's integral equation technique. It is shown that, in order to obtain the results of the combined loading case, the solutions of purely thermal and purely mechanical loading can simply be superimposed. Stress-intensity factors are calculated for various lengths and distances of the crack from the interface for each of these loading conditions.

  13. Effect of rolling on the high temperature tensile and stress-rupture properties of tungsten fiber-superalloy composites

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.

    1974-01-01

    An investigation was conducted to determine the effects of mechanical working on the 1093 C tensile and stress-rupture strength of tungsten alloy/superalloy composites. Hot pressed composites containing either conventional tungsten lamp filament wire or tungsten-1% ThO2 wire and a nickel base alloy matrix were hot rolled at 1093 C. The hot pressed and rolled composite specimens were then tested in tension and stress-rupture at 1093 C. Rolling decreased the degree of fiber-matrix reaction as a function of time of exposure at 1093 C. The stress-rupture properties of the rolled composites were superior to hot pressed composites containing equivalent diameter fibers. Rolling did not appreciably affect the 1093 C ultimate tensile strength of the composites.

  14. Effect of rolling on the high temperature tensile and stress-rupture properties of tungsten fiber-superalloy composites

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.

    1974-01-01

    An investigation was conducted to determine the effects of mechanical working on the 1093 C (2000 F) tensile and stress-rupture strength of tungsten alloy/superalloy composites. Hot pressed composites containing either conventional tungsten lamp filament wire or tungsten-1% ThO2 wire and a nickel base alloy matrix were hot rolled at 1093 C (2000 F). The hot pressed and rolled composite specimens were then tested in tension and stress-rupture at 1093 C (2000 F). Rolling decreased the degree of fiber-matrix reaction as a function of time of exposure at 1093 C (2000 F). The stress-rupture properties of the rolled composites were superior to hot pressed composites containing equivalent diameter fibers. Rolling did not appreciably affect the 1093 C (2000 F) ultimate tensile strength of the composites.

  15. Dynamic characterization of short duration stress pulses generated by a magnetic flyer plate in carbon-fiber/epoxy laminates

    SciTech Connect

    Bruck, H.A.; Epstein, J.S.; Perry, K.E. Jr.; Abdallah, M.G.

    1995-11-01

    There is a great deal of interest in characterizing the dynamic mechanical behavior of laminated carbon-fiber/epoxy composites for military and aerospace applications. Current research efforts have been directed at measuring the strength lost because of accumulated damage. Very little work has been done to determine how this damage is accumulated during dynamic mechanical loading. Of particular interest is the effect of short duration (< 1 {micro}s) stress pulses on mechanical behavior such as delamination. In this paper, a magnetic flyer plate apparatus is presented for generating a short duration stress pulse in a unidirectional carbon-fiber/epoxy laminated composite. The stress pulse is characterized using a dynamic moire interferometer.

  16. Effects of mechanical properties of adhesive resin cements on stress distribution in fiber-reinforced composite adhesive fixed partial dentures.

    PubMed

    Yokoyama, Daiichiro; Shinya, Akikazu; Gomi, Harunori; Vallittu, Pekka K; Shinya, Akiyoshi

    2012-01-01

    Using finite element analysis (FEA), this study investigated the effects of the mechanical properties of adhesive resin cements on stress distributions in fiber-reinforced resin composite (FRC) adhesive fixed partial dentures (AFPDs). Two adhesive resin cements were compared: Super-Bond C&B and Panavia Fluoro Cement. The AFPD consisted of a pontic to replace a maxillary right lateral incisor and retainers on a maxillary central incisor and canine. FRC framework was made of isotropic, continuous, unidirectional E-glass fibers. Maximum principal stresses were calculated using finite element method (FEM). Test results revealed that differences in the mechanical properties of adhesive resin cements led to different stress distributions at the cement interfaces between AFPD and abutment teeth. Clinical implication of these findings suggested that the safety and longevity of an AFPD depended on choosing an adhesive resin cement with the appropriate mechanical properties. PMID:22447051

  17. Stress-intensity factors of r-cracks in fiber-reinforced composites under thermal and mechanical loading

    NASA Astrophysics Data System (ADS)

    Mueller, W. H.; Schmauder, S.

    1993-02-01

    This paper is concerned with the problem of the calculation of stress-intensity factors at the tips of radial matrix cracks (r-cracks) in fiber-reinforced composites under thermal and/or transverse uniaxial or biaxial mechanical loading. The crack is either located in the immediate vicinity of a single fiber or it terminates at the interface between the fiber and the matrix. The problem is stated and solved numerically within the framework of linear elasticity using Erdogan's integral equation technique. It is shown that the solutions for purely thermal and purely mechanical loading can simply be superimposed in order to obtain the results of the combined loading case. Stress-intensity factors (SIFs) are calculated for various lengths and distances of the crack from the interface for each of these loading conditions. The behavior of the SIFs for cracks growing towards or away from the interface is examined. The role of the elastic mismatch between the fibers and the matrix is emphasized and studied extensively using the so-called Dundurs' parameters. It is shown that an r-crack, which is remotely located from the fiber, can either be stabilized or destabilized depending on both the elastic as well as the thermal mismatch of the fibrous composite. Furthermore, Dundurs' parameters are used to predict the exponent of the singularity of the crack tip elastic field and the behavior of the corresponding SIFs for cracks which terminate at the interface. An analytical solution for the SIFs is derived for all three loading conditions under the assumption that the elastic constants of the matrix and the fiber are equal. It is shown that the analytical solution is in good agreement with the corresponding numerical results. Moreover, another analytical solution from the literature, which is based upon Paris' equation for the calculation of stress-intensity factors, is compared with the numerical results and it is shown to be valid only for extremely short r-cracks touching the

  18. Finite element analysis of stress concentration in three popular brands of fiber posts systems used for maxillary central incisor teeth

    PubMed Central

    Aggarwal, Shalini; Garg, Vaibhav

    2011-01-01

    Aims and Objectives: To study the stress concentrations in endodontically treated maxillary central incisor teeth restored with 3 different fiber post systems subjected to various oblique occlusal loads. Materials and Methods: FEM analysis was used to analyze stress concentrations generated in maxillary anterior teeth. Computer aided designing was used to create a 2-D model of an upper central incisor. Post systems analyzed were the DT Light Post (RDT, Bisco), Luscent Anchor (Dentatus) & RelyX (3M-ESPE). The entire design assembly was subjected to analysis by ANSYS for oblique loading forces of 25N, 80N & 125 N Results: The resultant data showed that the RelyX generated the least amount of stress concentration. Conclusions: Minimal stress buildups contribute to the longevity of the restorations. Thus RelyX by virtue of judicious stress distribution is the better option for restoration of grossly decayed teeth. PMID:22025836

  19. Effect of preconditioning and stress relaxation on local collagen fiber re-alignment: inhomogeneous properties of rat supraspinatus tendon.

    PubMed

    Miller, Kristin S; Edelstein, Lena; Connizzo, Brianne K; Soslowsky, Louis J

    2012-03-01

    Repeatedly and consistently measuring the mechanical properties of tendon is important but presents a challenge. Preconditioning can provide tendons with a consistent loading history to make comparisons between groups from mechanical testing experiments. However, the specific mechanisms occurring during preconditioning are unknown. Previous studies have suggested that microstructural changes, such as collagen fiber re-alignment, may be a result of preconditioning. Local collagen fiber re-alignment is quantified throughout tensile mechanical testing using a testing system integrated with a polarized light setup, consisting of a backlight, 90 deg-offset rotating polarizer sheets on each side of the test sample, and a digital camera, in a rat supraspinatus tendon model, and corresponding mechanical properties are measured. Local circular variance values are compared throughout the mechanical test to determine if and where collagen fiber re-alignment occurred. The inhomogeneity of the tendon is examined by comparing local circular variance values, optical moduli and optical transition strain values. Although the largest amount of collagen fiber re-alignment was found during preconditioning, significant re-alignment was also demonstrated in the toe and linear regions of the mechanical test. No significant changes in re-alignment were seen during stress relaxation. The insertion site of the supraspinatus tendon demonstrated a lower linear modulus and a more disorganized collagen fiber distribution throughout all mechanical testing points compared to the tendon midsubstance. This study identified a correlation between collagen fiber re-alignment and preconditioning and suggests that collagen fiber re-alignment may be a potential mechanism of preconditioning and merits further investigation. In particular, the conditions necessary for collagen fibers to re-orient away from the direction of loading and the dependency of collagen reorganization on its initial distribution

  20. Free radical activity of industrial fibers: role of iron in oxidative stress and activation of transcription factors.

    PubMed Central

    Gilmour, P S; Brown, D M; Beswick, P H; MacNee, W; Rahman, I; Donaldson, K

    1997-01-01

    We studied asbestos, vitreous fiber (MMVF10), and refractory ceramic fiber (RCF1) from the Thermal Insulation Manufacturers' Association fiber repository regarding the following: free radical damage to plasmid DNA, iron release, ability to deplete glutathione (GSH), and activate redox-sensitive transcription factors in macrophages. Asbestos had much more free radical activity than any of the man-made vitreous fibers. More Fe3+ was released than Fe2+ and more of both was released at pH 4.5 than at pH 7.2. Release of iron from the different fibers was generally not a good correlate of ability to cause free radical injury to the plasmid DNA. All fiber types caused some degree of oxidative stress, as revealed by depletion of intracellular GSH. Amosite asbestos upregulated nuclear binding of activator protein 1 transcription factor to a greater level than MMVF10 and RCF1; long-fiber amosite was the only fiber to enhance activation of the transcription factor nuclear factor kappa B (NF kappa B). The use of cysteine methyl ester and buthionine sulfoximine to modulate GSH suggested that GSH homeostasis was important in leading to activation of transcription factors. We conclude that the intrinsic free radical activity is the major determinant of transcription factor activation and therefore gene expression in alveolar macrophages. Although this was not related to iron release or ability to deplete macrophage GSH at 4 hr, GSH does play a role in activation of NF kappa B. Images Figure 1. Figure 5. A Figure 5. B Figure 6. A Figure 6. B PMID:9400744

  1. The Evolution of Interfacial Sliding Stresses During Cyclic Push-in Testing of C- and BN-Coated Hi-Nicalon Fiber-Reinforced CMCs

    NASA Technical Reports Server (NTRS)

    Eldridge, J. I.; Bansal, N. P.; Bhatt, R. T.

    1998-01-01

    Interfacial debond cracks and fiber/matrix sliding stresses in ceramic matrix composites (CMCs) can evolve under cyclic fatigue conditions as well as with changes in the environment, strongly affecting the crack growth behavior, and therefore, the useful service lifetime of the composite. In this study, room temperature cyclic fiber push-in testing was applied to monitor the evolution of frictional sliding stresses and fiber sliding distances with continued cycling in both C- and BN-coated Hi-Nicalon SiC fiber-reinforced CMCs. A SiC matrix composite reinforced with C-coated Hi-Nical on fibers as well as barium strontium aluminosilicate (BSAS) matrix composites reinforced with BN-coated (four different deposition processes compared) Hi-Nicalon fibers were examined. For failure at a C interface, test results indicated progressive increases in fiber sliding distances during cycling in room air but not in nitrogen. These results suggest the presence of moisture will promote crack growth when interfacial failure occurs at a C interface. While short-term testing environmental effects were not apparent for failure at the BN interfaces, long-term exposure of partially debonded BN-coated fibers to humid air resulted in large increases in fiber sliding distances and decreases in interfacial sliding stresses for all the BN coatings, presumably due to moisture attack. A wide variation was observed in debond and frictional sliding stresses among the different BN coatings.

  2. Non-channel mechanosensors working at focal adhesion-stress fiber complex.

    PubMed

    Hirata, Hiroaki; Tatsumi, Hitoshi; Hayakawa, Kimihide; Sokabe, Masahiro

    2015-01-01

    Mechanosensitive ion channels (MSCs) have long been the only established molecular class of cell mechanosensors; however, in the last decade, a variety of non-channel type mechanosensor molecules have been identified. Many of them are focal adhesion-associated proteins that include integrin, talin, and actin. Mechanosensors must be non-soluble molecules firmly interacting with relatively rigid cellular structures such as membranes (in terms of lateral stiffness), cytoskeletons, and adhesion structures. The partner of MSCs is the membrane in which MSC proteins efficiently transduce changes in the membrane tension into conformational changes that lead to channel opening. By contrast, the integrin, talin, and actin filament form a linear complex of which both ends are typically anchored to the extracellular matrices via integrins. Upon cell deformation by forces, this structure turns out to be a portion that efficiently transduces the generated stress into conformational changes of composite molecules, leading to the activation of integrin (catch bond with extracellular matrices) and talin (unfolding to induce vinculin bindings). Importantly, this structure also serves as an "active" mechanosensor to detect substrate rigidity by pulling the substrate with contraction of actin stress fibers (SFs), which may induce talin unfolding and an activation of MSCs in the vicinity of integrins. A recent study demonstrates that the actin filament acts as a mechanosensor with unique characteristics; the filament behaves as a negative tension sensor in which increased torsional fluctuations by tension decrease accelerate ADF/cofilin binding, leading to filament disruption. Here, we review the latest progress in the study of those non-channel mechanosensors and discuss their activation mechanisms and physiological roles. PMID:24965068

  3. Thermal effects of fiber sensing coils in different winding pattern considering both thermal gradient and thermal stress

    NASA Astrophysics Data System (ADS)

    Ling, Weiwei; Li, Xuyou; Xu, Zhenlong; Zhang, Zhiyong; Wei, Yanhui

    2015-12-01

    By studying the temperature gradient and thermal stress of the difference-winding interferometric fiber optic gyroscope (IFOG) sensing coils, the improvement of the IFOG's temperature performance is realized. A new turn-by-turn quantization thermal-induced bias error model including the traditional "pure Shupe effect", elastic strain interactions and elasto-optical interactions are established. Compared with the traditional "pure Shupe effect" model, the experimental results show that the new model can more fully describe the thermal effect of the coils. Based on the temperature and stress distribution models mentioned above, the effects of the fiber coils with the quadrupolar (QAD) winding pattern, octupolar winding pattern and cross winding pattern on the temperature performance of IFOG are simulated under the same temperature gradient, respectively. The results show that the elastic strain and the elasto-optical effect must be considered when calculated the thermal-induced bias error of the fiber coil. Furthermore, we also come to the conclusion that cross-winding coil of the IFOG have more wonderful temperature performance than the fiber coil with quadruple winding and octupole-winding.

  4. Differential Contributions of Nonmuscle Myosin II Isoforms and Functional Domains to Stress Fiber Mechanics.

    PubMed

    Chang, Ching-Wei; Kumar, Sanjay

    2015-01-01

    While is widely acknowledged that nonmuscle myosin II (NMMII) enables stress fibers (SFs) to generate traction forces against the extracellular matrix, little is known about how specific NMMII isoforms and functional domains contribute to SF mechanics. Here we combine biophotonic and genetic approaches to address these open questions. First, we suppress the NMMII isoforms MIIA and MIIB and apply femtosecond laser nanosurgery to ablate and investigate the viscoelastic retraction of individual SFs. SF retraction dynamics associated with MIIA and MIIB suppression qualitatively phenocopy our earlier measurements in the setting of Rho kinase (ROCK) and myosin light chain kinase (MLCK) inhibition, respectively. Furthermore, fluorescence imaging and photobleaching recovery reveal that MIIA and MIIB are enriched in and more stably localize to ROCK- and MLCK-controlled central and peripheral SFs, respectively. Additional domain-mapping studies surprisingly reveal that deletion of the head domain speeds SF retraction, which we ascribe to reduced drag from actomyosin crosslinking and frictional losses. We propose a model in which ROCK/MIIA and MLCK/MIIB functionally regulate common pools of SFs, with MIIA crosslinking and motor functions jointly contributing to SF retraction dynamics and cellular traction forces. PMID:26336830

  5. Cell shape, spreading symmetry, and the polarization of stress-fibers in cells

    NASA Astrophysics Data System (ADS)

    Zemel, A.; Rehfeldt, F.; Brown, A. E. X.; Discher, D. E.; Safran, S. A.

    2010-05-01

    The active regulation of cellular forces during cell adhesion plays an important role in the determination of cell size, shape, and internal structure. While on flat, homogeneous and isotropic substrates some cells spread isotropically, others spread anisotropically and assume elongated structures. In addition, in their native environment as well as in vitro experiments, the cell shape and spreading asymmetry can be modulated by the local distribution of adhesive molecules and topography of the environment. We present a simple elastic model and experiments on stem cells to explain the variation of cell size with the matrix rigidity. In addition, we predict the experimental consequences of two mechanisms of acto-myosin polarization and focus here on the effect of the cell spreading asymmetry on the regulation of the stress-fiber alignment in the cytoskeleton. We show that when cell spreading is sufficiently asymmetric the alignment of acto-myosin forces in the cell increases monotonically with the matrix rigidity; however, in general this alignment is non-monotonic, as shown previously. These results highlight the importance of the symmetry characteristics of cell spreading in the regulation of cytoskeleton structure and suggest a mechanism by which different cell types may acquire different morphologies and internal structures in different mechanical environments.

  6. Differential Contributions of Nonmuscle Myosin II Isoforms and Functional Domains to Stress Fiber Mechanics

    PubMed Central

    Chang, Ching-Wei; Kumar, Sanjay

    2015-01-01

    While is widely acknowledged that nonmuscle myosin II (NMMII) enables stress fibers (SFs) to generate traction forces against the extracellular matrix, little is known about how specific NMMII isoforms and functional domains contribute to SF mechanics. Here we combine biophotonic and genetic approaches to address these open questions. First, we suppress the NMMII isoforms MIIA and MIIB and apply femtosecond laser nanosurgery to ablate and investigate the viscoelastic retraction of individual SFs. SF retraction dynamics associated with MIIA and MIIB suppression qualitatively phenocopy our earlier measurements in the setting of Rho kinase (ROCK) and myosin light chain kinase (MLCK) inhibition, respectively. Furthermore, fluorescence imaging and photobleaching recovery reveal that MIIA and MIIB are enriched in and more stably localize to ROCK- and MLCK-controlled central and peripheral SFs, respectively. Additional domain-mapping studies surprisingly reveal that deletion of the head domain speeds SF retraction, which we ascribe to reduced drag from actomyosin crosslinking and frictional losses. We propose a model in which ROCK/MIIA and MLCK/MIIB functionally regulate common pools of SFs, with MIIA crosslinking and motor functions jointly contributing to SF retraction dynamics and cellular traction forces. PMID:26336830

  7. High temperature fiber optic microphone having a pressure-sensing reflective membrane under tensile stress

    NASA Technical Reports Server (NTRS)

    Zuckerwar, Allan J. (Inventor); Cuomo, Frank W. (Inventor); Robbins, William E. (Inventor); Hopson, Purnell, Jr. (Inventor)

    1992-01-01

    A fiber optic microphone is provided for measuring fluctuating pressures. An optical fiber probe having at least one transmitting fiber for transmitting light to a pressure-sensing membrane and at least one receiving fiber for receiving light reflected from a stretched membrane is provided. The pressure-sensing membrane may be stretched for high frequency response. Further, a reflecting surface of the pressure-sensing membrane may have dimensions which substantially correspond to dimensions of a cross section of the optical fiber probe. Further, the fiber optic microphone can be made of materials for use in high temperature environments, for example greater than 1000 F. A fiber optic probe is also provided with a backplate for damping membrane motion. The backplate further provides a means for on-line calibration of the microphone.

  8. Elastic-plastic stress concentrations around crack-like notches in continuous fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Bigelow, C. A.

    1989-01-01

    Continuous fiber silicon-carbide/aluminum composite laminates with slits were tested statically to failure. Five different layups were examined: (0) sub 8, (0 sub 2/ + or - 45) sub s, (0/90) sub 2s), (0/ + or - 45/90 sub s), and (+ or - 45) sub 2s. Either a 9.5 or a 19 mm slit was machined in the center of each specimen. The strain distribution ahead of the slit tip was found experimentally with a series of strain gages bonded ahead of the slit tip. A three-dimensional finite element program (PAFAC) was used to predict the strain distribution ahead of the slit tip for several layups. For all layups, except the (0) sub 8, the yielding of the metal matrix caused the fiber stress concentration factor to increase with increasing load. This is contrary to the behavior seen in homogeneous materials where yielding causes the stress concentration to drop. For the (0) sub 8 laminate, yielding of the matrix caused a decrease in the fiber stress concentration. The finite element analysis predicted these trends correctly.

  9. Elastic-plastic stress concentrations around crack-like notches in continuous fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Bigelow, C. A.

    1987-01-01

    Continuous fiber silicon-carbide/aluminum composite laminates with slits were tested statically to failure. Five different layups were examined: (0) sub 8, (0 sub 2/ + or - 45) sub s, (0/90) sub 2s), (0/ + or - 45/90 sub s), and (+ or - 45) sub 2s. Either a 9.5 or a 19 mm slit was machined in the center of each specimen. The strain distribution ahead of the slit tip was found experimentally with a series of strain gages bonded ahead of the slit tip. A three-dimensional finite element program (PAFAC) was used to predict the strain distribution ahead of the slit tip for several layups. For all layups, except the (0) sub 8, the yielding of the metal matrix caused the fiber stress concentration factor to increase with increasing load. This is contrary to the behavior seen in homogeneous materials where yielding causes the stress concentration to drop. For the (0) sub 8 laminate, yielding of the matrix caused a decrease in the fiber stress concentration. The finite element analysis predicted these trends correctly.

  10. Actin stress fiber disruption and tropomysin isoform switching in normal thyroid epithelial cells stimulated by thyrotropin and phorbol esters

    SciTech Connect

    Roger, P.P.; Rickaert, F.; Lamy, F.; Authelet, M.; Dumont, J.E. )

    1989-05-01

    Thyrotropin (TSH), through cyclic AMP, promotes both proliferation and differentiation expression in dog thyroid epithelial cells in primary culture, whereas the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) also stimulates proliferation but antagonizes differentiating effects of TSH. In this study, within 20 min both factors triggered the disruption of actin-containing stress fibers. This process preceded distinct morphological changes: cytoplasmic retraction and arborization in response to TSH and cyclic AMP, cell shape distortion, and increased motility in response to TPA and diacylglycerol. TSH and TPA also induced a marked decrease in the synthesis of three high M{sub r} tropomyosin isoforms, which were not present in dog thyroid tissue but appeared in culture during cell spreading and stress fiber formation. The tropomyosin isoform switching observed here closely resembled similar processes in various cells transformed by oncogenic viruses. However, it did not correlate with differentiation or mitogenic activation. Contrasting with current hypothesis on this process in transformed cells, tropomyosin isoform switching in normal thyroid cells was preceded and thus might be caused by early disruption of stress fibers.

  11. Raman Study of Uncoated and P-bn/sic-coated Hi-nicalon Reinforced Celsian Matrix Composites. Part 2; Residual Stress in the Fibers

    NASA Technical Reports Server (NTRS)

    Gouadec, Gwenael; Colomban, Philippe; Bansal, Narottam P.

    2000-01-01

    Band shifts on Raman spectra were used to assess, at a microscopic scale, the residual strain existing in Hi-Nicalon fibers reinforcing celsian matrix composites. Uncoated as well as p-BN/SiC- and p-B(Si)N/SiC-coated Hi-Nicalon fibers were used as the reinforcements. We unambiguously conclude that the fibers are in a state of compressive residual stress. Quantitative determination of the residual stress was made possible by taking into account the heating induced by laser probing and by using a reference line, of fixed wavenumber. We found fiber compressive residual stress values between 110 and 960 MPa depending on the fiber/matrix coating in the composite. A stress relaxation-like phenomenon was observed at the surface of p-BN/SiC-coated Hi-Nicalon fibers whereas the uncoated or p-B(Si)N/SiC-coated Hi-Nicalon fibers did not show any stress relaxation in the Celsian matrix composites.

  12. Properties of fiber composites for advanced flywheel energy storage devices

    SciTech Connect

    DeTeresa, S J; Groves, S E

    2001-01-12

    The performance of commercial high-performance fibers is examined for application to flywheel power supplies. It is shown that actual delivered performance depends on multiple factors such as inherent fiber strength, strength translation and stress-rupture lifetime. Experimental results for recent stress-rupture studies of carbon fibers will be presented and compared with other candidate reinforcement materials. Based on an evaluation of all of the performance factors, it is concluded that carbon fibers are preferred for highest performance and E-glass fibers for lowest cost. The inferior performance of the low-cost E-glass fibers can be improved to some extent by retarding the stress-corrosion of the material due to moisture and practical approaches to mitigating this corrosion are discussed. Many flywheel designs are limited not by fiber failure, but by matrix-dominated failure modes. Unfortunately, very few experimental results for stress-rupture under transverse tensile loading are available. As a consequence, significant efforts are made in flywheel design to avoid generating any transverse tensile stresses. Recent results for stress-rupture of a carbon fiber/epoxy composite under transverse tensile load reveal that these materials are surprisingly durable under the transverse loading condition and that some radial tensile stress could be tolerated in flywheel applications.

  13. Feeding and lying behavior of heat-stressed early lactation cows fed low fiber diets containing roughage and nonforage fiber sources.

    PubMed

    Kanjanapruthipong, J; Junlapho, W; Karnjanasirm, K

    2015-02-01

    In addition to reduced nutrient intake, an environmental thermal load may directly affect milk yield in heat-stressed dairy cows. Feeding and lying behaviors of early lactation cows fed low fiber diets containing neutral detergent fiber (NDF) from roughage and nonforage fiber sources (NFFS) were investigated under summer conditions in Thailand. Immediately after calving, 30 multiparous cows (87.5% Holstein × 12.5% Sahiwal) were randomly allocated to dietary treatments for 63 d in a completely randomized design. The dietary treatments contained 25% of dry matter (DM) as dietary NDF. The control diet consisted of 13.9% roughage NDF from rice straw (RS). Two additional treatments were created by replacing 3.9% of DM with NDF from either soy hulls (SH) or cassava (Manihot esculenta Grantz) residues (CR), so that the roughage NDF content was reduced to 10%. During the experimental period, the minimum and maximum temperature-humidity indices (THI) were 86.4±2.5 and 91.5±2.7 during the day and 74.2±2.1 and 81.0±2.5 during the night, respectively, indicating conditions appropriate for induction of extreme heat stress. The duration of feeding and lying bouts decreased linearly with increasing THI. The DM intake during the day was greater for cows fed diets containing SH and CR than for those fed the diet containing NDF from RS. The number of meals during the day and night was lower, whereas meal size and meal length during the day and night were greater for cows fed diets containing SH and CR. Cows fed diets containing SH and CR lay down less frequently and longer during the day. These results suggest that under the severe heat stress during the day, early lactation cows fed the diet containing NFFS increased DM intake by increasing meal length and meal size rather than by increasing meal frequency and they spent more time lying. Cows fed diets containing NDF from SH and CR produced more 4% fat-corrected milk, lost less body weight, and had lower rectal temperatures

  14. VEGF induces stress fiber formation in fibroblasts isolated from dystrophic muscle.

    PubMed

    Gutpell, Kelly M; Hoffman, Lisa M

    2015-12-01

    Treatment with vascular endothelial growth factor (VEGF) to reduce ischemia and enhance both endogenous muscle repair and regenerative cell therapy in Duchenne muscular dystrophy (DMD) has been widely proposed in recent years. However, the interaction between angiogenesis and fibrosis, a hallmark feature of DMD, remains unclear. To date, it has not been determined whether VEGF exerts a pro-fibrotic effect on DMD-derived fibroblasts, which may contribute to further disease progression. Thus, the purpose of this study was to investigate the effect of exogenous VEGF on fibroblast cultures established from a murine model of DMD. Primary fibroblast cultures were established from gastrocnemius and diaphragm muscles of 10 week-old mdx/utrn+/- mice. Quantitative polymerase chain reaction (qPCR) was employed to assess changes in transcript expression of alpha-smooth muscle actin (Acta2), type-1 collagen (Col1a1), connective tissue growth factor (Ctgf/ccn2) and fibronectin (Fn1). Immunofluorescence and Western blot analysis was further employed to visualize changes in protein expression of alpha-smooth muscle actin (α-SMA), CTGF/CCN2 and fibronectin. mRNA levels of Col1a1, Ctgf/ccn2, and FN did not increase following treatment with VEGF in fibroblasts derived from either diaphragm or gastrocnemius muscles. Acta2 expression increased significantly in diaphragm-derived fibroblasts following treatment with VEGF. Morphological assessment revealed increased stress fiber formation in VEGF-treated fibroblasts compared to the untreated control fibroblasts. The findings from this study suggest that further investigation into the effect of VEGF on fibroblast function is required prior to the utilization of the growth factor as a treatment for DMD. PMID:26219981

  15. Fiber Bragg Grating Sensor to Monitor Stress Kinetics in Drying Process of Commercial Latex Paints

    PubMed Central

    de Lourenço, Ivo; Possetti, Gustavo R. C.; Muller, Marcia; Fabris, José L.

    2010-01-01

    In this paper, we report a study about the application of packaged fiber Bragg gratings used as strain sensors to monitor the stress kinetics during the drying process of commercial latex paints. Three stages of drying with distinct mechanical deformation and temporal behaviors were identified for the samples, with mechanical deformation from 15 μm to 21 μm in the longitudinal film dimension on time intervals from 370 to 600 minutes. Drying time tests based on human sense technique described by the Brazilian Technical Standards NBR 9558 were also done. The results obtained shows that human sense technique has a limited perception of the drying process and that the optical measurement system proposed can be used to characterize correctly the dry-through stage of paint. The influence of solvent (water) addition in the drying process was also investigated. The paint was diluted with four parts paint and one part water (80% paint), and one part paint and one part water (50% paint). It was observed that the increase of the water ratio mixed into the paint decreases both the mechanical deformation magnitude and the paint dry-through time. Contraction of 5.2 μm and 10.4 μm were measured for concentrations of 50% and 80% of paint in the mixture, respectively. For both diluted paints the dry-through time was approximately 170 minutes less than undiluted paint. The optical technique proposed in this work can contribute to the development of new standards to specify the drying time of paint coatings. PMID:22399906

  16. Thermal stress problem for a partly debonded rigid circular-arc fiber inclusion in an infinite matrix

    SciTech Connect

    Kattis, M.A.; Patia, A.P.

    1994-06-01

    The heat conduction and thermoelastic problem of a circular-arc fiber bonded along one of its faces to an elastic plate while the other face forms an interfacial crack, is examined. Explicit solutions in the form of the complex potentials are provided, when a uniform heat flow is applied at infinity and the interface crack is an insulated and an `open` crack. It is shown that the stress field at the crack tip exhibits two singularities of orders 0.75 and 0.25 and the well known logarithmic oscillation of the interface crack. Generalized stress intensity factors of the stress singularities are defined and analytical and numerical results of these are provided. 8 refs.

  17. The mechanics of delamination in fiber-reinforced composite materials. Part 1: Stress singularities and solution structure

    NASA Technical Reports Server (NTRS)

    Wang, S. S.; Choi, I.

    1983-01-01

    The fundamental mechanics of delamination in fiber composite laminates is studied. Mathematical formulation of the problem is based on laminate anisotropic elasticity theory and interlaminar fracture mechanics concepts. Stress singularities and complete solution structures associated with general composite delaminations are determined. For a fully open delamination with traction-free surfaces, oscillatory stress singularities always appear, leading to physically inadmissible field solutions. A refined model is introduced by considering a partially closed delamination with crack surfaces in finite-length contact. Stress singularities associated with a partially closed delamination having frictional crack-surface contact are determined, and are found to be diferent from the inverse square-root one of the frictionless-contact case. In the case of a delamination with very small area of crack closure, a simplified model having a square-root stress singularity is employed by taking the limit of the partially closed delamination. The possible presence of logarithmic-type stress singularity is examined; no logarithmic singularity of any kind is found in the composite delamination problem. Numerical examples of dominant stress singularities are shown for delaminations having crack-tip closure with different frictional coefficients between general (1) and (2) graphite-epoxy composites.

  18. Hygrothermomechanical fracture stress criteria for fiber composites with sense-parity

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Ginty, C. A.

    1983-01-01

    Hygrothermomechanical fracture stress criteria are developed and evaluated for unidirectional composites (plies) with sense-parity. These criteria explicity quantify the individual contributions of applied, hygral and thermal stresses as well as couplings among these stresses. The criteria are for maximum stress, maximum strain, internal friction, work-to-fracture and combined-stress fracture. Predicted results obtained indicate that first ply failure will occur at stress levels lower than those predicted using criteria currently available in the literature. Also, the contribution of the various stress couplings (predictable only by fracture criteria with sense-parity) is significant to first ply failure and attendant fracture modes.

  19. TECHNICAL NOTE: Active control for stress intensity of crack-tips under mixed mode by shape memory TiNi fiber epoxy composites

    NASA Astrophysics Data System (ADS)

    Shimamoto, A.; Zhao, H.; Azakami, T.

    2007-06-01

    The paper presented the effectiveness of a shape memory alloy hybrid composite. It was designed to actively suppress stress intensity in the vicinity of a crack-tip. A shape memory alloy (SMA) TiNi fiber reinforced epoxy composite was fabricated based on the proposed design concept and its material and mechanical properties were investigated by photoelastic examinations. The stress intensity factors, KI and KII, at a crack-tip decreased temperatures greater than Af under mixed mode. The phenomenon was caused by the recovery force of the TiNi fiber. The relationship of the stress intensity factors with the prestrain in the SMA fiber as well as with the ambient temperature in an isothermal furnace was clarified. On this basis, the active control for stress intensity by a shape memory composite was discussed.

  20. Polarization-maintaining, double-clad fiber amplifier employing externally applied stress-induced birefringence

    SciTech Connect

    Koplow, Jeffrey P.; Goldberg, Lew; Moeller, Robert P.; Kliner, Dahv A. V.

    2000-03-15

    We report a new approach to obtaining linear-polarization operation of a rare-earth-doped fiber amplifier in which the gain fiber is coiled under tension to induce birefringence. We demonstrated this method by constructing an Er/Yb-doped, double-clad, single-mode fiber amplifier with an output power of 530 mW and a polarization extinction ratio of >17 dB (when seeded with linearly polarized light) at a wavelength of {approx}1.5 {mu}m . The technique is achromatic, permits single- or multiple-pass operation of the amplifier, requires no additional components in the optical path, leaves the fiber ends unobstructed, and is inexpensive to implement. (c) 2000 Optical Society of America.

  1. Development of a fiber Bragg grating sensor for in-shoe shear stress measurement: design and preliminary results

    NASA Astrophysics Data System (ADS)

    Koulaxouzidis, Andreas V.; Roberts, V. C.; Holmes, Melanie J.; Handerek, Vincent A.

    2000-08-01

    In-shoe shear stress sensors are a required tool for the investigation of plantar ulcer development after the onset of diabetes. Recently, several transducers have been developed for measuring in-shoe shear stress using magneto- resistive technology, light intensity modulation, and copolymer piezoelectric materials. Common drawbacks in the previous methods are the relatively large size of the sensors and the difficulty in interrogating many sensors simultaneously in order to achieve distributed sensing. In this paper we demonstrate for the first time a shear stress sensor using Fiber Bragg gratings (FBGs). The small size and the multiplexing capability of FBGs enables quasi- distributed sensing of shear stress on the plantar surface by interrogating a large number of identical sensors. The sensor design is based on the theory of elastic bending of columns. The sensor consists of two FBGs fitted inside a metallic structure which is able to deform elastically under shear stress. This elastic deformation produces strain on the FBGs, which can be detected by measuring the Bragg wavelength shift of the reflected light of each FBG using a CCD spectrometer. Preliminary results on an enlarged version of the sensor have shown the applicability of FBGs for the implementation of the in-shoe sensor.

  2. Three-dimensional finite element analysis of stress distribution in a tooth restored with metal and fiber posts of varying diameters: An in-vitro study

    PubMed Central

    Kumar, Pradeep; Rao, R. Nageswar

    2015-01-01

    Objective: To compare stress distribution in a tooth restored with metal and fiber posts of varying diameters (1.2 and 1.4 mm) by means of three-dimensional finite element analysis (3D-FEA). Materials and Methods: Four 3D-FEA models were constructed: (1) fiber post (1.2 and 1.4 mm) and (2) metal post (1.2 and 1.4 mm). The material properties were assigned and a force of 100 N was applied at 45° angle to the longitudinal axis of the tooth onto the palatal surface incisal to the cingulum. Analysis was run and stress distribution pattern was studied. Results: Maximum stresses in the radicular tooth structure for fiber post were higher than that for metal post. In the former models, stresses in the tooth structure were slightly reduced with increase in fiber post diameter. Conclusions: To reduce stress in the remaining radicular tooth structure, it is better to use a fiber post of a large diameter. PMID:25829685

  3. Stress distribution of endodontically treated teeth with titanium alloy post and carbon fiber post with different alveolar bone height: A three-dimensional finite element analysis

    PubMed Central

    Singh, S. Vijay; Bhat, Manohar; Gupta, Saurabh; Sharma, Deepak; Satija, Harsha; Sharma, Sumeet

    2015-01-01

    Objective: A three-dimensional (3D) finite element analysis (FEA) on the stress distribution of endodontically treated teeth with titanium alloy post and carbon fiber post with different alveolar bone height. Materials and Methods: The 3D model was fabricated using software to represent an endodontically treated mandibular second premolar with post and restored with a full ceramic crown restoration, which was then analyzed using FEA using FEA ANSYS Workbench V13.0 (ANSYS Inc., Canonsburg, Pennsylvania, U.S.A) software. Results: The FEA showed the maximum stresses of 137.43 Mpa in dentin with alveolar bone height of 4 mm when the titanium post was used, 138.48 Mpa when carbon fiber post was used as compared to 105.91 Mpa in the model with alveolar bone height of 2 mm from the cement enamel junction (CEJ) when the titanium post was used and 107.37 Mpa when the carbon fiber post was used. Conclusions: Stress was observed more in alveolar bone height level of 4 mm from CEJ than 2 mm from CEJ. Stresses in the dentin were almost similar when the carbon fiber post was compared to titanium post. However, stresses in the post and the cement were much higher when titanium post was used as compared to carbon fiber post. PMID:26430375

  4. Mild heat stress enhances differentiation and proliferation of Japanese quail myoblasts and enhances slow muscle fiber characteristics.

    PubMed

    Choi, Y M; Chen, P R; Shin, S; Zhang, J; Hwang, S; Lee, K

    2016-08-01

    The objective of this study was to investigate the effect of mild heat stress on muscle fiber hyperplastic and hypertrophic growth in quail primary myogenic cells to better understand the mechanisms leading to increased skeletal muscle development in avian embryos incubated at a higher temperature. Compared to control cultures maintained at 37°C, incubation at 39°C enhanced myotube length (P < 0.01) and diameter (P < 0.001) at 3 days after differentiation (D3). This enlargement of the myotubes incubated at 39°C can be explained by differences in the fusion index (56.7 vs. 46.2%, P < 0.05) and nuclei number per myotube (18.1 vs. 10.8, P < 0.001) compared to the control cells at D3. Additionally, a higher density of myotubes at D3 in cultures exposed to a higher temperature were related to higher levels of Pax-7 (P < 0.05) compared to the control cells incubated continuously at 37°C. These results indicated a higher proliferative capacity in cells exposed to mild heat stress compared to the control cells. On the other hand, mild heat stress enhanced protein levels of slow myosin heavy chain isoform (P < 0.01) and cytochrome c oxidase subunit IV (P < 0.01) compared to the control cells at D3. These discrepancies in protein expression indicated maintenance of slow muscle fiber type characteristics in myotubes incubated at 39°C. Our results suggest that mild heat stress plays a significant role in myogenic mechanisms related to muscle mass and development. PMID:27038421

  5. On intrinsic stress fiber contractile forces in semilunar heart valve interstitial cells using a continuum mixture model.

    PubMed

    Sakamoto, Yusuke; Buchanan, Rachel M; Sacks, Michael S

    2016-02-01

    Heart valve interstitial cells (VICs) play a critical role in the maintenance and pathophysiology of heart valve tissues. Normally quiescent in the adult, VICs can become activated in periods of growth and disease. When activated, VICs exhibit increased levels of cytokines and extracellular matrix (ECM) synthesis, and upregulated expression and strong contraction of α-smooth muscle actin (α-SMA) fibers. However, it remains unknown how expression and contraction of the α-SMA fibers, which vary among different VIC types, contribute to the overall VIC mechanical responses, including the nucleus and cytoskeleton contributions. In the present study, we developed a novel solid-mixture model for VIC biomechanical behavior that incorporated 1) the underlying cytoskeletal network, 2) the oriented α-SMA stress fibers with passive elastic and active contractile responses, 3) a finite deformable elastic nucleus. We implemented the model in a full 3D finite element simulation of a VIC based on known geometry. Moreover, we examined the respective mechanical responses of aortic and pulmonary VICs (AVICs and PVICs, respectively), which are known to have different levels of α-SMA expression levels and contractile behaviors. To calibrate the model, we simulated the combined mechanical responses of VICs in both micropipette aspiration (MA) and atomic force microscopy (AFM) experiments. These two states were chosen as the VICs were under significantly different mechanical loading conditions and activation states, with the α-SMA fibers inactivated in the MA studies while fully activated in the AFM studies. We also used the AFM to study the mechanical property of the nucleus. Our model predicted that the substantial differences found in stiffening of the AVIC compared to the PVICs was due to a 9 to 16 times stronger intrinsic AVIC α-SMA stress fiber contractile force. Model validation was done by simulating a traction force microscopy experiment to estimate the forces the VICs

  6. The effect of microstructure on residual-stress development in short-fiber composites

    SciTech Connect

    Eduljee, R.F.

    1991-01-01

    The aim of this study was the identification of the key processing and microstructural parameters that affect thermal residual stresses through a series of parametric analyses on an infinite-plate geometry. In these analyses polycarbonate was chosen as a representative amorphous resin while polyetheretherketone (PEEK) was used as an example of a semicrystalline resin. The residual stress model of Indenbom was used to investigate residual stresses in amorphous polymers. Due to the inapplicability of this model to semicrystalline polymers and composites where the material properties varied through the thickness of the specimen, a residual stress model based on incremental stress analysis was developed. The parametric analyses on the neat polymers showed that the thermal history and the thermoelastic properties played major roles in the residual stress development in both amorphous and semicrystalline polymers. Crystallization increased the level of residual stresses. The mechanisms for this increase are discussed.

  7. Numerical analysis of stress distribution in embedded highly birefringent PANDA fibers

    NASA Astrophysics Data System (ADS)

    Lesiak, Piotr; Woliński, Tomasz

    2015-09-01

    The paper presents numerical analysis compared with experimental data of influence of polymerization shrinkage on highly birefringent (HB) PANDA optical fibers embedded in a composite material. Since polymerization is a chemical process consisting in combining single molecules in a macromolecular compound [1], principal directions of the polymerization shrinkage depend on a number of the composite layers associated with this process. In this paper a detailed analysis of the piezo-optic effects occurring in HB optical fibers before and after the lamination process answers the question to what extent a degree of the material degradation can be properly estimated.

  8. Self-affine nature of the stress-strain behavior of thin fiber networks

    NASA Astrophysics Data System (ADS)

    Balankin, Alexander S.; Susarrey, Orlando; Bravo, Armando

    2001-12-01

    The stress-strain behavior of toilet paper is studied. We find that the damaged parts of stress-strain curves possess a self-affine scaling invariance. Moreover, we find that the stress-strain behavior and the rupture line roughness are characterized by the same scaling (Hurst) exponent H, which is not universal: rather it changes from sample to sample. The variations on H are mainly due to fluctuations in the paper structure, which are larger than statistical errors within a sample. Furthermore, the same exponent governs the changes in the stress-strain curve as the strain rate increases. The fractal damage model is employed to explain experimental observations.

  9. Soluble fiber-enriched diets improve inflammation and oxidative stress biomarkers in Zucker fatty rats.

    PubMed

    Sánchez, David; Quiñones, Mar; Moulay, Leila; Muguerza, Begoña; Miguel, Marta; Aleixandre, Amaya

    2011-07-01

    In this study we evaluated the effect of the administration of different soluble fiber enriched-diets on inflammatory and redox state of Zucker fatty rats. Four groups of ten 8 week-old female Zucker fatty rats were used. The four groups were respectively fed the following diets until the 15th week of life: standard diet (obese control), 10% high methoxylated apple pectin (HMAP)-, 5% soluble cocoa fiber (SCF)-, and 10% β-glucan-enriched diets. A group of Zucker lean rats fed the standard diet was also used as control for normal values of this rat strain. The plasma levels of tumoral necrosis factor-α (TNF-α), adiponectin, and malondialdehyde (MDA) were measured at the end of treatment. The reduced glutathione liver levels were also obtained at that moment. TNF-α plasma levels decreased somewhat in Zucker fatty rats fed the different fibers, and MDA plasma levels significantly decreased in these animals. Nevertheless, adiponectin plasma levels increased in the Zucker fatty rats fed the SCF enriched diet, but did not change in the HMAP and the β-glucan group. The Zucker fatty rats fed the different fiber showed a trend towards increased the reduced glutathione liver levels, but significant differences with obese control rats were only obtained in the β-glucan group. The results obtained in this study suggest that the intake of the different soluble fiber-enriched diets that we have evaluated could prevent and/or attenuate the inflammatory and/or the prooxidative state of the metabolic syndrome. PMID:21349333

  10. Functional analyses of cotton (Gossypium hirsutum L.) immature fiber (im) mutant reveal that fiber cell wall development is associated with sensitivity to stress.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Background: Cotton fiber maturity refers the degree of fiber cell wall development and is an important factor for determining commercial value of cotton. The molecular mechanism regulating the fiber cell wall development has not been well characterized. Microscopic image analysis of the cross-sect...

  11. New molecular tools to study fiber develop and the effect of environmental stresses: development of transgenic cotton lines harboring fiber specific

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cotton is one of the most important cash crops in US agricultural industry. Cotton fibers are differentiated elongated epidermal cell of the seed coat. Fiber development consists of four distinct but overlapping stages, fiber initiation, cell elongation, secondary cell wall deposition, and matura...

  12. AtRAV1 and AtRAV2 overexpression in cotton increases fiber length differentially under drought stress and delays flowering.

    PubMed

    Mittal, Amandeep; Jiang, Yingwen; Ritchie, Glen L; Burke, John J; Rock, Christopher D

    2015-12-01

    There is a longstanding problem of an inverse relationship between cotton fiber qualities versus high yields. To better understand drought stress signaling and adaptation in cotton (Gossypium hirsutum) fiber development, we expressed the Arabidopsis transcription factors RELATED_TO_ABA-INSENSITIVE3/VIVIPAROUS1/(RAV1) and AtRAV2, which encode APETALA2-Basic3 domain proteins shown to repress transcription of FLOWERING_LOCUS_T (FT) and to promote stomatal opening cell-autonomously. In three years of field trials, we show that AtRAV1 and AtRAV2-overexpressing cotton had ∼5% significantly longer fibers with only marginal decreases in yields under well-watered or drought stress conditions that resulted in 40-60% yield penalties and 3-7% fiber length penalties in control plants. The longer transgenic fibers from drought-stressed transgenics could be spun into yarn which was measurably stronger and more uniform than that from well-watered control fibers. The transgenic AtRAV1 and AtRAV2 lines flowered later and retained bolls at higher nodes, which correlated with repression of endogenous GhFT-Like (FTL) transcript accumulation. Elevated expression early in development of ovules was observed for GhRAV2L, GhMYB25-Like (MYB25L) involved in fiber initiation, and GhMYB2 and GhMYB25 involved in fiber elongation. Altered expression of RAVs controlling critical nodes in developmental and environmental signaling hierarchies has the potential for phenotypic modification of crops. PMID:26706061

  13. Effect of Environment on Stress-Rupture Behavior of a Carbon Fiber-Reinforced Silicon Carbide (C/SiC) Ceramic Matrix Composite

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.; Opila, Elizabeth J.; Calomino, Anthony; Kiser, J. Douglas

    2002-01-01

    Stress-rupture tests were conducted in air, vacuum, and steam-containing environments to identify the failure modes and degradation mechanisms of a carbon fiber-reinforced silicon carbide (C/SiC) composite at two temperatures, 600 and 1200 C. Stress-rupture lives in air and steam containing environments (50 - 80% steam with argon) are similar for a composite stress of 69 MPa at 1200 C. Lives of specimens tested in a 20% steam/argon environment were about twice as long. For tests conducted at 600 C, composite life in 20% steam/argon was 20 times longer than life in air. Thermogravimetric analysis of the carbon fibers was conducted under similar conditions to the stress-rupture tests. The oxidation rate of the fibers in the various environments correlated with the composite stress-rupture lives. Examination of the failed specimens indicated that oxidation of the carbon fibers was the primary damage mode for specimens tested in air and steam environments at both temperatures.

  14. Mechanical Properties of Carbon Fiber-Reinforced Aluminum Manufactured by High-Pressure Die Casting

    NASA Astrophysics Data System (ADS)

    Kachold, Franziska; Singer, Robert

    2016-03-01

    Carbon fiber reinforced aluminum was produced by a specially adapted high-pressure die casting process. The MMC has a fiber volume fraction of 27%. Complete infiltration was achieved by preheating the bidirectional, PAN-based carbon fiber body with IR-emitters to temperatures of around 750 °C. The degradation of the fibers, due to attack of atmospheric oxygen at temperatures above 600 °C, was limited by heating them in argon-rich atmosphere. Additionally, the optimization of heating time and temperature prevented fiber degradation. Only the strength of the outer fibers is reduced by 40% at the most. The fibers in core of fiber body are nearly undamaged. In spite of successful manufacturing, the tensile strength of the MMC is below strength of the matrix material. Also unidirectional MMCs with a fiber volume fraction of 8% produced under the same conditions, lack of the reinforcing effect. Two main reasons for the unsatisfactory mechanical properties were identified: First, the fiber-free matrix, which covers the reinforced core, prevents effective load transfer from the matrix to the fibers. And second, the residual stresses in the fiber-free zones are as high as 100 MPa. This causes premature failure in the matrix. From this, it follows that the local reinforcement of an actual part is limited. The stress distribution caused by residual stresses and by loading needs to be known. In this way, the reinforcing phase can be placed and aligned accordingly. Otherwise delamination and premature failure might occur.

  15. Development of a self-stressing NiTiNb shape memory alloy (SMA)/fiber reinforced polymer (FRP) patch

    NASA Astrophysics Data System (ADS)

    El-Tahan, M.; Dawood, M.; Song, G.

    2015-06-01

    The objective of this research is to develop a self-stressing patch using a combination of shape memory alloys (SMAs) and fiber reinforced polymer (FRP) composites. Prestressed carbon FRP patches are emerging as a promising alternative to traditional methods to repair cracked steel structures and civil infrastructure. However, prestressing these patches typically requires heavy and complex fixtures, which is impractical in many applications. This paper presents a new approach in which the prestressing force is applied by restraining the shape memory effect of NiTiNb SMA wires. The wires are subsequently embedded in an FRP overlay patch. This method overcomes the practical challenges associated with conventional prestressing. This paper presents the conceptual development of the self-stressing patch with the support of experimental observations. The bond between the SMA wires and the FRP is evaluated using pull-out tests. The paper concludes with an experimental study that evaluates the patch response during activation subsequent monotonic tensile loading. The results demonstrate that the self-stressing patch with NiTiNb SMA is capable of generating a significant prestressing force with minimal tool and labor requirements.

  16. Paradox of plant growth promotion potential of rhizobacteria and their actual promotion effect on growth of barley (Hordeum vulgare L.) under salt stress.

    PubMed

    Cardinale, Massimiliano; Ratering, Stefan; Suarez, Christian; Zapata Montoya, Ana Maria; Geissler-Plaum, Rita; Schnell, Sylvia

    2015-12-01

    From the rhizosphere of two salt tolerant plant species, Hordeum secalinum and Plantago winteri growing in a naturally salt meadow, 100 strains were isolation on enrichment media for various plant growth-promoting (PGP) functions (ACC deaminase activity, auxin synthesis, calcium phosphate mobilization and nitrogen fixation). Based on the taxonomic affiliation of the isolated bacteria and their enrichment medium 22 isolates were selected to test their growth promotion effect on the crop barley (Hordeum vulgare) under salt stress in pot experiment. In parallel the isolates were characterized in pure culture for their plant growth-promoting activities. Surprisingly the best promotors did not display a promising set of PGP activities. Isolates with multiple PGP-activities in pure culture like Microbacterium natoriense strain E38 and Pseudomonas brassicacearum strain E8 did not promote plant growth. The most effective isolate was strain E108 identified as Curtobacterium flaccumfaciens, which increased barley growth up to 300%. In pure culture strain E108 showed only two out of six plant growth promoting activities and would have been neglected. Our results highlight that screening based on pure culture assays may not be suitable for recognition of best plant growth promotion candidates and could preclude the detection of both new PGPR and new plant promotion mechanisms. PMID:26640049

  17. Flax Fiber - Interfacial Bonding

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Measured flax fiber physical and chemical properties potentially impact bonding and thus stress transfer between the matrix and fiber within composites. These first attempts at correlating flax fiber quality and biofiber composites contain the initial steps towards identifying key flax fiber charac...

  18. Testing of Carbon Fiber Composite Overwrapped Pressure Vessel Stress-Rupture Lifetime

    NASA Technical Reports Server (NTRS)

    Grimes-Ledesma, Lorie; Phoenix, S. Leigh; Beeson, Harold; Yoder, Tommy; Greene, Nathaniel

    2006-01-01

    This paper contains summaries of testing procedures and analysis of stress rupture life testing for two stress rupture test programs, one for Kevlar COPVs performed at Lawrence Livermore National Laboratory, and the other a joint study between NASA JSC White Sands Test Facility and the Jet Propulsion Laboratory. These will be discussed in detail including test setup and issues encountered during testing. Lessons learned from testing in these two programs will be discussed.

  19. Inverted formin 2 in focal adhesions promotes dorsal stress fiber and fibrillar adhesion formation to drive extracellular matrix assembly

    PubMed Central

    Skau, Colleen T.; Plotnikov, Sergey V.; Doyle, Andrew D.; Waterman, Clare M.

    2015-01-01

    Actin filaments and integrin-based focal adhesions (FAs) form integrated systems that mediate dynamic cell interactions with their environment or other cells during migration, the immune response, and tissue morphogenesis. How adhesion-associated actin structures obtain their functional specificity is unclear. Here we show that the formin-family actin nucleator, inverted formin 2 (INF2), localizes specifically to FAs and dorsal stress fibers (SFs) in fibroblasts. High-resolution fluorescence microscopy and manipulation of INF2 levels in cells indicate that INF2 plays a critical role at the SF–FA junction by promoting actin polymerization via free barbed end generation and centripetal elongation of an FA-associated actin bundle to form dorsal SF. INF2 assembles into FAs during maturation rather than during their initial generation, and once there, acts to promote rapid FA elongation and maturation into tensin-containing fibrillar FAs in the cell center. We show that INF2 is required for fibroblasts to organize fibronectin into matrix fibers and ultimately 3D matrices. Collectively our results indicate an important role for the formin INF2 in specifying the function of fibrillar FAs through its ability to generate dorsal SFs. Thus, dorsal SFs and fibrillar FAs form a specific class of integrated adhesion-associated actin structure in fibroblasts that mediates generation and remodeling of ECM. PMID:25918420

  20. Parallel expression evolution of oxidative stress-related genes in fiber from wild and domesticated diploid and polyploid cotton (Gossypium)

    PubMed Central

    2009-01-01

    Background Reactive oxygen species (ROS) play a prominent role in signal transduction and cellular homeostasis in plants. However, imbalances between generation and elimination of ROS can give rise to oxidative stress in growing cells. Because ROS are important to cell growth, ROS modulation could be responsive to natural or human-mediated selection pressure in plants. To study the evolution of oxidative stress related genes in a single plant cell, we conducted comparative expression profiling analyses of the elongated seed trichomes ("fibers") of cotton (Gossypium), using a phylogenetic approach. Results We measured expression changes during diploid progenitor species divergence, allopolyploid formation and parallel domestication of diploid and allopolyploid species, using a microarray platform that interrogates 42,429 unigenes. The distribution of differentially expressed genes in progenitor diploid species revealed significant up-regulation of ROS scavenging and potential signaling processes in domesticated G. arboreum. Similarly, in two independently domesticated allopolyploid species (G. barbadense and G. hirsutum) antioxidant genes were substantially up-regulated in comparison to antecedent wild forms. In contrast, analyses of three wild allopolyploid species indicate that genomic merger and ancient allopolyploid formation had no significant influences on regulation of ROS related genes. Remarkably, many of the ROS-related processes diagnosed as possible targets of selection were shared among diploid and allopolyploid cultigens, but involved different sets of antioxidant genes. Conclusion Our data suggests that parallel human selection for enhanced fiber growth in several geographically widely dispersed species of domesticated cotton resulted in similar and overlapping metabolic transformations of the manner in which cellular redox levels have become modulated. PMID:19686594

  1. Single all-optical platform for measurement of twist and transverse stress using polarization modulation in distinct dual-mode fiber placed in a Sagnac loop.

    PubMed

    Khan, Saba N; Chatterjee, Sudip K; Chaudhuri, Partha Roy

    2016-01-01

    We report here the experimental demonstration of measurement of both twist and transverse stress using polarization modulation in a single all-fiber circuit consisting of a single-mode fiber (SMF)/dual-mode fiber (DMF) in a Sagnac interferometer (SI) loop. The SMF-SI prototype setup is seen to be suitable for precise measurement of twist over a broad range of ±50° and transverse stress up to 5 N with a sensitivity as high as 2.85×10(6)  pW/° and 2.08×10(7)  pW/N, respectively. It is envisaged that nearly ideal operation for twist measurement can be achieved by appropriately selecting the operating domain (pretwisted Sagnac loop for practical realization of the device) and required magnitude of applied transverse stress (weight yielding maximum sensitivity). Unlike SMF-SI, a DMF assisted SI exhibits asymmetric transmittance yielding a peak shift (∼45°) in addition to falling/rising peak amplitude of effective power(∼20  μW). This key characteristic is further utilized for tunable measurement of torsion (unidirectional from -70° to 40°) while keeping the sensitivity fixed. This research problem is then analyzed on the avenue of theoretical consideration and using classical polarization optics; we have derived the Jones birefringence matrix that accurately describes the transmission behavior of the configured fiber circuit (SMF-SI and DMF-SI) for each of the three cases, namely, transverse stress, twist, and both twist and transverse stress. Series of experimental measurements for various conditions of induced birefringence (linear/circular) were performed at length, and the results were compared with those determined theoretically towards configuring a twist and stress measuring device. The study provides an understanding of the underlying physics of dual-mode interference in a Sagnac configuration experiencing linear and circular birefringence. PMID:26831594

  2. Quasi-interferometric scheme improved by fiber Bragg grating for detection of outer mechanical stress influence on distributed sensor being silica multimode optical fiber operating in a few-mode regime

    NASA Astrophysics Data System (ADS)

    Kafarova, Anastasia M.; Faskhutdinov, Lenar M.; Kuznetzov, Artem A.; Minaeva, Alina Y.; Sevruk, Nikita L.; Nureev, Ilnur I.; Vasilets, Alexander A.; Bourdine, Anton V.; Morozov, Oleg G.; Burdin, Vladimir A.

    2016-03-01

    This work presents results of experimental approbation of modified fiber optic stress sensor based on a few-mode effects occurring during laser-excited optical signal propagation over silica multimode optical fiber (MMF). Modification is concerned with adding of quasi-interferometric scheme realized by two multimode Y-couplers with equalized arm lengths improved by fiber Bragg grating (FBG) and special offset launching conditions providing laser-based excitation of higher-order modes. We tested FBGs written on graded-index MMFs 50/125 with Bragg wavelength 1550 nm connected to different parts of proposed scheme. Researches are focused on comparing analysis of both spectral and pulse responses under changing of selected mode mixing and power diffusion processes due to stress local and distributed action to sensor fiber depending on scheme configuration. Here we considered FBGs not only as particular wavelength reflector during spectral response measurement but also as local periodic microstructure defect strongly effecting few-mode signal components mixing process that provides pulse response variation. Some results of spectral and pulse response measurements produced for different scheme configuration and their comparison analysis are represented.

  3. Weathering effects on tensile and stress rupture strength of glass fiber reinforced vinylester and epoxy thermoset pipes

    NASA Astrophysics Data System (ADS)

    Nizamuddin, Syed

    Glass fiber reinforced vinylester (GFRE) and epoxy (GFRE) pipes have been used for more than three decades to mitigate corrosion problems in oil fields, chemical and industrial plants. In these services, both GFRV and GFRE pipes are exposed to various environmental conditions. Long-term mechanical durability of these pipes after exposure to environmental conditions, which include natural weathering exposure to seasonal temperature variation, sea water, humidity and other corrosive fluids like crude oil, should be well known. Although extensive research has been undertaken, several major issues pertaining to the performance of these pipes under a number of environmental conditions still remain unresolved. The main objective of this study is to investigate the effects of natural weathering, combined natural weathering with seawater and crude oil exposure, for time periods ranging from 3 to 36 months respectively, on the tensile and stress rupture behavior of GFRV and GFRE pipes. Ring specimens are machined from GFRV and GFRE pipes and tested before and after exposure to different weathering conditions prevalent in the eastern region (Dhahran) of Saudi Arabia and present under service conditions. The natural weathering and combined natural weathering with crude oil exposure of GFRV specimens revealed increased tensile strength even after 36 months of exposure when compared with that of the as received samples. However, the combined natural weathering with seawater exposure of GFRV samples revealed better tensile behavior till 24 months of exposure, and after 36 months their tensile strength was seen to be below that of the as received GFRV samples. The stress rupture behavior of natural weather exposed GFRV samples showed an improvement after 12 months of exposure and it decreased after 24 and 36 months of exposure when compared with the as received GFRV samples. The combined natural weathering with crude oil and seawater exposure of GFRV sample revealed improved

  4. Fiber Breakage Model for Carbon Composite Stress Rupture Phenomenon: Theoretical Development and Applications

    NASA Technical Reports Server (NTRS)

    Murthy, Pappu L. N.; Phoenix, S. Leigh; Grimes-Ledesma, Lorie

    2010-01-01

    Stress rupture failure of Carbon Composite Overwrapped Pressure Vessels (COPVs) is of serious concern to Science Mission and Constellation programs since there are a number of COPVs on board space vehicles with stored gases under high pressure for long durations of time. It has become customary to establish the reliability of these vessels using the so called classic models. The classical models are based on Weibull statistics fitted to observed stress rupture data. These stochastic models cannot account for any additional damage due to the complex pressure-time histories characteristic of COPVs being supplied for NASA missions. In particular, it is suspected that the effects of proof test could significantly reduce the stress rupture lifetime of COPVs. The focus of this paper is to present an analytical appraisal of a model that incorporates damage due to proof test. The model examined in the current paper is based on physical mechanisms such as micromechanics based load sharing concepts coupled with creep rupture and Weibull statistics. For example, the classic model cannot accommodate for damage due to proof testing which every flight vessel undergoes. The paper compares current model to the classic model with a number of examples. In addition, several applications of the model to current ISS and Constellation program issues are also examined.

  5. Residual stress and debonding analysis using a fiber Bragg grating in a model composite specimen

    NASA Astrophysics Data System (ADS)

    Colpo, F.; Dunkel, G.; Humbert, L.; Botsis, J.

    2005-05-01

    Optical Fibre Bragg Grating (FBG) sensors are excellent non-destructive tools for internal strain characterization of composite materials and structures. They can be embedded at selected locations during material preparation to provide accurate in-situ measurements. In this study, long-gauge-FBGs are introduced in cylindrical specimens of epoxy. This configuration is particularly attractive because it simplifies the study of some relevant phenomena in micromechanics of composites, for instance residual stresses and fracture of the fibre-matrix interface. Because the matrix epoxy shrinks during the polymerisation process, the optical sensor undergoes substantial non-uniform strain along the fibre. The response of a FBG to a non-uniform strain distribution is investigated using a new Optical Low-Coherence Reflectometry (OLCR) technique developed at EPFL. This method provides a direct reconstruction of the optical period and the corresponding strain distribution along the grating without any a priori assumption about the strain field. Considering the non-uniform residual strain as a reference state, new Bragg wavelength distributions are obtained for two configurations. First, a new Bragg wavelength distribution is measured as a function of the depth of circular cracks machined in the radial direction. These measurements lead to the knowledge of (a) the zone of perturbation of the reinforcing fibre on the residual stresses and (b) the effect of the presence of the mechanically induced crack on the residual stress state in the specimen. A finite element modelling of the residual stress field based on an equivalent thermo-elastic approach is also proposed, showing a very good agreement with experimental data. Second, an interface crack (debonding) between the epoxy and the fibre is introduced by fatigue and monitored using a specifically designed video acquisition system. The induced variations in the FBG response are measured when the fibre is unloaded and then

  6. Stress and strain analysis of the bone-implant interface: a comparison of fiber-reinforced composite and titanium implants utilizing 3-dimensional finite element study.

    PubMed

    Shinya, Akikazu; Ballo, Ahmed M; Lassila, Lippo V J; Shinya, Akiyoshi; Närhi, Timo O; Vallittu, Pekka K

    2011-03-01

    This study analyzed stress and strain mediated by 2 different implant materials, titanium (Ti) and experimental fiber-reinforced composite (FRC), on the implant and on the bone tissue surrounding the implant. Three-dimensional finite element models constructed from a mandibular bone and an implant were subjected to a load of 50 N in vertical and horizontal directions. Postprocessing files allowed the calculation of stress and strain within the implant materials and stresses at the bone-to-implant interface (stress path). Maximum stress concentrations were located around the implant on the rim of the cortical bone in both implant materials; Ti and overall stresses decreased toward the Ti implant apex. In the FRC implant, a stress value of 0.6 to 2.0 MPa was detected not only on the screw threads but also on the implant surface between the threads. Clear differences were observed in the strain distribution between the materials. Based on the results, the vertical load stress range of the FRC implant was close to the stress level for optimal bone growth. Furthermore, the stress at the bone around the FRC implant was more evenly distributed than that with Ti implant. PMID:20545537

  7. The Self Actualized Reader.

    ERIC Educational Resources Information Center

    Marino, Michael; Moylan, Mary Elizabeth

    A study examined the commonalities that "voracious" readers share, and how their experiences can guide parents, teachers, and librarians in assisting children to become self-actualized readers. Subjects, 25 adults ranging in age from 20 to 67 years, completed a questionnaire concerning their reading histories and habits. Respondents varied in…

  8. Temperature Dependence on the Strength and Stress Rupture Behavior of a Carbon-Fiber Reinforced Silicon Carbide (C/SiC) Composite

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.; Calomino, Anthony

    2002-01-01

    Tensile strengths and stress rupture lives of carbon-fiber reinforced silicon carbide (C/SiC) specimens were measured at 800 C and are compared to previously reported 1200 C data. All tests were conducted in an environmental chamber containing 1000 ppm of oxygen in argon. The average 800 C tensile strength of 610 MPa is 10% greater than at 1200 C. Average stress rupture lives at 800 C were 2.5 times longer than those obtained at 1200 C. The difference in the 800 and 1200 C lives is related to the oxidation rate of the reinforcing carbon fibers, which is the primary damage mode of C/SiC composites in oxygen-containing environments.

  9. Ephrin-Bs Drive Junctional Downregulation and Actin Stress Fiber Disassembly to Enable Wound Re-epithelialization

    PubMed Central

    Nunan, Robert; Campbell, Jessica; Mori, Ryoichi; Pitulescu, Mara E.; Jiang, Wen G.; Harding, Keith G.; Adams, Ralf H.; Nobes, Catherine D.; Martin, Paul

    2015-01-01

    Summary For a skin wound to successfully heal, the cut epidermal-edge cells have to migrate forward at the interface between scab and healthy granulation tissue. Much is known about how lead-edge cells migrate, but very little is known about the mechanisms that enable active participation by cells further back. Here we show that ephrin-B1 and its receptor EphB2 are both upregulated in vivo, just for the duration of repair, in the first 70 or so rows of epidermal cells, and this signal leads to downregulation of the molecular components of adherens and tight (but not desmosomal) junctions, leading to loosening between neighbors and enabling shuffle room among epidermal cells. Additionally, this signaling leads to the shutdown of actomyosin stress fibers in these same epidermal cells, which may act to release tension within the wound monolayer. If this signaling axis is perturbed, then disrupted healing is a consequence in mouse and man. PMID:26549443

  10. Ephrin-Bs Drive Junctional Downregulation and Actin Stress Fiber Disassembly to Enable Wound Re-epithelialization.

    PubMed

    Nunan, Robert; Campbell, Jessica; Mori, Ryoichi; Pitulescu, Mara E; Jiang, Wen G; Harding, Keith G; Adams, Ralf H; Nobes, Catherine D; Martin, Paul

    2015-11-17

    For a skin wound to successfully heal, the cut epidermal-edge cells have to migrate forward at the interface between scab and healthy granulation tissue. Much is known about how lead-edge cells migrate, but very little is known about the mechanisms that enable active participation by cells further back. Here we show that ephrin-B1 and its receptor EphB2 are both upregulated in vivo, just for the duration of repair, in the first 70 or so rows of epidermal cells, and this signal leads to downregulation of the molecular components of adherens and tight (but not desmosomal) junctions, leading to loosening between neighbors and enabling shuffle room among epidermal cells. Additionally, this signaling leads to the shutdown of actomyosin stress fibers in these same epidermal cells, which may act to release tension within the wound monolayer. If this signaling axis is perturbed, then disrupted healing is a consequence in mouse and man. PMID:26549443

  11. Altered stress fibers and integrin expression in the Malpighian epithelium of Drosophila type IV collagen mutants

    PubMed Central

    Kiss, András A.; Popovics, Nikoletta; Szabó, Gábor; Csiszár, Katalin; Mink, Mátyás

    2016-01-01

    Basement membranes (BMs) are highly specialized extracellular matrices (ECMs) that provide support and polarization cues for epithelial cells. Proper adhesion to the BM is pivotal in epithelial cell function and survival. Type IV collagens are the predominant components of all types of BMs, that form an irregular, polygonal lattice and serve as a scaffold for numerous other BM components and BM-associated cells. Mutations in the ubiquitous human BM components COL4A1 and COL4A2 cause a multisystem disorder involving nephropathy. Affected patients develop renal dysfunction and chronic kidney failure with or without hematuria. Mouse Col4a1 and Col4a2 mutants recapitulate the human symptoms. In vertebrates, excretion is accomplished by the kidneys and by the Malpighian tubules in insects, including the fruit fly Drosophila. Our present results with dominant, temperature-sensitive mutation of the Drosophila col4a1 gene demonstrate altered integrin expression and amplified effects of mechanical stress on the Malpighian epithelial cytoskeleton. PMID:27077087

  12. Altered stress fibers and integrin expression in the Malpighian epithelium of Drosophila type IV collagen mutants.

    PubMed

    Kiss, András A; Popovics, Nikoletta; Szabó, Gábor; Csiszár, Katalin; Mink, Mátyás

    2016-06-01

    Basement membranes (BMs) are highly specialized extracellular matrices (ECMs) that provide support and polarization cues for epithelial cells. Proper adhesion to the BM is pivotal in epithelial cell function and survival. Type IV collagens are the predominant components of all types of BMs, that form an irregular, polygonal lattice and serve as a scaffold for numerous other BM components and BM-associated cells. Mutations in the ubiquitous human BM components COL4A1 and COL4A2 cause a multisystem disorder involving nephropathy. Affected patients develop renal dysfunction and chronic kidney failure with or without hematuria. Mouse Col4a1 and Col4a2 mutants recapitulate the human symptoms. In vertebrates, excretion is accomplished by the kidneys and by the Malpighian tubules in insects, including the fruit fly Drosophila. Our present results with dominant, temperature-sensitive mutation of the Drosophila col4a1 gene demonstrate altered integrin expression and amplified effects of mechanical stress on the Malpighian epithelial cytoskeleton. PMID:27077087

  13. SFRR-E Young Investigator AwardeeαB-crystallin modulation after acute exercise in skeletal muscle: the role of oxidative stress and fiber composition.

    PubMed

    Grazioli, Elisa; Dimauro, Ivan; Mercatelli, Neri; Barone, Rosario; Macaluso, Filippo; Fittipaldi, Simona; Di Felice, Valentina; Caporossi, Daniela

    2014-10-01

    αB-crystallin (CRYAB) is a member of the small heat shock proteins implicated in various biological functions, particularly in skeletal muscle where it is involved in adaptive remodelling processes, activation of gene transcription and stabilization of nascent proteins.In this research we analysed αB-crystallin' response in mouse gastrocnemius at 15' and 30' of recovery from an acute aerobic exercise (1hour), correlating its modulation with oxidative stress level and fiber composition, red (RG) and white gastrocnemius (WG).We found for the first time that the acute exercise lead to a short term, specific increase of phospho-αB-crystallin level (pCRYAB) in the RG, while no changes were observed in the WG. Moreover, this induction was correlated with increased level of 4-hydroxynonenal (HNE),suggesting a putative role for oxidative stress in driving CRYAB, but not hsp70 or hsp27, activity during exercise. Any increased level of αB-crystallin' protein was observed neither in RG nor in WG. These data were also supported by our in vitro experiments showing a significant enhancement of pCRYAB in H2O2-treated C2C12 myotubes.Although our results seem suggest a fiber-dependent role of CRYAB, further experiments are in progress to clarify both the molecular pathway driving CRYAB phosphorylation and its fiber-specific induction after exercise -induced oxidative stress.This work was supported by MIUR - PRIN 2012 grant. PMID:26461288

  14. Arg Kinase-binding Protein 2 (ArgBP2) Interaction with α-Actinin and Actin Stress Fibers Inhibits Cell Migration*

    PubMed Central

    Anekal, Praju Vikas; Yong, Jeffery; Manser, Ed

    2015-01-01

    Cell migration requires dynamic remodeling of the actomyosin network. We report here that an adapter protein, ArgBP2, is a component of α-actinin containing stress fibers and inhibits migration. ArgBP2 is undetectable in many commonly studied cancer-derived cell lines. COS-7 and HeLa cells express ArgBP2 (by Western analysis), but expression was detectable only in approximately half the cells by immunofluorescence. Short term clonal analysis demonstrated 0.2–0.3% of cells switch ArgBP2 expression (on or off) per cell division. ArgBP2 can have a fundamental impact on the actomyosin network: ArgBP2 positive COS-7 cells, for example, are clearly distinguishable by their denser actomyosin (stress fiber) network. ArgBP2γ binding to α-actinin appears to underlie its ability to localize to stress fibers and decrease cell migration. We map a small α-actinin binding region in ArgBP2 (residues 192–228) that is essential for these effects. Protein kinase A phosphorylation of ArgBP2γ at neighboring Ser-259 and consequent 14-3-3 binding blocks its interaction with α-actinin. ArgBP2 is known to be down-regulated in some aggressively metastatic cancers. Our work provides a biochemical explanation for the anti-migratory effect of ArgBP2. PMID:25429109

  15. Comment on 'Shang S. 2012. Calculating actual crop evapotranspiration under soil water stress conditions with appropriate numerical methods and time step. Hydrological Processes 26: 3338-3343. DOI: 10.1002/hyp.8405'

    NASA Technical Reports Server (NTRS)

    Yatheendradas, Soni; Narapusetty, Balachandrudu; Peters-Lidard, Christa; Funk, Christopher; Verdin, James

    2014-01-01

    A previous study analyzed errors in the numerical calculation of actual crop evapotranspiration (ET(sub a)) under soil water stress. Assuming no irrigation or precipitation, it constructed equations for ET(sub a) over limited soil-water ranges in a root zone drying out due to evapotranspiration. It then used a single crop-soil composite to provide recommendations about the appropriate usage of numerical methods under different values of the time step and the maximum crop evapotranspiration (ET(sub c)). This comment reformulates those ET(sub a) equations for applicability over the full range of soil water values, revealing a dependence of the relative error in numerical ET(sub a) on the initial soil water that was not seen in the previous study. It is shown that the recommendations based on a single crop-soil composite can be invalid for other crop-soil composites. Finally, a consideration of the numerical error in the time-cumulative value of ET(sub a) is discussed besides the existing consideration of that error over individual time steps as done in the previous study. This cumulative ET(sub a) is more relevant to the final crop yield.

  16. Humanistic Education and Self-Actualization Theory.

    ERIC Educational Resources Information Center

    Farmer, Rod

    1984-01-01

    Stresses the need for theoretical justification for the development of humanistic education programs in today's schools. Explores Abraham Maslow's hierarchy of needs and theory of self-actualization. Argues that Maslow's theory may be the best available for educators concerned with educating the whole child. (JHZ)

  17. Conditional knockout of Mn-SOD targeted to type IIB skeletal muscle fibers increases oxidative stress and is sufficient to alter aerobic exercise capacity

    PubMed Central

    Lustgarten, Michael S.; Jang, Youngmok C.; Liu, Yuhong; Muller, Florian L.; Qi, Wenbo; Steinhelper, Mark; Brooks, Susan V.; Larkin, Lisa; Shimizu, Takahiko; Shirasawa, Takuji; McManus, Linda M.; Bhattacharya, Arunabh; Richardson, Arlan

    2009-01-01

    In vitro studies of isolated skeletal muscle have shown that oxidative stress is limiting with respect to contractile function. Mitochondria are a potential source of muscle function-limiting oxidants. To test the hypothesis that skeletal muscle-specific mitochondrial oxidative stress is sufficient to limit muscle function, we bred mice expressing Cre recombinase driven by the promoter for the inhibitory subunit of troponin (TnIFast-iCre) with mice containing a floxed Sod2 (Sod2fl/fl) allele. Mn-SOD activity was reduced by 82% in glycolytic (mainly type II) muscle fiber homogenates from young TnIFastCreSod2fl/fl mice. Furthermore, Mn-SOD content was reduced by 70% only in type IIB muscle fibers. Aconitase activity was decreased by 56%, which suggests an increase in mitochondrial matrix superoxide. Mitochondrial superoxide release was elevated more than twofold by mitochondria isolated from glycolytic skeletal muscle in TnIFastCreSod2fl/fl mice. In contrast, the rate of mitochondrial H2O2 production was reduced by 33%, and only during respiration with complex II substrate. F2-isoprostanes were increased by 36% in tibialis anterior muscles isolated from TnIFastCreSod2fl/fl mice. Elevated glycolytic muscle-specific mitochondrial oxidative stress and damage in TnIFastCreSod2fl/fl mice were associated with a decreased ability of the extensor digitorum longus and gastrocnemius muscles to produce contractile force as a function of time, whereas force production by the soleus muscle was unaffected. TnIFastCreSod2fl/fl mice ran 55% less distance on a treadmill than wild-type mice. Collectively, these data suggest that elevated mitochondrial oxidative stress and damage in glycolytic muscle fibers are sufficient to reduce contractile muscle function and aerobic exercise capacity. PMID:19776389

  18. Stress-Dependent Matrix Cracking in 2D Woven SiC-Fiber Reinforced Melt-Infiltrated SiC Matrix Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.

    2003-01-01

    The matrix cracking of a variety of SiC/SiC composites has been characterized for a wide range of constituent variation. These composites were fabricated by the 2-dimensional lay-up of 0/90 five-harness satin fabric consisting of Sylramic fiber tows that were then chemical vapor infiltrated (CVI) with BN, CVI with SiC, slurry infiltrated with SiC particles followed by molten infiltration of Si. The composites varied in number of plies, the number of tows per length, thickness, and the size of the tows. This resulted in composites with a fiber volume fraction in the loading direction that ranged from 0.12 to 0.20. Matrix cracking was monitored with modal acoustic emission in order to estimate the stress-dependent distribution of matrix cracks. It was found that the general matrix crack properties of this system could be fairly well characterized by assuming that no matrix cracks originated in the load-bearing fiber, interphase, chemical vapor infiltrated Sic tow-minicomposites, i.e., all matrix cracks originate in the 90 degree tow-minicomposites or the large unreinforced Sic-Si matrix regions. Also, it was determined that the larger tow size composites had a much narrower stress range for matrix cracking compared to the standard tow size composites.

  19. Formation of contractile networks and fibers in the medial cell cortex through myosin-II turnover, contraction, and stress-stabilization.

    PubMed

    Nie, Wei; Wei, Ming-Tzo; Ou-Yang, H Daniel; Jedlicka, Sabrina S; Vavylonis, Dimitrios

    2015-01-01

    The morphology of adhered cells depends crucially on the formation of a contractile meshwork of parallel and cross-linked fibers along the contacting surface. The motor activity and minifilament assembly of non-muscle myosin-II is an important component of cortical cytoskeletal remodeling during mechanosensing. We used experiments and computational modeling to study cortical myosin-II dynamics in adhered cells. Confocal microscopy was used to image the medial cell cortex of HeLa cells stably expressing myosin regulatory light chain tagged with GFP (MRLC-GFP). The distribution of MRLC-GFP fibers and focal adhesions was classified into three types of network morphologies. Time-lapse movies show: myosin foci appearance and disappearance; aligning and contraction; stabilization upon alignment. Addition of blebbistatin, which perturbs myosin motor activity, leads to a reorganization of the cortical networks and to a reduction of contractile motions. We quantified the kinetics of contraction, disassembly and reassembly of myosin networks using spatio-temporal image correlation spectroscopy (STICS). Coarse-grained numerical simulations include bipolar minifilaments that contract and align through specified interactions as basic elements. After assuming that minifilament turnover decreases with increasing contractile stress, the simulations reproduce stress-dependent fiber formation in between focal adhesions above a threshold myosin concentration. The STICS correlation function in simulations matches the function measured in experiments. This study provides a framework to help interpret how different cortical myosin remodeling kinetics may contribute to different cell shape and rigidity depending on substrate stiffness. PMID:25641802

  20. Composite Overwrap Pressure Vessels: Mechanics and Stress Rupture Lifting Philosophy

    NASA Technical Reports Server (NTRS)

    Thesken, John C.; Murthy, Pappu L. N.; Phoenix, S. L.

    2009-01-01

    The NASA Engineering and Safety Center (NESC) has been conducting an independent technical assessment to address safety concerns related to the known stress rupture failure mode of filament wound pressure vessels in use on Shuttle and the International Space Station. The Shuttle s Kevlar-49 (DuPont) fiber overwrapped tanks are of particular concern due to their long usage and the poorly understood stress rupture process in Kevlar-49 filaments. Existing long term data show that the rupture process is a function of stress, temperature and time. However due to the presence of load sharing liners and the complex manufacturing procedures, the state of actual fiber stress in flight hardware and test articles is not clearly known. Indeed nonconservative life predictions have been made where stress rupture data and lifing procedures have ignored the contribution of the liner in favor of applied pressure as the controlling load parameter. With the aid of analytical and finite element results, this paper examines the fundamental mechanical response of composite overwrapped pressure vessels including the influence of elastic plastic liners and degraded/creeping overwrap properties. Graphical methods are presented describing the non-linear relationship of applied pressure to Kevlar-49 fiber stress/strain during manufacturing, operations and burst loadings. These are applied to experimental measurements made on a variety of vessel systems to demonstrate the correct calibration of fiber stress as a function of pressure. Applying this analysis to the actual qualification burst data for Shuttle flight hardware revealed that the nominal fiber stress at burst was in some cases 23 percent lower than what had previously been used to predict stress rupture life. These results motivate a detailed discussion of the appropriate stress rupture lifing philosophy for COPVs including the correct transference of stress rupture life data between dissimilar vessels and test articles.

  1. Composite Overwrap Pressure Vessels: Mechanics and Stress Rupture Lifing Philosophy

    NASA Technical Reports Server (NTRS)

    Thesken, John C.; Murthy, Pappu L. N.; Phoenix, Leigh

    2007-01-01

    The NASA Engineering and Safety Center (NESC) has been conducting an independent technical assessment to address safety concerns related to the known stress rupture failure mode of filament wound pressure vessels in use on Shuttle and the International Space Station. The Shuttle's Kevlar-49 fiber overwrapped tanks are of particular concern due to their long usage and the poorly understood stress rupture process in Kevlar-49 filaments. Existing long term data show that the rupture process is a function of stress, temperature and time. However due to the presence of load sharing liners and the complex manufacturing procedures, the state of actual fiber stress in flight hardware and test articles is not clearly known. Indeed non-conservative life predictions have been made where stress rupture data and lifing procedures have ignored the contribution of the liner in favor of applied pressure as the controlling load parameter. With the aid of analytical and finite element results, this paper examines the fundamental mechanical response of composite overwrapped pressure vessels including the influence of elastic-plastic liners and degraded/creeping overwrap properties. Graphical methods are presented describing the non-linear relationship of applied pressure to Kevlar-49 fiber stress/strain during manufacturing, operations and burst loadings. These are applied to experimental measurements made on a variety of vessel systems to demonstrate the correct calibration of fiber stress as a function of pressure. Applying this analysis to the actual qualification burst data for Shuttle flight hardware revealed that the nominal fiber stress at burst was in some cases 23% lower than what had previously been used to predict stress rupture life. These results motivate a detailed discussion of the appropriate stress rupture lifing philosophy for COPVs including the correct transference of stress rupture life data between dissimilar vessels and test articles.

  2. Whole optic fiber weighing technique and device of belt conveyor

    NASA Astrophysics Data System (ADS)

    Li, Weilai; Liu, Jie; Pan, Jianjun

    2015-07-01

    Whole optic fiber weighing technique and its device of belt conveyor are developed and put into application. Four FBG stress cells support a frame in a belt conveying line. In each cell, two FBG strain gauges are respectively installed at the stretching and compressing places to get the effects of sensitivity enhancement and temperature compensation. The weighing signals are from both FBG wavelength shift of loading cells and fiber belt speed meter. By means of integral algorithm, the weighing result is obtained. Actual coal weighing test shows that the accuracy of this weighing device is under 0.5%.

  3. Changes of nitric oxide synthase-containing nerve fibers and parameters for oxidative stress after unilateral cavernous nerve resection or manuplation in rat penis.

    PubMed

    Ozkara, Hamdi; Alan, Cabir; Atukeren, Pinar; Uyaner, Ilhan; Demirci, Cihan; Gümüştaş, M Koray; Alici, Bulent

    2006-06-30

    After pelvic surgeries such as radical prostatectomy, two major complications--urinary incontinence and erectile dysfunction (ED) may occur. Etiologies for ED are multiple pathologic mediators/systems. Oxidative stress, which is known to be induced after surgical trauma, could be a cause of ED. The purposes of in this study are to investigate the effect of unilateral manipulation/ dissection and resection of the cavernous nerve (neurotomy) to NOS (nitric oxide synthase)-containing nerve fibers and pressure after electro stimulation in rat corpus cavernosum, and to determine whether these procedures would produce oxidative stress within rat cavernous tissue 3 weeks and 6 months after the operation. Male rats were divided into 5 groups. Rats in groups 1 and 2 underwent unilateral cavernous nerve manipulation and sacrificed 3 weeks and 6 months after the operation, respectively. Rats in groups 3 and 4 underwent unilateral neurotomy of a 5-mm. segment of the cavernous nerve, and they were sacrificed 3 weeks and 6 months after nerve ablation, respectively. Group 5 rats were control animals for biochemical analysis. Intracavernous pressure following electro stimulation reduced is significantly 3 weeks after unilateral resection, as compared to that of the manipulated nerve (P < 0.05), and it recovered 6 months after neurotomy. The recovery was also confirmed by NADPH (nicotinamide adenine dinucleotide phosphate) diaphorase staining in neurotomy groups. Lipid peroxidation, which is an indicater of oxidative stress, was determined by measuring thiobarbituric acid reacting substance (TBARS) levels and superoxide dismutase (SOD) activity. These markers indicated that unilateral cavernous nerve manipulation or resection produced oxidative stress within rat corpus cavernosum. Oxidative stress was more prominent 3 weeks after unilateral neurotomy (P < 0.05). Also, compared to the control animal group, oxidative stress was observed three weeks after manipulation of unilateral

  4. Stress

    MedlinePlus

    ... sudden negative change, such as losing a job, divorce, or illness Traumatic stress, which happens when you ... stress, so you can avoid more serious health effects. NIH: National Institute of Mental Health

  5. An Elastic-Plastic Damage Model for Long-Fiber Thermoplastics

    SciTech Connect

    Nguyen, Ba Nghiep; Kunc, Vlastimil

    2009-08-11

    This article proposes an elastic-plastic damage model that combines micromechanical modeling with continuum damage mechanics to predict the stress-strain response of injection-molded long-fiber thermoplastics. The model accounts for distributions of orientation and length of elastic fibers embedded in a thermoplastic matrix whose behavior is elastic-plastic and damageable. The elastic-plastic damage behavior of the matrix is described by the modified Ramberg-Osgood relation and the three-dimensional damage model in deformation assuming isotropic hardening. Fiber/matrix debonding is accounted for using a parameter that governs the fiber/matrix interface compliance. A linear relationship between this parameter and the matrix damage variable is assumed. First, the elastic-plastic damage behavior of the reference aligned-fiber composite containing the same fiber volume fraction and length distribution as the actual composite is computed using an incremental Eshelby-Mori-Tanaka mean field approach. The incremental response of the latter is then obtained from the solution for the aligned-fiber composite by averaging over all fiber orientations. The model is validated against the experimental stress-strain results obtained for long-glass-fiber/polypropylene specimens.

  6. Black Beans, Fiber, and Antioxidant Capacity Pilot Study: Examination of Whole Foods vs. Functional Components on Postprandial Metabolic, Oxidative Stress, and Inflammation in Adults with Metabolic Syndrome.

    PubMed

    Reverri, Elizabeth J; Randolph, Jody M; Steinberg, Francene M; Kappagoda, C Tissa; Edirisinghe, Indika; Burton-Freeman, Britt M

    2015-08-01

    Beans (Phaseolus vulgaris) contain bioactive components with functional properties that may modify cardiovascular risk. The aims of this pilot study were to evaluate the ability of black beans to attenuate postprandial metabolic, oxidative stress, and inflammatory responses and determine relative contribution of dietary fiber and antioxidant capacity of beans to the overall effect. In this randomized, controlled, crossover trial, 12 adults with metabolic syndrome (MetS) consumed one of three meals (black bean (BB), fiber matched (FM), and antioxidant capacity matched (AM)) on three occasions that included blood collection before (fasting) and five hours postprandially. Insulin was lower after the BB meal, compared to the FM or AM meals (p < 0.0001). A significant meal × time interaction was observed for plasma antioxidant capacity (p = 0.002) revealing differences over time: AM > BB > FM. Oxidized LDL (oxLDL) was not different by meal, although a trend for declining oxLDL was observed after the BB and AM meals at five hours compared to the FM meal. Triglycerides and interleukin-6 (IL-6) increased in response to meals (p < 0.0001). Inclusion of black beans with a typical Western-style meal attenuates postprandial insulin and moderately enhances postprandial antioxidant endpoints in adults with MetS, which could only be partly explained by fiber content and properties of antioxidant capacity. PMID:26225995

  7. Black Beans, Fiber, and Antioxidant Capacity Pilot Study: Examination of Whole Foods vs. Functional Components on Postprandial Metabolic, Oxidative Stress, and Inflammation in Adults with Metabolic Syndrome

    PubMed Central

    Reverri, Elizabeth J.; Randolph, Jody M.; Steinberg, Francene M.; Kappagoda, C. Tissa; Edirisinghe, Indika; Burton-Freeman, Britt M.

    2015-01-01

    Beans (Phaseolus vulgaris) contain bioactive components with functional properties that may modify cardiovascular risk. The aims of this pilot study were to evaluate the ability of black beans to attenuate postprandial metabolic, oxidative stress, and inflammatory responses and determine relative contribution of dietary fiber and antioxidant capacity of beans to the overall effect. In this randomized, controlled, crossover trial, 12 adults with metabolic syndrome (MetS) consumed one of three meals (black bean (BB), fiber matched (FM), and antioxidant capacity matched (AM)) on three occasions that included blood collection before (fasting) and five hours postprandially. Insulin was lower after the BB meal, compared to the FM or AM meals (p < 0.0001). A significant meal × time interaction was observed for plasma antioxidant capacity (p = 0.002) revealing differences over time: AM > BB > FM. Oxidized LDL (oxLDL) was not different by meal, although a trend for declining oxLDL was observed after the BB and AM meals at five hours compared to the FM meal. Triglycerides and interleukin-6 (IL-6) increased in response to meals (p < 0.0001). Inclusion of black beans with a typical Western-style meal attenuates postprandial insulin and moderately enhances postprandial antioxidant endpoints in adults with MetS, which could only be partly explained by fiber content and properties of antioxidant capacity. PMID:26225995

  8. Use of an ultrasonic-acoustic technique for nondestructive evaluation of fiber composite strength

    NASA Technical Reports Server (NTRS)

    Vary, A.; Bowles, K. J.

    1978-01-01

    This report describes the ultrasonic-acoustic technique used to measure a 'Stress Wave Factor'. In a prior study this factor was found effective in evaluating the interlaminar shear strength of fiber-reinforced composites. Details of the method used to measure the stress wave factor are described. In addition, frequency spectra of the stress waves are analyzed in order to clarify the nature of the wave phenomena involved. The stress wave factor can be measured with simple contact probes requiring only one-side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus measure material properties in directions assumed by actual loads. Moreover, the technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite/polyimide composite panels and results obtained are compared with through transmission immersion ultrasonic scans.

  9. The stress-strain relationships in wood and fiber-reinforced plastic laminae of reinforced glued-laminated wood beams

    NASA Astrophysics Data System (ADS)

    Tingley, Daniel Arthur

    The reinforcement of wood and wood composite structural products to improve their mechanical properties has been in practice for many years. Recently, the use of high-strength fiber-reinforced plastic (FRP) as a reinforcement in such applications has been commercialized. The reinforcement is manufactured using a standard pultrusion process or alternatively a sheet-forming process commonly referred to as "pulforming". The high-modulus fibers are predominately unidirectional, although off-axis fibers are often used to enhance off-axis properties. The fibers used are either of a single type or multiple types, which are called "hybrids". Unidirectional, single, and hybrid fiber FRP physical properties and characteristics were compared to wood. Full-scale reinforced glulams were tested. Aramid-reinforced plastics (ARP) used as tensile reinforcements were found to be superior in strength applications to other types of FRP made with fiber, such as carbon and fiberglass. Carbon/aramid-reinforced plastic (CARP) was shown to be superior in both modulus and strength design situations. Fiberglass was shown to be suitable only in hybrid situations with another fiber such as aramid or carbon and only in limited use situations where modulus was a design criteria. The testing and analysis showed that the global response of reinforced glulam beams is controlled by localized strength variations in the wood such as slope of grain, knots, finger joints, etc. in the tensile zone. The elemental tensile strains in the extreme wood tensile laminae, due to global applied loads, were found to be well below the strain at failure in clear wood samples recovered from the failure area. Two areas affecting the relationship between the wood and the FRP were investigated: compatibility of the wood and FRP materials and interface characteristics between the wood and FRP. The optimum strain value at yield point for an FRP was assessed to be slightly higher than the clear wood value in tension for a

  10. On the thermally-induced residual stresses in thick fiber-thermoplastic matrix (PEEK) cross-ply laminated plates

    NASA Technical Reports Server (NTRS)

    Hu, Shoufeng; Nairn, John A.

    1992-01-01

    An analytical method for calculating thermally-induced residual stresses in laminated plates is applied to cross-ply PEEK laminates. We considered three cooling procedures: slow cooling (uniform temperature distribution); convective and radiative cooling; and rapid cooling by quenching (constant surface temperature). Some of the calculated stresses are of sufficient magnitude to effect failure properties such as matrix microcracking.

  11. The use of lamination analysis and the Tsai-Wu stress criterion in ASME standards for fiber reinforced plastic vessels

    SciTech Connect

    Conlisk, P.J.

    1996-12-01

    The ASME publishes two standards on FRP (Fiber Reinforced Plastic) vessels: Section X of the Boiler and Pressure Vessel Code, and RTP-1 (Reinforced Thermoset Plastic Corrosion Resistant Equipment), which concerns low pressure FRP vessels. The paper describes the application of lamination theory and the Tsai-Wu tensor strength criterion to qualifying designs to the two standards. Numerical examples of application of the theory to typical laminates subjected to pure membrane, pure bending, and combined membrane and bending loads are presented.

  12. An RGD spacing of 440 nm is sufficient for integrin alpha V beta 3- mediated fibroblast spreading and 140 nm for focal contact and stress fiber formation

    PubMed Central

    1991-01-01

    The synthetic peptide Gly-Arg-Gly-Asp-Tyr (GRGDY), which contains the RGD sequence of several adhesion molecules, was covalently grafted to the surface of otherwise poorly adhesive glass substrates and was used to determine the minimal number of ligand-receptor interactions required for complete spreading of human foreskin fibroblasts. Well- defined adhesion substrates were prepared with GRGDY between 10(-3) fmol/cm2 and 10(4) fmol/cm2. As the adhesion ligand surface concentration was varied, several distinct morphologies of adherent cells were observed and categorized. The population of fully spread cells at 4 h reached a maximum at 1 fmol/cm2, with no further increases up to 10(4) fmol/cm2. Although maximal cell spreading was obtained at 1 fmol/cm2, focal contacts and stress fibers failed to form at RGD surface concentrations below 10 fmol/cm2. The minimal peptide spacings obtained in this work correspond to 440 nm for spreading and 140 nm for focal contact formation, and are much larger than those reported in previous studies with adsorbed adhesion proteins, adsorbed RGD-albumin conjugates, or peptide-grafted polyacrylamide gels. Vitronectin receptor antiserum specific for integrin alpha V beta 3 blocked cell adhesion and spreading on substrates containing 100 fmol/cm2 of surface- bound GRGDY, while fibronectin receptor antiserum specific for alpha 5 beta 1 did not. Furthermore, alpha V beta 3 was observed to cluster into focal contacts in spread cells, but alpha 5 beta 1 did not. It was thus concluded that a peptide-to-peptide spacing of 440 nm was required for alpha V beta 3-mediated cellular spreading, while 140 nm was required for alpha V beta 3-mediated focal contact formation and normal stress fiber organization in human foreskin fibroblasts; these spacings represent much fewer ligands than were previously thought to be required. PMID:1714913

  13. Impact resistance of fiber composites

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1982-01-01

    Stress-strain curves are obtained for a variety of glass fiber and carbon fiber reinforced plastics in dynamic tension, over the stress-strain range of 0.00087-2070/sec. The test method is of the one-bar block-to-bar type, using a rotating disk or a pendulum as the loading apparatus and yielding accurate stress-strain curves up to the breaking strain. In the case of glass fiber reinforced plastic, the tensile strength, strain to peak impact stress, total strain and total absorbed energy all increase significantly as the strain rate increases. By contrast, carbon fiber reinforced plastics show lower rates of increase with strain rate. It is recommended that hybrid composites incorporating the high strength and rigidity of carbon fiber reinforced plastic with the high impact absorption of glass fiber reinforced plastics be developed for use in structures subjected to impact loading.

  14. Polyaniline fibers, films, and powders: X-ray studies of crystallinity and stress-induced preferred orientation

    SciTech Connect

    Fischer, J.E.; Zhu, Q.; Tang, X.; Scherr, E.M.; MacDiarmid, A.G. . Lab. for Research on the Structure of Matter); Cajipe, V.B. . Inst. des Materiaux des Nantes)

    1994-08-29

    Powder (hk0) and four-circle X-ray diffractometry are used to study the effects of hot-stretching on films and fibers of the emeralidine base form of polyaniline (EB-II). It is shown definitively that hot-stretching induces nucleation of new crystalline material rather than growth and/or orientation of pre-existing crystallites. The diffuse scattering from amorphous EB-II is dominated by short-range interchain correlations and develops preferred orientation in response to stretching but with a broader mosaic than the crystalline phase. For the maximally-stretched samples, the crystal fractions was determined by accounting for the different mosaic distributions of crystalline and amorphous phases, correcting for the mass of N-methylphenazolinium plasticizer and ruling out any significant contribution from NMP diffuse scattering to the amorphous EB-II profiles. Films stretched to L/L[sub 0] = 4.25 contain no more than 4% crystalline material while fibers with L/L[sub 0] = 4.5 are 24--30% crystalline. These fractional crystallinity values are significantly small than found for EB-II powder (60%). More importantly, these results have implications for models of electric properties which invoke interchain interactions.

  15. Direct numerical simulation of active fiber composite

    NASA Astrophysics Data System (ADS)

    Kim, Seung J.; Hwang, Joon S.; Paik, Seung H.

    2003-08-01

    Active Fiber Composites (AFC) possess desirable characteristics for smart structure applications. One major advantage of AFC is the ability to create anisotropic laminate layers useful in applications requiring off-axis or twisting motions. AFC is naturally composed of two different constituents: piezoelectric fiber and matrix. Therefore, homogenization method, which is utilized in the analysis of laminated composite material, has been used to characterize the material properties. Using this approach, the global behaviors of the structures are predicted in an averaged sense. However, this approach has intrinsic limitations in describing the local behaviors in the level of the constituents. Actually, the failure analysis of AFC requires the knowledge of the local behaviors. Therefore, microscopic approach is necessary to predict the behaviors of AFC. In this work, a microscopic approach for the analysis of AFC was performed. Piezoelectric fiber and matrix were modeled separately and finite element method using three-dimensional solid elements was utilized. Because fine mesh is essential, high performance computing technology was applied to the solution of the immense degree-of-freedom problem. This approach is called Direct Numerical Simulation (DNS) of structure. Through the DNS of AFC, local stress distribution around the interface of fiber and matrix was analyzed.

  16. Lifetime-applied stress response in air of a SiC-based Nicalon-fiber-reinforced composite with a carbon interfacial layer: Effects of temperature (300 to 1150 C)

    SciTech Connect

    Becher, P.F.; Lin, Hua-Tay; More, K.L.

    1998-07-01

    The lifetimes in air as a function of applied flexure stress and temperature (300--1,150 C) are described for a Si-O-C based (Nicalon) fiber plain-weave cloth reinforced SiC-matrix composite ({approximately}7% closed porosity) with an {approximately}0.3 {micro}m thick carbon interfacial layer. The measured lifetimes of both samples with and without an external SiC seal coating were similar and decreased with applied flexural stress (for stresses greater than {approximately}90 MPa) and with temperature. At temperatures of {ge}600 C, the external CVD SiC coating had negligible effect on the lifetimes; however, at 425 C, a detectable improvement in the lifetime was observed with an external SiC coating. When the applied stress was decreased below an apparent threshold stress (e.g., {approximately}90 MPa) for tests conducted at temperatures {le}950 C, no failures were observed for times of {ge}1,000 H. Electron microscopy observations show that the interfacial carbon layer is progressively removed during tests at 425 and 600 C. In these cases, failure is associated with fiber failure and pull-out. At 950 and 1,150 C, the carbon interface layer is eliminated and replaced by a thick silica layer due to the oxidation of the Nicalon fiber and the SiC matrix. This results in embrittling the composite.

  17. Stress distribution on dentin-cement-post interface varying root canal and glass fiber post diameters. A three-dimensional finite element analysis based on micro-CT data

    PubMed Central

    LAZARI, Priscilla Cardoso; de OLIVEIRA, Rodrigo Caldeira Nunes; ANCHIETA, Rodolfo Bruniera; de ALMEIDA, Erika Oliveira; FREITAS JUNIOR, Amilcar Chagas; KINA, Sidney; ROCHA, Eduardo Passos

    2013-01-01

    Objective The aim of the present study was to analyze the influence of root canal and glass fiber post diameters on the biomechanical behavior of the dentin/cement/post interface of a root-filled tooth using 3D finite element analysis. Material and Methods Six models were built using micro-CT imaging data and SolidWorks 2007 software, varying the root canal (C) and the glass fiber post (P) diameters: C1P1-C=1 mm and P=1 mm; C2P1-C=2 mm and P=1 mm; C2P2-C=2 mm and P=2 mm; C3P1-C=3 mm and P=1 mm; C3P2-C=3 mm and P=2 mm; and C3P3-C=3 mm and P=3 mm. The numerical analysis was conducted with ANSYS Workbench 10.0. An oblique force (180 N at 45º) was applied to the palatal surface of the central incisor. The periodontal ligament surface was constrained on the three axes (x=y=z=0). Maximum principal stress (σmax) values were evaluated for the root dentin, cement layer, and glass fiber post. Results: The most evident stress was observed in the glass fiber post at C3P1 (323 MPa), and the maximum stress in the cement layer occurred at C1P1 (43.2 MPa). The stress on the root dentin was almost constant in all models with a peak in tension at C2P1 (64.5 MPa). Conclusion The greatest discrepancy between root canal and post diameters is favorable for stress concentration at the post surface. The dentin remaining after the various root canal preparations did not increase the stress levels on the root. PMID:24473716

  18. Safety, Tolerance, and Enhanced Efficacy of a Bioavailable Formulation of Curcumin With Fenugreek Dietary Fiber on Occupational Stress: A Randomized, Double-Blind, Placebo-Controlled Pilot Study.

    PubMed

    Pandaran Sudheeran, Subash; Jacob, Della; Natinga Mulakal, Johannah; Gopinathan Nair, Gopakumar; Maliakel, Abhilash; Maliakel, Balu; Kuttan, Ramadasan; Im, Krishnakumar

    2016-06-01

    Drug delivery systems capable of delivering free (unconjugated) curcuminoids is of great therapeutic significance, since the absorption of bioactive and permeable form plays a key factor in mediating the efficacy of a substance which undergoes rapid biotransformation. Considering the recent understanding on the relatively high bioactivities and blood-brain-barrier permeability of free curcuminoids over their conjugated metabolites, the present human study investigated the safety, antioxidant efficacy, and bioavailability of CurQfen (curcumagalactomannoside [CGM]), a food-grade formulation of natural curcumin with fenugreek dietary fiber that has shown to possess improved blood-brain-barrier permeability and tissue distribution in rats. In this randomized double-blinded and placebo-controlled trial, 60 subjects experiencing occupational stress-related anxiety and fatigue were randomized to receive CGM, standard curcumin, and placebo for 30 days (500 mg twice daily). The study demonstrated the safety, tolerance, and enhanced efficacy of CGM in comparison with unformulated standard curcumin. A significant improvement in the quality of life (P < 0.05) with considerable reduction in stress (P < 0.001), anxiety (P < 0.001), and fatigue (P < 0.001) was observed among CGM-treated subjects as compared with the standard curcumin group, when monitored by SF-36, Perceived Stress Scale with 14 items, and Beck Anxiety Inventory scores. Improvement in the quality of life was further correlated with the significant enhancement in endogenous antioxidant markers (P < 0.01) and reduction in lipid peroxidation (P < 0.001). Further comparison of the free curcuminoids bioavailability after a single-dose (500 mg once per day) and repeated-dose (500 mg twice daily for 30 days) oral administration revealed enhanced absorption and improved pharmacokinetics of CGM upon both single- (30.7-fold) and repeated-dose (39.1-fold) administrations. PMID:27043120

  19. Stress.

    PubMed

    Chambers, David W

    2008-01-01

    We all experience stress as a regular, and sometimes damaging and sometimes useful, part of our daily lives. In our normal ups and downs, we have our share of exhaustion, despondency, and outrage--matched with their corresponding positive moods. But burnout and workaholism are different. They are chronic, dysfunctional, self-reinforcing, life-shortening habits. Dentists, nurses, teachers, ministers, social workers, and entertainers are especially susceptible to burnout; not because they are hard-working professionals (they tend to be), but because they are caring perfectionists who share control for the success of what they do with others and perform under the scrutiny of their colleagues (they tend to). Workaholics are also trapped in self-sealing cycles, but the elements are ever-receding visions of control and using constant activity as a barrier against facing reality. This essay explores the symptoms, mechanisms, causes, and successful coping strategies for burnout and workaholism. It also takes a look at the general stress response on the physiological level and at some of the damage American society inflicts on itself. PMID:18846841

  20. The optimal fiber volume fraction and fiber-matrix property compatibility in fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Pan, Ning

    1992-01-01

    Although the question of minimum or critical fiber volume fraction beyond which a composite can then be strengthened due to addition of fibers has been dealt with by several investigators for both continuous and short fiber composites, a study of maximum or optimal fiber volume fraction at which the composite reaches its highest strength has not been reported yet. The present analysis has investigated this issue for short fiber case based on the well-known shear lag (the elastic stress transfer) theory as the first step. Using the relationships obtained, the minimum spacing between fibers is determined upon which the maximum fiber volume fraction can be calculated, depending on the fiber packing forms within the composites. The effects on the value of this maximum fiber volume fraction due to such factors as fiber and matrix properties, fiber aspect ratio and fiber packing forms are discussed. Furthermore, combined with the previous analysis on the minimum fiber volume fraction, this maximum fiber volume fraction can be used to examine the property compatibility of fiber and matrix in forming a composite. This is deemed to be useful for composite design. Finally some examples are provided to illustrate the results.

  1. Linguistic Theory and Actual Language.

    ERIC Educational Resources Information Center

    Segerdahl, Par

    1995-01-01

    Examines Noam Chomsky's (1957) discussion of "grammaticalness" and the role of linguistics in the "correct" way of speaking and writing. It is argued that the concern of linguistics with the tools of grammar has resulted in confusion, with the tools becoming mixed up with the actual language, thereby becoming the central element in a metaphysical…

  2. Biomechanical analysis of a new carbon fiber/flax/epoxy bone fracture plate shows less stress shielding compared to a standard clinical metal plate.

    PubMed

    Bagheri, Zahra S; Tavakkoli Avval, Pouria; Bougherara, Habiba; Aziz, Mina S R; Schemitsch, Emil H; Zdero, Radovan

    2014-09-01

    Femur fracture at the tip of a total hip replacement (THR), commonly known as Vancouver B1 fracture, is mainly treated using rigid metallic bone plates which may result in "stress shielding" leading to bone resorption and implant loosening. To minimize stress shielding, a new carbon fiber (CF)/Flax/Epoxy composite plate has been developed and biomechanically compared to a standard clinical metal plate. For fatigue tests, experiments were done using six artificial femurs cyclically loaded through the femoral head in axial compression for four stages: Stage 1 (intact), stage 2 (after THR insertion), stage 3 (after plate fixation of a simulated Vancouver B1 femoral midshaft fracture gap), and stage 4 (after fracture gap healing). For fracture fixation, one group was fitted with the new CF/Flax/Epoxy plate (n = 3), whereas another group was repaired with a standard clinical metal plate (Zimmer, Warsaw, IN) (n = 3). In addition to axial stiffness measurements, infrared thermography technique was used to capture the femur and plate surface stresses during the testing. Moreover, finite element analysis (FEA) was performed to evaluate the composite plate's axial stiffness and surface stress field. Experimental results showed that the CF/Flax/Epoxy plated femur had comparable axial stiffness (fractured = 645 ± 67 N/mm; healed = 1731 ± 109 N/mm) to the metal-plated femur (fractured = 658 ± 69 N/mm; healed = 1751 ± 39 N/mm) (p = 1.00). However, the bone beneath the CF/Flax/Epoxy plate was the only area that had a significantly higher average surface stress (fractured = 2.10 ± 0.66 MPa; healed = 1.89 ± 0.39 MPa) compared to bone beneath the metal plate (fractured = 1.18 ± 0.93 MPa; healed = 0.71 ± 0.24 MPa) (p < 0.05). FEA bone surface stresses yielded peak of 13 MPa at distal epiphysis (stage 1), 16 MPa at distal epiphysis (stage 2), 85 MPa for composite and 129

  3. Dietary Fiber

    MedlinePlus

    Fiber is a substance in plants. Dietary fiber is the kind you eat. It's a type of carbohydrate. You may also see it listed on a food label as soluble fiber or insoluble fiber. Both types have important health benefits. Good sources of dietary fiber include Whole grains Nuts ...

  4. The Drosophila FHOD1-like formin Knittrig acts through Rok to promote stress fiber formation and directed macrophage migration during the cellular immune response.

    PubMed

    Lammel, Uwe; Bechtold, Meike; Risse, Benjamin; Berh, Dimitri; Fleige, Astrid; Bunse, Ingrid; Jiang, Xiaoyi; Klämbt, Christian; Bogdan, Sven

    2014-03-01

    A tight spatiotemporal control of actin polymerization is important for many cellular processes that shape cells into a multicellular organism. The formation of unbranched F-actin is induced by several members of the formin family. Drosophila encodes six formin genes, representing six of the seven known mammalian subclasses. Knittrig, the Drosophila homolog of mammalian FHOD1, is specifically expressed in the developing central nervous system midline glia, the trachea, the wing and in macrophages. knittrig mutants exhibit mild tracheal defects but survive until late pupal stages and mainly die as pharate adult flies. knittrig mutant macrophages are smaller and show reduced cell spreading and cell migration in in vivo wounding experiments. Rescue experiments further demonstrate a cell-autonomous function of Knittrig in regulating actin dynamics and cell migration. Knittrig localizes at the rear of migrating macrophages in vivo, suggesting a cellular requirement of Knittrig in the retraction of the trailing edge. Supporting this notion, we found that Knittrig is a target of the Rho-dependent kinase Rok. Co-expression with Rok or expression of an activated form of Knittrig induces actin stress fibers in macrophages and in epithelial tissues. Thus, we propose a model in which Rok-induced phosphorylation of residues within the basic region mediates the activation of Knittrig in controlling macrophage migration. PMID:24553290

  5. How People Actually Use Thermostats

    SciTech Connect

    Meier, Alan; Aragon, Cecilia; Hurwitz, Becky; Mujumdar, Dhawal; Peffer, Therese; Perry, Daniel; Pritoni, Marco

    2010-08-15

    Residential thermostats have been a key element in controlling heating and cooling systems for over sixty years. However, today's modern programmable thermostats (PTs) are complicated and difficult for users to understand, leading to errors in operation and wasted energy. Four separate tests of usability were conducted in preparation for a larger study. These tests included personal interviews, an on-line survey, photographing actual thermostat settings, and measurements of ability to accomplish four tasks related to effective use of a PT. The interviews revealed that many occupants used the PT as an on-off switch and most demonstrated little knowledge of how to operate it. The on-line survey found that 89% of the respondents rarely or never used the PT to set a weekday or weekend program. The photographic survey (in low income homes) found that only 30% of the PTs were actually programmed. In the usability test, we found that we could quantify the difference in usability of two PTs as measured in time to accomplish tasks. Users accomplished the tasks in consistently shorter times with the touchscreen unit than with buttons. None of these studies are representative of the entire population of users but, together, they illustrate the importance of improving user interfaces in PTs.

  6. Raman stress sensor for localized stress measurements in composite laminates

    NASA Astrophysics Data System (ADS)

    Arjyal, Bish; Galiotis, Costas

    1995-09-01

    A new stress/strain sensor for localized measurements in polymer based composites, has been developed and tested. The stress/strain dependent property is the frequency of the atomic vibrations of reinforcing fibers which can be proved with laser Raman spectroscopy. Measurements can be conducted in reinforcing fibers near the surface of laminates. For measurements in the bulk of composites, the exciting laser light has to be transported to the reinforcing fibers via an embedded fiber optic cable. The backscattered light is transmitted through the same fiber optic and is sent to the Raman spectrometer for analysis. The effect of the direction of the fiber optic cable with respect to the axis of the reinforcing fibers is examined. Finally, the relationships between the local fiber stress or strain obtained from the Raman sensor and the far field stress or strain measured conventionally, are established.

  7. Fiber Sagnac interferometer temperature sensor

    SciTech Connect

    Starodumov, A.N.; Zenteno, L.A.; Monzon, D.; De La Rosa, E.

    1997-01-01

    A modified Sagnac interferometer-based fiber temperature sensor is proposed. Polarization independent operation and high temperature sensitivity of this class of sensors make them cost effective instruments for temperature measurements. A comparison of the proposed sensor with Bragg grating and long-period grating fiber sensors is derived. A temperature-induced spectral displacement of 0.99 nm/K is demonstrated for an internal stress birefringent fiber-based Sagnac interferometer. {copyright} {ital 1997 American Institute of Physics.}

  8. Fiber biology

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cotton fiber cells arising from seed epidermis is the most important agricultural textile commodity in the world. To produce fully mature fibers, approximately two months of fiber developmental process are required. The timing of four distinctive fiber development stages consisting of initiation, ...

  9. Design Curve Generation for 3D SiC Fiber Architecture

    NASA Technical Reports Server (NTRS)

    Lang, Jerry; Dicarlo, James A.

    2014-01-01

    The design tool provides design curves that allow a simple and quick way to examine multiple factors that can influence the processing and key properties of the preforms and their final SiC-reinforced ceramic composites without over obligating financial capital for the fabricating of materials. Tool predictions for process and fiber fraction properties have been validated for a HNS 3D preform.The virtualization aspect of the tool will be used to provide a quick generation of solid models with actual fiber paths for finite element evaluation to predict mechanical and thermal properties of proposed composites as well as mechanical displacement behavior due to creep and stress relaxation to study load sharing characteristic between constitutes for better performance.Tool predictions for the fiber controlled properties of the SiCSiC CMC fabricated from the HNS preforms will be valuated and up-graded from the measurements on these CMC

  10. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  11. Some properties of an advanced boron fiber. [high strength, splittable fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1979-01-01

    An advanced coreless boron fiber exhibits tensile strengths which are more than twice that of the normal CVD B/W fibers. The coreless fiber is made by the chemical removal of the tungsten boride core exposed by splitting the as-grown fiber. The easily splittable fiber is made by the chemical vapor deposition of boron on a larger than usual tungsten substrate. It is expected that the ease of splitting is related to residual stresses in these fibers. Measurements of the axial residual stresses in both the normal and the splittable fibers are presented and the results compared. Differences in these stresses are discussed in connection with the ease of splitting in the splittable fibers.

  12. Effects of prepartum roughage neutral detergent fiber levels on periparturient dry matter intake, metabolism, and lactation in heat-stressed dairy cows.

    PubMed

    Kanjanapruthipong, J; Homwong, N; Buatong, N

    2010-06-01

    Heat stress of lactating cattle results in dramatic reductions in dry matter intake (DMI). As a result, energy input cannot satisfy energy needs and thus accelerates body fat mobilization. Decreasing the level of roughage neutral detergent fiber (NDF) in prepartum diets, and thereby increasing the amount of nonfiber carbohydrates, may provide an adequate supply of energy and glucose precursors to maintain and minimize the decrease in DMI while reducing mobilization of adipose tissue. The effects of 3-wk prepartum diets containing different amounts of roughage NDF on DMI, blood metabolites, and lactation performance of dairy cows were investigated under summer conditions in Thailand. Thirty cross-bred cows (87.5% Holstein x 12.5% Sahiwal) were dried off 60 d before their expected calving date and were assigned immediately to a nonlactating cow diet containing the net energy for lactation recommended by the National Research Council (2001) model. The treatment diets contained 17.4, 19.2, and 21.0% DM as roughage NDF from bana grass (Pennisetum purpureum x Pennisetum glaucum) silage. Levels of concentrate NDF were 39.8, 40.2, and 38.6% of dietary NDF, so the levels of dietary NDF were 28.9, 32.1, and 34.2% of DM. After parturition, all cows received a lactating cow diet containing 12.7% roughage NDF and 23% dietary NDF. During the entire experiment, the minimum and maximum temperature-humidity index averaged 77.7 and 86.8, respectively, indicating conditions appropriate for the induction of extreme heat stress. As parturition approached, DMI decreased steadily, resulting in a 12.9, 25, and 32.8% decrease in DMI from d -21 until calving for nonlactating cows fed prepartum diets containing 17.4, 19.2, and 21% roughage NDF, respectively. During the 3-wk prepartum period, intakes of DM and net energy for lactation and concentrations of plasma glucose and serum insulin were higher for cows fed diets containing less roughage NDF. In cows fed the 3-wk prepartum diets

  13. The actual goals of geoethics

    NASA Astrophysics Data System (ADS)

    Nemec, Vaclav

    2014-05-01

    The most actual goals of geoethics have been formulated as results of the International Conference on Geoethics (October 2013) held at the geoethics birth-place Pribram (Czech Republic): In the sphere of education and public enlightenment an appropriate needed minimum know how of Earth sciences should be intensively promoted together with cultivating ethical way of thinking and acting for the sustainable well-being of the society. The actual activities of the Intergovernmental Panel of Climate Changes are not sustainable with the existing knowledge of the Earth sciences (as presented in the results of the 33rd and 34th International Geological Congresses). This knowledge should be incorporated into any further work of the IPCC. In the sphere of legislation in a large international co-operation following steps are needed: - to re-formulate the term of a "false alarm" and its legal consequences, - to demand very consequently the needed evaluation of existing risks, - to solve problems of rights of individuals and minorities in cases of the optimum use of mineral resources and of the optimum protection of the local population against emergency dangers and disasters; common good (well-being) must be considered as the priority when solving ethical dilemmas. The precaution principle should be applied in any decision making process. Earth scientists presenting their expert opinions are not exempted from civil, administrative or even criminal liabilities. Details must be established by national law and jurisprudence. The well known case of the L'Aquila earthquake (2009) should serve as a serious warning because of the proven misuse of geoethics for protecting top Italian seismologists responsible and sentenced for their inadequate superficial behaviour causing lot of human victims. Another recent scandal with the Himalayan fossil fraud will be also documented. A support is needed for any effort to analyze and to disclose the problems of the deformation of the contemporary

  14. Homogenization of long fiber reinforced composites including fiber bending effects

    NASA Astrophysics Data System (ADS)

    Poulios, Konstantinos; Niordson, Christian F.

    2016-09-01

    This paper presents a homogenization method, which accounts for intrinsic size effects related to the fiber diameter in long fiber reinforced composite materials with two independent constitutive models for the matrix and fiber materials. A new choice of internal kinematic variables allows to maintain the kinematics of the two material phases independent from the assumed constitutive models, so that stress-deformation relationships, can be expressed in the framework of hyper-elasticity and hyper-elastoplasticity for the fiber and the matrix materials respectively. The bending stiffness of the reinforcing fibers is captured by higher order strain terms, resulting in an accurate representation of the micro-mechanical behavior of the composite. Numerical examples show that the accuracy of the proposed model is very close to a non-homogenized finite-element model with an explicit discretization of the matrix and the fibers.

  15. Fiber Pulling Apparatus

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.; Smith, Guy A.; OBrien, Sue; Adcock, Leonard

    1998-01-01

    The fiber optics industry has grown into a multi-billion marketplace that will continue to grow into the 21st century. Optical fiber communications is currently dominated by silica glass technology. Successful efforts to improve upon the low loss transmission characteristics of silica fibers have propelled the technology into the forefront of the communications industry. However, reaching the theoretical transmission capability of silica fiber through improved processing has still left a few application areas in which other fiber systems can provide an influential role due to specific characteristics of high theoretical transmission in the 2 - 3 micron wavelength region. One of the other major materials used for optical fibers is the systems based upon Heavy Metal Fluoride Glass (HMFG). Commercial interest is driven primarily by the potential for low loss repeaterless infrared fibers. An example of the major communications marketplace which would benefit from the long distance repeaterless capability of infrared fibers is the submarine cables which link the continents. When considering commercial interests, optical fiber systems provide a healthy industrial position which continues to expand. Major investments in the systems used for optical fiber communications have continued to increase each year and are predicted to continue well into the next century. Estimates of 8.5% compounded annually are predicted through 1999 for the North American market and 1 1 % worldwide. The growth for the optical fiber cable itself is expected to continue between 44 and 50 per cent of the optical fiber communications budget through 1999. The total budget in 1999 world-wide is expected to be in the neighborhood of $9 billion. Another survey predicts that long haul telecommunications represents 15% of a world-wide fiber optics market in 1998. The actual amount allotted to cable was not specified. However, another market research had predicted that the cable costs alone represents more

  16. Comparison of silica-core optical fibers

    NASA Astrophysics Data System (ADS)

    McCann, Brian P.

    1991-07-01

    Silica-core optical fibers have become a standard vehicle to remotely deliver high-power laser energy from surgical lasers operating between 200 and 2400 nm. The three primary types of silica-core fibers: plastic-clad; hard-clad; and silica-clad; are discussed. The performance advantages of each are addressed and actual general-surgery medical applications are provided.

  17. Specialty fiber optic applications for harsh and high radiation environments

    NASA Astrophysics Data System (ADS)

    Risch, Brian G.

    2015-05-01

    Since the first commercial introduction in the 1980s, optical fiber technology has undergone an almost exponential growth. Currently over 2 billion fiber kilometers are deployed globally with 2014 global optical fiber production exceeding 300 million fiber kilometers. 1 Along with the staggering growth in optical fiber production and deployment, an increase in optical fiber technologies and applications has also followed. Although the main use of optical fibers by far has been for traditional data transmission and communications, numerous new applications are introduced each year. Initially the practical application of optical fibers was limited by cost and sensitivity of the optical fibers to stress, radiation, and other environmental factors. Tremendous advances have taken place in optical fiber design and materials allowing optical fibers to be deployed in increasingly harsh environments with exposure to increased mechanical and environmental stresses while maintaining high reliability. With the increased reliability, lower cost, and greatly expanded range of optical fiber types now available, new optical fiber deployments in harsh and high radiation environments is seeing a tremendous increase for data, communications, and sensing applications. An overview of key optical fiber applications in data, communications, and sensing for harsh environments in industrial, energy exploration, energy generation, energy transmission, and high radiation applications will be presented. Specific recent advances in new radiation resistant optical fiber types, other specialty optical fibers, optical fiber coatings, and optical fiber cable materials will be discussed to illustrate long term reliability for deployment of optical fibers in harsh and high radiation environments.

  18. Dietary Fiber

    MedlinePlus

    Fiber is a substance in plants. Dietary fiber is the kind you eat. It's a type of carbohydrate. You may also see it listed on a food label as soluble ... types have important health benefits. Good sources of dietary fiber include Whole grains Nuts and seeds Fruit and ...

  19. Microsensor coils for miniature fiber optic gyroscopes

    NASA Astrophysics Data System (ADS)

    Ruffin, Paul B.; Baeder, Janet S.

    2004-10-01

    Depolarized Interferometric Fiber Optic Gyroscopes (D-IFOGs) that are constructed with inexpensive single mode (SM) fiber have provided an opportunity for developers to meet Army emerging missions goals for affordable, small volume, reliable inertial guidance systems for use in small missiles, munitions, and future micro-unmanned autonomous vehicles. However, there remain several vital issues associated with substantially reducing the diameter of the sensor coil. Optical fiber that is precision-wound onto a micro coil experiences increased stress due to small radius bending, fiber distortions at crossover sites, and increased interlayer pressures as a result of multiple layers of fiber wound under tension. Tension and small radius bending stresses can have a detrimental effect on the performance of D-IFOGs. Therefore, other scenarios for the application of SM fiber to a micro-sensor coil must be considered. One scheme involves taking advantage of the bending-induced birefringence and employing the low cost SM fiber as a polarization-maintaining (PM) fiber. The mechanics of how a substantial reduction in the coil radius produces PM fiber properties in SM fiber is investigated under this research effort. Conventional and specialty SM fibers are characterized to identify optimal fibers for the development of micro-sensor coils. The results from extinction ratio measurements on the SM fibers and micro-sensor coils are presented in this paper. The significant cross coupling suggests that scattering centers are present in very small radius bending. Also, measurements show that optical loss is significant in micro IFOG coils.

  20. Experimental research on continuous basalt fiber and basalt-fibers-reinforced polymers

    NASA Astrophysics Data System (ADS)

    Zhang, Xueyi; Zou, Guangping; Shen, Zhiqiang

    2008-11-01

    The interest for continuous basalt fibers and reinforced polymers has recently grown because of its low price and rich natural resource. Basalt fiber was one type of high performance inorganic fibers which were made from natural basalt by the method of melt extraction. This paper discusses basic mechanical properties of basalt fiber. The other work in this paper was to conduct tensile testing of continuous basalt fiber-reinforced polymer rod. Tensile strength and stress-strain curve were obtained in this testing. The strength of rod was fairly equal to rod of E-glass fibers and weaker than rod of carbon fibers. Surface of crack of rod was studied. An investigation of fracture mechanism between matrix and fiber was analyzed by SEM (Scanning electron microscopy) method. A poor adhesion between the matrix and fibers was also shown for composites analyzing SEM photos. The promising tensile properties of the presented basalt fibers composites have shown their great potential as alternative classical composites.

  1. Self Similar Optical Fiber

    NASA Astrophysics Data System (ADS)

    Lai, Zheng-Xuan

    This research proposes Self Similar optical fiber (SSF) as a new type of optical fiber. It has a special core that consists of self similar structure. Such a structure is obtained by following the formula for generating iterated function systems (IFS) in Fractal Theory. The resulted SSF can be viewed as a true fractal object in optical fibers. In addition, the method of fabricating SSF makes it possible to generate desired structures exponentially in numbers, whereas it also allows lower scale units in the structure to be reduced in size exponentially. The invention of SSF is expected to greatly ease the production of optical fiber when a large number of small hollow structures are needed in the core of the optical fiber. This dissertation will analyze the core structure of SSF based on fractal theory. Possible properties from the structural characteristics and the corresponding applications are explained. Four SSF samples were obtained through actual fabrication in a laboratory environment. Different from traditional conductive heating fabrication system, I used an in-house designed furnace that incorporated a radiation heating method, and was equipped with automated temperature control system. The obtained samples were examined through spectrum tests. Results from the tests showed that SSF does have the optical property of delivering light in a certain wavelength range. However, SSF as a new type of optical fiber requires a systematic research to find out the theory that explains its structure and the associated optical properties. The fabrication and quality of SSF also needs to be improved for product deployment. As a start of this extensive research, this dissertation work opens the door to a very promising new area in optical fiber research.

  2. Spectral characteristics of draw-tower step-chirped fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Idrisov, Ravil F.; Varzhel, Sergey V.; Kulikov, Andrey V.; Meshkovskiy, Igor K.; Rothhardt, Manfred; Becker, Martin; Schuster, Kay; Bartelt, Hartmut

    2016-06-01

    This paper presents research results on the spectral properties of step-chirped fiber Bragg grating arrays written during the fiber drawing process into a birefringent optical fiber with an elliptical stress cladding. The dependences of resonance shift of the step-chirped fiber Bragg grating on bending, on applied tensile stress and on temperature have been investigated. A usage of such step-chirped fiber Bragg gratings in fiber-optic sensing elements creation has been considered.

  3. Fiber sensing with photorefractive fiber

    NASA Astrophysics Data System (ADS)

    Yu, Francis T. S.; Guo, Ruyan; Wang, Bo; Liu, Yuexin

    2002-11-01

    Optical fibers have been widely used for transmitting temporal signal. However, the transmission of spatial signal has not been fully exploited. Although multimode fiber has a large space-bandwidth product, transmitting spatial signals by using a fiber is rather difficult. When a laser beam is lached into a multimode fiber, the exit light field produces a complicated speckle pattern caused by the modal phasing of the fiber. It is difficult to recover the transmitted informati from the speckle field. However, the fiber speckle field can be used to fiber sensing with a hologrpahic method. In other words, if a hologram is made with the speckle fiber field, the information of the fiber status can be recovered. Thus by reading the hologram by the same speckle field, the reference beam can be reconstructed, which represents the detection of the speckle field. In other words, instead of exploiting the temporal content, the spatial content from a multimode fiber can be exploited for sensing. Our analyses and experimentations have shown that the fiber specklegram sensor (FSS) is highly senstiive to perturbation, and it is less vulnerable to the environment factors. Applications of the FSS to temperature, transversal displacement, and dynamic sensing are also included.

  4. Effect of thermal cycling on interface bonding requirements in Al2O3 fiber-reinforced superalloy composites

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.

    1993-01-01

    CTE (coefficient of thermal expansion) mismatch-induced stresses as they affect the fiber-matrix bond integrity of Al2O3 fiber-reinforced superalloy composites are examined. Of the three individual stress components, only the radial stress directly affects the integrity of the fiber-matrix interface. It is noted that a compressive radial stress leads to a clamping action on the fiber and is therefore beneficial to the integrity of the fiber-matrix bond. A radial tensile stress, on the other hand, can cause debonding of the fiber from the matrix for a weak fiber-matrix bond.

  5. MICROMECHANICS IN CONTINOUS GRAPHITE FIBER/EPOXY COMPOSITES DURING CREEP

    SciTech Connect

    C. ZHOU; ET AL

    2001-02-01

    Micro Raman spectroscopy and classic composite shear-lag models were used to analyze the evolution with time of fiber and matrix strain/stress around fiber breaks in planar model graphite fiber-epoxy matrix composites. Impressive agreements were found between the model predictions and the experimental results. The local matrix creep leads to an increase in the load transfer length around the break under a constant load. This increases the chance of fiber breakage in the neighboring intact fibers.

  6. Optical Fiber Spectroscopy

    NASA Technical Reports Server (NTRS)

    Buoncristiani, A. M.

    1999-01-01

    This is the final report of work done on NASA Grant NAG-1-443. The work covers the period from July 1, 1992 to December 1, 1998. During this period several distinct but related research studies and work tasks were undertaken. These different subjects are enumerated below with a description of the work done on each of them. The focus of the research was the development of optical fibers for use as distributed temperature and stress sensors. The initial concept was to utilize the utilize the temperature and stress dependence of emission from rare earth and transition metal ions substitutionally doped into crystalline or glass fibers. During the course of investigating this it became clear that fiber Bragg gratings provided a alternative for making the desired measurements and there was a shift of research focus on to include the photo-refractive properties of germano-silicate glasses used for most gratings and to the possibility of developing fiber laser sources for an integrated optical sensor in the research effort. During the course of this work several students from Christopher Newport University and other universities participated in this effort. Their names are listed below. Their participation was an important part of their education.

  7. Moral Reasoning in Hypothetical and Actual Situations.

    ERIC Educational Resources Information Center

    Sumprer, Gerard F.; Butter, Eliot J.

    1978-01-01

    Results of this investigation suggest that moral reasoning of college students, when assessed using the DIT format, is the same whether the dilemmas involve hypothetical or actual situations. Subjects, when presented with hypothetical situations, become deeply immersed in them and respond as if they were actual participants. (Author/BEF)

  8. Factors Related to Self-Actualization.

    ERIC Educational Resources Information Center

    Hogan, H. Wayne; McWilliams, Jettie M.

    1978-01-01

    Provides data to further support the notions that females score higher in self-actualization measures and that self-actualization scores correlate inversely to the degree of undesirability individuals assign to their heights and weights. Finds that, contrary to predictions, greater androgyny was related to lower, not higher, self-actualization…

  9. Stress relaxation of swine growth plate in semi-confined compression: depth dependent tissue deformational behavior versus extracellular matrix composition and collagen fiber organization.

    PubMed

    Amini, Samira; Mortazavi, Farhad; Sun, Jun; Levesque, Martin; Hoemann, Caroline D; Villemure, Isabelle

    2013-01-01

    Mechanical environment is one of the regulating factors involved in the process of longitudinal bone growth. Non-physiological compressive loading can lead to infantile and juvenile musculoskeletal deformities particularly during growth spurt. We hypothesized that tissue mechanical behavior in sub-regions (reserve, proliferative and hypertrophic zones) of the growth plate is related to its collagen and proteoglycan content as well as its collagen fiber orientation. To characterize the strain distribution through growth plate thickness and to evaluate biochemical content and collagen fiber organization of the three histological zones of growth plate tissue. Distal ulnar growth plate samples (N = 29) from 4-week old pigs were analyzed histologically for collagen fiber organization (N = 7) or average zonal thickness (N = 8), or trimmed into the three average zones, based on the estimated thickness of each histological zone, for biochemical analysis of water, collagen and glycosaminoglycan content (N = 7). Other samples (N = 7) were tested in semi-confined compression under 10% compressive strain. Digital images of the fluorescently labeled nuclei were concomitantly acquired by confocal microscopy before loading and after tissue relaxation. Strain fields were subsequently calculated using a custom-designed 2D digital image correlation algorithm. Depth-dependent compressive strain patterns and collagen content were observed. The proliferative and hypertrophic zone developed the highest axial and transverse strains, respectively, under compression compared to the reserve zone, in which the lowest axial and transverse strains arose. The collagen content per wet mass was significantly lower in the proliferative and hypertrophic zones compared to the reserve zone, and all three zones had similar glycosaminoglycan and water content.Polarized light microscopy showed that collagen fibers were mainly organized horizontally in the reserve zone and vertically aligned with the

  10. Mechanical reliability of double clad fibers in typical fiber laser deployment conditions

    NASA Astrophysics Data System (ADS)

    Walorny, Michael; Abramczyk, Jaroslaw; Jacobson, Nick; Tankala, Kanishka

    2016-03-01

    With the rapid acceptance of fiber lasers and amplifiers for various materials processing and defense applications the long term optical and mechanical reliability of the fiber laser, and therefore the components that make up the laser, is of significant interest to the industrial and defense communities. The double clad fiber used in a fiber laser is a key component whose lifetime in typical deployment conditions needs to be understood. The optical reliability of double clad fiber has recently been studied and a predictive model of fiber lifetime has been published. In contrast, a rigorous model for the mechanical reliability of the fiber and an analysis of the variables affecting the lifetime of the fiber in typical deployment conditions has not been studied. This paper uses the COST-218 model which is widely used for analyzing the mechanical lifetime of fiber used in the telecom industry. The factors affecting lifetime are analyzed to make the reader aware of the design choices a laser manufacturer can make, and the information they must seek from fiber suppliers, to ensure excellent lifetime for double clad fiber and consequently for the fiber laser. It is shown that the fiber's stress corrosion susceptibility, its proof strength, the coil diameter and the length of fiber coiled to achieve good beam quality all have important implications on fiber lifetime.

  11. Thermomechanical Behavior of Advanced SiC Fiber Multifilament Tows

    NASA Technical Reports Server (NTRS)

    Yun, Hee Mann; DiCarlo, James A.

    1997-01-01

    In order to relate single fiber behavior to multiple fiber behavior in composites, fast-fracture tensile strength, creep, and stress-rupture studies were conducted on advanced SiC fiber multifilament tows in the temperature range from 20 to 1400 C in air as well as in inert environments. For conditions of small fiber creep (short times and low temperatures), the tow results of this study confirm the ability of limited single fiber data to model the strength behavior of multiple fibers in a bundle. For conditions of high creep (long times and high temperatures), further studies are needed to explain tow rupture behavior being better than average single fiber behavior.

  12. Effects of interphase on fiber fracture in a single fiber composite specimen

    SciTech Connect

    Davis, J.E.; Qu, J.

    1995-12-31

    A single fiber composite (SFC) specimen containing a silicon carbide fiber in an aluminum matrix is used to investigate the effect of an interphase layer between the fiber and the matrix. The interphase layer consists of a reaction zone between the fiber and the matrix that occurs during fabrication. The interphase layer, when damaged during fiber fracture, introduces imperfect interfacial bonding between the fiber and the matrix. The effect of imperfect interfacial bonding is qualified in this study by evaluating the tensile stiffness degradation and the nonlinear effective stress-strain relationship caused by successive fiber fracture for an SFC subjected to axial tension. The finite element method (FEM) is used to obtain numerical solutions for the stress and strain fields in the SFC specimens for various fiber fragmentation lengths under a prescribed axial displacement loading. The fiber fractures are assumed to be uniformly distributed such that the fragment lengths are equal at each given load level. The Weibull strength distribution is used to relate the fiber fragment length to the tensile strength of the brittle fiber. The FEM stress and strain results are used to calculate the effective modulus of the SFC, which characterizes the degradation in tensile stiffness caused by successive fiber fracture. The effective stress is determined for a given fracture density using the effective applied strain and the corresponding effective modulus. The final result is the relationship between the effective stress and effective strain. Qualitative comparisons of the stiffness degradation and the effective stress-strain relationship are made between models with perfect and imperfect interfacial bonding to evaluate the effect of a interphase layer.

  13. Carbon Fiber Biocompatibility for Implants

    PubMed Central

    Petersen, Richard

    2016-01-01

    Carbon fibers have multiple potential advantages in developing high-strength biomaterials with a density close to bone for better stress transfer and electrical properties that enhance tissue formation. As a breakthrough example in biomaterials, a 1.5 mm diameter bisphenol-epoxy/carbon-fiber-reinforced composite rod was compared for two weeks in a rat tibia model with a similar 1.5 mm diameter titanium-6-4 alloy screw manufactured to retain bone implants. Results showed that carbon-fiber-reinforced composite stimulated osseointegration inside the tibia bone marrow measured as percent bone area (PBA) to a great extent when compared to the titanium-6-4 alloy at statistically significant levels. PBA increased significantly with the carbon-fiber composite over the titanium-6-4 alloy for distances from the implant surfaces of 0.1 mm at 77.7% vs. 19.3% (p < 10−8) and 0.8 mm at 41.6% vs. 19.5% (p < 10−4), respectively. The review focuses on carbon fiber properties that increased PBA for enhanced implant osseointegration. Carbon fibers acting as polymer coated electrically conducting micro-biocircuits appear to provide a biocompatible semi-antioxidant property to remove damaging electron free radicals from the surrounding implant surface. Further, carbon fibers by removing excess electrons produced from the cellular mitochondrial electron transport chain during periods of hypoxia perhaps stimulate bone cell recruitment by free-radical chemotactic influences. In addition, well-studied bioorganic cell actin carbon fiber growth would appear to interface in close contact with the carbon-fiber-reinforced composite implant. Resulting subsequent actin carbon fiber/implant carbon fiber contacts then could help in discharging the electron biological overloads through electrochemical gradients to lower negative charges and lower concentration. PMID:26966555

  14. Two Fiber Optical Fiber Thermometry

    NASA Technical Reports Server (NTRS)

    Jones, Mathew R.; Farmer, Jeffery T.; Breeding, Shawn P.

    2000-01-01

    An optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber is essentially an isothermal cavity, so the emission from this cavity will be approximately equal to the emission from a blackbody. Temperature readings are obtained by measuring the spectral radiative heat flux at the end of the fiber at two wavelengths. The ratio of these measurements and Planck's Law are used to infer the temperature at the sensing tip. Optical fiber thermometers have high accuracy, excellent long-term stability and are immune to electromagnetic interference. In addition, they can be operated for extended periods without requiring re-calibration. For these reasons. it is desirable to use optical fiber thermometers in environments such as the International Space Station. However, it has recently been shown that temperature readings are corrupted by emission from the fiber when extended portions of the probe are exposed to elevated temperatures. This paper will describe several ways in which the reading from a second fiber can be used to correct the corrupted temperature measurements. The accuracy and sensitivity to measurement uncertainty will be presented for each method.

  15. Optical fiber sensors for damage analysis in aerospace materials

    NASA Technical Reports Server (NTRS)

    Schindler, Paul; May, Russell; Claus, Richard

    1995-01-01

    Under this grant, fiber optic sensors were investigated for use in the nondestructive evaluation of aging aircraft. Specifically, optical fiber sensors for detection and location of impacts on a surface, and for detection of corrosion in metals were developed. The use of neural networks was investigated for determining impact location by processing the output of a network of fiberoptic strain sensors distributed on a surface. This approach employs triangulation to determine location by comparing the arrival times at several sensors, of the acoustic signal generated by the impact. For this study, a neural network simulator running on a personal computer was used to train a network using a back-propagation algorithm. Fiber optic extrinsic Fabry-Perot interferometer (EFPI) strain sensors are attached to or embedded in the surface, so that stress waves emanating from an impact can be detected. The ability of the network to determine impact location by time-or-arrival of acoustic signals was assessed by comparing network outputs with actual experimental results using impacts on a panel instrumented with optical fiber sensors. Using the neural network to process the sensor outputs, the impact location can be inferred to centimeter range accuracy directly from the arrival time data. In addition, the network can be trained to determine impact location, regardless of material anisotropy. Results demonstrate that a back-propagation network identifies impact location for an anisotropic graphite/bismaleimide plate with the same accuracy as that for an isotropic aluminum plate. Two different approaches were investigated for the development of fiber optic sensors for corrosion detection in metals, both utilizing optical fiber sensors with metal coatings. In the first approach, an extrinsic Fabry-Perot interferometric fiber optic strain sensor was placed under tensile stress, and while in the resulting strained position, a thick coating of metal was applied. Due to an increase in

  16. Optical Fibers

    NASA Astrophysics Data System (ADS)

    Ghatak, Ajoy; Thyagarajan, K.

    With the development of extremely low-loss optical fibers and their application to communication systems, a revolution has taken fiber glass place during the last 40 years. In 2001, using glass fibers as the transmission medium and lightwaves as carrier wave waves, information was transmitted at a rate more than 1 Tbit/s (which is roughly equivalent to transmission of about 15 million simultaneous telephone conversations) through one hair thin optical fiber. Experimental demonstration of transmission at the rate of 14 Tbit/s over a 160 km long single fiber was demonstrated in 2006, which is equivalent to sending 140 digital high definition movies in 1 s. Very recently record transmission of more than 100 Tbit/s over 165 km single mode fiber has been reported. These can be considered as extremely important technological achievements. In this chapter we will discuss the propagation characteristics of optical fibers with special applications to optical communication systems and also present some of the noncommunication applications such as sensing.

  17. The characterization of carbon nanotube infused glass fibers by single filament fragmentation test methods

    NASA Astrophysics Data System (ADS)

    Roach, Andrew Michael

    Single filament fragmentation tests were completed for individual glass fibers with varying surface treatments and carbon nanostructure infusions. Fiber fragmentation was analyzed by embedding a single filament into a standard tensile interface, which provided shear stress transfer between a conventional epoxy resin system and the constituent filament. Established single filament fragmentation techniques were used to characterize fiber and interface properties. A novel method of comparing fibers is introduced by correlating bundle tow test results to fiber fragmentation critical length data to qualitatively relate fiber performance. Photoelastic birefringent stress fringes were processed at select fiber fragmentation locations to further characterize the fiber-resin, or fiber-carbon nanostructure-resin, interface. Overall, the performance matrix qualitative comparison method, coupled with stress fringe analysis, proved to be an effective means of qualitatively evaluating fiber and processing parameters, and efficiently identifies the most fruitful path forward for optimized fiber development.

  18. Rapid Quantification of 3D Collagen Fiber Alignment and Fiber Intersection Correlations with High Sensitivity

    PubMed Central

    Sun, Meng; Bloom, Alexander B.; Zaman, Muhammad H.

    2015-01-01

    Metastatic cancers aggressively reorganize collagen in their microenvironment. For example, radially orientated collagen fibers have been observed surrounding tumor cell clusters in vivo. The degree of fiber alignment, as a consequence of this remodeling, has often been difficult to quantify. In this paper, we present an easy to implement algorithm for accurate detection of collagen fiber orientation in a rapid pixel-wise manner. This algorithm quantifies the alignment of both computer generated and actual collagen fiber networks of varying degrees of alignment within 5°°. We also present an alternative easy method to calculate the alignment index directly from the standard deviation of fiber orientation. Using this quantitative method for determining collagen alignment, we demonstrate that the number of collagen fiber intersections has a negative correlation with the degree of fiber alignment. This decrease in intersections of aligned fibers could explain why cells move more rapidly along aligned fibers than unaligned fibers, as previously reported. Overall, our paper provides an easier, more quantitative and quicker way to quantify fiber orientation and alignment, and presents a platform in studying effects of matrix and cellular properties on fiber alignment in complex 3D environments. PMID:26158674

  19. Rapid Quantification of 3D Collagen Fiber Alignment and Fiber Intersection Correlations with High Sensitivity.

    PubMed

    Sun, Meng; Bloom, Alexander B; Zaman, Muhammad H

    2015-01-01

    Metastatic cancers aggressively reorganize collagen in their microenvironment. For example, radially orientated collagen fibers have been observed surrounding tumor cell clusters in vivo. The degree of fiber alignment, as a consequence of this remodeling, has often been difficult to quantify. In this paper, we present an easy to implement algorithm for accurate detection of collagen fiber orientation in a rapid pixel-wise manner. This algorithm quantifies the alignment of both computer generated and actual collagen fiber networks of varying degrees of alignment within 5°°. We also present an alternative easy method to calculate the alignment index directly from the standard deviation of fiber orientation. Using this quantitative method for determining collagen alignment, we demonstrate that the number of collagen fiber intersections has a negative correlation with the degree of fiber alignment. This decrease in intersections of aligned fibers could explain why cells move more rapidly along aligned fibers than unaligned fibers, as previously reported. Overall, our paper provides an easier, more quantitative and quicker way to quantify fiber orientation and alignment, and presents a platform in studying effects of matrix and cellular properties on fiber alignment in complex 3D environments. PMID:26158674

  20. Visualizing balloon stresses

    NASA Astrophysics Data System (ADS)

    Winker, James A.

    1994-02-01

    In a structure as indeterminate as a partially inflalted balloon it is very difficult to determine either the stress at any given point or a stress pattern over an area. Finite element analysis for this purpose is under development, but this will not likely bear fruit for years. This paper describes a process using desktop computers to convert actual experimental stress data into graphic, visual displays. The results provide valuable insight into the nature of balloon stresses.

  1. A Multiscale Progressive Failure Modeling Methodology for Composites that Includes Fiber Strength Stochastics

    NASA Technical Reports Server (NTRS)

    Ricks, Trenton M.; Lacy, Thomas E., Jr.; Bednarcyk, Brett A.; Arnold, Steven M.; Hutchins, John W.

    2014-01-01

    A multiscale modeling methodology was developed for continuous fiber composites that incorporates a statistical distribution of fiber strengths into coupled multiscale micromechanics/finite element (FE) analyses. A modified two-parameter Weibull cumulative distribution function, which accounts for the effect of fiber length on the probability of failure, was used to characterize the statistical distribution of fiber strengths. A parametric study using the NASA Micromechanics Analysis Code with the Generalized Method of Cells (MAC/GMC) was performed to assess the effect of variable fiber strengths on local composite failure within a repeating unit cell (RUC) and subsequent global failure. The NASA code FEAMAC and the ABAQUS finite element solver were used to analyze the progressive failure of a unidirectional SCS-6/TIMETAL 21S metal matrix composite tensile dogbone specimen at 650 degC. Multiscale progressive failure analyses were performed to quantify the effect of spatially varying fiber strengths on the RUC-averaged and global stress-strain responses and failure. The ultimate composite strengths and distribution of failure locations (predominately within the gage section) reasonably matched the experimentally observed failure behavior. The predicted composite failure behavior suggests that use of macroscale models that exploit global geometric symmetries are inappropriate for cases where the actual distribution of local fiber strengths displays no such symmetries. This issue has not received much attention in the literature. Moreover, the model discretization at a specific length scale can have a profound effect on the computational costs associated with multiscale simulations.models that yield accurate yet tractable results.

  2. Alloy 600 corrosion monitor based on fiber optic strain gage

    SciTech Connect

    Berthold, J.W.; Passell, T.O.

    1996-10-01

    There is a real need to measure strain at high temperatures in many applications. For example, in nuclear steam generators that contain Alloy 600 tubing, intergranular attack (IGA) and stress corrosion cracking (SCC) are significant problems. Measuring strain in this tubing might provide an early warning of the onset of IGA/SCC and the rate of SCC progression. This report describes a method to measure the onset of IGA and the progression of SCC that occurs at a crevice on the inside surface of a tube. The measurement is accomplished by monitoring strain on the outside surface of the tube using welded, fiber-optic strain gages. In an actual application of this approach in a power plant, the strain gages must survive temperatures above 600 F for extended periods (months or years) and must provide repeatable measurements.

  3. Fireblocking Fibers

    NASA Technical Reports Server (NTRS)

    1986-01-01

    PBI was originally developed for space suits. In 1980, the need for an alternative to asbestos and stricter government anti-pollution standards led to commercialization of the fire blocking fiber. PBI is used for auto racing driver suits and aircraft seat covers. The fiber does not burn in air, is durable and easily maintained. It has been specified by a number of airliners and is manufactured by Hoechst-Celanese Corporation.

  4. Fiber and prebiotics: mechanisms and health benefits.

    PubMed

    Slavin, Joanne

    2013-04-01

    The health benefits of dietary fiber have long been appreciated. Higher intakes of dietary fiber are linked to less cardiovascular disease and fiber plays a role in gut health, with many effective laxatives actually isolated fiber sources. Higher intakes of fiber are linked to lower body weights. Only polysaccharides were included in dietary fiber originally, but more recent definitions have included oligosaccharides as dietary fiber, not based on their chemical measurement as dietary fiber by the accepted total dietary fiber (TDF) method, but on their physiological effects. Inulin, fructo-oligosaccharides, and other oligosaccharides are included as fiber in food labels in the US. Additionally, oligosaccharides are the best known "prebiotics", "a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-bring and health." To date, all known and suspected prebiotics are carbohydrate compounds, primarily oligosaccharides, known to resist digestion in the human small intestine and reach the colon where they are fermented by the gut microflora. Studies have provided evidence that inulin and oligofructose (OF), lactulose, and resistant starch (RS) meet all aspects of the definition, including the stimulation of Bifidobacterium, a beneficial bacterial genus. Other isolated carbohydrates and carbohydrate-containing foods, including galactooligosaccharides (GOS), transgalactooligosaccharides (TOS), polydextrose, wheat dextrin, acacia gum, psyllium, banana, whole grain wheat, and whole grain corn also have prebiotic effects. PMID:23609775

  5. Fiber and Prebiotics: Mechanisms and Health Benefits

    PubMed Central

    Slavin, Joanne

    2013-01-01

    The health benefits of dietary fiber have long been appreciated. Higher intakes of dietary fiber are linked to less cardiovascular disease and fiber plays a role in gut health, with many effective laxatives actually isolated fiber sources. Higher intakes of fiber are linked to lower body weights. Only polysaccharides were included in dietary fiber originally, but more recent definitions have included oligosaccharides as dietary fiber, not based on their chemical measurement as dietary fiber by the accepted total dietary fiber (TDF) method, but on their physiological effects. Inulin, fructo-oligosaccharides, and other oligosaccharides are included as fiber in food labels in the US. Additionally, oligosaccharides are the best known “prebiotics”, “a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-bring and health.” To date, all known and suspected prebiotics are carbohydrate compounds, primarily oligosaccharides, known to resist digestion in the human small intestine and reach the colon where they are fermented by the gut microflora. Studies have provided evidence that inulin and oligofructose (OF), lactulose, and resistant starch (RS) meet all aspects of the definition, including the stimulation of Bifidobacterium, a beneficial bacterial genus. Other isolated carbohydrates and carbohydrate-containing foods, including galactooligosaccharides (GOS), transgalactooligosaccharides (TOS), polydextrose, wheat dextrin, acacia gum, psyllium, banana, whole grain wheat, and whole grain corn also have prebiotic effects. PMID:23609775

  6. Numerical studies of fibrous composites from the view point of fiber-matrix interface and fiber-matrix bonding

    NASA Astrophysics Data System (ADS)

    Yilmaz, Yahya Ilyas

    In the present research, the micromechanics of fibrous composites was studied numerically. The effects of the fiber/matrix interphase region and fiber/matrix bonding were the main goals of this research. Throughout the research NASTRAN finite element analyses were used. First we investigated the effect of the interphase region on the stress field by varying the thickness of the interphase region and the material properties in the interphase region. Second, we numerically simulated the bonding qualities between the fiber and the matrix by the implementation of the fiber/matrix interphase region. The change for bonding between the fiber and the matrix were simulated through a periodic material property change in the interphase region. Third, we developed a bi-dimensional concentric cylindrical model for stress transfer between the fiber and the matrix model in case of a broken fiber or short fiber composites. This model is unique in accounting for the real non-linear stress-strain relationship for the matrix material. The stress transfer between the fiber and the matrix was also analyzed by finite element models. Toward this end finite element analysis proved a useful tool to help us evaluate key model parameters, most importantly the radius of fiber influence. This parameter is also a key parameter of simple models upon which the new model is based. Finally we applied our stress transfer model to analyze single fiber fragmentation test data obtained at Kansas State University.

  7. Beneficial regulation of fibrillar collagens, heat shock protein-47, elastin fiber components, transforming growth factor-β1, vascular endothelial growth factor and oxidative stress effects by copper in dermal fibroblasts.

    PubMed

    Philips, Neena; Samuel, Philips; Parakandi, Harit; Gopal, Sesha; Siomyk, Halyna; Ministro, Abraham; Thompson, Terrel; Borkow, Gadi

    2012-01-01

    Skin aging is associated with the loss of the structural collagens and the elastin fiber components that form the extracellular matrix (ECM). It is associated with reduced transforming growth factor-β (TGF-β), angiogenesis and increased oxidative stress. Copper has been incorporated into cosmetics for anti-skin aging. This research investigated the mechanism for the anti-skin aging effect copper ions, from cuprous oxide powders. Dermal fibroblasts were exposed to copper and examined for expression (protein and/or promoter levels) of types I, III, V collagen, heat shock protein-47 (HSP-47), elastin, fibrillin-1, and fibrillin-2, TGF-β1, vascular endothelial growth factor (VEGF), and in addition for membrane damage and lipid peroxidation. The direct antioxidant activity of copper was also determined. The research indicates that copper's anti-skin aging and skin regeneration potential is through its stimulation of ECM proteins, TGF-β1, VEGF, and inhibition of oxidative stress effects at physiological concentrations; and supports its use in cosmetics. PMID:22324999

  8. Production and Testing of Transgenic Cotton that Expresses Transcription Factors for Enhanced Seed and Fiber Traits and Productivity Under Drought Stress

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Abscisic acid (ABA) is a plant hormone involved in abiotic and biotic stress adaptation and seed development. We have previously shown that Basic3 (B3) domain and basic leucine zipper (b-ZIP) transcription factors from the model plant species maize and Arabidopsis thaliana can transactivate monocot...

  9. Crack initiation in borosilicate glass-SiC fiber composites

    SciTech Connect

    Dutton, R.E.; Pagano, N.J.; Kim, R.Y.

    1996-04-01

    The initiation of matrix microcracking was investigated in unidirectional glass matrix composites having controlled fiber spacing. Observations were taken from composites consisting of regular arrays of TiB{sub 2}-coated SIGMA 1240 and carbon-coated SCS-6 monofilament SiC fibers in a series of borosilicate glasses. The thermal expansion mismatch between the fibers and glass matrix was varied such that the resulting radial stresses after processing ranged from tensile to compressive. The glass strongly bonds to the TiB{sub 2}-coated SIGMA 1240 fiber but weakly bonds to the carbon coating of the SCS-6 fiber, allowing the investigation of the effects of bonding at the fiber/matrix interface. The observed crack initiation stresses of the various composites are compared to predictions based on a previously developed semiempirical model and used to study the influence of the volume fraction of fibers, residual stress state and interface strength.

  10. A Model for Fiber Length Attrition in Injection-Molded Long-Fiber Composites

    SciTech Connect

    TuckerIII, Charles L.; Phelps, Jay H; El-Rahman, Ahmed Abd; Kunc, Vlastimil

    2013-01-01

    Long-fiber thermoplastic (LFT) composites consist of an engineering thermoplastic matrix with glass or carbon reinforcing fibers that are initially 10 to 13 mm long. When an LFT is injection molded, flow during mold filling orients the fibers and degrades the fiber length. Fiber orientation models for injection molding are well developed, and special orientation models for LFTs have been developed. Here we present a detailed quantitative model for fiber length attrition in a flowing fiber suspension. The model tracks a discrete fiber length distribution (FLD) at each spatial node. Key equations are a conservation equation for total fiber length, and a breakage rate equation. The breakage rate is based on buckling of fibers due to hydrodynamic forces, when the fibers are in unfavorable orientations. The FLD model is combined with a mold filling simulation to predict spatial and temporal variations in fiber length distribution in a mold cavity during filling. The predictions compare well to experiments on a glassfiber/ PP LFT molding. Fiber length distributions predicted by the model are easily incorporated into micromechanics models to predict the stress-strain behavior of molded LFT materials. Author to whom correspondence should be addressed; electronic mail: ctucker@illinois.edu 1

  11. Realizing actual feedback control of complex network

    NASA Astrophysics Data System (ADS)

    Tu, Chengyi; Cheng, Yuhua

    2014-06-01

    In this paper, we present the concept of feedbackability and how to identify the Minimum Feedbackability Set of an arbitrary complex directed network. Furthermore, we design an estimator and a feedback controller accessing one MFS to realize actual feedback control, i.e. control the system to our desired state according to the estimated system internal state from the output of estimator. Last but not least, we perform numerical simulations of a small linear time-invariant dynamics network and a real simple food network to verify the theoretical results. The framework presented here could make an arbitrary complex directed network realize actual feedback control and deepen our understanding of complex systems.

  12. High performance fibers. Final report

    SciTech Connect

    Economy, J.

    1994-01-01

    A two and a half year ONR/ARPA funded program to develop a low cost process for manufacture of a high strength/high modulus sigma/E boron nitride (BN) fiber was initiated on 7/1/90 and ended on 12/31/92. The preparation of high sigma/E BN fibers had been demonstrated in the late 1960's by the PI using a batch nitriding of B2O3 fiber with NH3 followed by stress graphitization at approx. 2000 deg C. Such fibers displayed values comparable to PAN based carbon fibers but the mechanicals were variable most likely because of redeposition of volatiles at 2000 deg C. In addition, the cost of the fibers was very high due to the need for many hours of nitriding necessary to convert the B2O3 fibers. The use of batch nitriding negated two possible cost advantages of this concept, namely, the ease of drawing very fine, multi-filament yarn of B2O3 and more importantly the very low cost of the starting materials.

  13. Inert strength of pristine silica glass fibers

    SciTech Connect

    Smith, W.L.; Michalske, T.A.

    1993-11-01

    Silica glass fibers have been produced and tested under ultra high vacuum (UHV) conditions to investigate the inert strength of pristine fibers in absence of reactive agents. Analysis of the coefficient of variation in diameter ({upsilon}{sub d}) vs the coefficient of variation of breaking strength ({upsilon}{sub {sigma}}) does not adequately explain the variation of breaking stress. Distribution of fiber tensile strength data suggests that the inert strength of such fibers is not single valued and that the intrinsic strength is controlled by defects in the glass. Furthermore, comparison of room temperature UHV data with LN{sub 2} data indicates that these intrinsic strengths are not temperature dependent.

  14. Influence of fiber content on mechanical performance of SiC-fiber-reinforced reaction-bonded silicon nitride composites

    SciTech Connect

    Singh, D.; Singh, J.P.; Bhatt, R.T.

    1995-01-01

    The effect of fiber content on the resulting mechanical properties (first matrix cracking stress, ultimate strength, and work-of-fracture) of silicon carbide (SiC)-fiber-reinforced reaction-bonded silicon nitride (RBSN) matrix composites was investigated. Flexure tests were used to evaluate mechanical properties of composites containing various fiber contents. The first matrix cracking stress, ultimate strength, and work-of-fracture of the composites increased with increasing fiber content, reaching a peak value at a fiber content of {approximately} 16 vol.%. Further increases in fiber content degraded the mechanical properties of the composites. The variations in mechanical properties with fiber contents were correlated to the residual stresses in the matrix phase, processing related flaws, and failure modes observed in these composites.

  15. 50 CFR 253.16 - Actual cost.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 50 Wildlife and Fisheries 9 2011-10-01 2011-10-01 false Actual cost. 253.16 Section 253.16 Wildlife and Fisheries NATIONAL MARINE FISHERIES SERVICE, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE AID TO FISHERIES FISHERIES ASSISTANCE PROGRAMS Fisheries Finance Program §...

  16. 50 CFR 253.16 - Actual cost.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 50 Wildlife and Fisheries 11 2013-10-01 2013-10-01 false Actual cost. 253.16 Section 253.16 Wildlife and Fisheries NATIONAL MARINE FISHERIES SERVICE, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE AID TO FISHERIES FISHERIES ASSISTANCE PROGRAMS Fisheries Finance Program §...

  17. Children's Rights and Self-Actualization Theory.

    ERIC Educational Resources Information Center

    Farmer, Rod

    1982-01-01

    Educators need to seriously reflect upon the concept of children's rights. Though the idea of children's rights has been debated numerous times, the idea remains vague and shapeless; however, Maslow's theory of self-actualization can provide the children's rights idea with a needed theoretical framework. (Author)

  18. Culture Studies and Self-Actualization Theory.

    ERIC Educational Resources Information Center

    Farmer, Rod

    1983-01-01

    True citizenship education is impossible unless students develop the habit of intelligently evaluating cultures. Abraham Maslow's theory of self-actualization, a theory of innate human needs and of human motivation, is a nonethnocentric tool which can be used by teachers and students to help them understand other cultures. (SR)

  19. Group Counseling for Self-Actualization.

    ERIC Educational Resources Information Center

    Streich, William H.; Keeler, Douglas J.

    Self-concept, creativity, growth orientation, an integrated value system, and receptiveness to new experiences are considered to be crucial variables to the self-actualization process. A regular, year-long group counseling program was conducted with 85 randomly selected gifted secondary students in the Farmington, Connecticut Public Schools. A…

  20. Racial Discrimination in Occupations: Perceived and Actual.

    ERIC Educational Resources Information Center

    Turner, Castellano B.; Turner, Barbara F.

    The relationship between the actual representation of Blacks in certain occupations and individual perceptions of the occupational opportunity structure were examined. A scale which rated the degree of perceived discrimination against Blacks in 21 occupations was administered to 75 black male, 70 black female, 1,429 white male and 1,457 white…

  1. Developing Human Resources through Actualizing Human Potential

    ERIC Educational Resources Information Center

    Clarken, Rodney H.

    2012-01-01

    The key to human resource development is in actualizing individual and collective thinking, feeling and choosing potentials related to our minds, hearts and wills respectively. These capacities and faculties must be balanced and regulated according to the standards of truth, love and justice for individual, community and institutional development,…

  2. Fatigue damage growth mechanisms in continuous fiber reinforced titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Naik, R. A.; Pollock, W. D.

    1990-01-01

    The role of fiber/matrix interface strength, residual thermal stresses, and fiber and matrix properties on fatigue damage accumulation in continuous fiber metal matrix composites (MMC) will be discussed. Results from titanium matrix/silicon-carbide fiber composites will be the primary topic of discussion. Results have been obtained from both notched and unnotched specimens at room and elevated temperatures. The stress in the 0 deg fibers has been indentified as the controlling factor in fatigue life. Fatigue of the notched specimens indicated that cracks can grow many fiber spacings in the matrix materials without breaking fibers.

  3. Whiteheadian Actual Entitities and String Theory

    NASA Astrophysics Data System (ADS)

    Bracken, Joseph A.

    2012-06-01

    In the philosophy of Alfred North Whitehead, the ultimate units of reality are actual entities, momentary self-constituting subjects of experience which are too small to be sensibly perceived. Their combination into "societies" with a "common element of form" produces the organisms and inanimate things of ordinary sense experience. According to the proponents of string theory, tiny vibrating strings are the ultimate constituents of physical reality which in harmonious combination yield perceptible entities at the macroscopic level of physical reality. Given that the number of Whiteheadian actual entities and of individual strings within string theory are beyond reckoning at any given moment, could they be two ways to describe the same non-verifiable foundational reality? For example, if one could establish that the "superject" or objective pattern of self- constitution of an actual entity vibrates at a specific frequency, its affinity with the individual strings of string theory would be striking. Likewise, if one were to claim that the size and complexity of Whiteheadian 'societies" require different space-time parameters for the dynamic interrelationship of constituent actual entities, would that at least partially account for the assumption of 10 or even 26 instead of just 3 dimensions within string theory? The overall conclusion of this article is that, if a suitably revised understanding of Whiteheadian metaphysics were seen as compatible with the philosophical implications of string theory, their combination into a single world view would strengthen the plausibility of both schemes taken separately. Key words: actual entities, subject/superjects, vibrating strings, structured fields of activity, multi-dimensional physical reality.

  4. Mechanics of networks of aliphatic fibers in aqueous surfactant media

    NASA Astrophysics Data System (ADS)

    Zanchetta, Giuliano; Caggioni, Marco; Guida, Vincenzo; Trappe, Veronique

    2012-02-01

    We investigate the structural and rheological properties of aliphatic fibers dispersed in aqueous solutions of anionic surfactants, typically used in liquid detergents to provide yield stress. This system displays an onset to solid-like properties that depends on fiber concentration. In this contribution we will discuss how tuning the state of the surfactant background influences the fiber-fiber interactions and the mechanical properties of the gel.

  5. Fiber/matrix interfaces for SiC/SiC composites: Multilayer SiC coatings

    SciTech Connect

    Halverson, H.; Curtin, W.A.

    1996-08-01

    Tensile tests have been performed on composites of CVI SiC matrix reinforced with 2-d Nicalon fiber cloth, with either pyrolitic carbon or multilayer CVD SiC coatings [Hypertherm High-Temperature Composites Inc., Huntington Beach, CA.] on the fibers. To investigate the role played by the different interfaces, several types of measurements are made on each sample: (i) unload-reload hysteresis loops, and (ii) acoustic emission. The pyrolitic carbon and multilayer SiC coated materials are remarkably similar in overall mechanical responses. These results demonstrate that low-modulus, or compliant, interface coatings are not necessary for good composite performance, and that complex, hierarchical coating structures may possibly yield enhanced high-temperature performance. Analysis of the unload/reload hysteresis loops also indicates that the usual {open_quotes}proportional limit{close_quotes} stress is actually slightly below the stress at which the 0{degrees} load-bearing fibers/matrix interfaces slide and are exposed to atmosphere.

  6. Photovoltaic fibers

    NASA Astrophysics Data System (ADS)

    Gaudiana, Russell; Eckert, Robert; Cardone, John; Ryan, James; Montello, Alan

    2006-08-01

    It was realized early in the history of Konarka that the ability to produce fibers that generate power from solar energy could be applied to a wide variety of applications where fabrics are utilized currently. These applications include personal items such as jackets, shirts and hats, to architectural uses such as awnings, tents, large covers for cars, trucks and even doomed stadiums, to indoor furnishings such as window blinds, shades and drapes. They may also be used as small fabric patches or fiber bundles for powering or recharging batteries in small sensors. Power generating fabrics for clothing is of particular interest to the military where they would be used in uniforms and body armor where portable power is vital to field operations. In strong sunlight these power generating fabrics could be used as a primary source of energy, or they can be used in either direct sunlight or low light conditions to recharge batteries. Early in 2002, Konarka performed a series of proof-of-concept experiments to demonstrate the feasibility of building a photovoltaic cell using dye-sensitized titania and electrolyte on a metal wire core. The approach taken was based on the sequential coating processes used in making fiber optics, namely, a fiber core, e.g., a metal wire serving as the primary electrode, is passed through a series of vertically aligned coating cups. Each of the cups contains a coating fluid that has a specific function in the photocell. A second wire, used as the counter electrode, is brought into the process prior to entering the final coating cup. The latter contains a photopolymerizable, transparent cladding which hardens when passed through a UV chamber. Upon exiting the UV chamber, the finished PV fiber is spooled. Two hundred of foot lengths of PV fiber have been made using this process. When the fiber is exposed to visible radiation, it generates electrical power. The best efficiency exhibited by these fibers is 6% with an average value in the 4

  7. The Actual Apollo 13 Prime Crew

    NASA Technical Reports Server (NTRS)

    1970-01-01

    The actual Apollo 13 lunar landing mission prime crew from left to right are: Commander, James A. Lovell Jr., Command Module pilot, John L. Swigert Jr.and Lunar Module pilot, Fred W. Haise Jr. The original Command Module pilot for this mission was Thomas 'Ken' Mattingly Jr. but due to exposure to German measles he was replaced by his backup, Command Module pilot, John L. 'Jack' Swigert Jr.

  8. Strength degradation of SiC fiber during manufacture of titanium matrix composites by plasma spraying and hot pressing

    NASA Astrophysics Data System (ADS)

    Baik, K. H.; Grant, P. S.

    2001-12-01

    Titanium matrix composites (TMCs) reinforced with Sigma 1140+ SiC fiber have been manufactured by a combination of low pressure plasma spraying (LPPS spray/wind) and simultaneous fiber winding, followed by vacuum hot pressing (VHP). Fiber damage during TMC manufacture has been evaluated by measuring fiber tensile strength after fiber extraction from the TMCs at various processing stages, followed by fitting of these data to a Weibull distribution function. The LPPS spray/wind processing caused a decrease in mean fiber strength and Weibull modulus in comparison with as-received fibers. A number of fiber surface flaws, primarily in the outer C layer of the fiber, formed as a result of mechanical impact of poorly melted particles from the plasma spray. Coarse feedstock powders promoted an increase in the population of fiber surface flaws, leading to significant reduction in fiber strength. The VHP consolidation promoted further development of fiber surface flaws by fiber bending and stress localization because of nonuniform matrix shrinkage, resulting in further degradation in fiber strength. In the extreme case of fibers touching, the stress concentration on the fibers was sufficient to cause fiber cracking. Fractographic studies revealed that low strength fibers failed by surface flaw induced failure and contained a large fracture mirror zone. Compared with the more widely investigated foil-fiber-foil route to manufacture TMCs, LPPS/VHP resulted in less degradation in fiber strength for Sigma 1140+ fiber. Preliminary results for Textron SCS-6 fiber indicated a much greater tolerance to LPPS/VHP damage.

  9. Fiber crops

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Much research continues to develop renewable, recyclable, sustainable, and bio-based products from agricultural feed stocks such as cotton and flax fiber. Primary requirements are sustainable production, low cost, and consistent and known quality. To better understand these products, research contin...

  10. Design of the fiber optic support system and fiber bundle accelerated life test for VIRUS

    NASA Astrophysics Data System (ADS)

    Soukup, Ian M.; Beno, Joseph H.; Hayes, Richard J.; Heisler, James T.; Mock, Jason R.; Mollison, Nicholas T.; Good, John M.; Hill, Gary J.; Vattiat, Brian L.; Murphy, Jeremy D.; Anderson, Seth C.; Bauer, Svend M.; Kelz, Andreas; Roth, Martin M.; Fahrenthold, Eric P.

    2010-07-01

    The quantity and length of optical fibers required for the Hobby-Eberly Telescope* Dark Energy eXperiment (HETDEX) create unique fiber handling challenges. For HETDEX‡, at least 33,600 fibers will transmit light from the focal surface of the telescope to an array of spectrographs making up the Visible Integral-Field Replicable Unit Spectrograph (VIRUS). Up to 96 Integral Field Unit (IFU) bundles, each containing 448 fibers, hang suspended from the telescope's moving tracker located more than 15 meters above the VIRUS instruments. A specialized mechanical system is being developed to support fiber optic assemblies onboard the telescope. The discrete behavior of 448 fibers within a conduit is also of primary concern. A life cycle test must be conducted to study fiber behavior and measure Focal Ratio Degradation (FRD) as a function of time. This paper focuses on the technical requirements and design of the HETDEX fiber optic support system, the electro-mechanical test apparatus for accelerated life testing of optical fiber assemblies. Results generated from the test will be of great interest to designers of robotic fiber handling systems for major telescopes. There is concern that friction, localized contact, entanglement, and excessive tension will be present within each IFU conduit and contribute to FRD. The test apparatus design utilizes six linear actuators to replicate the movement of the telescope over 65,000 accelerated cycles, simulating five years of actual operation.

  11. Influence of Reinforcement Anisotropy on the Stress Distribution in Tension and Shear of a Fusion Magnet Insulation System

    NASA Astrophysics Data System (ADS)

    Humer, K.; Raff, S.; Prokopec, R.; Weber, H. W.

    2008-03-01

    A glass fiber reinforced plastic laminate, which consists of half-overlapped wrapped Kapton/R-glass-fiber reinforcing tapes vacuum-pressure impregnated in a cyanate ester/epoxy blend, is proposed as the insulation system for the ITER Toroidal Field coils. In order to assess its mechanical performance under the actual operating conditions, cryogenic (77 K) tensile and interlaminar shear tests were done after irradiation to the ITER design fluence of 1×1022 m-2 (E>0.1 MeV). The data were then used for a Finite Element Method (FEM) stress analysis. We find that the mechanical strength and the fracture behavior as well as the stress distribution and the failure criteria are strongly influenced by the winding direction and the wrapping technique of the reinforcing tapes.

  12. INFLUENCE OF REINFORCEMENT ANISOTROPY ON THE STRESS DISTRIBUTION IN TENSION AND SHEAR OF A FUSION MAGNET INSULATION SYSTEM

    SciTech Connect

    Humer, K.; Prokopec, R.; Weber, H. W.; Raff, S.

    2008-03-03

    A glass fiber reinforced plastic laminate, which consists of half-overlapped wrapped Kapton/R-glass-fiber reinforcing tapes vacuum-pressure impregnated in a cyanate ester/epoxy blend, is proposed as the insulation system for the ITER Toroidal Field coils. In order to assess its mechanical performance under the actual operating conditions, cryogenic (77 K) tensile and interlaminar shear tests were done after irradiation to the ITER design fluence of 1x10{sup 22} m{sup -2} (E>0.1 MeV). The data were then used for a Finite Element Method (FEM) stress analysis. We find that the mechanical strength and the fracture behavior as well as the stress distribution and the failure criteria are strongly influenced by the winding direction and the wrapping technique of the reinforcing tapes.

  13. Stress echocardiography

    MedlinePlus

    Echocardiography stress test; Stress test - echocardiography; CAD - stress echocardiography; Coronary artery disease - stress Echocardiography; Chest pain - stress echocardiography; Angina - stress echocardiography; ...

  14. Simulations of Fiber Distribution Effects in Fiber-Reinforced Cement Composites

    SciTech Connect

    Bolander, John E.; Lim, Yun Mook

    2008-02-15

    This paper describes a lattice model for coupled moisture transport/stress analyses of fiber-reinforced cement composites (FRCC). Each fiber, and its interface with the matrix material, is explicitly represented within the three-dimensional material volume. This enables the direct study of fiber orientation and distribution effects on composite performance. Realistic, nonuniform fiber distributions can be specified as model input. Basic applications of the model are presented, with emphasis toward simulating the durability mechanics of FRCC exposed to drying environments. The modeling of functionally graded FRCC is an obvious potential extension of this work.

  15. Air resistance measurements on actual airplane parts

    NASA Technical Reports Server (NTRS)

    Weiselsberger, C

    1923-01-01

    For the calculation of the parasite resistance of an airplane, a knowledge of the resistance of the individual structural and accessory parts is necessary. The most reliable basis for this is given by tests with actual airplane parts at airspeeds which occur in practice. The data given here relate to the landing gear of a Siemanms-Schuckert DI airplane; the landing gear of a 'Luftfahrzeug-Gesellschaft' airplane (type Roland Dlla); landing gear of a 'Flugzeugbau Friedrichshafen' G airplane; a machine gun, and the exhaust manifold of a 269 HP engine.

  16. Biaxial shear/tension failure criteria of spectra single fibers

    NASA Astrophysics Data System (ADS)

    Sun, Jianzhuo

    An experimental study was conducted to develop the biaxial failure surface criteria of single Spectra 130d and 100d filaments in a torsion-tension environment. The cross-sectional profiles of single Spectra fibers were investigated using scanning electron microscopy and X-ray computed tomography. A pin-gripping method to fix the ends of a polyethylene single fiber was developed. Effects of pin diameter on failure stress for both Spectra 130d and 100d were characterized. It was found that the perturbed stress field effect can be neglected when the pin diameter is larger than 0.8 mm. Additionally, the effect of the sample's gage length on fiber tensile strength was investigated. The gage length of 5.5 mm was determined as an appropriate length for single fiber samples under stress-wave loading. A twisting apparatus was built for a single fiber to achieve specific degrees of shear strains. Quasi-static experiments were conducted using an MTS servo-hydraulic system to apply tensile loads on pre-twisted Spectra fibers. A tension Kolsky bar was employed to study the biaxial shear/tensile behavior of Spectra fibers at high strain rates. A decreasing trend of tensile strength, with increasing torsional strain, for Spectra fibers was observed. Furthermore, a torsional pendulum apparatus was developed to determine the torsional shear stresses in fibers at various levels of axial loading. The relationship between apparent shear stress and axial stress was discovered. Finally, a biaxial shear/tension failure criterion envelope of each of the Spectra fibers was established. Scanning electron microscopy images revealed the specific feature on the surface of twisted fibers and fracture surface of failure fibers.

  17. Finite element analysis of the fiber twist test

    SciTech Connect

    Gaudette, F.; Ertuerk, T.; Robertson, S.

    1995-10-01

    Interface and torsional shear stresses in the fiber twist test (FTT) were computed using the ABAQUS finite element program. Interface stress singularities were compared with an elasticity solution for the torsion of a fiber embedded in an elastic half space. Single fiber composite systems having perfectly bonded interfaces and fiber/matrix shear modulus ratios of G{sub f}/G{sub m} = 1--3 were considered. The decay rates and depths of the interface shear stress {delta}{sub r{theta}} and the torsional shear stress {delta}{sub Z{theta}} in the fiber and matrix were evaluated for each G{sub f}/G{sub m} ratio.

  18. Digital-image-correlation-based experimental stress analysis of reinforced concrete beams, strengthened using carbon composites

    NASA Astrophysics Data System (ADS)

    Helm, Jeffrey; Kurtz, Stephen

    2004-12-01

    The strengthening of reinforced concrete beams through the use of epoxy-bonded carbon composites has been widely researched in the United States since 1991. Despite the widespread attention of researchers, however, there are no reliable methods of predicting the failure of the repaired and strengthened beams by peeling of the fiber reinforced polymer (FRP) material from the parent concrete. To better understand peeling failure, several investigators have presented analytical work to predict the distribution of stresses along the interface between the FRP and the concrete. Several closed-form solutions can be found in the literature to predict the levels of shear stress present between the bonded composite plate and the parent concrete beam. However, there has been very little experimental verification of these analytical predictions because few experiments on large-scale beams have had sufficient instrumentation to facilitate the comparison. Some experiments have been presented1 in which electrical resistance strain gages were placed along the length of the carbon plate in order to deduce the interfacial shear stress using first differences. This method, though very crude, demonstrated that there are substantial differences between the distributions of interfacial shear stresses in actual repaired beams versus the analytical predictions. This paper presents a new test program in which large-scale carbon-fiber-strengthened reinforced concrete beams are load-tested to failure, while employing digital image correlation (DIC) to record the strains in the carbon fiber plate. Relying on the linear elasticity of carbon fiber, the interfacial shear can be determined and compared with the analytical predictions of the literature. The focus of this paper is the presentation of the experimental shear stress distributions and comparisons of these distributions with previous results available in the literature.

  19. Digital-image-correlation-based experimental stress analysis of reinforced concrete beams strengthened using carbon composites

    NASA Astrophysics Data System (ADS)

    Helm, Jeffrey; Kurtz, Stephen

    2005-01-01

    The strengthening of reinforced concrete beams through the use of epoxy-bonded carbon composites has been widely researched in the United States since 1991. Despite the widespread attention of researchers, however, there are no reliable methods of predicting the failure of the repaired and strengthened beams by peeling of the fiber reinforced polymer (FRP) material from the parent concrete. To better understand peeling failure, several investigators have presented analytical work to predict the distribution of stresses along the interface between the FRP and the concrete. Several closed-form solutions can be found in the literature to predict the levels of shear stress present between the bonded composite plate and the parent concrete beam. However, there has been very little experimental verification of these analytical predictions because few experiments on large-scale beams have had sufficient instrumentation to facilitate the comparison. Some experiments have been presented1 in which electrical resistance strain gages were placed along the length of the carbon plate in order to deduce the interfacial shear stress using first differences. This method, though very crude, demonstrated that there are substantial differences between the distributions of interfacial shear stresses in actual repaired beams versus the analytical predictions. This paper presents a new test program in which large-scale carbon-fiber-strengthened reinforced concrete beams are load-tested to failure, while employing digital image correlation (DIC) to record the strains in the carbon fiber plate. Relying on the linear elasticity of carbon fiber, the interfacial shear can be determined and compared with the analytical predictions of the literature. The focus of this paper is the presentation of the experimental shear stress distributions and comparisons of these distributions with previous results available in the literature.

  20. Tensile properties of an ultrahigh-strength graphite fiber in an epoxy matrix

    NASA Technical Reports Server (NTRS)

    Chiao, T. T.; Hamstad, M. A.; Jessop, E. S.

    1974-01-01

    The fiber performance and reinforcement potential for fiber composites of a special PAN-based graphite fiber were evaluated by testing the fiber's tensile properties in an epoxy matrix. Representative strand samples were taken from 30 spools of single-end, 1500-filament fiber to make over 5000 fiber/epoxy strand specimens using the filament-winding process. Characteristics studied were fiber uniformity, strength and modulus distributions at room and liquid-nitrogen temperatures, stress-strain behavior, the effect of strain rate on fiber strength, and acoustic emission during tensile loading to failure. The fiber was found to have a 3570-MPa failure stress, a 1.7% failure strain, a 206-GPa modulus, and a density of 1.77 Mg/cu m at 23 C. Liquid-nitrogen temperature and various strain rates had no significant effect on fiber tensile properties.

  1. Relative sliding durability of candidate high temperature fiber seal materials

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Steinetz, Bruce M.

    1992-01-01

    The relative sliding durability behavior of six candidate ceramic fibers for high temperature sliding seal applications is reviewed and compared. Pin on disk tests were used to evaluate potential seal materials by sliding a tow or bundle of the candidate ceramic fiber against a superalloy test disk. Tests were conducted in air under a 2.65 N load, at a sliding velocity of 0.025 m/sec and at temperatures from 25 to 900 C. Friction was measured during the tests and fiber wear, indicated by the extent of fibers broken in the tow or bundle, was measured at the end of each test. For most of the fibers, friction and wear increase with test temperature. The relative fiber durability ranking correlates with tensile strength, indicating that tensile data, which is more readily available than sliding durability data, may be useful in predicting fiber wear behavior under various conditions. A dimensional analysis of the wear data shows that the fiber durability is related to a dimensionless durability ratio which represents the ratio of the fiber strength to the fiber stresses imposed by sliding. The analysis is applicable to fibers with similar diameters and elastic moduli. Based upon the results of the research program, three fiber candidates are recommended for further study as potential seal materials. They are a silicon based complex carbide-oxide fiber, an alumina-boria-silica and an aluminosilicate fiber.

  2. Fatigue of continuous fiber reinforced titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1991-01-01

    Several lay-ups of SCS-6/Ti-15-3 composites were investigated. Static and fatigue tests were conducted for both notched and unnotched specimens at room and elevated temperatures. Test results indicated that the stress in the 0 fibers is the controlling factor in fatigue life. The static and fatigue strength of these materials is shown to be dependent on the level of residual stresses and the fiber/ matrix interfacial strength. Fatigue tests of notched specimens showed that cracks can initiate and grow many fiber spacings in the matrix material without breaking fibers. These matrix cracks can significantly reduce the residual strength of notched composite.

  3. Longitudinal interfacial shearing of a unidirectional fiber composite

    SciTech Connect

    Yang, M.; Kurth, R.E.

    1995-12-31

    In this work, longitudinal interfacial shearing of a unidirectional fiber composite which sustains slippage at the interface between fiber and matrix is analyzed. Based on the experimental work on the fiber pull-out, the interface between the fiber and the matrix can be divided as three regions, depending on the longitudinal shear stress. These three regions are the bonded region, frictional slip regions, and the free-friction slid region. The problem is formulated as a nonlinear system of singular integral equations and solved numerically. It has been shown that when the longitudinal shear stress is less than a critical value, the fiber and the matrix can be assumed to be bonded perfectly. When the longitudinal shear stress is greater than this critical value, the slippage at the interface between the fiber and the interface takes place. From the recent fiber pull-out test, the phenomena of fiber frictional slip followed by free slide has been observed and analyzed. Thus, there are three stages for the deformation of interfacial shearing of a unidirectional fiber composite under longitudinal shearing. The first stage occurs when the applied longitudinal shear stress is less than the critical value corresponding to the onset of slippage. In the second stage, the interface is divided into two regions, namely, the bonded region and the frictional slip region in which the shear stress is either assumed to be constant or governed by a friction law. The third stage occurs when the longitudinal shear stress is greater than the critical value corresponding to free sliding or when the friction limit is exceeded. In the third stage, the interface between the fiber and the matrix can be divided into three regions, depending on the longitudinal shear stress. These three regions are the bonded region, the frictional slip regions, and the free-friction slide region in which the shear stress is neglected.

  4. Effect of reinforcement and fiber-matrix interface on dynamic fracture of fiber-reinforced composite materials

    SciTech Connect

    Khanna, S.K.

    1992-01-01

    The experimental technique of dynamic photoelasticity coupled with high speed photography has been used to study the interaction of running cracks with brittle and ductile fibers embedded in a brittle polymeric matrix. The effect of reinforcement and the fiber-matrix interface on dynamic stress intensity factor, crack bridging phenomena, crack surface morphology and toughening mechanisms occurring during dynamic fracturing of reinforced brittle matrix composites has been investigated. It is found that reinforcement reduces the crack velocity and the stress intensity factor. Thus the energy supplied to the crack tip is reduced resulting in reduction of the crack jump distance. Fiber pullout experiments were done to characterize the fiber-matrix interface. Rapid pullout results in an increase in interface shear strength. For rapid pullout of fibers the difference between maximum pullout loads. for well and weakly bonded fibers, is much smaller than for very slow pullout. A fiber-matrix interface which is weaker in the vicinity of the crack path, termed the partly debonded interface, produces higher crack closing forces and lower stress intensity factor compared to well bonded fibers. The former interface condition results in low fracture energy and shorter crack jump compared to the later. The interface condition significantly affects the fracture surface morphology. The fracture surface roughness is lower for reinforced materials compared to monolithic. Further the partly debonded fibers result in lower surface roughness compared to the well bonded fibers. Inclined fibers with various interface conditions have no significant effect on the stress intensity factor. The fiber debonded length, however, decreases, as compared to fibers which are aligned with the loading direction, due to the kinking of the fibers.

  5. Fatigue damage growth mechanisms in continuous fiber reinforced titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Naik, R. A.; Pollock, W. D.

    1990-01-01

    The role of fiber/matrix interface strength, residual thermal stresses, and fiber and matrix properties on fatigue damage accumulation in continuous fiber metal matrix composites (MMC) is discussed. Results from titanium matrix silicon carbide fiber composites is the primary topic of discussion. Results were obtained from both notched and unnotched specimens at room and elevated temperatures. The stress in the 0 deg fibers was identified as the controlling factor in fatigue life. Fatigue of the notched specimens indicated that cracks can grow in the matrix materials without breaking fibers.

  6. Fatigue strength of woven kenaf fiber reinforced composites

    NASA Astrophysics Data System (ADS)

    Ismail, A. E.; Aziz, M. A. Che Abdul

    2015-12-01

    Nowadays, green composites provide alternative to synthetic fibers for non-bearing and load-bearing applications. According to literature review, lack of information is available on the fatigue performances especially when the woven fiber is used instead of randomly oriented fibers. In order to overcome this problem, this paper investigates the fatigue strength of different fiber orientations and number of layers of woven kenaf fiber reinforced composites. Four types of fiber orientations are used namely 0°, 15°, 30° and 45°. Additionally, two numbers of layers are also considered. It is revealed that the fatigue life has no strong relationship with the fiber orientations. For identical fiber orientations, the fatigue life can be predicted considerably using the normalized stress. However as expected, the fatigue life enhancement occur when the number of layer is increased.

  7. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 10 2012-01-01 2012-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  8. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 10 2014-01-01 2014-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  9. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 10 2013-01-01 2013-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  10. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 10 2011-01-01 2011-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  11. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 10 2010-01-01 2010-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  12. Strong, conductive carbon nanotube fibers as efficient hole collectors

    PubMed Central

    2012-01-01

    We present the photovoltaic properties of heterojunctions made from single-walled carbon nanotube (SWNT) fibers and n-type silicon wafers. The use of the opaque SWNT fiber allows photo-generated holes to transport along the axis direction of the fiber. The heterojunction solar cells show conversion efficiencies of up to 3.1% (actual) and 10.6% (nominal) at AM1.5 condition. In addition, the use of strong, environmentally benign carbon nanotube fibers provides excellent structural stability of the photovoltaic devices. PMID:22340519

  13. The actual status of Astronomy in Moldova

    NASA Astrophysics Data System (ADS)

    Gaina, A.

    The astronomical research in the Republic of Moldova after Nicolae Donitch (Donici)(1874-1956(?)) were renewed in 1957, when a satellites observations station was open in Chisinau. Fotometric observations and rotations of first Soviet artificial satellites were investigated under a program SPIN put in action by the Academy of Sciences of former Socialist Countries. The works were conducted by Assoc. prof. Dr. V. Grigorevskij, which conducted also research in variable stars. Later, at the beginning of 60-th, an astronomical Observatory at the Chisinau State University named after Lenin (actually: the State University of Moldova), placed in Lozovo-Ciuciuleni villages was open, which were coordinated by Odessa State University (Prof. V.P. Tsesevich) and the Astrosovet of the USSR. Two main groups worked in this area: first conducted by V. Grigorevskij (till 1971) and second conducted by L.I. Shakun (till 1988), both graduated from Odessa State University. Besides this research areas another astronomical observations were made: Comets observations, astroclimate and atmospheric optics in collaboration with the Institute of the Atmospheric optics of the Siberian branch of the USSR (V. Chernobai, I. Nacu, C. Usov and A.F. Poiata). Comets observations were also made since 1988 by D. I. Gorodetskij which came to Chisinau from Alma-Ata and collaborated with Ukrainean astronomers conducted by K.I. Churyumov. Another part of space research was made at the State University of Tiraspol since the beggining of 70-th by a group of teaching staff of the Tiraspol State Pedagogical University: M.D. Polanuer, V.S. Sholokhov. No a collaboration between Moldovan astronomers and Transdniestrian ones actually exist due to War in Transdniestria in 1992. An important area of research concerned the Radiophysics of the Ionosphere, which was conducted in Beltsy at the Beltsy State Pedagogical Institute by a group of teaching staff of the University since the beginning of 70-th: N. D. Filip, E

  14. What Galvanic Vestibular Stimulation Actually Activates

    PubMed Central

    Curthoys, Ian S.; MacDougall, Hamish Gavin

    2012-01-01

    In a recent paper in Frontiers Cohen et al. (2012) asked “What does galvanic vestibular stimulation actually activate?” and concluded that galvanic vestibular stimulation (GVS) causes predominantly otolithic behavioral responses. In this Perspective paper we show that such a conclusion does not follow from the evidence. The evidence from neurophysiology is very clear: galvanic stimulation activates primary otolithic neurons as well as primary semicircular canal neurons (Kim and Curthoys, 2004). Irregular neurons are activated at lower currents. The answer to what behavior is activated depends on what is measured and how it is measured, including not just technical details, such as the frame rate of video, but the exact experimental context in which the measurement took place (visual fixation vs total darkness). Both canal and otolith dependent responses are activated by GVS. PMID:22833733

  15. MODIS Solar Diffuser: Modelled and Actual Performance

    NASA Technical Reports Server (NTRS)

    Waluschka, Eugene; Xiong, Xiao-Xiong; Esposito, Joe; Wang, Xin-Dong; Krebs, Carolyn (Technical Monitor)

    2001-01-01

    The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument's solar diffuser is used in its radiometric calibration for the reflective solar bands (VIS, NTR, and SWIR) ranging from 0.41 to 2.1 micron. The sun illuminates the solar diffuser either directly or through a attenuation screen. The attenuation screen consists of a regular array of pin holes. The attenuated illumination pattern on the solar diffuser is not uniform, but consists of a multitude of pin-hole images of the sun. This non-uniform illumination produces small, but noticeable radiometric effects. A description of the computer model used to simulate the effects of the attenuation screen is given and the predictions of the model are compared with actual, on-orbit, calibration measurements.

  16. Techniques for increasing boron fiber fracture strain

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1977-01-01

    Improvement in the strain-to-failure of CVD boron fibers is shown possible by contracting the tungsten boride core region and its inherent flaws. The results of three methods are presented in which etching and thermal processing techniques were employed to achieve core flaw contraction by internal stresses available in the boron sheath. After commercially and treatment induced surface flaws were removed from 203 micrometers (8 mil) fibers, the core flaw was observed to be essentially the only source of fiber fracture. Thus, fiber strain-to-failure was found to improve by an amount equal to the treatment induced contraction on the core flaw. Commercial feasibility considerations suggest as the most cost effective technique that method in which as-produced fibers are given a rapid heat treatment above 700 C. Preliminary results concerning the contraction kinetics and fracture behavior observed are presented and discussed both for high vacuum and argon gas heat treatment environments.

  17. Elevated temperature fiber push-out testing

    SciTech Connect

    Eldridge, J.I.

    1995-10-01

    The potential use of fiber-reinforced composite materials for high temperature applications makes the development of interface test methodology at those high temperatures very desirable. A facility for performing high temperature fiber push-out tests will be described with emphasis on critical issues in experimental procedure. Examples from several composite systems illustrate the temperature dependence and environmental sensitivity of fiber debonding and sliding. Interpretation of the temperature dependence will be made primarily in terms of changes in residual stresses along with additional effects due to changes in matrix ductility and interfacial wear. Examples will show that high temperature fiber push-out testing can often distinguish between chemical and frictional fiber/matrix bonding in cases where room temperature only testing cannot.

  18. Dynamic response of damaged angleplied fiber composites

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.; Lark, R. F.

    1979-01-01

    An investigation was conducted to determine the effects of low level damage induced by monotonic load, cyclic load and/or residual stresses on the vibration frequencies and damping factors of fiber composite angleplied laminates. Two different composite systems were studied - low modulus fiber and ultra high modulus fiber composites. The results obtained showed that the frequencies and damping factors of angleplied laminates made from low modulus fiber composites are sensitive to low level damage while those made from ultra high modulus composites are not. Also, vibration tests may not be sufficiently sensitive to assess concentrated local damage in angleplied laminates. And furthermore, dynamic response determined from low-velocity impact coupled with the Fast Fourier Transform and packaged in a minicomputer can be a convenient procedure for assessing low-level damage in fiber composite angleplied laminates.

  19. Experimental Study on Tensile Behavior of Carbon Fiber and Carbon Fiber Reinforced Aluminum at Different Strain Rate

    NASA Astrophysics Data System (ADS)

    Zhou, Yuanxin; Wang, Ying; Jeelani, Shaik; Xia, Yuanming

    2007-01-01

    In this study, dynamic and quasi-static tensile behaviors of carbon fiber and unidirectional carbon fiber reinforced aluminum composite have been investigated. The complete stress strain curves of fiber bundles and the composite at different strain rates were obtained. The experimental results show that carbon fiber is a strain rate insensitive material, but the tensile strength and critical strain of the Cf/Al composite increased with increasing of strain rate because of the strain rate strengthening effect of aluminum matrix. Based on experimental results, a fiber bundles model has been combined with Weibull strength distribution function to establish a one-dimensional damage constitutive equation for the Cf/Al composite.

  20. Aging studies of Kevlar 49 fibers

    SciTech Connect

    Morgan, R.J.; Pruneda, C.O.; Kong, F.M.

    1983-11-01

    The aging mechanisms in service environment of Kevlar 49 fibers, E.I. duPont, (poly(p-phenylene)terephthalamide) are reviewed. The principal aging mechanisms considered are (i) u.v.-, (ii) hydrolytic- and (iii) stress-induced macromolecular chain scission and microvoid growth. U.V.-induced strength degradation can be significant as a result of photo-oxidative and photodegradative radical formation but in Kevlar 49-epoxy composites only the exterior yarn layer is deteriorated. Hydrolytic chain scission of the amide linkage and corresponding fiber strength deterioration is considered in terms of R.H., time, temperature and stress level. The rates of hydrolytic degradation at 100% R.H. in the 100 to 200/sup 0/C range are reported. The estimated rates of fiber degradation in various service environment conditions are also reported and shown not to be serious. The stress-induced aging of Kevlar 49 fibers is considered in terms of the growth and coalescence of inherent microvoids along the fiber axis together with the generation of new microvoids. (These growth processes involve no detectable macromolecular chain scission or deterioration in fiber strength.) At a critical microvoid volume fraction catastrophic failure occurs by interconnection of such voids.

  1. Fatigue of continuous fiber reinforced metallic materials

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Mirdamadi, M.; Bakuckas, J. G., Jr.

    1993-01-01

    The complex damage mechanisms that occur in fiber reinforced advanced metallic materials are discussed. As examples, results for several layups of SCS-6/Ti-15-3 composites are presented. Fatigue tests were conducted and analyzed for both notched and unnotched specimens at room and elevated temperatures. Test conditions included isothermal, non-isothermal, and simulated mission profile thermomechanical fatigue. Test results indicated that the stress in the 0 degree fibers is the controlling factor for fatigue life for a given test condition. An effective strain approach is presented for predicting crack initiation at notches. Fiber bridging models were applied to crack growth behavior.

  2. Fiber distributed feedback laser

    NASA Technical Reports Server (NTRS)

    Elachi, C.; Evans, G. A.; Yeh, C. (Inventor)

    1976-01-01

    Utilizing round optical fibers as communication channels in optical communication networks presents the problem of obtaining a high efficiency coupling between the optical fiber and the laser. A laser is made an integral part of the optical fiber channel by either diffusing active material into the optical fiber or surrounding the optical fiber with the active material. Oscillation within the active medium to produce lasing action is established by grating the optical fiber so that distributed feedback occurs.

  3. Caustic-Side Solvent Extraction: Prediction of Cesium Extraction for Actual Wastes and Actual Waste Simulants

    SciTech Connect

    Delmau, L.H.; Haverlock, T.J.; Sloop, F.V., Jr.; Moyer, B.A.

    2003-02-01

    This report presents the work that followed the CSSX model development completed in FY2002. The developed cesium and potassium extraction model was based on extraction data obtained from simple aqueous media. It was tested to ensure the validity of the prediction for the cesium extraction from actual waste. Compositions of the actual tank waste were obtained from the Savannah River Site personnel and were used to prepare defined simulants and to predict cesium distribution ratios using the model. It was therefore possible to compare the cesium distribution ratios obtained from the actual waste, the simulant, and the predicted values. It was determined that the predicted values agree with the measured values for the simulants. Predicted values also agreed, with three exceptions, with measured values for the tank wastes. Discrepancies were attributed in part to the uncertainty in the cation/anion balance in the actual waste composition, but likely more so to the uncertainty in the potassium concentration in the waste, given the demonstrated large competing effect of this metal on cesium extraction. It was demonstrated that the upper limit for the potassium concentration in the feed ought to not exceed 0.05 M in order to maintain suitable cesium distribution ratios.

  4. Strong fibers

    SciTech Connect

    Li, Che-Yu.

    1991-03-01

    This program was directed to a new and generic approach to the development of new materials with novel and interesting properties, and to the precision fabrication of these materials in one and two-dimensional forms. Advanced deposition processes and microfabrication technology were used to produce fibers and grids of metals, semiconductors, ceramics, and mixtures of controlled composition and structure, and with new and interesting mechanical and physical properties. Deposition processes included electron beam evaporation, co-deposition of mixtures by dual electron beam evaporation, thermal evaporation, sputtering of a single element or compound, sputtering of a single element in a gaseous atmosphere to produce compounds, plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD), and selective tungsten chemical vapor deposition (W-CVD). The approach was to use the deposition processes in coordination with patterns generated by optical lithography to produce fibers with transverse dimensions in the micron range, and lengths from less than a millimeter to several centimeters. The approach is also applicable to the production of two-dimensional grids and particulates of controlled sizes and geometries.

  5. Carbon-fiber technology

    NASA Technical Reports Server (NTRS)

    Hansen, C. F.; Parker, J. A.

    1980-01-01

    The state of the art of PAN based carbon fiber manufacture and the science of fiber behavior is surveyed. A review is given of the stabilization by oxidation and the subsequent carbonization of fibers, of the apparent structure of fibers deduced from scanning electron microscopy, from X-ray scattering, and from similarities with soft carbons, and of the known relations between fiber properties and heat treatment temperature. A simplified model is invoked to explain the electrical properties of fibers and recent quantum chemical calculations on atomic clusters are used to elucidate some aspects of fiber conductivity. Some effects of intercalation and oxidative modification of finished fibers are summarized.

  6. The preparation and investigation into properties of ionomer fiber

    NASA Astrophysics Data System (ADS)

    Ejigiri, Everest Emmanuel

    The purpose of this study was to demonstrate the preparation and characterization of ionomer fiber. Two outstanding features of oriented-fiber composites are their high strength-to- weight ratio and controlled anisotropy which is because fibers are formed when polymer chains (in case of polymeric materials) are all lined up in the same direction. And the chains can pack together tightly. Materials can be made into fiber for the purpose of getting better properties and to make the application flexible. In this study, ionomer fiber was prepared. The physical and mechanical properties were examined through a variety of tests- including tensile test, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), free shape recovery test, and constrained stress recovery test. The ionomer fibers were made into muscles fiber, and the tensile actuation behavior of the muscle was studied. From the DMA, Storage modulus, loss modulus, tan delta and glass transition temperature were obtained. DSC was also used to obtain the glass transition temperature which also closely aligned with glass transition obtained from DMA. Also according to the test results, ionomer fiber (filament) demonstrated considerable stress recovery, high ductility and however, the filament did not produce high recovery ratio. The fiber was made into artificial muscle and actuation test was also carried out, which indicated that because the fiber being too much elastic - the fiber was not able to expand and contract when heat was applied to it. Instead it showed continuous expansion.

  7. Fiber Length and Orientation in Long-Fiber Injection-Molded Thermoplastics. Part I: Modeling of Microstructure and Elastic Properties

    SciTech Connect

    Nguyen, Ba Nghiep; Bapanapalli, Satish K.; Holbery, James D.; Smith, Mark T.; Kunc, Vlastimil; Frame, Barbara J.; Phelps, Jay; Tucker III, Charles L.

    2008-05-01

    This paper investigates the effects of fiber length and orientation distributions on the elastic properties of long-fiber injection-molded thermoplastics (LFTs). The corrected experimental fiber length distribution and the predicted and experimental orientation distributions were used in modeling to compute the elastic properties of the composite. First, from the fiber length distribution (FLD) data in terms of number of fibers versus fiber length, the probability density functions were built and used in the computation. Also, it has been shown that the two-parameter Weibull’s distribution can be used to represent the actual FLD. Next, the Mori-Tanaka model that employs the Eshelby’s equivalent inclusion method was applied to calculate the stiffness matrix of the aligned fiber composite containing the established FLD. The stiffness of the actual as-formed composite was then determined from the stiffness of the computed aligned fiber composite that was averaged over all possible orientations using the orientation averaging method. The methodology to predict the elastic properties of LFTs was validated via experimental verification of the longitudinal and transverse moduli determined for long glass fiber injection-molded polypropylene specimens. Finally, a sensitivity analysis was conducted to determine the effect of a variation of FLD on the composite elastic properties.

  8. Micromechanical modeling of fiber fragmentation in a single fiber metal matrix composite specimen

    NASA Astrophysics Data System (ADS)

    Davis, Jean E.

    Micromechanical models have been developed in this study to predict the longitudinal mechanical behavior of unidirectional continuous fiber composite materials under a uniaxial applied effective strain of sufficient magnitude to cause irreversible damage in the form of brittle fiber fracture, interface damage resulting in a compliant interphase region, and matrix plasticity. A single fiber composite (SFC) specimen that consists of a single silicon carbide fiber embedded in an aluminum matrix with a thin interphase layer was used to investigate these effects. The objective of this research was to create a micromechanical model to predict the longitudinal constitutive behavior of the composite as damage occurs and to determine if the interfacial shear stress can be estimated from the fiber fragment length at a given effective strain. The aluminum matrix was modeled as either linear elastic, elastic-perfectly plastic, linear strain hardening, or power-law strain hardening. Before fiber fracture, the interphase layer forms a perfect bond between the fiber and matrix. During fiber fracture, the interphase is damaged and the interfacial bond becomes imperfect. The imperfect interface may be compliant or compliant and weak, and was modeled as a spring layer with vanishing thickness. The fiber fragments are assumed to be uniformly distributed such that the fragment lengths are equal at each load level. The Weibull distribution was used to relate the fiber fragment length to the tensile strength of the fiber. An increase in the applied effective strain causes successive fiber fractures, in that the fragments become increasingly shorter. The SFCs studied had either no fiber fractures, one fracture, or successive fractures; one of the four matrix material types; and either perfect, compliant, or compliant and weak interfaces. The finite element method was used to provide numerical solutions for the state of stress and fiber length at a given applied effective strain which

  9. The measurement of fracture energy at fiber-matrix interfaces

    SciTech Connect

    Pegoretti, A.; DiBenedetto, A.T.

    1996-12-31

    The primary function of the fiber-matrix interface in composite materials is to transmit stress from the polymer matrix to the high strength reinforcing fibers. When a fiber filament breaks, cracks will propagate from the broken fiber end either by interfacial debonding, transverse and conical matrix cracking or combinations of the three modes. The strength of the interface has been characterized using micromechanical tests, such as the single fiber fragmentation test and a variety of single fiber pull-out tests. Results are generally analyzed in terms of an {open_quotes}interfacial shear stress{close_quotes}, {tau}, or a critical energy release rate, G{sub c}. It is the objective of this study to measure directly the strain energy release rate, G{sub c} associated with each observable fracture mode and to determine the effect of constituent physical properties and interfacial adhesion on its magnitude.

  10. Mechanical analysis of wood-fiber cement sheets under constant and repeated loading

    NASA Astrophysics Data System (ADS)

    Teixeira, Divino Eterno

    Inorganic-bonded panels have been successfully utilized for many years around the world. Cellulose materials are extensively used for cement-bonded particleboard (CBP) and for fiber-reinforced cement (FRC) composites worldwide. Particularly in Europe, this family of composites is used, among other applications, for building construction. Use of wood-fiber cement (WFC) composites in North America has been steadily increasing over the last 10 years. Problems encountered with resin-bonded wood products used in exterior environments have resulted in litigation and search for viable products. WFC sheets are currently filling this need and gaining market share by virtue of their own superior properties. This study was designed to provide basic information currently lacking in literature and important to the wise application of WFC sheets. Experimental autoclaved WFC flat sheets made with kraft Douglas fir fiber and with recycled old corrugated containers (OCC) fiber were manufactured and the results compared with an available commercial product. This experimental program was subdivided into three manuscripts. The first manuscript evaluates whether the actual mechanical properties of WFC sheets can be predicted using nondestructive parameters of the material by applying stress wave time techniques. The second manuscript deals with characterization of the WFC sheets. Physical and mechanical properties were evaluated and results discussed with the use of a scanning electronic microscopic (SEM) analysis. Manuscript three examines the viscoelastic behavior of the material at constant and repeated loading conditions. The nondestructive evaluation (NDE) of the material showed good correlation between dynamic and static modulus of elasticity (MOE). A multivariate linear regression analysis provided the strongest correlation (R = 0.828) for static MOE as a function of wave speed, density, and dynamic MOE. Results from Manuscript 2 revealed that WFC sheets manufactured with

  11. Improved theoretical estimation of mechanical reliability of optical fibers

    NASA Astrophysics Data System (ADS)

    Tachikura, Masao; Kurosawa, Yoshinori; Namekawa, Yoshikazu

    2005-01-01

    We propose an enhanced theory that can be commonly applied to fiber reliability evaluations under various stress and failure probability levels, under prolonged stress and in stressed fiber distribution conditions. In the theory, the inert strength distribution of fibers is composed of two types of Weibull distributions with different slope parameters. We included proof-test conditions that adhere to Mitsunaga's theory in the calculations. New parameters that express the high-strength distribution can be obtained from the tensile strength data using a theoretical equation. We analyzed the static fatigue characteristics under uniform bending and two-point bending using this theory. The experimental results agreed well with the calculated results for bent fibers. We believe that the theory will play a vital role in the design of optical fiber cords for sharp-bending uses and in the minimization of various optical packages.

  12. Thermoelastic response of metal matrix composites with large-diameter fibers subjected to thermal gradients

    NASA Technical Reports Server (NTRS)

    Aboudi, Jacob; Pindera, Marek-Jerzy; Arnold, Steven M.

    1993-01-01

    A new micromechanical theory is presented for the response of heterogeneous metal matrix composites subjected to thermal gradients. In contrast to existing micromechanical theories that utilize classical homogenization schemes in the course of calculating microscopic and macroscopic field quantities, in the present approach the actual microstructural details are explicitly coupled with the macrostructure of the composite. Examples are offered that illustrate limitations of the classical homogenization approach in predicting the response of thin-walled metal matrix composites with large-diameter fibers when subjected to thermal gradients. These examples include composites with a finite number of fibers in the thickness direction that may be uniformly or nonuniformly spaced, thus admitting so-called functionally gradient composites. The results illustrate that the classical approach of decoupling micromechanical and macromechanical analyses in the presence of a finite number of large-diameter fibers, finite dimensions of the composite, and temperature gradient may produce excessively conservative estimates for macroscopic field quantities, while both underestimating and overestimating the local fluctuations of the microscopic quantities in different regions of the composite. Also demonstrated is the usefulness of the present approach in generating favorable stress distributions in the presence of thermal gradients by appropriately tailoring the internal microstructure details of the composite.

  13. Luminescent nanocrystal stress gauge

    PubMed Central

    Choi, Charina L.; Koski, Kristie J.; Olson, Andrew C. K.; Alivisatos, A. Paul

    2010-01-01

    Microscale mechanical forces can determine important outcomes ranging from the site of material fracture to stem cell fate. However, local stresses in a vast majority of systems cannot be measured due to the limitations of current techniques. In this work, we present the design and implementation of the CdSe-CdS core-shell tetrapod nanocrystal, a local stress sensor with bright luminescence readout. We calibrate the tetrapod luminescence response to stress and use the luminescence signal to report the spatial distribution of local stresses in single polyester fibers under uniaxial strain. The bright stress-dependent emission of the tetrapod, its nanoscale size, and its colloidal nature provide a unique tool that may be incorporated into a variety of micromechanical systems including materials and biological samples to quantify local stresses with high spatial resolution. PMID:21098301

  14. Annealing Effects on Creep and Rupture of Polycrystalline Alumina-Based Fibers

    NASA Technical Reports Server (NTRS)

    Goldsby, J. C.; Yun, H. M.; Morscher, G. N.; DiCarlo, J. A.

    1998-01-01

    Continuous-length polycrystalline aluminum-oxide-based fibers are being considered as reinforcements for advanced high-temperature composite materials. For these fine-grained fibers, basic issues arise concerning grain growth and microstructural instability during composite fabrication and the resulting effects on the fiber's thermo-mechanical properties. To examine these issues, commercially available Nextel 610 (alumina) and Altex (alumina-silica) fibers were annealed at 1100 and 1300 C for up to 100 hr in air. Changes in fiber microstructure, fiber tensile creep, stress rupture, and bend stress relaxation (BSR) that occurred with annealing were then determined. BSR tests were also used to compare as-received and annealed fibers to other polycrystalline oxide fibers. Annealing was shown to have a significant effect, particularly on the Altex fiber, and caused it to have increased creep resistance.

  15. Stress-induced fragmentation of multiwall carbon nanotubes in a polymer matrix

    NASA Astrophysics Data System (ADS)

    Wagner, H. D.; Lourie, O.; Feldman, Y.; Tenne, R.

    1998-01-01

    We report the observation of single nanotube fragmentation, under tensile stresses, using nanotube-containing thin polymeric films. Similar fragmentation tests with single fibers instead of nanotubes are routinely performed to study the fiber-matrix stress transfer ability in fiber composite materials, and thus the efficiency and quality of composite interfaces. The multiwall nanotube-matrix stress transfer efficiency is estimated to be at least one order of magnitude larger than in conventional fiber-based composites.

  16. Flow sensor using optical fiber strain gauges

    NASA Astrophysics Data System (ADS)

    Schmitt, Nicolas F.; Morgan, R.; Scully, Patricia J.; Lewis, Elfed; Chandy, Rekha

    1995-09-01

    A novel technique for the measurement of air flow velocity using an optical fiber sensor is reported. The sensor measures the deformation of a rubber cantilever beam when subjected to the stresses induced by drag forces in the presence of the airflow. Tests performed in a wind tunnel have indicated a sensitivity of 2 (mu) /(m/s). A qualitative model based on fiber mode propagation has been developed which allows the sensor to be characterized in terms of optical losses. A single 1 mm diameter polymer fiber is mounted on the rectangular section rubber cantilever (section 14 mm by 6 mm) and six grooves are etched into the fiber which extend into the core of the fiber. As the beam deviates the surface deforms (stretches or contracts) and the fiber is subjected to strain. As the strain is increased the grooves become wider and the amount of light transmitted through the fiber is reduced due to increased losses. The sensor described has all the advantages of optical fiber sensors including electrical noise immunity and intrinsic safety for use in hazardous environments. However, its simple construction, robustness, versatility for a number of different fluid applications, as well as relatively low cost make it attractive for use in a wide variety of measurement applications e.g. wind velocity measurement where airborne moisture or chemicals are present.

  17. Fiber transport of spatially entangled photons

    NASA Astrophysics Data System (ADS)

    Löffler, W.; Eliel, E. R.; Woerdman, J. P.; Euser, T. G.; Scharrer, M.; Russell, P.

    2012-03-01

    High-dimensional entangled photons pairs are interesting for quantum information and cryptography: Compared to the well-known 2D polarization case, the stronger non-local quantum correlations could improve noise resistance or security, and the larger amount of information per photon increases the available bandwidth. One implementation is to use entanglement in the spatial degree of freedom of twin photons created by spontaneous parametric down-conversion, which is equivalent to orbital angular momentum entanglement, this has been proven to be an excellent model system. The use of optical fiber technology for distribution of such photons has only very recently been practically demonstrated and is of fundamental and applied interest. It poses a big challenge compared to the established time and frequency domain methods: For spatially entangled photons, fiber transport requires the use of multimode fibers, and mode coupling and intermodal dispersion therein must be minimized not to destroy the spatial quantum correlations. We demonstrate that these shortcomings of conventional multimode fibers can be overcome by using a hollow-core photonic crystal fiber, which follows the paradigm to mimic free-space transport as good as possible, and are able to confirm entanglement of the fiber-transported photons. Fiber transport of spatially entangled photons is largely unexplored yet, therefore we discuss the main complications, the interplay of intermodal dispersion and mode mixing, the influence of external stress and core deformations, and consider the pros and cons of various fiber types.

  18. Fiber Contraction Approaches for Improving CMC Proportional Limit

    NASA Technical Reports Server (NTRS)

    DiCarlo, James A.; Yun, Hee Mann

    1997-01-01

    The fact that the service life of ceramic matrix composites (CMC) decreases dramatically for stresses above the CMC proportional limit has triggered a variety of research activities to develop microstructural approaches that can significantly improve this limit. As discussed in a previous report, both local and global approaches exist for hindering the propagation of cracks through the CMC matrix, the physical source for the proportional limit. Local approaches include: (1) minimizing fiber diameter and matrix modulus; (2) maximizing fiber volume fraction, fiber modulus, and matrix toughness; and (3) optimizing fiber-matrix interfacial shear strength; all of which should reduce the stress concentration at the tip of cracks pre existing or created in the matrix during CMC service. Global approaches, as with pre-stressed concrete, center on seeking mechanisms for utilizing the reinforcing fiber to subject the matrix to in-situ compressive stresses which will remain stable during CMC service. Demonstrated CMC examples for the viability of this residual stress approach are based on strain mismatches between the fiber and matrix in their free states, such as, thermal expansion mismatch and creep mismatch. However, these particular mismatch approaches are application limited in that the residual stresses from expansion mismatch are optimum only at low CMC service temperatures and the residual stresses from creep mismatch are typically unidirectional and difficult to implement in complex-shaped CMC.

  19. Life extension of elevated-temperature reactors considering actual operating conditions

    SciTech Connect

    Ziada, H.H.

    1993-01-01

    Many reactors have experienced operating conditions less severe than those specified in the design. Their actual operating conditions may involve fewer or less severe transients, lower operating temperatures, or a combination of these. Thus the actual operating conditions become important considerations in efforts to extend the life of reactor components. If the number of transients experienced is fewer than the number specified in the design, the actual transients must be reconstructed to determine extended life. When operating temperature is below 800 [degrees]F, fatigue damage becomes the controlling factor in life assessment. At operating temperatures above 800 [degrees]F (e.g., breeder reactors), creep damage becomes another controlling factor because residual stresses have a longer time for relaxation, a fact that will reduce creep damage. This study presents an approach to assessing the life of breeder reactor components when the actual transients are fewer in number than those specified in the design. It also discusses the sensitivity of creep-fatigue damage in such factors when actual operating temperatures and the actual severity of transients fall below the design specifications.

  20. Life extension of elevated-temperature reactors considering actual operating conditions

    SciTech Connect

    Ziada, H.H.

    1993-01-01

    Many reactors have experienced operating conditions less severe than those specified in the design. Their actual operating conditions may involve fewer or less severe transients, lower operating temperatures, or a combination of these. Thus the actual operating conditions become important considerations in efforts to extend the life of reactor components. If the number of transients experienced is fewer than the number specified in the design, the actual transients must be reconstructed to determine extended life. When operating temperature is below 800 {degrees}F, fatigue damage becomes the controlling factor in life assessment. At operating temperatures above 800 {degrees}F (e.g., breeder reactors), creep damage becomes another controlling factor because residual stresses have a longer time for relaxation, a fact that will reduce creep damage. This study presents an approach to assessing the life of breeder reactor components when the actual transients are fewer in number than those specified in the design. It also discusses the sensitivity of creep-fatigue damage in such factors when actual operating temperatures and the actual severity of transients fall below the design specifications.

  1. Phase-Compensating System For Fiber-Optic Holography

    NASA Technical Reports Server (NTRS)

    Mercer, Carolyn R.; Beheim, Glenn

    1990-01-01

    Phase-compensating system controls relative phase of laser light emitted from two optical fibers. Stabilized for conventional holographic applications, or stepped through sequence of 90 degree phase shifts for phase-stepping holographic interferometry. Closed-loop system compensates for phase fluctuations caused by mechanical stresses and temperature changes in fibers, providing long-term phase stability and phase steps accurate to within 0.02 degrees. Controls environmental fluctuations in phases of light emitted by output fibers.

  2. A simple test for thermomechanical evaluation of ceramic fibers

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Dicarlo, James A.

    1991-01-01

    A simple bend stress relaxation (BSR) test was developed to measure the creep related properties of ceramic fibers and whiskers. The test was applied to a variety of commercial and developmental Si based fibers to demonstrate capabilities and to evaluate the relative creep resistance of the fibers at 1200 to 1400 C. The implications of these results and the advantages of the BSR test over typical tensile creep tests are discussed.

  3. Consequences of Predicted or Actual Asteroid Impacts

    NASA Astrophysics Data System (ADS)

    Chapman, C. R.

    2003-12-01

    Earth impact by an asteroid could have enormous physical and environmental consequences. Impactors larger than 2 km diameter could be so destructive as to threaten civilization. Since such events greatly exceed any other natural or man-made catastrophe, much extrapolation is necessary just to understand environmental implications (e.g. sudden global cooling, tsunami magnitude, toxic effects). Responses of vital elements of the ecosystem (e.g. agriculture) and of human society to such an impact are conjectural. For instance, response to the Blackout of 2003 was restrained, but response to 9/11 terrorism was arguably exaggerated and dysfunctional; would society be fragile or robust in the face of global catastrophe? Even small impacts, or predictions of impacts (accurate or faulty), could generate disproportionate responses, especially if news media reports are hyped or inaccurate or if responsible entities (e.g. military organizations in regions of conflict) are inadequately aware of the phenomenology of small impacts. Asteroid impact is the one geophysical hazard of high potential consequence with which we, fortunately, have essentially no historical experience. It is thus important that decision makers familiarize themselves with the hazard and that society (perhaps using a formal procedure, like a National Academy of Sciences study) evaluate the priority of addressing the hazard by (a) further telescopic searches for dangerous but still-undiscovered asteroids and (b) development of mitigation strategies (including deflection of an oncoming asteroid and on- Earth civil defense). I exemplify these issues by discussing several representative cases that span the range of parameters. Many of the specific physical consequences of impact involve effects like those of other geophysical disasters (flood, fire, earthquake, etc.), but the psychological and sociological aspects of predicted and actual impacts are distinctive. Standard economic cost/benefit analyses may not

  4. Failure analysis of high performance ballistic fibers

    NASA Astrophysics Data System (ADS)

    Spatola, Jennifer S.

    High performance fibers have a high tensile strength and modulus, good wear resistance, and a low density, making them ideal for applications in ballistic impact resistance, such as body armor. However, the observed ballistic performance of these fibers is much lower than the predicted values. Since the predictions assume only tensile stress failure, it is safe to assume that the stress state is affecting fiber performance. The purpose of this research was to determine if there are failure mode changes in the fiber fracture when transversely loaded by indenters of different shapes. An experimental design mimicking transverse impact was used to determine any such effects. Three different indenters were used: round, FSP, and razor blade. The indenter height was changed to change the angle of failure tested. Five high performance fibers were examined: KevlarRTM KM2, SpectraRTM 130d, DyneemaRTM SK-62 and SK-76, and ZylonRTM 555. Failed fibers were analyzed using an SEM to determine failure mechanisms. The results show that the round and razor blade indenters produced a constant failure strain, as well as failure mechanisms independent of testing angle. The FSP indenter produced a decrease in failure strain as the angle increased. Fibrillation was the dominant failure mechanism at all angles for the round indenter, while through thickness shearing was the failure mechanism for the razor blade. The FSP indenter showed a transition from fibrillation at low angles to through thickness shearing at high angles, indicating that the round and razor blade indenters are extreme cases of the FSP indenter. The failure mechanisms observed with the FSP indenter at various angles correlated with the experimental strain data obtained during fiber testing. This indicates that geometry of the indenter tip in compression is a contributing factor in lowering the failure strain of the high performance fibers. TEM analysis of the fiber failure mechanisms was also attempted, though without

  5. Optimum Interfacial Layers For Fiber/Metal Composites

    NASA Technical Reports Server (NTRS)

    Lerch, Bradley A.; Ghosn, Louis J.

    1993-01-01

    Report presents theoretical stress-analysis study of some of factors affecting choice of thin layer of material placed at interface between each fiber and matrix of ceramic-fiber/metal-matrix composite. Effects of thickness, modulus of elasticity, and coefficient of thermal expansion considered.

  6. Leaf spring made of fiber-reinforced resin

    NASA Technical Reports Server (NTRS)

    Hori, J.

    1986-01-01

    A leaf spring made of a matrix reinforced by at least two types of reinforcing fibers with different Young's modulus is described in this Japanese patent. At least two layers of reinforcing fibers are formed by partially arranging the reinforcing fibers toward the direction of the thickness of the leaf spring. A mixture of different types of reinforced fibers is used at the area of boundary between the two layers of reinforced fibers. The ratio of blending of each type of reinforced fiber is frequently changed to eliminate the parts where discontinuous stress may be applied to the leaf spring. The objective of this invention is to prevent the rapid change in Young's modulus at the boundary area between each layer of reinforced fibers in the leaf spring.

  7. Fiber shape effects on metal matrix composite behavior

    NASA Technical Reports Server (NTRS)

    Brown, H. C.; Lee, H.-J.

    1992-01-01

    The effects of different fiber shapes on the behavior of metal matrix composites is computationally simulated. A three-dimensional finite element model consisting of a group of nine unidirectional fibers in a three by three unit cell array of a SiC/Ti-15-3 metal matrix composite is used in the analysis. The model is employed to represent five fiber shapes that include a circle, an ellipse, a kidney, and two different cross shapes. The distribution of stresses and the composite material properties, such as moduli, coefficients of thermal expansion, and Poisson's ratios, are obtained from the finite element analysis using the various fiber shapes. Comparisons of these results are used to determine the sensitivity of the composite behavior to the different fiber shapes. In general, fiber dominated properties are not affected by fiber geometry and matrix dominated properties are only moderately affected.

  8. A 0.63 micrometers polarization maintaining optical fiber cable

    NASA Astrophysics Data System (ADS)

    Yoshida, H.; Kikuchi, Y.; Tamaki, Y.

    1986-11-01

    Polarization maintaining single mode optical fiber cable was developed with negligible small loss increase and high crosstalk for optical interferometric measuring system of JT-60 (Japan Atomic Energy Research Institute TOKAMAK-60). Optical interferometric measuring system is required for high precise non-contact measurement of distance or vibration. Polarization maintaining optical fiber enabled to measure them in extremely high electromagnetic field of JT-60. Developed cable is flame-resistant non-metallic type complex 16 fiber cable for 0.6 micron use, that has 8 polarization maintaining optical fibers (stress applying, called PANDA fiber) and 8 single mode optical fibers. This paper shows the experimental result and the possibility of manufacturing polarization maintaining single mode optical fiber cable for 0.63 micron use.

  9. Modeling of statistical tensile strength of short-fiber composites

    SciTech Connect

    Zhu, Y.T.; Blumenthal, W.R.; Stout, M.G.; Lowe, T.C.

    1995-10-01

    This paper develops a statistical strength theory for three-dimensionally (3-D) oriented short-fiber reinforced composites. Short-fiber composites are usually reinforced with glass and ceramic short fibers and whiskers. These reinforcements are brittle and display a range of strength values, which can be statistically characterized by a Weibull distribution. This statistical nature of fiber strength needs to be taken into account in the prediction of composite strength. In this paper, the statistical nature of fiber strength is incorporated into the calculation of direct fiber strengthening, and a maximum-load composite failure criterion is adopted to calculate the composite strength. Other strengthening mechanisms such as residual thermal stress, matrix work hardening, and short-fiber dispersion hardening are also briefly discussed.

  10. High-fiber foods

    MedlinePlus

    Dietary fiber - self-care ... Dietary fiber adds bulk to your diet. Because it makes you feel full faster, it can help you ... Grains are another important source of dietary fiber. Eat more: ... Whole-grain breads Brown rice Popcorn High-fiber cereals, such ...

  11. The characterization of the double fiber Bragg gratings fiber ring laser and its applications in a real time fiber sensing system

    NASA Astrophysics Data System (ADS)

    Ko, C. L.; Yang, C. Y.; Huang, K. R.; Shih, Ming Chang

    2008-09-01

    We demonstrate a fiber sensing system by using a fiber resonator which is formed by two fiber Bragg gratings. It is able to measure real time strain and stress directly by the variation of the intensity of the output power due to the modulation in the fiber resonator. It shows that recording of the strain variation can be achieved as high as 2K Hz. The frequency response, signal noise ratio, and maximum range of the sensing system are studied with various reflectivity of the FBG, and the coupling ratios of the couplers used in the system.

  12. Fiber optic connector

    DOEpatents

    Rajic, S.; Muhs, J.D.

    1996-10-22

    A fiber optic connector and method for connecting composite materials within which optical fibers are imbedded are disclosed. The fiber optic connector includes a capillary tube for receiving optical fibers at opposing ends. The method involves inserting a first optical fiber into the capillary tube and imbedding the unit in the end of a softened composite material. The capillary tube is injected with a coupling medium which subsequently solidifies. The composite material is machined to a desired configuration. An external optical fiber is then inserted into the capillary tube after fluidizing the coupling medium, whereby the optical fibers are coupled. 3 figs.

  13. Fiber optic connector

    DOEpatents

    Rajic, Slobodan; Muhs, Jeffrey D.

    1996-01-01

    A fiber optic connector and method for connecting composite materials within which optical fibers are imbedded. The fiber optic connector includes a capillary tube for receiving optical fibers at opposing ends. The method involves inserting a first optical fiber into the capillary tube and imbedding the unit in the end of a softened composite material. The capillary tube is injected with a coupling medium which subsequently solidifies. The composite material is machined to a desired configuration. An external optical fiber is then inserted into the capillary tube after fluidizing the coupling medium, whereby the optical fibers are coupled.

  14. Fiber optic temperature sensor

    NASA Technical Reports Server (NTRS)

    Sawatari, Takeo (Inventor); Gaubis, Philip A. (Inventor); Mattes, Brenton L. (Inventor); Charnetski, Clark J. (Inventor)

    1999-01-01

    A fiber optic temperature sensor uses a light source which transmits light through an optical fiber to a sensor head at the opposite end of the optical fiber from the light source. The sensor head has a housing coupled to the end of the optical fiber. A metallic reflective surface is coupled to the housing adjacent the end of the optical fiber to form a gap having a predetermined length between the reflective surface and the optical fiber. A detection system is also coupled to the optical fiber which determines the temperature at the sensor head from an interference pattern of light which is reflected from the reflective surface.

  15. Fiber optic temperature sensor

    NASA Technical Reports Server (NTRS)

    Sawatari, Takeo (Inventor); Gaubis, Philip A. (Inventor)

    2000-01-01

    A fiber optic temperature sensor uses a light source which transmits light through an optical fiber to a sensor head at the opposite end of the optical fiber from the light source. The sensor head has a housing coupled to the end of the optical fiber. A metallic reflective surface is coupled to the housing adjacent the end of the optical fiber to form a gap having a predetermined length between the reflective surface and the optical fiber. A detection system is also coupled to the optical fiber which determines the temperature at the sensor head from an interference pattern of light which is reflected from the reflective surface.

  16. Postcrack creep of polymeric fiber-reinforced concrete in flexure

    SciTech Connect

    Kurtz, S.; Balaguru, P.

    2000-02-01

    Results of an experimental investigation of the creep-time behavior of polypropylene and nylon fiber-reinforced concrete (FRC) are presented. Gravity loads were applied in flexure to precracked low volume fraction (0.1%) polypropylene and nylon FRC beams. Beams were tested at a range of stress levels to produce three outcomes: load sustained indefinitely (low stress), creep failure (intermediate stress), and rapid failure (high stress). Emphasis was placed on determining the maximum flexural stress that is sustainable indefinitely. The results indicate that polypropylene FRC has higher initial strength but nylon FRC can sustain a higher stress level. For both groups the sustainable stress is much lower than the postcrack strength.

  17. Thermal stress effects in intermetallic matrix composites

    NASA Technical Reports Server (NTRS)

    Wright, P. K.; Sensmeier, M. D.; Kupperman, D. S.; Wadley, H. N. G.

    1993-01-01

    Intermetallic matrix composites develop residual stresses from the large thermal expansion mismatch (delta-alpha) between the fibers and matrix. This work was undertaken to: establish improved techniques to measure these thermal stresses in IMC's; determine residual stresses in a variety of IMC systems by experiments and modeling; and, determine the effect of residual stresses on selected mechanical properties of an IMC. X ray diffraction (XRD), neutron diffraction (ND), synchrotron XRD (SXRD), and ultrasonics (US) techniques for measuring thermal stresses in IMC were examined and ND was selected as the most promising technique. ND was demonstrated on a variety of IMC systems encompassing Ti- and Ni-base matrices, SiC, W, and Al2O3 fibers, and different fiber fractions (Vf). Experimental results on these systems agreed with predictions of a concentric cylinder model. In SiC/Ti-base systems, little yielding was found and stresses were controlled primarily by delta-alpha and Vf. In Ni-base matrix systems, yield strength of the matrix and Vf controlled stress levels. The longitudinal residual stresses in SCS-6/Ti-24Al-llNb composite were modified by thermomechanical processing. Increasing residual stress decreased ultimate tensile strength in agreement with model predictions. Fiber pushout strength showed an unexpected inverse correlation with residual stress. In-plane shear yield strength showed no dependence on residual stress. Higher levels of residual tension led to higher fatigue crack growth rates, as suggested by matrix mean stress effects.

  18. Coatings for graphite fibers

    NASA Technical Reports Server (NTRS)

    Galasso, F. S.; Scola, D. A.; Veltri, R. D.

    1980-01-01

    Graphite fibers released from composites during burning or an explosion caused shorting of electrical and electronic equipment. Silicon carbide, silica, silicon nitride and boron nitride were coated on graphite fibers to increase their electrical resistances. Resistances as high as three orders of magnitude higher than uncoated fiber were attained without any significant degradation of the substrate fiber. An organo-silicone approach to produce coated fibers with high electrical resistance was also used. Celion 6000 graphite fibers were coated with an organo-silicone compound, followed by hydrolysis and pyrolysis of the coating to a silica-like material. The shear and flexural strengths of composites made from high electrically resistant fibers were considerably lower than the shear and flexural strengths of composites made from the lower electrically resistant fibers. The lower shear strengths of the composites indicated that the coatings on these fibers were weaker than the coating on the fibers which were pyrolyzed at higher temperature.

  19. Fiber optic monitoring device

    DOEpatents

    Samborsky, James K.

    1993-01-01

    A device for the purpose of monitoring light transmissions in optical fibers comprises a fiber optic tap that optically diverts a fraction of a transmitted optical signal without disrupting the integrity of the signal. The diverted signal is carried, preferably by the fiber optic tap, to a lens or lens system that disperses the light over a solid angle that facilitates viewing. The dispersed light indicates whether or not the monitored optical fiber or system of optical fibers is currently transmitting optical information.

  20. Alumina fiber strength improvement

    NASA Technical Reports Server (NTRS)

    Pepper, R. T.; Nelson, D. C.

    1982-01-01

    The effective fiber strength of alumina fibers in an aluminum composite was increased to 173,000 psi. A high temperature heat treatment, combined with a glassy carbon surface coating, was used to prevent degradation and improve fiber tensile strength. Attempts to achieve chemical strengthening of the alumina fiber by chromium oxide and boron oxide coatings proved unsuccessful. A major problem encountered on the program was the low and inconsistent strength of the Dupont Fiber FP used for the investigation.

  1. A multi-wavelength fiber laser based on superimposed fiber grating and chirp fiber Bragg grating for wavelength selection

    NASA Astrophysics Data System (ADS)

    Wang, Feng; Bi, Wei-hong; Fu, Xing-hu; Jiang, Peng; Wu, Yang

    2015-11-01

    In this paper, a new type of multi-wavelength fiber laser is proposed and demonstrated experimentally. Superimposed fiber grating (SIFG) and chirp fiber Bragg grating (CFBG) are used for wavelength selection. Based on gain equalization technology, by finely adjusting the stress device in the cavity, the gain and loss are equal, so as to suppress the modal competition and achieve multi-wavelength lasing at room temperature. The experimental results show that the laser can output stable multi-wavelength lasers simultaneously. The laser coupling loss is small, the structure is simple, and it is convenient for integration, so it can be widely used in dense wavelength division multiplexing (DWDM) system and optical fiber sensors.

  2. Matrix cracking in fiber-reinforced ceramic composites. Ph.D. Thesis

    SciTech Connect

    Danchaivijit, S.

    1994-01-01

    Matrix cracking in fiber-reinforced ceramic composites with unbonded frictional interface was studied using fracture mechanics theory. The critical stress for extension of a fiber-bridged crack was analyzed using the stress-intensity approach. The analysis used a new shear-lag formulation of the crack-closure traction applied by the bridging fibers based on the assumption of a constant sliding friction stress over the sliding length of the fiber-matrix interface. The new formulation satisfied two required limiting conditions: (1) when the stress in the bridging fiber approached the far-field applied stress, the crack-opening displacement approached a steady-state upper limit that was in agreement with the previous formulations; and (2) in the limit of zero crack opening, the stress in the bridging fiber approached the far-field fiber stress. This lower limit of the bridging stress was distinctly different from the previous formulations. Numerical calculations using the stress-intensity approach indicated that the critical stress for crack extension decreased with increasing crack length and approached a constant steady-state value for large cracks. The steady-state matrix-cracking stress agreed with a steady-state energy balance analysis applied to the continuum model, but it was slightly less than the matrix-cracking stress predicted by such theories of steady-state cracking as that of Aveston, Cooper, and Kelly (ACK). The origin of this difference and a method for reconciliation of the two theoretical approaches were discussed. The effects of residual stresses and partially bridged crack was studied and incorporated into the calculation of the critical stress for extension of matrix cracks. Matrix cracking was studied in a model, unidirectional SiC (fiber)-reinforced epoxy-alumina matrix composite. The fiber-matrix interface was tailored with coatings to achieve an unbonded frictional interface.

  3. Research on key problems for LAMOST optical fiber detection system

    NASA Astrophysics Data System (ADS)

    Wang, Mengxin; Chen, Jianjun; Luo, Ali; Chen, Xiaoran

    2014-07-01

    The large sky area multi-object fiber spectroscopic telescope (LAMOST) is an innovative reflecting schmidt telescope, promising a very high spectrum acquiring rate of several ten-thousands of spectra per night. By using the parallel controllable fiber positioning technique, LAMOST makes reconfiguration of fibers accurately according to the positions of objects in minutes and fine adjusting the fibers. During telescope observation period, each optical fiber unit positional accuracy directly determines the quality of subsequent spectrum acqusition, yet for real-time optical fiber positional accuracy, there only exists an internal information feedback which focus on the corresponding stepper motor driving conditions, however, this available information is not comprehensive, it can not offer the actual positional information for each fiber unit. Considering the LAMOST on-site environment, a novel real-time optical fiber positional accuracy detection system which can be integrated in the existing observation and control system need to be developed to solve this problem. During the observation interval, this system can offer a comprehensive and effective information feedback about the focal optical fiber positional accuracy. Based on this feedback, the observation assistants can properly adjust the observation strategies to ensure the effectiveness and accuracy of acquired spectrum. Furthermore, this fiber positional accuracy feedback can provide prior spectral quality information to the spectral processing personnel and optimal the spectrum processing efficiency.

  4. Anelastic deformation of boron fibers. [vapor deposited fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1975-01-01

    The flexural deformation behavior of vapor-deposited boron fibers was examined from 100 to 1100 K by stress-relaxation and internal friction techniques. Only strong thermally-activated anelasticity was observed with no evidence of plasticity up to surface strains of 0.006. The parameters governing the relaxation processes within the anelastic spectra of as-received and annealed fibers were determined. These parameters were correlated with X-ray structure studies to develop preliminary models for the sources of boron's anelasticity. The large relaxation strengths of the dominant Ia processes coupled with their relaxation times and energies suggest a sliding mechanism between certain basic structural subunits common to both the beta-rhombohedral and vapor-deposited boron structures.

  5. Friction and wear of TPS fibers: A study of the adhesion and friction of high modulus fibers

    NASA Technical Reports Server (NTRS)

    Bascom, Willard D.; Lee, Ilzoo

    1990-01-01

    The adhesional and frictional forces between filaments in a woven fabric or felt, strongly influenced the processability of the fiber and the mechanical durability of the final product. Even though the contact loads between fibers are low, the area of contact is extremely small giving rise to very high stresses; principally shear stresses. One consequence of these strong adhesional and frictional forces is the resistance of fibers to slide past each other during weaving or when processed into nonwoven mats or felts. Furthermore, the interfiber frictional forces may cause surface damage and thereby reduce the fiber strength. Once formed into fabrics, flexural handling and manipulation of the material again causes individual filaments to rub against each other resulting in modulus, brittle fibers such as those used in thermal protection systems (TPS). The adhesion and friction of organic fibers, notably polyethylene terephthalate (PET) fibers, have been extensively studied, but there has been very little work reported on high modulus inorganic fibers. An extensive study was made of the adhesion and friction of flame drawn silica fibers in order to develop experimental techniques and a scientific basis for data interpretation. Subsequently, these methods were applied to fibers of interest in TPS materials.

  6. Fiber Bragg Grating Filter High Temperature Sensors

    NASA Technical Reports Server (NTRS)

    Lyons, Donald R.; Brass, Eric D.; Pencil, Eric (Technical Monitor)

    2001-01-01

    We present a scaled-down method for determining high temperatures using fiber-based Bragg gratings. Bragg gratings are distributed along the length of the optical fiber, and have high reflectivities whenever the optical wavelength is twice the grating spacing. These spatially distinct Bragg regions (located in the core of a fiber) are sensitive to local temperature changes. Since these fibers are silica-based they are easily affected by localized changes in temperature, which results in changes to both the grating spacing and the wavelength reflectivity. We exploit the shift in wavelength reflectivity to measure the change in the local temperature. Note that the Bragg region (sensing area) is some distance away from where the temperature is being measured. This is done so that we can measure temperatures that are much higher than the damage threshold of the fiber. We do this by affixing the fiber with the Bragg sensor to a material with a well-known coefficient of thermal expansion, and model the heat gradient from the region of interest to the actual sensor. The research described in this paper will culminate in a working device as well as be the second portion of a publication pending submission to Optics Letters.

  7. Stress waves in transversely isotropic media: The homogeneous problem

    NASA Technical Reports Server (NTRS)

    Marques, E. R. C.; Williams, J. H., Jr.

    1986-01-01

    The homogeneous problem of stress wave propagation in unbounded transversely isotropic media is analyzed. By adopting plane wave solutions, the conditions for the existence of the solution are established in terms of phase velocities and directions of particle displacements. Dispersion relations and group velocities are derived from the phase velocity expressions. The deviation angles (e.g., angles between the normals to the adopted plane waves and the actual directions of their propagation) are numerically determined for a specific fiber-glass epoxy composite. A graphical method is introduced for the construction of the wave surfaces using magnitudes of phase velocities and deviation angles. The results for the case of isotropic media are shown to be contained in the solutions for the transversely isotropic media.

  8. Time-dependent failure in fiber-reinforced composites by fiber degradation

    SciTech Connect

    Iyengar, N.; Curtin, W.A.

    1997-04-01

    The failure of fiber-reinforced ceramic and metal matrix composites under a fixed load for extended times occurs because of strength degradation in the constituent fibers. Specifically, the ceramic fibers possess a Weibull strength distribution caused by crack-like flaws, which can grow according to a power-law growth mechanism. Failure of individual fibers causes interfacial slippage and stress redistribution to unfailed fibers, which in turn accelerates the degradation rate of the remaining fibers, and culminates in abrupt failure of the composite after sufficient damage has accumulated. This sequence of events is modeled both analytically and numerically within the Global Load Sharing (GLS) approximation previously utilized for quasi-static loading. Analytically, a general constitutive model for the relationship between the stress on the damaged fiber bundle, the strain in the unbroken fibers, and the extent of damage, is combined with a time-dependent damage evolution equation derived from the slow-crack-growth kinetics to yield an integral equation for the strain vs time at fixed applied load. A simple, accurate but approximate relationship between applied load, time to failure, fiber Weibull modulus, and slow crack growth exponent is presented. The numerical simulations of the same degradation process verify the general accuracy of the failure time obtained from the analytic results. The remaining tensile strength after some time at load but prior to failure is also studied, and the simulation results generally exhibited a more sudden-death failure than the analytical predictions. A specific application to the failure of a Nicalon fiber composite is presented.

  9. Overview of the carbon fiber problem

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Carbon fibers (CF) composite structures are being utilized more as alternatives to metals in both civilian and military applications. They are valued for their light weight and high strength as well as for their ease of designing structures with specific shapes and sizes. However, a problem may exist due to the high conductivity of CF. CF are manufactured from a precursor material which is subjected to great stress and heat treatment causing a change in the physical and electrical properties. The fibers are bound together by a matrix of epoxy. In the event of fire (aircraft accident) the epoxy would burn away releasing these fibers into the atmosphere. When these fibers come in contact with electronic equipment, they might cause damage to by settling on electrical junctions. An overview is given of the objectives for a study, and the approach and methodology developed for determination of risk profiles.

  10. Thermophysical ESEM Characterization of Carbon Fibers

    NASA Technical Reports Server (NTRS)

    Sue, Jiwoong; Ochoa, Ozden O.; Effinger, Michael R.; Munafo, Paul M. (Technical Monitor)

    2002-01-01

    Coefficients of thermal expansion (CTE) of carbon fibers create residual stresses in aggressive manufacturing and service environments. In this effort, environmental scanning electron microscope (ESEM) is used for in situ observations of a carbon fiber cross-section up to 1000 C in order to evaluate the much neglected transverse CTE. The perimeter of fiber cross-section is calculated with the Scion image processing program from images that were taken at every 100 C increments. CTE values are calculated by linear regression of the strain data based on the perimeter changes. Furthermore, through SEM, WDS and TEM observations, we are in the process of bringing an interactive rationale between CTE, crystallinity and surface roughness of carbon fibers.

  11. Transparent conductive graphene textile fibers.

    PubMed

    Neves, A I S; Bointon, T H; Melo, L V; Russo, S; de Schrijver, I; Craciun, M F; Alves, H

    2015-01-01

    Transparent and flexible electrodes are widely used on a variety of substrates such as plastics and glass. Yet, to date, transparent electrodes on a textile substrate have not been explored. The exceptional electrical, mechanical and optical properties of monolayer graphene make it highly attractive as a transparent electrode for applications in wearable electronics. Here, we report the transfer of monolayer graphene, grown by chemical vapor deposition on copper foil, to fibers commonly used by the textile industry. The graphene-coated fibers have a sheet resistance as low as ~1 kΩ per square, an equivalent value to the one obtained by the same transfer process onto a Si substrate, with a reduction of only 2.3 per cent in optical transparency while keeping high stability under mechanical stress. With this approach, we successfully achieved the first example of a textile electrode, flexible and truly embedded in a yarn. PMID:25952133

  12. Transparent conductive graphene textile fibers

    PubMed Central

    Neves, A. I. S.; Bointon, T. H.; Melo, L. V.; Russo, S.; de Schrijver, I.; Craciun, M. F.; Alves, H.

    2015-01-01

    Transparent and flexible electrodes are widely used on a variety of substrates such as plastics and glass. Yet, to date, transparent electrodes on a textile substrate have not been explored. The exceptional electrical, mechanical and optical properties of monolayer graphene make it highly attractive as a transparent electrode for applications in wearable electronics. Here, we report the transfer of monolayer graphene, grown by chemical vapor deposition on copper foil, to fibers commonly used by the textile industry. The graphene-coated fibers have a sheet resistance as low as ~1 kΩ per square, an equivalent value to the one obtained by the same transfer process onto a Si substrate, with a reduction of only 2.3 per cent in optical transparency while keeping high stability under mechanical stress. With this approach, we successfully achieved the first example of a textile electrode, flexible and truly embedded in a yarn. PMID:25952133

  13. Transparent conductive graphene textile fibers

    NASA Astrophysics Data System (ADS)

    Neves, A. I. S.; Bointon, T. H.; Melo, L. V.; Russo, S.; de Schrijver, I.; Craciun, M. F.; Alves, H.

    2015-05-01

    Transparent and flexible electrodes are widely used on a variety of substrates such as plastics and glass. Yet, to date, transparent electrodes on a textile substrate have not been explored. The exceptional electrical, mechanical and optical properties of monolayer graphene make it highly attractive as a transparent electrode for applications in wearable electronics. Here, we report the transfer of monolayer graphene, grown by chemical vapor deposition on copper foil, to fibers commonly used by the textile industry. The graphene-coated fibers have a sheet resistance as low as ~1 kΩ per square, an equivalent value to the one obtained by the same transfer process onto a Si substrate, with a reduction of only 2.3 per cent in optical transparency while keeping high stability under mechanical stress. With this approach, we successfully achieved the first example of a textile electrode, flexible and truly embedded in a yarn.

  14. Study of modeling aspects of long period fiber grating using three-layer fiber geometry

    NASA Astrophysics Data System (ADS)

    Singh, Amit

    2015-03-01

    The author studied and demonstrated the various modeling aspects of long period fiber grating (LPFG) such as the core effective index, cladding effective index, coupling coefficient, coupled mode theory, and transmission spectrum of the LPFG using three-layer fiber geometry. Actually, there are two different techniques used for theoretical modeling of the long period fiber grating. The first technique was used by Vengsarkar et al who described the phenomenon of long-period fiber gratings, and the second technique was reported by Erdogan who revealed the inaccuracies and shortcomings of the original method, thereby providing an accurate and updated alternative. The main difference between these two different approaches lies in their fiber geometry. Venserkar et al used two-layer fiber geometry which is simple but employs weakly guided approximation, whereas Erdogan used three-layer fiber geometry which is complex but also the most accurate technique for theoretical study of the LPFG. The author further discussed about the behavior of the transmission spectrum by altering different grating parameters such as the grating length, ultraviolet (UV) induced-index change, and grating period to achieve the desired flexibility. The author simulated the various results with the help of MATLAB.

  15. Specialty optical fibers: revisited

    NASA Astrophysics Data System (ADS)

    Romaniuk, Ryszard S.

    2011-10-01

    The paper contains description of chosen aspects of analysis and design of tailored optical fibers. By specialty optical fibers we understand here the fibers which have complex construction and which serve for the functional processing of optical signal rather than long distance transmission. Thus, they are called also instrumentation optical fibers. The following issues are considered: transmission properties, transformation of optical signal, fiber characteristics, fiber susceptibility to external reactions. The technology of tailored optical fibers offers a wider choice of the design tools for the fiber itself, and then various devices made from these fiber, than classical technology of communication optical fibers. The consequence is different fiber properties, nonstandard dimensions and different metrological problems. The price to be paid for wider design possibilities are bigger optical losses of these fibers and weaker mechanical properties, and worse chemical stability. These fibers find their applications outside the field of telecommunications. The applications of instrumentation optical fibers combine other techniques apart from the photonics ones like: electronic, chemical and mechatronic.

  16. Mechanical model for fiber-laden membranes

    NASA Astrophysics Data System (ADS)

    Rey, Alejandro D.; Murugesan, Yogesh K.

    2011-01-01

    An integrated mechanical model for fiber-laden membranes is presented and representative predictions of relevance to cellulose ordering and orientation in the plant cell wall are presented. The model describes nematic liquid crystalline self-assembly of rigid fibers on an arbitrarily curved fluid membrane. The mechanics of the fluid membrane is described by the Helfrich bending-torsion model, the fiber self-assembly is described by the 2D Landau-de Gennes quadrupolar Q-tensor order parameter model, and the fiber-membrane interactions (inspired by an extension of the 2D Maier-Saupe model to curved surfaces) include competing curvo-philic (curvature-seeking) and curvo-phobic (curvature-avoiding) effects. Analysis of the free energy reveals three fiber orientation regimes: (a) along the major curvature, (b) along the minor curvature, (c) away from the principal curvatures, according to the competing curvo-philic and curvo-phobic interactions. The derived shape equation (normal stress balance) now includes curvature-nematic ordering contributions, with both bending and torsion renormalizations. Integration of the shape and nematic order equations gives a complete model whose solution describes the coupled membrane shape/fiber order state. Applications to cylindrical membranes, relevant to the plant cell wall, shows how growth decreases the fiber order parameter and moves the fibers' director from the axial direction towards the azimuthal orientation, eventually leading to a state of stress predicted by pure membranes. The ubiquitous 54.7° cellulose fibril orientation with respect to the long axis in a cylindrical plant cell wall is shown to be predicted by the preset model when the ratio of curvo-phobic and curvo-philic interactions is in the range of the cylinder radius.

  17. Bounds on the strength distribution of unidirectional fiber composites

    SciTech Connect

    Mahesh, S.; Phoenix, S.L.; Beyerlein, I.J.

    1999-06-01

    Failure mechanisms under tensile loading of unidirectional fiber composites comprising of Weibull fibers embedded in a matrix are studied using Monte-Carlo simulations. Two fundamental mechanisms of failure are recognized--stress concentration driven failure and strength driven failure. It is shown that the cumulative distribution function for composite strength predicted by the stress concentration -driven failure and strength-driven failure form apparent upper and lower bounds respectively and also that failure mechanism switches from one to the other as fiber strength variability changes.

  18. Methods and optical fibers that decrease pulse degradation resulting from random chromatic dispersion

    DOEpatents

    Chertkov, Michael; Gabitov, Ildar

    2004-03-02

    The present invention provides methods and optical fibers for periodically pinning an actual (random) accumulated chromatic dispersion of an optical fiber to a predicted accumulated dispersion of the fiber through relatively simple modifications of fiber-optic manufacturing methods or retrofitting of existing fibers. If the pinning occurs with sufficient frequency (at a distance less than or are equal to a correlation scale), pulse degradation resulting from random chromatic dispersion is minimized. Alternatively, pinning may occur quasi-periodically, i.e., the pinning distance is distributed between approximately zero and approximately two to three times the correlation scale.

  19. Fiber pushout and interfacial shear in metal-matrix composites

    NASA Technical Reports Server (NTRS)

    Koss, Donald A.; Hellmann, John R.; Kallas, M. N.

    1993-01-01

    Recent thin-slice pushout tests have suggested that MMC matrix-fiber interface failure processes depend not only on such intrinsic factors as bond strength and toughness, and matrix plasticity, but such extrinsic factors as specimen configuration, thermally-induced residual stresses, and the mechanics associated with a given test. After detailing the contrasts in fiber-pullout and fiber-pushout mechanics, attention is given to selected aspects of thin-slice fiber pushout behavior illustrative of the physical nature of interfacial shear response and its dependence on both intrinsic and extrinsic factors.

  20. Elasto-plastic analysis of interface layers for fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Doghri, I.; Leckie, F. A.

    1991-01-01

    The mismatch in coefficients of thermal expansion (CTE) of fiber and matrix in metal matrix composites reinforced with ceramic fibers induces high thermal stresses in the matrix. Elasto-plastic analyses - with different degrees of simplification and modelization - show that an interface layer with a sufficiently high CTE can reduce the tensile hoop stress in the matrix substantially.

  1. Creep of chemically vapor deposited SiC fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1984-01-01

    The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with neglible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

  2. Stress and stress counselling.

    PubMed Central

    Matheson, K. H.

    1990-01-01

    This is a report by the 1989 National Association of Clinical Tutors Wyeth Travelling Fellow to the United States of America. The stresses of postgraduate training and attempts to modify these are described, including stress counselling. The significance of stress and the relevance of the findings for postgraduate training in the United Kingdom are considered. PMID:2235808

  3. Cyclic Fiber Push-In Test Monitors Evolution of Interfacial Behavior in Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Eldridge, Jeffrey I.

    1998-01-01

    SiC fiber-reinforced ceramic matrix composites are being developed for high-temperature advanced jet engine applications. Obtaining a strong, tough composite material depends critically on optimizing the mechanical coupling between the reinforcing fibers and the surrounding matrix material. This has usually been accomplished by applying a thin C or BN coating onto the surface of the reinforcing fibers. The performance of these fiber coatings, however, may degrade under cyclic loading conditions or exposure to different environments. Degradation of the coating-controlled interfacial behavior will strongly affect the useful service lifetime of the composite material. Cyclic fiber push-in testing was applied to monitor the evolution of fiber sliding behavior in both C- and BN-coated small-diameter (15-mm) SiC-fiber-reinforced ceramic matrix composites. The cyclic fiber push-in tests were performed using a desktop fiber push-out apparatus. At the beginning of each test, the fiber to be tested was aligned underneath a 10- mm-diameter diamond punch; then, the applied load was cycled between selected maximum and minimum loads. From the measured response, the fiber sliding distance and frictional sliding stresses were determined for each cycle. Tests were performed in both room air and nitrogen. Cyclic fiber push-in tests of C-coated, SiC-fiber-reinforced SiC showed progressive increases in fiber sliding distances along with decreases in frictional sliding stresses for continued cycling in room air. This rapid degradation in interfacial response was not observed for cycling in nitrogen, indicating that moisture exposure had a large effect in immediately lowering the frictional sliding stresses of C-coated fibers. These results indicate that matrix cracks bridged by C-coated fibers will not be stable, but will rapidly grow in moisture-containing environments. In contrast, cyclic fiber push-in tests of both BN-coated, SiC-fiber-reinforced SiC and BNcoated, SiC-fiber

  4. Optical fiber configurations for transmission of laser energy over great distances

    SciTech Connect

    Rinzler, Charles C; Zediker, Mark S

    2013-10-29

    There are provided optical fiber configurations that provide for the delivery of laser energy, and in particular, the transmission and delivery of high power laser energy over great distances. These configurations further are hardened to protect the optical fibers from the stresses and conditions of an intended application. The configurations provide means for determining the additional fiber length (AFL) need to obtain the benefits of such additional fiber, while avoiding bending losses.

  5. Optical fiber configurations for transmission of laser energy over great distances

    SciTech Connect

    Rinzler, Charles C; Zediker, Mark S

    2014-11-04

    There are provided optical fiber configurations that provide for the delivery of laser energy, and in particular, the transmission and delivery of high power laser energy over great distances. These configurations further are hardened to protect the optical fibers from the stresses and conditions of an intended application. The configurations provide means for determining the additional fiber length (AFL) need to obtain the benefits of such additional fiber, while avoiding bending losses.

  6. Strength and failure mechanisms of polyimide-coated optical fibers

    NASA Astrophysics Data System (ADS)

    Skontorp, Arne

    2000-06-01

    Embedded optical fibers and sensors must survive and remain functional for the lifetime of the structure being monitored, as repairs are generally impossible. Thus, the feasibility of an embedded optical fiber monitoring concept depends heavily on the durability of the optical fiber. Processes that degrade the mechanical properties of these fibers are therefore of great concern. During the process of writing a Bragg grating sensor in a fiber, the polyimide coating is damaged locally by ablation, making the fiber vulnerable to moisture degradation. To rectify this situation, the coating in the area around the grating is commonly removed and the fiber is recoated. However, this procedure itself makes the fiber susceptible to degradation by moisture and handling. Tensile experiments were conducted on both virgin fiber and on fibers that had been recoated to study deterioration related to the recoating process. Weibull theory was used to model the strength distributions and a fracture mechanics approach was used in conjunction with microscopy to study failure initiation and to evaluate the relative significance of coating defects. The results indicated that two independent flaw populations existed in the fibers, one associated with manufacturing defects and the other with inherent flaws on the surface of the glass fiber. The failure was always initiated on the glass surface, not in the coating, and the condition of the coating did not effect the failure location. The recoated fibers always failed in the recoated section at a significantly reduced load, due to degradation after exposure of the glass to the environment. This suggested that the recoating process might actually worsen the situation.

  7. Investigation of fiber/matrix interfacial mechanical behavior in ceramic matrix composites by cyclic fiber push-in testing

    SciTech Connect

    Eldridge, J.I.; Bhatt, R.T.; Bansal, N.P.; Olmstead, F.A.

    1996-12-31

    Cyclic fiber push-in testing is used to examine the stability of interfacial frictional sliding stresses and fiber debond lengths with continued push-in load/unload cycles. The measured response to applying load cycling to a single fiber reveals the susceptibility of the fiber/matrix interface to degrade under cyclic loading conditions, and thus, helps evaluate the contribution of the interface to the cyclic fatigue behavior of the composite after the occurrence of matrix cracks. From cyclic push-in testing in room temperature air, decreasing interfacial sliding stresses and increasing debond lengths are observed with continued load cycling for SCS-6 SiC fiber reinforced reaction-bonded silicon nitride (SCS-6/RBSN), whereas stable interfacial sliding stresses and no increase in debond lengths are observed with continued load cycling for SCS-6 SiC fiber reinforced strontium aluminosilicate (SCS-6/SAS). These results indicate that fiber-bridged matrix cracks should be stable under cyclic fatigue loading conditions in SCS-6/SAS, but should exhibit increasing crack opening displacements and fiber pull-out with continued cycling in SCS-6/RBSN. In addition, changing the test environment from room air to nitrogen significantly affects the cyclic push-in test results for SCS-6/RBSN, but not for SCS-6/SAS. The different responses to this change in test environment are attributed to different locations of interfacial failure.

  8. Ceramic fiber reinforced filter

    DOEpatents

    Stinton, David P.; McLaughlin, Jerry C.; Lowden, Richard A.

    1991-01-01

    A filter for removing particulate matter from high temperature flowing fluids, and in particular gases, that is reinforced with ceramic fibers. The filter has a ceramic base fiber material in the form of a fabric, felt, paper of the like, with the refractory fibers thereof coated with a thin layer of a protective and bonding refractory applied by chemical vapor deposition techniques. This coating causes each fiber to be physically joined to adjoining fibers so as to prevent movement of the fibers during use and to increase the strength and toughness of the composite filter. Further, the coating can be selected to minimize any reactions between the constituents of the fluids and the fibers. A description is given of the formation of a composite filter using a felt preform of commercial silicon carbide fibers together with the coating of these fibers with pure silicon carbide. Filter efficiency approaching 100% has been demonstrated with these filters. The fiber base material is alternately made from aluminosilicate fibers, zirconia fibers and alumina fibers. Coating with Al.sub.2 O.sub.3 is also described. Advanced configurations for the composite filter are suggested.

  9. Micromechanical simulation of the failure of fiber reinforced composites

    NASA Astrophysics Data System (ADS)

    Landis, Chad M.; Beyerlein, Irene J.; McMeeking, Robert M.

    2000-03-01

    The strength of unidirectionally reinforced fiber composites is simulated using the three dimensional shear lag model of Landis, C. M., McGlockton, M. A. and McMeeking, R. M. (1999) (An improved shear lag model for broken fibers in composites. J. Comp. Mat. 33, 667-680) and Weibull fiber statistics. The governing differential equations for the fiber displacements and stresses are solved exactly for any configuration of breaks using an influence superposition technique. The model predicts the tensile strength of well bonded, elastic fiber/matrix systems with fibers arranged in a square array. Length and strength scalings are used which are relevant for elastic, local load sharing composites. Several hundred Monte Carlo simulations were executed to determine the statistical strength distributions of the composite for three values of the fiber Weibull modulus, m=5, 10 and 20. Stress-strain behavior and the evolution of fiber damage are studied. Bundle sizes of 10×10, 15×15, 20×20, 25×25, 30×30 and 35×35 fibers of various lengths are investigated to determine the dependence of strength on the composite size. The validity of weakest link statistics for composite strength is examined as well.

  10. Stress and temperature self-sensing fibres

    NASA Astrophysics Data System (ADS)

    Psarras, G. C.; Parthenios, J.; Bollas, D.; Galiotis, C.

    2003-01-01

    The Raman response of aramid fibers is examined as a function of the applied stress and temperature. Noticeable wavenumber shifts are recorded for the 1611 and 1648 cm -1 Raman bands with increasing stress. In contrast, only the 1611 cm -1 band is affected by temperature within the -50 to 200 °C range. The existence of two adjacent vibrational modes sensitive to stress with only one of the two being temperature dependent, allows the development of a simultaneous stress and temperature spectroscopic sensor. The applicability of this sensor is evaluated on an epoxy resin - aramid fiber composite activated by a shape-memory-alloy actuator.

  11. Fiber optics in adverse environments

    SciTech Connect

    Lyous, P.B.

    1982-01-01

    Radiation effects in optical fibers are considered, taking into account recent progress in the investigation of radiation resistant optical fibers, radiation damage in optical fibers, radiation-induced transient absorption in optical fibers, X-ray-induced transient attenuation at low temperatures in polymer clad silica (PCS) fibers, optical fiber composition and radiation hardness, the response of irradiated optical waveguides at low temperatures, and the effect of ionizing radiation on fiber-optic waveguides. Other topics explored are related to environmental effects on components of fiber optic systems, and radiation detection systems using optical fibers. Fiber optic systems in adverse environments are also discussed, giving attention to the survivability of Army fiber optics systems, space application of fiber optics systems, fiber optic wavelength multiplexing for civil aviation applications, a new fiber optic data bus topology, fiber optics for aircraft engine/inlet control, and application of fiber optics in high voltage substations.

  12. Stress Management

    MedlinePlus

    ... Awards Healthy Workplace Food and Beverage Toolkit Stress Management Banner 1 - To Stress or Not to Stress - ... Decide But We Can Help What Is Stress Management? Banner 2 - Stress Continuum Graphic Banner Live life ...

  13. Strain transferring of embedded fiber Bragg grating sensors

    NASA Astrophysics Data System (ADS)

    Li, Dong-Sheng; Li, Hong-Nan

    2005-05-01

    The relationship between the strains measured by a fiber Bragg grating sensor and the actual structural strains is deduced, then the average strain transfer rate computed by the formulation developed in this paper is compared with available experimental data. The critical adherence length of an optical fiber sensor is determined by a strain lag parameter, which contains both the effects of the geometry and the relative stiffness of the structural components. The analyses shows that the critical adherence length of a fiber sensing segment is the minimum length with which the fiber has to be tightly glued to a structure for adequate sensing. The strain transfer rate of an optical fiber sensor embedded in a multi-layered structure is developed in a similar way, and the factors that influence the efficiency of optical fiber sensor strain transferring are discussed. It is concluded that the strains, sensed by a fiber Bragg grating, have to be magnified by a factor (strain transfer rate) to equal exactly to the actual structural strains.

  14. Efficiency of Sampling and Analysis of Asbestos Fibers on Filter Media: Implications for Exposure Assessment

    EPA Science Inventory

    To measure airborne asbestos and other fibers, an air sample must represent the actual number and size of fibers. Typically, mixed cellulose ester (MCE, 0.45 or 0.8 µm pore size) and to a much lesser extent, capillary-pore polycarbonate (PC, 0.4 µm pore size) membrane filters are...

  15. Application of fiber bridging models to fatigue crack growth in unidirectional titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Bakuckas, J. G., Jr.; Johnson, W. S.

    1992-01-01

    Several fiber bridging models were reviewed and applied to study the matrix fatigue crack growth behavior in center notched (0)(sub 8) SCS-6/Ti-15-3 and (0)(sub 4) SCS-6/Ti-6Al-4V laminates. Observations revealed that fatigue damage consisted primarily of matrix cracks and fiber matrix interfacial failure in the (0)(sub 8) SCS-6/Ti-15-3 laminates. Fiber-matrix interface failure included fracture of the brittle reaction zone and cracking between the two carbon rich fiber coatings. Intact fibers in the wake of the matrix cracks reduce the stress intensity factor range. Thus, an applied stress intensity factor range is inappropriate to characterize matrix crack growth behavior. Fiber bridging models were used to determine the matrix stress intensity factor range in titanium metal matrix composites. In these models, the fibers in the wake of the crack are idealized as a closure pressure. An unknown constant frictional shear stress is assumed to act along the debond or slip length of the bridging fibers. The frictional shear stress was used as a curve fitting parameter to available data (crack growth data, crack opening displacement data, and debond length data). Large variations in the frictional shear stress required to fit the experimental data indicate that the fiber bridging models in their present form lack predictive capabilities. However, these models provide an efficient and relatively simple engineering method for conducting parametric studies of the matrix growth behavior based on constituent properties.

  16. Fiber optic chemical sensors

    NASA Astrophysics Data System (ADS)

    Jung, Chuck C.; McCrae, David A.; Saaski, Elric W.

    1998-09-01

    This paper provides a broad overview of the field of fiber optic chemical sensors. Several different types of fiber optic sensors and probes are described, and references are cited for each category discussed.

  17. Soluble vs. insoluble fiber

    MedlinePlus

    ... soluble and insoluble. Both are important for health, digestion, and preventing diseases. Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in ...

  18. Omnidirectional fiber optic tiltmeter

    DOEpatents

    Benjamin, B.C.; Miller, H.M.

    1983-06-30

    A tiltmeter is provided which is useful in detecting very small movements such as earth tides. The device comprises a single optical fiber, and an associated weight affixed thereto, suspended from a support to form a pendulum. A light source, e.g., a light emitting diode, mounted on the support transmits light through the optical fiber to a group of further optical fibers located adjacent to but spaced from the free end of the single optical fiber so that displacement of the single optical fiber with respect to the group will result in a change in the amount of light received by the individual optical fibers of the group. Photodetectors individually connectd to the fibers produce corresponding electrical outputs which are differentially compared and processed to produce a resultant continuous analog output representative of the amount and direction of displacement of the single optical fiber.

  19. Soluble vs. insoluble fiber

    MedlinePlus

    ... diseases. Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, ...

  20. Fiber Optics Instrumentation Development

    NASA Technical Reports Server (NTRS)

    Chan, Patrick Hon Man; Parker, Allen R., Jr.; Richards, W. Lance

    2010-01-01

    This is a general presentation of fiber optics instrumentation development work being conducted at NASA Dryden for the past 10 years and recent achievements in the field of fiber optics strain sensors.

  1. Fiber Optics Technology.

    ERIC Educational Resources Information Center

    Burns, William E.

    1986-01-01

    Discusses various applications of fiber optics technology: information systems, industrial robots, medicine, television, transportation, and training. Types of jobs that will be available with fiber optics training (such as electricians and telephone cable installers and splicers) are examined. (CT)

  2. Competitive Stress and the Youth Sport Experience.

    ERIC Educational Resources Information Center

    Scanlan, Tara K.; Passer, Michael

    1981-01-01

    Competitive stress occurs when a child perceives that he is not performing to athletic standards. Results of a study done on boys from 16 soccer teams indicate that pregame stress was influenced by the child's perceived capabilities, and postgame stress was influenced by his perception of his actual performance. (JN)

  3. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-04-01

    A bend stress relaxation (BSR) test has been utilized to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Qualitative, S-shaped 1hr BSR curves were compared for three selected advanced SiC fiber types and standard Nicalon CG fiber. The temperature corresponding to the middle of the S-curve (where the BSR parameter m = 0.5) is a measure of a fiber`s thermal stability as well as it creep resistance. In order of decreasing thermal creep resistance, the measured transition temperatures were Nicalon S (1450{degrees}C), Sylramic (1420{degrees}C), Hi-Nicalon (1230{degrees}C) and Nicalon CG (1110{degrees}C).

  4. Helical Fiber Amplifier

    DOEpatents

    Koplow, Jeffrey P.; Kliner, Dahy; Goldberg, Lew

    2002-12-17

    A multi-mode gain fiber is provided which affords substantial improvements in the maximum pulse energy, peak power handling capabilities, average output power, and/or pumping efficiency of fiber amplifier and laser sources while maintaining good beam quality (comparable to that of a conventional single-mode fiber source). These benefits are realized by coiling the multimode gain fiber to induce significant bend loss for all but the lowest-order mode(s).

  5. Fiber pulling apparatus modification

    NASA Technical Reports Server (NTRS)

    Smith, Guy A.; Workman, Gary L.

    1992-01-01

    A reduced gravity fiber pulling apparatus (FPA) was constructed in order to study the effects of gravity on glass fiber formation. The apparatus was specifically designed and built for use on NASA's KC-135 aircraft. Four flights have been completed to date during which E-glass fiber was successfully produced in simulated zero, high, and lunar gravity environments. In addition simulated lunar soil samples were tested for their fiber producing properties using the FPA.

  6. Irradiation creep of advanced silicon carbide fibers

    NASA Astrophysics Data System (ADS)

    Scholz, R.; Youngblood, G. E.

    2000-12-01

    The bend stress relaxation (BSR) method was applied to study irradiation enhanced creep (IEC) of small diameter silicon carbide (SiC) fibers after 10 MeV proton irradiation. A first series of tests was conducted on Sylramic™ fibers irradiated at 600°C with average bending stresses of 400 and 667 MPa and for irradiation doses smaller than 0.04 dpa. The BSR results are compared to previously obtained torsional creep test results for the Textron SCS-6™ type SiC fibers by calculating the tensile equivalents for both testing methods. For the Sylramic fibers, the creep constant κ=4.7×10-6 Mpa-1 dpa-1, was a factor of 6 smaller than the κ-value determined for SCS-6 fibers at 600°C. In contrast, for T<900°C the κ-value determined by R.J. Price [Nucl. Technol. 35 (1977) 320] for high purity monolithic β-Si after 7.7 dpa neutron irradiation was only 0.4×10-6 MPa-1 dpa-1.

  7. Piezoresistive effect in carbon nanotube fibers.

    PubMed

    Lekawa-Raus, Agnieszka; Koziol, Krzysztof K K; Windle, Alan H

    2014-11-25

    The complex structure of the macroscopic assemblies of carbon nanotubes and variable intrinsic piezoresistivity of nanotubes themselves lead to highly interesting piezoresistive performance of this new type of conductive material. Here, we present an in-depth study of the piezoresistive effect in carbon nanotube fibers, i.e., yarnlike assemblies made purely of aligned carbon nanotubes, which are expected to find applications as electrical and electronic materials. The resistivity changes of carbon nanotube fibers were measured on initial loading, through the elastic/plastic transition, on cyclic loading and on stress relaxation. The various regimes of stress/strain behavior were modeled using a standard linear solid model, which was modified with an additional element in series to account for the observed creep behavior. On the basis of the experimental and modeling results, the origin of piezoresistivity is discussed. An additional effect on the resistivity was found as the fiber was held under load which led to observations of the effect of humidity and the associated water adsorption level on the resistivity. We show that the equilibrium uptake of moisture leads to the decrease in gauge factor of the fiber decrease, i.e., the reduction in the sensitivity of fiber resistivity to loading. PMID:25337627

  8. Fiber optic coupled optical sensor

    DOEpatents

    Fleming, Kevin J.

    2001-01-01

    A displacement sensor includes a first optical fiber for radiating light to a target, and a second optical fiber for receiving light from the target. The end of the first fiber is adjacent and not axially aligned with the second fiber end. A lens focuses light from the first fiber onto the target and light from the target onto the second fiber.

  9. Bend Properties of Sapphire Fibers at Elevated Temperatures. 1; Bend Survivability

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Sayir, Haluk

    1995-01-01

    The effect of temperature on the bend radius that a c-axis-oriented sapphire fiber can withstand was determined for fibers of various diameter. Bend stress rupture tests were performed for times of 1-100 h and temperatures of 300-1700 C. Fibers would survive the bend test undeformed, would fracture or would deform. The bend survival radius was determined to be the radius above which no fibers fractured or deformed for a given time-temperature treatment. It was found that the ability of fibers to withstand curvature decreases substantially with time and increasing temperature and that fibers of smaller diameter (46-83 micron) withstood smaller bend radii than would be expected from just a difference in fiber diameter when compared with the bend results of the fibers of large diameter (144 micron). This was probably due to different flaw populations, causing high temperature bend failure for the tested sapphire fibers of different diameters.

  10. Advanced Engineering Fibers.

    ERIC Educational Resources Information Center

    Edie, Dan D.; Dunham, Michael G.

    1987-01-01

    Describes Clemson University's Advanced Engineered Fibers Laboratory, which was established to provide national leadership and expertise in developing the processing equipment and advance fibers necessary for the chemical, fiber, and textile industries to enter the composite materials market. Discusses some of the laboratory's activities in…

  11. Oxynitride glass fibers

    NASA Technical Reports Server (NTRS)

    Patel, Parimal J.; Messier, Donald R.; Rich, R. E.

    1991-01-01

    Research at the Army Materials Technology Laboratory (AMTL) and elsewhere has shown that many glass properties including elastic modulus, hardness, and corrosion resistance are improved markedly by the substitution of nitrogen for oxygen in the glass structure. Oxynitride glasses, therefore, offer exciting opportunities for making high modulus, high strength fibers. Processes for making oxynitride glasses and fibers of glass compositions similar to commercial oxide glasses, but with considerable enhanced properties, are discussed. We have made glasses with elastic moduli as high as 140 GPa and fibers with moduli of 120 GPa and tensile strengths up to 2900 MPa. AMTL holds a U.S. patent on oxynitride glass fibers, and this presentation discusses a unique process for drawing small diameter oxynitride glass fibers at high drawing rates. Fibers are drawn through a nozzle from molten glass in a molybdenum crucible at 1550 C. The crucible is situated in a furnace chamber in flowing nitrogen, and the fiber is wound in air outside of the chamber, making the process straightforward and commercially feasible. Strengths were considerably improved by improving glass quality to minimize internal defects. Though the fiber strengths were comparable with oxide fibers, work is currently in progress to further improve the elastic modulus and strength of fibers. The high elastic modulus of oxynitride glasses indicate their potential for making fibers with tensile strengths surpassing any oxide glass fibers, and we hope to realize that potential in the near future.

  12. Mineral Fiber Toxicology

    EPA Science Inventory

    The chemical and physical properties of different forms of mineral fibers impact biopersistence and pathology in the lung. Fiber chemistry, length, aspect ratio, surface area and dose are critical factors determining mineral fiber-associated health effects including cancer and as...

  13. Linearly polarized fiber amplifier

    DOEpatents

    Kliner, Dahv A.; Koplow, Jeffery P.

    2004-11-30

    Optically pumped rare-earth-doped polarizing fibers exhibit significantly higher gain for one linear polarization state than for the orthogonal state. Such a fiber can be used to construct a single-polarization fiber laser, amplifier, or amplified-spontaneous-emission (ASE) source without the need for additional optical components to obtain stable, linearly polarized operation.

  14. The Fiber Optic Connection.

    ERIC Educational Resources Information Center

    Reese, Susan

    2003-01-01

    Describes the fiber optics programs at the Career and Technical Center in Berlin, Pennsylvania and the Charles S. Monroe Technology Center in Loudoun County, Virginia. Discusses the involvement of the Fiber Optic Association with education, research and development, manufacturing, sales, distribution, installation, and maintenance of fiber optic…

  15. Mechanical characterization and structural analysis of recycled fiber-reinforced-polymer resin-transfer-molded beams

    NASA Astrophysics Data System (ADS)

    Tan, Eugene Wie Loon

    1999-09-01

    The present investigation was focussed on the mechanical characterization and structural analysis of resin-transfer-molded beams containing recycled fiber-reinforced polymers. The beams were structurally reinforced with continuous unidirectional glass fibers. The reinforcing filler materials consisted entirely of recycled fiber-reinforced polymer wastes (trim and overspray). The principal resin was a 100-percent dicyclo-pentadiene unsaturated polyester specially formulated with very low viscosity for resin transfer molding. Variations of the resin transfer molding technique were employed to produce specimens for material characterization. The basic materials that constituted the structural beams, continuous-glass-fiber-reinforced, recycled-trim-filled and recycled-overspray-filled unsaturated polyesters, were fully characterized in axial and transverse compression and tension, and inplane and interlaminar shear, to ascertain their strengths, ultimate strains, elastic moduli and Poisson's ratios. Experimentally determined mechanical properties of the recycled-trim-filled and recycled-overspray-filled materials from the present investigation were superior to those of unsaturated polyester polymer concretes and Portland cement concretes. Mechanical testing and finite element analyses of flexure (1 x 1 x 20 in) and beam (2 x 4 x 40 in) specimens were conducted. These structurally-reinforced specimens were tested and analyzed in four-point, third-point flexure to determine their ultimate loads, maximum fiber stresses and mid-span deflections. The experimentally determined load capacities of these specimens were compared to those of equivalent steel-reinforced Portland cement concrete beams computed using reinforced concrete theory. Mechanics of materials beam theory was utilized to predict the ultimate loads and mid-span deflections of the flexure and beam specimens. However, these predictions proved to be severely inadequate. Finite element (fracture propagation

  16. Nonlinear laminate analysis for metal matrix fiber composites

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1981-01-01

    A nonlinear laminate analysis is described for predicting the mechanical behavior (stress-strain relationships) of angle-ply laminates in which the matrix is strained nonlinearly by both the residual stress and the mechanical load and in which additional nonlinearities are induced due to progressive fiber fractures and ply relative rotations. The nonlinear laminate analysis is based on linear composite mechanics and a piece-wise linear laminate analysis to handle the nonlinear responses. Results obtained by using this nonlinear analysis on boron-fiber/aluminum-matrix angle-ply laminates agree well with experimental data. The results shown illustrate the in situ ply stress-strain behavior and synergistic strength enhancement.

  17. Nonlinear laminate analysis for metal matrix fiber composites

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1981-01-01

    A nonlinear laminate analysis is described for predicting the mechanical behavior (stress-strain relationships) of angleplied laminates in which the matrix is strained nonlinearly by both the residual stress and the mechanical load and in which additional nonlinearities are induced due to progressive fiber fractures and ply relative rotations. The nonlinear laminate analysis (NLA) is based on linear composite mechanics and a piece wise linear laminate analysis to handle the nonlinear responses. Results obtained by using this nonlinear analysis on boron fiber/aluminum matrix angleplied laminates agree well with experimental data. The results shown illustrate the in situ ply stress-strain behavior and synergistic strength enhancement.

  18. 26 CFR 1.953-2 - Actual United States risks.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ..., and water damage risks incurred when property is actually located in the United States and marine... 26 Internal Revenue 10 2014-04-01 2013-04-01 true Actual United States risks. 1.953-2 Section 1... coverage as “.825% plus .3% fire, etc. risks plus .12% water risks = 1.245%”, a reasonable basis exists...

  19. Self-actualization: Its Use and Misuse in Teacher Education.

    ERIC Educational Resources Information Center

    Ivie, Stanley D.

    1982-01-01

    The writings of Abraham Maslow are analyzed to determine the meaning of the psychological term "self-actualization." After pointing out that self-actualization is a rare quality and that it has little to do with formal education, the author concludes that the concept has little practical relevance for teacher education. (PP)

  20. The Self-Actualization of Polk Community College Students.

    ERIC Educational Resources Information Center

    Pearsall, Howard E.; Thompson, Paul V., Jr.

    This article investigates the concept of self-actualization introduced by Abraham Maslow (1954). A summary of Maslow's Needs Hierarchy, along with a description of the characteristics of the self-actualized person, is presented. An analysis of humanistic education reveals it has much to offer as a means of promoting the principles of…

  1. From Self-Awareness to Self-Actualization

    ERIC Educational Resources Information Center

    Cangemi, Joseph P.; Englander, Meryl R.

    1974-01-01

    Highest priority of education is to help students utilize as much of their talent as is possible. Third Force psychologists would interpret this as becoming self-actualized. Self-awareness is required for psychological growth. Without self-awareness there can be no growth, no mental hygiene, and no self-actualization. (Author)

  2. 12 CFR 1806.203 - Selection Process, actual award amounts.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 12 Banks and Banking 7 2010-01-01 2010-01-01 false Selection Process, actual award amounts. 1806... OF THE TREASURY BANK ENTERPRISE AWARD PROGRAM Awards § 1806.203 Selection Process, actual award... round: (1) To select Applicants not previously selected, using the calculation and selection...

  3. Self-Actualization and the Effective Social Studies Teacher.

    ERIC Educational Resources Information Center

    Farmer, Rodney B.

    1980-01-01

    Discusses a study undertaken to investigate the relationship between social studies teachers' degrees of self-actualization and their teacher effectiveness. Investigates validity of using Maslow's theory of self-actualization as a way of identifying the effective social studies teacher personality. (Author/DB)

  4. Facebook as a Library Tool: Perceived vs. Actual Use

    ERIC Educational Resources Information Center

    Jacobson, Terra B.

    2011-01-01

    As Facebook has come to dominate the social networking site arena, more libraries have created their own library pages on Facebook to create library awareness and to function as a marketing tool. This paper examines reported versus actual use of Facebook in libraries to identify discrepancies between intended goals and actual use. The results of a…

  5. Perceived and Actual Student Support Needs in Distance Education.

    ERIC Educational Resources Information Center

    Visser, Lya; Visser, Yusra Laila

    2000-01-01

    This study sought to determine the academic, affective, and administrative support expectations of distance education students, and to compare actual expectations of distance education students with the instructor's perceptions of such expectations. Results demonstrated divergence between perceived and actual expectations of student support in…

  6. Gebrauchstexte im Fremdsprachenunterricht ("Actual" Texts in Foreign Language Teaching)

    ERIC Educational Resources Information Center

    Ziegesar, Detlef von

    1976-01-01

    Presents for analysis actual texts and texts specially written for teaching, arriving at a basis for a typology of actual texts. Defines teaching aims using such texts, and develops, from a TV program, a teaching unit used in a Karlsruhe school. (Text is in German.) (IFS/WGA)

  7. Self-Actualizing Men and Women: A Comparison Study.

    ERIC Educational Resources Information Center

    Hall, Eleanor G.; Hansen, Jan B.

    1997-01-01

    The self-actualization of 167 women who lived in the Martha Cook (MC) dormitory of the University of Michigan (1950-1970) was compared to that of a group of Ivy League men researched in another study. In addition, two groups of MC women were compared to each other to identify differences which might explain why some self-actualized while other did…

  8. SELF-ACTUALIZATION AND THE UTILIZATION OF TALENT.

    ERIC Educational Resources Information Center

    FRENCH, JOHN R.P.; MILLER, DANIEL R.

    THIS STUDY ATTEMPTED (1) TO DEVELOP A THEORY OF THE CAUSES AND CONSEQUENCES OF SELF-ACTUALIZATION AS RELATED TO THE UTILIZATION OF TALENT, (2) TO FIT THE THEORY TO EXISTING DATA, AND (3) TO PLAN ONE OR MORE RESEARCH PROJECTS TO TEST THE THEORY. TWO ARTICLES ON IDENTITY AND MOTIVATION AND SELF-ACTUALIZATION AND SELF-IDENTITY THEORY REPORTED THE…

  9. Self-Actualization Effects Of A Marathon Growth Group

    ERIC Educational Resources Information Center

    Jones, Dorothy S.; Medvene, Arnold M.

    1975-01-01

    This study examined the effects of a marathon group experience on university student's level of self-actualization two days and six weeks after the experience. Gains in self-actualization as a result of marathon group participation depended upon an individual's level of ego strength upon entering the group. (Author)

  10. 26 CFR 1.962-3 - Treatment of actual distributions.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 26 Internal Revenue 10 2013-04-01 2013-04-01 false Treatment of actual distributions. 1.962-3... TAX (CONTINUED) INCOME TAXES (CONTINUED) Controlled Foreign Corporations § 1.962-3 Treatment of actual... a foreign corporation. (ii) Treatment of section 962 earnings and profits under § 1.959-3....

  11. School Guidance Counselors' Perceptions of Actual and Preferred Job Duties

    ERIC Educational Resources Information Center

    Edwards, John Dexter

    2010-01-01

    The purpose of this study was to provide process data for school counselors, administrators, and the public, regarding school counselors' actual roles within the guidance counselor preferred job duties and actual job duties. In addition, factors including National Certification or no National Certification, years of counseling experience, and…

  12. Tensile Modulus Measurements of Carbon Nanotube Incorporated Electrospun Polymer Fibers

    NASA Astrophysics Data System (ADS)

    Ozturk, Yavuz; Kim, Jaemin; Shin, Kwanwoo

    2006-03-01

    Electrospinning has become a popular method for producing continuous polymer fibers with diameters in sub-micron scale. By this technique uniaxially aligned fibers can also be obtained, by using two separate parallel strips as conductive collectors. Uniaxial alignment of polymer fibers gives us the chance to well-characterize their structural properties via tensile modulus measurements. Here we report a simple and new technique for tensile testing of polymer fibers which employs a computerized spring-balance/step-motor setup. The key point in our technique is the production of fibers directly on the tensile tester by using two vertical strips as collectors. By this way, even fibers of very brittle nature can be tested without handling them. Calculation of total cross-sectional areas - which is crucial for determining stress values - was done by using scanning electron and optical microscope images for each sample. In this study we have investigated mechanical properties of Polystyrene (PS), Polymethylmethacrylate (PMMA) and PS/PMMA blend fibers; as well as Carbon Nanotube (CNT) incorporated PS, PMMA and PS/PMMA blend fibers. It is expected that the extraordinary mechanical properties of CNTs can be transferred into polymer matrix, by their incorporation into confined space within electrospun fibers. Here we analyzed the influence of CNT on polymer fibers as function of CNT amounts.

  13. Honeywell FLASH fiber optic motherboard evaluations

    NASA Astrophysics Data System (ADS)

    Stange, Kent

    1996-10-01

    The use of fiber optic data transmission media can make significant contributions in achieving increasing performance and reduced life cycle cost requirements placed on commercial and military transport aircraft. For complete end-to-end fiber optic transmission, photonics technologies and techniques need to be understood and applied internally to the aircraft line replaceable units as well as externally on the interconnecting aircraft cable plant. During a portion of the Honeywell contribution to Task 2A on the Fly- by-Light Advanced System Hardware program, evaluations were done on a fiber optic transmission media implementation internal to a Primary Flight Control Computer (PFCC). The PFCC internal fiber optic transmission media implementation included a fiber optic backplane, an optical card-edge connector, and an optical source/detector coupler/installation. The performance of these optical media components were evaluated over typical aircraft environmental stresses of temperature, vibration, and humidity. These optical media components represent key technologies to the computer end-to-end fiber optic transmission capability on commercial and military transport aircraft. The evaluations and technical readiness assessments of these technologies will enable better perspectives on productization of fly-by-light systems requiring their utilizations.

  14. The hygroscopic behavior of plant fibers: a review

    PubMed Central

    Célino, Amandine; Fréour, Sylvain; Jacquemin, Frédéric; Casari, Pascal

    2013-01-01

    Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and eco-friendly image, they are increasingly being employed as reinforcements in polymer matrix composites. Indeed, their complex microstructure as a composite material makes plant fiber a really interesting and challenging subject to study. Research subjects about such fibers are abundant because there are always some issues to prevent their use at large scale (poor adhesion, variability, low thermal resistance, hydrophilic behavior). The choice of natural fibers rather than glass fibers as filler yields a change of the final properties of the composite. One of the most relevant differences between the two kinds of fiber is their response to humidity. Actually, glass fibers are considered as hydrophobic whereas plant fibers have a pronounced hydrophilic behavior. Composite materials are often submitted to variable climatic conditions during their lifetime, including unsteady hygroscopic conditions. However, in humid conditions, strong hydrophilic behavior of such reinforcing fibers leads to high level of moisture absorption in wet environments. This results in the structural modification of the fibers and an evolution of their mechanical properties together with the composites in which they are fitted in. Thereby, the understanding of these moisture absorption mechanisms as well as the influence of water on the final properties of these fibers and their composites is of great interest to get a better control of such new biomaterials. This is the topic of this review paper. PMID:24790971

  15. The hygroscopic behavior of plant fibers: a review.

    PubMed

    Célino, Amandine; Fréour, Sylvain; Jacquemin, Frédéric; Casari, Pascal

    2013-01-01

    Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and eco-friendly image, they are increasingly being employed as reinforcements in polymer matrix composites. Indeed, their complex microstructure as a composite material makes plant fiber a really interesting and challenging subject to study. Research subjects about such fibers are abundant because there are always some issues to prevent their use at large scale (poor adhesion, variability, low thermal resistance, hydrophilic behavior). The choice of natural fibers rather than glass fibers as filler yields a change of the final properties of the composite. One of the most relevant differences between the two kinds of fiber is their response to humidity. Actually, glass fibers are considered as hydrophobic whereas plant fibers have a pronounced hydrophilic behavior. Composite materials are often submitted to variable climatic conditions during their lifetime, including unsteady hygroscopic conditions. However, in humid conditions, strong hydrophilic behavior of such reinforcing fibers leads to high level of moisture absorption in wet environments. This results in the structural modification of the fibers and an evolution of their mechanical properties together with the composites in which they are fitted in. Thereby, the understanding of these moisture absorption mechanisms as well as the influence of water on the final properties of these fibers and their composites is of great interest to get a better control of such new biomaterials. This is the topic of this review paper. PMID:24790971

  16. Toughened Matrix SiC Fiber Reinforced Composites

    NASA Technical Reports Server (NTRS)

    Levine, Stanley R.; Bhatt, Ramakrishna T.; Morscher, Gregory N.; Kiser, James D.

    2005-01-01

    First matrix cracking stress is a critical parameter for application of Sic fiber reinforced composites in highly stressed, environmentally demanding applications such as turbine blades. High matrix fracture toughness is a key property that contributes to high composite fracture stress. Silicon nitride offers reduced matrix elastic modulus, lower coefficient of thermal expansion, and potentially high fracture toughness compared to Sic matrices. All of these factors can be used to advantage to increase matrix fracture stress. As a first model system we are pursuing toughened silicon nitride matrix composites reinforced with SCS-9 fibers. Fabrication is by tape casting the matrix plies and tape lay-up with fiber plies followed by hot pressing at 1800 C. Progress toward this end will be reported.

  17. Fiber optic monitoring device

    DOEpatents

    Samborsky, J.K.

    1993-10-05

    A device for the purpose of monitoring light transmissions in optical fibers comprises a fiber optic tap that optically diverts a fraction of a transmitted optical signal without disrupting the integrity of the signal. The diverted signal is carried, preferably by the fiber optic tap, to a lens or lens system that disperses the light over a solid angle that facilitates viewing. The dispersed light indicates whether or not the monitored optical fiber or system of optical fibers is currently transmitting optical information. 4 figures.

  18. Fiber optic sensors

    NASA Technical Reports Server (NTRS)

    Hesse, J.; Sohler, W.

    1984-01-01

    A survey of the developments in the field of fiber optics sensor technology is presented along with a discussion of the advantages of optical measuring instruments as compared with electronic sensors. The two primary types of fiber optics sensors, specifically those with multiwave fibers and those with monowave fibers, are described. Examples of each major sensor type are presented and discussed. Multiwave detectors include external and internal fiber optics sensors. Among the monowave detectors are Mach-Zender interferometers, Michelson interferometers, Sagnac interferometers (optical gyroscopes), waveguide resonators, and polarimeter sensors. Integrated optical sensors and their application in spectroscopy are briefly discussed.

  19. Multimaterial Acoustic Fibers

    NASA Astrophysics Data System (ADS)

    Chocat, Noemie

    The emergence of multimaterial fibers that combine a multiplicity of solid materials with disparate electrical, optical, and mechanical properties into a single fiber presents new opportunities for extending fiber applications well beyond optical transmission. Fiber reflectors, thermal detectors, photodetectors, chemical sensors, surface-emitting fiber lasers, fiber diodes, and other functional fiber devices have been demonstrated with this approach. Yet, throughout this development and indeed the development of fibers in general, a key premise has remained unchanged : that fibers are essentially static devices incapable of controllably changing their properties at high frequencies. Unique opportunities would arise if a rapid, electrically-driven mechanism for changing fiber properties existed. A wide spectrum of hitherto passive fiber devices could at once become active with applications spanning electronics, mechanics, acoustics, and optics, with the benefits of large surface-area, structural robustness, and mechanical flexibility. This thesis addresses the challenges and opportunities associated with the realization of electromechanical transduction in fibers through the integration of internal piezoelectric and electrostrictive domains. The fundamental challenges related to the fabrication of piezoelectric devices in fiber form are analyzed from a materials perspective, and candidate materials and geometries are selected that are compatible with the thermal drawing process. The first realization of a thermally drawn piezoelectric fiber device is reported and its piezoelectric response is established over a wide range of frequencies. The acoustic properties of piezoelectric fiber devices are characterized and related to their mechanical and geometric properties. Collective effects in multi-fiber constructs are discussed and demonstrated by the realization of a linear phased array of piezoelectric fibers capable of acoustic beam steering. High strain actuation

  20. Hybrid matrix fiber composites

    DOEpatents

    Deteresa, Steven J.; Lyon, Richard E.; Groves, Scott E.

    2003-07-15

    Hybrid matrix fiber composites having enhanced compressive performance as well as enhanced stiffness, toughness and durability suitable for compression-critical applications. The methods for producing the fiber composites using matrix hybridization. The hybrid matrix fiber composites include two chemically or physically bonded matrix materials, whereas the first matrix materials are used to impregnate multi-filament fibers formed into ribbons and the second matrix material is placed around and between the fiber ribbons that are impregnated with the first matrix material and both matrix materials are cured and solidified.

  1. Fiber optic laser rod

    DOEpatents

    Erickson, G.F.

    1988-04-13

    A laser rod is formed from a plurality of optical fibers, each forming an individual laser. Synchronization of the individual fiber lasers is obtained by evanescent wave coupling between adjacent optical fiber cores. The fiber cores are dye-doped and spaced at a distance appropriate for evanescent wave coupling at the wavelength of the selected dye. An interstitial material having an index of refraction lower than that of the fiber core provides the optical isolation for effective lasing action while maintaining the cores at the appropriate coupling distance. 2 figs.

  2. Fiber optic monitoring device

    SciTech Connect

    Samborsky, J.K.

    1992-12-31

    This invention is comprised of a device for the purpose of monitoring light transmissions in optical fibers comprises a fiber optic tap that optically diverts a fraction of a transmitted optical signal without disrupting the integrity of the signal. The diverted signal is carried, preferably by the fiber optic tap, to a lens or lens system that disperses the light over a solid angle that facilitates viewing. The dispersed light indicates whether or not the monitored optical fiber or system of optical fibers is currently transmitting optical information.

  3. Fiber coating method

    DOEpatents

    Corman, Gregory Scot

    2001-01-01

    A coating is applied to reinforcing fibers arranged into a tow by coaxially aligning the tow with an adjacent separation layer and winding or wrapping the tow and separation layer onto a support structure in an interleaved manner so that the separation layer separates a wrap of the tow from an adjacent wrap of the tow. A coating can then be uniformly applied to the reinforcing fibers without defects caused by fiber tow to fiber tow contact. The separation layer can be a carbon fiber veil.

  4. Fiber coating method

    DOEpatents

    Corman, Gregory Scot

    2003-04-15

    A coating is applied to reinforcing fibers arranged into a tow by coaxially aligning the tow with an adjacent separation layer and winding or wrapping the tow and separation layer onto a support structure in an interleaved manner so that the separation layer separates a wrap of the tow from an adjacent wrap of the tow. A coating can then be uniformly applied to the reinforcing fibers without defects caused by fiber tow to fiber tow contact. The separation layer can be a carbon fiber veil.

  5. Stress and stress reduction.

    PubMed

    Straub, Heather; Qadir, Sameen; Miller, Greg; Borders, Ann

    2014-09-01

    Chronic stress contributes to preterm birth (PTB), through direct physiological mechanisms or behavioral pathways. This review identified interventions to prevent PTB through decreased maternal stress. Studies were grouped according to intervention: group prenatal care (11 studies), care coordination (8 studies), health insurance expansion (4 studies), expanded prenatal education/support in the clinic (8 studies), home visitation (9 studies), telephone contact (2 studies), or stress-reduction strategies (5 studies). Group prenatal care had the most evidence for PTB prevention. Comparative studies of PTB prevention through different models of prenatal care and maternal support, education, empowerment, stress-reduction, and coping strategies are needed. PMID:24979355

  6. Modelling of the glass fiber length and the glass fiber length distribution in the compounding of short glass fiber-reinforced thermoplastics

    NASA Astrophysics Data System (ADS)

    Kloke, P.; Herken, T.; Schöppner, V.; Rudloff, J.; Kretschmer, K.; Heidemeyer, P.; Bastian, M.; Walther, Dridger, A.

    2014-05-01

    The use of short glass fiber-reinforced thermoplastics for the production of highly stressed parts in the plastics processing industry has experienced an enormous boom in the last few years. The reasons for this are primarily the improvements to the stiffness and strength properties brought about by fiber reinforcement. These positive characteristics of glass fiber-reinforced polymers are governed predominantly by the mean glass fiber length and the glass fiber length distribution. It is not enough to describe the properties of a plastics component solely as a function of the mean glass fiber length [1]. For this reason, a mathematical-physical model has been developed for describing the glass fiber length distribution in compounding. With this model, it is possible on the one hand to optimize processes for the production of short glass fiber-reinforced thermoplastics, and, on the other, to obtain information on the final distribution, on the basis of which much more detailed statements can be made about the subsequent properties of the molded part. Based on experimental tests, it was shown that this model is able to accurately describe the change in glass fiber length distribution in compounding.

  7. Comparison of two reference methods for detemining cotton fiber moisture

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Moisture is an important quality and processing property for the cotton industry. The standard reference method for determining the moisture content in cotton fiber is the ASTM oven method (gravimetric weight loss). Several concerns have expressed on its ability to measure the actual moisture cont...

  8. Reviving the Bowen Ratio method for Actual Evaporation with Distributed Temperature Sensing

    NASA Astrophysics Data System (ADS)

    Luxemburg, W. M. J.; Euser, T.; Everson, C. S.; Mengistu, M. G.; Clulow, A. D.

    2012-04-01

    We have used the technique of distributed temperature sensing (DTS) with a fiber optic cable to determine actual evaporation over land. The results were compared with measurements using a surface layer scintilometer, surface renewal and eddy covariance techniques. Dry and wetted sections of a fiber optic cable were suspended from a six meter high tower in a sugar beet trial in KwaZulu-Natal, South Africa. From the principle of a psychrometer, a near continuous observation of vapor pressure and temperature at 0.20 m intervals of a vertical column of air above the field could be derived. Subsequently it allowed accurate determination of the ratio of sensible and latent heat, i.e. the Bowen ratio over time and in the vertical. Using measurements of the net radiation, soil heat flux and the Bowen ratio sensible heat flux, the actual evaporation could be determined as the residual of the shortened energy balance equation. The advantage of the DTS method over the traditional Bowen ratio method is that one and the same sensor (the fiber optic cable) is used, with sufficient accuracy to discriminate small differences in temperature and vapor pressure respectively, hence giving numerous gradient measurements over the vertical. The traditional Bowen ratio method relies on only a few sensors that require careful calibration to detect the real differences of temperature and vapor pressure. Comparing the improved method with the traditional Bowen Ratio method, shows that the improved method gives more stable and constant results than the standard method. The DTS data were reliable, provided that water blown by strong wind from the wetted cable does not affect the temperature of air at the location of the dry cable. Under these conditions the vertical air temperature was not representative for the air temperature over the fetch of the crop. The experiments were carried out in South Africa, in November 2011 (summer) under varying radiation conditions. In this way it was

  9. Kinetics of fiber solidification

    PubMed Central

    Mercader, C.; Lucas, A.; Derré, A.; Zakri, C.; Moisan, S.; Maugey, M.; Poulin, P.

    2010-01-01

    Many synthetic or natural fibers are produced via the transformation of a liquid solution into a solid filament, which allows the wet processing of high molecular weight polymers, proteins, or inorganic particles. Synthetic wet-spun fibers are used in our everyday life from clothing to composite reinforcement applications. Spun fibers are also common in nature. Silk solidification results from the coagulation of protein solutions. The chemical phenomena involved in the formation of all these classes of fibers can be quite different but they all share the same fundamental transformation from a liquid to a solid state. The solidification process is critical because it governs the production rate and the strength that fibers can sustain to be drawn and wound. An approach is proposed in this work to investigate the kinetics of fiber solidification. This approach consists in circulating solidifying fibers in the extensional flow of a surrounding liquid. Such as polymers in extensional flows, the fibers break if resultant drag forces exceed the fiber tensile strength. The solidification kinetics of nanotube composite fibers serves as a validation example of this approach. The method could be extended to other systems and advance thereby the science and technology of fiber and textile materials. It is also a way to directly visualize the scission of chain-like systems in extensional flows. PMID:20937910

  10. Kinetics of fiber solidification.

    PubMed

    Mercader, C; Lucas, A; Derré, A; Zakri, C; Moisan, S; Maugey, M; Poulin, P

    2010-10-26

    Many synthetic or natural fibers are produced via the transformation of a liquid solution into a solid filament, which allows the wet processing of high molecular weight polymers, proteins, or inorganic particles. Synthetic wet-spun fibers are used in our everyday life from clothing to composite reinforcement applications. Spun fibers are also common in nature. Silk solidification results from the coagulation of protein solutions. The chemical phenomena involved in the formation of all these classes of fibers can be quite different but they all share the same fundamental transformation from a liquid to a solid state. The solidification process is critical because it governs the production rate and the strength that fibers can sustain to be drawn and wound. An approach is proposed in this work to investigate the kinetics of fiber solidification. This approach consists in circulating solidifying fibers in the extensional flow of a surrounding liquid. Such as polymers in extensional flows, the fibers break if resultant drag forces exceed the fiber tensile strength. The solidification kinetics of nanotube composite fibers serves as a validation example of this approach. The method could be extended to other systems and advance thereby the science and technology of fiber and textile materials. It is also a way to directly visualize the scission of chain-like systems in extensional flows. PMID:20937910

  11. Fiber draw synthesis

    PubMed Central

    Orf, Nicholas D.; Shapira, Ofer; Sorin, Fabien; Danto, Sylvain; Baldo, Marc A.; Joannopoulos, John D.; Fink, Yoel

    2011-01-01

    The synthesis of a high-melting temperature semiconductor in a low-temperature fiber drawing process is demonstrated, substantially expanding the set of materials that can be incorporated into fibers. Reagents in the solid state are arranged in proximate domains within a fiber preform. The preform is fluidized at elevated temperatures and drawn into fiber, reducing the lateral dimensions and bringing the domains into intimate contact to enable chemical reaction. A polymer preform containing a thin layer of selenium contacted by tin–zinc wires is drawn to yield electrically contacted crystalline ZnSe domains of sub-100-nm scales. The in situ synthesized compound semiconductor becomes the basis for an electronic heterostructure diode of arbitrary length in the fiber. The ability to synthesize materials within fibers while precisely controlling their geometry and electrical connectivity at submicron scales presents new opportunities for increasing the complexity and functionality of fiber structures.

  12. Fiber optic vibration sensor

    DOEpatents

    Dooley, J.B.; Muhs, J.D.; Tobin, K.W.

    1995-01-10

    A fiber optic vibration sensor utilizes two single mode optical fibers supported by a housing with one optical fiber fixedly secured to the housing and providing a reference signal and the other optical fiber having a free span length subject to vibrational displacement thereof with respect to the housing and the first optical fiber for providing a signal indicative of a measurement of any perturbation of the sensor. Damping or tailoring of the sensor to be responsive to selected levels of perturbation is provided by altering the diameter of optical fibers or by immersing at least a portion of the free span length of the vibration sensing optical fiber into a liquid of a selected viscosity. 2 figures.

  13. Fiber optic vibration sensor

    DOEpatents

    Dooley, Joseph B.; Muhs, Jeffrey D.; Tobin, Kenneth W.

    1995-01-01

    A fiber optic vibration sensor utilizes two single mode optical fibers supported by a housing with one optical fiber fixedly secured to the housing and providing a reference signal and the other optical fiber having a free span length subject to vibrational displacement thereof with respect to the housing and the first optical fiber for providing a signal indicative of a measurement of any perturbation of the sensor. Damping or tailoring of the sensor to be responsive to selected levels of perturbation is provided by altering the diameter of optical fibers or by immersing at least a portion of the free span length of the vibration sensing optical fiber into a liquid of a selected viscosity.

  14. Fiber Accelerating Structures

    SciTech Connect

    Hammond, Andrew P.; /Reed Coll. /SLAC

    2010-08-25

    One of the options for future particle accelerators are photonic band gap (PBG) fiber accelerators. PBG fibers are specially designed optical fibers that use lasers to excite an electric field that is used to accelerate electrons. To improve PBG accelerators, the basic parameters of the fiber were tested to maximize defect size and acceleration. Using the program CUDOS, several accelerating modes were found that maximized these parameters for several wavelengths. The design of multiple defects, similar to having closely bound fibers, was studied to find possible coupling or the change of modes. The amount of coupling was found to be dependent on distance separated. For certain distances accelerating coupled modes were found and examined. In addition, several non-periodic fiber structures were examined using CUDOS. The non-periodic fibers produced several interesting results and promised more modes given time to study them in more detail.

  15. Tapered fiber amplifier

    NASA Astrophysics Data System (ADS)

    Russell, Stephen D.; Stamnitz, Timothy C.

    1990-07-01

    A tapered optical fiber amplifier is designed to provide for long-distance, un-repeatered fiber optic communications. Two single-mode fiber portions are tapered to efficiently intensify and couple an information signal from a laser diode and a pump signal at a shorter wavelength into a fused, tapered single-mode fiber optic coupler. The concentrated information signal and concentrated pump signal are combined via the coupler which is coupled to a several-kilometer length of a relatively small core diametered single-mode fiber to create nonlinear optical effect (stimulated Raman scattering) (SRS). The SRS causes Raman shift of the pump light into the small core diametered single-mode fiber length, thereby generating SRS to result in a signal amplification and an efficient extraction of the amplified signal via the tapered output fiber portion or pigtail.

  16. Fiber optic moisture sensor

    DOEpatents

    Kirkham, R.R.

    1984-08-03

    A method and apparatus for sensing moisture changes by utilizing optical fiber technology. One embodiment uses a reflective target at the end of an optical fiber. The reflectance of the target varies with its moisture content and can be detected by a remote unit at the opposite end of the fiber. A second embodiment utilizes changes in light loss along the fiber length. This can be attributed to changes in reflectance of cladding material as a function of its moisture content. It can also be affected by holes or inserts interposed in the cladding material and/or fiber. Changing light levels can also be coupled from one fiber to another in an assembly of fibers as a function of varying moisture content in their overlapping lengths of cladding material.

  17. Indium fluoride glass fibers

    NASA Astrophysics Data System (ADS)

    Saad, Mohammed

    2012-03-01

    Fluoride glasses are the only material that transmit light from ultraviolet to mid-infrared and can be drawn into industrial optical fibers. The mechanical and optical properties of new indium fluoride glass fibers have been investigated. Multimode fiber 190 microns, has very high mechanical strength greater than 100 kpsi and optical loss as low as 45 dB/km between 2 and 4 microns. Unlike chalcogenide glass fibers, indium fluoride fiber has a wide transmission window from 0.3 to 5.5 microns without any absorption peak. Indium fluoride glass fibers are the technology of choice for all application requiring transmission up to 5 micron such as infrared contour measure (IRCM) and chemical sensing. Furthermore, Indium fluoride glasses have low phonon energy and can be heavily doped and co-doped whit rare-earth elements. Therefore they are very promising candidates for infrared fiber lasers.

  18. Investigation of failure modes in fiber-reinforced ceramic-matrix composites. Master's thesis

    SciTech Connect

    Moschler, J.W.

    1988-12-01

    This experimental study was conducted to investigate the damage progression in fiber-reinforced ceramic-matrix composites under tensile loading. As part of this study, the effect of the residual stresses at the fiber-matrix interface on damage progression was evaluated. Composite samples were fabricated from silicon carbide fibers and borosilicate glass matrices. Each glass had a different coefficient of thermal expansion than the fiber and through the variation of this mismatch, the residual stresses at the fiber-matrix interface were varied resulting in different bonding conditions at the fiber-matrix interface. The mechanical properties of the composites were measured using a servo-hydraulic mechanical testing machine. During these tests, transverse strain reversal was observed that is believed to be caused by axial matrix cracks and fiber-matrix debonding. Tensile tests were conducted on the composites using a constant-load straining device in which damage progression was observed using an optical microscope.

  19. Effects of Fiber Coating Composition on Mechanical Behavior of Silicon Carbide Fiber-Reinforced Celsian Composites

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Elderidge, Jeffrey I.

    1998-01-01

    Celsian matrix composites reinforced with Hi-Nicalon fibers, precoated with a dual layer of BN/SiC by chemical vapor deposition in two separate batches, were fabricated. Mechanical properties of the composites were measured in three-point flexure. Despite supposedly identical processing, the composite panels fabricated with fibers coated in two batches exhibited substantially different mechanical behavior. The first matrix cracking stresses (sigma(sub mc)) of the composites reinforced with fibers coated in batch 1 and batch 2 were 436 and 122 MPa, respectively. This large difference in sigma(sub mc) was attributed to differences in fiber sliding stresses(tau(sub friction)), 121.2+/-48.7 and 10.4+/-3.1 MPa, respectively, for the two composites as determined by the fiber push-in method. Such a large difference in values of tau(sub friction) for the two composites was found to be due to the difference in the compositions of the interface coatings. Scanning Auger microprobe analysis revealed the presence of carbon layers between the fiber and BN, and also between the BN and SiC coatings in the composite showing lower tau(sub friction). This resulted in lower sigma(sub mc) in agreement with the ACK theory. The ultimate strengths of the two composites, 904 and 759 MPa, depended mainly on the fiber volume fraction and were not significantly effected by tau(sub friction) values, as expected. The poor reproducibility of the fiber coating composition between the two batches was judged to be the primary source of the large differences in performance of the two composites.

  20. Carbon fiber content measurement in composite

    NASA Astrophysics Data System (ADS)

    Wang, Qiushi

    Carbon fiber reinforced polymers (CFRPs) have been widely used in various structural applications in industries such as aerospace and automotive because of their high specific stiffness and specific strength. Their mechanical properties are strongly influenced by the carbon fiber content in the composites. Measurement of the carbon fiber content in CFRPs is essential for product quality control and process optimization. In this work, a novel carbonization-in-nitrogen method (CIN) is developed to characterize the fiber content in carbon fiber reinforced thermoset and thermoplastic composites. In this method, a carbon fiber composite sample is carbonized in a nitrogen environment at elevated temperatures, alongside a neat resin sample. The carbon fibers are protected from oxidization while the resin (the neat resin and the resin matrix in the composite sample) is carbonized under the nitrogen environment. The residue of the carbonized neat resin sample is used to calibrate the resin carbonization rate and calculate the amount of the resin matrix in the composite sample. The new method has been validated on several thermoset and thermoplastic resin systems and found to yield an accurate measurement of fiber content in carbon fiber polymer composites. In order to further understand the thermal degradation behavior of the high temperature thermoplastic polymer during the carbonization process, the mechanism and the kinetic model of thermal degradation behavior of carbon fiber reinforced poly (phenylene sulfide) (CPPS) are studied using thermogravimetry analysis (TGA). The CPPS is subjected to TGA in an air and nitrogen atmosphere at heating rates from 5 to 40°C min--1. The TGA curves obtained in air are different from those in nitrogen. This demonstrates that weight loss occurs in a single stage in nitrogen but in two stages in air. To elucidate this difference, thermal decomposition kinetics is analyzed by applying the Kissinger, Flynn-Wall-Ozawa, Coat-Redfern and