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Sample records for strain rate effects

  1. Strain rate effects in stress corrosion cracking

    SciTech Connect

    Parkins, R.N. . Dept. of Metallurgy and Engineering Materials)

    1990-03-01

    Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

  2. Effects of Applied Strain on Rates of Ageing: Project Overview

    NASA Technical Reports Server (NTRS)

    Campion, R. P.

    1997-01-01

    One of the stated intents of this project has been to make some assessment of effects of strain on rates of ageing of project thermoplastics exposed to project fluids. To this end, certain straining jigs which apply in various modes - tensile, four-point bending and crack growth using compact tension samples - were designed and made for holding samples during fluid exposures. During testing, features of the thermoplastics have been observed which have tended to confuse apparent strain effects on the polymers' aged performance, but recent assessments of the topic and its data have led to considerable progress being made in identifying test procedures necessary for strain and related effects on chemical deterioration to manifest themselves. It is the intent of this report to provide a summary of what has been determined on strain and related effects thus far, and provide recommendations for clarifying them in Phase 2 by means of further test procedures which will increase and focus the severity of the conditions applying. The choice of flexible pipe rather than umbilicals service for assessing service strain conditions reflects the major interest of project members. However, Tefzel data are still provided.

  3. Effect of dynamic strain rate on micro-indentation properties of pure aluminum

    NASA Astrophysics Data System (ADS)

    Yamada, Hiroyuki; Hotta, Midori; Kami, Tsuyoshi; Ogasawara, Nagahisa; Chen, Xi

    2015-09-01

    Indentation is widely used to investigate the elastic and plastic properties of mechanical materials, which includes the strain rate sensitivity. The indentation exhibits an inhomogeneous strain distribution in contrast to compression and tensile tests with homogeneous deformation. Thus, the strain rate of the indentation may form the inhomogeneous distribution. Therefore, the effect of strain rate distribution of the indentation on pure aluminum with respect to the strain rate dependence of strength in order to clarify the effect of the strain rate on the indentation technique. First, the numerical simulation was established using the Cowper-Symonds equation as the dynamic constitutive equation. Secondary, the strain rate distribution was calculated from the equivalent plastic strain distribution. The strain rate distribution was quite different from the strain distribution, which showed that the strain rate at the crater rim was higher than that beneath the indenter. Finally, we try to perform the averaging of strain rate distribution in order to make an index of strain rate in the indentation. The average of strain rate distribution was calculated using the equivalent plastic strain above a boundary value that is the critical strain and the representative strain. There is correlation between the average strain rate and the loading curvature, which shows that the average strain rate can express as the representative of strain rate for the indentation technique.

  4. Effect of strain rate on the compressive deformation behaviors of lotus-type porous copper

    NASA Astrophysics Data System (ADS)

    Liu, Xin-hua; Huang, Hai-you; Xie, Jian-xin

    2014-07-01

    Lotus-type porous copper was fabricated by unidirectional solidification, and compressive experiments were subsequently conducted in the strain rate range of 10-3-2400 s-1 with the compressive direction parallel to the pores. A GLEEBLE-1500 thermal-mechanical simulation system and a split Hopkinson pressure bar (SHPB) were used to investigate the effect of strain rate on the compressive deformation behaviors of lotus-type porous copper. The influence mechanism of strain rate was also analyzed by the strain-controlling method and by high-speed photography. The results indicated that the stress-strain curves of lotus-typed porous copper consist of a linear elastic stage, a plateau stage, and a densification stage at various strain rates. At low strain rate (< 1.0 s-1), the strain rate had little influence on the stress-strain curves; but when the strain rate exceeded 1.0 s-1, it was observed to strongly affect the plateau stage, showing obvious strain-rate-hardening characteristics. Strain rate also influenced the densification initial strain. The densification initial strain at high strain rate was less than that at low strain rate. No visible inhomogeneous deformation caused by shockwaves was observed in lotus-type porous copper during high-strain-rate deformation. However, at high strain rate, the bending deformation characteristics of the pore walls obviously differed from those at low strain rate, which was the main mechanism by which the plateau stress exhibited strain-rate sensitivity when the strain rate exceeded a certain value and exhibited less densification initial strain at high strain rate.

  5. Shock Compression and Strain Rate Effect in Composites and Polymers

    SciTech Connect

    Brown, Eric

    2012-06-20

    Polymers are increasingly being utilized as monolithic materials and composite matrices for structural applications historically reserved for metals. High strain and high strain-rate applications in aerospace, defense, and automotive industries have lead to interest in utilizing the ability of many polymers to withstand extensions to failure of several hundred percent, often without localization or necking and their strong rate dependence. A broad range of characterization techniques will be presented for semi-crystalline polymers and composites including elastic-plastic fracture, split Hopkinson pressure bar (SHPB), plate impact including soft-recovery and lateral gage measurements and Taylor Impact. Gas-launched, plate impact experiments have been performed on pedigreed PTFE 7C, mounted in momentum-trapped, shock assemblies, with impact pressures above and below the phase II to phase III crystalline transition to probe subtle changes in the crystallinity, microstructure, and mechanical response of PTFE. Observed strong anisotropy on the hugoniot and spall behavior of fiber-reinforced composites will be discussed. Polymers are known to exhibit a strong dependence of the yield stress on temperature and strain-rate that are often observed to be linear for temperature and logarithmic for strain-rate. Temperature and strain-rate dependence will be reviewed in terms of classic time-temperature superposition and an empirical mapping function for superposition between temperature and strain-rate. The recent extension of the new Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) technique to probe the dynamic tensile responses of polymers will be discussed, where more irregular deformation and stochastic-based damage and failure mechanisms than the stable plastic elongation and shear instabilities observed that in metals. The opportunity to use of Dyn-Ten-Ext to probe incipient damage at very high strain-rate by linking in situ and post mortem experimental observations with high

  6. Strain rate effects on medium carbon steel and its effects on autofrettage

    SciTech Connect

    Song, J.; Xu, B.Y.; Tang, C.Y.; Lee, W.B.

    1994-01-15

    Most metals are rate-sensitive under high loading speeds. In metal forming, the quasi-static analysis is commonly employed since the strain rate is comparably low. Recently, Krempl shows that the difference between the static analysis and the experimental result is insignificant when the strain rate is less than 10{sup {minus}4}s{sup {minus}1}. Under ambient conditions, the constitutive relationship proposed by Marciniak may be applied in low strain rates ranged from 10{sup {minus}4}s{sup {minus}1} to 10{sup {minus}1}s{sup {minus}1}. However, the effects of strain rate on constitutive relationships under cyclic loading should not be neglected in certain cases. In this study, uniaxial tensile and compressive tests have been carried out to determine the material parameters of medium carbon steel. Hysteresis loops have been obtained under different loading speeds. The effects of strain rate on the elastic modulus, the yield stress, the reverse yield stress and the hardening parameters are determined. Autofrettage is a special forming process by which beneficial compressive residual stresses are introduced into thick-walled tubes. The magnitude of the residual stress field induced by autofrettage depends greatly on the reverse hardening characteristics of the tubing material. Based on the experimental results and the assumption that the difference in the magnitude between the tensile and the reverse yield stresses is independent of strain rate, an elasto-visco-plastic model is proposed. Therefore, the influences of two different strain rates on the residual stresses can be predicted. The analysis also shows that the strain rate has a significant effect on the magnitude of the residual stress field of the autofrettage.

  7. Effect of Strain Rate on Mechanical Properties of Wrought Sintered Tungsten at Temperatures above 2500 F

    NASA Technical Reports Server (NTRS)

    Sikora, Paul F.; Hall, Robert W.

    1961-01-01

    Specimens of wrought sintered commercially pure tungsten were made from 1/8-inch swaged rods. All the specimens were recrystallized at 4050 F for 1 hour prior to testing at temperatures from 2500 to 4000 F at various strain rates from 0.002 to 20 inches per inch per minute. Results showed that, at a constant temperature, increasing the strain rate increased the ultimate tensile strength significantly. The effects of both strain rate and temperature on the ultimate tensile strength of tungsten may be correlated by the linear parameter method of Manson and Haferd and may be used to predict the ultimate tensile strength at higher temperatures, 4500 and 5000 F. As previously reported, ductility, as measured by reduction of area in a tensile test, decreases with increasing temperature above about 3000 F. Increasing the strain rate at temperatures above 3000 F increases the ductility. Fractures are generally transgranular at the higher strain rates and intergranular at the lower strain rates.

  8. Strain rate effects on compressive behavior of covalently bonded CNT networks

    NASA Astrophysics Data System (ADS)

    Kirkayak, Levent

    2016-06-01

    In this study, strain rate effects on the compressive mechanical properties of randomly structured carbon nanotube (CNT) networks were examined. For this purpose, three-dimensional atomistic models of CNT networks with covalently-bonded junctions were generated. After that, molecular dynamics (MD) simulations of compressive loading were performed at five different strain rates to investigate the basic deformation characteristic mechanisms of CNT networks and determine the effect of strain rate on stress-strain curves. The simulation results showed that the strain rate of compressive loading increases, so that a higher resistance of specimens to deformation is observed. Furthermore, the local deformation characteristics of CNT segments, which are mainly driven by bending and buckling modes, and their prevalence are strongly affected by the deformation rate. It was also observed that CNT networks have superior features to metal foams such as metal matrix syntactic foams (MMSFs) and porous sintered fiber metals (PSFMs) in terms of energy absorbing capabilities.

  9. Effect of Strain Rate on the Mechanical Behavior of Red Blood Cells Entering a Constriction

    NASA Astrophysics Data System (ADS)

    Mancuso, Jordan; Ristenpart, William

    2014-11-01

    Most work on the effect of hydrodynamic stress on red blood cells (RBCs) has focused on linear velocity profiles. Microfluidic devices have provided a means to examine the mechanical behavior of RBCs undergoing a sudden increase in shear stress at the entrance of a constriction, with previous work primarily focused on a fixed constriction taper angle and corresponding hydrodynamic strain rate. Here we investigate the effect of strain rate on the stretching dynamics exhibited by RBCs as they enter a microfluidic constriction. Systematic variations in the constriction taper angle allow the strain rate to be precisely tuned, and high speed video yields precise measurements of the corresponding RBC deformations. We demonstrate that maximal RBC stretching occurs at an intermediate constriction taper angle, despite the lower magnitude of the strain rate. We interpret the results in terms of the time integral of the elongational strain rate, and we discuss the implications for shear-induced mechanotransduction.

  10. Temperature and Strain-Rate Effects on Low-Cycle Fatigue Behavior of Alloy 800H

    NASA Technical Reports Server (NTRS)

    Rao, K. Bhanu Sankara; Schiffers, H.; Schuster, H.; Halford, G. R.

    1996-01-01

    The effects of strain rate (4 x 10(exp -6) to 4 x 10(exp -3)/s) and temperature on the Low-Cycle Fatigue (LCF) behavior of alloy 800H have been evaluated in the range 750 C to 950 C. Total axial strain controlled LCF tests were conducted in air at a strain amplitude of +/- 0.30 pct. LCF life decreased with decreasing strain rate and increasing temperature. The cyclic stress response behavior showed a marked variation with temperature and strain rate. The time- and temperature- dependent processes which influence the cyclic stress response and life have been identified and their relative importance assessed. Dynamic strain aging, time-dependent deformation, precipitation of parallel platelets of M(23)C6 on grain boundaries and incoherent ledges of twins, and oxidation were found to operate depending on the test conditions. The largest effect on life was shown by oxidation processes.

  11. Biaxial load effects on the crack border elastic strain energy and strain energy rate

    NASA Technical Reports Server (NTRS)

    Eftis, J.; Subramonian, N.; Liebowitz, H.

    1977-01-01

    The validity of the singular solution (first term of a series representation) is investigated for the crack tip stress and displacement field in an infinite sheet with a flat line crack with biaxial loads applied to the outer boundaries. It is shown that if one retains the second contribution to the series approximations for stress and displacement in the calculation of the local elastic strain energy density and elastic strain energy rate in the crack border region, both these quantities have significant biaxial load dependency. The value of the J-integral does not depend on the presence of the second term of the series expansion for stress and displacement. Thus J(I) is insensitive to the presence of loads applied parallel to the plane of the crack.

  12. Microstructure-dependent deformation behaviour of bcc-metals - indentation size effect and strain rate sensitivity

    NASA Astrophysics Data System (ADS)

    Maier, Verena; Schunk, Christopher; Göken, Mathias; Durst, Karsten

    2015-06-01

    In this work, the indentation size effect and the influence of the microstructure on the time-dependent deformation behaviour of body-centred cubic (bcc) metals are studied by performing nanoindentation strain rate jump tests at room temperature. During these experiments, the strain rate is abruptly changed, and from the resulting hardness difference the local strain rate sensitivity has been derived. Single-crystalline materials exhibit a strong indentation size effect; ultrafine-grained metals have nearly a depth-independent hardness. Tungsten as a bcc metal shows the opposite behaviour as generally found for face-centered cubic metals. While for UFG-W only slightly enhanced strain rate sensitivity was observed, SX-W exhibits a pronounced influence of the strain rate on the resulting hardness at room temperature. This is due to the effects of the high lattice friction of bcc metals at low temperatures, where the thermally activated motion of screw dislocations is the dominating deformation mechanisms, which causes the enhanced strain rate sensitivity. For the SX-materials, it was found that the degree of the indentation size effect directly correlates with the homologous testing temperature and thus, the material specific parameter of the critical temperature Tc. However, for the resultant strain rate sensitivity no depth-dependent change was found.

  13. The effect of an acute bout of resistance exercise on carotid artery strain and strain rate.

    PubMed

    Black, Jane M; Stöhr, Eric J; Stone, Keeron; Pugh, Christopher J A; Stembridge, Mike; Shave, Rob; Esformes, Joseph I

    2016-09-01

    Arterial wall mechanics likely play an integral role in arterial responses to acute physiological stress. Therefore, this study aimed to determine the impact of low and moderate intensity double-leg press exercise on common carotid artery (CCA) wall mechanics using 2D vascular strain imaging. Short-axis CCA ultrasound images were collected in 15 healthy men (age: 21 ± 3 years; stature: 176.5 ± 6.2 cm; body mass; 80.6 ± 15.3 kg) before, during, and immediately after short-duration isometric double-leg press exercise at 30% and 60% of participants' one-repetition maximum (1RM: 317 ± 72 kg). Images were analyzed for peak circumferential strain (PCS), peak systolic and diastolic strain rate (S-SR and D-SR), and arterial diameter. Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP) were simultaneously assessed and arterial stiffness indices were calculated post hoc. A two-way repeated measures ANOVA revealed that during isometric contraction, PCS and S-SR decreased significantly (P < 0.01) before increasing significantly above resting levels post exercise (P < 0.05 and P < 0.01, respectively). Conversely, D-SR was unaltered throughout the protocol (P = 0.25). No significant differences were observed between the 30% and 60% 1RM trials. Multiple regression analysis highlighted that HR, BP, and arterial diameter did not fully explain the total variance in PCS, S-SR, and D-SR Acute double-leg press exercise is therefore associated with similar transient changes in CCA wall mechanics at low and moderate intensities. CCA wall mechanics likely provide additional insight into localized intrinsic vascular wall properties beyond current measures of arterial stiffness. PMID:27624687

  14. Effects of Strain Rates on Mechanical Properties and Fracture Mechanism of DP780 Dual Phase Steel

    NASA Astrophysics Data System (ADS)

    Li, Shengci; Kang, Yonglin; Zhu, Guoming; Kuang, Shuang

    2015-06-01

    The mechanical properties of DP780 dual phase steel were measured by quasi-static and high-speed tensile tests at strain rates between 0.001 and 1000 s-1 at room temperature. The deformation and fracture mechanisms were analyzed by observation of the tensile fracture and microstructure near the fracture. Dynamic factor and feret ratio quantitative methods were applied to study the effect of strain rate on the microstructure and properties of DP780 steel. The constitutive relation was described by a modified Johnson-Cook and Zerilli-Armstrong model. The results showed that the strain rate sensitivity of yield strength is bigger than that of ultimate tensile strength; as strain rate increased, the formation of microcracks and voids at the ferrite/martensite interface can be alleviated; the strain rate effect is unevenly distributed in the plastic deformation region. Moreover, both models can effectively describe the experimental results, while the modified Zerilli-Armstrong model is more accurate because the strain-hardening rate of this model is independent of strain rate.

  15. Strong strain rate effect on the plasticity of amorphous silica nanowires

    SciTech Connect

    Yue, Yonghai; Zheng, Kun

    2014-06-09

    With electron-beam (e-beam) off, in-situ tensile experiments on amorphous silica nanowires (NWs) were performed inside a transmission electron microscope (TEM). By controlling the loading rates, the strain rate can be adjusted accurately in a wide range. The result shows a strong strain rate effect on the plasticity of amorphous silica NWs. At lower strain rate, the intrinsic brittle materials exhibit a pronounced elongation higher than 100% to failure with obvious necking near ambient temperature. At the strain rate higher than 5.23 × 10{sup −3}/s, the elongation of the NW decreased dramatically, and a brittle fracture feature behavior was revealed. This ductile feature of the amorphous silica NWs has been further confirmed with the in-situ experiments under optical microscopy while the effect of e-beam irradiation could be eliminated.

  16. The Effect Analysis of Strain Rate on Power Transmission Tower-Line System under Seismic Excitation

    PubMed Central

    Wang, Wenming

    2014-01-01

    The effect analysis of strain rate on power transmission tower-line system under seismic excitation is studied in this paper. A three-dimensional finite element model of a transmission tower-line system is created based on a real project. Using theoretical analysis and numerical simulation, incremental dynamic analysis of the power transmission tower-line system is conducted to investigate the effect of strain rate on the nonlinear responses of the transmission tower and line. The results show that the effect of strain rate on the transmission tower generally decreases the maximum top displacements, but it would increase the maximum base shear forces, and thus it is necessary to consider the effect of strain rate on the seismic analysis of the transmission tower. The effect of strain rate could be ignored for the seismic analysis of the conductors and ground lines, but the responses of the ground lines considering strain rate effect are larger than those of the conductors. The results could provide a reference for the seismic design of the transmission tower-line system. PMID:25105157

  17. The effect analysis of strain rate on power transmission tower-line system under seismic excitation.

    PubMed

    Tian, Li; Wang, Wenming; Qian, Hui

    2014-01-01

    The effect analysis of strain rate on power transmission tower-line system under seismic excitation is studied in this paper. A three-dimensional finite element model of a transmission tower-line system is created based on a real project. Using theoretical analysis and numerical simulation, incremental dynamic analysis of the power transmission tower-line system is conducted to investigate the effect of strain rate on the nonlinear responses of the transmission tower and line. The results show that the effect of strain rate on the transmission tower generally decreases the maximum top displacements, but it would increase the maximum base shear forces, and thus it is necessary to consider the effect of strain rate on the seismic analysis of the transmission tower. The effect of strain rate could be ignored for the seismic analysis of the conductors and ground lines, but the responses of the ground lines considering strain rate effect are larger than those of the conductors. The results could provide a reference for the seismic design of the transmission tower-line system. PMID:25105157

  18. The effect analysis of strain rate on power transmission tower-line system under seismic excitation.

    PubMed

    Tian, Li; Wang, Wenming; Qian, Hui

    2014-01-01

    The effect analysis of strain rate on power transmission tower-line system under seismic excitation is studied in this paper. A three-dimensional finite element model of a transmission tower-line system is created based on a real project. Using theoretical analysis and numerical simulation, incremental dynamic analysis of the power transmission tower-line system is conducted to investigate the effect of strain rate on the nonlinear responses of the transmission tower and line. The results show that the effect of strain rate on the transmission tower generally decreases the maximum top displacements, but it would increase the maximum base shear forces, and thus it is necessary to consider the effect of strain rate on the seismic analysis of the transmission tower. The effect of strain rate could be ignored for the seismic analysis of the conductors and ground lines, but the responses of the ground lines considering strain rate effect are larger than those of the conductors. The results could provide a reference for the seismic design of the transmission tower-line system.

  19. Effects of strain rate on the mechanical properties of tricalcium phosphate/poly(L: -lactide) composites.

    PubMed

    Yamadi, Shusaku; Kobayashi, Satoshi

    2009-01-01

    Bioactive ceramic/bioresorbable plastic composites have been expected as materials for the bone fracture fixations which have more biocompatibility than monolithic bioresorbable plastics. Many studies have been conducted on these materials. Most studies, however, focused on the mechanical properties under static loading. In the actual usage, these materials are loaded dynamically. In this study, effects of strain rate on the mechanical properties of tricalcium phosphate/poly(L: -lactide) (TCP/PLLA) composites were investigated experimentally and analytically. The TCP/PLLA composites containing three different TCP contents (5, 10 and 15 wt.%) were prepared by injection molding. In order to characterize the mechanical properties, tensile and compressive tests were conducted. The results of tensile tests indicated that the Young's moduli of composites increased with increasing TCP contents. For each TCP contents, tensile Young's modulus kept constant up to strain rate of 10(-1)/s. On the other hand, tensile strength increased with increasing strain rate. The effect of strain rate became larger with decreasing TCP contents, which means the strain rate dependency of the PLLA is more effective than that of TCP. From the results of compressive tests, similar results with tensile tests were obtained. That is, compressive Young's modulus kept constant up to strain rate of 10(-1)/s and the 0.2% proof stress increased with increasing strain rate. In order to predict the mechanical behavior of TCP/PLLA composites, the micro-damage mechanics was proposed. In this analysis, 3-phases particle reinforced composites, which include the intact particles, damaged particles and matrix, are assumed. The elastic constants are calculated with micromechanics based on the analyses by Eshelby and Mori and Tanaka. Only the debonding between particle and matrix are assumed as the damage. The nonlinearity in the stress-strain behavior of matrix PLLA is also considered. The debonding particles

  20. Numerical study of strain-rate effect in cold rolls forming of steel

    NASA Astrophysics Data System (ADS)

    Falsafi, J.; Demirci, E.; Silberschmidt, V. V.

    2013-07-01

    Cold roll forming (CRF) is a well-known continuous manufacturing process, in which a flat strip is deformed by successive rotating pairs of tools, without changing the material thickness. In the past decades, to lessen the process-development efforts, finite-element simulations have been increasingly employed to improve the process design and predict the manufacturing-induced defects. One of the important aspects in design of the CRF process is consideration of resulting strains in the final product as the material passes through several complex forming stands. Sufficient knowledge of longitudinal strain in the workpiece is required to set various process parameters. Increasing a process speed in a roll forming operation can bring cost advantages, but the influence of the forming speed on the strain distribution should be explored. This study is focussed on a strain-rate effect in the CRF process of steel sheets. The strain-rate dependency of a plastic behaviour observed in most metals can affect the finished product's quality as well as process parameters. This paper investigates the influence of the strain rate on longitudinal strains induced in the roll forming operation by incorporating a phenomenological Johnson-Cook constitutive model, which allows studying the impact of the process speed on the output product. Taking advantage of 3D finite element analysis, a roll forming process was simulated using MCS.Marc, comprising a complete set of forming stations. Through the changing of the process speed, the strain rate impact on longitudinal peak strains and forming length was investigated. The results highlight the effect of the strain rate on edge thinning and subsequent undesirable distortions in the product.

  1. The Effect of Temperature and Strain Rate on Porosity Loss in Granular Material

    NASA Astrophysics Data System (ADS)

    Choens, R. C.; Chester, F. M.

    2013-12-01

    Experimental rock deformation was used to quantify the relationship between temperature, stress, and strain rate for brittle consolidation of wet quartz sand at hydrostatic conditions. Petrographic analysis of natural quartz sandstone employing cathode luminescence has shown that grain-scale fracture and grain rearrangement, and associated sealing of fractures, can contribute significantly to consolidation during burial, and that fracturing is similar to that produced during pressure induced consolidation in experiments. The crushing pressure (P*) for granular material, which largely depends on grain size and porosity, is typically defined by room temperature laboratory experiments at strain rates of 10-4 to 10-5 sec-1. Failure envelopes determined for natural sandstones based on measurement of P* generally imply burial depths in excess of inferred burial history. Previous work has shown that elevated temperature decreases the failure strength necessary to cause intergranular fractures, and thus P* should be a strong function of temperature and time. We use soil mechanics principles to determine rate laws for brittle consolidation of sand to better estimate in situ failure conditions of porous geomaterials. Experiments were conducted on St. Peter's sand, a sub rounded quartz sand sieved to 250 to 350 μm grain size. Three different hydrostatic load paths were used for this study: constant plastic strain rate consolidation, plastic strain rate stepping consolidation, and secondary creep consolidation experiments. Constant rate experiments were performed at 10-5 to 10-7 sec-1, and at 20, 150, and 225 C. Creep experiments reached strain rates as low as 10-10 sec-1. Comparison of results from consolidation experiments at different temperatures and strain rates in volume strain versus log pressure space show the consolidation curves are parallel and the effect of increase in temperature and decrease in plastic strain rate is to shift the curves to lower pressures

  2. Compressive behavior of bulk metallic glass under different conditions --- Coupled effect of temperature and strain rate

    NASA Astrophysics Data System (ADS)

    Yin, Weihua

    Metallic glass was first reported in 1960 by rapid quenching of Au-Si alloys. But, due to the size limitation, this material did not attract remarkable interest until the development of bulk metallic glasses (BMGs) with specimen sizes in excess of 1 mm. BMGs are considered to be promising engineering materials because of their ultrahigh strength, high elastic limit and wear resistance. However, they usually suer from a strong tendency for localized plastic deformation with catastrophic failure. Many basic questions, such as the origin of shear softening and the strain rate eect remain unclear. In this thesis, the mechanical behavior of the Zr55Al 10Ni5Cu30 bulk metallic glass and a metallic glass composite is investigated. The stress-strain relationship for Zr55Al10Ni 5Cu30 over a wide range of strain rate (5x10 --5 to 2x103 s--1) was investigated in uniaxial compression loading using both MTS servo-hydraulic system (quasi-static) and compression Kolsky bar system (dynamic). The effect of the strain rate on the fracture stress at room temperature was discussed. Based on the experimental results, the strain rate sensitivity of the bulk metallic glass changes from a positive value to a negative value at high strain rate, which is a consequence of the significant adiabatic temperature rise during the dynamic testing. In order to characterize the temperature eect on the mechanical behavior of the metallic glass, a synchronically assembled heating unit was designed to be attached onto the Kolsky bar system to perform high temperature and high strain rate mechanical testing. A transition from inhomogeneous deformation to homogeneous deformation has been observed during the quasi-static compressive experiments at testing temperatures close to the glass transition temperature. However, no transition has been observed at high strain rates at all the testing temperatures. A free volume based model is applied to analyze the stress-strain behavior of the homogeneous

  3. Tensile strain rate effect in mechanical properties of dummy HTPB propellants

    SciTech Connect

    Chung, H.L.; Kawata, K.; Itabashi, M. . Dept. of Materials Science and Technology)

    1993-10-05

    The tensile strain rate effect in tensile strength and elongation at break for a series of filled dummy hydroxy-terminated polybutadiene (HTPB) propellant binders was studied. The data were obtained at various tensile strain rates from 10[sup [minus]4] to 10[sup [minus]1] s[sup [minus]1] on two types of specimens at room temperature. The high velocity ductility behavior, which is qualitatively similar to those of unfilled elastomers, was revealed. This means that the breaking strain increases markedly at elevated strain rates. For Bukkon-type and rod-shaped specimens, test results are consistent with each other. The fact that the increased filled solids level leads to a decreased breaking elongation capability and an increased tensile strength was obviously found.

  4. The direct effects of strain on burning rates of composite solid propellants

    NASA Technical Reports Server (NTRS)

    Langhenry, M. T.

    1984-01-01

    A mathematical model is developed to predict burn rate augmentation due to strain in a composite solid propellant. The model assumes the effect is due to the ability of the flame to penetrate the small fissures and voids that form when a propellant is strained. The number and size of these fissures is obtained by applying a flaw propagation analysis to randomly distributed flaws that form when the binder-oxidizer particle bonds break under stress. A flame height is calculated with Summerfield's burn rate equation and is used to compute the burn rate augmentation based upon the additional burn area created when the flame penetrates the fissures. Comparisons are made with data obtained from published sources. The existence of threshold pressure and strains, above which augmentation occurs, is verified although the model predicts a lower threshold pressure and higher threshold strain than expected. Further results and applications of the model are discussed.

  5. Effects of temperature and strain rate on the mechanical properties of silicene

    SciTech Connect

    Pei, Qing-Xiang Zhang, Yong-Wei; Sha, Zhen-Dong; Zhang, Ying-Yan

    2014-01-14

    Silicene, a graphene-like two-dimensional silicon, has attracted great attention due to its fascinating electronic properties similar to graphene and its compatibility with existing semiconducting technology. So far, the effects of temperature and strain rate on its mechanical properties remain unexplored. We investigate the mechanical properties of silicene under uniaxial tensile deformation by using molecular dynamics simulations. We find that the fracture strength and fracture strain of silicene are much higher than those of bulk silicon, though the Young's modulus of silicene is lower than that of bulk silicon. An increase in temperature decreases the fracture strength and fracture strain of silicene significantly, while an increase in strain rate enhances them slightly. The fracture process of silicene is also studied and brittle fracture behavior is observed in the simulations.

  6. Temperature and strain rate effects in high strength high conductivity copper alloys tested in air

    SciTech Connect

    Edwards, D.J.

    1998-03-01

    The tensile properties of the three candidate alloys GlidCop{trademark} Al25, CuCrZr, and CuNiBe are known to be sensitive to the testing conditions such as strain rate and test temperature. This study was conducted on GlidCop Al25 (2 conditions) and Hycon 3HP (3 conditions) to ascertain the effect of test temperature and strain rate when tested in open air. The results show that the yield strength and elongation of the GlidCop Al25 alloys exhibit a strain rate dependence that increases with temperature. Both the GlidCop and the Hycon 3 HP exhibited an increase in strength as the strain rate increased, but the GlidCop alloys proved to be the most strain rate sensitive. The GlidCop failed in a ductile manner irrespective of the test conditions, however, their strength and uniform elongation decreased with increasing test temperature and the uniform elongation also decreased dramatically at the lower strain rates. The Hycon 3 HP alloys proved to be extremely sensitive to test temperature, rapidly losing their strength and ductility when the temperature increased above 250 C. As the test temperature increased and the strain rate decreased the fracture mode shifted from a ductile transgranular failure to a ductile intergranular failure with very localized ductility. This latter observation is based on the presence of dimples on the grain facets, indicating that some ductile deformation occurred near the grain boundaries. The material failed without any reduction in area at 450 C and 3.9 {times} 10{sup {minus}4} s{sup {minus}1}, and in several cases failed prematurely.

  7. Effects of strain energy release rate on delamination in temperature environment

    NASA Astrophysics Data System (ADS)

    Sankarabatla, Venkata Naga Ravitej

    Delamination is the weakest and major failure mode in laminated composites. Extensive efforts on initiation and growth of delamination under mechanical load have been investigated. A little emphasis was made earlier to account for the delamination in laminates under temperature loading. Strain energy release rate, a fracture mechanics parameter has been widely accepted to use for study the characteristics of delamination growth. In order to conduct a quick assessment of delamination growth, a closed form expression is developed to quantify the strain energy release rate of the laminate subjected to temperature environment. A finite element model is also developed to use for validating the analytical expression. A parametric study is also conducted to study the effects of strain energy release rate with percentage of angle ply variation in [02/+/-theta 3/∓theta3/02]s.

  8. Effect of strain rate and dislocation density on the twinning behavior in tantalum

    NASA Astrophysics Data System (ADS)

    Florando, Jeffrey N.; El-Dasher, Bassem S.; Chen, Changqiang; Swift, Damian C.; Barton, Nathan R.; McNaney, James M.; Ramesh, K. T.; Hemker, Kevin J.; Kumar, Mukul

    2016-04-01

    The conditions which affect twinning in tantalum have been investigated across a range of strain rates and initial dislocation densities. Tantalum samples were subjected to a range of strain rates, from 10-4/s to 103/s under uniaxial stress conditions, and under laser-induced shock-loading conditions. In this study, twinning was observed at 77K at strain rates from 1/s to 103/s, and during laser-induced shock experiments. The effect of the initial dislocation density, which was imparted by deforming the material to different amounts of pre-strain, was also studied, and it was shown that twinning is suppressed after a given amount of pre-strain, even as the global stress continues to increase. These results indicate that the conditions for twinning cannot be represented solely by a critical global stress value, but are also dependent on the evolution of the dislocation density. In addition, the analysis shows that if twinning is initiated, the nucleated twins may continue to grow as a function of strain, even as the dislocation density continues to increase.

  9. Negative strain rate sensitivity in bulk metallic glass and its similarities with the dynamic strain aging effect during deformation

    SciTech Connect

    Dalla Torre, Florian H.; Dubach, Alban; Siegrist, Marco E.; Loeffler, Joerg F.

    2006-08-28

    Detailed investigations were carried out on the deformation behavior of Zr-based monolithic bulk metallic glass and bulk metallic glass matrix composites. The latter, due to splitting and multiplication of shear bands, exhibits larger compressive strains than the former, without significant loss of strength. Serrated flow in conjunction with a negative strain rate sensitivity was observed in both materials. This observation, together with an increase in stress drops with increasing strain and their decrease with increasing strain rate, indicates phenomenologically close similarities with the dynamic strain aging deformation mechanism known for crystalline solids. The micromechanical mechanism of a shear event is discussed in light of these results.

  10. Effect of Strain Rate and Temperature Gradient on Warm Formability of Aluminum Alloy Sheet

    NASA Astrophysics Data System (ADS)

    Bagheriasl, R.; Ghavam, K.; Worswick, M. J.

    2011-08-01

    The effect of temperature gradient and forming speed on warm formability of aluminum alloy sheet has been studied using a coupled thermal mechanical finite element model of cup deep drawing. A user-defined material model was developed using the Bergstrom temperature and strain-rate dependant hardening model and Barlat YLD2000 anisotropic yield surface, which was implemented within LS-DYNA. The stress-strain curves for AA3003 at elevated temperatures and different strain rates were used to fit the Bergstrom hardening parameters. The anisotropy parameters were considered to be non-temperature dependant. The numerical model was validated against experiments from previous work and was found to accurately predict punch force for warm deep drawing. Increases in forming speed are shown to have a negative effect on formability. It is concluded that non-isothermal warm forming can be used to improve the formability of aluminum alloy sheet.

  11. Effect of temperature and strain rate on the compressive behaviour of supramolecular polyurethane

    NASA Astrophysics Data System (ADS)

    Tang, Xuegang; Siviour, Clive R.; Buckley, C. Paul; Feula, Antonio; Hayes, Wayne

    2015-09-01

    Supramolecular polyurethanes (SPUs) possess thermoresponsive and thermoreversible properties, and those characteristics are highly desirable in both bulk commodity and value-added applications such as adhesives, shape-memory materials, healable coatings and lightweight, impact-resistant structures (e.g. protection for mobile electronics). A better understanding of the mechanical properties, especially the rate and temperature sensitivity, of these materials are required to assess their suitability for different applications. In this paper, a newly developed SPU with tuneable thermal properties was studied, and the response of this SPU to compressive loading over strain rates from 10-3 to 104 s-1 was presented. Furthermore, the effect of temperature on the mechanical response was also demonstrated. The sample was tested using an Instron mechanical testing machine for quasi-static loading, a home-made hydraulic system for moderate rates and a traditional split Hopkinson pressure bars (SHPBs) for high strain rates. Results showed that the compression stress-strain behaviour was affected significantly by the thermoresponsive nature of SPU, but that, as expected for polymeric materials, the general trends of the temperature and the rate dependence mirror each other. However, this behaviour is more complicated than observed for many other polymeric materials, as a result of the richer range of transitions that influence the behaviour over the range of temperatures and strain rates tested.

  12. Effects of strain rate on delamination fracture toughness of graphite/epoxy

    NASA Technical Reports Server (NTRS)

    Daniel, I. M.; Aliyu, A. A.

    1985-01-01

    The objective of this paper is to evaluate various experimental techniques and analysis methods for the characterization of interlaminar fracture toughness, and to determine the effects of strain rate on that property for a graphite/epoxy composite. Mode I interlaminar fracture was investigated by means of a double-cantilever beam (DCB) specimen for AS-4/3501-6 graphite/epoxy. Hinged tabs were used to insure unrestrained rotation at the free ends. Specimens were loaded at quasi-static deflection rates of up to 8.5 mm/s corresponding to crack extension rates of over 51 mm/s. Crack extension was monitored by means of strain gages mounted on the surface of the specimen, or a conductive-paint circuit attached to the edge of the DCB specimen. Continuous records were obtained of load, deflection, and crack extension for determination of the strain energy release rate. The latter was expressed as a power law of the crack extension velocity. Results indicate that the strain energy release rate increases with crack velocity by up to 28 percent for the range of rates considered.

  13. A Study on the Effect of Strain Rate on the Dynamic Recrystallization Mechanism of Alloy 617B

    NASA Astrophysics Data System (ADS)

    Jiang, He; Dong, Jianxin; Zhang, Maicang; Yao, Zhihao

    2016-10-01

    The effect of strain rate on dynamic recrystallization (DRX) behavior and mechanism of alloy 617B was investigated by isothermal compression test in a temperature range of 1393 K to 1483 K (1120 °C to 1210 °C) with a wide strain rate scope of 0.01 to 20 s-1. The microstructure evolution was investigated comprehensively by optical microscopy, electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI), and transmission electron microscopy (TEM) to provide detailed insight into the effect of strain rate on DRX mechanism. The study shows that DRX is accelerated at both low strain rate and high strain rate conditions with an apparent sluggish kinetics at the intermediate strain rate of 1 s-1. In the low strain rate condition ( i.e., <1 s-1), DRX is mainly controlled by the growth of DRX nuclei due to the sufficient time. When the strain rate is higher than 1 s-1, besides the commonly accepted reason of adiabatic heat generated by high strain rate, enhanced DRX nucleation mechanism is crucial for the promotion of DRX at high strain rate. High strain rate could lead to enhanced pile-up of dislocation and higher stored energy, which can facilitate the process of DRX. In addition, distortion or subdivision of twins and "grain fragment" are detected when the strain rate is higher than 1 s-1, which provide additional DRX nucleation mechanism. As a result, the combined effect leads to the higher DRX nucleation rate to promote DRX at high strain rate. The effect of strain rate on DRX is the completion result between sufficiency of time on the one hand and adiabatic heat and enhanced nucleation mechanism on the other.

  14. A Study on the Effect of Strain Rate on the Dynamic Recrystallization Mechanism of Alloy 617B

    NASA Astrophysics Data System (ADS)

    Jiang, He; Dong, Jianxin; Zhang, Maicang; Yao, Zhihao

    2016-07-01

    The effect of strain rate on dynamic recrystallization (DRX) behavior and mechanism of alloy 617B was investigated by isothermal compression test in a temperature range of 1393 K to 1483 K (1120 °C to 1210 °C) with a wide strain rate scope of 0.01 to 20 s-1. The microstructure evolution was investigated comprehensively by optical microscopy, electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI), and transmission electron microscopy (TEM) to provide detailed insight into the effect of strain rate on DRX mechanism. The study shows that DRX is accelerated at both low strain rate and high strain rate conditions with an apparent sluggish kinetics at the intermediate strain rate of 1 s-1. In the low strain rate condition (i.e., <1 s-1), DRX is mainly controlled by the growth of DRX nuclei due to the sufficient time. When the strain rate is higher than 1 s-1, besides the commonly accepted reason of adiabatic heat generated by high strain rate, enhanced DRX nucleation mechanism is crucial for the promotion of DRX at high strain rate. High strain rate could lead to enhanced pile-up of dislocation and higher stored energy, which can facilitate the process of DRX. In addition, distortion or subdivision of twins and "grain fragment" are detected when the strain rate is higher than 1 s-1, which provide additional DRX nucleation mechanism. As a result, the combined effect leads to the higher DRX nucleation rate to promote DRX at high strain rate. The effect of strain rate on DRX is the completion result between sufficiency of time on the one hand and adiabatic heat and enhanced nucleation mechanism on the other.

  15. Strain rate effects on symmetric diblock copolymer liquid bridges: order-induced stability of polymer fibres.

    PubMed

    Peters, Robert D; Dalnoki-Veress, Kari

    2014-10-01

    Optical microscopy is used to study the effect of lamellar order on the evolution of polymer-melt bridges. Measurements are performed on symmetric diblock copolymers and linear homopolymers in the melt state. Diblock copolymer bridges measured in the disordered phase are shown to exhibit the same strain rate response as their homopolymer counterparts: shear thinning at low strain rates and shear thickening at high strain rates. However, when measured in the ordered phase, copolymer-melt bridges demonstrate an increased effective viscosity due to the lamellar order and a shear thinning response over the entire range of strain rates probed. The increased viscosity demonstrates an enhanced stability in lamellae forming diblock liquid bridges, presumed to be caused by the isotropic orientational order of lamellar domains that provide energy barriers to flow within the bridge. The shear thinning can be understood as an alignment of lamellae along the axis of the bridge due to flow, facilitating unimpeded diffusion of polymer out of the liquid bridge along lamellar boundaries.

  16. Effects of strain rate and confining pressure on the deformation and failure of shale

    SciTech Connect

    Cook, J.M. ); Sheppard, M.C. ); Houwen, O.H. )

    1991-06-01

    Previous work on shale mechanical properties has focused on the slow deformation rates appropriate to wellbore deformation. Deformation of shale under a drill bit occurs at a very high rate, and the failure properties of the rock under these conditions are crucial in determining bit performance and in extracting lithology and pore-pressure information from drilling parameters. Triaxial tests were performed on two nonswelling shales under a wide range of strain rates and confining and pore pressures. At low strain rates, when fluid is relatively free to move within the shale, shale deformation and failure are governed by effective stress or pressure (i.e., total confining pressure minus pore pressure), as is the case for ordinary rock. If the pore pressure in the shale is high, increasing the strain rate beyond about 0.1%/sec causes large increases in the strength and ductility of the shale. Total pressure begins to influence the strength. At high stain rates, the influence of effective pressure decreases, except when it is very low (i.e., when pore pressure is very high); ductility then rises rapidly. This behavior is opposite that expected in ordinary rocks. This paper briefly discusses the reasons for these phenomena and their impact on wellbore and drilling problems.

  17. Strain-rate effects on microstructural deformation in irradiated 316 SS

    NASA Astrophysics Data System (ADS)

    Cole, James I.; Tsai, Hanchung; Allen, Todd R.; Yoshitake, Tsunemitsu; Akasaka, Naoaki; Yamagata, Ichiro; Nakamura, Yasuo

    2006-06-01

    A series of studies have been performed to investigate the post-irradiation deformation and failure behavior of 12% cold-worked 316 stainless steel following irradiation to variety of doses and temperatures in the outer rows of the experimental breeder reactor II (EBR-II). In the current phase of these studies, three sets of samples with different radiation-induced microstructures have been characterized with transmission electron microscopy (TEM) following tensile testing to failure at a 'fast' strain-rate (1 × 10 -3 s -1) and a 'slow' strain-rate (1 × 10 -7 s -1). The samples were irradiated to doses between 9 and 41 dpa at temperatures between 383 and 443 °C. Tensile tests were conducted at a temperature of 430 °C and only regions outside of the necked region were examined. Over the parameters tested, strain-rate had a negligible effect on the deformation microstructure. In addition, there was no clear evidence of localized deformation behavior and the deformation appeared relatively homogeneous, characterized by unfaulting and incorporation of faulted dislocation loops into the general dislocation network structure. The influence of the defect microstructures and strain-rate on deformation behavior is discussed.

  18. The effect of strain rate on the compressive strength of dry and saturated tuff

    SciTech Connect

    Olsson, W.A.

    1989-09-01

    The uniaxial compressive strength of air-dry and water-saturated ashfall tuff from the Nevada Test Site was measured as a function of strain rate from 10{sup {minus}6} to 10{sup 3} s{sup {minus}1}. Two different testing devices were used to achieve this wide range in rate, an electro-hydraulic, servo-controlled load frame, and a Kolsky bar. Critical strain rates of 82 s{sup {minus}1} and 22{sup {minus}1} were found for dry and saturated tuffs, respectively. Below the critical rate the strength is a weak function of strain rate and above the critical rate strength varies as the cube root of strain rate. The strengths of the dry and saturated tuff are the same above the critical rate. At slower rates, the saturated tuff is weaker at all rates and shows a slightly stronger strain-rate sensitivity. 26 refs., 5 figs.

  19. Temperature effects on high strain rate properties of graphite/epoxy composites

    NASA Technical Reports Server (NTRS)

    Yaniv, G.; Daniel, I. M.; Cokeing, S.; Martinez, G. M.

    1991-01-01

    A unidirectional graphite epoxy material (AS4/3501-6) was characterized at strain rates ranging from 5 x 10(exp 6) s(exp -1) to 5(exp -1), at room temperature and at 128 C. Results are presented in the form of stress-strain curves to failure. The longitudinal properties remain nearly unchanged with strain rate and temperature. The transverse modulus increases with strain rate but decreases with temperature. The transverse strength and transverse ultimate tensile strain have a positive rate sensitivity at low rates, which changes to negative at intermediate rates and returns to positive rate sensitivity at the highest rates tested. A temperature-time equivalence principle was applied and master curves were obtained for the transverse mechanical properties. The in-plane shear modulus and in-plane shear strength have a positive rate sensitivity. The ultimate intralaminar shear strain has a positive rate sensitivity at low rates, which changes to negative at high rates. At the elevated temperature of 128 C, the ultimate shear strain is 25 to 30 percent higher than the room temperature value, but its strain rate dependence is moderate.

  20. The Effects of Stress Triaxiality, Temperature and Strain Rate on the Fracture Characteristics of a Nickel-Base Superalloy

    NASA Astrophysics Data System (ADS)

    Wang, Jianjun; Guo, Weiguo; Guo, Jin; Wang, Ziang; Lu, Shengli

    2016-05-01

    In this work, to study the effects of stress triaxiality, temperature, and strain rate on the fracture behaviors of a single-crystal Nickel-base superalloy, a series of experiments over a temperature range of 293 to 1373 K, strain rate range of 0.001 to 4000/s, and stress triaxiality range of -0.6 to 1.1 are conducted. Anomalous peak of stress is noticed in the yield stress versus temperature curves, and strain rate effect on the anomalous peak of yield stress is analyzed. The anomalous peak shifts to higher temperature as the strain rate increases. Then the effects of stress triaxiality, temperature, and strain rate on its fracture behaviors, including strain to fracture, path of crack propagation, and fracture surface, are observed and analyzed. A valley of the fracture strain is formed in the fracture strain versus temperature curve over the selected temperature range. The micrograph of fracture surface is largely dependent on the temperature, stress triaxiality, and strain rate. Finally, the original Johnson-Cook (J-C) fracture criterion cannot describe the effect of stress triaxiality and temperature on the fracture behaviors of single-crystal Nickel-base superalloy. A modified J-C fracture criterion is developed, which takes the anomalous stress triaxiality and temperature effects on the fracture behaviors of single-crystal Nickel-base superalloy into account.

  1. The Effect of Electric Current and Strain Rate on Serrated Flow of Sheet Aluminum Alloy 5754

    NASA Astrophysics Data System (ADS)

    Zhao, Kunmin; Fan, Rong; Wang, Limin

    2016-03-01

    Electrically assisted tensile tests are carried out on sheet aluminum alloy AA5754 at electric current densities ranging from 0 to 30.4 A/mm2 and strain rates ranging from 10-3 to 10-1 s-1. The strain rate sensitivity and the serrated flow behavior are investigated in accordance with dynamic strain aging mechanism. The strain rate sensitivity changes from negative to positive and keeps increasing with current density. The tendency toward serrated flow is characterized by the onset of Portevin-Le Chatelier (PLC) instabilities, which are influenced by strain rate, temperature, and electric current. The evolutions of three types of serrated flow are observed and analyzed with respect to strain rate and current density. The magnitude of serration varies with strain rate and current density. The serrated flow can be suppressed by a high strain rate, a high temperature, or a strong electric current. The threshold values of these parameters are determined and discussed. Conventional oven-heated tensile tests are conducted to distinguish the electroplasticity. The flow stress reduces more in electrically assisted tension compared to oven-heated tension at the same temperature level. The electric current helps suppress the serrated flow at the similar temperature level of oven-heating.

  2. Strain Rate Effect on the Mechanical Behaviour of Sandstones with Different Grain Sizes

    NASA Astrophysics Data System (ADS)

    Wasantha, P. L. P.; Ranjith, P. G.; Zhao, J.; Shao, S. S.; Permata, G.

    2015-09-01

    Sandstone specimens with different grain sizes were tested under uniaxial compression at a range of strain rates to investigate the coupled influence of strain rate and grain size on the mechanical behaviour of sandstone. Average grain sizes of sandstones were 105.4 µm (fine grained, FG), 228 µm (medium grained, MG) and 321 µm (coarse grained, CG), and the considered strain rates were 10-6, 10-5, 10-4 and 10-3 S-1. We used an optical deformation and strain measuring system for all the tests to determine the deformation characteristics of specimens during loading. The peak strength was observed to increase non-linearly with an increasing gradient against logarithmic strain rate for FG sandstone, while the trend was a linear increase for MG sandstone and unsystematic for CG sandstone. The relationships of elastic modulus versus logarithmic strain rate for the three types of sandstones showed similar trends as for the peak strength. This observation suggests that the FG sandstones are more responsive to strain rate compared to coarser-grained sandstones and this was attributed to the differences in micro-crack development patterns of sandstones with different grain sizes. A surprising behaviour was observed for CG sandstone, which displayed an increase of strength at the slowest strain rate, reversing the general decreasing trend of strength with decreasing strain rate. Stress redistribution associated with grain fracturing was proposed as a possible mechanism to explain this counter-intuitive behaviour. Finally, the results of this paper suggest that the size of constituent grains is a critical parameter that needs to be incorporated in considerations of the mechanical behaviour of sandstones under different strain rates.

  3. Evidence concerning crack-tip constraint and strain-rate effects in fracture-toughness testing

    SciTech Connect

    Merkle, J.G.

    1986-01-01

    The procedures for measuring the plane strain fracture toughness, K/sub Ic/, of metals were originally developed for relatively high yield strength materials, the toughnesses of which were not affected by stain rate. The application of these procedures to lower yield strength and higher toughness structural and pressure vessel steels have since revealed a perplexing combination of problems involving the effects of geometry, stable crack growth and strain rate on the measured values of toughness. Only the geometric problems were encountered in the development of the procedures for measuring K/sub Ic/. For fracture in the linear elastic range of the load-displacement curve, these problems were overcome by specifying specimen dimensions sufficiently large with respect of the plastic zone size at fracture. However, in the case of structural and pressure vessel steels, it is not always possible to test specimens large enough for fracture to occur prior to general yielding. Therefore, in these cases, the effects of large-scale yielding prior to fracture cannot be avoided, but since they presently have no analytical explanation they are being treated empirically.

  4. Strain rate and manufacturing technique effects on the damage tolerance of composite laminates

    NASA Astrophysics Data System (ADS)

    McManus, Hugh L.; Mak, Yew-Po

    1993-04-01

    The tensile failure and damage tolerance of graphite/epoxy laminates under uniaxial tensile loading at strain rates ranging from 0.0042 epsilon/min to 2 epsilon/min was studied experimentally. Two materials (IM7/977-2 and AS4/938) and two manufacturing methods (manual tape layup and automated tow placement) were used. The failure strengths, failure modes and laminate properties of both unnotched and notched specimens were measured. IM7/977-2 specimens were insensitive to strain rates, except for observed differences in the failure modes of the notched specimens. The unnotched response of the AS4/938 laminates was not dependent on strain rate or manufacturing technique, but their damage tolerance was dependent on both factors. Notched specimens were up to 20 percent weaker at the highest strain rates. Tow placed specimens were less notch sensitive than tape layup specimens, and also less sensitive to strain rates. Strain rates and manufacturing techniques appeared to affect the progression from initiation of failure at the notch tip to final failure.

  5. Physically-based strength model of tantalum incorporating effects of temperature, strain rate and pressure

    DOE PAGESBeta

    Lim, Hojun; Battaile, Corbett C.; Brown, Justin L.; Weinberger, Christopher R.

    2016-06-14

    In this work, we develop a tantalum strength model that incorporates e ects of temperature, strain rate and pressure. Dislocation kink-pair theory is used to incorporate temperature and strain rate e ects while the pressure dependent yield is obtained through the pressure dependent shear modulus. Material constants used in the model are parameterized from tantalum single crystal tests and polycrystalline ramp compression experiments. It is shown that the proposed strength model agrees well with the temperature and strain rate dependent yield obtained from polycrystalline tantalum experiments. Furthermore, the model accurately reproduces the pressure dependent yield stresses up to 250 GPa.more » The proposed strength model is then used to conduct simulations of a Taylor cylinder impact test and validated with experiments. This approach provides a physically-based multi-scale strength model that is able to predict the plastic deformation of polycrystalline tantalum through a wide range of temperature, strain and pressure regimes.« less

  6. Thixoforming of Steel: New Tools Conception to Analyse Thermal Exchanges and Strain Rate Effects

    NASA Astrophysics Data System (ADS)

    Cezard, P.; Bigot, R.; Becker, E.; Mathieu, S.; Pierret, J. C.; Rassili, A.

    2007-04-01

    Through different papers, authors shown that the influence of thermal exchanges was a first order parameter on the semi-solid steel behaviour, and certainly for every semi-solid metallic materials. These thermal exchanges hide other parameters effect like, for example, the strain rate influence. This paper tries to determine the influence of these two parameters by using a new extrusion device on a hydraulic press. This new tools conception annihilated the influence of the decrease of the punch speed before stopping and permitted to have a constant speed during the experiment. This work also deals with the homogeneous flow during thixoforming of steel and shows the importance to couple initial temperature of the slug with punch speed. This paper presents different conditions which permitted to have a homogeneous flow by keeping a low load.

  7. Effects of strain rate, test temperature and test environment on tensile properties of vandium alloys

    SciTech Connect

    Gubbi, A.N.; Rowcliffe, A.F.; Eatherly, W.S.; Gibson, L.T.

    1996-10-01

    Tensile testing was carried out on SS-3 tensile specimens punched from 0.762-mm-thick sheets of the large heat of V-4Cr-4Ti and small heats of V-3Cr-3Ti and V-6Cr-6Ti. The tensile specimens were annealed at 1000{degrees} for 2 h to obtain a fully recrystallized, fine grain microstructure with a grain size in the range of 10-19 {mu}m. Room temperature tests at strain rates ranging from 10{sup {minus}3} to 5 x 10{sup {minus}1}/s were carried out in air; elevated temperature testing up to 700{degrees}C was conducted in a vacuum better than 1 x 10{sup {minus}5} torr (<10{sup {minus}3} Pa). To study the effect of atomic hydrogen on ductility, tensile tests were conducted at room temperature in an ultra high vacuum chamber (UHV) with a hydrogen leak system.

  8. A Study of Strain Rate Effects for Turbulent Premixed Flames with Application to LES of a Gas Turbine Combustor Model

    DOE PAGESBeta

    Kemenov, Konstantin A.; Calhoon, William H.

    2015-03-24

    Large-scale strain rate field, a resolved quantity which is easily computable in large-eddy simulations (LES), could have profound effects on the premixed flame properties by altering the turbulent flame speed and inducing local extinction. The role of the resolved strain rate has been investigated in a posterior LES study of GE lean premixed dry low NOx emissions LM6000 gas turbine combustor model. A novel approach which is based on the coupling of the lineareddy model with a one-dimensional counter-flow solver has been applied to obtain the parameterizations of the resolved premixed flame properties in terms of the reactive progress variable,more » the local strain rate measure, and local Reynolds and Karlovitz numbers. The strain rate effects have been analyzed by comparing LES statistics for several models of the turbulent flame speed, i.e, with and without accounting for the local strain rate effects, with available experimental data. The sensitivity of the simulation results to the inflow velocity conditions as well as the grid resolution have been also studied. Overall, the results suggest the necessity to represent the strain rate effects accurately in order to improve LES modeling of the turbulent flame speed.« less

  9. A Study of Strain Rate Effects for Turbulent Premixed Flames with Application to LES of a Gas Turbine Combustor Model

    SciTech Connect

    Kemenov, Konstantin A.; Calhoon, William H.

    2015-03-24

    Large-scale strain rate field, a resolved quantity which is easily computable in large-eddy simulations (LES), could have profound effects on the premixed flame properties by altering the turbulent flame speed and inducing local extinction. The role of the resolved strain rate has been investigated in a posterior LES study of GE lean premixed dry low NOx emissions LM6000 gas turbine combustor model. A novel approach which is based on the coupling of the lineareddy model with a one-dimensional counter-flow solver has been applied to obtain the parameterizations of the resolved premixed flame properties in terms of the reactive progress variable, the local strain rate measure, and local Reynolds and Karlovitz numbers. The strain rate effects have been analyzed by comparing LES statistics for several models of the turbulent flame speed, i.e, with and without accounting for the local strain rate effects, with available experimental data. The sensitivity of the simulation results to the inflow velocity conditions as well as the grid resolution have been also studied. Overall, the results suggest the necessity to represent the strain rate effects accurately in order to improve LES modeling of the turbulent flame speed.

  10. Strain rate effects on mechanical properties in tension of aluminium alloys used in armour applications

    NASA Astrophysics Data System (ADS)

    Cadoni, E.; Dotta, M.; Forni, D.; Bianchi, S.; Kaufmann, H.

    2012-08-01

    The mechanical properties in tension of two aluminium alloys (AA5059-H131 and AA7039-T651) used in armour applications were determined from tests carried out over a wide range of strain-rates on round specimens. The experimental research was developed in the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. The target strain rates were set at the following four levels: 10-3, 30, 300 and 1000s-1. The quasi-static tests were performed with a universal electromechanical machine, whereas a hydro-pneumatic machine and a Split Hopkinson Tensile Bar apparatus were used for medium and high strain-rates respectively. The required parameters by the Johnson-Cook constitutive law were also determined.

  11. High strain rates effects in quasi-isentropic compression of solids

    SciTech Connect

    Ravelo, Ramon; Holian, Brad L; Germann, Timothy C

    2009-01-01

    We have performed large-scale molecular-dynamics (MD) simulations of shock loading and quasi-isentropic compression in defective copper crystals, modeling the interatomic interactions with an embedded-atom method potential. For samples with a relatively low density of pre-existing defects, the strain rate dependence of the flow stress follows a power law in the 10{sup 9}-10{sup 12} s{sup -1} regime with an exponent of 0.40. For initially damaged, isotropic crystals the flow stress exhibits a narrow linear region in strain rate, which then bends over at high strain rates in a manner reminiscent of shear thinning in fluids. The MD results can be described by a modification of Eyring's theory of Couette shear flow in fluids.

  12. Effect of Strain Rate on Tensile Properties of Carbon Fiber Epoxy-Impregnated Bundle Composite

    NASA Astrophysics Data System (ADS)

    Naito, Kimiyoshi

    2014-03-01

    The tensile tests for high tensile strength polyacrylonitrile (PAN)-based (T1000GB) carbon fiber epoxy-impregnated bundle composite at various strain rates ranging from 3.33 × 10-5 to 6.0 × 102 s-1 (various crosshead speeds ranging from 8.33 × 10-7 to 1.5 × 101 m/s) were investigated. The statistical distributions of the tensile strength were also evaluated. The results clearly demonstrated that the tensile strength of bundle composite slightly increased with an increase in the strain rate (crosshead speed) and the Weibull modulus of tensile strength for the bundle composite decreased with an increase in the strain rate (crosshead speed), there is a linear relation between the Weibull modulus and the average tensile strength on log-log scale.

  13. The Effect of Strain-rate and Temperature on the Mechanical Properties of a Metal/Polymer Mixture

    NASA Astrophysics Data System (ADS)

    Woody, Diana L.; Pritchard, Rob; Davis, Jeffrey J.

    1999-06-01

    Research has been going on in materials that are energetic yet have mechanical properties suitable in structural components. A series of experiments have been performed to determine the mechanical properties of a metal/polymer composite. The high strain-rate mechanical properties were determined using a split-Hopkinson pressure bar at strain rates of 10^3. The high strain-rate work was complemented by investigating the effect of slow strain on the order of .02 inches/minute to 200 inches/minute obtained using an Instron machine. The effect of temperature upon the stress strain curves was also observed. This paper will discuss one of the mixtures investigated containing titanium (35 μm) and Teflon (35μm) in a 80/20 ratio by weight. The low rate strain curves will be compared to the data achieved at higher strain-rates. The mechanical properties obtained in this study as well as others determined in prior work are being used in a modeling effort of this material under deformation.

  14. Effects of cold-treatment and strain-rate on mechanical properties of NbTi/Cu superconducting composite wires.

    PubMed

    Guan, Mingzhi; Wang, Xingzhe; Zhou, Youhe

    2015-01-01

    During design and winding of superconducting magnets at room temperature, a pre-tension under different rate is always applied to improve the mechanical stability of the magnets. However, an inconsistency rises for superconductors usually being sensitive to strain and oversized pre-stress which results in degradation of the superconducting composites' critical performance at low temperature. The present study focused on the effects of the cold-treatment and strain-rate of tension deformation on mechanical properties of NbTi/Cu superconducting composite wires. The samples were immersed in a liquid nitrogen (LN2) cryostat for the adiabatic cold-treatment, respectively with 18-hour, 20-hour, 22-hour and 24-hour. A universal testing machine was utilized for tension tests of the NbTi/Cu superconducting composite wires at room temperature; a small-scale extensometer was used to measure strain of samples with variable strain-rate. The strength, elongation at fracture and yield strength of pre-cold-treatment NbTi/Cu composite wires were drawn. It was shown that, the mechanical properties of the superconducting wires are linearly dependent on the holding time of cold-treatment at lower tensile strain-rate, while they exhibit notable nonlinear features at higher strain-rate. The cold-treatment in advance and the strain-rate of pre-tension demonstrate remarkable influences on the mechanical property of the superconducting composite wires. PMID:25713767

  15. Effects of cold-treatment and strain-rate on mechanical properties of NbTi/Cu superconducting composite wires.

    PubMed

    Guan, Mingzhi; Wang, Xingzhe; Zhou, Youhe

    2015-01-01

    During design and winding of superconducting magnets at room temperature, a pre-tension under different rate is always applied to improve the mechanical stability of the magnets. However, an inconsistency rises for superconductors usually being sensitive to strain and oversized pre-stress which results in degradation of the superconducting composites' critical performance at low temperature. The present study focused on the effects of the cold-treatment and strain-rate of tension deformation on mechanical properties of NbTi/Cu superconducting composite wires. The samples were immersed in a liquid nitrogen (LN2) cryostat for the adiabatic cold-treatment, respectively with 18-hour, 20-hour, 22-hour and 24-hour. A universal testing machine was utilized for tension tests of the NbTi/Cu superconducting composite wires at room temperature; a small-scale extensometer was used to measure strain of samples with variable strain-rate. The strength, elongation at fracture and yield strength of pre-cold-treatment NbTi/Cu composite wires were drawn. It was shown that, the mechanical properties of the superconducting wires are linearly dependent on the holding time of cold-treatment at lower tensile strain-rate, while they exhibit notable nonlinear features at higher strain-rate. The cold-treatment in advance and the strain-rate of pre-tension demonstrate remarkable influences on the mechanical property of the superconducting composite wires.

  16. Effect of Orientation and Strain Rate on Crush Strength of Cellulose Fiberboard Assemblies

    SciTech Connect

    Smith, A.C.

    2001-01-10

    Cane fiberboard is widely used as the impact absorption and thermal insulation material in overpacks for radioactive materials packages. The study described here investigated the properties of cane fiberboard assemblies under conditions important to radioactive materials packaging applications. Tests were performed for loading perpendicular and parallel to the planes of the fiberboard sheets for both slow and impact strain rates. Specimens loaded parallel to the plane of the fiberboard typically fail by buckling and consequently are less stiff than those loaded perpendicular to the plane of the fiberboard sheets. Specimens subjected to impact loading appear stiffer than those tested at slow strain rates.

  17. Effect of Strain Rate on Deformation Behavior of AlCoCrFeNi High-Entropy Alloy by Nanoindentation

    NASA Astrophysics Data System (ADS)

    Tian, L.; Jiao, Z. M.; Yuan, G. Z.; Ma, S. G.; Wang, Z. H.; Yang, H. J.; Zhang, Y.; Qiao, J. W.

    2016-06-01

    In this study, nanoindentation tests with continuous stiffness measurement technique were measured to investigate the deformation behavior of a high-entropy alloy AlCoCrFeNi under different indentation strain rates at room temperature. Results suggest that the creep behavior exhibits remarkable strain rate dependence. In-situ scanning images showed a conspicuous pileup around the indents, indicating that an extremely localized plastic deformation occurred during the nanoindentation. Under different strain rates, elastic modulus basically remains unchanged, while the hardness decreases with increasing indentation depth due to the indentation size effect. Furthermore, the modulus and hardness of AlCoCrFeNi HEAs are greater than that of the Al x CoCrFeNi ( x = 0.3,0.5) at the strain rate of 0.2 s-1 due to its higher negative enthalpy of mixing related to the atomic binding force, and the solid solution strengthening induced by the lattice distortion, respectively.

  18. Effect of growth rate on plasmid DNA production and metabolic performance of engineered Escherichia coli strains.

    PubMed

    Wunderlich, Martin; Taymaz-Nikerel, Hilal; Gosset, Guillermo; Ramírez, Octavio T; Lara, Alvaro R

    2014-03-01

    Two engineered Escherichia coli strains, designated VH33 and VH34, were compared to their parent strain W3110 in chemostat mode during plasmid DNA (pDNA) production. In strain VH33 the glucose uptake system was modified with the aim of reducing overflow metabolism. The strain VH34 has an additional deletion of the pyruvate kinase A gene (pykA) to increase pDNA formation. pDNA formation rates as well as kinetic and stoichiometric parameters were investigated in dependence of the growth rate within a range from 0.02 to 0.25 h(-1). Differences between strains were found in terms of the biomass yields on nitrogen and oxygen, as well as on the cell maintenance coefficients. The deletion of pykA led to a significantly increased pDNA yield and productivity. At an optimal growth rate of 0.20 h(-1) it was nearly 60% higher than that of W3110 and VH33. Metabolic fluxes calculated by metabolite balance analysis showed differences mainly in reactions catalyzed by pyruvate kinase and glucose 6-phosphate dehydrogenase. The obtained data are useful for the design of cultivation schemes for pDNA production by E. coli. PMID:24012107

  19. Strain rate effects on the mechanical behavior of two Dual Phase steels in tension

    NASA Astrophysics Data System (ADS)

    Cadoni, E.; Singh, N. K.; Forni, D.; Singha, M. K.; Gupta, N. K.

    2016-05-01

    This paper presents an experimental investigation on the strain rate sensitivity of Dual Phase steel 1200 (DP1200) and Dual Phase steel 1400 (DP1400) under uni-axial tensile loads in the strain rate range from 0.001 s-1 to 600 s-1. These materials are advanced high strength steels (AHSS) having high strength, high capacity to dissipate crash energy and high formability. Flat sheet specimens of the materials having gauge length 10 mm, width 4 mm and thickness 2 mm (DP1200) and 1.25 mm (DP1400), are tested at room temperature (20∘C) on electromechanical universal testing machine to obtain their stress-strain relation under quasi-static condition (0.001 s-1), and on Hydro-Pneumatic machine and modified Hopkinson bar to study their mechanical behavior at medium (3 s-1, and 18 s-1) and high strain rates (200 s-1, 400 s-1, and 600 s-1) respectively. Tests under quasi-static condition are performed at high temperature (200∘C) also, and found that tensile flow stress is a increasing function of temperature. The stress-strain data has been analysed to determine the material parameters of the Cowper-Symonds and the Johnson-Cook models. A simple modification of the Johnson-Cook model has been proposed in order to obtain a better fit of tests at high temperatures. Finally, the fractographs of the broken specimens are taken by scanning electron microscope (SEM) to understand the fracture mechanism of these advanced high strength steels at different strain rates.

  20. Analytical and experimental studies on the strain rate effects in penetration of 10wt % ballistic gelatin

    NASA Astrophysics Data System (ADS)

    Liu, L.; Jia, Z.; Ma, X. L.; Fan, Y. R.

    2013-07-01

    This work concentrates on modeling the super-elastic behavior of 10wt% ballistic gelatin at 4°C and the mechanical responses at quasi-static and high-speed penetrations. Uniaxial compression and simple shearing experiments were carried out to determine the moduli in Mooney-Rivlin model describing the elastic behavior of gelatin at low strain rates. The failure mode is determined to be elastic fracture as the tensile stretch ratio exceeds a critical value. For high compression strain rates, the available results from the split Hopkinson pressure bar (SHPB) experiments for 10wt% gelatin were carefully examined and assessed. Linear relationship between the moduli and the strain rate is established. Based on these material parameters, an analytic solution of stress for the quasi-static and quasi-dynamic expansion of spherical cavity in gelatin is derived. As a consequence, the work needed to open unit volume of cavity, Ps, which is the key parameter in studying penetration problems, is linearly increasing with the characteristic strain rate. The application of Ps to our quasi-static and high-speed penetration experiments is discussed and assessed.

  1. Hydrostatic Stress Effects Incorporated Into the Analysis of the High-Strain-Rate Deformation of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Roberts, Gary D.

    2003-01-01

    Procedures for modeling the effect of high strain rate on composite materials are needed for designing reliable composite engine cases that are lighter than the metal cases in current use. The types of polymer matrix composites that are likely to be used in such an application have a deformation response that is nonlinear and that varies with strain rate. The nonlinearity and strain rate dependence of the composite response is primarily due to the matrix constituent. Therefore, in developing material models to be used in the design of impact-resistant composite engine cases, the deformation of the polymer matrix must be correctly analyzed. However, unlike in metals, the nonlinear response of polymers depends on the hydrostatic stresses, which must be accounted for within an analytical model. An experimental program has been carried out through a university grant with the Ohio State University to obtain tensile and shear deformation data for a representative polymer for strain rates ranging from quasi-static to high rates of several hundred per second. This information has been used at the NASA Glenn Research Center to develop, characterize, and correlate a material model in which the strain rate dependence and nonlinearity (including hydrostatic stress effects) of the polymer are correctly analyzed. To obtain the material data, Glenn s researchers designed and fabricated test specimens of a representative toughened epoxy resin. Quasi-static tests at low strain rates and split Hopkinson bar tests at high strain rates were then conducted at the Ohio State University. The experimental data confirmed the strong effects of strain rate on both the tensile and shear deformation of the polymer. For the analytical model, Glenn researchers modified state variable constitutive equations previously used for the viscoplastic analysis of metals to allow for the analysis of the nonlinear, strain-rate-dependent polymer deformation. Specifically, we accounted for the effects of

  2. Incorporation of Mean Stress Effects into the Micromechanical Analysis of the High Strain Rate Response of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

    2002-01-01

    The results presented here are part of an ongoing research program, to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. A micromechanics approach is employed in this work, in which state variable constitutive equations originally developed for metals have been modified to model the deformation of the polymer matrix, and a strength of materials based micromechanics method is used to predict the effective response of the composite. In the analysis of the inelastic deformation of the polymer matrix, the definitions of the effective stress and effective inelastic strain have been modified in order to account for the effect of hydrostatic stresses, which are significant in polymers. Two representative polymers, a toughened epoxy and a brittle epoxy, are characterized through the use of data from tensile and shear tests across a variety of strain rates. Results computed by using the developed constitutive equations correlate well with data generated via experiments. The procedure used to incorporate the constitutive equations within a micromechanics method is presented, and sample calculations of the deformation response of a composite for various fiber orientations and strain rates are discussed.

  3. Effect of pulse duration and strain rate on incipient spall fracture in copper

    SciTech Connect

    Johnson, J.N.; Gray, G.T. III; Bourne, N.K.

    1999-11-01

    Data are presented on real time (VISAR) measurements of the spall fracture of copper for various pulse durations and tensile strain rates at the spall plane. The impactors consist of Teflon, {ital Y}-cut quartz, and a tungsten heavy alloy. VISAR data are compared with finite-difference calculations employing a rate-dependent void-growth model. The data and comparisons show little dependence of the onset of void growth on either pulse duration or tensile strain rate. Also, it is shown that hydrodynamics (wave propagation properties) involving the transmission of the spall signal from the spall plane to the free surface (plane of the VISAR measurement) can mask slight differences in the void-growth or fracture response. In addition, new results are presented for the elastic description of planar wave propagation in {ital Y}-cut quartz; expressions are given for the six independent stress components to second order in infinitesimal Lagrangian strains. A discussion with regard to additional use of {ital Y}-cut quartz in impact experiments is presented. {copyright} {ital 1999 American Institute of Physics.}

  4. Effect of forging strain rate and deformation temperature on the mechanical properties of warm-worked 304L stainless steel

    SciTech Connect

    Switzner, N. T.; Van Tyne, C. J.; Mataya, M. C.

    2010-01-25

    Stainless steel 304L forgings were produced with four different types of production forging equipment – hydraulic press, mechanical press, screw press, and high-energy rate forging (HERF). Each machine imparted a different nominal strain rate during the deformation. The final forgings were done at the warm working (low hot working) temperatures of 816 °C, 843°C, and 871°C. The objectives of the study were to characterize and understand the effect of industrial strain rates (i.e. processing equipment), and deformation temperature on the mechanical properties for the final component. Some of the components were produced with an anneal prior to the final forging while others were deformed without the anneal. The results indicate that lower strain rates produced lower strength and higher ductility components, but the lower strain rate processes were more sensitive to deformation temperature variation and resulted in more within-part property variation. The highest strain rate process, HERF, resulted in slightly lower yield strength due to internal heating. Lower processing temperatures increased strength, decreased ductility but decreased within-part property variation. The anneal prior to the final forging produced a decrease in strength, a small increase in ductility, and a small decrease of within-part property variation.

  5. Numerical Evaluation of Strain Rate Effect on Mechanical and Electromechanical Coupling Responses in BaTiO3 Single-Crystal Nanofilm

    NASA Astrophysics Data System (ADS)

    Tian, Xiao Bao; Yang, Xin Hua; Cao, Wei Zhong

    2014-02-01

    The mechanical and electromechanical coupling responses of a ferroelectric single-crystal nanofilm under displacement loading at different strain rates have been simulated using the molecular dynamics method based on the shell model. While the linear stress-strain relation is independent of the strain rate, strong strain rate dependence is exhibited in the electromechanical coupling response for strain rates between 0 ns-1 and 0.5 ns-1. There is an approximate semilogarithmic linear relationship between the polarization stability strain and the strain rate. With increasing strain rate, local 180° domain switches take place sequentially from inside to outside in the stable domain structure evolution, and the number of domain walls increases. However, after the strain rate exceeds 0.5 ns-1, it has almost no effect on the␣domain structure. This work is helpful for improving ferroelectric device design and expanding ferroelectric application fields.

  6. The effect of shearing strain-rate on the ultimate shearing resistance of clay

    NASA Technical Reports Server (NTRS)

    Cheng, R. Y. K.

    1975-01-01

    An approach for investigating the shearing resistance of cohesive soils subjected to a high rate of shearing strain is described. A fast step-loading torque apparatus was used to induce a state of pure shear in a hollow cylindrical soil specimen. The relationship between shearing resistance and rate of shear deformation was established for various soil densities expressed in terms of initial void ratio or water content. For rate of shearing deformation studies, the shearing resistance increases initially with shearing velocity, but subsequently reaches a terminal value as the shearing velocity increases. The terminal shearing resistance is also found to increase as the density of the soil increases. The results of this investigation are useful in the rheological study of clay. It is particularly important for mobility problems of soil runways, since the soil resistance is found to be sensitive to the rate of shearing.

  7. The effect of shearing strain-rate on the ultimate shearing resistance of clay

    NASA Technical Reports Server (NTRS)

    Cheng, R. Y. K.

    1976-01-01

    The shearing resistance of cohesive soils subjected to a high rate of shearing strain was investigated. A fast step-loading torque apparatus was used to induce a state of pure shear in a hollow cylindrical soil specimen. The relationship between shearing resistance and rate of shear deformation was established for various soil densities expressed in terms of initial void ratio or water content. For rate of shearing deformation studies to date, the shearing resistance increases initially with shearing velocity but subsequently reaches a terminal value as the shearing velocity increases. The terminal shearing resistance is also found to increase as the density of the soil increases. The results are useful in the rheological study of clay. It is particularly important for mobility problems of soil runways, since the soil resistance is found to be sensitive to the rate of shearing.

  8. Mixed-mode strain-energy-release rate effects on edge delamination of composites

    NASA Technical Reports Server (NTRS)

    Obrien, T. K.

    1983-01-01

    Unnotched graphite/epoxy laminates, designed to delaminate at the edges under static and cyclic tensile loads, were tested and analyzed. The specimen stacking sequences were chosen so that the total strain-energy-release rate, G, for edge delamination was identical for all three layups. However, each layup had different percentages of crack-opening and shear-mode strain-energy-release rates, G sub 1 and G sub 2, respectively. Results with composites made from T300 graphite fibers and 5208 epoxy, a brittle resin, indicated that only G sub 1 contributed to delamination onset under static loading. However, results with composites made from C6000 fibers and H205 epoxy, a tougher resin, indicated that the total F governed the onset of edge delaminations under cyclic loads. In addition, for both materials, the threshold level of G for delamination onset in fatigue was significantly less than the critical G sub c measured in static tests. Futhermore, although the C6000/H205 material had a much higher static G sub c than T300/5208, its fatigue resistance was only slightly better. A series of mixed-mode tests, like the ones in this study, may be needed to evaluate toughened-resin composites developed for highly strained composite structures subjected to cyclic loads.

  9. Effect of strain rates on deformation behaviors of an in situ Ti-based metallic glass matrix composite

    NASA Astrophysics Data System (ADS)

    Jiao, Z. M.; Wang, Z. H.; Chu, M. Y.; Wang, Y. S.; Yang, H. J.; Qiao, J. W.

    2016-06-01

    Quasi-static and dynamic deformation behaviors of an in situ dendrite-reinforced metallic glass matrix composite: Ti56Zr18V10Cu4Be12 were investigated. Upon quasi-static compression, the composite exhibits distinguished work hardening, accompanied by the ultimate strength of 1290 MPa and the plasticity of 20 %. The improved plasticity is attributed to the multiplication of shear bands within the glass matrix and pileups of dislocations within the dendrites. Upon dynamic compression, the stable plastic flow prevails and the yielding stress increases with the strain rate. The macroscopic plasticity decreases considerably, since the shear bands cannot be effectively hindered by dendrites with deteriorated toughness. The dendrite-dominated mechanism results in the positive strain-rate sensitivity, and the Cowper-Symonds model is employed to depict the strain-rate dependency of yielding strength.

  10. An experimental investigation of strain rate, temperature and humidity effects on the mechanical behavior of a perfluorosulfonic acid membrane

    NASA Astrophysics Data System (ADS)

    Lu, Zongwen; Lugo, Melissa; Santare, Michael H.; Karlsson, Anette M.; Busby, F. Colin; Walsh, Peter

    2012-09-01

    The time-dependent hygro-thermal mechanical behavior of a perfluorosulfonic acid (PFSA) membrane (Nafion® 211 membrane) commonly used in Proton Exchange Membrane Fuel Cells (PEMFCs) is investigated at selected strain rates for a broad range of temperatures and humidities. Tensile tests and relaxation tests are conducted to determine Young's modulus and proportional limit stress as functions of strain rate, temperature and humidity. The results show that Young's modulus and proportional limit stress increase as the strain rate increases, and decrease as the temperature or humidity increases. The results also show that the mechanical response of Nafion® 211 membrane is more sensitive to typical changes in strain rate or temperature than to typical changes in humidity. In addition, two temperature/humidity cycles are conducted to determine the steady state swelling behavior of Nafion® 211 membrane as a function of temperature and humidity. The results show that the membrane swells with increasing temperature and humidity, and that there is little or no hygro-thermal history effect for the swelling strains.

  11. Effect of strain rate and temperature on mechanical properties of selected building Polish steels

    NASA Astrophysics Data System (ADS)

    Moćko, Wojciech; Kruszka, Leopold

    2015-09-01

    Currently, the computer programs of CAD type are basic tool for designing of various structures under impact loading. Application of the numerical calculations allows to substantially reduce amount of time required for the design stage of such projects. However, the proper use of computer aided designing technique requires input data for numerical software including elastic-plastic models of structural materials. This work deals with the constitutive model developed by Rusinek and Klepaczko (RK) applied for the modelling of mechanical behaviour of selected grades structural St0S, St3SX, 18GS and 34GS steels and presents here results of experimental and empirical analyses to describe dynamic elastic-plastic behaviours of tested materials at wide range of temperature. In order to calibrate the RK constitutive model, series of compression tests at wide range of strain rates, including static, quasi-static and dynamic investigations at lowered, room and elevated temperatures, were carried out using two testing stands: servo-hydraulic machine and split Hopkinson bar. The results were analysed to determine influence of temperature and strain rate on visco-plastic response of tested steels, and show good correlation with experimental data.

  12. Microstructural evolution during ultra-rapid annealing of severely deformed low-carbon steel: strain, temperature, and heating rate effects

    NASA Astrophysics Data System (ADS)

    Mostafaei, M. A.; Kazeminezhad, M.

    2016-07-01

    An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The kinetics of recrystallization and transformation is affected by high heating rate and such an interaction. In this study, different levels of strain are applied to low-carbon steel using a severe plastic deformation method. Then, ultra-rapid annealing is performed at different heating rates of 200-1100°C/s and peak temperatures of near critical temperature. Five regimes are proposed to investigate the effects of heating rate, strain, and temperature on the interaction between recrystallization and transformation. The microstructural evolution of severely deformed low-carbon steel after ultra-rapid annealing is investigated based on the proposed regimes. Regarding the intensity and start temperature of the interaction, different microstructures consisting of ferrite and pearlite/martensite are formed. It is found that when the interaction is strong, the microstructure is refined because of the high kinetics of transformation and recrystallization. Moreover, strain shifts an interaction zone to a relatively higher heating rate. Therefore, severely deformed steel should be heated at relatively higher heating rates for it to undergo a strong interaction.

  13. Acute Radiation Effects on Cardiac Function Detected by Strain Rate Imaging in Breast Cancer Patients

    SciTech Connect

    Erven, Katrien; Jurcut, Ruxandra; Weltens, Caroline; Giusca, Sorin; Ector, Joris; Wildiers, Hans; Van den Bogaert, Walter; Voigt, Jens-Uwe

    2011-04-01

    Purpose: To investigate the occurrence of early radiation-induced changes in regional cardiac function using strain rate imaging (SRI) by tissue Doppler echocardiography. Methods and Materials: We included 20 left-sided and 10 right-sided breast cancer patients receiving radiotherapy (RT) to the breast or chest wall. Standard echocardiography and SRI were performed before RT (baseline), immediately after RT (post-RT), and at 2 months follow-up (FUP) after RT. Regional strain (S) and strain rate (SR) values were obtained from all 18 left ventricular (LV) segments. Data were compared to the regional radiation dose. Results: A reduction in S was observed post-RT and at FUP in left-sided patients (S{sub post-RT}: -17.6 {+-} 1.5%, and S{sub FUP}: -17.4 {+-} 2.3%, vs. S{sub baseline}: -19.5 {+-} 2.1%, p < 0.001) but not in right-sided patients. Within the left-sided patient group, S and SR were significantly reduced after RT in apical LV segments (S{sub post-RT}: -15.3 {+-} 2.5%, and S{sub FUP}: -14.3 {+-} 3.7%, vs. S{sub baseline}: -19.3 {+-} 3.0%, p < 0.01; and SR{sub post-RT}: -1.06 {+-} 0.15 s {sup -1}, and SR{sub FUP}: -1.16 {+-} 0.28 s {sup -1}, vs. SR{sub baseline}: -1.29 {+-} 0.27s {sup -1}, p = 0.01), but not in mid- or basal segments. Furthermore, we observed that segments exposed to more than 3 Gy showed a significant decrease in S after RT (S{sub post-RT}: -16.1 {+-} 1.6%, and S{sub FUP}: -15.8 {+-} 3.4%, vs. S{sub baseline}: -18.9 {+-} 2.6%, p < 0.001). This could not be observed in segments receiving less than 3 Gy. Conclusions: SRI shows a dose-related regional decrease in myocardial function after RT. It might be a useful tool in the evaluation of modern RT techniques, with respect to cardiac toxicity.

  14. Effect of strain rate on shear properties and fracture characteristics of DP600 and AA5182-O sheet metal alloys

    NASA Astrophysics Data System (ADS)

    Rahmaan, Taamjeed; Butcher, Cliff; Abedini, Armin; Worswick, Michael

    2015-09-01

    Shear tests were performed at strain rates ranging from quasi-static (.01 s-1) to 600 s-1 for DP600 steel and AA5182-O sheet metal alloys at room temperature. A miniature sized shear specimen was modified and validated in this work to perform high strain rate shear testing. Digital image correlation (DIC) techniques were employed to measure the strains in the experiments, and a criterion to detect the onset of fracture based on the hardening rate of the materials is proposed. At equivalent strains greater than 20%, the DP600 and AA5182 alloys demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the DP600 shows positive rate sensitivity while the AA5182 was not sensitive to strain rate. For both alloys, the equivalent fracture strain and elongation to failure decreased with strain rate. A conversion of the shear stress to an equivalent stress using the von Mises yield criterion provided excellent agreement with the results from tensile tests at elevated strain rates. Unlike the tensile test, the shear test is not limited by the onset of necking so the equivalent stress can be determined over a larger range of strain.

  15. Microstructure and strain rate effects on the mechanical behavior of particle reinforced epoxy-based reactive materials

    NASA Astrophysics Data System (ADS)

    White, Bradley William

    The effects of reactive metal particles on the microstructure and mechanical properties of epoxy-based composites is investigated in this work. Particle reinforced polymer composites show promise as structural energetic materials that can provide structural strength while simultaneously being capable of releasing large amounts of chemical energy through highly exothermic reactions occurring between the particles and with the matrix. This advanced class of materials is advantageous due to the decreased amount of high density inert casings needed for typical energetic materials and for their ability to increase payload expectancy and decrease collateral damage. Structural energetic materials can be comprised of reactive particles that undergo thermite or intermetallic reactions. In this work nickel (Ni) and aluminum (Al) particles were chosen as reinforcing constituents due to their well characterized mechanical and energetic properties. Although, the reactivity of nickel and aluminum is well characterized, the effects of their particle size, volume fractions, and spatial distribution on the mechanical behavior of the epoxy matrix and composite, across a large range of strain rates, are not well understood. To examine these effects castings of epoxy reinforced with 20--40 vol.% Al and 0--10 vol.% Ni were prepared, while varying the aluminum nominal particle size from 5 to 50 mum and holding the nickel nominal particle size constant at 50 mum. Through these variations eight composite materials were produced, possessing unique microstructures exhibiting different particle spatial distributions and constituent makeup. In order to correlate the microstructure to the constitutive response of the composites, techniques such as nearest-neighbor distances, and multiscale analysis of area fractions (MSAAF) were used to quantitatively characterize the microstructures. The composites were investigated under quasi-static and dynamic compressive loading conditions to characterize

  16. The effects of molecular weight on the single lap shear creep and constant strain rate behavior of thermoplastic polyimidesulfone adhesive

    NASA Technical Reports Server (NTRS)

    Dembosky, Stanley K.; Sancaktar, Erol

    1985-01-01

    The bonded shear creep and constant strain rate behaviors of zero, one, and three percent endcapped thermoplastic polyimidesulfone adhesive were examined at room and elevated temperatures. Endcapping was accomplished by the addition of phthalic anhydrides. The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Ludwik's and Crochet's relations were used to describe the experimental failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed. The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Crochet's relations based on Maxwell and Chase-Goldsmith models were fit to delayed failure data. Ludwik's equations revealed negligible rate dependence. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.

  17. Effect of Buffer Conditions and Organic Cosolvents on the Rate of Strain-Promoted Azide-Alkyne Cycloaddition.

    PubMed

    Davis, Derek L; Price, Erin K; Aderibigbe, Sabrina O; Larkin, Maureen X-H; Barlow, Emmett D; Chen, Renjie; Ford, Lincoln C; Gray, Zackery T; Gren, Stephen H; Jin, Yuwei; Keddington, Keith S; Kent, Alexandra D; Kim, Dasom; Lewis, Ashley; Marrouche, Rami S; O'Dair, Mark K; Powell, Daniel R; Scadden, Mick'l H C; Session, Curtis B; Tao, Jifei; Trieu, Janelle; Whiteford, Kristen N; Yuan, Zheng; Yun, Goyeun; Zhu, Judy; Heemstra, Jennifer M

    2016-08-01

    We investigate the effect of buffer identity, ionic strength, pH, and organic cosolvents on the rate of strain-promoted azide-alkyne cycloaddition with the widely used DIBAC cyclooctyne. The rate of reaction between DIBAC and a hydrophilic azide is highly tolerant to changes in buffer conditions but is impacted by organic cosolvents. Thus, bioconjugation reactions using DIBAC can be carried out in the buffer that is most compatible with the biomolecules being labeled, but the use of organic cosolvents should be carefully considered.

  18. Effects that different types of sports have on the hearts of children and adolescents and the value of two-dimensional strain-strain-rate echocardiography.

    PubMed

    Binnetoğlu, Fatih Köksal; Babaoğlu, Kadir; Altun, Gürkan; Kayabey, Özlem

    2014-01-01

    Whether the hypertrophy found in the hearts of athletes is physiologic or a risk factor for the progression of pathologic hypertrophy remains controversial. The diastolic and systolic functions of athletes with left ventricular (LV) hypertrophy usually are normal when measured by conventional methods. More precise assessment of global and regional myocardial function may be possible using a newly developed two-dimensional (2D) strain echocardiographic method. This study evaluated the effects that different types of sports have on the hearts of children and adolescents and compared the results of 2D strain and strain-rate echocardiographic techniques with conventional methods. Athletes from clubs for five different sports (basketball, swimming, football, wrestling, and tennis) who had practiced regularly at least 3 h per week during at least the previous 2 years were included in the study. The control group consisted of sedentary children and adolescents with no known cardiac or systemic diseases (n = 25). The athletes were grouped according to the type of exercise: dynamic (football, tennis), static (wrestling), or static and dynamic (basketball, swimming). Shortening fraction and ejection fraction values were within normal limits for the athletes in all the sports disciplines. Across all 140 athletes, LV geometry was normal in 58 athletes (41.4 %), whereas 22 athletes (15.7 %) had concentric remodeling, 20 (14.3 %) had concentric hypertrophy, and 40 (28.6 %) had eccentric hypertrophy. Global LV longitudinal strain values obtained from the average of apical four-, two-, and three-chamber global strain values were significantly lower for the basketball players than for all the other groups (p < 0.001).

  19. Effect of trabecular bone loss on cortical strain rate during impact in an in vitro model of avian femur

    PubMed Central

    Reich, Tal; Gefen, Amit

    2006-01-01

    Background Osteoporotic hip fractures occur due to loss of cortical and trabecular bone mass and consequent degradation in whole bone strength. The direct cause of most fractures is a fall, and hence, characterizing the mechanical behavior of a whole osteopenic bone under impact is important. However, very little is known about the mechanical interactions between cortical and trabecular bone during impact, and it is specifically unclear to what extent epiphyseal trabecular bone contributes to impact resistance of whole bones. We hypothesized that trabecular bone serves as a structural support to the cortex during impact, and hence, loss of a critical mass of trabecular bone reduces internal constraining of the cortex, and, thereby, decreases the impact tolerance of the whole bone. Methods To test this hypothesis, we conducted cortical strain rate measurements in adult chicken's proximal femora subjected to a Charpy impact test, after removing different trabecular bone core masses to simulate different osteopenic severities. Results We found that removal of core trabecular bone decreased by ~10-fold the cortical strain rate at the side opposite to impact (p < 0.01), i.e. from 359,815 ± 1799 μm/m per second (mean ± standard error) for an intact (control) specimen down to 35,997 ± 180 μm/m per second where 67% of the total trabecular bone mass (~0.7 grams in adult chicken) were removed. After normalizing the strain rate by the initial weight of bone specimens, a sigmoid relation emerged between normalized strain rate and removed mass of trabecular bone, showing very little effect on the cortex strain rate if below 10% of the trabecular mass is removed, but most of the effect was already apparent for less than 30% trabecular bone loss. An analytical model of the experiments supported this behavior. Conclusion We conclude that in our in vitro avian model, loss of over 10% of core trabecular bone substantially altered the deformation response of whole bone to impact

  20. High strain rate behaviour of polypropylene microfoams

    NASA Astrophysics Data System (ADS)

    Gómez-del Río, T.; Garrido, M. A.; Rodríguez, J.; Arencón, D.; Martínez, A. B.

    2012-08-01

    Microcellular materials such as polypropylene foams are often used in protective applications and passive safety for packaging (electronic components, aeronautical structures, food, etc.) or personal safety (helmets, knee-pads, etc.). In such applications the foams which are used are often designed to absorb the maximum energy and are generally subjected to severe loadings involving high strain rates. The manufacture process to obtain polymeric microcellular foams is based on the polymer saturation with a supercritical gas, at high temperature and pressure. This method presents several advantages over the conventional injection moulding techniques which make it industrially feasible. However, the effect of processing conditions such as blowing agent, concentration and microfoaming time and/or temperature on the microstructure of the resulting microcellular polymer (density, cell size and geometry) is not yet set up. The compressive mechanical behaviour of several microcellular polypropylene foams has been investigated over a wide range of strain rates (0.001 to 3000 s-1) in order to show the effects of the processing parameters and strain rate on the mechanical properties. High strain rate tests were performed using a Split Hopkinson Pressure Bar apparatus (SHPB). Polypropylene and polyethylene-ethylene block copolymer foams of various densities were considered.

  1. Frequency and load ratio effects on critical strain energy release rate Gc thresholds of graphite/epoxy composites

    NASA Technical Reports Server (NTRS)

    Adams, Donald F.; Zimmerman, richard S.; Odom, Edwin M.

    1987-01-01

    Graphite/epoxy composite laminates of T300/BP907 and AS6/HST-7 were axial-tension fatigue tested. Tests were conducted at 5 and 10 Hz, and at loading ratios of R = 0.1 and R = 0.5. Edge delamination was monitored as a function of number of fatigue cycles by monitoring stiffness reduction during fatigue testing. Delamination was confirmed and documented using dye-enhanced X-ray and optical photography. Critical strain energy release rates were then calculated. The composites delaminated readily, with loading ratio having a significant influence. Frequency effects were negligible.

  2. The Strain Rate Effect on the Buckling of Single-Layer MoS2

    PubMed Central

    Jiang, Jin-Wu

    2015-01-01

    The Euler buckling theory states that the buckling critical strain is an inverse quadratic function of the length for a thin plate in the static compression process. However, the suitability of this theory in the dynamical process is unclear, so we perform molecular dynamics simulations to examine the applicability of the Euler buckling theory for the fast compression of the single-layer MoS2. We find that the Euler buckling theory is not applicable in such dynamical process, as the buckling critical strain becomes a length-independent constant in the buckled system with many ripples. However, the Euler buckling theory can be resumed in the dynamical process after restricting the theory to an individual ripple in the buckled structure. PMID:25588352

  3. The Effect of transient change in strain rate on plastic flow behaviour of Al-Mg-Si alloy at elevated temperatures

    SciTech Connect

    Petrov, P.; Voronkov, V.; Potapenko, K.; Ivanov, V.

    2011-05-04

    In extrusion forging processes, the abrupt changes in strain rate follows the plastic deformation of a material within the deforming zone. To simulate accurately this effect, the specific experimental investigation of the plastic flow during the transient change in strain rate should be performed. The present paper deals with the investigation of this effect on the flow stress of an Al-Mg-Si alloy during its deformation at 350 deg. C. The investigation consists of two steps. Both steps are connected to the monotonic uniaxial compression loading of a cylindrical specimen. During the first step the flow behaviour of the alloy is investigated at the constant strain rate wihin the range of 0.1-50 s{sup -1} at the temperature range of 350-430 deg. C. During the second step the strain rate is abruptly increased or decreased from its current value at a fixed engineering strain of 17-21%. From the beginning of the test up to the strain of 17-21% the value of the strain rate is constant and equal to either 1 s{sup -1} or 10 s{sup -1}. At the strain of 17-21% the value of a strain rate is either increased to 10 s{sup -1} or decreased to 1 s{sup -1}.The results of the experimental investigations were used to determine the isothermal flow stress-strain curves of the Al-Mg-Si alloy as well as the heat effect of plastic deformation of the alloy. On basis of these curves, the strain rate sensitivity index m as a function of true strain and temperature was determined. This parameter allows to optimize a technological process of hot forging of the aluminium alloy as well as it is very important data for the construction of a phenomenological flow stress model.

  4. Effects of surface cracks and strain rate on the tensile behavior of Balmoral Red granite

    NASA Astrophysics Data System (ADS)

    Mardoukhi, Ahmad; Hokka, Mikko; Kuokkala, Veli-Tapani

    2015-09-01

    This paper presents an experimental procedure for studying the effects of surface cracks on the mechanical behavior of Balmoral Red granite under dynamic and quasi-static loading. Three different thermal shocks were applied on the surface of the Brazilian Disc test samples by keeping a flame torch at a fixed distance from the sample surface for 10, 30, and 60 seconds. Microscopy clearly shows that the number of the surface cracks increases with the duration of the thermal shock. After the thermal shock, the Brazilian Disc tests were performed using a servohydraulic materials testing machine and a compression Split Hopkinson Pressure Bar (SHPB) device. The results show that the tensile strength of the rock decreases and the rate sensitivity of the rock increases as more cracks are introduced to the structure. The DIC analysis of the Brazilian disc tests shows that the fracture of the sample initiates at the center of the samples or slightly closer to the incident bar contact point. This is followed by crushing of the samples at both contact points with the stress bars.

  5. The effect of heat developed during high strain rate deformation on the constitutive modeling of amorphous polymers

    NASA Astrophysics Data System (ADS)

    Safari, Keivan H.; Zamani, Jamal; Guedes, Rui M.; Ferreira, Fernando J.

    2016-02-01

    An adiabatic constitutive model is proposed for large strain deformation of polycarbonate (PC) at high strain rates. When the strain rate is sufficiently high such that the heat generated does not have time to transfer to the surroundings, temperature of material rises. The high strain rate deformation behavior of polymers is significantly affected by temperature-dependent constants and thermal softening. Based on the isothermal model which first was introduced by Mulliken and Boyce et al. (Int. J. Solids Struct. 43:1331-1356, 2006), an adiabatic model is proposed to predict the yield and post-yield behavior of glassy polymers at high strain rates. When calculating the heat generated and the temperature changes during the step by step simulation of the deformation, temperature-dependent elastic constants are incorporated to the constitutive equations. Moreover, better prediction of softening phenomena is achieved by the new definition for softening parameters of the proposed model. The constitutive model has been implemented numerically into a commercial finite element code through a user material subroutine (VUMAT). The experimental results, obtained using a split Hopkinson pressure bar, are supported by dynamic mechanical thermal analysis (DMTA) and Decompose/Shift/Reconstruct (DSR) method. Comparison of adiabatic model predictions with experimental data demonstrates the ability of the model to capture the characteristic features of stress-strain curve of the material at very high strain rates.

  6. Compressive strain rate sensitivity of ballistic gelatin.

    PubMed

    Kwon, Jiwoon; Subhash, Ghatu

    2010-02-10

    Gelatin is a popular tissue simulant used in biomedical applications. The uniaxial compressive stress-strain response of gelatin was determined at a range of strain rates. In the quasistatic regime, gelatin strength remained relatively constant. With increase in loading rate, the compressive strength increased from 3kPa at a strain rate of around 0.0013/s to 6MPa at a strain rate of around 3200/s. This dramatic increase in strength of gelatin at high rates is attributed to its shear-thickening behavior and is argued on the basis of hydrocluster formation mechanism and differences in internal energy dissipation mechanism under static and dynamic loading. PMID:19863960

  7. Implementation of an Associative Flow Rule Including Hydrostatic Stress Effects Into the High Strain Rate Deformation Analysis of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

    2003-01-01

    A previously developed analytical formulation has been modified in order to more accurately account for the effects of hydrostatic stresses on the nonlinear, strain rate dependent deformation of polymer matrix composites. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical J2 plasticity theory definitions of effective stress and effective inelastic strain, along with the equations used to compute the components of the inelastic strain rate tensor, are appropriately modified. To verify the revised formulation, the shear and tensile deformation of two representative polymers are computed across a wide range of strain rates. Results computed using the developed constitutive equations correlate well with experimental data. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite for several fiber orientation angles across a variety of strain rates. The computed values compare well to experimentally obtained results.

  8. Modeling the Nonlinear, Strain Rate Dependent Deformation of Shuttle Leading Edge Materials with Hydrostatic Stress Effects Included

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Carney, Kelly S.

    2004-01-01

    An analysis method based on a deformation (as opposed to damage) approach has been developed to model the strain rate dependent, nonlinear deformation of woven ceramic matrix composites, such as the Reinforced Carbon Carbon (RCC) material used on the leading edges of the Space Shuttle. In the developed model, the differences in the tension and compression deformation behaviors have also been accounted for. State variable viscoplastic equations originally developed for metals have been modified to analyze the ceramic matrix composites. To account for the tension/compression asymmetry in the material, the effective stress and effective inelastic strain definitions have been modified. The equations have also been modified to account for the fact that in an orthotropic composite the in-plane shear response is independent of the stiffness in the normal directions. The developed equations have been implemented into LS-DYNA through the use of user defined subroutines (UMATs). Several sample qualitative calculations have been conducted, which demonstrate the ability of the model to qualitatively capture the features of the deformation response present in woven ceramic matrix composites.

  9. Modeling the Nonlinear, Strain Rate Dependent Deformation of Woven Ceramic Matrix Composites With Hydrostatic Stress Effects Included

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Carney, Kelly S.

    2004-01-01

    An analysis method based on a deformation (as opposed to damage) approach has been developed to model the strain rate dependent, nonlinear deformation of woven ceramic matrix composites with a plain weave fiber architecture. In the developed model, the differences in the tension and compression response have also been considered. State variable based viscoplastic equations originally developed for metals have been modified to analyze the ceramic matrix composites. To account for the tension/compression asymmetry in the material, the effective stress and effective inelastic strain definitions have been modified. The equations have also been modified to account for the fact that in an orthotropic composite the in-plane shear stiffness is independent of the stiffness in the normal directions. The developed equations have been implemented into a commercially available transient dynamic finite element code, LS-DYNA, through the use of user defined subroutines (UMATs). The tensile, compressive, and shear deformation of a representative plain weave woven ceramic matrix composite are computed and compared to experimental results. The computed values correlate well to the experimental data, demonstrating the ability of the model to accurately compute the deformation response of woven ceramic matrix composites.

  10. Strain Rate Effects on the Energy Absorption of Rapidly Manufactured Composite Tubes

    SciTech Connect

    Brighton, Aaron M; Forrest, Mark; Starbuck, J Michael; ERDMAN III, DONALD L; Fox, Bronwyn

    2009-01-01

    Quasi-static and intermediate rate axial crush tests were conducted on tubular specimens of Carbon/Epoxy (Toray T700/G83C) and Glass/Polypropylene (Twintex). The quasi-static tests were conducted at 10 mm/min (1.67x10-4 m/s); five different crush initiators were used. Tests at intermediate rates were performed at speeds of 0.25 m/s, 0.5 m/s, 0.75 m/s 1m/s, 2 m/s and 4 m/s. Quasi-static tests of tubular specimens showed high specific energy absorption (SEA) values with 86 kJ/kg for Carbon/Epoxy specimens. The specific energy absorption of the Glass/Polypropylene specimens was measured to be 29 kJ/kg. Results from the intermediate test rates showed that while a decrease in specific energy absorbed was observed as speeds increased, values did not fall below 55kj/kg for carbon specimens or 35 kJ/kg for the Glass/Polypropylene specimens. When compared with steel and aluminium, specific energy absorption values of 15 kJ/kg and 30 kJ/kg respectively, the benefits of using composite materials in crash structures are apparent.

  11. Microstructural and strain rate effects on the environment-assisted cracking of alpha/beta-titanium alloys in aqueous chloride

    NASA Astrophysics Data System (ADS)

    Richey, Edward, III

    2000-10-01

    The objectives of this research are to determine the effect of microstructure and crack tip strain rate on environment assisted cracking (EAC) of Ti-6Al-2Sn-2Zr-2Mo-2Cr-Si, and to understand crack tip damage in terms of hydrogen/microstructure/plasticity interaction. Beta-extrusion of Ti-6-22-22, in the alpha/beta solution treated and aged (STA) condition, is susceptible to EAC under active loading in NaCl. KJTH is as low as 33% of KJIC and a fracture mode transition to transgranular (alpha-cleavage is affected by chloride exposure. Ti-6-4 (ELI) in chloride solution exhibits a minimum KJTH of 65 MPa√m, corresponding to a mill-annealed microstructure with alpha2 (K JIC = 79 MPa√m), and higher EAC resistance for a Widmanstatten microstructure. EAC growth rates in Ti-6-4 (ELI) average 3mum/s and are 10-fold slower than those for Ti-6-22-22. Ti-6-22-22 was susceptible to EAC for active loading rates ranging between 10--4 MPa√m/s and 5 Mpa√m/s. alpha2, formed during slow cooling or isothermal aging, dominates the EAC susceptibility of Ti-6-22-22. alpha/beta microstructures without intermetallics or alphas exhibit the highest EAC resistance (KJTH = 50 MPa√m, KJIC = 74 MPa√m). alpha 2 promotes a large reduction in the EAC threshold; KJTH = 34 MPa√m when alpha2 and alphas are present (KJIC = 69 MPa√m). For all microstructures, the fracture path is transgranular through alpha plates. Based on hydrogen environment embrittlement, the increased EAC in STA Ti-6-22-22 vs STA Ti-6-4 is due to increased strain localization occurring in the Ti-6-22-22 which results in larger slip offsets at the surface and increased hydrogen uptake. alphas precipitates in Ti-6--22--22 may exacerbate strain localization; alphas precipitates were not observed in Ti-6-4. A change in the operative dislocation mechanism to dislocation looping would have homogenized deformation and reduced EAC susceptibility; rather, severe EAC was observed in all aged Ti-6-22-22 microstructures

  12. Impact Damage and Strain Rate Effects for Toughened Epoxy Composite Structures

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Minnetyan, Levon

    2006-01-01

    Structural integrity of composite systems under dynamic impact loading is investigated herein. The GENOA virtual testing software environment is used to implement the effects of dynamic loading on fracture progression and damage tolerance. Combinations of graphite and glass fibers with a toughened epoxy matrix are investigated. The effect of a ceramic coating for the absorption of impact energy is also included. Impact and post impact simulations include verification and prediction of (1) Load and Impact Energy, (2) Impact Damage Size, (3) Maximum Impact Peak Load, (4) Residual Strength, (5) Maximum Displacement, (6) Contribution of Failure Modes to Failure Mechanisms, (7) Prediction of Impact Load Versus Time, and (8) Damage, and Fracture Pattern. A computer model is utilized for the assessment of structural response, progressive fracture, and defect/damage tolerance characteristics. Results show the damage progression sequence and the changes in the structural response characteristics due to dynamic impact. The fundamental premise of computational simulation is that the complete evaluation of composite fracture requires an assessment of ply and subply level damage/fracture processes as the structure is subjected to loads. Simulation results for the graphite/epoxy composite were compared with the impact and tension failure test data, correlation and verification was obtained that included: (1) impact energy, (2) damage size, (3) maximum impact peak load, (4) residual strength, (5) maximum displacement, and (6) failure mechanisms of the composite structure.

  13. The effect of moisture content on the dynamic fragmentation of wet sand at high strain rates

    NASA Astrophysics Data System (ADS)

    Xue, Kun

    2014-03-01

    A comprehensive model is established to account for the instability onset of rapidly expanding granular shells subject to the explosion loadings generated by the detonation of the central explosives. The moisture content strongly influences the shock interactions in the wet particle beds and the ensuing evolvement of the granular compacts. A material model for granular materials which can account for the degree of saturation was incorporated into a non-linear dynamic simulation program to investigate the moisture of effect on the shock responses of wet granular materials. In conjunction with our instability model, the predicted instability diameters of the expanding dry/wet granular shells are in a good agreement with the experimental results. Particularly the postponed instability onset of the wet granular shell found both experimentally and analytically can largely be attributed to the significantly greater kinetic energy obtained by wet particles thanks to less energy of shock wave consumed in compacting the granular materials.

  14. A comparison of eastern North American seismic strain-rates to glacial rebound strain-rates

    NASA Technical Reports Server (NTRS)

    James, Thomas S.; Bent, Allison L.

    1994-01-01

    Glacial rebound strain-rates computed using a simple Laurentide glacial loading model are of the order of 10(exp -9) per year within the region of glaciation and extending several hundred kilometers beyond. The horizontal strain-rates receive approximately equal contributions from horizontal and vertical velocities, a consequence of the spherical geometry adopted for the Earth model. In the eastern United States and southeastern Canada the computed strain-rates are 1-3 orders of magnitude greater than an estimate of the average seismic strain-rate (Anderson, 1986) and approximately 1 order of magnitude greater than predicted erosional strain-rates. The predicted glacial rebound strain-rates are not, in general, oriented in such a way as to augment the observed state of deviatoric stress, possibly explaining why the seismic strain-rates are much smaller than the glacial rebound strain-rates. An exception to this may be seismically active regions in the St. Lawrence valley.

  15. Environmental and strain rate effects on graphite/epoxy composites. Final Report; M.S. Thesis, 1987

    NASA Technical Reports Server (NTRS)

    Peimandis, Konstantinos

    1991-01-01

    The hygrothermal characterization of unidirectional graphite/epoxy composites over a range of strain rates was investigated. Special techniques developed for such hygrothermal characterization are also described. The mechanical properties of the composite material were obtained and analyzed by means of a time-temperature-moisture superposition principle. The results show the following: (1) the embedded gage technique was thoroughly examined and found to be appropriate for both hygrothermal expansion and mechanical strain measurements; (2) all transverse properties were found to decrease with increasing temperature and moisture content; and (3) ultimate transverse properties were found to increase with strain rate at low temperatures but follow an opposite trend at high temperatures compared to dry specimens.

  16. High strain rate damage of Carrara marble

    NASA Astrophysics Data System (ADS)

    Doan, Mai-Linh; Billi, Andrea

    2011-10-01

    Several cases of rock pulverization have been observed along major active faults in granite and other crystalline rocks. They have been interpreted as due to coseismic pervasive microfracturing. In contrast, little is known about pulverization in carbonates. With the aim of understanding carbonate pulverization, we investigate the high strain rate (c. 100 s-1) behavior of unconfined Carrara marble through a set of experiments with a Split Hopkinson Pressure Bar. Three final states were observed: (1) at low strain, the sample is kept intact, without apparent macrofractures; (2) failure is localized along a few fractures once stress is larger than 100 MPa, corresponding to a strain of 0.65%; (3) above 1.3% strain, the sample is pulverized. Contrary to granite, the transition to pulverization is controlled by strain rather than strain rate. Yet, at low strain rate, a sample from the same marble displayed only a few fractures. This suggests that the experiments were done above the strain rate transition to pulverization. Marble seems easier to pulverize than granite. This creates a paradox: finely pulverized rocks should be prevalent along any high strain zone near faults through carbonates, but this is not what is observed. A few alternatives are proposed to solve this paradox.

  17. The effects of temperature and strain rate on the yielding behavior of the single crystal superalloy PWA 1480

    NASA Technical Reports Server (NTRS)

    Milligan, Walter W.; Antolovich, Stephen D.

    1988-01-01

    Interrupted tensile tests were conducted on (001) oriented single crystals at temperatures from 20 to 1093 C. Two strain rates were used, 0.5 and 50 percent/min. After the tests, the deformation substructures were characterized by transmission electron microscopy. Results of these tests are given.

  18. Effect of test temperature and strain rate on the tensile properties of high-strength, high-conductivity copper alloys

    SciTech Connect

    Zinkle, S.J.; Eatherly, W.S.

    1997-04-01

    The unirradiated tensile properties of wrought GlidCop AL25 (ITER grade zero, IGO) solutionized and aged CuCrZr, and cold-worked and aged and solutionized and aged Hycon 3HP{trademark} CuNiBe have been measured over the temperature range of 20-500{degrees}C at strain rates between 4 x 10{sup {minus}4} s{sup {minus}1} and 0.06 s{sup {minus}1}. The measured room temperature electrical conductivity ranged from 64 to 90% IACS for the different alloys. All of the alloys were relatively insensitive to strain rate at room temperature, but the strain rate sensitivity of GlidCop Al25 increased significantly with increasing temperature. The CuNiBe alloys exhibited the best combination of high strength and high conductivity at room temperature. The strength of CuNiBe decreased slowly with increasing temperature. However, the ductility of CuNiBe decreased rapidly with increasing temperature due to localized deformation near grain boundaries, making these alloy heats unsuitable for typical structural applications above 300{degrees}C. The strength and uniform elongation of GlidCop Al25 decreased significantly with increasing temperature at a strain rate of 1 x 10{sup {minus}3} s{sup {minus}1}, whereas the total elongation was independent of test temperature. The strength and ductility of CuCrZr decreased slowly with increasing temperature.

  19. Effect of glucose concentration on the rate of fructose consumption in native strains isolated from the fermentation of Agave duranguensis.

    PubMed

    Díaz-Campillo, M; Urtíz, N; Soto, O; Barrio, E; Rutiaga, M; Páez, J

    2012-12-01

    Studies on hexose consumption by Saccharomyces cerevisiae show that glucose is consumed faster than fructose when both are present (9:1 fructose to glucose) in the medium during the fermentation of Agave. The objective of this work was to select strains of S. cerevisiae that consume fructose equal to or faster than glucose at high fructose concentrations by analyzing the influence of different glucose concentrations on the fructose consumption rate. The optimal growth conditions were determined by a kinetics assay using high performance liquid chromatography (HPLC) using 50 g of glucose and 50 g of fructose per liter of synthetic medium containing peptone and yeast extract. Using the same substrate concentrations, strain ITD-00185 was shown to have a higher reaction rate for fructose over glucose. At 75 g of fructose and 25 g of glucose per liter, strain ITD-00185 had a productivity of 1.02 gL(-1) h(-1) after 40 h and a fructose rate constant of 0.071 h(-1). It was observed that glucose concentration positively influences fructose consumption when present in a 3:1 ratio of fructose to glucose. Therefore, adapted strains at high fructose concentrations could be used as an alternative to traditional fermentation processes. PMID:22886556

  20. The effects of strain rate and temperature on commercial acrylic artist paints aged one year to decades

    NASA Astrophysics Data System (ADS)

    Hagan, Eric W. S.; Charalambides, Maria N.; Young, Christina R. T.; Learner, Thomas J. S.

    2015-11-01

    Acrylic artist paints are viscoelastic composites containing a high molecular weight copolymer, pigment and a variety of additives. The glass transition temperature of the latex binder is typically slightly below ambient conditions, giving mechanical properties that are strongly dependent on strain rate and temperature. In previous work, the viscoelastic behaviour of custom-formulated latex artist paints was reported for films with known volume fractions of pigment using data from uniaxial tensile tests at different strain rates and temperatures. Secant Young's modulus and failure strain master curves were constructed for each film through time-temperature superposition, allowing predictions beyond the experimental timescale at a selected reference temperature. A similar analysis is now presented for a small set of commercial artist paints tested at ages of 1 and 27 years. Experimental shift factor values are reported with fits to the Arrhenius, WLF and Vogel Fulcher equations, along with a comparison with published data for acrylic polymers. The tensile results highlight a spectrum of properties that acrylic paints may exhibit—brittle glass to hyperelastic—depending on the conditions during deformation. Strong similarities are shown between products from different manufacturers, and the findings suggest a high degree of stability with age. A method for predicting failure as a function of strain rate and temperature is also presented, and the methodology gives a framework for investigating other artist materials and the factors influencing their mechanical properties.

  1. Effect of glucose concentration on the rate of fructose consumption in native strains isolated from the fermentation of Agave duranguensis.

    PubMed

    Díaz-Campillo, M; Urtíz, N; Soto, O; Barrio, E; Rutiaga, M; Páez, J

    2012-12-01

    Studies on hexose consumption by Saccharomyces cerevisiae show that glucose is consumed faster than fructose when both are present (9:1 fructose to glucose) in the medium during the fermentation of Agave. The objective of this work was to select strains of S. cerevisiae that consume fructose equal to or faster than glucose at high fructose concentrations by analyzing the influence of different glucose concentrations on the fructose consumption rate. The optimal growth conditions were determined by a kinetics assay using high performance liquid chromatography (HPLC) using 50 g of glucose and 50 g of fructose per liter of synthetic medium containing peptone and yeast extract. Using the same substrate concentrations, strain ITD-00185 was shown to have a higher reaction rate for fructose over glucose. At 75 g of fructose and 25 g of glucose per liter, strain ITD-00185 had a productivity of 1.02 gL(-1) h(-1) after 40 h and a fructose rate constant of 0.071 h(-1). It was observed that glucose concentration positively influences fructose consumption when present in a 3:1 ratio of fructose to glucose. Therefore, adapted strains at high fructose concentrations could be used as an alternative to traditional fermentation processes.

  2. Effect of cooling rate after hot rolling and of multistage strain aging on the drawability of low-carbon-steel wire rod

    NASA Astrophysics Data System (ADS)

    Taheri, A. Karimi; Maccagno, T. M.; Jonas, J. J.

    1995-05-01

    Tensile testing was used to simulate the multistage strain aging occurring in low-C steel during the relatively short intervals between dies in a multiple-die wire-drawing machine. The effects were examined of three simulated post-hot-rolling cooling rates and three thermal treatments on the strain-aging susceptibility of a high- and a low-N steel. This was measured by applying a 6 pct tensile strain, followed by aging at either 65° or 100 °C for 20 seconds, and then pulling the specimen to failure at room temperature. Increases in flow stress and decreases in the elongation to fracture both indicated high susceptibility to strain aging. It was found that the nitrogen content, the cooling rate from the hot-rolling temperature to about 300 °C, as well as the cooling rate below 300 °C, all have dramatic effects on the strain-aging behavior. Moreover, multistage strain aging is more severe than single-stage strain aging. The implications of these observations on increasing the drawability of low-carbon-steel wire are discussed.

  3. Matrix dominated stress/strain behavior in polymeric composites: Effects of hold time, nonlinearity and rate dependency

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.

    1992-01-01

    In order to understand matrix dominated behavior in laminated polymer matrix composites, an elastic/viscoplastic constitutive model was developed and used to predict stress strain behavior of off-axis and angle-ply symmetric laminates under in-plane, tensile axial loading. The model was validated for short duration tests at elevated temperatures. Short term stress relaxation and short term creep, strain rate sensitivity, and material nonlinearity were accounted for. The testing times were extended for longer durations, and periods of creep and stress relaxation were used to investigate the ability of the model to account for long term behavior. The model generally underestimated the total change in strain and stress for both long term creep and long term relaxation respectively.

  4. Recent advances in echocardiography: strain and strain rate imaging

    PubMed Central

    Mirea, Oana; Duchenne, Jurgen; Voigt, Jens-Uwe

    2016-01-01

    Deformation imaging by echocardiography is a well-established research tool which has been gaining interest from clinical cardiologists since the introduction of speckle tracking. Post-processing of echo images to analyze deformation has become readily available at the fingertips of the user. New parameters such as global longitudinal strain have been shown to provide added diagnostic value, and ongoing efforts of the imaging societies and industry aimed at harmonizing methods will improve the technique further. This review focuses on recent advances in the field of echocardiographic strain and strain rate imaging, and provides an overview on its current and potential future clinical applications. PMID:27158476

  5. Experimental Techniques for Evaluating the Effects of Aging on Impact and High Strain Rate Properties of Triaxial Braided Composite Materials

    NASA Technical Reports Server (NTRS)

    Pereira, J. Michael; Roberts, Gary D.; Ruggeri, Charles R.; Gilat, Amos; Matrka, Thomas

    2010-01-01

    An experimental program is underway to measure the impact and high strain rate properties of triaxial braided composite materials and to quantify any degradation in properties as a result of thermal and hygroscopic aging typically encountered during service. Impact tests are being conducted on flat panels using a projectile designed to induce high rate deformation similar to that experienced in a jet engine fan case during a fan blade-out event. The tests are being conducted on as-fabricated panels and panels subjected to various numbers of aging cycles. High strain rate properties are being measured using a unique Hopkinson bar apparatus that has a larger diameter than conventional Hopkinson bars. This larger diameter is needed to measure representative material properties because of the large unit cell size of the materials examined in this work. In this paper the experimental techniques used for impact and high strain rate testing are described and some preliminary results are presented for both as-fabricated and aged composites.

  6. Coupled effect of size, strain rate, and temperature on the shape memory of a pentagonal Cu nanowire

    NASA Astrophysics Data System (ADS)

    Sutrakar, Vijay Kumar; Mahapatra, D. Roy

    2009-01-01

    A body-centered pentagonal nanobridge structure with lattice constants c = 2.35 and a = 2.53 Å has been observed under high strain rate tensile loading on an initially constrained \\langle 100\\rangle \\mbox {/} \\{100\\} Cu nanowire at various temperatures. Extensive molecular dynamics (MD) simulations have been performed using the embedded atom method (EAM) for cross-sectional dimensions ranging from 0.723 × 0.723 to 2.169 × 2.169 nm2, temperature ranging from 10 to 600 K, and strain rates of 109-107 s-1. Formations of such pentagonal nanowire are observed for a temperature range 200-600 K for particular cross-sectional dimensions and strain rates. A large inelastic deformation of ~50% is obtained under both isothermal loading and adiabatic loading. With very high degree of repeatability of such pentagonal nanowire formation, the present findings indicate that the interesting stability property and high strength of elongated nanowires have various potential applications in nanomechanical and nanoelectronic devices. Further, we demonstrate a novel thermomechanical unloading mechanism by which it is possible to impart recovery from a pentagonal nanowire following a hysteresis loop: \\langle 100\\rangle \\mbox {/}\\{100\\}\\to \\mathrm {pentagonal}\\to \\langle 110\\rangle \\mbox {/}\\{111\\}\\to \\langle 100\\rangle \\mbox {/} \\{100\\} .

  7. Strain rate sensitivity of the flow stress in a Ti-Al alloy: Analysis of the anomalous strengthening effect

    SciTech Connect

    Morris, M.A.; Lipe, T. . Inst. of Structural Metallurgy)

    1994-09-15

    An analysis has been made of the mechanisms controlling the strain rate dependence of the flow stress as a function of temperature in a Ti-Al alloy, based on the dislocation configurations observed together with the activation volumes measured at each temperature. At low temperatures (20--200 C), the low values of activation volume measured and their independence on strain have confirmed that a Peierls lattice friction mechanism controls the mobility of screw segments of either ordinary or superdislocations. At the higher temperatures (500--700 C) a climbing process of ordinary 1/2<110> dislocation segments with variable length is responsible for the slightly strain dependent activation volumes measured. The strongly strain dependent activation volumes obtained between 400--450 C has confirmed that the mechanism responsible for the anomalous peak in flow stress is produced by a jog dragging process as an increased density of jogs is created with increasing temperature, due to the increasing number of forest cutting events between ordinary 1/2<110> dislocations.

  8. A multi-scale model of dislocation plasticity in α-Fe: Incorporating temperature, strain rate and non-Schmid effects

    SciTech Connect

    Lim, H.; Hale, L. M.; Zimmerman, J. A.; Battaile, C. C.; Weinberger, C. R.

    2015-01-05

    In this study, we develop an atomistically informed crystal plasticity finite element (CP-FE) model for body-centered-cubic (BCC) α-Fe that incorporates non-Schmid stress dependent slip with temperature and strain rate effects. Based on recent insights obtained from atomistic simulations, we propose a new constitutive model that combines a generalized non-Schmid yield law with aspects from a line tension (LT) model for describing activation enthalpy required for the motion of dislocation kinks. Atomistic calculations are conducted to quantify the non-Schmid effects while both experimental data and atomistic simulations are used to assess the temperature and strain rate effects. The parameterized constitutive equation is implemented into a BCC CP-FE model to simulate plastic deformation of single and polycrystalline Fe which is compared with experimental data from the literature. This direct comparison demonstrates that the atomistically informed model accurately captures the effects of crystal orientation, temperature and strain rate on the flow behavior of siangle crystal Fe. Furthermore, our proposed CP-FE model exhibits temperature and strain rate dependent flow and yield surfaces in polycrystalline Fe that deviate from conventional CP-FE models based on Schmid's law.

  9. A multi-scale model of dislocation plasticity in α-Fe: Incorporating temperature, strain rate and non-Schmid effects

    DOE PAGESBeta

    Lim, H.; Hale, L. M.; Zimmerman, J. A.; Battaile, C. C.; Weinberger, C. R.

    2015-01-05

    In this study, we develop an atomistically informed crystal plasticity finite element (CP-FE) model for body-centered-cubic (BCC) α-Fe that incorporates non-Schmid stress dependent slip with temperature and strain rate effects. Based on recent insights obtained from atomistic simulations, we propose a new constitutive model that combines a generalized non-Schmid yield law with aspects from a line tension (LT) model for describing activation enthalpy required for the motion of dislocation kinks. Atomistic calculations are conducted to quantify the non-Schmid effects while both experimental data and atomistic simulations are used to assess the temperature and strain rate effects. The parameterized constitutive equationmore » is implemented into a BCC CP-FE model to simulate plastic deformation of single and polycrystalline Fe which is compared with experimental data from the literature. This direct comparison demonstrates that the atomistically informed model accurately captures the effects of crystal orientation, temperature and strain rate on the flow behavior of siangle crystal Fe. Furthermore, our proposed CP-FE model exhibits temperature and strain rate dependent flow and yield surfaces in polycrystalline Fe that deviate from conventional CP-FE models based on Schmid's law.« less

  10. Study of High Strain Rate Response of Composites

    NASA Technical Reports Server (NTRS)

    Gilat, Amos

    2003-01-01

    The objective of the research was to continue the experimental study of the effect of strain rate on mechanical response (deformation and failure) of epoxy resins and carbon fibers/epoxy matrix composites, and to initiate a study of the effects of temperature by developing an elevated temperature test. The experimental data provide the information needed for NASA scientists for the development of a nonlinear, rate dependent deformation and strength models for composites that can subsequently be used in design. This year effort was directed into testing the epoxy resin. Three types of epoxy resins were tested in tension and shear at various strain rates that ranges from 5 x 10(exp -5), to 1000 per second. Pilot shear experiments were done at high strain rate and an elevated temperature of 80 C. The results show that all, the strain rate, the mode of loading, and temperature significantly affect the response of epoxy.

  11. The effect of time step, thermostat, and strain rate on ReaxFF simulations of mechanical failure in diamond, graphene, and carbon nanotube.

    PubMed

    Jensen, Benjamin D; Wise, Kristopher E; Odegard, Gregory M

    2015-08-01

    As the sophistication of reactive force fields for molecular modeling continues to increase, their use and applicability has also expanded, sometimes beyond the scope of their original development. Reax Force Field (ReaxFF), for example, was originally developed to model chemical reactions, but is a promising candidate for modeling fracture because of its ability to treat covalent bond cleavage. Performing reliable simulations of a complex process like fracture, however, requires an understanding of the effects that various modeling parameters have on the behavior of the system. This work assesses the effects of time step size, thermostat algorithm and coupling coefficient, and strain rate on the fracture behavior of three carbon-based materials: graphene, diamond, and a carbon nanotube. It is determined that the simulated stress-strain behavior is relatively independent of the thermostat algorithm, so long as coupling coefficients are kept above a certain threshold. Likewise, the stress-strain response of the materials was also independent of the strain rate, if it is kept below a maximum strain rate. Finally, the mechanical properties of the materials predicted by the Chenoweth C/H/O parameterization for ReaxFF are compared with literature values. Some deficiencies in the Chenoweth C/H/O parameterization for predicting mechanical properties of carbon materials are observed.

  12. High-Strain-Rate Compression Testing of Ice

    NASA Technical Reports Server (NTRS)

    Shazly, Mostafa; Prakash, Vikas; Lerch, Bradley A.

    2006-01-01

    In the present study a modified split Hopkinson pressure bar (SHPB) was employed to study the effect of strain rate on the dynamic material response of ice. Disk-shaped ice specimens with flat, parallel end faces were either provided by Dartmouth College (Hanover, NH) or grown at Case Western Reserve University (Cleveland, OH). The SHPB was adapted to perform tests at high strain rates in the range 60 to 1400/s at test temperatures of -10 and -30 C. Experimental results showed that the strength of ice increases with increasing strain rates and this occurs over a change in strain rate of five orders of magnitude. Under these strain rate conditions the ice microstructure has a slight influence on the strength, but it is much less than the influence it has under quasi-static loading conditions. End constraint and frictional effects do not influence the compression tests like they do at slower strain rates, and therefore the diameter/thickness ratio of the samples is not as critical. The strength of ice at high strain rates was found to increase with decreasing test temperatures. Ice has been identified as a potential source of debris to impact the shuttle; data presented in this report can be used to validate and/or develop material models for ice impact analyses for shuttle Return to Flight efforts.

  13. Suppression of Low Strain Rate Nonpremixed Flames by an Agent

    NASA Technical Reports Server (NTRS)

    Hamins, A.; Bundy, M.; Puri, I. K.; McGrattan, K.; Park, W. C.

    2001-01-01

    The agent concentration required to achieve the suppression of low strain rate nonpremixed flames is an important consideration for fire protection in a microgravity environment such as a space platform. Currently, there is a lack of understanding of the structure and extinction of low strain rate (<20 s(exp -1)) nonpremixed flames. The exception to this statement is the study by Maruta et al., who reported measurements of low strain rate suppression of methane-air diffusion flames with N2 added to the fuel stream under microgravity conditions. They found that the nitrogen concentration required to achieve extinction increased as the strain rate decreased until a critical value was obtained. As the strain rate was further decreased, the required N2 concentration decreased. This phenomenon was termed "turning point" behavior and was attributed to radiation-induced nonpremixed flame extinction. In terms of fire safety, a critical agent concentration assuring suppression under all flow conditions represents a fundamental limit for nonpremixed flames. Counterflow flames are a convenient configuration for control of the flame strain rate. In high and moderately strained near-extinction nonpremixed flames, analysis of flame structure typically neglects radiant energy loss because the flames are nonluminous and the hot gas species are confined to a thin reaction zone. In counterflowing CH4-air flames, for example, radiative heat loss fractions ranging from 1 to 6 percent have been predicted and measured. The objective of this study is to investigate the impact of radiative emission, flame strain, agent addition, and buoyancy on the structure and extinction of low strain rate nonpremixed flames through measurements and comparison with flame simulations. The suppression effectiveness of a number of suppressants (N2, CO2, or CF3Br) was considered as they were added to either the fuel or oxidizer streams of low strain rate methane-air diffusion flames.

  14. Strain-Energy-Release Rates In Delamination

    NASA Technical Reports Server (NTRS)

    Raju, I. S.

    1988-01-01

    Q3DG computer program developed to perform quasi-three-dimensional stress analysis of composite laminates containing delaminations. Calculates strain-energy-release rates for long, rectangular composite laminates containing delaminations and subjected to any combination of mechanical, thermal, and hygroscopic loading. Written in FORTRAN V.

  15. High strain-rate magnetoelasticity in Galfenol

    NASA Astrophysics Data System (ADS)

    Domann, J. P.; Loeffler, C. M.; Martin, B. E.; Carman, G. P.

    2015-09-01

    This paper presents the experimental measurements of a highly magnetoelastic material (Galfenol) under impact loading. A Split-Hopkinson Pressure Bar was used to generate compressive stress up to 275 MPa at strain rates of either 20/s or 33/s while measuring the stress-strain response and change in magnetic flux density due to magnetoelastic coupling. The average Young's modulus (44.85 GPa) was invariant to strain rate, with instantaneous stiffness ranging from 25 to 55 GPa. A lumped parameters model simulated the measured pickup coil voltages in response to an applied stress pulse. Fitting the model to the experimental data provided the average piezomagnetic coefficient and relative permeability as functions of field strength. The model suggests magnetoelastic coupling is primarily insensitive to strain rates as high as 33/s. Additionally, the lumped parameters model was used to investigate magnetoelastic transducers as potential pulsed power sources. Results show that Galfenol can generate large quantities of instantaneous power (80 MW/m3 ), comparable to explosively driven ferromagnetic pulse generators (500 MW/m3 ). However, this process is much more efficient and can be cyclically carried out in the linear elastic range of the material, in stark contrast with explosively driven pulsed power generators.

  16. Experimental and Numerical Investigation into the Effect of Strain Rate Changes on Failure of AA7075 at the Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Zand, H.; Zhalehfar, F.; Vafaeesefat, A.

    2016-08-01

    This paper represents the temperature-dependent study which is performed on AA7075. This was performed through the application of deep drawing experiments at high temperature of 250, 300, 350, 400, 450 and 500°C and different forming speeds. FEM study is applied at room and 300 and 400 0C temperature with different strain rates. Softening model is used to model the thermo-mechanical constitutive equation. Forming limit curve models (based on M-K model) were used in the analysis of simulation results in order to predict the onset of necking. Simulation results were compared with experimental data to evaluate the accuracy of onset of necking simulation and failure location prediction

  17. Suppression and Structure of Low Strain Rate Nonpremixed Flames

    NASA Technical Reports Server (NTRS)

    Hamins, Anthony; Bundy, Matthew; Park, Woe Chul; Lee, Ki Yong; Logue, Jennifer

    2003-01-01

    The agent concentration required to achieve suppression of low strain rate nonpremixed flames is an important fire safety consideration. In a microgravity environment such as a space platform, unwanted fires will likely occur in near quiescent conditions where strain rates are very low. Diffusion flames typically become more robust as the strain rate is decreased. When designing a fire suppression system for worst-case conditions, low strain rates should be considered. The objective of this study is to investigate the impact of radiative emission, flame strain, agent addition, and buoyancy on the structure and extinction of low strain rate nonpremixed flames through measurements and comparison with flame simulations. The suppression effectiveness of a suppressant (N2) added to the fuel stream of low strain rate methane-air diffusion flames was measured. Flame temperature measurements were attained in the high temperature region of the flame (T greater than 1200 K) by measurement of thin filament emission intensity. The time varying temperature was measured and simulated as the flame made the transition from normal to microgravity conditions and as the flame extinguished.

  18. Deformation twinning: Influence of strain rate

    SciTech Connect

    Gray, G.T. III

    1993-11-01

    Twins in most crystal structures, including advanced materials such as intermetallics, form more readily as the temperature of deformation is decreased or the rate of deformation is increased. Both parameters lead to the suppression of thermally-activated dislocation processes which can result in stresses high enough to nucleate and grow deformation twins. Under high-strain rate or shock-loading/impact conditions deformation twinning is observed to be promoted even in high stacking fault energy FCC metals and alloys, composites, and ordered intermetallics which normally do not readily deform via twinning. Under such conditions and in particular under the extreme loading rates typical of shock wave deformation the competition between slip and deformation twinning can be examined in detail. In this paper, examples of deformation twinning in the intermetallics TiAl, Ti-48Al-lV and Ni{sub 3}A as well in the cermet Al-B{sub 4}C as a function of strain rate will be presented. Discussion includes: (1) the microstructural and experimental variables influencing twin formation in these systems and twinning topics related to high-strain-rate loading, (2) the high velocity of twin formation, and (3) the influence of deformation twinning on the constitutive response of advanced materials.

  19. Material mechanical characterization method for multiple strains and strain rates

    DOEpatents

    Erdmand, III, Donald L.; Kunc, Vlastimil; Simunovic, Srdjan; Wang, Yanli

    2016-01-19

    A specimen for measuring a material under multiple strains and strain rates. The specimen including a body having first and second ends and a gage region disposed between the first and second ends, wherein the body has a central, longitudinal axis passing through the first and second ends. The gage region includes a first gage section and a second gage section, wherein the first gage section defines a first cross-sectional area that is defined by a first plane that extends through the first gage section and is perpendicular to the central, longitudinal axis. The second gage section defines a second cross-sectional area that is defined by a second plane that extends through the second gage section and is perpendicular to the central, longitudinal axis and wherein the first cross-sectional area is different in size than the second cross-sectional area.

  20. A new radial strain and strain rate estimation method using autocorrelation for carotid artery

    NASA Astrophysics Data System (ADS)

    Ye, Jihui; Kim, Hoonmin; Park, Jongho; Yeo, Sunmi; Shim, Hwan; Lim, Hyungjoon; Yoo, Yangmo

    2014-03-01

    Atherosclerosis is a leading cause of cardiovascular disease. The early diagnosis of atherosclerosis is of clinical interest since it can prevent any adverse effects of atherosclerotic vascular diseases. In this paper, a new carotid artery radial strain estimation method based on autocorrelation is presented. In the proposed method, the strain is first estimated by the autocorrelation of two complex signals from the consecutive frames. Then, the angular phase from autocorrelation is converted to strain and strain rate and they are analyzed over time. In addition, a 2D strain image over region of interest in a carotid artery can be displayed. To evaluate the feasibility of the proposed radial strain estimation method, radiofrequency (RF) data of 408 frames in the carotid artery of a volunteer were acquired by a commercial ultrasound system equipped with a research package (V10, Samsung Medison, Korea) by using a L5-13IS linear array transducer. From in vivo carotid artery data, the mean strain estimate was -0.1372 while its minimum and maximum values were -2.961 and 0.909, respectively. Moreover, the overall strain estimates are highly correlated with the reconstructed M-mode trace. Similar results were obtained from the estimation of the strain rate change over time. These results indicate that the proposed carotid artery radial strain estimation method is useful for assessing the arterial wall's stiffness noninvasively without increasing the computational complexity.

  1. Strain rate dependency of oceanic intraplate earthquake b-values at extremely low strain rates

    NASA Astrophysics Data System (ADS)

    Sasajima, Ryohei; Ito, Takeo

    2016-06-01

    We discovered a clear positive dependence of oceanic intraplate earthquake (OCEQ) b-values on the age of the oceanic lithosphere. OCEQ b-values in the youngest (<10 Ma) oceanic lithosphere are around 1.0, while those in middle to old (>20 Ma) oceanic lithosphere exceed 1.5, which is significantly higher than the average worldwide earthquake b-value (around 1.0). On the other hand, the b-value of intraplate earthquakes in the Ninety East-Sumatra orogen, where oceanic lithosphere has an anomalously higher strain rate compared with normal oceanic lithosphere, is 0.93, which is significantly lower than the OCEQ b-value (about 1.9) with the same age (50-110 Ma). Thus, the variation in b-values relates to the strain rate of the oceanic lithosphere and is not caused by a difference in thermal structure. We revealed a negative strain rate dependency of the b-value at extremely low strain rates (<2 × 10-10/year), which can clearly explain the above b-values. We propose that the OCEQ b-value depends strongly on strain rate (either directly or indirectly) at extremely low strain rates. The high OCEQ b-values (>1.5) in oceanic lithosphere >20 Ma old imply that future improvement in seismic observation will capture many smaller magnitude OCEQs, which will provide valuable information on the evolution of the oceanic lithosphere and the driving mechanism of plate tectonics.

  2. Strain rate behavior of magnetorheological materials

    NASA Astrophysics Data System (ADS)

    Seminuk, Kenneth; Joshi, Vasant; Gump, Jared; Stoltz, Chad; Forbes, Jerry

    2014-05-01

    Strain rate response of two Hydroxyl-terminated Polybutadiene/ Iron (HTPB/Fe) compositions under electromagnetic fields has been investigated using a Split Hopkinson Pressure bar arrangement equipped with aluminum bars. Two HTPB/Fe compositions were developed, the first without plasticizer and the second containing plasticizer. Samples were tested with and without the application of a 0.01 Tesla magnetic field. Strain gauge data taken from the Split Hopkinson Pressure Bar has been used to determine the extent of change in mechanical properties by inducing a mild electromagnetic field onto each sample. Raw data from strain gages was processed using commercial software (Signo) and Excel spreadsheet. It is of particular interest to determine whether the mechanical properties of binder systems can be manipulated by adding ferrous or Magnetostrictive particulates. Data collected from the Split Hopkinson Pressure bar indicate changes in the Mechanical Stress-Strain curves and suggest that the impedance of a binder system can be altered by means of a magnetic field.

  3. The influence of strain rate and hydrogen on the plane-strain ductility of Zircaloy cladding

    SciTech Connect

    Link, T.M.; Motta, A.T.; Koss, D.A.

    1998-03-01

    The authors studied the ductility of unirradiated Zircaloy-4 cladding under loading conditions prototypical of those found in reactivity-initiated accidents (RIA), i.e.: near plane-strain deformation in the hoop direction (transverse to the cladding axis) at room temperature and 300 C and high strain rates. To conduct these studies, they developed a specimen configuration in which near plane-strain deformation is achieved in the gage section, and a testing methodology that allows one to determine both the limit strain at the onset of localized necking and the fracture strain. The experiments indicate that there is little effect of strain rate (10{sup {minus}3} to 10{sup 2} s{sup {minus}1}) on the ductility of unhydrided Zircaloy tubing deformed under near plane-strain conditions at either room temperature or 300 C. Preliminary experiments on cladding containing 190 ppm hydrogen show only a small loss of fracture strain but no clear effect on limit strain. The experiments also indicate that there is a significant loss of Zircaloy ductility when surface flaws are present in the form of thickness imperfections.

  4. Characterisation of human diaphragm at high strain rate loading.

    PubMed

    Gaur, Piyush; Chawla, Anoop; Verma, Khyati; Mukherjee, Sudipto; Lalvani, Sanjeev; Malhotra, Rajesh; Mayer, Christian

    2016-07-01

    Motor vehicle crashes (MVC׳s) commonly results in life threating thoracic and abdominal injuries. Finite element models are becoming an important tool in analyzing automotive related injuries to soft tissues. Establishment of accurate material models including tissue tolerance limits is critical for accurate injury evaluation. The diaphragm is the most important skeletal muscle for respiration having a bi-domed structure, separating the thoracic cavity from abdominal cavity. Traumatic rupture of the diaphragm is a potentially serious injury which presents in different forms depending upon the mechanisms of the causative trauma. A major step to gain insight into the mechanism of traumatic rupture of diaphragm is to understand the high rate failure properties of diaphragm tissue. Thus, the main objective of this study was to estimate the mechanical and failure properties of human diaphragm at strain rates associated with blunt thoracic and abdominal trauma. A total of 23 uniaxial tensile tests were performed at various strain rates ranging from 0.001-200s(-1) in order to characterize the mechanical and failure properties on human diaphragm tissue. Each specimen was tested to failure at one of the four strain rates (0.001s(-1), 65s(-1), and 130s(-1), 190s(-1)) to investigate the effects of strain rate dependency. High speed video and markers placed on the grippers were used to measure the gripper to gripper displacement. Engineering stresses reported in the study is calculated from the ratio of force measured and initial cross sectional area whereas engineering strain is calculated from the ratio of the elongation to the undeformed length (gauge length) of the specimen.The results of this study showed that the diaphragm tissues is rate dependent with higher strain rate tests giving higher failure stress and higher failure strains. The failure stress for all tests ranged from 1.17MPa to 4.1MPa and failure strain ranged from 12.15% to 24.62%. PMID:27062242

  5. Strain energy release rate distributions for double cantilever beam specimens

    NASA Technical Reports Server (NTRS)

    Crews, J. H., Jr.; Shivakumar, K. N.; Raju, I. S.

    1991-01-01

    A 24-ply composite double cantilever-beam specimen under mode I (opening) loading has been analyzed by a 3D FEM code that calculated along a straight delamination starter for several different specimen materials. An isotropic specimen was found to have a strain-energy release rate distribution which varied along its delamination front due to the boundary-layer effect and another effect associated with the anticlastic curvature of the bent specimen arms. A 0-deg graphite-reinforced epoxy specimen had a nearly-uniform strain-energy release rate distribution which dropped only near the edge, due to the boundary-layer effect, and a +/- 45-deg graphite/epoxy specimen exhibited a pronounced strain-energy release rate variation across the specimen width.

  6. Associative Flow Rule Used to Include Hydrostatic Stress Effects in Analysis of Strain-Rate-Dependent Deformation of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Roberts, Gary D.

    2004-01-01

    designing reliable composite engine cases that are lighter than the metal cases in current use. The types of polymer matrix composites that are likely to be used in such an application have a deformation response that is nonlinear and that varies with strain rate. The nonlinearity and the strain-rate dependence of the composite response are due primarily to the matrix constituent. Therefore, in developing material models to be used in the design of impact-resistant composite engine cases, the deformation of the polymer matrix must be correctly analyzed. However, unlike in metals, the nonlinear response of polymers depends on the hydrostatic stresses, which must be accounted for within an analytical model. By applying micromechanics techniques along with given fiber properties, one can also determine the effects of the hydrostatic stresses in the polymer on the overall composite deformation response. First efforts to account for the hydrostatic stress effects in the composite deformation applied purely empirical methods that relied on composite-level data. In later efforts, to allow polymer properties to be characterized solely on the basis of polymer data, researchers at the NASA Glenn Research Center developed equations to model the polymers that were based on a non-associative flow rule, and efforts to use these equations to simulate the deformation of representative polymer materials were reasonably successful. However, these equations were found to have difficulty in correctly analyzing the multiaxial stress states found in the polymer matrix constituent of a composite material. To correct these difficulties, and to allow for the accurate simulation of the nonlinear strain-rate-dependent deformation analysis of polymer matrix composites, in the efforts reported here Glenn researchers reformulated the polymer constitutive equations from basic principles using the concept of an associative flow rule. These revised equations were characterized and validated in an

  7. Strain rate dependency of laser sintered polyamide 12

    NASA Astrophysics Data System (ADS)

    Cook, J. E. T.; Goodridge, R. D.; Siviour, C. R.

    2015-09-01

    Parts processed by Additive Manufacturing can now be found across a wide range of applications, such as those in the aerospace and automotive industry in which the mechanical response must be optimised. Many of these applications are subjected to high rate or impact loading, yet it is believed that there is no prior research on the strain rate dependence in these materials. This research investigates the effect of strain rate and laser energy density on laser sintered polyamide 12. In the study presented here, parts produced using four different laser sintered energy densities were exposed to uniaxial compression tests at strain rates ranging from 10-3 to 10+3 s-1 at room temperature, and the dependence on these parameters is presented.

  8. Effect of strain rates from 10/sup -2/ to 10 sec/sup -1/ in triaxial compression tests on three rocks

    SciTech Connect

    Blanton, T.L.

    1981-02-01

    Room-temperature, compression tests at strain rates from 10/sup -2/ to 10 sec/sup -1/ have been run on Charcoal Granodiorite to 0.45 GPa confining pressure and on Berea Sandstone and Indiana Limestone to 0.25 GPa confining pressure. For each rock at each confining pressure, the differential stress at failure is relatively constant up to a strain rate of 1 sec/sup -1/ and apparently increases abruptly above this strain rate. Dynamic analysis of the testing apparatus indicates that the apparent sudden increase in strength is due to machine inertia and does not reflect a real increase in the strength of the rocks. Taking inertia into account, the actual failure stresses of the three rocks are relatively independent of strain rate betweeen 10/sup -2/ and 10 sec/sup -1/. In the same interval, the strains at which the unconfined rocks begin to fragment tend to be lower at higher strain rates. The combination of decreasing strains and relatively constant stresses with increasing strain rate suggests that the energy necessary to fragment the unconfined rocks is lower at higher strain rates.

  9. Strain-rate effects on the texture evolution of low-symmetry metals: Modeling and validation using the Taylor cylinder impact test

    NASA Astrophysics Data System (ADS)

    Plunkett, B.; Cazacu, O.; Lebensohn, R. A.

    2006-08-01

    In this paper, a model for describing the influence of evolving texture on the response of pre-textured metals for dynamic loading conditions is proposed. Yielding is described using a recently developed criterion which captures simultaneously anisotropy and compression-tension asymmetry associated with deformation twinning. The anisotropy coefficients as well as the size of the elastic domain are considered to be functions of the accumulated plastic strain. The specific expressions for the evolution laws are determined based on experimental data and numerical test results performed with a self-consistent viscoplastic model together with a macroscopic scale interpolation technique. An overstress approach is used to incorporate rate effects in the formulation. Application of the model to the description of the high-strain rate response of low-symmetry (clock-rolled hexagonal-closed-packed zirconium) is presented. The very good agreement between the simulated and experimental post-test geometries of the Taylor impact specimens in terms of major and minor side profiles and impact-interface footprints shows the ability of the model to describe the evolution of anisotropy as a function of the strain rate.

  10. Strain rate and stress field in Switzerland

    NASA Astrophysics Data System (ADS)

    Houlié, Nicolas; Woessner, Jochen; Giardini, Domenico; Rothacher, Markus

    2016-04-01

    In this study we test whether the surface deformation and the seismic activity are in agreement in terms of seismic moment release and stress/strain orientations within the territory of Switzerland. We find that for most of the country, the stress released (~2.0 10E11 N·m/yr) is consistent with the lithosphere deformation (<5 10E-8 /yr) constrained using the Global Positioning System (GPS). South of the Alpine front, we note that surface strain rates displays few agreement with long-term (and deep) deformation of the upper mantle. In this area, we propose that shear strain is being distributed in the upper crust as a result of the clockwise rotation of the Adria plate. For three regions (Basel, Swiss Jura and Ticino), we find that seismic current activity and surface deformation not to be in agreement. In the Basel area, deep seismicity exists while surface deformation is absent. This situation contrasts to what is found in the Ticino and the Swiss Jura, where seismic activity is close to absent but surface deformation is detected (~2 10E-8 /yr). While the surface deformation and seismic activity is inconsistent for the Ticino, we find them to comply in the Valais region where MW≥6 events are historically documented. Our comparison implies that the Ticino faces the potential of damaging earthquakes every hundred to few hundred years.

  11. Path dependent high strain, strain-rate deformation of polymer toroidal elements

    NASA Astrophysics Data System (ADS)

    Lee, Chien-Wei; Nesterenko, Vitali F.

    2014-08-01

    The dynamic behavior of toroidal elements (o-rings) is investigated at the range of global engineering strains up to 0.7 and strain rates about 100 s-1. It was observed that the corresponding average dynamic stiffness of rubber toroidal elements increases up to 3 times in comparison with their quasistatic compression. The viscoelastic dynamic model using linear strain-rate dependence and Hertz damped model did not satisfactory agree with experimental data in investigated range of strains and strain-rates. In order to reflect experimental results, a modified viscoelastic model with power-law strain-rate dependence was proposed. Path dependent deformation of o-rings with different levels of pre-compression was investigated under dynamic loading conditions. It was found that dynamic response of pre-compressed o-rings at the initial strain range of 0.04-0.25 is similar to the behavior of uncompressed o-rings, but further increasing pre-compression to 0.4 and 0.5 results in different force-strain curves demonstrating memory effect. This phenomenon is explained using a model incorporating dependence of dynamic force on initial pre-compression introducing critical level of dynamic strain, after which memory of initial pre-compression fades. This model predicts that force history of weakly compressed o-rings (initial strain 4%) on the stage of loading represents an envelope for all other data in agreement with experiments. In all cases, the dynamic behavior was characterized by stiffer force-displacement curves in comparison with quasistatic compression of o-rings.

  12. Analysis of Changing Swarm Rate using Volumetric Strain

    NASA Astrophysics Data System (ADS)

    Kumazawa, T.; Ogata, Y.; Kimura, K.; Maeda, K.; Kobayashi, A.

    2015-12-01

    Near the eastern coast of Izu peninsula is an active submarine volcanic region in Japan, where magma intrusions have been observed many times. The forecast of earthquake swarm activities and eruptions are serious concern particularly in nearby hot spring resort areas. It is well known that temporal durations of the swarm activities have been correlated with early volumetric strain changes at a certain observation station of about 20 km distance apart. Therefore the Earthquake Research Committee (2010) investigated some empirical statistical relations to predict sizes of the swarm activity. Here we looked at the background seismicity rate changes during these swarm periods using the non-stationary ETAS model (Kumazawa and Ogata, 2013, 2014), and have found the followings. The modified volumetric strain data, by removing the effect of earth tides, precipitation and coseismic jumps, have significantly higher cross-correlations to the estimated background rates of the ETAS model than to the swarm rate-changes. Specifically, the background seismicity rate synchronizes clearer to the strain change by the lags around a half day. These relations suggest an enhanced prediction of earthquakes in this region using volumetric strain measurements. Hence we propose an extended ETAS model where the background rate is modulated by the volumetric strain data. We have also found that the response function to the strain data can be well approximated by an exponential functions with the same decay rate, but that their intersects are inversely proportional to the distances between the volumetric strain-meter and the onset location of the swarm. Our numerical results by the same proposed model show consistent outcomes for the various major swarms in this region.

  13. Critical scaling with strain rate in overdamped sheared disordered solids

    NASA Astrophysics Data System (ADS)

    Clemmer, Joel; Salerno, Kenneth; Robbins, Mark

    In the limit of quasistatic shear, disordered solids demonstrate non-equilibrium critical behavior including power-law distributions of avalanches. Using molecular dynamics simulations of 2D and 3D overdamped binary LJ glasses, we explore the critical behavior in the limit of finite strain rate. We use finite-size scaling to find the critical exponents characterizing shear stress, kinetic energy, and measures of temporal and spatial correlations. The shear stress of the system rises as a power β of the strain rate. Larger system size extends this power law to lower rates. This behavior is governed by a power law drop of the dynamic correlation length with increasing shear stress defined by the exponent ν. This finite-size effect also impacts the scaling of the RMS kinetic energy with strain rate as avalanches begin nucleating simultaneously leading to continuous deformation of the solid. As system size increases, avalanches begin overlapping at lower rates. The correlation function of non-affine displacement exhibits novel anisotropic power law scaling with the magnitude of the wave vector. Its strain rate dependence is used to determine the scaling of the dynamic correlation length. Support provided by: DMR-1006805; NSF IGERT-0801471; OCI-0963185; CMMI-0923018.

  14. High strain rate deformation of layered nanocomposites.

    PubMed

    Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A; Thomas, Edwin L

    2012-01-01

    Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers. PMID:23132014

  15. Strain rate and temperature dependent mechanical behavior of nanocrystalline gold

    NASA Astrophysics Data System (ADS)

    Karanjgaokar, Nikhil J.

    by about 50% due to the extended temperature gradient along the specimen gauge section that causes plastic strain localization. On the contrary, the microheater based uniform heating method results in uniform temperature and strain fields during tensile experiments and was more suited for experiments at elevated temperatures. This uniform heating method was applied to annealed Au films with average grain size of 64 nm and for strain rates 10-5-10 s-1 , and temperatures 298-383 K. Activation volume calculations based on the combined temperature and strain rate experimental results pointed to two rate limiting mechanisms of inelastic deformation: Creep-driven and dislocation-mediated plasticity, with the transition occurring at increasing strain rates for increasing temperatures. The activation volume for the creep-dominated regime increased monotonically from 6.4b3 to 29.5b3 between 298 and 383 K, signifying GB diffusion processes and dislocation-mediated creep, respectively. The trends in the dislocationmediated plasticity regime followed an abnormally decreasing trend in the activation volume values with temperature, which was explained by a model for thermally activated dislocation depinning. Furthermore, the experimental data allowed us to evaluate the hardening behavior for Au films and model it using a linear hardening law and exponential relationships for the state variable and the saturation stress. The creep response of nanocrystalline Au films with 40 nm grain size was also obtained experimentally in an effort to assess its contribution to the overall mechanical response under uniaxial tension. Unusually high primary creep rates (3.3 x 10-8 to 2.7 x 10-7 s-1) and steady state creep rates (5.5 x 10-9 - 1.1 x 10-8 s-1) were measured with the primary creep regime lasting up to 5-6 hr for some stress amplitudes. A non-linear model based on the kinetics of thermal activation was applied to model the creep behavior of Au films, which captured very well the effect

  16. HIGH-RATE FORMABILITY OF HIGH-STRENGTH ALUMINUM ALLOYS: A STUDY ON OBJECTIVITY OF MEASURED STRAIN AND STRAIN RATE

    SciTech Connect

    Upadhyay, Piyush; Rohatgi, Aashish; Stephens, Elizabeth V.; Davies, Richard W.; Catalini, David

    2015-02-18

    Al alloy AA7075 sheets were deformed at room temperature at strain-rates exceeding 1000 /s using the electrohydraulic forming (EHF) technique. A method that combines high speed imaging and digital image correlation technique, developed at Pacific Northwest National Laboratory, is used to investigate high strain rate deformation behavior of AA7075. For strain-rate sensitive materials, the ability to accurately model their high-rate deformation behavior is dependent upon the ability to accurately quantify the strain-rate that the material is subjected to. This work investigates the objectivity of software-calculated strain and strain rate by varying different parameters within commonly used commercially available digital image correlation software. Except for very close to the time of crack opening the calculated strain and strain rates are very consistent and independent of the adjustable parameters of the software.

  17. The effect of size, crack depth and strain rate on fracture toughness—temperature curves of a low activation martensitic stainless steel

    NASA Astrophysics Data System (ADS)

    Edsinger, K.; Odette, G. R.; Lucas, G. E.; Sheckherd, J. W.

    1996-10-01

    Fracture toughness K( T) curves for F82H were determined as a function of specimen size, crack size and strain rate. It was found that F82H shows a relatively abrupt transition from lower-shelf, quasi-cleavage fracture to upper-shelf ductile fracture. However, decreasing specimen size, crack size and strain rate resulted in a shift of the K( T) curve to lower temperatures. The differences in the lower shelf/knee regime were reconciled by combining a critical stressed area criteria for quasi-cleavage fracture with stress fields determined by finite element methods for the different specimen geometries. The results demonstrated that the large effective toughness for small specimens or specimens with shallow cracks are a consequence of having to deform the specimens to much higher Js before the stressed-area criteria are met ahead of the crack. Such large toughnesses and low transition temperatures support the contention that thin-walled ferritic structures should remain a viable option for advanced fusion reactors.

  18. The effects of crystallographic texture and hydrogen on sulfide stress corrosion cracking behavior of a steel using slow strain rate test method

    NASA Astrophysics Data System (ADS)

    Baik, Youl; Choi, Yong

    2014-12-01

    The effects of pre-charged hydrogen inside steel and the hydrogen ions on its surface on the sulfide stress corrosion cracking (SSCC) behavior was studied by slow strain rate tests. The specimen had an ASTM grain size number of about 11. Most of precipitates were 30-50 nm in size, and their distribution density was about 106 mm-2. The crystallographic texture consisted of major α-fiber (<110>//RD) components with a maximum peak at {115}<110> relatively close to {001}<110>, and minor γ-fiber (<111>//ND) components with a peak slightly shifted from {111}<112> to {332}<113>. Hydrogen was pre-charged inside the steel by a high-temperature cathodic hydrogen charging (HTCHC) method. SSCC and corrosion tests were carried out in an electrolytic solution (NaCl: CH3COOH: H2O: FeCl2 = 50: 5: 944: 1, pH = 2.7). The corrosion potentials and the corrosion rates of the specimen without hydrogen charging for 24 hours were -490 mVSHE and 1.2 × 10-4 A cm-2, and those with charging were -520 mVSHE and 2.8 × 10-4 A cm-2, respectively. The corrosion resistance in the solution with 1000 ppm iron chloride added was decreased significantly, such that the corrosion potential and corrosion rate were -575 mVSHE and 3.5 × 10-4 A cm-2, respectively. Lower SSCC resistance of the pin-hole pre-notched specimen was observed at the open circuit potential than at the 100 mV cathodically polarized condition. Pre-charged hydrogen inside of the specimen had a greater influence on the SSCC behavior than hydrogen ions on the surface of the specimen during the slow strain rate test.

  19. High strain rate loading of polymeric foams and solid plastics

    NASA Astrophysics Data System (ADS)

    Dick, Richard D.; Chang, Peter C.; Fourney, William L.

    2000-04-01

    The split-Hopkinson pressure bar (SHPB) provided a technique to determine the high strain rate response for low density foams and solid ABS and polypropylene plastics. These materials are used in the interior safety panels of automobiles and crash test dummies. Because the foams have a very low impedance, polycarbonate bars were used to acquire the strain rate data in the 100 to 1600 l/s range. An aluminum SPHB setup was used to obtain the solid plastics data which covered strain rates of 1000 to 4000 l/s. The curves for peak strain rate versus peak stress for the foams over the test range studied indicates only a slight strain rate dependence. Peak strain rate versus peak stress curves for polypropylene shows a strain rate dependence up to about 1500 l/s. At that rate the solid poly propylene indicates no strain rate dependence. The ABS plastics are strain rate dependent up to 3500 l/s and then are independent at larger strain rates.

  20. High Strain Rate Compression Testing of Ceramics and Ceramic Composites.

    SciTech Connect

    Blumenthal, W. R.

    2005-01-01

    The compressive deformation and failure behavior of ceramics and ceramic-metal composites for armor applications has been studied as a function of strain rate at Los Alamos National Laboratory since the late 1980s. High strain rate ({approx}10{sup 3} s{sup -1}) uniaxial compression loading can be achieved using the Kolsky-split-Hopkinson pressure bar (SHPB) technique, but special methods must be used to obtain valid strength results. This paper reviews these methods and the limitations of the Kolsky-SHPB technique for this class of materials. The Kolsky-split-Hopkinson pressure bar (Kolsky-SHPB) technique was originally developed to characterize the mechanical behavior of ductile materials such as metals and polymers where the results can be used to develop strain-rate and temperature-dependent constitutive behavior models that empirically describe macroscopic plastic flow. The flow behavior of metals and polymers is generally controlled by thermally-activated and rate-dependent dislocation motion or polymer chain motion in response to shear stresses. Conversely, the macroscopic mechanical behavior of dense, brittle, ceramic-based materials is dominated by elastic deformation terminated by rapid failure associated with the propagation of defects in the material in response to resolved tensile stresses. This behavior is usually characterized by a distribution of macroscopically measured failure strengths and strains. The basis for any strain-rate dependence observed in the failure strength must originate from rate-dependence in the damage and fracture process, since uniform, uniaxial elastic behavior is rate-independent (e.g. inertial effects on crack growth). The study of microscopic damage and fracture processes and their rate-dependence under dynamic loading conditions is a difficult experimental challenge that is not addressed in this paper. The purpose of this paper is to review the methods that have been developed at the Los Alamos National Laboratory to

  1. Strain rate insensitive plasticity in aluminum alloy 5083

    SciTech Connect

    Patankar, S.N.; Jen, T.M.

    1998-03-13

    Superplastic forming offers a cost effective means to produce stress free, complex shaped components in one operation with consistency and dimensional accuracy. With the emphasis for light weight structural materials increasing, several aluminum alloys, which include Supral 2004, 7475, 5083 and 8090 have been studied for their superplastic properties with the ultimate objective of using them in automotive and aerospace structures. Among these, non heat treatable 5083 because of its moderate strength, better corrosion resistance, weldability and ability to take surface finishes coupled with its low cost, is preferred for applications involving superplastic forming. Research into the various metallurgical aspects of AA 5083 has been pursued by several groups around the world. In general, development of superplastic alloys has been concerned with grain refinement through elemental additions, recrystallization and thermo-mechanical processing of existing alloys. While the primary role of Mg in 5083 AA is solid solution strengthening many modified Al-Mg alloys have been developed by addition of different elements like Cu, Mn, Zr, etc. in different proportions to AA 5083 with an aim to reduce the tendency of cavitation and improve overall superplastic properties. AA 5083 has been categorized as statically recrystallizing rather than dynamically recrystallizing prior to superplastic deformation that occurs during thermo-mechanical processing. All the studies done so far share one thing and that is the direct dependence of flow stress on the strain. This strain hardening which increases with strain rate is attributed to the grain coarsening that occurs during the deformation of the 5083 alloy. Also found in this alloy is the higher total elongation at lower strain rates. The purpose of this paper is to report and explain the unusual stress strain behavior and strain rate independent plasticity observed in 5083 aluminum alloy.

  2. High strain-rate testing of parachute materials

    NASA Astrophysics Data System (ADS)

    Gwinn, Kenneth W.; Totten, John J.; Waye, Donald E.

    1994-12-01

    Research at Sandia National Laboratories has shown a strain rate dependence of many materials used in the production of parachutes. Differences in strength of 30% have been found between strain rates of 12/s and slow rates normally used to define material properties for lightweight nylon cloth. These structures are sometimes deployed in a rapid fashion and the loading is experienced in milliseconds; the production of material data in the same loading regime is required for full understanding of material response. Also, material behavior suitable for structural analysis of these structures is required for successful analysis. This is especially important when different materials are used in the same fabric structure. Determining the distribution of load to various portions of a nylon and Kevlar parachute requires the correct moduli and material behavior in the analytical model. The effect of strain rate on the material properties of nylon and Kevlar components commonly used in parachute construction are reported in this paper. These properties are suitable for use in analytical models of these fabric structures.

  3. High strain-rate testing of parachute materials

    SciTech Connect

    Gwinn, K.W.; Totten, J.J.; Waye, D.E.

    1994-12-31

    Research at Sandia National Laboratories has shown a strain rate dependence of many materials used in the production of parachutes. Differences in strength of 30% have been found between strain rates of 12 sec{sup {minus}1} and slow rates normally used to define material properties for lightweight nylon cloth. These structures are sometimes deployed in a rapid fashion and the loading is experienced in milliseconds; the production of material data in the same loading regime is required for full understanding of material response. Also, material behavior suitable for structural analysis of these structures is required for successful analysis. This is especially important when different materials are used in the same fabric structure. Determining the distribution of load to various portions of a nylon and Kevlar parachute requires the correct moduli and material behavior in the analytical model. The effect of strain rate on the material properties of nylon and Kevlar components commonly used in parachute construction are reported in this paper. These properties are suitable for use in analytical models of these fabric structures.

  4. Analysis of the strain-rate sensitivity at high strain rates in FCC and BCC metals

    SciTech Connect

    Follansbee, P.S.

    1988-01-01

    The development of a constitutive model based on the use of internal state variables and phenomenological models describing glide kinetics is reviewed. Application of the model to the deformation of fcc metals and alloys is illustrated, with an emphasis on the behavior at high strain rates. Preliminary results in pure iron and 4340 steel are also presented. Deformation twinning is observed in iron samples deformed in the Hopkinson pressure bar. The influence of twinning on the proposed constitutive is discussed. 11 refs., 8 figs.

  5. Effect of irradiation temperature and strain rate on the mechanical properties of V-4Cr-4Ti irradiated to low doses in fission reactors

    SciTech Connect

    Zinkle, S.J.; Snead, L.L.; Rowcliffe, A.F.; Alexander, D.J.; Gibson, L.T.

    1998-09-01

    Tensile tests performed on irradiated V-(3-6%)Cr-(3-6%)Ti alloys indicate that pronounced hardening and loss of strain hardening capacity occurs for doses of 0.1--20 dpa at irradiation temperatures below {approximately}330 C. The amount of radiation hardening decreases rapidly for irradiation temperatures above 400 C, with a concomitant increase in strain hardening capacity. Low-dose (0.1--0.5 dpa) irradiation shifts the dynamic strain aging regime to higher temperatures and lower strain rates compared to unirradiated specimens. Very low fracture toughness values were observed in miniature disk compact specimens irradiated at 200--320 C to {approximately}1.5--15 dpa and tested at 200 C.

  6. Impact of heat release on strain rate field in turbulent premixed Bunsen flames

    DOE PAGESBeta

    Coriton, Bruno Rene Leon; Frank, Jonathan H.

    2016-08-10

    The effects of combustion on the strain rate field are investigated in turbulent premixed CH4/air Bunsen flames using simultaneous tomographic PIV and OH LIF measurements. Tomographic PIV provides three-dimensional velocity measurements, from which the complete strain rate tensor is determined. The OH LIF measurements are used to determine the position of the flame surface and the flame-normal orientation within the imaging plane. This combination of diagnostic techniques enables quantification of divergence as well as flame-normal and tangential strain rates, which are otherwise biased using only planar measurements. Measurements are compared in three lean-to-stoichiometric flames that have different amounts of heatmore » release and Damköhler numbers greater than unity. The effects of heat release on the principal strain rates and their alignment relative to the local flame normal are analyzed. The extensive strain rate preferentially aligns with the flame normal in the reaction zone, which has been indicated by previous studies. The strength of this alignment increases with increasing heat release and, as a result, the flame-normal strain rate becomes highly extensive. These effects are associated with the gas expansion normal to the flame surface, which is largest for the stoichiometric flame. In the preheat zone, the compressive strain rate has a tendency to align with the flame normal. Away from the flame front, the flame – strain rate alignment is arbitrary in both the reactants and products. The flame-tangential strain rate is on average positive across the flame front, and therefore the turbulent strain rate field contributes to the enhancement of scalar gradients as in passive scalar turbulence. As a result, increases in heat release result in larger positive values of the divergence as well as flame-normal and tangential strain rates, the tangential strain rate has a weaker dependence on heat release than the flame-normal strain rate and the

  7. The effect of strain rate on the precision of penetration of short densely-packed microprojection array patches coated with vaccine.

    PubMed

    Crichton, Michael L; Ansaldo, Alexander; Chen, Xianfeng; Prow, Tarl W; Fernando, Germain J P; Kendall, Mark A F

    2010-06-01

    If skin's non-linear viscoelastic properties are mechanically exploited for precise antigen placement, there is tremendous promise for improved vaccines. To achieve this, we designed a Nanopatch-densely packed micro-nanoprojections (>20,000/cm(2)) to directly deposit antigen to large numbers of epidermal Langerhans cells and dermal dendritic cells. Here, we controllably applied our Nanopatches with discrete conditions between peak strain rates of approximately 100 s(-1)-7000 s(-1) and quantified resulting penetration depths, delivery payloads and skin mechanics. Increasing the strain rate of application, we overcame key skin variability, achieving increases in both projection penetration depth (by over 50% length) and area coverage of a full array (from 50% to 100%). This delivery depth precision opens the way for more fully utilizing the skin's immune function. Furthermore, we yielded new insights on mechanical behaviour of skin, including: 1) internal skin property changes that could affect/facilitate penetration; 2) projection design to dictate penetration depth; 3) puncture mechanics of skin in this strain rate range. Indeed, we show delivery of a model vaccine using our tested range of strain rates achieved functionally relevant tunable systemic antibody generation in mice. These findings could be of great utility in extending skin strata vaccine targeting approaches to human use.

  8. Influence of strain rate and temperature on the radial compression behavior of wet spruce

    SciTech Connect

    Uhmeier, A.; Salmen, L.

    1995-12-31

    In this study, the influences of moisture content, density, strain rate and temperature on the mechanical response of spruce compressed radially to 50% strain were investigated. Regression models were obtained for the plateau stress, energy absorption, plastic strain and reduction of plateau stress after the first compression. Temperature and strain rate had a great influence on the mechanical behaviour of spruce. It was found that lumen water had a significant effect on the deformation process at high strain rates. The reduction in plateau stress after one compression was about 30-55%, which might increase the collapsibility of the wood fibers.

  9. Stress Corrosion Cracking Behavior of Interstitial Free Steel Via Slow Strain Rate Technique

    NASA Astrophysics Data System (ADS)

    Murkute, Pratik; Ramkumar, J.; Mondal, K.

    2016-07-01

    An interstitial free steel is subjected to slow strain rate tests to investigate the stress corrosion cracking (SCC) behavior at strain rates ranging from 10-4 to 10-6s-1 in air and 3.5 wt.% NaCl solution. The ratios of time to failure, failure strain, and ultimate tensile stress at different strain rates in air to that in corrosive were considered as SCC susceptibility. Serrated stress-strain curve observed at lowest strain rate is explained by the Portevin-Le Chatelier effect. Maximum susceptibility to SCC at lowest strain rate is attributed to the soluble γ-FeOOH in the rust analyzed by Fourier Transformed Infrared spectroscopy. Mechanism for SCC relates to the anodic dissolution forming the groove, where hydrogen embrittlement can set in and finally fracture happens due to triaxiality.

  10. Effects of strain rate and curvature on the propagation of a spherical flame kernel in the thin-reaction-zones regime

    SciTech Connect

    Jenkins, K.W.; Klein, M.; Chakraborty, N.; Cant, R.S.

    2006-04-15

    Strain rate and curvature effects on the propagation of turbulent premixed flame kernels have been investigated in the thin-reaction-zones regime using three-dimensional compressible direct numerical simulations (DNS) with single-step Arrhenius chemistry. An initially spherical laminar flame kernel is allowed to interact with the surrounding turbulent fluid motion to provide a propagating turbulent flame with a strong mean spherical curvature. The statistical behavior of the local displacement speed in response to strain and curvature is investigated in detail. The results demonstrate clearly that the mean curvature inherent to the flame kernel configuration has a significant influence on the propagation of the flame. It has been found that the mean density-weighted displacement speed rS{sub d} in the case of flame kernels varies significantly over the flame brush and remains different from r{sub 0}S{sub L} (where r{sub 0} is the reactant density and S{sub L} is laminar flame speed), unlike statistically planar flames. It is also shown that the magnitude of reaction progress variable gradient ||c| is negatively correlated with curvature in the case of flame kernels, in contrast to the weak correlation between ||c| and curvature in the case of planar flames. This correlation induces a net positive correlation between the combined reaction and normal diffusion components of displacement speed (S{sub r}+S{sub n}) and curvature in flame kernels, whereas the previous studies based on statistically planar flames did not observe any appreciable correlation between (S{sub r}+S{sub n}) and curvature. (author)

  11. Finite Element Modeling of the Behavior of Armor Materials Under High Strain Rates and Large Strains

    NASA Astrophysics Data System (ADS)

    Polyzois, Ioannis

    propagated outwards diagonally towards the front and back edges forming an hourglass pattern. This pattern matched the failure behavior of specimens tested experimentally, which also exhibited failure through the formation of adiabatic shear bands. Adiabatic shear bands are known to lead to a complete shear failure. Both mechanical and thermal mechanisms contribute to the formation of shear bands. However, the finite element simulations did not show the effects of temperature rise within the material, a phenomenon which is known to contribute to thermal instabilities, whereby strain hardening effects are outweighed by thermal softening effects and adiabatic shear bands begin to form. In the simulations, the purely mechanical maximum shear stress failure, nucleating from the center of the specimens, was used as an indicator of the time at which these shear bands begin to form. The time and compressive stress at the moment of thermal instability in experimental results which have shown to form adiabatic shear bands, matched closely to those at which shear failure was first observed in the simulations. Although versatile in modeling BCC behavior, the Johnson-Cook model did not show the correct stress response in face-centered cubic (FCC) metals, such as aluminum 5083, where effects of strain rate and temperature depend on strain. Similar observations have been reported in literature. In the Johnson-Cook model, temperature, strain rate and strain" parameters are independent of each other. To this end, a more physical-based model based on dislocation mechanics, namely the Feng and Bassim constitutive model, would be more appropriate.

  12. Spall Response of Tantalum at Extreme Strain-Rates

    NASA Astrophysics Data System (ADS)

    Hahn, Eric; Germann, Tim; Meyers, Marc

    Strain-rate and microstructure play a significant role in the ultimate mechanical response of materials. Using non-equilibrium molecular dynamics simulations, we characterize the ductile tensile failure of single and nanocrystalline tantalum over multiple orders of magnitude of strain-rate. This comparison is extended to over nine orders of magnitude including experimental results from resent laser shock campaigns. Spall strength primarily follows a power law dependence with strain-rate over this extensive range. In all cases, voids nucleate heterogeneously at pre-existing defects. Predictions based on traditional theory suggest that, as strain-rate increases, tensile strength should increase. Alternatively, as grain size decreases, tensile strength may decrease due to an increased propensity to fail at a growing volume fraction of grain boundaries. Strain-rate and grain size dictate void nucleation sites by changing the type and density of available defects: vacancies, dislocations, twins, and grain boundaries.

  13. Uncovering high-strain rate protection mechanism in nacre.

    PubMed

    Huang, Zaiwang; Li, Haoze; Pan, Zhiliang; Wei, Qiuming; Chao, Yuh J; Li, Xiaodong

    2011-01-01

    Under high-strain-rate compression (strain rate approximately 10(3) s(-1)), nacre (mother-of-pearl) exhibits surprisingly high fracture strength vis-à-vis under quasi-static loading (strain rate 10(-3) s(-1)). Nevertheless, the underlying mechanism responsible for such sharply different behaviors in these two loading modes remains completely unknown. Here we report a new deformation mechanism, adopted by nacre, the best-ever natural armor material, to protect itself against predatory penetrating impacts. It involves the emission of partial dislocations and the onset of deformation twinning that operate in a well-concerted manner to contribute to the increased high-strain-rate fracture strength of nacre. Our findings unveil that Mother Nature delicately uses an ingenious strain-rate-dependent stiffening mechanism with a purpose to fight against foreign attacks. These findings should serve as critical design guidelines for developing engineered body armor materials. PMID:22355664

  14. Uncovering high-strain rate protection mechanism in nacre

    PubMed Central

    Huang, Zaiwang; Li, Haoze; Pan, Zhiliang; Wei, Qiuming; Chao, Yuh J.; Li, Xiaodong

    2011-01-01

    Under high-strain-rate compression (strain rate ∼103 s−1), nacre (mother-of-pearl) exhibits surprisingly high fracture strength vis-à-vis under quasi-static loading (strain rate 10−3 s−1). Nevertheless, the underlying mechanism responsible for such sharply different behaviors in these two loading modes remains completely unknown. Here we report a new deformation mechanism, adopted by nacre, the best-ever natural armor material, to protect itself against predatory penetrating impacts. It involves the emission of partial dislocations and the onset of deformation twinning that operate in a well-concerted manner to contribute to the increased high-strain-rate fracture strength of nacre. Our findings unveil that Mother Nature delicately uses an ingenious strain-rate-dependent stiffening mechanism with a purpose to fight against foreign attacks. These findings should serve as critical design guidelines for developing engineered body armor materials. PMID:22355664

  15. A numerical method for determining the strain rate intensity factor under plane strain conditions

    NASA Astrophysics Data System (ADS)

    Alexandrov, S.; Kuo, C.-Y.; Jeng, Y.-R.

    2016-07-01

    Using the classical model of rigid perfectly plastic solids, the strain rate intensity factor has been previously introduced as the coefficient of the leading singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. Since then, many strain rate intensity factors have been determined by means of analytical and semi-analytical solutions. However, no attempt has been made to develop a numerical method for calculating the strain rate intensity factor. This paper presents such a method for planar flow. The method is based on the theory of characteristics. First, the strain rate intensity factor is derived in characteristic coordinates. Then, a standard numerical slip-line technique is supplemented with a procedure to calculate the strain rate intensity factor. The distribution of the strain rate intensity factor along the friction surface in compression of a layer between two parallel plates is determined. A high accuracy of this numerical solution for the strain rate intensity factor is confirmed by comparison with an analytic solution. It is shown that the distribution of the strain rate intensity factor is in general discontinuous.

  16. Strain rate change transients during cyclic deformation of copper

    SciTech Connect

    Kaschner, G.C.; Gibeling, J.C.

    1996-12-15

    In the present study, the authors have undertaken to apply the strain rate change method to mechanically probe the mechanisms of cyclic deformation in copper. The goals of this work were twofold: to carefully explore differences in results obtained under conventional displacement control with those recorded under plastic strain control and to apply the formalism for monotonic deformation described above to cyclic deformation. To achieve these goals, it has been necessary to utilize computed-variable servo-hydraulic control to develop a new test technique incorporating strain rate change tests performed during low cycle fatigue. Plastic strain is used as the control variable to ensure a constant plastic strain rate between pre-determined plastic strain limits.

  17. On the response of rubbers at high strain rates.

    SciTech Connect

    Niemczura, Johnathan Greenberg

    2010-02-01

    In this report, we examine the propagation of tensile waves of finite deformation in rubbers through experiments and analysis. Attention is focused on the propagation of one-dimensional dispersive and shock waves in strips of latex and nitrile rubber. Tensile wave propagation experiments were conducted at high strain-rates by holding one end fixed and displacing the other end at a constant velocity. A high-speed video camera was used to monitor the motion and to determine the evolution of strain and particle velocity in the rubber strips. Analysis of the response through the theory of finite waves and quantitative matching between the experimental observations and analytical predictions was used to determine an appropriate instantaneous elastic response for the rubbers. This analysis also yields the tensile shock adiabat for rubber. Dispersive waves as well as shock waves are also observed in free-retraction experiments; these are used to quantify hysteretic effects in rubber.

  18. Effect of severe plastic deformation on microstructure and mechanical properties of magnesium and aluminium alloys in wide range of strain rates

    NASA Astrophysics Data System (ADS)

    Skripnyak, Vladimir; Skripnyak, Evgeniya; Skripnyak, Vladimir; Vaganova, Irina; Skripnyak, Nataliya

    2013-06-01

    Results of researches testify that a grain size have a strong influence on the mechanical behavior of metals and alloys. Ultrafine grained HCP and FCC metal alloys present higher values of the spall strength than a corresponding coarse grained counterparts. In the present study we investigate the effect of grain size distribution on the flow stress and strength under dynamic compression and tension of aluminium and magnesium alloys. Microstructure and grain size distribution in alloys were varied by carrying out severe plastic deformation during the multiple-pass equal channel angular pressing, cyclic constrained groove pressing, and surface mechanical attrition treatment. Tests were performed using a VHS-Instron servo-hydraulic machine. Ultra high speed camera Phantom V710 was used for photo registration of deformation and fracture of specimens in range of strain rates from 0,01 to 1000 1/s. In dynamic regime UFG alloys exhibit a stronger decrease in ductility compared to the coarse grained material. The plastic flow of UFG alloys with a bimodal grain size distribution was highly localized. Shear bands and shear crack nucleation and growth were recorded using high speed photography.

  19. Effects of heat treatment on stress corrosion cracking of a discontinuously reinforced aluminum (DRA) 7XXX alloy during slow strain rate testing

    SciTech Connect

    Singh, P.M.; Lewandowski, J.J.

    1995-11-01

    Discontinuously reinforced aluminum (DRA) alloys are being developed as candidate materials for the automotive and aerospace industry. Although the corrosion and stress corrosion cracking (SCC) susceptibility of aluminum alloys have been extensively studied, comparatively little is known about the corrosion and SCC behavior of DRA materials. The intent of the present work was to study the effects of changes in microstructure/heat treatment on the crack nucleation mechanisms in DRAs and their monolithic atrices on the overall slow strain rate SCC performance in a 3.5% NaCl solution (pH = 3.0). For a given heat treatment, MB78 DRA materials show more susceptibility to stress corrosion cracking than the equivalent monolithic material. For the MB78 composite, the UAII material exhibited the maximum susceptibility to SCC. Both the UAI and UAII material were more susceptible to SCC than the OA material. MB78 DRA and monolithic specimens which have been shown to have a continuous ({eta} and {eta}{prime}) layer along the grain boundaries also showed higher susceptibility to stress corrosion cracking. Significantly more crack coalescence to form larger cracks was observed for the DRA specimens tested in the NaCl solution compared to the DRA specimens tested in dry-air. Monolithic specimens (OA as well as UA) did not exhibit visible micro-cracks or significant crack coalescence on the surfaces.

  20. FAST TRACK COMMUNICATION High rate straining of tantalum and copper

    NASA Astrophysics Data System (ADS)

    Armstrong, R. W.; Zerilli, F. J.

    2010-12-01

    High strain rate measurements reported recently for several tantalum and copper crystal/polycrystal materials are shown to follow dislocation mechanics-based constitutive relations, first at lower strain rates, for dislocation velocity control of the imposed plastic deformations and, then at higher rates, transitioning to nano-scale dislocation generation control by twinning or slip. For copper, there is the possibility of added-on slip dislocation displacements to be accounted for from the newly generated dislocations.

  1. High strain rate properties of unidirectional composites, part 1

    NASA Technical Reports Server (NTRS)

    Daniel, I. M.

    1991-01-01

    Experimental methods were developed for testing and characterization of composite materials at strain rates ranging from quasi-static to over 500 s(sup -1). Three materials were characterized, two graphite/epoxies and a graphite/S-glass/epoxy. Properties were obtained by testing thin rings 10.16 cm (4 in.) in diameter, 2.54 cm (1 in.) wide, and six to eight plies thick under internal pressure. Unidirectional 0 degree, 90 degree, and 10 degree off-axis rings were tested to obtain longitudinal, transverse, and in-plane shear properties. In the dynamic tests internal pressure was applied explosively through a liquid and the pressure was measured with a calibrated steel ring. Strains in the calibration and specimen rings were recorded with a digital processing oscilloscope. The data were processed and the equation of motion solved numerically by the mini-computer attached to the oscilloscope. Results were obtained and plotted in the form of dynamic stress-strain curves. Longitudinal properties which are governed by the fibers do not vary much with strain rate with only a moderate (up to 20 percent) increase in modulus. Transverse modulus and strength increase sharply with strain rate reaching values up to three times the static values. The in-plane shear modulus and shear strength increase noticeably with strain rate by up to approximately 65 percent. In all cases ultimate strains do not vary significantly with strain rates.

  2. Compliant Intracortical Implants Reduce Strains and Strain Rates in Brain Tissue In Vivo

    PubMed Central

    Sridharan, Arati; Nguyen, Jessica K.; Capadona, Jeffrey R.; Muthuswamy, Jit

    2015-01-01

    Objective The objective of this research is to characterize the mechanical interactions of (1) soft, compliant and (2) non-compliant implants with the surrounding brain tissue in a rodent brain. Understanding such interactions will enable the engineering of novel materials that will improve stability and reliability of brain implants. Approach Acute force measurements were made using a load cell in n=3 live rats, each with 4 craniotomies. Using an indentation method, brain tissue was tested for changes in force using established protocols. A total of 4 non-compliant, bare silicon microshanks, 3 non-compliant polyvinyl acetate (PVAc)-coated silicon microshanks, and 6 compliant, nanocomposite microshanks were tested. Stress values were calculated by dividing the force by surface area and strain was estimated using a linear stress-strain relationship. Micromotion effects from breathing and vascular pulsatility on tissue stress were estimated from a 5 sec interval of steady-state measurements. Viscoelastic properties were estimated using a second-order Prony series expansion of stress-displacement curves for each shank. Main results The distribution of strain values imposed on brain tissue for both compliant nanocomposite microshanks and PVAc-coated, non-compliant silicon microshanks were significantly lower compared to non-compliant bare silicon shanks. Interestingly, step-indentation experiments also showed that compliant, nanocomposite materials significantly decreased stress relaxation rates in the brain tissue at the interface (p<0.05) compared to non-compliant silicon and PVAc-coated silicon materials. Further, both PVAc-coated non-compliant silicon and compliant nanocomposite shanks showed significantly reduced (by 4–5 fold) stresses due to tissue micromotion at the interface. Significance The results of this study showed that soft, adaptive materials reduce strains and strain rates and micromotion induced stresses in the surrounding brain tissue

  3. Compliant intracortical implants reduce strains and strain rates in brain tissue in vivo

    NASA Astrophysics Data System (ADS)

    Sridharan, Arati; Nguyen, Jessica K.; Capadona, Jeffrey R.; Muthuswamy, Jit

    2015-06-01

    Objective. The objective of this research is to characterize the mechanical interactions of (1) soft, compliant and (2) non-compliant implants with the surrounding brain tissue in a rodent brain. Understanding such interactions will enable the engineering of novel materials that will improve stability and reliability of brain implants. Approach. Acute force measurements were made using a load cell in n = 3 live rats, each with 4 craniotomies. Using an indentation method, brain tissue was tested for changes in force using established protocols. A total of 4 non-compliant, bare silicon microshanks, 3 non-compliant polyvinyl acetate (PVAc)-coated silicon microshanks, and 6 compliant, nanocomposite microshanks were tested. Stress values were calculated by dividing the force by surface area and strain was estimated using a linear stress-strain relationship. Micromotion effects from breathing and vascular pulsatility on tissue stress were estimated from a 5 s interval of steady-state measurements. Viscoelastic properties were estimated using a second-order Prony series expansion of stress-displacement curves for each shank. Main results. The distribution of strain values imposed on brain tissue for both compliant nanocomposite microshanks and PVAc-coated, non-compliant silicon microshanks were significantly lower compared to non-compliant bare silicon shanks. Interestingly, step-indentation experiments also showed that compliant, nanocomposite materials significantly decreased stress relaxation rates in the brain tissue at the interface (p < 0.05) compared to non-compliant silicon and PVAc-coated silicon materials. Furthermore, both PVAc-coated non-compliant silicon and compliant nanocomposite shanks showed significantly reduced (by 4-5 fold) stresses due to tissue micromotion at the interface. Significance. The results of this study showed that soft, adaptive materials reduce strains and strain rates and micromotion induced stresses in the surrounding brain tissue

  4. Bone strain magnitude is correlated with bone strain rate in tetrapods: implications for models of mechanotransduction

    PubMed Central

    Aiello, B. R.; Iriarte-Diaz, J.; Blob, R. W.; Butcher, M. T.; Carrano, M. T.; Espinoza, N. R.; Main, R. P.; Ross, C. F.

    2015-01-01

    Hypotheses suggest that structural integrity of vertebrate bones is maintained by controlling bone strain magnitude via adaptive modelling in response to mechanical stimuli. Increased tissue-level strain magnitude and rate have both been identified as potent stimuli leading to increased bone formation. Mechanotransduction models hypothesize that osteocytes sense bone deformation by detecting fluid flow-induced drag in the bone's lacunar–canalicular porosity. This model suggests that the osteocyte's intracellular response depends on fluid-flow rate, a product of bone strain rate and gradient, but does not provide a mechanism for detection of strain magnitude. Such a mechanism is necessary for bone modelling to adapt to loads, because strain magnitude is an important determinant of skeletal fracture. Using strain gauge data from the limb bones of amphibians, reptiles, birds and mammals, we identified strong correlations between strain rate and magnitude across clades employing diverse locomotor styles and degrees of rhythmicity. The breadth of our sample suggests that this pattern is likely to be a common feature of tetrapod bone loading. Moreover, finding that bone strain magnitude is encoded in strain rate at the tissue level is consistent with the hypothesis that it might be encoded in fluid-flow rate at the cellular level, facilitating bone adaptation via mechanotransduction. PMID:26063842

  5. Spatiotemporal correlation between seismicity and strain rate change in Japan

    NASA Astrophysics Data System (ADS)

    Kawamura, M.; Kudo, T.; Yamaoka, K.

    2007-12-01

    Large spatial change of strain rate is considered to be a manifestation of the abrupt spatial change of underground structure such as a subsurface fault with high gravity anomaly, where seismicity is higher than the surrounding area in many cases. Meanwhile, large temporal change of strain rate is considered to be a reflection of the abrupt temporal change of stress accumulation rate, for example, due to an episodic geophysical event. Possible physical causality between seismicity and these spatial and temporal underground condition changes motivated us to examine spatiotemporal correlation between seismicity and strain rate change in Japan. Inquiring into spatiotemporal correlations between various geophysical indices is very important for understanding the subsurface conditions for earthquake occurrence. For this research, we developed a tool for constructing spatially continuous strain rate distribution using daily position coordinates of GPS stations operated by Geographical Survey Institute (GSI), Japan with MATLAB script. Strain rate distribution for a time period, which is composed of gridded data covering the Japanese islands, was calculated based on the position changes per year for GPS stations densely deployed over the Japanese islands. We also made some gridded indices for seismicity using hypocentral data provided by Japan Meteorological Agency. We introduce the preliminary result on spatiotemporal correlation between each index for seismicity and strain rate change.

  6. Elastocaloric cooling processes: The influence of material strain and strain rate on efficiency and temperature span

    NASA Astrophysics Data System (ADS)

    Schmidt, Marvin; Schütze, Andreas; Seelecke, Stefan

    2016-06-01

    This paper discusses the influence of material strain and strain rate on efficiency and temperature span of elastocaloric cooling processes. The elastocaloric material, a newly developed quaternary Ni-Ti-Cu-V alloy, is characterized at different maximum strains and strain rates. The experiments are performed with a specially designed test setup, which enables the measurement of mechanical and thermal process parameters. The material efficiency is compared to the efficiency of the Carnot process at equivalent thermal operation conditions. This method allows for a direct comparison of the investigated material with other caloric materials.

  7. Mapping Strain-rate Dependent Dislocation-Defect Interactions by Atomistic Simulations

    SciTech Connect

    Fan, Yue; Osetskiy, Yury N; Yip, Sidney; Yildiz-Botterud, Bilge

    2013-01-01

    Probing the mechanisms of defect-defect interactions at strain rates lower than 106 s-1 is an unresolved challenge to date to molecular dynamics (MD) techniques. Here we propose a novel atomistic approach based on transition state theory and the concept of a strain-dependent effective activation barrier that is capable of simulating the kinetics of dislocation-defect interactions at virtually any strain rate, exemplified within 10-7 to 107 s-1. We apply this approach to the problem of an edge dislocation colliding with a cluster of self-interstitial atoms (SIA) under shear deformation. Using an activation-relaxation algorithm (1), we uncover a unique strain-rate dependent trigger mechanism that allows the SIA cluster to be absorbed during the process leading to dislocation climb. Guided by this finding, we determine the activation barrier of the trigger mechanism as a function of shear strain, and use that in a coarse-graining rate equation formulation for constructing a mechanism map in the phase space of strain-rate and temperature. Our predictions of a crossover from a defect recovery at the low strain rate regime to defect absorption behavior in the high strain-rate regime are validated against our own independent, direct MD simulations at 105 to 107 s-1. Implications of the present approach for probing molecular-level mechanisms in strain-rate regimes previously considered inaccessible to atomistic simulations are discussed.

  8. Sensitive, high-strain, high-rate bodily motion sensors based on graphene-rubber composites.

    PubMed

    Boland, Conor S; Khan, Umar; Backes, Claudia; O'Neill, Arlene; McCauley, Joe; Duane, Shane; Shanker, Ravi; Liu, Yang; Jurewicz, Izabela; Dalton, Alan B; Coleman, Jonathan N

    2014-09-23

    Monitoring of human bodily motion requires wearable sensors that can detect position, velocity and acceleration. They should be cheap, lightweight, mechanically compliant and display reasonable sensitivity at high strains and strain rates. No reported material has simultaneously demonstrated all the above requirements. Here we describe a simple method to infuse liquid-exfoliated graphene into natural rubber to create conducting composites. These materials are excellent strain sensors displaying 10(4)-fold increases in resistance and working at strains exceeding 800%. The sensitivity is reasonably high, with gauge factors of up to 35 observed. More importantly, these sensors can effectively track dynamic strain, working well at vibration frequencies of at least 160 Hz. At 60 Hz, we could monitor strains of at least 6% at strain rates exceeding 6000%/s. We have used these composites as bodily motion sensors, effectively monitoring joint and muscle motion as well and breathing and pulse.

  9. Suppression of Low Strain Rate Nonpremixed Flames by an Agent

    NASA Technical Reports Server (NTRS)

    Olson, Sandra L. (Technical Monitor); Hamins, A.; Bundy, M.; Oh, C. B.; Park, J.; Puri, I. K.

    2004-01-01

    The extinction and structure of non-premixed methane/air flames were investigated in normal gravity and microgravity through the comparison of experiments and calculations using a counterflow configuration. From a fire safety perspective, low strain rate conditions are important for several reasons. In normal gravity, many fires start from small ignition sources where the convective flow and strain rates are weak. Fires in microgravity conditions, such as a manned spacecraft, may also occur in near quiescent conditions where strain rates are very low. When designing a fire suppression system, worst-case conditions should be considered. Most diffusion flames become more robust as the strain rate is decreased. The goal of this project is to investigate the extinction limits of non-premixed flames using various agents and to compare reduced gravity and normal gravity conditions. Experiments at the NASA Glenn Research Center's 2.2-second drop tower were conducted to attain extinction and temperature measurements in low-strain non-premixed flames. Extinction measurements using nitrogen added to the fuel stream were performed for global strain rates from 7/s to 50/s. The results confirmed the "turning point" behavior observed previously by Maruta et al. in a 10 s drop tower. The maximum nitrogen volume fraction in the fuel stream needed to assure extinction for all strain rates was measured to be 0.855+/-0.016, associated with the turning point determined to occur at a strain rate of 15/s. The critical nitrogen volume fraction in the fuel stream needed for extinction of 0-g flames was measured to be higher than that of 1-g flames.

  10. Residual thermal and moisture influences on the strain energy release rate analysis of edge delamination

    NASA Technical Reports Server (NTRS)

    Obrien, T. K.; Raju, I. S.; Garber, D. P.

    1985-01-01

    A laminated plate theory analysis is developed to calculate the strain energy release rate associated with edge delamination growth in a composite laminate. The analysis includes the contribution of residual thermal and moisture stresses to the strain energy released. The strain energy release rate, G, increased when residual thermal effects were combined with applied mechanical strains, but then decreased when increasing moisture content was included. A quasi-three-dimensional finite element analysis indicated identical trends and demonstrated these same trends for the individual strain energy release rate components, G sub I and G sub II, associated with interlaminar tension and shear. An experimental study indicated that for T300/5208 graphite-epoxy composites, the inclusion of residual thermal and moisture stresses did not significantly alter the calculation of interlaminar fracture toughness from strain energy release rate analysis of edge delamination data taken at room temperature, ambient conditions.

  11. Residual thermal and moisture influences on the strain energy release rate analysis of edge delamination

    NASA Technical Reports Server (NTRS)

    Obrien, T. K.; Raju, I. S.; Garber, D. P.

    1986-01-01

    A laminated plate theory analysis is developed to calculate the strain energy release rate associated with edge delamination growth in a composite laminate. The analysis includes the contribution of residual thermal and moisture stresses to the strain energy released. The strain energy release rate, G, increased when residual thermal effects were combined with applied mechanical strains, but then decreased when increasing moisture content was included. A quasi-three-dimensional finite element analysis indicated identical trends and demonstrated these same trends for the individual strain energy release rate components, G sub I and G sub II, associated with interlaminar tension and shear. An experimental study indicated that for T300/5208 graphite-epoxy composites, the inclusion of residual thermal and moisture stresses did not significantly alter the calculation of interlaminar fracture toughness from strain energy release rate analysis of edge delamination data taken at room temperature, ambient conditions.

  12. Tantalum strength model incorporating temperature, strain rate and pressure

    NASA Astrophysics Data System (ADS)

    Lim, Hojun; Battaile, Corbett; Brown, Justin; Lane, Matt

    Tantalum is a body-centered-cubic (BCC) refractory metal that is widely used in many applications in high temperature, strain rate and pressure environments. In this work, we propose a physically-based strength model for tantalum that incorporates effects of temperature, strain rate and pressure. A constitutive model for single crystal tantalum is developed based on dislocation kink-pair theory, and calibrated to measurements on single crystal specimens. The model is then used to predict deformations of single- and polycrystalline tantalum. In addition, the proposed strength model is implemented into Sandia's ALEGRA solid dynamics code to predict plastic deformations of tantalum in engineering-scale applications at extreme conditions, e.g. Taylor impact tests and Z machine's high pressure ramp compression tests, and the results are compared with available experimental data. Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  13. High strain rate fracture behavior of fused silica

    NASA Astrophysics Data System (ADS)

    Ruggiero, Andrew; Iannitti, Gianluca; Testa, Gabriel; Limido, Jerome; Lacome, Jean; Olovsson, Lars; Ferraro, Mario; Bonora, Nicola

    2013-06-01

    Fused silica is a high purity synthetic amorphous silicon dioxide characterized by low thermal expansion coefficient, excellent optical qualities and exceptional transmittance over a wide spectral range. Because of its wide use in the military industry as window material, it may be subjected to high-energy ballistic impacts. Under such dynamic conditions, post-yield response of the ceramic as well as the strain rate related effects become significant and should be accounted for in the constitutive modeling. In this study, the procedure for constitutive model validation and model parameters identification, is presented. Taylor impact tests and drop weight tests were designed and performed at different impact velocities, from 1 to 100 m/s, and strain rates, from 102 up to 104 s-1. Numerical simulation of both tests was performed with IMPETUS-FEA, a general non-linear finite element software which offers NURBS finite element technology for the simulation of large deformation and fracture in materials. Model parameters were identified by optimization using multiple validation metrics. The validity of the parameters set determined with the proposed procedure was verified comparing numerical predictions and experimental results for an independent designed test consisting in a fused silica tile impacted at prescribed velocity by a steel sphere.

  14. Mapping strain rate dependence of dislocation-defect interactions by atomistic simulations

    PubMed Central

    Fan, Yue; Osetskiy, Yuri N.; Yip, Sidney; Yildiz, Bilge

    2013-01-01

    Probing the mechanisms of defect–defect interactions at strain rates lower than 106 s−1 is an unresolved challenge to date to molecular dynamics (MD) techniques. Here we propose an original atomistic approach based on transition state theory and the concept of a strain-dependent effective activation barrier that is capable of simulating the kinetics of dislocation–defect interactions at virtually any strain rate, exemplified within 10−7 to 107 s−1. We apply this approach to the problem of an edge dislocation colliding with a cluster of self-interstitial atoms (SIAs) under shear deformation. Using an activation–relaxation algorithm [Kushima A, et al. (2009) J Chem Phys 130:224504], we uncover a unique strain-rate–dependent trigger mechanism that allows the SIA cluster to be absorbed during the process, leading to dislocation climb. Guided by this finding, we determine the activation barrier of the trigger mechanism as a function of shear strain, and use that in a coarse-graining rate equation formulation for constructing a mechanism map in the phase space of strain rate and temperature. Our predictions of a crossover from a defect recovery at the low strain-rate regime to defect absorption behavior in the high strain-rate regime are validated against our own independent, direct MD simulations at 105 to 107 s−1. Implications of the present approach for probing molecular-level mechanisms in strain-rate regimes previously considered inaccessible to atomistic simulations are discussed. PMID:24114271

  15. Creep Strain and Strain Rate Response of 2219 Al Alloy at High Stress Levels

    NASA Technical Reports Server (NTRS)

    Taminger, Karen M. B.; Wagner, John A.; Lisagor, W. Barry

    1998-01-01

    As a result of high localized plastic deformation experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the deformation response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, creep tests were conducted in the temperature range from ambient temperature to 107 C (225 F) at stress levels approaching the ultimate tensile strength of 2219-T851 Al. Strain-time histories and strain rate responses were examined. The strain rate response was extremely high initially, but decayed rapidly, spanning as much as five orders of magnitude during primary creep. Select specimens were subjected to incremental step loading and exhibited initial creep rates of similar magnitude for each load step. Although the creep rates decreased quickly at all loads, the creep rates dropped faster and reached lower strain rate levels for lower applied loads. The initial creep rate and creep rate decay associated with primary creep were similar for specimens with and without prestrain; however, prestraining (strain hardening) the specimens, as in the aforementioned proof test, resulted in significantly longer creep life.

  16. High-strain-rate superplasticity of SiC p /8090 aluminum composite

    NASA Astrophysics Data System (ADS)

    Han, B. Q.; Chan, K. C.; Yue, T. M.; Lau, W. S.

    1996-11-01

    Superplastic tensile tests of a 17 vol.% SiC p /8090 Al-Li composite were carried out at strain rates ranging from 7.25 × 10-4 s-1 to 3.46 × 10-1 s-1 and at temperatures from 773 K to 873 K. A maximum elongation of 300% was obtained at a strain rate of 1.83 × 10-1 s-1 when tested at a temperature of 848 K which was slightly above the solidus temperature of the composite. The effect of a small fraction of liquid phase on high-strain-rate superplasticity was discussed. Finally, the activation energy of high-strain-rate superplastic deformation was calculated and high-strain-rate superplastic mechanism was discussed.

  17. Computational Simulation of the High Strain Rate Tensile Response of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.

    2002-01-01

    A research program is underway to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. Under these types of loading conditions, the material response can be highly strain rate dependent and nonlinear. State variable constitutive equations based on a viscoplasticity approach have been developed to model the deformation of the polymer matrix. The constitutive equations are then combined with a mechanics of materials based micromechanics model which utilizes fiber substructuring to predict the effective mechanical and thermal response of the composite. To verify the analytical model, tensile stress-strain curves are predicted for a representative composite over strain rates ranging from around 1 x 10(exp -5)/sec to approximately 400/sec. The analytical predictions compare favorably to experimentally obtained values both qualitatively and quantitatively. Effective elastic and thermal constants are predicted for another composite, and compared to finite element results.

  18. Experimental and Numerical Study on Tensile Strength of Concrete under Different Strain Rates

    PubMed Central

    Min, Fanlu; Yao, Zhanhu; Jiang, Teng

    2014-01-01

    The dynamic characterization of concrete is fundamental to understand the material behavior in case of heavy earthquakes and dynamic events. The implementation of material constitutive law is of capital importance for the numerical simulation of the dynamic processes as those caused by earthquakes. Splitting tensile concrete specimens were tested at strain rates of 10−7 s−1 to 10−4 s−1 in an MTS material test machine. Results of tensile strength versus strain rate are presented and compared with compressive strength and existing models at similar strain rates. Dynamic increase factor versus strain rate curves for tensile strength were also evaluated and discussed. The same tensile data are compared with strength data using a thermodynamic model. Results of the tests show a significant strain rate sensitive behavior, exhibiting dynamic tensile strength increasing with strain rate. In the quasistatic strain rate regime, the existing models often underestimate the experimental results. The thermodynamic theory for the splitting tensile strength of concrete satisfactorily describes the experimental findings of strength as effect of strain rates. PMID:24883355

  19. Magnetic Implosion for Novel Strength Measurements at High Strain Rates

    SciTech Connect

    Lee, H.; Preston, D.L.; Bartsch, R.R.; Bowers, R.L.; Holtkamp, D.; Wright, B.L.

    1998-10-19

    Recently Lee and Preston have proposed to use magnetic implosions as a new method for measuring material strength in a regime of large strains and high strain rates inaccessible to previously established techniques. By its shockless nature, this method avoids the intrinsic difficulties associated with an earlier approach using high explosives. The authors illustrate how the stress-strain relation for an imploding liner can be obtained by measuring the velocity and temperature history of its inner surface. They discuss the physical requirements that lead us to a composite liner design applicable to different test materials, and also compare the code-simulated prediction with the measured data for the high strain-rate experiments conducted recently at LANL. Finally, they present a novel diagnostic scheme that will enable us to remove the background in the pyrometric measurement through data reduction.

  20. A constitutive model for ballistic gelatin at surgical strain rates.

    PubMed

    Ravikumar, Nishant; Noble, Christopher; Cramphorn, Edward; Taylor, Zeike A

    2015-07-01

    This paper describes a constitutive model for ballistic gelatin at the low strain rates experienced, for example, by soft tissues during surgery. While this material is most commonly associated with high speed projectile penetration and impact investigations, it has also been used extensively as a soft tissue simulant in validation studies for surgical technologies (e.g. surgical simulation and guidance systems), for which loading speeds and the corresponding mechanical response of the material are quite different. We conducted mechanical compression experiments on gelatin specimens at strain rates spanning two orders of magnitude (~0.001-0.1s(-1)) and observed a nonlinear load-displacement history and strong strain rate-dependence. A compact and efficient visco-hyperelastic constitutive model was then formulated and found to fit the experimental data well. An Ogden type strain energy density function was employed for the elastic component. A single Prony exponential term was found to be adequate to capture the observed rate-dependence of the response over multiple strain rates. The model lends itself to immediate use within many commercial finite element packages. PMID:25863009

  1. Strain rate influence on fracture development in experimental ductile multilayers

    NASA Astrophysics Data System (ADS)

    Gomez-Rivas, Enrique; Griera, Albert

    2011-04-01

    The far-field strain rate is a crucial parameter that controls the transition between brittle and ductile deformation. We have used analogue experiments to study the strain rate influence on the development of brittle fractures in a ductile composite material. Plasticine multilayer models were deformed under coaxial boundary conditions at three different strain rates to analyse the transition from non-localised deformation to the development of a brittle fracture network that accommodates part of the deformation. The results show that tension cracks and voids are the first macroscopic structures that nucleate after an early stage of ductile deformation. Coalescence and collapse of these structures lead to the development of brittle shear fractures. The evolution of fracture orientations, lengths and displacements was systematically analysed. The ratio of the accumulated fracture displacement vs. fracture length ( dmax/ L) depends not only on the total deformation, but also on the strain rate at which the system is deformed. The accumulated displacement with respect to fracture length increases with strain rate.

  2. Effects of H2O, CO2, and N2 air contaminants on critical airside strain rates for extinction of hydrogen-air counterflow diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Guerra, Rosemary

    1989-01-01

    Dish-shaped counterflow diffusion flames centered by opposing laminar jets of H2 and clean and contaminant O2/N2 mixtures in an argon bath at 1 atm were used to study the effects of contaminants on critical airside strain. The jet velocities for both flame extinction and restoration are found for a wide range of contaminant and O2 concentrations in the air jet. The tests are also conducted for a variety of input H2 concentrations. The results are compared with those from several other studies.

  3. High strain rate superplasticity in metals and composites

    SciTech Connect

    Nieh, T.G.; Wadsworth, J.; Higashi, K.

    1993-07-01

    Superplastic behavior at very high strain rates (at or above 1 s{sup {minus}1}) in metallic-based materials is an area of increasing interest. The phenomenon has been observed quite extensively in metal alloys, metal-matrix composites (MMC), and mechanically-alloyed (MA) materials. In the present paper, experimental results on high strain rate behavior in 2124 Al-based materials, including Zr-modified 2124, SiC-reinforced 2124, MA 2124, and MA 2124 MMC, are presented. Except for the required fine grain size, details of the structural requirements of this phenomenon are not yet understood. Despite this, a systematic approach to produce high strain rate superplasticity (HSRS) in metallic materials is given in this paper. Evidences indicate that the presence of a liquid phase, or a low melting point region, at boundary interfaces is responsible for HSRS.

  4. Stress, strain rate and anisotropy in Kyushu, Japan

    NASA Astrophysics Data System (ADS)

    Savage, M. K.; Aoki, Y.; Unglert, K.; Ohkura, T.; Umakoshi, K.; Shimizu, H.; Iguchi, M.; Tameguri, T.; Ohminato, T.; Mori, J.

    2016-04-01

    Seismic anisotropy, the directional dependence of wave speeds, may be caused by stress-oriented cracks or by strain-oriented minerals, yet few studies have quantitatively compared anisotropy to stress and strain over large regions. Here we compare crustal stress and strain rates on the Island of Kyushu, Japan, as measured from inversions of focal mechanisms, GPS and shear wave splitting. Over 85,000 shear wave splitting measurements from local and regional earthquakes are obtained from the NIED network between 2004 and 2012, and on Aso, Sakurajima, Kirishima and Unzen volcano networks. Strain rate measurements are made from the Japanese Geonet stations. JMA-determined S arrival times processed with the MFAST shear wave splitting code measure fast polarisations (Φ), related to the orientation of the anisotropic medium and time delays (dt), related to the path length and the percent anisotropy. We apply the TESSA 2-D delay time tomography and spatial averaging code to the highest quality events, which have nearly vertical incidence angles, separating the 3455 shallow (depth < 40 km) from the 4957 deep (> = 40 km) earthquakes. Using square grids with 30 km sides for all the inversions, the best correlations are observed between splitting from shallow earthquakes and stress. Axes of maximum horizontal stress (SHmax) and Φ correlate with a coefficient c of 0.56, significant at the 99% confidence level. Their mean difference is 31.9°. Axes of maximum compressional strain rate and SHmax are also well aligned, with an average difference of 28°, but they do not correlate with each other, meaning that where they differ, the difference is not systematic. Anisotropy strength is negatively correlated with the stress ratio parameter determined from focal mechanism inversion (c = - 0.64; significant at the 99% confidence level). The anisotropy and stress results are consistent with stress-aligned microcracks in the crust in a dominantly strike-slip regime. Eigenvalues of

  5. Prediction of FV520B Steel Flow Stresses at High Temperature and Strain Rates

    NASA Astrophysics Data System (ADS)

    Han, Xiaolan; Zhao, Shengdun; Zhang, Chenyang; Fan, Shuqin; Xu, Fan

    2015-10-01

    In order to develop reliable constitutive equations for the simulation, the hot deformation behavior of FV520B steel was investigated through isothermal compression tests in a wide range of temperatures from 900 °C to 1100 °C at an interval of 50 °C and strain rate from 0.01 to 10 s-1 on Gleeble-1500D simulator. The effects of temperature and strain rate on deformation behavior were represented by Zener-Holloman parameter in an exponent-type equation of Arrhenius constitutive. The influence of strain was incorporated in the constitutive analysis by material constants expressed as a polynomial function of strain. The constitutive equation (considering the compensation of strain) could precisely predict the flow stress only at strain rate 0.01 s-1 except at the temperatures of 900 °C and 1000 °C, whereas the flow stress predicted by a modified equation (incorporating both the strain and strain rate) demonstrated a well agreement with the experimental data throughout the entire range of temperatures and strain rates. Correlation coefficient (R) of 0.988 and average absolute relative error (AARE) of 5.7% verified the validity of developed equation from statistical analysis, which further confirmed that the modified constitutive equation could accurately predict the flow stress of FV520B steel.

  6. High strain-rate model for fiber-reinforced composites

    SciTech Connect

    Aidun, J.B.; Addessio, F.L.

    1995-07-01

    Numerical simulations of dynamic uniaxial strain loading of fiber-reinforced composites are presented that illustrate the wide range of deformation mechanisms that can be captured using a micromechanics-based homogenization technique as the material model in existing continuum mechanics computer programs. Enhancements to the material model incorporate high strain-rate plastic response, elastic nonlinearity, and rate-dependent strength degradation due to material damage, fiber debonding, and delamination. These make the model relevant to designing composite structural components for crash safety, armor, and munitions applications.

  7. The high strain-rate behaviour of selected tissue analogues.

    PubMed

    Appleby-Thomas, G J; Hazell, P J; Sheldon, R P; Stennett, C; Hameed, A; Wilgeroth, J M

    2014-05-01

    The high strain-rate response of four readily available tissue simulants has been investigated via plate-impact experiments. Comparison of the shock response of gelatin, ballistic soap (both sub-dermal tissue simulants), lard (adipose layers) and Sylgard(®) (a potential brain simulant) allowed interrogation of the applicability of such monolithic tissue surrogates in the ballistic regime. The gelatin and lard exhibited classic linear Hugoniot equations-of-state in the US-uP plane; while for the ballistic soap and Sylgard(®) a polymer-like non-linear response was observed. In the P/σX-v/v0 plane there was evidence of separation of the simulant materials into distinct groups, suggesting that a single tissue simulant is inadequate to ensure a high-fidelity description of the high strain-rate response of complex mammalian tissue. Gelatin appeared to behave broadly hydrodynamically, while soap, lard and Sylgard(®) were observed to strengthen in a material-dependent manner under specific loading conditions at elevated shock loading pressures/stresses. This strengthening behaviour was tentatively attributed to a further polymeric-like response in the form of a re-arrangement of the molecular chains under loading (a steric effect). In addition, investigation of lateral stress data from the literature showed evidence of operation of a material-independent strengthening mechanism when these materials were stressed above 2.5-3.0GPa, tentatively linked to the generically polymeric-like underlying microstructure of the simulants under consideration. PMID:23778063

  8. The high strain-rate behaviour of selected tissue analogues.

    PubMed

    Appleby-Thomas, G J; Hazell, P J; Sheldon, R P; Stennett, C; Hameed, A; Wilgeroth, J M

    2014-05-01

    The high strain-rate response of four readily available tissue simulants has been investigated via plate-impact experiments. Comparison of the shock response of gelatin, ballistic soap (both sub-dermal tissue simulants), lard (adipose layers) and Sylgard(®) (a potential brain simulant) allowed interrogation of the applicability of such monolithic tissue surrogates in the ballistic regime. The gelatin and lard exhibited classic linear Hugoniot equations-of-state in the US-uP plane; while for the ballistic soap and Sylgard(®) a polymer-like non-linear response was observed. In the P/σX-v/v0 plane there was evidence of separation of the simulant materials into distinct groups, suggesting that a single tissue simulant is inadequate to ensure a high-fidelity description of the high strain-rate response of complex mammalian tissue. Gelatin appeared to behave broadly hydrodynamically, while soap, lard and Sylgard(®) were observed to strengthen in a material-dependent manner under specific loading conditions at elevated shock loading pressures/stresses. This strengthening behaviour was tentatively attributed to a further polymeric-like response in the form of a re-arrangement of the molecular chains under loading (a steric effect). In addition, investigation of lateral stress data from the literature showed evidence of operation of a material-independent strengthening mechanism when these materials were stressed above 2.5-3.0GPa, tentatively linked to the generically polymeric-like underlying microstructure of the simulants under consideration.

  9. Low Strain Rate Compression Measurements of PBX 9501, PBXN-9, and Mock 9501

    NASA Astrophysics Data System (ADS)

    Idar, D. J.; Peterson, P. D.; Scott, P. D.; Funk, D. J.

    1997-07-01

    Low strain rate (10-3 to 10-1 1/s) compression measurements have been obtained on three different composite materials: PBX 9501, PBXN-9, and a sugar mock of PBX 9501. These measurements expand on earlier efforts to identify the behavior of PBX 9501 and sugar mocks at different rates, aspect ratios (L/d) and temperatures. PBX 9501 samples at three different L/d's were strained at the same rate to evalute the effect of aspect ration on stress-strain parameters. Extensometer and strain gage data obtained with these measurements were also compared for precision. PBXN-9 data were obtained at two different L/d's, two different temperatures, an at three different rates. The PBXN-9 data exhibit similar trends to other energetic materials data, i.e. 1) increased ultimate compressive strength and modulus of elasticity with either an increase in strain rate, or decrease in temperature, and 2) small changes in the strain at maximum stress with changes in temperature or strain rate. A comparison of the PBXN-9 data to the PBX 9501 data shows that both begin to fail at comparable strains. However, PBXN-9 is considerably weaker in terms of the ultimate compressive strength.

  10. Low strain rate compression measurements of PBXN-9, PBX 9501, and mock 9501

    SciTech Connect

    Idar, D.J.; Scott, P.D.; Funk, D.J.; Peterson, P.D.

    1998-07-01

    Low strain rate (10{sup {minus}3} to 10{sup {minus}1}s{sup {minus}1}) compression measurements have been obtained on three different composite materials: PBXN-9, PBX 9501, and a 9501 sugar mock. These measurements expand on earlier efforts to identify the behavior of PBX 9501 and sugar mocks at different rates, sample aspect ratios (L/d) and temperatures. PBX 9501 samples at three different L/d{close_quote}s were strained at the same strain rate to evaluate L/d effects on the stress-strain parameters. PBXN-9 data were obtained at two different L/d{close_quote}s, two different temperatures, and at three different rates. The PBXN-9 data exhibit similar trends to other energetic materials data, i.e. 1)increased ultimate compressive strength and modulus of elasticity with either an increase in strain rate, or decrease in temperature, and 2)small increases in the strain at maximum stress with decreases in temperature or strain rate. A comparison of the PBXN-9 data to the PBX 9501 data shows that both begin to fail at comparable strains, however the PBXN-9 data is considerably weaker in terms of the ultimate compressive strength. {copyright} {ital 1998 American Institute of Physics.}

  11. Low strain rate compression measurements of PBX 9501, PBXN-9, and MOCK 9501

    SciTech Connect

    Idar, D.J.; Peterson, P.D.; Scott, P.D.; Funk, D.J.

    1997-07-01

    Low strain rate (10{sup -3} to 10{sup -1} 1/s) compression measurements have been obtained on three different composite materials: PBX 9501, PBXN-9, and a sugar mock of PBX 9501. These measurements expand on earlier efforts to identify the behavior of PBX 9501 and sugar mocks at different rates, aspect ratios (L/d) and temperatures. PBX 9501 samples at three different L/d`s were strained at the same rate to evaluate Lid effects on the stress strain parameters. Extensometer and strain gage data obtained with these measurements were also compared for precision. PBXN-9 data were obtained at two different L/ds, two different temperatures, and at three different rates. The PBXN-9 data exhibit similar trends to other energetic materials data, i.e. 1) increased ultimate compressive strength and modulus of elasticity with either an increase in strain rate, or decrease in temperature, and 2) small changes in the strain at maximum stress with changes in temperature or strain rate. A comparison of the PBXN-9 data to the PBX 9501 data shows that both begin to fail at comparable strains, however the PBXN- 9 data is considerably weaker in terms of the ultimate compressive strength.

  12. Low strain rate compression measurements of PBXN-9, PBX 9501, and mock 9501

    NASA Astrophysics Data System (ADS)

    Idar, D. J.; Peterson, P. D.; Scott, P. D.; Funk, D. J.

    1998-07-01

    Low strain rate (10-3 to 10-1 s-1) compression measurements have been obtained on three different composite materials: PBXN-9, PBX 9501, and a 9501 sugar mock. These measurements expand on earlier efforts to identify the behavior of PBX 9501 and sugar mocks at different rates, sample aspect ratios (L/d) and temperatures. PBX 9501 samples at three different L/d's were strained at the same strain rate to evaluate L/d effects on the stress-strain parameters. PBXN-9 data were obtained at two different L/d's, two different temperatures, and at three different rates. The PBXN-9 data exhibit similar trends to other energetic materials data, i.e. 1)increased ultimate compressive strength and modulus of elasticity with either an increase in strain rate, or decrease in temperature, and 2)small increases in the strain at maximum stress with decreases in temperature or strain rate. A comparison of the PBXN-9 data to the PBX 9501 data shows that both begin to fail at comparable strains, however the PBXN-9 data is considerably weaker in terms of the ultimate compressive strength.

  13. Time and strain rate dependent mechanical behavior of individual polymeric nanofibers

    NASA Astrophysics Data System (ADS)

    Naraghi, Mohammad; Kolluru, Pavan V.; Chasiotis, Ioannis

    2014-01-01

    In this work, the small and large strain mechanical behavior of nanofibers electrospun from glassy polymers was shown to be diameter and time-dependent. Specifically, the creep compliance of as-elecrospun polyacrylonitrile (PAN) nanofibers increased with increasing diameter, while the tangent modulus, yield stress and tensile strength followed decreasing trends, which were attributed to increased molecular orientation with reduced nanofiber diameter. Furthermore, the nanofiber capacity for energy dissipation increased dramatically with the applied strain rate, as the yield and ultimate tensile strengths increased steadily with increasing strain rate. The effect of strain rate was less significant on the ductility of PAN nanofibers, and insignificant on the ductility of polystyrene (PS) nanofibers. This outstanding mechanical response was demonstrated by homogeneously deforming PAN nanofibers at strain rates as high as 200 s-1 and by PS nanofibers exhibiting necking at local plastic strain rates as high as 27,000 s-1. The small strain time-dependent response of PAN nanofibers was modeled with a linear viscoelasticity model with diameter dependent constants, which provided a good description of the creep and strain rate behavior. The large deformation behavior was modeled via a modified rubber elasticity model which predicted quite well the overall mechanical response of PAN nanofibers.

  14. On Estimation of GPS-based Indonesian Strain Rate Map

    NASA Astrophysics Data System (ADS)

    Susilo, Susilo; Abidin, Hasanuddin Z.; Meilano, Irwan; Sapiie, Benyamin; Wijanarto, Antonius B.

    2016-04-01

    Using the GPS-derived rates at survey mode (sGPS) stations and continuous GPS stations across Indonesian region, covering the 22 years period from 1993 to 2014, the linear deformation velocities with an accuracy of about 2 to 3 mm/year level are derived. These velocities are corrected to the coseismic and postseismic deformation caused by significant earthquakes in that period. In this study, we use this GPS velocities field to construct a crustal strain rate map without including the physical model yet. An interpolation method was used to compute the velocity model. By differentiation of the continuous velocity model, we derive the strain rate map of Indonesia. At present, our result is only the magnitude of the strain rate. The Indonesian strain rate map is very important for studying the deformation characteristics in the region and to establish a deformation (velocity) model for supporting the implementation of the Indonesian Geospatial Reference System 2013 (IGRS 2013). This is a new semi-dynamic geocentric datum of Indonesia, which uses the global ITRF2008 reference frame, with a reference epoch of 1 January 2012. A deformation (velocity) model is required to transform coordinates from an observation epoch to or from this reference epoch.

  15. A simplified approach to strain energy release rate computations for interlaminar fracture of composites

    NASA Technical Reports Server (NTRS)

    Armanios, Erian A.; Rehfield, Lawrence W.

    1989-01-01

    A simple approach for the strain energy release rate computations based on the finite element method and a singular fitting model is presented. The model uses the stress and displacement distributions at the delamination front. The method is applied to a mixed-mode double cracked-lap-shear composite configuration. The strain energy release rate components predicted by the model are compared with the finite element crack-closure method. The effect of the mesh size on the stress and displacement distribution is isolated. The strain energy release rates predicted by relatively coarse mesh sizes are in good agreement with the finite element crack closure method.

  16. Mechanical and microstructural response of Ni sub 3 Al at high strain rate and elevated temperatures

    SciTech Connect

    Sizek, H.W.; Gray, G.T. III.

    1990-01-01

    In this paper, the effect of strain rate and temperature on the substructure evolution and mechanical response of Ni{sub 3}Al will be presented. The strain rate response of Ni{sub 3}Al was studied at strain rates from 10{sup {minus}3} s{sup {minus}1} (quasi-static) to 10{sup 4} s{sup {minus}1} using a Split Hopkinson Pressure Bar. The Hopkinson Bar tests were conducted at temperatures ranging from 77K to 1273K. At high strain rates the flow strength increased significantly with increasing temperature, similar to the behavior observed at quasi-static rates. The work hardening rates increased with strain rate and varied with temperatures. The work hardening rates, appeared to be significantly higher than those found for Ni270. The substructure evolution was characterized utilizing TEM. The defect generation and rate sensitivity of Ni{sub 3}Al are also discussed as a function of strain rate and temperature. 15 refs., 4 figs.

  17. A fast and accurate method for echocardiography strain rate imaging

    NASA Astrophysics Data System (ADS)

    Tavakoli, Vahid; Sahba, Nima; Hajebi, Nima; Nambakhsh, Mohammad Saleh

    2009-02-01

    Recently Strain and strain rate imaging have proved their superiority with respect to classical motion estimation methods in myocardial evaluation as a novel technique for quantitative analysis of myocardial function. Here in this paper, we propose a novel strain rate imaging algorithm using a new optical flow technique which is more rapid and accurate than the previous correlation-based methods. The new method presumes a spatiotemporal constancy of intensity and Magnitude of the image. Moreover the method makes use of the spline moment in a multiresolution approach. Moreover cardiac central point is obtained using a combination of center of mass and endocardial tracking. It is proved that the proposed method helps overcome the intensity variations of ultrasound texture while preserving the ability of motion estimation technique for different motions and orientations. Evaluation is performed on simulated, phantom (a contractile rubber balloon) and real sequences and proves that this technique is more accurate and faster than the previous methods.

  18. Analytical Modeling of the High Strain Rate Deformation of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

    2003-01-01

    The results presented here are part of an ongoing research program to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric matrix materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical 5 plasticity theory definitions of effective stress and effective plastic strain are modified by applying variations of the Drucker-Prager yield criterion. To verify the revised formulation, the shear and tensile deformation of a representative toughened epoxy is analyzed across a wide range of strain rates (from quasi-static to high strain rates) and the results are compared to experimentally obtained values. For the analyzed polymers, both the tensile and shear stress-strain curves computed using the analytical model correlate well with values obtained through experimental tests. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. In the micromechanics, the unit cell is divided up into a number of independently analyzed slices, and laminate theory is then applied to obtain the effective deformation of the unit cell. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite (composed using the representative polymer analyzed for the correlation of the polymer constitutive equations) for several fiber orientation angles across a variety of strain rates. The computed values compare favorably to experimentally obtained results.

  19. Abnormal myocardial strain rate in noncompaction of the left ventricle.

    PubMed

    Williams, R Ian; Masani, Navroz D; Buchalter, Maurice B; Fraser, Alan G

    2003-03-01

    A 28-year-old woman presented in the second trimester of pregnancy with palpitations and left heart failure. Transthoracic echocardiography showed features consistent with isolated noncompaction of the left ventricle. Doppler tissue echocardiography with strain-rate imaging revealed unique appearances of paradoxical alternating bands of compression and expansion throughout systole and diastole. These features may be pathognomonic for this disease.

  20. Temperature-strain rate deformation conditions of aluminum alloys

    NASA Astrophysics Data System (ADS)

    Kitaeva, D. A.; Pazylov, Sh. T.; Rudaev, Ya. I.

    2016-03-01

    This paper presents the results of an experimental study of the deformation and structural parameters of 1561 anisotropic alloy. It has been found that the lowest anisotropy factor corresponds to the formation of an ultrafine-grained equiaxed structure under temperature-strain rate conditions of superplasticity.

  1. High Strain Rate Tensile Testing of DOP-26 Iridium

    SciTech Connect

    Schneibel, Joachim H; Carmichael Jr, Cecil Albert; George, Easo P

    2007-11-01

    The iridium alloy DOP-26 was developed through the Radioisotope Power Systems Program in the Office of Nuclear Energy of the Department of Energy. It is used for clad vent set cups containing radioactive fuel in radioisotope thermoelectric generator (RTG) heat sources which provide electric power for spacecraft. This report describes mechanical testing results for DOP-26. Specimens were given a vacuum recrystallization anneal of 1 hour at 1375 C and tested in tension in orientations parallel and perpendicular to the rolling direction of the sheet from which they were fabricated. The tests were performed at temperatures ranging from room temperature to 1090 C and strain rates ranging from 1 x 10{sup -3} to 50 s{sup -1}. Room temperature testing was performed in air, while testing at elevated temperatures was performed in a vacuum better than 1 x 10{sup -4} Torr. The yield stress (YS) and the ultimate tensile stress (UTS) decreased with increasing temperature and increased with increasing strain rate. Between 600 and 1090 C, the ductility showed a slight increase with increasing temperature. Within the scatter of the data, the ductility did not depend on the strain rate. The reduction in area (RA), on the other hand, decreased with increasing strain rate. The YS and UTS values did not differ significantly for the longitudinal and transverse specimens. The ductility and RA values of the transverse specimens were marginally lower than those of the longitudinal specimens.

  2. Determination of the strain rate dependent thermal softening behavior of thermoplastic materials for crash simulations

    NASA Astrophysics Data System (ADS)

    Hopmann, Christian; Klein, Jan; Schöngart, Maximilian

    2016-03-01

    Thermoplastic materials are increasingly used as a light weight replacement for metal, especially in automotive applications. Typical examples are frontends and bumpers. The loads on these structures are very often impulsive, for example in a crash situation. A high rate of loading causes a high strain rate in the material which has a major impact on the mechanical behavior of thermoplastic materials. The stiffness as well as the rigidity of polymers increases to higher strain rates. The increase of the mechanical properties is superimposed at higher rates of loading by another effect which works reducing on stiffness and rigidity, the increase of temperature caused by plastic deformation. The mechanical behavior of thermoplastic materials is influenced by temperature opposing to strain rate. The stiffness and rigidity are decreased to higher values of temperature. The effect of thermal softening on thermoplastic materials is investigated at IKV. For this purpose high-speed tensile tests are performed on a blend, consisting of Polybutylenterephthalate (PBT) and Polycarbonate (PC). In preliminary investigations the effects of strain rate on the thermomechanical behavior of thermoplastic materials was studied by different authors. Tensile impact as well as split Hopkinson pressure bar (SHPB) tests were conducted in combination with high-speed temperature measurement, though, the authors struggled especially with temperature measurement. This paper presents an approach which uses high-speed strain measurement to transpire the link between strain, strain rate and thermal softening as well as the interdependency between strain hardening and thermal softening. The results show a superimposition of strain hardening and thermal softening, which is consistent to preliminary investigations. The advantage of the presented research is that the results can be used to calibrate damage and material models to perform mechanical simulations using Finite Element Analysis.

  3. Quasi-Static and High Strain Rate Compressive Response of Injection-Molded Cenosphere/HDPE Syntactic Foam

    NASA Astrophysics Data System (ADS)

    Bharath Kumar, B. R.; Singh, Ashish Kumar; Doddamani, Mrityunjay; Luong, Dung D.; Gupta, Nikhil

    2016-07-01

    High strain rate compressive properties of high-density polyethylene (HDPE) matrix syntactic foams containing cenosphere filler are investigated. Thermoplastic matrix syntactic foams have not been studied extensively for high strain rate deformation response despite interest in them for lightweight underwater vehicle structures and consumer products. Quasi-static compression tests are conducted at 10-4 s-1, 10-3 s-1 and 10-2 s-1 strain rates. Further, a split-Hopkinson pressure bar is utilized for characterizing syntactic foams for high strain rate compression. The compressive strength of syntactic foams is higher than that of HDPE resin at the same strain rate. Yield strength shows an increasing trend with strain rate. The average yield strength values at high strain rates are almost twice the values obtained at 10-4 s-1 for HDPE resin and syntactic foams. Theoretical models are used to estimate the effectiveness of cenospheres in reinforcing syntactic foams.

  4. Intermediate Strain-Rate Loading - Techniques and Applications

    SciTech Connect

    Chhabildas, L.C.; Reinhart, W.D.; Holland, K.G.

    1999-07-22

    A new test methodology is described which allows access to loading rates that lie between split Hopkinson bar and shock-loading techniques. Gas gun experiments combined with velocity interferometry techniques have been used to experimentally determine the intermediate strain-rate loading behavior of Coors AD995 alumina and Cercom silicon-carbide rods. Graded-density materials have been used as impactors; thereby eliminating the tension states generated by the radial stress components during the loading phase. Results of these experiments demonstrate that the time-dependent stress pulse generated during impact allows an efficient transition from the initial uniaxial strain loading to a uniaxial stress state as the stress pulse propagates through the rod. This allows access to intermediate loading rates over 5 x 10{sup 3}/s to a few times 10{sup 4}/s.

  5. Effect of Thermal Aging on the Mechanical Properties of Sn3.0Ag0.5Cu/Cu Solder Joints Under High Strain Rate Conditions

    NASA Astrophysics Data System (ADS)

    Nguyen, Van Luong; Kim, Ho-Kyung

    2015-07-01

    Shear tests with velocities between 0.5 m/s and 2.5 m/s were conducted to investigate the deformation characteristics of 0.76 mm lead-free Sn-3Ag-0.5Cu solder ball joints after thermal aging at 373 K up to 1000 h. A scanning electron microscope equipped with energy dispersive spectroscopy was then used to examine the fracture surfaces and microstructures of the solder joints. The results showed that the main failure mode of the solder joints was the brittle interfacial fracture mode with cleavage failure in the intermetallic compound (IMC). The maximum shear strength and the fracture toughness ( K C) of the solder joint decreased substantially after aging for the initial aging time, after which they decreased gradually with further aging or an increase in the strain rate. The evolution of the IMC layer when it was thicker and had coarser nodules due to thermal aging was the primary cause of the reduction in the shear strength and fracture toughness in this study.

  6. Distribution of strain rates in the Taiwan orogenic wedge

    NASA Astrophysics Data System (ADS)

    Mouthereau, F.; Fillon, C.; Ma, K.-F.

    2009-07-01

    To constrain the way Eurasian crust is accreted to the Taiwan orogenic wedge we investigate the present-day 3D seismogenic deformation field using the summation of 1129 seismic moment tensors of events ( Mw > 4) covering a period of 11 years (1995 to 2005). Based on the analysis of the principal strain-rate field, including dilatation and maximum shear rates, we distinguish four domains. Domain I comprises the Coastal Plain and the Western Foothills. It is mainly contractional in both the horizontal plane and in cross-section. Domain II comprises the eastern Western Foothills, the Hsuehshan Range and the Backbone Range. It is characterized by the highest contraction rates of 10 - 6 yr - 1 in association with area expansion in cross-section and area contraction in the horizontal plane. Domain III corresponds to the Central Range. It is characterized by area contraction in cross-section and area expansion in the horizontal plane. The maximum contractional axis is typically low and plunges ~ 30°E. Extension is larger, horizontal and strikes parallel to the axis of the mountain range. Domain IV corresponding to the Coastal Range and offshore Luzon Arc shows deformation patterns similar to domain II. This seismogenic strain-rate field, which is found in good agreement with the main features of the geodetic field, supports shortening within a thick wedge whose basal décollement is relatively flat and located in the middle-to-lower crust > 20 km. The east plunges of maximum strain-rate axes below the Central Range argue for the development of top-to-the-east transport of rocks resulting from the extrusion of the whole crust along west-dipping crustal-scale shear zones. The study of seismogenic strain rates argues that the initiation of subduction reversal has already started in the Taiwan collision domain.

  7. High strain rate properties of angle-ply composite laminates, part 3

    NASA Technical Reports Server (NTRS)

    Daniel, I. M.

    1991-01-01

    Angle-ply graphite/epoxy and graphite/S-glass/epoxy laminates were characterized in uniaxial tension at strain rates ranging from quasi-static to over 500 s(sup -1). Laminate ring specimens of +/-15(sub 2s), +/-22.5(sub 2s), +/-30(sub 2s), +/-45(sub 2s), +/-60(sub 2s), +/-67.5(sub 2s), and +/-75(sub 2s) degree layups were loaded under internal pressure. Results were presented in the form of stress-strain curves to failure. Properties determined included moduli, Poisson's ratios, strength, and ultimate strain. In all seven laminates for the two materials tested the modulus and strength increase with strain rate. The effect of strain rate varies with layup, being lowest for the fiber dominated +/-15(sub 2s) degree laminates and highest for the matrix dominated +/-75(sub 2s) degree laminates. The highest increments over the static values are 10 to 25 percent for the +/-15(sub 2s) degree layup and 200 to 275 percent for the +/-75(sub 2s) degree layup. Ultimate strains do not show any significant trends with strain rate. In almost all cases the ultimate strain values are within +/-20 percent of the mean value and in half of the cases the deviation from the mean are less than 10 percent.

  8. Implementation of Laminate Theory Into Strain Rate Dependent Micromechanics Analysis of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.

    2000-01-01

    A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to impact loads. Previously, strain rate dependent inelastic constitutive equations developed to model the polymer matrix were implemented into a mechanics of materials based micromechanics method. In the current work, the computation of the effective inelastic strain in the micromechanics model was modified to fully incorporate the Poisson effect. The micromechanics equations were also combined with classical laminate theory to enable the analysis of symmetric multilayered laminates subject to in-plane loading. A quasi-incremental trapezoidal integration method was implemented to integrate the constitutive equations within the laminate theory. Verification studies were conducted using an AS4/PEEK composite using a variety of laminate configurations and strain rates. The predicted results compared well with experimentally obtained values.

  9. Implementation of Fiber Substructuring Into Strain Rate Dependent Micromechanics Analysis of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.

    2001-01-01

    A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to impact loads. Previously, strain rate dependent inelastic constitutive equations developed to model the polymer matrix were incorporated into a mechanics of materials based micromechanics method. In the current work, the micromechanics method is revised such that the composite unit cell is divided into a number of slices. Micromechanics equations are then developed for each slice, with laminate theory applied to determine the elastic properties, effective stresses and effective inelastic strains for the unit cell. Verification studies are conducted using two representative polymer matrix composites with a nonlinear, strain rate dependent deformation response. The computed results compare well to experimentally obtained values.

  10. Strain rate, temperature and representative length scale influence on plasticity and yield stress in copper

    SciTech Connect

    Dupont, Virginie; Germann, Timothy C

    2011-01-18

    Shock compression of materials constitutes a complex process involving high strain rates, elevated temperatures and compression of the lattice. Materials properties are greatly affected by temperature, the representative length scale and the strain rate of the deformation. Experimentally, it is difficult to study the dynamic microscopic mechanisms that affect materials properties following high intensity shock loading, but they can be investigated using molecular dynamics (MD) simulations. Moreover, MD allows a better control over some parameters. We are using MD simulations to study the effect of the strain rate, representative length scale and temperature on the properties of metals during compression. A half-million-atom Cu sample is subjected to strain rates ranging from 10{sup 7} s{sup -1} to 10{sup 12} s{sup -1} at different temperatures ranging from 50K to 1500K. Single crystals as well as polycrystals are investigated. Plasticity mechanisms as well as the evolution of the micro- and macro-yield stress are observed. Our results show that the yield stress increases with increasing strain rate and decreasing temperature. We also show that the strain rate at which the transition between constant and increasing yield stress as a function of the temperature occurs increases with increasing temperature. Calculations at different grain sizes will give an insight into the grain size effect on the plasticity mechanisms and the yield stress.

  11. Measurement and Interpretation of High Strain Rates Near Bishkek, Kyrgyzstan

    NASA Astrophysics Data System (ADS)

    Hager, B. H.; Herring, T. A.; Bragin, V. D.; Zubovicz, A. V.; Molnar, P.; Hamburger, M. A.

    2001-12-01

    In 1996, scientists at the IVTRAN Poligon began frequent measurement of a 25-site GPS network around Bishkek, the capital of Kyrgyzstan. Most of the marks in this network are concentrated near the range front and are measured in campaigns ~6 times/year . Two continuously operating sites spanning the Chu basin to the north and south of Bishkek anchor the network. Outcrop is sparse within the network and most of the campaign sites are mounted on boulders in alluvium. The frequent measurements and dense spacing of the network allow us to judge the stability of the marks, which appears to be, in general, surprisingly good. The geodetic velocity field is dominated by north-south convergence of 3 mm/yr across the network. Most of the convergence occurs over a distance of about 10 km at the southern edge of the basin, resulting in a strain rate of ~0.3 microstrain/yr. This strain rate is high - comparable to that across the San Andreas fault in southern California. Interpretation of this high strain rate in terms of a conventional model using a dislocation in a uniform elastic halfspace would require a shallow locking depth, leading to an inference of relatively low moment release from the earthquakes expected to release the accumulated strain. An alternative explanation is that the strain concentration near the range front results not from a shallow locking depth but from the low elastic modulus of the sediments in the basin. If this model is correct, the rupture area, moment release, and seismic hazard are greater. The network is located just to the west of the surface rupture of the 1911 M ~8 Chon Kemin earthquake, which demonstrated that major earthquakes do occur in this region.

  12. Strain-rate dependence for Ni/Al hybrid foams

    NASA Astrophysics Data System (ADS)

    Jung, Anne; Larcher, Martin; Jirousek, Ondrej; Koudelka, Petr; Solomos, George

    2015-09-01

    Shock absorption often needs stiff but lightweight materials that exhibit a large kinetic energy absorption capability. Open-cell metal foams are artificial structures, which due to their plateau stress, including a strong hysteresis, can in principle absorb large amounts of energy. However, their plateau stress is too low for many applications. In this study, we use highly novel and promising Ni/Al hybrid foams which consist of standard, open-cell aluminium foams, where nanocrystalline nickel is deposited by electrodeposition as coating on the strut surface. The mechanical behaviour of cellular materials, including their behaviour under higher strain-rates, is governed by their microstructure due to the properties of the strut material, pore/strut geometry and mass distribution over the struts. Micro-inertia effects are strongly related to the microstructure. For a conclusive model, the exact real microstructure is needed. In this study a micro-focus computer tomography (μCT) system has been used for the analysis of the microstructure of the foam samples and for the development of a microstructural Finite Element (micro-FE) mesh. The microstructural FE models have been used to model the mechanical behaviour of the Ni/Al hybrid foams under dynamic loading conditions. The simulations are validated by quasi-static compression tests and dynamic split Hopkinson pressure bar tests.

  13. High strain rate behavior of pure metals at elevated temperature

    NASA Astrophysics Data System (ADS)

    Testa, Gabriel; Bonora, Nicola; Ruggiero, Andrew; Iannitti, Gianluca; Domenico, Gentile

    2013-06-01

    In many applications and technology processes, such as stamping, forging, hot working etc., metals and alloys are subjected to elevated temperature and high strain rate deformation process. Characterization tests, such as quasistatic and dynamic tension or compression test, and validation tests, such as Taylor impact and DTE - dynamic tensile extrusion -, provide the experimental base of data for constitutive model validation and material parameters identification. Testing material at high strain rate and temperature requires dedicated equipment. In this work, both tensile Hopkinson bar and light gas gun where modified in order to allow material testing under sample controlled temperature conditions. Dynamic tension tests and Taylor impact tests, at different temperatures, on high purity copper (99.98%), tungsten (99.95%) and 316L stainless steel were performed. The accuracy of several constitutive models (Johnson and Cook, Zerilli-Armstrong, etc.) in predicting the observed material response was verified by means of extensive finite element analysis (FEA).

  14. Modeling Void Nucleation in Metals at High Strain-rates

    NASA Astrophysics Data System (ADS)

    Belak, J.; Bales, G. S.; Glosli, J.

    1997-08-01

    Isotropic tension is simulated in nanoscale polycrystalline metals using large-scale molecular dynamics. The nanocrystalline metal is fabricated on the computer by growing randomly oriented grains from random positions or lattice positions in the simulation cell. Constant volume strain rates of 10^7 - 10^9 are considered for systems ranging from 10^5 - 10^7 atoms using an EAM interatomic potential. The spacing between voids for room temperature simulations is found to scale approximately as l ~ 0.005 * Cs / dotɛ, where Cs is the sound speed and dotɛ is the strain rate. The growth of small voids is simulated by cutting a void out of the simulation cell and repeating the isotropic expansion. Results are presented for several microstructures and void sizes and compared to macroscopic models.

  15. Strain and strain rate: An emerging technology in the perioperative period

    PubMed Central

    Malik, Vishwas; Subramaniam, Arun; Kapoor, Poonam Malhotra

    2016-01-01

    Newer noninvasive parameters are being used for perioperative detection of myocardial ischaemia. TDI and global strain rate are some of these parameters. TDI signal is a modification of the routine Doppler flow signal. It is obtained by using thresholding and filtering algorithms that reject echoes originating from the blood pool (by-passing the high pass filter). Set-Up of the machine by activating the TDI function allows decreasing the system gain using a low pass filter and eliminates the signal produced by blood flow. Doppler shift obtained from myocardial tissue motion are of higher amplitudes (reflectivity 40 dB higher) and move about 10 times slower than blood (velocity range: 0.06 to 0.24 m/s). Speckle tracking echocardiography (tissue tracking, 2D strain) utilizes routine gray-scale 2D echo images to calculate myocardial strain. Interactions of ultrasound with myocardium result in reflection and scattering. These interactions generate a finely gray-shaded, speckled pattern (acoustic marker). This speckled pattern is unique for each myocardial region and relatively stable throughout the cardiac cycle. Spatial and temporal image processing of acoustic speckles in both 2D and 3D allows for the calculation of myocardial velocity, strain, and Strain rate. PMID:26750682

  16. Strain and strain rate: An emerging technology in the perioperative period.

    PubMed

    Malik, Vishwas; Subramaniam, Arun; Kapoor, Poonam Malhotra

    2016-01-01

    Newer noninvasive parameters are being used for perioperative detection of myocardial ischaemia. TDI and global strain rate are some of these parameters. TDI signal is a modification of the routine Doppler flow signal. It is obtained by using thresholding and filtering algorithms that reject echoes originating from the blood pool (by-passing the high pass filter). Set-Up of the machine by activating the TDI function allows decreasing the system gain using a low pass filter and eliminates the signal produced by blood flow. Doppler shift obtained from myocardial tissue motion are of higher amplitudes (reflectivity 40 dB higher) and move about 10 times slower than blood (velocity range: 0.06 to 0.24 m/s). Speckle tracking echocardiography (tissue tracking, 2D strain) utilizes routine gray-scale 2D echo images to calculate myocardial strain. Interactions of ultrasound with myocardium result in reflection and scattering. These interactions generate a finely gray-shaded, speckled pattern (acoustic marker). This speckled pattern is unique for each myocardial region and relatively stable throughout the cardiac cycle. Spatial and temporal image processing of acoustic speckles in both 2D and 3D allows for the calculation of myocardial velocity, strain, and Strain rate.

  17. Effects of feeder space allocations during rearing, female strain, and feed increase rate from photostimulation to peak egg production on broiler breeder female performance.

    PubMed

    Leksrisompong, N; Romero-Sanchez, H; Oviedo-Rondón, E O; Brake, J

    2014-05-01

    A study was conducted to determine if there were differences in female broiler breeder performance of 2 strains that had been subjected to 2 feeder space allocations during the growing period followed by 2 feeding to peak programs. Ross 308 and 708 pullets were reared with a single feeding program to 23 wk of age and with 2 circumferential feeder space allocations (5.3 cm/female or 7.0 cm/female) and then assigned to 2 feed increase programs (slow or fast) from photostimulation to peak egg production. The flock was moved to the laying house with 8.8 cm/female of female feeder space and photostimulated at 23 wk of age when Ross 344 males were added to create 16 pens with 60 females and 7 males each in a 2 × 2 × 2 design. The fast feed increase program significantly increased female BW at 31 wk of age, which could have contributed to an increased female mortality during the summer weather of early lay. The 708 females with 5.3 cm/female feeder space produced smaller eggs at 28 and 30 wk of age. The 708 females exhibited better fertile hatchability than 308 females due to fewer late dead embryos. There were no differences in egg production, fertility, or fertile hatchability due to the main effects of feeding to peak program or growing feeder space, but the slow feed increase from photostimulation to peak production reduced cumulative mortality.

  18. Spall fracture in aluminium alloy at high strain rates

    NASA Astrophysics Data System (ADS)

    Joshi, K. D.; Rav, Amit; Sur, Amit; Kaushik, T. C.; Gupta, Satish C.

    2016-05-01

    Spall fracture strength and dynamic yield strength has been measured in 8mm thick target plates of aluminium alloy Al2024-T4 at high strain rates generated in three plate impact experiments carried out at impact velocities of 180 m/s, 370 m/s and 560m/s, respectively, using single stage gas gun facility. In each experiment, the free surface velocity history of the Al2024-T4 sample plate measured employing velocity interferometer system for any reflector (VISAR) is used to determine the spall strength and dynamic yield strength of this material. The spall strength of 1.11 GPa, 1.16 GPa and 1.43 GPa, determined from measured free surface velocity history of sample material in three experiments performed at impact velocity of 180 m/s, 370 m/s and 560 m/s, respectively, are higher than the quasi static value of 0.469 GPa and display almost linearly increasing trend with increasing impact velocity or equivalently with increasing strain rates. The average strain rates just ahead of the spall fracture are determined to be 1.9×10 4/s, 2.0×104/s and 2.5×104/s, respectively. The dynamic yield strength determined in the three experiments range from 0.383 GPa to 0.407 GPa, which is higher than the quasi static value of 0.324GPa.

  19. High-Speed Tomographic PIV Measurements of Strain Rate Properties in Turbulent Partially-Premixed Jet Flames

    NASA Astrophysics Data System (ADS)

    Coriton, Bruno; Frank, Jonathan H.

    2014-11-01

    The effects of combustion on the strain rate field in turbulent jets were studied using 10 kHz tomographic particle image velocimetry (TPIV). Measurements were performed in a series of turbulent partially-premixed jet flames with increasing jet Reynolds numbers and increasing probabilities of localized extinction. Properties of the strain rate were analyzed including the relative ratios of principal strain rates, the preferential alignment of the principal strain rates with vorticity, and the strain rate clustering and intermittency. Comparisons with measurements in turbulent air jets revealed the effects of heat release on the structure and dynamics of the strain rate field. This material is based upon work supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.

  20. Strain-rate sensitivity of the lateral collateral ligament of the knee.

    PubMed

    Bonner, Timothy J; Newell, Nicolas; Karunaratne, Angelo; Pullen, Andy D; Amis, Andrew A; M J Bull, Anthony; Masouros, Spyros D

    2015-01-01

    The material properties of ligaments are not well characterized at rates of deformation that occur during high-speed injuries. The aim of this study was to measure the material properties of lateral collateral ligament of the porcine stifle joint in a uniaxial tension model through strain rates in the range from 0.01 to 100/s. Failure strain, tensile modulus and failure stress were calculated. Across the range of strain rates, tensile modulus increased from 288 to 905 MPa and failure stress increased from 39.9 to 77.3 MPa. The strain-rate sensitivity of the material properties decreased as deformation rates increased, and reached a limit at approximately 1/s, beyond which there was no further significant change. In addition, time resolved microfocus small angle X-ray scattering was used to measure the effective fibril modulus (stress/fibril strain) and fibril to tissue strain ratio. The nanoscale data suggest that the contribution of the collagen fibrils towards the observed tissue-level deformation of ligaments diminishes as the loading rate increases. These findings help to predict the patterns of limb injuries that occur at different speeds and improve computational models used to assess and develop mitigation technology.

  1. Strain rates, stress markers and earthquake clustering (Invited)

    NASA Astrophysics Data System (ADS)

    Fry, B.; Gerstenberger, M.; Abercrombie, R. E.; Reyners, M.; Eberhart-Phillips, D. M.

    2013-12-01

    The 2010-present Canterbury earthquakes comprise a well-recorded sequence in a relatively low strain-rate shallow crustal region. We present new scientific results to test the hypothesis that: Earthquake sequences in low-strain rate areas experience high stress drop events, low-post seismic relaxation, and accentuated seismic clustering. This hypothesis is based on a physical description of the aftershock process in which the spatial distribution of stress accumulation and stress transfer are controlled by fault strength and orientation. Following large crustal earthquakes, time dependent forecasts are often developed by fitting parameters defined by Omori's aftershock decay law. In high-strain rate areas, simple forecast models utilizing a single p-value fit observed aftershock sequences well. In low-strain rate areas such as Canterbury, assumptions of simple Omori decay may not be sufficient to capture the clustering (sub-sequence) nature exhibited by the punctuated rise in activity following significant child events. In Canterbury, the moment release is more clustered than in more typical Omori sequences. The individual earthquakes in these clusters also exhibit somewhat higher stress drops than in the average crustal sequence in high-strain rate regions, suggesting the earthquakes occur on strong Andersonian-oriented faults, possibly juvenile or well-healed . We use the spectral ratio procedure outlined in (Viegas et al., 2010) to determine corner frequencies and Madariaga stress-drop values for over 800 events in the sequence. Furthermore, we will discuss the relevance of tomographic results of Reyners and Eberhart-Phillips (2013) documenting post-seismic stress-driven fluid processes following the three largest events in the sequence as well as anisotropic patterns in surface wave tomography (Fry et al., 2013). These tomographic studies are both compatible with the hypothesis, providing strong evidence for the presence of widespread and hydrated regional

  2. A parametric study on the dynamic behavior of porous bronze at various strain rates

    NASA Astrophysics Data System (ADS)

    Zhang, Yue; Hu, Jianxing; Lei, Jianyin; Wang, Zhihua; Zhao, Longmao

    2016-10-01

    An experimental investigation on the porous bronze at various strain rates is firstly carried out in this study to explore the effects of relative density and strain rate in the mechanical behavior. Furthermore, a multi-parameter constitutive model of describing the rate-dependent behavior for porous bronze is developed. The parameters in the constitutive model are density dependent, and the specific forms of these parameters as functions of relative density are obtained. It can be concluded from the test results and constitutive model that the high relative density leads to increase in yield strength and energy absorption capacity of the materials and the strain rate also has positive effects on the yield strength and energy absorption capacity of porous bronze.

  3. Strain Rate Behavior of HTPB-Based Magnetorheological Materials

    NASA Astrophysics Data System (ADS)

    Stoltz, Chad; Seminuk, Kenneth; Joshi, Vasant

    2013-06-01

    It is of particular interest to determine whether the mechanical properties of binder systems can be manipulated by adding ferrous or Magnetostrictive particulates. Strain rate response of two HTPB/Fe (Hydroxyl-terminated Polybutadiene/Iron) compositions under electromagnetic fields has been investigated using a Split Hopkinson Pressure bar arrangement equipped with aluminum bars. Two HTPB/Fe compositions were developed, the first without plasticizer and the second containing plasticizer. Samples were tested with and without the application of a 0.01 Tesla magnetic field coil. Strain gauge data taken from the Split Hopkinson Pressure bar has been used to determine what mechanical properties were changed by inducing a mild electromagnetic field onto each sample. The data reduction method to obtain stress-strain plots included dispersion corrections for deciphering minute changes due to compositional alterations. Data collected from the Split Hopkinson Pressure bar indicate changes in the Mechanical Stress-Strain curves and suggest that the impedance of a binder system can be altered by means of a magnetic field. We acknowledge the Defense Threat Reduction Agency for funding.

  4. Evolution of plastic anisotropy for high-strain-rate computations

    SciTech Connect

    Schiferl, S.K.; Maudlin, P.J.

    1994-12-01

    A model for anisotropic material strength, and for changes in the anisotropy due to plastic strain, is described. This model has been developed for use in high-rate, explicit, Lagrangian multidimensional continuum-mechanics codes. The model handles anisotropies in single-phase materials, in particular the anisotropies due to crystallographic texture--preferred orientations of the single-crystal grains. Textural anisotropies, and the changes in these anisotropies, depend overwhelmingly no the crystal structure of the material and on the deformation history. The changes, particularly for a complex deformations, are not amenable to simple analytical forms. To handle this problem, the material model described here includes a texture code, or micromechanical calculation, coupled to a continuum code. The texture code updates grain orientations as a function of tensor plastic strain, and calculates the yield strength in different directions. A yield function is fitted to these yield points. For each computational cell in the continuum simulation, the texture code tracks a particular set of grain orientations. The orientations will change due to the tensor strain history, and the yield function will change accordingly. Hence, the continuum code supplies a tensor strain to the texture code, and the texture code supplies an updated yield function to the continuum code. Since significant texture changes require relatively large strains--typically, a few percent or more--the texture code is not called very often, and the increase in computer time is not excessive. The model was implemented, using a finite-element continuum code and a texture code specialized for hexagonal-close-packed crystal structures. The results for several uniaxial stress problems and an explosive-forming problem are shown.

  5. Volume dilatation in a polycarbonate blend at varying strain rates

    NASA Astrophysics Data System (ADS)

    Hiermaier, S.; Huberth, F.

    2012-05-01

    Impact loaded polymers show a variety of strain-rate dependent mechanical properties in their elastic, plastic and failure behaviour. In contrast to purely crystalline materials, the volume of polymeric materials can significantly change under irreversible deformations. In this paper, uni-axial tensile tests were performed in order to measure the dilatation in the Polycarbonate-Acrylnitril-Butadien-Styrol (PC-ABS) Bayblend T65. The accumulation of dilatation was measured at deformation speeds of 0.1 and 500 [ mm/ s]. Instrumented with a pair of two high-speed cameras, volume segments in the samples were observed. The change in volume was quantified as relation between the deformed and initial volumes of the segments. It was observed that the measured dilatations are of great significance for the constitutive models. This is specifically demonstrated through comparisons of stress-strain relations derived from the two camera-perspectives with isochoric relations based on single-surface observations of the same experiments.

  6. High- and low-strain rate compression properties of several energetic material composites as a function of strain rate and temperature

    SciTech Connect

    Gray, G.T. III; Idar, D.J.; Blumenthal, W.R.; Cady, C.M.; Peterson, P.D.

    1998-12-31

    High- and low-strain rate compression data were obtained on several different energetic composites: PBX 9501, X0242-92-4-4, PBXN-9, as well as the polymeric binder used in PBX 9501 and X0242-92-4-4 composites. The effects of energetic-to-binder ratios, different binder systems, and different energetic formulations were investigated. All the energetic composites exhibit increasing elastic modulus, E, maximum flow stresses, {sigma}{sub m}, and strain-at-maximum stress, {var_epsilon}{sub m}, with increasing strain rate at ambient temperature. PBX 9501 displays marginally higher ultimate flow strength than X0242-92-4-4, and significantly higher ultimate compressive strength than PBXN-9 at quasi-static and dynamic strain rates. The failure mode of PBX 9501 and X0242-92-4-4 under high-rate loading changes from a mixture of ductile binder tearing and transgranular cleavage and cracking of the HMX when tested at 20 C to transgranular brittle HMX cleavage and glassy fracture of the binder at {minus}40 C.

  7. Mechanical Behavior of Glidcop Al-15 at High Temperature and Strain Rate

    NASA Astrophysics Data System (ADS)

    Scapin, M.; Peroni, L.; Fichera, C.

    2014-05-01

    Strain rate and temperature are variables of fundamental importance for the definition of the mechanical behavior of materials. In some elastic-plastic models, the effects, coming from these two quantities, are considered to act independently. This approach should, in some cases, allow to greatly simplify the experimental phase correlated to the parameter identification of the material model. Nevertheless, in several applications, the material is subjected to dynamic load at very high temperature, as, for example, in case of machining operation or high energy deposition on metals. In these cases, to consider the effect of strain rate and temperature decoupled could not be acceptable. In this perspective, in this work, a methodology for testing materials varying both strain rate and temperature was described and applied for the mechanical characterization of Glidcop Al-15, a copper-based composite reinforced with alumina dispersion, often used in nuclear applications. The tests at high strain rate were performed using the Hopkinson Bar setup for the direct tensile tests. The heating of the specimen was performed using an induction coil system and the temperature was controlled on the basis of signals from thermocouples directly welded on the specimen surface. Varying the strain rate, Glidcop Al-15 shows a moderate strain-rate sensitivity at room temperature, while it considerably increases at high temperature: material thermal softening and strain-rate hardening are strongly coupled. The experimental data were fitted using a modified formulation of the Zerilli-Armstrong model able to reproduce this kind of behavior with a good level of accuracy.

  8. Stress state and strain rate dependence of the human placenta.

    PubMed

    Weed, Benjamin C; Borazjani, Ali; Patnaik, Sourav S; Prabhu, R; Horstemeyer, M F; Ryan, Peter L; Franz, Thomas; Williams, Lakiesha N; Liao, Jun

    2012-10-01

    Maternal trauma (MT) in automotive collisions is a source of injury, morbidity, and mortality for both mothers and fetuses. The primary associated pathology is placental abruption in which the placenta detaches from the uterus leading to hemorrhaging and termination of pregnancy. In this study, we focused on the differences in placental tissue response to different stress states (tension, compression, and shear) and different strain rates. Human placentas were obtained (n = 11) for mechanical testing and microstructure analysis. Specimens (n = 4+) were tested in compression, tension, and shear, each at three strain rates (nine testing protocols). Microstructure analysis included scanning electron microscopy, histology, and interrupted mechanical tests to observe tissue response to various loading states. Our data showed the greatest stiffness in tension, followed by compression, and then by shear. The study concludes that mechanical behavior of human placenta tissue (i) has a strong stress state dependence and (ii) behaves in a rate dependent manner in all three stress states, which had previously only been shown in tension. Interrupted mechanical tests revealed differences in the morphological microstructure evolution that was driven by the kinematic constraints from the different loading states. Furthermore, these structure-property data can be used to develop high fidelity constitutive models for MT simulations. PMID:22581478

  9. Strain-Rate Frequency Superposition (SRFS) - A rheological probe of structural relaxation in soft materials

    NASA Astrophysics Data System (ADS)

    Wyss, Hans M.

    2007-03-01

    The rheological properties of soft materials such as concentrated suspensions, emulsions, or foams often exhibit surprisingly universal linear and nonlinear features. Here we show that their linear and nonlinear viscoelastic responses can be unified in a single picture by considering the effect of the strain-rate amplitude on the structural relaxation of the material. We present a new approach to oscillatory rheology, which keeps the strain rate amplitude fixed as the oscillation frequency is varied. This allows for a detailed study of the effects of strain rate on the structural relaxation of soft materials. Our data exhibits a characteristic scaling, which isolates the response due to structural relaxation, even when it occurs at frequencies too low to be accessible with standard techniques. Our approach is reminiscent of a technique called time-temperature superposition (TTS), where rheological curves measured at different temperatures are shifted onto a single master curve that reflects the viscoelastic behavior in a dramatically extended range of frequencies. By analogy, we call our approach strain-rate frequency superposition (SRFS). Our experimental results show that nonlinear viscoelastic measurements contain useful information on the slow relaxation dynamics of soft materials. The data indicates that the yielding behavior of soft materials directly probes the structural relaxation process itself, shifted towards higher frequencies by an applied strain rate. This suggests that SRFS will provide new insight into the physical mechanisms that govern the viscoelastic response of a wide range of soft materials.

  10. Strain Rate Sensitivity of Epoxy Resin in Tensile and Shear Loading

    NASA Technical Reports Server (NTRS)

    Gilat, Amos; Goldberg, Robert K.; Roberts, Gary D.

    2005-01-01

    The mechanical response of E-862 and PR-520 resins is investigated in tensile and shear loadings. At both types of loading the resins are tested at strain rates of about 5x10(exp 5), 2, and 450 to 700 /s. In addition, dynamic shear modulus tests are carried out at various frequencies and temperatures, and tensile stress relaxation tests are conducted at room temperature. The results show that the toughened PR-520 resin can carry higher stresses than the untoughened E-862 resin. Strain rate has a significant effect on the response of both resins. In shear both resins show a ductile response with maximum stress that is increasing with strain rate. In tension a ductile response is observed at low strain rate (approx. 5x10(exp 5) /s), and brittle response is observed at the medium and high strain rates (2, and 700 /s). The hydrostatic component of the stress in the tensile tests causes premature failure in the E-862 resin. Localized deformation develops in the PR-520 resin when loaded in shear. An internal state variable constitutive model is proposed for modeling the response of the resins. The model includes a state variable that accounts for the effect of the hydrostatic component of the stress on the deformation.

  11. Atomic Scale Modeling of High Strain Rate Deformation and Failure of HCP Metals

    NASA Astrophysics Data System (ADS)

    Mackenchery, Karoon; Agarwal, Garvit; Dongare, Avinash

    2015-06-01

    A fundamental understanding of the microstructure effects on the defect evolution at the atomic resolution and the related contribution to plasticity at the macro-scales is needed to obtain a reliable performance of metallic materials in extreme environments. Large-scale molecular dynamics simulations are carried out to characterize the dynamic evolution of defect/damage structures during the deformation and failure behavior of HCP (Mg, Ti) metallic systems (single crystal and nanocrystalline at high strain rates as well as under shock loading conditions. The evolution of various types of dislocations, twins, faults, etc. and the related deformation and failure response (nucleation and growth of voids/cracks) will be discussed. The effects of strain rates on relationships between the microstructure and the strength of these materials at high strain rates and the underlying micromechanisms related to deformation and failure will be discussed.

  12. Evaluation of a theory for pressure-strain rate

    NASA Technical Reports Server (NTRS)

    Weinstock, J.; Shariff, K.

    1987-01-01

    A theoretical expression for the slow part (the nonlinear fluctuation part) of the pressure-strain rate is compared with simulations of anisotropic homogeneous flows. The objective is to determine the quantitative accuracy of the theory and to test its prediction that the generalized Rotta coefficient, a non-dimensionalized ratio of slow term to the Reynolds stress anisotropy, varies with direction and can be negative. Comparisons are made between theoretical and simulation values of the slow term itself and of the generalized Rotta coefficients. The implications of the comparison for two-point closure theories and for Reynolds stress modeling are pointed out.

  13. Evolution of the martensitic transformation in shape memory alloys under high strain rates

    NASA Astrophysics Data System (ADS)

    Saletti, D.; Pattofatto, S.; Zhao, H.

    2010-06-01

    The specific properties of the shape memory alloys are mainly due to the martensitic transformation occuring in the material when mechanical or thermal loadings are applied. Here, the effect of strain rate on the transformation on an NiTi SMA is studied in tension. Different tests were performed at different strain rates in the range of 0,0001 /s to 15 /s. Two distinct methods were used to measure the extension rate of the martensitic phase region in the specimen: digital image correlation technique and infrared thermography (IR during quasi-static tensile tests only). For the dynamic tensile tests, a Split Hopkinson Tensile Bar set-up was used with a fast camera recording at 45’000 fps. A superimposition of DIC and IR measurements in time and space can be done during quasi-static tests and results show that the temperature peak, as expected, follows the transformation front. As a consequence of the former validation of the DIC procedure, the velocity of the transformation front at high strain rate is deduced from space-time figures. As a conclusion, in the range of strain rates investigated in this paper, no strain rate sensitivity is observed for dynamics of extension of the transformation region.

  14. Measurement of strain and strain rate in embryonic chick heart using spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Dou, Shidan; Suo, Yanyan; Liang, Chengbo; Wang, Yi; Zhao, Yuqian; Liu, Jian; Xu, Tao; Wang, Ruikang; Ma, Zhenhe

    2016-03-01

    It is important to measure embryonic heart myocardial wall strain and strain rate for understanding the mechanisms of embryonic heart development. Optical coherence tomography (OCT) can provide depth resolved images with high spatial and temporal resolution, which makes it have the potential to reveal the complex myocardial activity in the early stage embryonic heart. We develop a novel method to measure strain in embryonic chick heart based on spectral domain OCT images and subsequent image processing. We perform 4D(x,y,z,t) scanning on the outflow tract (OFT) of chick embryonic hearts in HH18 stage (~3 days of incubation). Only one image sequence acquired at the special position is selected based on the Doppler blood flow information where the probe beam penetrates through the OFT perpendicularly. For each image of the selected sequence, the cross-section of the myocardial wall can be approximated as an annulus. The OFT is segmented with a semi-automatic boundary detection algorithm, thus the area and mean circumference of the annular myocardial wall can be achieved. The myocardial wall thickness was calculated using the area divided by the mean circumference, and then the strain was obtained. The results demonstrate that OCT can be a useful tool to describe the biomechanical characteristics of the embryonic heart.

  15. High strain rate compressive characterization of aluminum alloy/fly ash cenosphere composites

    NASA Astrophysics Data System (ADS)

    Luong, Dung D.; Gupta, Nikhil; Daoud, Atef; Rohatgi, Pradeep K.

    2011-02-01

    The strain rate dependence of compressive response is determined for aluminum alloy/hollow fly ash cenosphere composites. A4032 alloy is used as the matrix material. Quasi-static and high strain rate compression tests are conducted on the matrix alloy and the composite. A split-Hopkinson pressure bar is used for high strain rate testing. While the matrix alloy does not show any appreciable strain rate sensitivity, the composite shows higher strength at higher strain rates. The energy absorption capability of A4032/fly ash cenosphere composites is found to be higher at higher strain rates.

  16. Strain-Rate-Free Diffusion Flames: Initiation, Properties, and Quenching

    NASA Technical Reports Server (NTRS)

    Fendell, Francis; Rungaldier, Harald; Gokoglu, Suleyman; Schultz, Donald

    1997-01-01

    For about a half century, the stabilization of a steady planar deflagration on a heat-sink-type flat-flame burner has been of extraordinary service for the theoretical modeling and diagnostic probing of combusting gaseous mixtures. However, most engineering devices and most unwanted fire involve the burning of initially unmixed reactants. The most vigorous burning of initially separated gaseous fuel and oxidizer is the diffusion flame. In this useful idealization (limiting case), the reactants are converted to product at a mathematically thin interface, so no interpenetration of fuel and oxidizer occurs. This limit is of practical importance because it often characterizes the condition of optimal performance (and sometimes environmentally objectionable operation) of a combustor. A steady planar diffusion flame is most closely approached in the laboratory in the counterflow apparatus. The utility of this simple-strain-rate flow for the modeling and probing of diffusion flames was noted by Pandya and Weinberg 35 years ago, though only in the last decade or so has its use become internationally common place. However, typically, as the strain rate a is reduced below about 20 cm(exp -1), and the diffusion-flame limit (reaction rate much faster than the flow rate) is approached, the burning is observed to become unstable in earth gravity. The advantageous steady planar flow is not available in the diffusion-flame limit in earth gravity. This is unfortunate because the typical spatial scale in a counterflow is (k/a)(sup 1/2), where k denotes a characteristic diffusion coefficient; thus, the length scale becomes large, and the reacting flow is particularly amenable to diagnostic probing, as the diffusion-flame limit is approached. The disruption of planar symmetry is owing the fact that, as the strain rate a decreases, the residence time (l/a) of the throughput in the counterflow burner increases. Observationally, when the residence time exceeds about 50 msec, the

  17. Computational modeling of dynamic mechanical properties of pure polycrystalline magnesium under high loading strain rates

    NASA Astrophysics Data System (ADS)

    Li, Qizhen

    2015-09-01

    Computational simulations were performed to investigate the dynamic mechanical behavior of pure polycrystalline magnesium under different high loading strain rates with the values of 800, 1000, 2000, and 3600 s-1. The Johnson-Cook model was utilized in the simulations based on finite element modeling. The results showed that the simulations provided well-matched predictions of the material behavior such as the strain rate-time history, the stress-strain curve, and the temperature increase. Under high loading strain rates, the tested material experienced linear strain hardening at the early stage of plastic deformation, increased strain hardening at the intermediate plastic deformation region, and decreased strain hardening at the region before fracture. The strain hardening rates for the studied high loading strain rate cases do not vary much with the change of strain rates.

  18. A numerical basis for strain-gradient plasticity theory: Rate-independent and rate-dependent formulations

    NASA Astrophysics Data System (ADS)

    Nielsen, K. L.; Niordson, C. F.

    2014-02-01

    A numerical model formulation of the higher order flow theory (rate-independent) by Fleck and Willis [2009. A mathematical basis for strain-gradient plasticity theory - part II: tensorial plastic multiplier. Journal of the Mechanics and Physics of Solids 57, 1045-1057.], that allows for elastic-plastic loading/unloading and the interaction of multiple plastic zones, is proposed. The predicted model response is compared to the corresponding rate-dependent version of visco-plastic origin, and coinciding results are obtained in the limit of small strain-rate sensitivity. First, (i) the evolution of a single plastic zone is analyzed to illustrate the agreement with earlier published results, whereafter examples of (ii) multiple plastic zone interaction, and (iii) elastic-plastic loading/unloading are presented. Here, the simple shear problem of an infinite slab constrained between rigid plates is considered, and the effect of strain gradients, strain hardening and rate sensitivity is brought out. For clarity of results, a 1D model is constructed following a procedure suitable for generalization to 2D and 3D.

  19. Influence of temperature and strain rate on the compressive behavior of PMMA and polycarbonate polymers

    SciTech Connect

    Cady, C. M.; Lopez, M. F.; Gray, G. T. , III; Idar, D. J.; Blumenthal, W. R.

    2001-01-01

    Compression stress-strain measurements have been made on commercial polymethylmethacrylate (PMMA) and polycarbonate (PC) polymers as a function of tcmperature (-197 C to 220 C) and strain rate. A split-Hopkinson-pressure bar (SJIPU) was used to achieve strain rates of about 2500 s-' and a servohydraulic tester was used for lower strain rate testing (0.001 to 5 s-'). The mechanical response of these transparent polymers is quite different. The strength of PC is weakly dependent on strain rate, only moderately dependent on temperature, and remains ductile to -197OC. In contrast, the strength of PMMA is linearly dependent on temperature and strongly dependent on strain rate. Significantly, PMMA develops cracking and fails in compression with little ductility ( 7 4 % total strain) at either low strain rates and very low temperatures (-197OC) or at high strain rates and temperatures very near ambient.

  20. Strain-rate-dependent model for the dynamic compression of elastoplastic spheres

    NASA Astrophysics Data System (ADS)

    Burgoyne, Hayden A.; Daraio, Chiara

    2014-03-01

    We present a force-displacement contact model for the compressive loading of elastoplastic spheres. This model builds from the well known Hertz contact law for elastic, quasistatic compression to incorporate a material's strain-rate-dependent plasticity in order to describe collisions between particles. In the quasistatic regime, finite-element analysis is used to derive an empirical function of the material properties. A Johnson-Cook strain rate dependence is then included into the model to study dynamic effects. We validate the model using split Hopkinson bar experiments and show that the model can accurately simulate the force-displacement response of strain-rate-dependent elastoplastic spheres during dynamic compression and unloading.

  1. Strain-rate-dependent model for the dynamic compression of elastoplastic spheres.

    PubMed

    Burgoyne, Hayden A; Daraio, Chiara

    2014-03-01

    We present a force-displacement contact model for the compressive loading of elastoplastic spheres. This model builds from the well known Hertz contact law for elastic, quasistatic compression to incorporate a material's strain-rate-dependent plasticity in order to describe collisions between particles. In the quasistatic regime, finite-element analysis is used to derive an empirical function of the material properties. A Johnson-Cook strain rate dependence is then included into the model to study dynamic effects. We validate the model using split Hopkinson bar experiments and show that the model can accurately simulate the force-displacement response of strain-rate-dependent elastoplastic spheres during dynamic compression and unloading. PMID:24730833

  2. Patterns of Stress and Strain Rate in Southern Africa

    NASA Astrophysics Data System (ADS)

    Ben-Avraham, Z.; Bird, P.; Schubert, G.; Andreoli, M.; Viola, G.

    2005-12-01

    The southward propagation of the East Africa rift presents an opportunity to study incipient plate-boundary formation. We tabulate orientation data which confirm the province of NW-SE-directed most-compressive horizontal principal stress ("Wegener stress anomaly") earlier tentatively attributed to ridge-push. We use thin-shell finite-element models with realistic rheology to test three causes of stress: (1) lateral variations in density moment; (2) resistance of unbroken lithosphere to relative plate rotation; and (3) stress concentration ahead of a crack tip. Models in which stress is due primarily to variations in density moment are relatively unsuccessful in their predictions (59~73% incorrect regimes; 32~40° azimuth errors). Models in which Africa-Somalia spreading is regulated at realistic rates by remote boundary conditions are more accurate (18~41% incorrect regimes; 25~35° azimuth errors). Treating the East Africa rift as a frictionless crack degrades the fit in either case. This suggests that the "Wegener stress anomaly" is caused primarily by the relative rotation between the Somalia and Africa plates. The East Africa rift north of 21°S may be weakened by strain, but must have residual friction >0.1. The expected greater strength of oceanic lithosphere is likely to cause dramatic stress increases, reorientations, and regime changes offshore. The predicted strain rate map has high rates along the rift, curving at 12°S into a western arc through Angola-Namibia-South Africa. Seismic hazard in Namibia may be greater than the instrumental catalog suggests. However, a number of unfit data indicate that these models represent only a first step.

  3. Strain Rate and Anisotropic Microstructure Dependent Mechanical Behaviors of Silkworm Cocoon Shells

    PubMed Central

    Xu, Jun; Zhang, Wen; Gao, Xiang; Meng, Wanlin; Guan, Juan

    2016-01-01

    Silkworm cocoons are multi-layered composite structures comprised of high strength silk fiber and sericin, and their mechanical properties have been naturally selected to protect pupas during metamorphosis from various types of external attacks. The present study attempts to gain a comprehensive understanding of the mechanical properties of cocoon shell materials from wild silkworm species Antheraea pernyi under dynamic loading rates. Five dynamic strain rates from 0.00625 s-1 to 12.5 s-1 are tested to show the strain rate sensitivity of the cocoon shell material. In the meantime, the anisotropy of the cocoon shell is considered and the cocoon shell specimens are cut along 0°, 45° and 90° orientation to the short axis of cocoons. Typical mechanical properties including Young’s modulus, yield strength, ultimate strength and ultimate strain are extracted and analyzed from the stress-strain curves. Furthermore, the fracture morphologies of the cocoon shell specimens are observed under scanning electron microscopy to help understand the relationship between the mechanical properties and the microstructures of the cocoon material. A discussion on the dynamic strain rate effect on the mechanical properties of cocoon shell material is followed by fitting our experimental results to two previous models, and the effect could be well explained. We also compare natural and dried cocoon materials for the dynamic strain rate effect and interestingly the dried cocoon shells show better overall mechanical properties. This study provides a different perspective on the mechanical properties of cocoon material as a composite material, and provides some insight for bio-inspired engineering materials. PMID:26939063

  4. Strain Rate and Anisotropic Microstructure Dependent Mechanical Behaviors of Silkworm Cocoon Shells.

    PubMed

    Xu, Jun; Zhang, Wen; Gao, Xiang; Meng, Wanlin; Guan, Juan

    2016-01-01

    Silkworm cocoons are multi-layered composite structures comprised of high strength silk fiber and sericin, and their mechanical properties have been naturally selected to protect pupas during metamorphosis from various types of external attacks. The present study attempts to gain a comprehensive understanding of the mechanical properties of cocoon shell materials from wild silkworm species Antheraea pernyi under dynamic loading rates. Five dynamic strain rates from 0.00625 s-1 to 12.5 s-1 are tested to show the strain rate sensitivity of the cocoon shell material. In the meantime, the anisotropy of the cocoon shell is considered and the cocoon shell specimens are cut along 0°, 45° and 90° orientation to the short axis of cocoons. Typical mechanical properties including Young's modulus, yield strength, ultimate strength and ultimate strain are extracted and analyzed from the stress-strain curves. Furthermore, the fracture morphologies of the cocoon shell specimens are observed under scanning electron microscopy to help understand the relationship between the mechanical properties and the microstructures of the cocoon material. A discussion on the dynamic strain rate effect on the mechanical properties of cocoon shell material is followed by fitting our experimental results to two previous models, and the effect could be well explained. We also compare natural and dried cocoon materials for the dynamic strain rate effect and interestingly the dried cocoon shells show better overall mechanical properties. This study provides a different perspective on the mechanical properties of cocoon material as a composite material, and provides some insight for bio-inspired engineering materials. PMID:26939063

  5. Interlaminar stress and strain energy release rate predictions in composites by singular fitting

    NASA Astrophysics Data System (ADS)

    Armanios, Erian A.

    A singular fitting method is developed in order to predict the interlaminar stress distribution in a quasi-isotropic double cracked-lap-shear configuration made of graphite/epoxy material. The method is based on an improved finite element scheme using the stress predicted by a constant strain element. The oscillatory component of the stress singularity is investigated, and the order of the singularity is estimated from a logarithmic plot of interlaminar shear stress data. The effect of the mesh size on the stress and displacement distributions is isolated. The strain energy release rate components are predicted based on the singular stress distribution and its associated displacement field. The effect of smearing the material properties on the accuracy of the strain energy release rates and interlaminar stresses is investigated. Results are compared with the finite element crack-closure method. A comparison of the stress-intensity factor with an analytical solution is provided.

  6. Strain rate viscoelastic analysis of soft and highly hydrated biomaterials

    PubMed Central

    Tirella, A; Mattei, G; Ahluwalia, A

    2014-01-01

    Measuring the viscoelastic behavior of highly hydrated biological materials is challenging because of their intrinsic softness and labile nature. In these materials, it is difficult to avoid prestress and therefore to establish precise initial stress and strain conditions for lumped parameter estimation using creep or stress-relaxation (SR) tests. We describe a method ( or epsilon dot method) for deriving the viscoelastic parameters of soft hydrated biomaterials which avoids prestress and can be used to rapidly test degradable samples. Standard mechanical tests are first performed compressing samples using different strain rates. The dataset obtained is then analyzed to mathematically derive the material's viscoelastic parameters. In this work a stable elastomer, polydimethylsiloxane, and a labile hydrogel, gelatin, were first tested using the, in parallel SR was used to compare lumped parameter estimation. After demonstrating that the elastic parameters are equivalent and that the estimation of short-time constants is more precise using the proposed method, the viscoelastic behavior of porcine liver was investigated using this approach. The results show that the constitutive parameters of hepatic tissue can be quickly quantified without the application of any prestress and before the onset of time-dependent degradation phenomena. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3352–3360, 2014 PMID:23946054

  7. High strain rate and high temperature behaviour of metallic materials for jet engine turbine containment

    NASA Astrophysics Data System (ADS)

    Gálvez, F.; Cendón, D.; Enfedaque, A.; Sánchez-Gálvez, V.

    2006-08-01

    This work presents a study on the mechanical characterisation of the materials involved in air jet engine turbines. The final objective is to analyse the phenomenon of a turbine blade off failure, to verify the requirements of the case containment. The materials in the turbine are under high temperatures, ranging from 400circC to 800circC and when the fail of the blade occurs if impacts against the case, reaching strain rates up to 103 s - 1. To obtain the behaviour of the materials, testing at high strain rate and high temperature at one time is necessary. The experimental set-up used was a split Hopkinson pressure bar, with a high temperature furnace adapted. The bars used on the device were high strength nickel alloys with a cooling system to decrease the temperature of the measurement devices. The effect of wave dispersion due to the temperature gradient has been also studied to correct the measurements if necessary. The material tested has been the FV535 stainless steel used on the case. The full stress-strain curves at different temperatures and at strain rates up to 103 s-1 have been obtained. The experimental results show a marked influence of the strain rate and the temperature that cannot be neglected. The Johnson-Cook material model has been used to fit the results of the material tests.

  8. Intermediate strain-rate loading experiments -- Techniques and applications

    SciTech Connect

    Chhabildas, L.C.; Reinhart, W.D.

    1998-09-01

    Gas guns and velocity interferometric techniques have been used to determine the loading behavior of AD995 alumina rods 19 mm in diameter by 75 mm and 150 mm long, respectively. Graded-density materials were used to impact both bare and sleeved alumina rods while the velocity interferometer was used to monitor the axial-velocity of the free end of the rods. Results of these experiments demonstrate that (1) a time-dependent stress pulse generated during impact allows an efficient transition from the initial uniaxial strain loading to a uniaxial stress state as the stress pulse propagates through the rod, and (2) the intermediate loading rates obtained in this configuration lie between split Hopkinson bar and shock-loading techniques.

  9. Potential pitfalls of strain rate imaging: angle dependency

    NASA Technical Reports Server (NTRS)

    Castro, P. L.; Greenberg, N. L.; Drinko, J.; Garcia, M. J.; Thomas, J. D.

    2000-01-01

    Strain Rate Imaging (SRI) is a new echocardiographic technique that allows for the real-time determination of myocardial SR, which may be used for the early and accurate detection of coronary artery disease. We sought to study whether SR is affected by scan line alignment in a computer simulation and an in vivo experiment. Through the computer simulation and the in vivo experiment we generated and validated safe scanning sectors within the ultrasound scan sector and showed that while SRI will be an extremely valuable tool in detecting coronary artery disease there are potential pitfalls for the unwary clinician. Only after accounting for these affects due to angle dependency, can clinicians utilize SRI's potential as a valuable tool in detecting coronary artery disease.

  10. Microscale consolidation analysis of relaxation behavior of single living chondrocytes subjected to varying strain-rates.

    PubMed

    Nguyen, Trung Dung; Oloyede, Adekunle; Singh, Sanjleena; Gu, YuanTong

    2015-09-01

    Besides the elastic stiffness, the relaxation behavior of single living cells is also of interest of various researchers when studying cell mechanics. It is hypothesized that the relaxation response of the cells is governed by both intrinsic viscoelasticity of the solid phase and fluid-solid interactions mechanisms. There are a number of mechanical models have been developed to investigate the relaxation behavior of single cells. However, there is lack of model enable to accurately capture both of the mechanisms. Therefore, in this study, the porohyperelastic (PHE) model, which is an extension of the consolidation theory, combined with inverse Finite Element Analysis (FEA) technique was used at the first time to investigate the relaxation response of living chondrocytes. This model was also utilized to study the dependence of relaxation behavior of the cells on strain-rates. The stress-relaxation experiments under the various strain-rates were conducted with the Atomic Force Microscopy (AFM). The results have demonstrated that the PHE model could effectively capture the stress-relaxation behavior of the living chondrocytes, especially at intermediate to high strain-rates. Although this model gave some errors at lower strain-rates, its performance was acceptable. Therefore, the PHE model is properly a promising model for single cell mechanics studies. Moreover, it has been found that the hydraulic permeability of living chondrocytes reduced with decreasing of strain-rates. It might be due to the intracellular fluid volume fraction and the fluid pore pressure gradients of chondrocytes were higher when higher strain-rates applied. PMID:26093345

  11. Effect of the temperature, strain rate and microstructure on flow and fracture characteristics of Ti-45Al-2Nb-2Mn+0.8vol.% TiB2 XD alloy

    NASA Astrophysics Data System (ADS)

    Erice, B.; Pérez-Martín, M. J.; Cendón, D. A.; Gálvez, F.

    2012-05-01

    A series of quasi-static and dynamic tensile tests at varying temperatures were carried out to determine the mechanical behaviour of Ti-45Al-2Nb-2Mn+0.8vol.% TiB2 XD as-HIPed alloy. The temperature for the tests ranged from room temperature to 850 ∘C. The effect of the temperature on the ultimate tensile strength, as expected, was almost negligible within the selected temperature range. Nevertheless, the plastic flow suffered some softening because of the temperature. This alloy presents a relatively low ductility; thus, a low tensile strain to failure. The dynamic tests were performed in a Split Hopkinson Tension Bar, showing an increase of the ultimate tensile strength due to the strain rate hardening effect. Johnson-Cook constitutive relation was used to model the plastic flow. A post-testing microstructural of the specimens revealed an inhomogeneous structure, consisting of lamellar α2 + γ structure and γ phase equiaxed grains in the centre, and a fully lamellar structure on the rest. The assessment of the duplex-fully lamellar area ratio showed a clear relationship between the microstructure and the fracture behaviour.

  12. Global Earthquake Activity Rate models based on version 2 of the Global Strain Rate Map

    NASA Astrophysics Data System (ADS)

    Bird, P.; Kreemer, C.; Kagan, Y. Y.; Jackson, D. D.

    2013-12-01

    Global Earthquake Activity Rate (GEAR) models have usually been based on either relative tectonic motion (fault slip rates and/or distributed strain rates), or on smoothing of seismic catalogs. However, a hybrid approach appears to perform better than either parent, at least in some retrospective tests. First, we construct a Tectonic ('T') forecast of shallow (≤ 70 km) seismicity based on global plate-boundary strain rates from version 2 of the Global Strain Rate Map. Our approach is the SHIFT (Seismic Hazard Inferred From Tectonics) method described by Bird et al. [2010, SRL], in which the character of the strain rate tensor (thrusting and/or strike-slip and/or normal) is used to select the most comparable type of plate boundary for calibration of the coupled seismogenic lithosphere thickness and corner magnitude. One difference is that activity of offshore plate boundaries is spatially smoothed using empirical half-widths [Bird & Kagan, 2004, BSSA] before conversion to seismicity. Another is that the velocity-dependence of coupling in subduction and continental-convergent boundaries [Bird et al., 2009, BSSA] is incorporated. Another forecast component is the smoothed-seismicity ('S') forecast model of [Kagan & Jackson, 1994, JGR; Kagan & Jackson, 2010, GJI], which was based on optimized smoothing of the shallow part of the GCMT catalog, years 1977-2004. Both forecasts were prepared for threshold magnitude 5.767. Then, we create hybrid forecasts by one of 3 methods: (a) taking the greater of S or T; (b) simple weighted-average of S and T; or (c) log of the forecast rate is a weighted average of the logs of S and T. In methods (b) and (c) there is one free parameter, which is the fractional contribution from S. All hybrid forecasts are normalized to the same global rate. Pseudo-prospective tests for 2005-2012 (using versions of S and T calibrated on years 1977-2004) show that many hybrid models outperform both parents (S and T), and that the optimal weight on S

  13. The compressive behaviour and constitutive equation of polyimide foam in wide strain rate and temperature

    NASA Astrophysics Data System (ADS)

    Yoshimoto, Akifumi; Kobayashi, Hidetoshi; Horikawa, Keitaro; Tanigaki, Kenichi

    2015-09-01

    These days, polymer foams, such as polyurethane foam and polystyrene foam, are used in various situations as a thermal insulator or shock absorber. In general, however, their strength is insufficient in high temperature environments because of their low glass transition temperature. Polyimide is a polymer which has a higher glass transition temperature and high strength. Its mechanical properties do not vary greatly, even in low temperature environments. Therefore, polyimide foam is expected to be used in the aerospace industry. Thus, the constitutive equation of polyimide foam that can be applied across a wide range of strain rates and ambient temperature is very useful. In this study, a series of compression tests at various strain rates, from 10-3 to 103 s-1 were carried out in order to examine the effect of strain rate on the compressive properties of polyimide foam. The flow stress of polyimide foam increased rapidly at dynamic strain rates. The effect of ambient temperature on the properties of polyimide foam was also investigated at temperature from - 190 °C to 270°∘C. The flow stress decreased with increasing temperature.

  14. Strain Rate Dependant Material Model for Orthotropic Metals

    NASA Astrophysics Data System (ADS)

    Vignjevic, Rade

    2016-08-01

    In manufacturing processes anisotropic metals are often exposed to the loading with high strain rates in the range from 102 s-1 to 106 s-1 (e.g. stamping, cold spraying and explosive forming). These types of loading often involve generation and propagation of shock waves within the material. The material behaviour under such a complex loading needs to be accurately modelled, in order to optimise the manufacturing process and achieve appropriate properties of the manufactured component. The presented research is related to development and validation of a thermodynamically consistent physically based constitutive model for metals under high rate loading. The model is capable of modelling damage, failure and formation and propagation of shock waves in anisotropic metals. The model has two main parts: the strength part which defines the material response to shear deformation and an equation of state (EOS) which defines the material response to isotropic volumetric deformation [1]. The constitutive model was implemented into the transient nonlinear finite element code DYNA3D [2] and our in house SPH code. Limited model validation was performed by simulating a number of high velocity material characterisation and validation impact tests. The new damage model was developed in the framework of configurational continuum mechanics and irreversible thermodynamics with internal state variables. The use of the multiplicative decomposition of deformation gradient makes the model applicable to arbitrary plastic and damage deformations. To account for the physical mechanisms of failure, the concept of thermally activated damage initially proposed by Tuller and Bucher [3], Klepaczko [4] was adopted as the basis for the new damage evolution model. This makes the proposed damage/failure model compatible with the Mechanical Threshold Strength (MTS) model Follansbee and Kocks [5], 1988; Chen and Gray [6] which was used to control evolution of flow stress during plastic deformation. In

  15. The compressive behavior of isocyanate-crosslinked silica aerogel at high strain rates

    NASA Astrophysics Data System (ADS)

    Luo, H.; Lu, H.; Leventis, N.

    2006-06-01

    Aerogels are low-density, highly nano-porous materials. Their engineering applications are limited due to their brittleness and hydrophilicity. Recently, a strong lightweight crosslinked silica aerogel has been developed by encapsulating the skeletal framework of amine-modified silica aerogels with polyureas derived by isocyanate. The mesoporous structure of the underlying silica framework is preserved through conformal polymer coating, and the thermal conductivity remains low. Characterization has been conducted on the thermal, physical properties and the mechanical properties under quasi-static loading conditions. In this paper, we present results on the dynamic compressive behavior of the crosslinked silica aerogel (CSA) using a split Hopkinson pressure bar (SHPB). A new tubing pulse shaper was employed to help reach the dynamic stress equilibrium and constant strain rate. The stress-strain relationship was determined at high strain rates within 114-4386 s-1. The effects of strain rate, density, specimen thickness and water absorption on the dynamic behavior of the CSA were investigated through a series of dynamic experiments. The Young’s moduli (or 0.2% offset compressive yield strengths) at a strain rate ˜350 s-1 were determined as 10.96/2.08, 159.5/6.75, 192.2/7.68, 304.6/11.46, 407.0/20.91 and 640.5/30.47 MPa for CSA with densities 0.205, 0.454, 0.492, 0.551, 0.628 and 0.731 g cm-3, respectively. The deformation and failure behaviors of a native silica aerogel with density (0.472 g cm-3), approximately the same as a typical CSA sample were observed with a high speed digital camera. Digital image correlation technique was used to determine the surface strains through a series of images acquired using high speed photography. The relative uniform axial deformation indicated that localized compaction did not occur at a compressive strain level of ˜17%, suggesting most likely failure mechanism at high strain rate to be different from that under quasi

  16. The Compressive Behavior of Isocyanate-crosslinked Silica Aerogel at High Strain Rates

    NASA Technical Reports Server (NTRS)

    Luo, H.; Lu, H.; Leventis, N.

    2006-01-01

    Aerogels are low-density, highly nano-porous materials. Their engineering applications are limited due to their brittleness and hydrophilicity. Recently, a strong lightweight crosslinked silica aerogel has been developed by encapsulating the skeletal framework of amine-modified silica aerogels with polyureas derived by isocyanate. The mesoporous structure of the underlying silica framework is preserved through conformal polymer coating, and the thermal conductivity remains low. Characterization has been conducted on the thermal, physical properties and the mechanical properties under quasi-static loading conditions. In this paper, we present results on the dynamic compressive behavior of the crosslinked silica aerogel (CSA) using a split Hopkinson pressure bar (SHPB). A new tubing pulse shaper was employed to help reach the dynamic stress equilibrium and constant strain rate. The stress-strain relationship was determined at high strain rates within 114-4386/s. The effects of strain rate, density, specimen thickness and water absorption on the dynamic behavior of the CSA were investigated through a series of dynamic experiments. The Young's moduli (or 0.2% offset compressive yield strengths) at a strain rate approx.350/s were determined as 10.96/2.08, 159.5/6.75, 192.2/7.68, 304.6/11.46, 407.0/20.91 and 640.5/30.47 MPa for CSA with densities 0.205, 0.454, 0.492, 0.551,0.628 and 0.731 g/cu cm, respectively. The deformation and failure behaviors of a native silica aerogel with density (0.472 g/cu cm ), approximately the same as a typical CSA sample were observed with a high speed digital camera. Digital image correlation technique was used to determine the surface strains through a series of images acquired using high speed photography. The relative uniform axial deformation indicated that localized compaction did not occur at a compressive strain level of approx.17%, suggesting most likely failure mechanism at high strain rate to be different from that under quasi

  17. Mechanical strain effects on black phosphorus nanoresonators.

    PubMed

    Wang, Cui-Xia; Zhang, Chao; Jiang, Jin-Wu; Park, Harold S; Rabczuk, Timon

    2016-01-14

    We perform classical molecular dynamics simulations to investigate the effects of mechanical strain on single-layer black phosphorus nanoresonators at different temperatures. We find that the resonant frequency is highly anisotropic in black phosphorus due to its intrinsic puckered configuration, and that the quality factor in the armchair direction is higher than in the zigzag direction at room temperature. The quality factors are also found to be intrinsically larger than those in graphene and MoS2 nanoresonators. The quality factors can be increased by more than a factor of two by applying tensile strain, with uniaxial strain in the armchair direction being the most effective. However, there is an upper bound for the quality factor increase due to nonlinear effects at large strains, after which the quality factor decreases. The tension induced nonlinear effect is stronger along the zigzag direction, resulting in a smaller maximum strain for quality factor enhancement. PMID:26649476

  18. Mechanical strain effects on black phosphorus nanoresonators.

    PubMed

    Wang, Cui-Xia; Zhang, Chao; Jiang, Jin-Wu; Park, Harold S; Rabczuk, Timon

    2016-01-14

    We perform classical molecular dynamics simulations to investigate the effects of mechanical strain on single-layer black phosphorus nanoresonators at different temperatures. We find that the resonant frequency is highly anisotropic in black phosphorus due to its intrinsic puckered configuration, and that the quality factor in the armchair direction is higher than in the zigzag direction at room temperature. The quality factors are also found to be intrinsically larger than those in graphene and MoS2 nanoresonators. The quality factors can be increased by more than a factor of two by applying tensile strain, with uniaxial strain in the armchair direction being the most effective. However, there is an upper bound for the quality factor increase due to nonlinear effects at large strains, after which the quality factor decreases. The tension induced nonlinear effect is stronger along the zigzag direction, resulting in a smaller maximum strain for quality factor enhancement.

  19. Assessment of strain and strain rate in embryonic chick heart in vivo using tissue Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Li, Peng; Liu, Aiping; Shi, Liang; Yin, Xin; Rugonyi, Sandra; Wang, Ruikang K.

    2011-11-01

    We present a method to assess the in vivo radial strain and strain rate of the myocardial wall, which is of great importance to understand the biomechanics of cardiac development, using tissue Doppler optical coherence tomography (tissue-DOCT). Combining the structure and velocity information acquired from tissue-DOCT, the velocity distribution in the myocardial wall is plotted, from which the radial strain and strain rate are evaluated. The results demonstrate that tissue-DOCT can be used as a useful tool to describe tissue deformation, especially, the biomechanical characteristics of the embryonic heart.

  20. Effect of dilution rate and nutrients addition on the fermentative capability and synthesis of aromatic compounds of two indigenous strains of Saccharomyces cerevisiae in continuous cultures fed with Agave tequilana juice.

    PubMed

    Morán-Marroquín, G A; Córdova, J; Valle-Rodríguez, J O; Estarrón-Espinosa, M; Díaz-Montaño, D M

    2011-11-15

    Knowledge of physiological behavior of indigenous tequila yeast used in fermentation process is still limited. Yeasts have significant impact on the productivity fermentation process as well as the sensorial characteristics of the alcoholic beverage. For these reasons a better knowledge of the physiological and metabolic features of these yeasts is required. The effects of dilution rate, nitrogen and phosphorus source addition and micro-aeration on growth, fermentation and synthesis of volatile compounds of two native Saccharomyces cerevisiae strains, cultured in continuous fed with Agave tequilana juice were studied. For S1 and S2 strains, maximal concentrations of biomass, ethanol, consumed sugars, alcohols and esters were obtained at 0.04 h⁻¹. Those concentrations quickly decreased as D increased. For S. cerevisiae S1 cultures (at D=0.08 h⁻¹) supplemented with ammonium phosphate (AP) from 1 to 4 g/L, concentrations of residual sugars decreased from 29.42 to 17.60 g/L and ethanol increased from 29.63 to 40.08 g/L, respectively. The S1 culture supplemented with AP was then micro-aerated from 0 to 0.02 vvm, improving all the kinetics parameters: biomass, ethanol and glycerol concentrations increased from 5.66, 40.08 and 3.11 g/L to 8.04, 45.91 and 4.88 g/L; residual sugars decreased from 17.67 g/L to 4.48 g/L; and rates of productions of biomass and ethanol, and consumption of sugars increased from 0.45, 3.21 and 7.33 g/L·h to 0.64, 3.67 and 8.38 g/L·h, respectively. Concentrations of volatile compounds were also influenced by the micro-aeration rate. Ester and alcohol concentrations were higher, in none aerated and in aerated cultures respectively. PMID:21903290

  1. Comparison of strain rates of dart impacted plaques and pendulum impacted bumpers

    SciTech Connect

    Scammell, K.L.

    1987-01-01

    The difference in strain rates prevailing during pendulum impact of bumpers versus high speed dart impact of plaques was investigated. Uni-axial strain gages were applied to the tension side of the plaques and bumpers directly opposite the point of impact. The plaques were impacted with an instrumented high rate dart impact tester and the bumpers impacted with a full scale bumper pendulum impact tester. Theoretical calculations and actual strain rate data support the conclusion that the strain rate of a plaque during dart impact significantly exceeds that of bumper strain rate during pendulum impact.

  2. Strain-rate dependence of ramp-wave evolution and strength in tantalum

    NASA Astrophysics Data System (ADS)

    Lane, J. Matthew D.; Foiles, Stephen M.; Lim, Hojun; Brown, Justin L.

    2016-08-01

    We have conducted molecular dynamics (MD) simulations of quasi-isentropic ramp-wave compression to very high pressures over a range of strain rates from 1011 down to 108 1/s. Using scaling methods, we collapse wave profiles from various strain rates to a master profile curve, which shows deviations when material response is strain-rate dependent. Thus, we can show with precision where, and how, strain-rate dependence affects the ramp wave. We find that strain rate affects the stress-strain material response most dramatically at strains below 20%, and that above 30% strain the material response is largely independent of strain rate. We show good overall agreement with experimental stress-strain curves up to approximately 30% strain, above which simulated response is somewhat too stiff. We postulate that this could be due to our interatomic potential or to differences in grain structure and/or size between simulation and experiment. Strength is directly measured from per-atom stress tensor and shows significantly enhanced elastic response at the highest strain rates. This enhanced elastic response is less pronounced at higher pressures and at lower strain rates.

  3. Growth rate and nutrient limitation affect the transport of Rhodococcus sp. strain DN22 through sand.

    PubMed

    Priestley, James T; Coleman, Nicholas V; Duxbury, Trevor

    2006-12-01

    Rhodococcus strain DN22 grows on the nitramine explosive RDX as a sole nitrogen source, and is potentially useful for bioremediation of explosives-contaminated soil. In order for strain DN22 to be effectively applied in situ, inoculum cells must reach zones of RDX contamination via passive transport, a process that is difficult to predict at field-scale. We examined the effect of growth conditions on the transport of DN22 cells through sand columns, using chemostat-grown cultures. Strain DN22 formed smaller coccoid cells at low dilution rate (0.02 h(-1)) and larger rods at high dilution rate (0.1 h(-1)). Under all nutrient limitation conditions studied, smaller cells grown at low dilution rate were retained more strongly by sand columns than larger cells grown at high dilution rate. At a dilution rate of 0.05, cells from nitrate-limited cultures were retained more strongly than cells from RDX-limited or succinate-limited cultures. Breakthrough concentrations (C/C (0)) from sand columns ranged from 0.04 (nitrate-limited, D=0.02 h(-1)) to 0.98 (succinate-limited, D=0.1 h(-1)). The observed strong effect of culture conditions on transport of DN22 cells emphasizes the importance of physiology studies in guiding the development of bioremediation technologies.

  4. Servohydraulic methods for mechanical testing in the Sub-Hopkinson rate regime up to strain rates of 500 1/s.

    SciTech Connect

    Crenshaw, Thomas B.; Boyce, Brad Lee

    2005-10-01

    Tensile and compressive stress-strain experiments on metals at strain rates in the range of 1-1000 1/s are relevant to many applications such as gravity-dropped munitions and airplane accidents. While conventional test methods cover strain rates up to {approx}10 s{sup -1} and split-Hopkinson and other techniques cover strain rates in excess of {approx}1000 s{sup -1}, there are no well defined techniques for the intermediate or ''Sub-Hopkinson'' strain-rate regime. The current work outlines many of the challenges in testing in the Sub-Hopkinson regime, and establishes methods for addressing these challenges. The resulting technique for obtaining intermediate rate stress-strain data is demonstrated in tension on a high-strength, high-toughness steel alloy (Hytuf) that could be a candidate alloy for earth penetrating munitions and in compression on a Au-Cu braze alloy.

  5. Implementation of Improved Transverse Shear Calculations and Higher Order Laminate Theory Into Strain Rate Dependent Analyses of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Zhu, Lin-Fa; Kim, Soo; Chattopadhyay, Aditi; Goldberg, Robert K.

    2004-01-01

    A numerical procedure has been developed to investigate the nonlinear and strain rate dependent deformation response of polymer matrix composite laminated plates under high strain rate impact loadings. A recently developed strength of materials based micromechanics model, incorporating a set of nonlinear, strain rate dependent constitutive equations for the polymer matrix, is extended to account for the transverse shear effects during impact. Four different assumptions of transverse shear deformation are investigated in order to improve the developed strain rate dependent micromechanics model. The validities of these assumptions are investigated using numerical and theoretical approaches. A method to determine through the thickness strain and transverse Poisson's ratio of the composite is developed. The revised micromechanics model is then implemented into a higher order laminated plate theory which is modified to include the effects of inelastic strains. Parametric studies are conducted to investigate the mechanical response of composite plates under high strain rate loadings. Results show the transverse shear stresses cannot be neglected in the impact problem. A significant level of strain rate dependency and material nonlinearity is found in the deformation response of representative composite specimens.

  6. Ultra-high strain rate behavior of FCC nanostructures

    NASA Astrophysics Data System (ADS)

    Crum, Ryan Scott

    This work addresses the influence of ultra-high strain rates loading observed in our world today via ballistics, explosions and astrophysical collisions on well-defined metal structures. There is a plentiful amount of research examining metals at a macroscopic level that are subjected to ballistics and explosions but observing the microstructure is difficult as those procedures are fairly destructive testing mechanisms. Therefore, to understand the true mechanisms that occur in these loading situations a more novel technique is necessary. Modifications were made to the Laser Spallation Technique in order to load structures under a single transient wave pulse. This study characterized FCC nanostructures shock loaded at extreme pressures, strain rates and temperatures. By utilizing nanostructures, extremely large values of stain could be produced within the structure. It was first observed that at lower laser fluence levels and subsequently low stress states that there was a chemical activation of the surface of Cu nanopillars. This occurred due to nanofacet formation on the surface of the nanopillars which left pristine Cu surfaces to recombine with the environment. Dislocation motion was also observed and clearly identified in Cu nanopillars, Cu nanobenches and Al nanopillars. Further studies analyzed Cu nanopillars subjected to higher laser fluence generated stress waves, which led to bending and axial shortening deformation. These deformations were observed at laser fluence values of 144 kJ/m2 for bending and 300 kJ/m 2 for bulging similar to that of Taylor Impact experiments. To explore an even more extreme loading environment, a specialized test setup was employed to cryogenically cool the copper nanopillars to a temperature of 83K in an attempt to elucidate brittle behavior. Under these loading conditions the nanopillars continued to deform in a ductile manner but with delayed onset of both bending deformation and bulging deformation compared to the room

  7. The effective viscosity of a dispersive medium under strain oscillations

    NASA Astrophysics Data System (ADS)

    Fedotovskii, V. S.; Vereshchagina, T. N.

    2015-03-01

    The hydrodynamic dissipative processes that accompany strain oscillations of a dispersive medium with solid spherical inclusions are considered. Based on a simple cell model, the dependence is obtained for the energy dissipation rate, which determines the effective shear viscosity of a suspension under high-frequency strain oscillations. It is shown that the well-known formulas for the effective viscosity should be supplemented with an essential dynamic term depending on the strain oscillation frequency, the inclusion radius, and the viscosity of the liquid.

  8. Fiber-Optic Strain Gauge With High Resolution And Update Rate

    NASA Technical Reports Server (NTRS)

    Figueroa, Fernando; Mahajan, Ajay; Sayeh, Mohammad; Regez, Bradley

    2007-01-01

    An improved fiber-optic strain gauge is capable of measuring strains in the approximate range of 0 to 50 microstrains with a resolution of 0.1 microstrain. (To some extent, the resolution of the strain gauge can be tailored and may be extensible to 0.01 microstrain.) The total cost of the hardware components of this strain gauge is less than $100 at 2006 prices. In comparison with prior strain gauges capable of measurement of such low strains, this strain gauge is more accurate, more economical, and more robust, and it operates at a higher update rate. Strain gauges like this one are useful mainly for measuring small strains (including those associated with vibrations) in such structures as rocket test stands, buildings, oilrigs, bridges, and dams. The technology was inspired by the need to measure very small strains on structures supporting liquid oxygen tanks, as a way to measure accurately mass of liquid oxygen during rocket engine testing. This improved fiber-optic strain gauge was developed to overcome some of the deficiencies of both traditional foil strain gauges and prior fiber-optic strain gauges. Traditional foil strain gages do not have adequate signal-to-noise ratios at such small strains. Fiber-optic strain gauges have been shown to be potentially useful for measuring such small strains, but heretofore, the use of fiberoptic strain gauges has been inhibited, variously, by complexity, cost, or low update rate.

  9. Investigation of thermomechanical couplings, strain localization and shape memory properties in a shape memory polymer subjected to loading at various strain rates

    NASA Astrophysics Data System (ADS)

    Pieczyska, E. A.; Staszczak, M.; Maj, M.; Kowalczyk-Gajewska, K.; Golasiński, K.; Cristea, M.; Tobushi, H.; Hayashi, S.

    2016-08-01

    This paper presents experimental and modeling results of the effects of thermomechanical couplings occurring in a polyurethane shape memory polymer (SMP) subjected to tension at various strain rates within large strains. The SMP mechanical curves, recorded using a testing machine, and the related temperature changes, measured in a contactless manner using an IR camera, were used to investigate the polymer deformation process at various loading stages. The effects of thermomechanical couplings allowed the determination of the material yield point in the initial loading stage, the investigation of nucleation and development of the strain localization at larger strains and the estimation of the effects of thermoelastic behavior during the unloading process. The obtained stress–strain and thermal characteristics, the results of the dynamic mechanical analysis and estimated values of the shape fixity and shape recovery parameters confirmed that the shape memory polymer (T g = 45 °C) is characterized by good mechanical and shape memory properties, as well as high sensitivity to the strain rate. The mechanical response of the SMP subjected to tension was simulated using the finite element method and applying the large strain, two-phase model. Strain localization observed in the experiment was well reproduced in simulations and the temperature spots were correlated with the accumulated viscoplastic deformation of the SMP glassy phase.

  10. Investigation of thermomechanical couplings, strain localization and shape memory properties in a shape memory polymer subjected to loading at various strain rates

    NASA Astrophysics Data System (ADS)

    Pieczyska, E. A.; Staszczak, M.; Maj, M.; Kowalczyk-Gajewska, K.; Golasiński, K.; Cristea, M.; Tobushi, H.; Hayashi, S.

    2016-08-01

    This paper presents experimental and modeling results of the effects of thermomechanical couplings occurring in a polyurethane shape memory polymer (SMP) subjected to tension at various strain rates within large strains. The SMP mechanical curves, recorded using a testing machine, and the related temperature changes, measured in a contactless manner using an IR camera, were used to investigate the polymer deformation process at various loading stages. The effects of thermomechanical couplings allowed the determination of the material yield point in the initial loading stage, the investigation of nucleation and development of the strain localization at larger strains and the estimation of the effects of thermoelastic behavior during the unloading process. The obtained stress-strain and thermal characteristics, the results of the dynamic mechanical analysis and estimated values of the shape fixity and shape recovery parameters confirmed that the shape memory polymer (T g = 45 °C) is characterized by good mechanical and shape memory properties, as well as high sensitivity to the strain rate. The mechanical response of the SMP subjected to tension was simulated using the finite element method and applying the large strain, two-phase model. Strain localization observed in the experiment was well reproduced in simulations and the temperature spots were correlated with the accumulated viscoplastic deformation of the SMP glassy phase.

  11. Flow Stress-Strain Rate Behavior of Ti-3Al-2.5V Alloy at Low Temperatures in the Superplastic Range

    NASA Astrophysics Data System (ADS)

    Salam, A.

    2012-02-01

    Flow stress-strain rate behavior of Ti-3Al-2.5V, an α + β titanium alloy was studied at 750 and 800 °C by using the method of crosshead speed cycling. The alloy was found to exhibit superplasticity at these temperatures on the basis of complete flow stress, strain rate and strain rate sensitivity data. Strain-induced softening was observed in the alloy to a small extent at 750 °C and was thought to be related to the grain refinement occurring in both α- and β-phases during the initial stages of deformation. However, at 800 °C the effect was seen only under increasing strain-rate conditions. Flow stress versus strain rate curves generally exhibited only region II which corresponded to low- and intermediate-strain rates and region III corresponding to high-strain rates.

  12. High strain rate modeling of ceramics and ceramic composites

    NASA Astrophysics Data System (ADS)

    Espinosa, H. D.

    1994-07-01

    The high strain rate response of an AlN/AlN/Al composite manufactured by Lanxide Armor Products, Inc., has been studied through normal and pressure-shear plate impact experiments. Differences in the measured shear resistance, as a function of the impact configuration, motivated the examination of the material response by means of a microcracking multiple-plane model and a continuum elasto-viscoplastic constitutive model. Numerical simulations of the normal impact experiments do not support microcracking as the dominant inelastic mechanism. By contrast, an elasto-viscoplastic description of the material behavior predicts the main features of the normal stress history and the thickness dependence of the Hugoniot elastic limit. Nonetheless, the elasto-viscoplastic model cannot reproduce both the normal and pressure-shear experiments with a single set of model parameters. The inadequacy of the continuum elasto-viscoplastic model seems to result from the isotropic assumption embodied in its formulation. The shear resistance measured in the pressure-shear experiments is adequately predicted by a microcracking multiple-plane model. The agreement seems to hinge in the continuous shearing of the material on a micro-localized fashion, i.e. only one orientation becomes dominant and controls the inelastic shear deformation rate. This event does not occur in the normal impact configuration, in which the amount of inelasticity is primarily controlled by the elastic compressibility of the material. These findings explain the higher sensitivity to damage and microplasticity observed in the pressure-shear configuration, as well as the softer material response recorded in this configuration.

  13. High Strain Rate Response of Sandwich Composites with Nanophased Cores

    NASA Astrophysics Data System (ADS)

    Mahfuz, Hassan; Uddin, Mohammed F.; Rangari, Vijaya K.; Saha, Mrinal C.; Zainuddin, Shaik; Jeelani, Shaik

    2005-05-01

    Polyurethane foam materials have been used as core materials in a sandwich construction with S2-Glass/SC-15 facings. The foam material has been manufactured from liquid polymer precursors of polyurethane. The precursors are made of two components; part-A (diphenylmethane diisocyanate) and part-B (polyol). In one set of experiments, part-A was mixed with part-B to manufacture the foam. In another set, TiO2 nanoparticles have been dispersed in part-A through ultrasonic cavitation technique. The loading of nanoparticles was 3% by weight of the total polymer precursor. The TiO2 nanoparticles were spherical in shape, and were about 29 nm in diameter. Sonic cavitation was carried out with a vibrasound liquid processor at 20 kHz frequency with a power intensity of about 100 kW/m2. The two categories of foams manufactured in this manner were termed as neat and nanophased. Sandwich composites were then fabricated using these two categories of core materials using a co-injection resin transfer molding (CIRTM) technique. Test samples extracted from the panel were subjected to quasi-static as well as high strain rate loadings. Rate of loading varied from 0.002 s-1 to around 1300 s-1. It has been observed that infusion of nanoparticles had a direct correlation with the cell geometry. The cell dimensions increased by about 46% with particle infusion suggesting that nanoparticles might have worked as catalysts during the foaming process. Correspondingly, enhancement in thermal properties was also noticed especially in the TGA experiments. There was also a significant improvement in mechanical properties due to nanoparticle infusion. Average increase in sandwich strength and energy absorption with nanophased cores was between 40 60% over their neat counterparts. Details of manufacturing and analyses of thermal and mechanical tests are presented in this paper.

  14. Yield strength dependence on strain rate of molybdenum-alloy nanofibers

    SciTech Connect

    Loya, P. E.; Peng, C.; Zhang, P.; Zhang, J.; Lou, J.; Xia, Y. Z.; Bei, H.; George, E. P.; Gao, Y. F.

    2014-06-23

    The yield strength dependence on strain rate was studied for molybdenum-alloy nanofibers with varying initial dislocation density at three different pre-strain levels. In-situ tensile experiments at three displacement rates were carried out in a scanning electron microscope. Yield strength and its scatter decreased as a function of the pre-strain level for different displacement rates. A statistical model was used to analyze the results, and a negative strain rate dependence was inferred from the yield experiments. This finding suggests the need for theoretical investigations since classical models such as dynamic strain aging may have limitations at such nanoscales.

  15. On the influence of strain rate sensitivity on wear in the Archard regime

    NASA Astrophysics Data System (ADS)

    Brechet, Y.; Estrin, Y.

    1994-06-01

    As shown in the study, the wear rate is affected by the strain rate sensitivity of the flow stress: the smaller S, the larger the wear rate. Of importance is the strain rate sensitivity correction to the wear coefficient in the Archard regime.

  16. Distributed strain monitoring for bridges: temperature effects

    NASA Astrophysics Data System (ADS)

    Regier, Ryan; Hoult, Neil A.

    2014-03-01

    To better manage infrastructure assets as they reach the end of their service lives, quantitative data is required to better assess structural behavior and allow for more informed decision making. Distributed fiber optic strain sensors are one sensing technology that could provide comprehensive data for use in structural assessments as these systems potentially allow for strain to be measured with the same accuracy and gage lengths as conventional strain sensors. However, as with many sensor technologies, temperature can play an important role in terms of both the structure's and sensor's performance. To investigate this issue a fiber optic distributed strain sensor system was installed on a section of a two span reinforced concrete bridge on the TransCanada Highway. Strain data was acquired several times a day as well as over the course of several months to explore the effects of changing temperature on the data. The results show that the strain measurements are affected by the bridge behavior as a whole. The strain measurements due to temperature are compared to strain measurements that were taken during a load test on the bridge. The results show that even a small change in temperature can produce crack width and strain changes similar to those due to a fully loaded transport truck. Future directions for research in this area are outlined.

  17. Controlling the Lithiation-Induced Strain and Charging Rate in Nanowire Electrodes by Coating

    SciTech Connect

    Zhang, Li Q.; Liu, Xiao H.; Liu, Yang; Huang, Shan; Zhu, Ting; Gui, Liangjin; Mao, Scott X.; Ye, Zhi Zhen; Wang, Chong M.; Sullivan, J. P.; Huang, Jian Yu

    2011-05-04

    Lithiation-induced-strain (LIS) in electrode materials plagues the performance and lifetime of lithium ion batteries (LIBs). Controlling the LIS is one of the ultimate goals for making better LIBs. Here we report that by carbon or aluminum coating, the charging rate and LIS of individual SnO2 nanowire electrodes can be altered dramatically: namely the carbon or aluminum coated nanowires can be charged about 10 times faster than the non-coated nanowires, and the radial expansion of the coated nanowires was completely suppressed, resulting little or no mismatch strain at the reaction front, as evidenced by the lack of dislocations near the reaction front. The improved charging rate and the suppression of the radial expansion were attributed to the mechanical confinement of the coatings. These studies demonstrate an effective route to control the charging rate and LIS, enabling the design of better LIBs.

  18. High-rate Plastic Deformation of Nanocrystalline Tantalum to Large Strains: Molecular Dynamics Simulation

    SciTech Connect

    Rudd, R E

    2009-02-05

    Recent advances in the ability to generate extremes of pressure and temperature in dynamic experiments and to probe the response of materials has motivated the need for special materials optimized for those conditions as well as a need for a much deeper understanding of the behavior of materials subjected to high pressure and/or temperature. Of particular importance is the understanding of rate effects at the extremely high rates encountered in those experiments, especially with the next generation of laser drives such as at the National Ignition Facility. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum to investigate the processes associated with plastic deformation for strains up to 100%. We use initial atomic configurations that were produced through simulations of solidification in the work of Streitz et al [Phys. Rev. Lett. 96, (2006) 225701]. These 3D polycrystalline systems have typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures.

  19. On the influence of strain rate in acousto-elasticity : experimental results for Berea sandstone

    NASA Astrophysics Data System (ADS)

    Riviere, J. V.; Candela, T.; Scuderi, M.; Marone, C.; Guyer, R. A.; Johnson, P. A.

    2013-12-01

    Elastic nonlinear effects are pervasive in the Earth, including during strong ground motion, tidal forcing and earthquake slip processes. We study elastic nonlinear effects in the laboratory with the goal of developing new methods to probe elastic changes in the Earth, and to characterize and understand their origins. Here we report on nonlinear, frequency dispersion effects by applying a method termed dynamic acousto-elasticity (DAE), analogous to quasi-static acousto-elasticity. DAE allows one to obtain the elastic behavior over the entire dynamic cycle, detailing the full nonlinear behavior under tension and compression, including hysteresis and memory effects. We perform DAE on samples of Berea sandstone subject to 0.5 MPa uniaxial and biaxial loading conditions with oscillating loads at frequencies from 0.001 to 10 Hz and amplitudes of a few 100 kPa. We compare results to DAE measurements made in the kHz range. We observe that the average decrease in modulus due to nonlinear material softening increases with frequency, suggesting a frequency and/or a strain rate dependence. Previous quasi-static measurements (Claytor et al., GRL 2009) show that stress-strain nonlinear hysteretic behavior disappears when the experiment is performed at a very low strain-rate, implying that a rate dependent nonlinear elastic model would be useful (Gusev et al., PRB 2004). Our results also suggest that when elastic nonlinear Earth processes are studied, stress forcing frequency is an important consideration, and may lead to unexpected behaviors.

  20. The variation of the yield stress of Ti alloys with strain rate at high temperatures

    NASA Astrophysics Data System (ADS)

    Rosen, R. S.; Paddon, S. P.; Kassner, M. E.

    1999-06-01

    This study extended investigation on the elevated-temperature yield-strength dependence of beta-phase titanium alloys on strain rate and temperature. Yield stresses were found to increase substantially with increasing strain rate at elevated temperatures due to the high strain-rate sensitivity of titanium at high temperatures. Above 1000 °C, the strain-rate sensitivities were found to increase substantially with increasing temperature and/or decreasing strain rate. The six alloys examined were TIMETAL 21S, Ti-15-3, Ti-6-4, Ti-13-11-3, Beta C, and Beta III. There was particular interest in determining the strain-rate sensitivity of these alloys through strain-rate change tests above 1000 °C. The yield stresses of all the titanium alloys at temperatures above 1093 °C were less than 1% of their ambient temperature values. Strain hardening was negligible in the alloys tested at these high temperatures. Extended tensile ductilities of 100 to 200% were observed due to the pronounced strain-rate sensitivity. The rate controlling mechanism for plasticity, based on activation energy and the strain-rate sensitivity measurements, is discussed.

  1. Predicting Offshore Swarm Rate Changes by Volumetric Strain Changes in Izu Peninsula, Japan

    NASA Astrophysics Data System (ADS)

    Kumazawa, T.; Ogata, Y.; Kimura, Y.; Maeda, K.; Kobayashi, A.

    2014-12-01

    The eastern offshore of Izu peninsula is one of the well known volcanic active regions in Japan, where magma intrusions have been observed several times since 1980s monitored by strain-meters located nearby. Major swarm activities have been synchronously associated with coseismic and preseismic significant sizes of a volumetric strain changes (Earthquake Research Committee, 2010). We investigated the background seismicity changes during these earthquake swarms using the nonstationary ETAS model (Kumazawa and Ogata, 2013), and have found the followings. The modified volumetric strain change data by removing the effect of earth tides and precipitation as well as removing coseismic jumps have much higher cross-correlations to the background rates of the ETAS model than to the whole seismicity rate change of the ETAS, and further the strain changes precede the background seismicity by lag of about a day. This relation suggests an enhanced prediction of earthquakes in this region using volumetric strain measurements. Thus we propose an extended ETAS model where the background seismicity rate is predicted by the time series of preceding volumetric strain changes. Our numerical results for Izu region show consistent outcomes throughout the major swarms in this region. References Earthquake Research Committee (2010). Report on "Prediction of seismic activity in the Izu Eastern Region" (in Japanese), http://www.jishin.go.jp/main/yosoku/izu/index.htm Kumazawa, T. and Ogata, Y. (2013). Quantitative description of induced seismic activity before and after the 2011 Tohoku-Oki earthquake by nonstationary ETAS model, J Geophys.Res. 118, 6165-6182.

  2. High-strain-rate brain injury model using submerged acute rat brain tissue slices.

    PubMed

    Sarntinoranont, Malisa; Lee, Sung J; Hong, Yu; King, Michael A; Subhash, Ghatu; Kwon, Jiwoon; Moore, David F

    2012-01-20

    Blast-induced traumatic brain injury (bTBI) has received increasing attention in recent years due to ongoing military operations in Iraq and Afghanistan. Sudden impacts or explosive blasts generate stress and pressure waves that propagate at high velocities and affect sensitive neurological tissues. The immediate soft tissue response to these stress waves is difficult to assess using current in vivo imaging technologies. However, these stress waves and resultant stretching and shearing of tissue within the nano- to microsecond time scale of blast and impact are likely to cause initial injury. To visualize the effects of stress wave loading, we have developed a new ex vivo model in which living tissue slices from rat brain, attached to a ballistic gelatin substrate, were subjected to high-strain-rate loads using a polymer split Hopkinson pressure bar (PSHPB) with real-time high-speed imaging. In this study, average peak fluid pressure within the test chamber reached a value of 1584±63.3 psi. Cavitation due to a trailing underpressure wave was also observed. Time-resolved images of tissue deformation were collected and large maximum eigenstrains (0.03-0.42), minimum eigenstrains (-0.33 to -0.03), maximum shear strains (0.09-0.45), and strain rates (8.4×10³/sec) were estimated using digital image correlation (DIC). Injury at 4 and 6 h was quantified using Fluoro-Jade C. Neuronal injury due to PSHPB testing was found to be significantly greater than injury associated with the tissue slice paradigm alone. While large pressures and strains were encountered for these tests, this system provides a controllable test environment to study injury to submerged brain slices over a range of strain rate, pressure, and strain loads. PMID:21970544

  3. Investigation of the mechanical behavior of kangaroo humeral head cartilage tissue by a porohyperelastic model based on the strain-rate-dependent permeability.

    PubMed

    Thibbotuwawa, Namal; Oloyede, Adekunle; Senadeera, Wijitha; Li, Tong; Gu, YuanTong

    2015-11-01

    Solid-interstitial fluid interaction, which depends on tissue permeability, is significant to the strain-rate-dependent mechanical behavior of humeral head (shoulder) cartilage. Due to anatomical and biomechanical similarities to that of the human shoulder, kangaroos present a suitable animal model. Therefore, indentation experiments were conducted on kangaroo shoulder cartilage tissues from low (10(-4)/s) to moderately high (10(-2)/s) strain-rates. A porohyperelastic model was developed based on the experimental characterization; and a permeability function that takes into account the effect of strain-rate on permeability (strain-rate-dependent permeability) was introduced into the model to investigate the effect of rate-dependent fluid flow on tissue response. The prediction of the model with the strain-rate-dependent permeability was compared with those of the models using constant permeability and strain-dependent permeability. Compared to the model with constant permeability, the models with strain-dependent and strain-rate-dependent permeability were able to better capture the experimental variation at all strain-rates (p < 0.05). Significant differences were not identified between models with strain-dependent and strain-rate-dependent permeability at strain-rate of 5 × 10(-3)/s (p = 0.179). However, at strain-rate of 10(-2)/s, the model with strain-rate-dependent permeability was significantly better at capturing the experimental results (p < 0.005). The findings thus revealed the significance of rate-dependent fluid flow on tissue behavior at large strain-rates, which provides insights into the mechanical deformation mechanisms of cartilage tissues.

  4. Investigation of the mechanical behavior of kangaroo humeral head cartilage tissue by a porohyperelastic model based on the strain-rate-dependent permeability.

    PubMed

    Thibbotuwawa, Namal; Oloyede, Adekunle; Senadeera, Wijitha; Li, Tong; Gu, YuanTong

    2015-11-01

    Solid-interstitial fluid interaction, which depends on tissue permeability, is significant to the strain-rate-dependent mechanical behavior of humeral head (shoulder) cartilage. Due to anatomical and biomechanical similarities to that of the human shoulder, kangaroos present a suitable animal model. Therefore, indentation experiments were conducted on kangaroo shoulder cartilage tissues from low (10(-4)/s) to moderately high (10(-2)/s) strain-rates. A porohyperelastic model was developed based on the experimental characterization; and a permeability function that takes into account the effect of strain-rate on permeability (strain-rate-dependent permeability) was introduced into the model to investigate the effect of rate-dependent fluid flow on tissue response. The prediction of the model with the strain-rate-dependent permeability was compared with those of the models using constant permeability and strain-dependent permeability. Compared to the model with constant permeability, the models with strain-dependent and strain-rate-dependent permeability were able to better capture the experimental variation at all strain-rates (p < 0.05). Significant differences were not identified between models with strain-dependent and strain-rate-dependent permeability at strain-rate of 5 × 10(-3)/s (p = 0.179). However, at strain-rate of 10(-2)/s, the model with strain-rate-dependent permeability was significantly better at capturing the experimental results (p < 0.005). The findings thus revealed the significance of rate-dependent fluid flow on tissue behavior at large strain-rates, which provides insights into the mechanical deformation mechanisms of cartilage tissues. PMID:26275487

  5. Material dynamics under extreme conditions of pressure and strain rate

    SciTech Connect

    Remington, B A; Allen, P; Bringa, E; Hawreliak, J; Ho, D; Lorenz, K T; Lorenzana, H; Meyers, M A; Pollaine, S W; Rosolankova, K; Sadik, B; Schneider, M S; Swift, D; Wark, J; Yaakobi, B

    2005-09-06

    Solid state experiments at extreme pressures (10-100 GPa) and strain rates ({approx}10{sup 6}-10{sup 8}s{sup -1}) are being developed on high-energy laser facilities, and offer the possibility for exploring new regimes of materials science. These extreme solid-state conditions can be accessed with either shock loading or with a quasi-isentropic ramped pressure drive. Velocity interferometer measurements establish the high pressure conditions. Constitutive models for solid-state strength under these conditions are tested by comparing 2D continuum simulations with experiments measuring perturbation growth due to the Rayleigh-Taylor instability in solid-state samples. Lattice compression, phase, and temperature are deduced from extended x-ray absorption fine structure (EXAFS) measurements, from which the shock-induced {alpha}-{omega} phase transition in Ti and the {alpha}-{var_epsilon} phase transition in Fe are inferred to occur on sub-nanosec time scales. Time resolved lattice response and phase can also be measured with dynamic x-ray diffraction measurements, where the elastic-plastic (1D-3D) lattice relaxation in shocked Cu is shown to occur promptly (< 1 ns). Subsequent large-scale molecular dynamics (MD) simulations elucidate the microscopic dynamics that underlie the 3D lattice relaxation. Deformation mechanisms are identified by examining the residual microstructure in recovered samples. The slip-twinning threshold in single-crystal Cu shocked along the [001] direction is shown to occur at shock strengths of {approx}20 GPa, whereas the corresponding transition for Cu shocked along the [134] direction occurs at higher shock strengths. This slip-twinning threshold also depends on the stacking fault energy (SFE), being lower for low SFE materials. Designs have been developed for achieving much higher pressures, P > 1000 GPa, in the solid state on the National Ignition Facility (NIF) laser.

  6. The variation of the yield stress of Ti alloys with strain rate at high temperatures

    SciTech Connect

    Rosen, R.S.; Paddon, S.P.; Kassner, M.E.

    1999-06-01

    This study extended investigation on the elevated-temperature yield-strength dependence of beta-phase titanium alloys on strain rate and temperature. Yield stresses were found to increase substantially with increasing strain rate at elevated temperatures due to the high strain-rate sensitivity of titanium at high temperatures. Above 1000 C, the strain-rate sensitivities were found to increase substantially with increasing temperature and/or decreasing strain rate. The six alloys examined were TIMETAL 21S, Ti-15-3-, Ti-6-4, Ti-13-11-3, Beta C, and Beta III. There was particular interest in determining the strain-rate sensitivity of these alloys through strain-rate change tests above 1000 C. The yield stresses of all the titanium alloys at temperatures above 1093 C were less than 1% of their ambient temperature values. strain hardening was negligible in the alloys tested at these high temperatures. Extended tensile ductilities of 100 to 200% were observed due to the pronounced strain-rare sensitivity. The rate controlling mechanism for plasticity, based on activation energy and the strain-rate sensitivity measurements, is discussed.

  7. Grain-size-independent plastic flow at ultrahigh pressures and strain rates.

    PubMed

    Park, H-S; Rudd, R E; Cavallo, R M; Barton, N R; Arsenlis, A; Belof, J L; Blobaum, K J M; El-dasher, B S; Florando, J N; Huntington, C M; Maddox, B R; May, M J; Plechaty, C; Prisbrey, S T; Remington, B A; Wallace, R J; Wehrenberg, C E; Wilson, M J; Comley, A J; Giraldez, E; Nikroo, A; Farrell, M; Randall, G; Gray, G T

    2015-02-13

    A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion. PMID:25723227

  8. Grain-size-independent plastic flow at ultrahigh pressures and strain rates.

    PubMed

    Park, H-S; Rudd, R E; Cavallo, R M; Barton, N R; Arsenlis, A; Belof, J L; Blobaum, K J M; El-dasher, B S; Florando, J N; Huntington, C M; Maddox, B R; May, M J; Plechaty, C; Prisbrey, S T; Remington, B A; Wallace, R J; Wehrenberg, C E; Wilson, M J; Comley, A J; Giraldez, E; Nikroo, A; Farrell, M; Randall, G; Gray, G T

    2015-02-13

    A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion.

  9. The high-strain-rate and spallation response of tantalum, Ta-10W, and T-111

    SciTech Connect

    Gray, G.T. III; Rollett, A.D.

    1991-01-01

    The compressive true stress-true response of tantalum, Ta-10W, and T-111 were found to depend on the applied strain rate, in the range 0.001 to 7000 s{sup {minus}1}. The strain-rate sensitivities of the flow stress of tantalum, Ta-10W, and T-111 a 1% strain are 0.062, 0.031, and 0.024, respectively. The rates of strain hardening in Tantalum, Ta-10W, and T-111 are seen to exhibit differing behavior with increasing strain rate. The calculated average strain-hardening rate in tantalum, {Theta}, for the quasi-static (0.001 s{sup {minus}1}) data at 25{degrees}C is 2080 MPa/unit strain. The hardening rate at 3000s{sup {minus}1} at 25{degrees}C decreases to 846 MPa/unit strain. Normalizing the work hardening rate in tantalum with the Taylor Factor for a random polycrystal, ({Theta} / (3.07){sup 2}), yields work hardening rates of {mu}/276 at quasi-static strain rates and {mu}/680 at high-rates, assuming a shear modulus of 61 GPa for tantalum at room temperature. While the work hardening of all the tantalum-based materials are similar at quasi-static rates, alloying results in a small reduction in hardening rate. With increasing strain rate, the work hardening rate in tantalum decreases by approximately a factor of two compared to the alloys. Alloying tantalum with substitutional or interstitial elements is thought to result in increased edge dislocation storage and screw dislocation cross-slip due to interactions with the alloying elements at high strain rates. 28 refs.

  10. High-strain-rate characterization of TPOs and graphite/epoxy and graphite/peek composites

    NASA Astrophysics Data System (ADS)

    Brar, N. S.; Simha, H.; Pratap, A.

    2001-06-01

    Tensile and compressive stress-strain response of two types of TPOs and graphite-epoxy composites are investigated at strain rates in the range 0.001/s-1000/s. Specimen strain in the low strain rate regime 0.001-100/s was determined using an optical extensometer in conjunction with standard MTS machine. Tensile test at high strain rate were performed on newly developed tensile version of All- Polymeric Split Hopkinson Bar. Tensile TPO specimens in the dog-bone configuration are placed in specially designed grips fabricated from nylatron. Compression response of TPO specimens at high strain rate is determined using 25.4-mm diameter aluminum bars. Peak compressive stress increases from 10 MPa at a strain rate of 100/s to 35 MPa at a strain rate of 1000/s. Preliminary data on high strain rate tensile response of graphite-epoxy and graphite-peek composites are presented. These data are intended to develop a material model incorporating strain rate sensitivity for TPOs and to be used in car crash simulations.

  11. Sequential Effects in Essay Ratings

    ERIC Educational Resources Information Center

    Attali, Yigal

    2011-01-01

    Contrary to previous research on sequential ratings of student performance, this study found that professional essay raters of a large-scale standardized testing program produced ratings that were drawn toward previous ratings, creating an assimilation effect. Longer intervals between the two adjacent ratings and higher degree of agreement with…

  12. EXPLOMET 90 international conference on shock-wave and high-strain-rate phenomena in materials

    NASA Astrophysics Data System (ADS)

    Meyers, Marc A.; Murr, Lawrence E.; Staudhammer, Karl P.

    1992-01-01

    This report describes the major components and activities of EXPLOMET 90, an international conference on shock-wave and high-strain-rate effects held at UCSD August 12-17, 1990. The conference was attended by approximately 200 scientists and engineers from throughout the world and was enriched by invited/keynote lectures by a group of world-renowned scientists. Over 110 talks were presented and twenty posters were displayed. The proceedings are being published by M. Dekker and will appear in February 1992. Sessions were devoted to the following topics: (1) High Strain Rate Deformation; (2) Shock and Combustion Synthesis; (3) Dynamic Consolidation; (4) Shaped Charge Phenomena; (5) Shear Localization; (6) Dynamic Fracture; (7) Shock Phenomena and Superconductivity; (8) Shock Waves and Shock Loading; (9) Shock and Dynamic Phenomena in Ceramics; and (10) Explosive Welding and Metalworking.

  13. Application of a nanosecond laser pulse to evaluate dynamic hardness under ultra-high strain rate

    NASA Astrophysics Data System (ADS)

    Radziejewska, Joanna

    2016-04-01

    The paper presents results of experimental tests of plastic metals deformation generated by a shock wave induced by laser pulse. Tests were carried out on the Nd:YAG laser with a wavelength of 1064 nm and the laser pulse of 10 ns duration. The shock wave generate by the laser pulse was used to induced local plastic deformation of the material surface. The study examined the possibility of application the process to develop a new method of measuring the dynamic hardness of materials under ultra-high strain rate. It has been shown that the shock wave induced by the laser pulse with an energy of 0.35-1.22 J causes a repeatable plastic deformation of surface of commercially available metals and alloys without thermal effects on the surfaces. Based on the knowledge of an imprint geometry, it is possible to evaluate the dynamic hardness of materials at strain rate in the range of 107 s-1.

  14. Maximum Principal Strain and Strain Rate Associated with Concussion Diagnosis Correlates with Changes in Corpus Callosum White Matter Indices

    PubMed Central

    MCALLISTER, THOMAS W.; FORD, JAMES C.; JI, SONGBAI; BECKWITH, JONATHAN G.; FLASHMAN, LAURA A.; PAULSEN, KEITH; GREENWALD, RICHARD M.

    2014-01-01

    On-field monitoring of head impacts, combined with finite element (FE) biomechanical simulation, allow for predictions of regional strain associated with a diagnosed concussion. However, attempts to correlate these predictions with in vivo measures of brain injury have not been published. This article reports an approach to and preliminary results from the correlation of subject-specific FE model-predicted regions of high strain associated with diagnosed concussion and diffusion tensor imaging to assess changes in white matter integrity in the corpus callosum (CC). Ten football and ice hockey players who wore instrumented helmets to record head impacts sustained during play completed high field magnetic resonance imaging preseason and within 10 days of a diagnosed concussion. The Dartmouth Subject-Specific FE Head model was used to generate regional predictions of strain and strain rate following each impact associated with concussion. Maps of change in fractional anisotropy (FA) and median diffusivity (MD) were generated for the CC of each athlete to correlate strain with change in FA and MD. Mean and maximum strain rate correlated with change in FA (Spearman ρ = 0.77, p = 0.01; 0.70, p = 0.031), and there was a similar trend for mean and maximum strain (0.56, p = 0.10; 0.6, p = 0.07), as well as for maximum strain with change in MD (−0.63, p = 0.07). Change in MD correlated with injury-to-imaging interval (ρ = −0.80, p = 0.006) but change in FA did not (ρ = 0.18, p = 0.62). These results provide preliminary confirmation that model-predicted strain and strain rate in the CC correlate with changes in indices of white matter integrity. PMID:21994062

  15. Myocardial Strain and Strain Rate in Kawasaki Disease: Range, Recovery, and Relationship to Systemic Inflammation/Coronary Artery Dilation

    PubMed Central

    Frank, Benjamin; Davidson, Jesse; Tong, Suhong; Martin, Blake; Heizer, Heather; Anderson, Marsha S; Glode, Mary P; Dominguez, Samuel R; Jone, Pei-Ni

    2016-01-01

    Background Kawasaki Disease (KD), a systemic vasculitis of medium sized vessels, is the most common cause of acquired heart disease among children in the developed world. Some KD patients demonstrate echocardiographic evidence of depressed myocardial mechanics. However, the incidence, etiology, and reversibility of abnormal mechanics in KD patients remain undefined. Methods and results We retrospectively studied 41 KD patients and measured myocardial strain and strain rate by velocity vector imaging from pre-treatment and convalescent echocardiograms. Pre-treatment procalcitonin, C-reactive protein (CRP), and coronary artery z-scores were obtained in all patients and compared between the groups with preserved versus depressed acute phase mechanics. The change in mechanics between the acute and convalescent phases was also assessed. Patients with initially low longitudinal strain improved by the convalescent period (mean difference - 4.0%; p<0.005) with the greatest improvement occurring in patients with the lowest initial strain (−7.3%; p<0.05). Patients with higher initial strain did not change significantly by the convalescent period. Patients with lower longitudinal and circumferential strain demonstrated higher median procalcitonin levels (1.2 vs. 0.3 ng/mL; p<0.05 and 1.8 vs. 0.4 ng/mL; p<0.05 respectively) and a trend towards higher CRP, but no difference in coronary artery z-scores. Strain rate was not associated with inflammatory markers or coronary artery z-scores. Conclusions The range of strain found in our cohort was large. Improvement in mean strain was driven primarily by patients with lower initial strain. Lower strain was associated with increased markers of systemic inflammation, but not proximal coronary artery changes. PMID:27182455

  16. A mechanistic study for strain rate sensitivity of rabbit patellar tendon

    PubMed Central

    Clemmer, John; Liao, Jun; Davis, Debbie; Horstemeyer, Mark F.; Williams, Lakiesha N.

    2014-01-01

    The ultrastructural mechanism for strain rate sensitivity of collagenous tissue has not been well studied at the collagen fibril level. Our objective is to reveal the mechanistic contribution of tendon's key structural component to strain rate sensitivity. We have investigated the structure of the collagen fibril undergoing tension at different strain rates. Tendon fascicles were pulled and fixed within the linear region (12% local tissue strain) at multiple strain rates. Although samples were pulled to the same percent elongation, the fibrils were noticed to elongate differently, increasing with strain rate. For the 0.1, 10, and 70%/s strain rates, there were 1.84±3.6%, 5.5±1.9%, and 7.03±2.2% elongations (mean±S.D.), respectively. We concluded that the collagen fibrils underwent significantly greater recruitment (fibril strain relative to global tissue strain) at higher strain rates. A better understanding of tendon mechanisms at lower hierarchical levels would help establish a basis for future development of constitutive models and assist in tissue replacement design. PMID:20678772

  17. Background rates of swarm earthquakes that are synchronized with volumetric strain changes

    NASA Astrophysics Data System (ADS)

    Kumazawa, Takao; Ogata, Yosihiko; Kimura, Kazuhiro; Maeda, Kenji; Kobayashi, Akio

    2016-05-01

    Off the east coast of the Izu Peninsula in Japan, there is a submarine volcanic region where earthquake swarms occur caused by magma intrusions. We investigated the background seismicity rates of the swarm activity by removing the triggering effect of aftershocks. We found that such background rate changes coincide with the changes of exponentially weighted averages of volumetric strain increments at the Higashi-Izu station. We further found that such a relationship consistently depends on the distance between the strainmeter station and the location of the swarm onset. The quantitative relationships revealed here may be used to monitor magma intrusions that drive the stress changes.

  18. Compressive properties of a closed-cell aluminum foam as a function of strain-rate and temperature

    SciTech Connect

    Cady, Carl M; Gray, Ill, George T; Liu, Cheng; Lovato, Manuel L; Mukai, T

    2008-01-01

    The compressive constitutive behavior of a closed-cell aluminum foam (ALPORAS) manufactured by Shinko Wire Co. in Japan was evaluated under static and dynamic loading conditions as a function of temperature. High-strain-rate tests (1000-2000 s{sup -1}) were conducted using a split-Hopkinson pressure bar (SHPB). Quasi-static and intermediate-strain-rate tests were conducted on a hydraulic load frame. A small but discernable change in the flow stress behavior as a function of strain rate was measured. The deformation behavior of the Al-foam was however found to be strongly temperature dependent under both quasi-static and dynamic loading. Localized deformation and stress state instability during testing of metal foams is discussed in detail since the mechanical behavior over the entire range of strain rates indicates non-uniform deformation. Additionally, investigation of the effect of residual stresses created during manufacturing on the mechanical behavior was investigated.

  19. The role of reactant unmixedness, strain rate, and length scale on premixed combustor performance

    SciTech Connect

    Samuelsen, S.; LaRue, J.; Vilayanur, S.; Guillaume, D.

    1995-12-31

    Lean premixed combustion provides a means to reduce pollutant formation and increase combustion efficiency. However, fuel-air mixing is rarely uniform in space and time. This nonuniformity in concentration will lead to relative increases in pollutant formation and decreases in combustion efficiency. The nonuniformity of the concentration at the exit of the premixer has been defined by Lyons (1981) as the ``unmixedness.`` Although turbulence properties such as length scales and strain rate are known to effect unmixedness, the exact relationship is unknown. Evaluating this relationship and the effect of unmixedness in premixed combustion on pollutant formation and combustion efficiency are an important part of the overall goal of US Department of Energy`s Advanced Turbine System (ATS) program and are among the goals of the program described herein. The information obtained from ATS is intended to help to develop and commercialize gas turbines. The contributions to the program which the University of California (Irvine) Combustion Lab (UCICL) will provide are: (1) establish the relationship of inlet unmixedness, length scales, and mean strain rate to performance, (2) determine the optimal levels of inlet unmixedness, length scales, and mean strain rates to maximize combustor performance, and (3) identify efficient premixing methods for achieving the necessary inlet conditions. The program during this reporting period is focused on developing a means to measure and qualify different degrees of temporal and spatial unmixedness. Laser diagnostic methods for planer unmixedness measurements are being developed and preliminary results are presented herein. These results will be used to (1), aid in the design of experimental premixers, and (2), determine the unmixedness which will be correlated with the emissions of the combustor. This measure of unmixedness coupled with length scale, strain rate and intensity information is required to attain the UCI goals.

  20. Growth of voids in porous ductile materials at high strain rate

    NASA Astrophysics Data System (ADS)

    Wang, Ze-Ping

    1994-08-01

    A hollow-sphere model, with temperature-dependent viscoplastic material response, is developed to investigate the inertial and thermal effects on dynamic growth of voids in ductile materials. Theoretical analysis indicates that the inertial effect (kinetic energy of void growth) mainly dominates the behavoir of the void growth in temperature-dependent and high-strain-rate cases. Otherwise, the viscoplastic effect dominanes and the inertial effect can be negelcted. The rate of the dyanmic growth of voids increases when the thermal effect is considered. An expression of the threshold stress for the void growth is obtained, which depends on the initial porosity, the porosity, the yield strength, the density of surface energy of voids, the initial temperature, and the melting temperature.

  1. Modelling the rheology of MgO under Earth's mantle pressure, temperature and strain rates.

    PubMed

    Cordier, Patrick; Amodeo, Jonathan; Carrez, Philippe

    2012-01-12

    Plate tectonics, which shapes the surface of Earth, is the result of solid-state convection in Earth's mantle over billions of years. Simply driven by buoyancy forces, mantle convection is complicated by the nature of the convecting materials, which are not fluids but polycrystalline rocks. Crystalline materials can flow as the result of the motion of defects--point defects, dislocations, grain boundaries and so on. Reproducing in the laboratory the extreme deformation conditions of the mantle is extremely challenging. In particular, experimental strain rates are at least six orders of magnitude larger than in nature. Here we show that the rheology of MgO at the pressure, temperature and strain rates of the mantle is accessible by multiscale numerical modelling starting from first principles and with no adjustable parameters. Our results demonstrate that extremely low strain rates counteract the influence of pressure. In the mantle, MgO deforms in the athermal regime and this leads to a very weak phase. It is only in the lowermost lower mantle that the pressure effect could dominate and that, under the influence of lattice friction, a viscosity of the order of 10(21)-10(22) pascal seconds can be defined for MgO. PMID:22237109

  2. A renewed argument for crystal size control of ice sheet strain rates

    NASA Astrophysics Data System (ADS)

    Cuffey, K. M.; Thorsteinsson, T.; Waddington, E. D.

    2000-12-01

    At present, it is generally believed that crystal size has no direct influence on strain rate in the ice sheets and that the fraction of strain rate enhancement there which is not ascribable to c axis fabric is due to impurity content. Here we challenge this view because it is not consistent with recent results from analyses of deformation at Meserve Glacier and instead ascribe residual enhancement in the ice sheets to variations in crystal size. We resurrect the idea that variations of crystal size can be an important part of the total shear enhancement in the ice sheets, though agree with Paterson that this effect is generally dominated by variations of crystal fabric. We propose that the enhanced shear strain rate of ice age ice in southern Greenland, as inferred from tilt of the Dye 3 borehole, can be explained as a result of combined fabric variations and crystal size variations, with these two ice properties accounting for roughly 70% and 30% of the average enhancement, respectively. Permitting a grain size dependence of ice viscosity also resolves the quandary concerning closure and tilt of the Agassiz Ice Cap borehole.

  3. Modeling Anisotropic Plasticity: 3D Eulerian Hydrocode Simulations of High Strain Rate Deformation Processes

    NASA Astrophysics Data System (ADS)

    Burkett, Michael; Clancy, Sean; Maudlin, Paul; Holian, Kathleen

    2001-06-01

    : Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength has been implemented in the three-dimensional CONEJO hydrodynamics code. CONEJO is an explicit, Eulerian continuum mechanics code that is utilized to predict formation processes associated with material deformation at elevated strain-rates and is a code development project under the Accelerated Strategic Computing Initiative (ASCI) program. Some special features of CONEJO include a high-order advection algorithm, a material interface tracking scheme, and van Leer monotonic advection-limiting. The anisotropic constitutive modeling is posed in an unrotated material frame using the theorem of polar decomposition to describe rigid body rotation. An Euler-Rodrigues description is used to quantify the rigid body rotations. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Associative flow formulations incorporating these yield functions were solved using a geometric normal return method. Simple rectangular shear problems, "R-value" problems, and Taylor cylinder impact test data were utilized to verify and validate the implementation of the anisotropic model. A "stretching rod" problem (involving large strain and strain-rate deformation) was selected to investigate the effects of material anisotropy for this deformation process. The rod necking rate and topology was compared for CONEJO simulations using several isotropic and anisotropic descriptions that utilized the Mechanical Threshold Stress (MTS) model.

  4. Tensile Strength of Carbon Nanotubes Under Realistic Temperature and Strain Rate

    NASA Technical Reports Server (NTRS)

    Wei, Chen-Yu; Cho, Kyeong-Jae; Srivastava, Deepak; Biegel, Bryan (Technical Monitor)

    2002-01-01

    Strain rate and temperature dependence of the tensile strength of single-wall carbon nanotubes has been investigated with molecular dynamics simulations. The tensile failure or yield strain is found to be strongly dependent on the temperature and strain rate. A transition state theory based predictive model is developed for the tensile failure of nanotubes. Based on the parameters fitted from high-strain rate and temperature dependent molecular dynamics simulations, the model predicts that a defect free micrometer long single-wall nanotube at 300 K, stretched with a strain rate of 1%/hour, fails at about 9 plus or minus 1% tensile strain. This is in good agreement with recent experimental findings.

  5. Experimental study of vorticity-strain rate interaction in turbulent partially-premixed jet flames using tomographic particle image velocimetry

    DOE PAGESBeta

    Coriton, Bruno; Frank, Jonathan H.

    2016-02-16

    In turbulent flows, the interaction between vorticity, ω, and strain rate, s, is considered a primary mechanism for the transfer of energy from large to small scales through vortex stretching. The ω-s coupling in turbulent jet flames is investigated using tomographic particle image velocimetry (TPIV). TPIV provides a direct measurement of the three-dimensional velocity field from which ω and s are determined. The effects of combustion and mean shear on the ω-s interaction are investigated in turbulent partially premixed methane/air jet flames with high and low probabilities of localized extinction as well as in a non-reacting isothermal air jet withmore » Reynolds number of approximately 13,000. Results show that combustion causes structures of high vorticity and strain rate to agglomerate in highly correlated, elongated layers that span the height of the probe volume. In the non-reacting jet, these structures have a more varied morphology, greater fragmentation, and are not as well correlated. The enhanced spatiotemporal correlation of vorticity and strain rate in the stable flame results in stronger ω-s interaction characterized by increased enstrophy and strain-rate production rates via vortex stretching and straining, respectively. The probability of preferential local alignment between ω and the eigenvector of the intermediate principal strain rate, s2, which is intrinsic to the ω-s coupling in turbulent flows, is larger in the flames and increases with the flame stability. The larger mean shear in the flame imposes a preferential orientation of ω and s2 tangential to the shear layer. The extensive and compressive principal strain rates, s1 and s3, respectively, are preferentially oriented at approximately 45° with respect to the jet axis. As a result, the production rates of strain and vorticity tend to be dominated by instances in which ω is parallel to the s1¯-s2¯ plane and orthogonal to s3¯.« less

  6. High Strain Rate Response Testing with the Split Hopkinson Pressure Bar Technique

    NASA Astrophysics Data System (ADS)

    Zwiessler, R.; Kenkmann, T.; Poelchau, M. H.; Nau, S.; Hess, S.

    2016-08-01

    We present a newly developed split Hopkinson pressure bar which is used to quantify the rate dependent uniaxial stress-strain response of rocks in the high strain rate regime as well as results of our first study on a sandstone and Carrara marble.

  7. The strain-rate sensitivity of high-strength high-toughness steels.

    SciTech Connect

    Dilmore, M.F.; Crenshaw, Thomas B.; Boyce, Brad Lee

    2006-01-01

    The present study examines the strain-rate sensitivity of four high strength, high-toughness alloys at strain rates ranging from 0.0002 s-1 to 200 s-1: Aermet 100, a modified 4340, modified HP9-4-20, and a recently developed Eglin AFB steel alloy, ES-1c. A refined dynamic servohydraulic method was used to perform tensile tests over this entire range. Each of these alloys exhibit only modest strain-rate sensitivity. Specifically, the strain-rate sensitivity exponent m, is found to be in the range of 0.004-0.007 depending on the alloy. This corresponds to a {approx}10% increase in the yield strength over the 7-orders of magnitude change in strain-rate. Interestingly, while three of the alloys showed a concominant {approx}3-10% drop in their ductility with increasing strain-rate, the ES1-c alloy actually exhibited a 25% increase in ductility with increasing strain-rate. Fractography suggests the possibility that at higher strain-rates ES-1c evolves towards a more ductile dimple fracture mode associated with microvoid coalescence.

  8. A comparative study of high strain rate behavior of three martensitic steels

    NASA Astrophysics Data System (ADS)

    Last, H. R.; Garrett, R. K.; Rajendran, A. M.

    1996-05-01

    This paper describes the high strain rate response of HY100, HY130 and AF1410 steels determined from the split Hopkinson bar and quasi-static experiments under room and high temperatures. Differences in the macroscopic high strain rate response of these steels were observed. Metallurgical fracture surface analysis provided insight into the microstructural response and the observed macroscopic behavior of each steel.

  9. Dynamic High-Temperature Characterization of an Iridium Alloy in Compression at High Strain Rates

    SciTech Connect

    Song, Bo; Nelson, Kevin; Lipinski, Ronald J.; Bignell, John L.; Ulrich, G. B.; George, E. P.

    2014-06-01

    Iridium alloys have superior strength and ductility at elevated temperatures, making them useful as structural materials for certain high-temperature applications. However, experimental data on their high-temperature high-strain-rate performance are needed for understanding high-speed impacts in severe elevated-temperature environments. Kolsky bars (also called split Hopkinson bars) have been extensively employed for high-strain-rate characterization of materials at room temperature, but it has been challenging to adapt them for the measurement of dynamic properties at high temperatures. Current high-temperature Kolsky compression bar techniques are not capable of obtaining satisfactory high-temperature high-strain-rate stress-strain response of thin iridium specimens investigated in this study. We analyzed the difficulties encountered in high-temperature Kolsky compression bar testing of thin iridium alloy specimens. Appropriate modifications were made to the current high-temperature Kolsky compression bar technique to obtain reliable compressive stress-strain response of an iridium alloy at high strain rates (300 – 10000 s-1) and temperatures (750°C and 1030°C). Uncertainties in such high-temperature high-strain-rate experiments on thin iridium specimens were also analyzed. The compressive stress-strain response of the iridium alloy showed significant sensitivity to strain rate and temperature.

  10. Mechanical deformation model of the western United States instantaneous strain-rate field

    USGS Publications Warehouse

    Pollitz, F.F.; Vergnolle, M.

    2006-01-01

    system is systematically underpredicted by models which account only for relaxation from known large earthquakes. This strongly suggests that in addition to viscoelastic-cycle effects, steady deep slip in the lower lithosphere is needed to explain the observed strain-rate field. ?? 2006 The Authors Journal compilation ?? 2006 RAS.

  11. Influence of strain rate and temperature on the mechanical behavior of beryllium

    SciTech Connect

    Blumenthal, W. R.; Abeln, S. P.; Cannon, D. D.; Gray, G. T. III; Carpenter, R. W.

    1998-07-10

    The compressive stress-strain response of three grades of beryllium were studied as a function of strain rate and temperature. Grades S200D, E, and F represent a historical perspective of beryllium processing from the 1960's through 1990's technology. The purpose of this study was to measure the mechanical behavior of beryllium over a range of deformation conditions for constitutive model development and to obtain microstructural evidence for deformation mechanisms. The compressive stress-strain response was found to be independent of grade and strongly dependent on the applied strain rate between 0.001 and 8000 s{sup -1}. The strain-hardening response displayed a moderate temperature dependence between 77 deg. K and 873 deg. K. Microstructural examination of SHPB specimens revealed that twinning was extensive at strains above 7%. A SHPB sample deformed to over 20% strain contained both twinning and grain boundary microcracking.

  12. High strain rate properties of off-axis composite laminates, part 2

    NASA Technical Reports Server (NTRS)

    Daniel, I. M.

    1991-01-01

    Unidirectional off-axis graphite/epoxy and graphite/S-glass/epoxy laminates were characterized in uniaxial tension at strain rates ranging from quasi-static to over 500 s(sup -1). Laminate ring specimens were loaded by internal pressure with the tensile stress at 22.5, 30, and 45 degrees relative to the fiber direction. Results were presented in the form of stress-strain curves to failure. Properties determined included moduli, Poisson's ratios, strength, and ultimate strain. In all three laminates of both materials the modulus and strength increase sharply with strain rate, reaching values roughly 100, 150, and 200 percent higher than corresponding static values for the 22.5(sub 8), 30(sub 8), and 45(sub 8) degree laminates, respectively. In the case of ultimate strain no definite trends could be established, but the maximum deviation from the average of any value for any strain rate was less than 18 percent.

  13. High strain rate characterization of low-density low-strength materials

    NASA Astrophysics Data System (ADS)

    Sawas, O.; Brar, N. S.; Brockman, R. A.

    1998-07-01

    The Conventional Split Hopkinson Bar (CSHB) is a reliable experimental technique for measuring high strain rate properties of high-strength materials. Attempts to use the CSHB for similar measurements in more compliant materials, such as plastics and foams, are limited by the maximum achievable strain and high noise-to-signal ratios. This work introduces an all-polymeric split Hopkinson bar (APSHB) experiment, which overcomes these limitations. The proposed method uses polymeric pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials, thus providing both low noise-to-signal ratio data and a longer input pulse for higher maximum strain. Data reduction procedures for APSHB that account for the viscoelastic behavior of the pressure bars are presented. Comparing the high strain rate response of 1100 Al obtained from CSHB and APSHB validates these procedures. Stress-strain data at strain rates of 500-2000/s for polycarbonate, polyurethane foam, and styrofoam are presented.

  14. How to test brain and brain simulant at ballistic and blast strain rates.

    PubMed

    Zhang, Jiangyue; Song, Bo; Pintar, Frank A; Yoganandan, Narayan; Chen, Weinong; Gennarelli, Thomas A

    2008-01-01

    Mechanical properties of brain tissue and brain simulant at strain rate in the range of 1000 s-1 are essential for computational simulation of intracranial responses for ballistic and blast traumatic brain injury. Testing these ultra-soft materials at high strain rates is a challenge to most conventional material testing methods. The current study developed a modified split Hopkinson bar techniques using the combination of a few improvements to conventional split Hopkinson bar including: using low impedance aluminum bar, semiconductor strain gauge, pulse shaping technique and annular specimen. Feasibility tests were conducted using a brain stimulant, Sylgard 527. Stress-strain curves of the simulant were successfully obtained at strain rates of 2600 and 2700 s-1 for strain levels up to 60%. This confirmed the applicability of Hopkinson bar for mechanical properties testing of brain tissue in the ballistic and blast domain.

  15. Modeling anisotropy plasticity : 3D Eulerian hydrocode simulations of high strain rate deformation processes.

    SciTech Connect

    Burkett, M. W.; Clancy, S. P.; Maudlin, P. J.; Holian, K. S.

    2001-01-01

    Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength have been implemented in the three-dimensional Conejo hydrodynamics code. The anisotropic constitutive modeling is posed in an unrotated material frame of reference using the theorem of polar decomposition to obtain rigid body rotation. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Simple rectangular shear problems, R-value problems, and Taylor cylinder impact data were used to verify and validate the implementation of the anisotropic model. A stretching rod problem (involving large strain and high strain-rate deformation) was selected to investigate the effects of material anisotropy. Conejo simulations of rod topology were compared for two anisotropic cases.

  16. Modeling Anisotropic Plasticity: 3D Eulerian Hydrocode Simulations of High Strain Rate Deformation Processes

    NASA Astrophysics Data System (ADS)

    Burkett, Michael W.; Clancy, Sean P.; Maudlin, Paul J.; Holian, Kathleen S.

    2002-07-01

    Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength have been implemented in the three-dimensional Conejo hydrodynamics code. The anisotropic constitutive modeling is posed in an unrotated material frame of reference using the theorem of polar decomposition to obtain rigid body rotation. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Simple rectangular shear problems, R-Value problems, and Taylor cylinder impact data were used to verify and validate the implementation of the anisotropic model. A stretching rod problem (involving large strain and high strain-rate deformation) was selected to investigate the effects of material anisotropy. Conejo simulations of rod topology were compared for two anisotropic cases.

  17. Strain Rate Dependence of Compressive Yield and Relaxation in DGEBA Epoxies

    NASA Astrophysics Data System (ADS)

    Arechederra, Gabriel K.; Reprogle, Riley C.; Clarkson, Caitlyn M.; McCoy, John D.; Kropka, Jamie M.; Long, Kevin N.; Chambers, Robert S.

    2015-03-01

    The mechanical response in uniaxial compression of two diglycidyl ether of bisphenol-A epoxies were studied. These were 828DEA (Epon 828 cured with diethanolamine (DEA)) and 828T403 (Epon 828 cured with Jeffamine T-403). Two types of uniaxial compression tests were performed: A) constant strain rate compression and B) constant strain rate compression followed by a constant strain relaxation. The peak (yield) stress was analyzed as a function of strain rate from Eyring theory for activation volume. Runs at different temperatures permitted the construction of a mastercurve, and the resulting shift factors resulted in an activation energy. Strain and hold tests were performed for a low strain rate where a peak stress was lacking and for a higher strain rate where the peak stress was apparent. Relaxation from strains at different places along the stress-strain curve was tracked and compared. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  18. Refined models of gravitational potential energy compared with stress and strain rate patterns in Iberia

    NASA Astrophysics Data System (ADS)

    Neves, Maria C.; Fernandes, Rui M.; Adam, Claudia

    2014-11-01

    This study examines the role of gravitational potential energy (GPE) in generating second-order (spatial scale ∼102 km) variations in the Iberia stress and strain-rate patterns. We present a new map of present-day strain rate field derived from the secular velocity field computed using all available continuously operating Global Navigation Satellite Systems (GNSS) stations in Iberia. The estimated strain rate field is generally consistent with the tectonic framework of the Iberian region, even though sporadic sharp local variations downgrade its correlation with the regional stress patterns. Many of the sharp spatial variations in the strain rate map are consistent with local changes of deformation style determined by prevailing faults. To obtain a more accurate estimate of GPE we use new data on the structure of the crust and apply a thin sheet approach using a 3-D definition of deviatoric stress. The GPE is derived from two isostatically compensated models (GPEd and GPEe compensated by density and elevation adjustment, respectively) and from the truncated geoid (GPEg). The GPE stresses are then summed with the first-order stress field due to the Eurasia-Nubia (EU-NU) convergence and the results compared with both the stress and strain rate data. In agreement with previous studies, we find that the GPE does not significantly change the NW-SE average direction of the most compressive stress (SHmax) imposed by the EU-NU collision, its main effect being to cause spatially changing stress regimes. From the analysis of the different GPE models we find: (1) in the Pyrenees, the tectonic forces have a secondary role when compared to the GPE. In this region, the model that best correlates with observations is the one emphasizing the role of surface elevation as a source of GPE (GPEe); (2) in the Iberian Chain and the Betics, the GPE imposes NE-SW extension consistent with a strike-slip regime and is equally (GPEe) or more (GPEg) important than the tectonic forces. In

  19. Evaluation and prediction of material response during superplastic forming at various strain rates

    NASA Astrophysics Data System (ADS)

    Agarwal, Sumit

    Current trends in the automotive industry include replacing steel body components by superplastically formed aluminum alloys. The application of aluminum alloys is largely limited by the slow forming rates required for the superplastic forming process. In order to overcome the difficulties associated with this process, considerable research is being done to study the behavior of AA5083 at high strain rates. However, the microstructure evolution under these deformation conditions has not been characterized previously. In this study we have studied the microstructure evolution in tensile specimens of AA5083 deformed at a wide range of strain rates. Strain rates between 0.0005 and 3/s were used for the tests, which were performed with the samples at 450°C. The results showed that a strong crystallographic texture develops and the most highly strained regions of the samples recrystallize dynamically at strain rates greater than 0.01/s. For strain rates at or below 0.01/s, no recrystallization occurred. This recrystallization is stimulated by the constituent particles. The recrystallized grain size was smallest at the highly-strained, fracture point and increased in size as one moved away from the fracture end towards the grip of the sample. Below a critical strain, no further recrystallization was observed. This critical strain decreased with increasing strain rate and with an increase in the diameter of the largest constituent particles in the sample. Analysis of the results showed that both a critical strain rate and critical strain were required to achieve dynamic recrystallization. A model for critical strain rate by Humphreys and Kalu gave qualitative agreement with the experimental results. Tests were also conducted at room temperature followed by annealing at 450°C. Study of these specimens enabled a comparison of dynamic recrystallization with the critical strain driven static recrystallization process. Finite element simulations were used to predict the

  20. Constitutive equation for hardened SKD11 steel at high temperature and high strain rate using the SHPB technique

    NASA Astrophysics Data System (ADS)

    Tang, D. W.; Wang, C. Y.; Hu, Y. N.; Song, Y. X.

    2010-03-01

    In this present work, dynamic tests have been performed on hardened SKD11 steel (62 Rockwell C hardness) specimens by means of a high temperature split Hopkinson pressure bar (SHPB) test system. Effects of temperature as well as those of strain and strain rate for the hardened steel are taken into account by using two ellipsoidal radiant heating reflectors with two halogen lamps and magnetic valve. The result obtained at high stain rates were compared with those at low strain rates under the different temperature. It was seen that the flow stress curves are found to include a work hardening region and a work softening region and the mechanical behavior of the hardened steel is highly sensitive to both the strain rate and the temperature. To determine the true flow stress- true strain, temperature relationship, specimens are tested from room temperature to 1073K at a strain rate form 0.01 s-1 to 104 s-1: The parameters for a Johnson-Cook constitutive equation and a modified Johnson-Cook constitutive equation are determined from the test results by fitting the data from both quasi-static compression and high temperature-dynamic compression tests. The modified Johnson-Cook constitutive equation is more suitable for expressing the dynamic behavior of the hardened SKD11 steel above the vicinity of the recrystallization temperature.

  1. Constitutive equation for hardened SKD11 steel at high temperature and high strain rate using the SHPB technique

    NASA Astrophysics Data System (ADS)

    Tang, D. W.; Wang, C. Y.; Hu, Y. N.; Song, Y. X.

    2009-12-01

    In this present work, dynamic tests have been performed on hardened SKD11 steel (62 Rockwell C hardness) specimens by means of a high temperature split Hopkinson pressure bar (SHPB) test system. Effects of temperature as well as those of strain and strain rate for the hardened steel are taken into account by using two ellipsoidal radiant heating reflectors with two halogen lamps and magnetic valve. The result obtained at high stain rates were compared with those at low strain rates under the different temperature. It was seen that the flow stress curves are found to include a work hardening region and a work softening region and the mechanical behavior of the hardened steel is highly sensitive to both the strain rate and the temperature. To determine the true flow stress- true strain, temperature relationship, specimens are tested from room temperature to 1073K at a strain rate form 0.01 s-1 to 104 s-1: The parameters for a Johnson-Cook constitutive equation and a modified Johnson-Cook constitutive equation are determined from the test results by fitting the data from both quasi-static compression and high temperature-dynamic compression tests. The modified Johnson-Cook constitutive equation is more suitable for expressing the dynamic behavior of the hardened SKD11 steel above the vicinity of the recrystallization temperature.

  2. Tensile behaviour of geopolymer-based materials under medium and high strain rates

    NASA Astrophysics Data System (ADS)

    Menna, Costantino; Asprone, Domenico; Forni, Daniele; Roviello, Giuseppina; Ricciotti, Laura; Ferone, Claudio; Bozza, Anna; Prota, Andrea; Cadoni, Ezio

    2015-09-01

    Geopolymers are a promising class of inorganic materials typically obtained from an alluminosilicate source and an alkaline solution, and characterized by an amorphous 3-D framework structure. These materials are particularly attractive for the construction industry due to mechanical and environmental advantages they exhibit compared to conventional systems. Indeed, geopolymer-based concretes represent a challenge for the large scale uses of such a binder material and many research studies currently focus on this topic. However, the behaviour of geopolymers under high dynamic loads is rarely investigated, even though it is of a fundamental concern for the integrity/vulnerability assessment under extreme dynamic events. The present study aims to investigate the effect of high dynamic loading conditions on the tensile behaviour of different geopolymer formulations. The dynamic tests were performed under different strain rates by using a Hydro-pneumatic machine and a modified Hopkinson bar at the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. The results are processed in terms of stress-strain relationships and strength dynamic increase factor at different strain-rate levels. The dynamic increase factor was also compared with CEB recommendations. The experimental outcomes can be used to assess the constitutive laws of geopolymers under dynamic load conditions and implemented into analytical models.

  3. Studies on Dynamic Damage Evolution for Pp/pa Polymer Blends Under High Strain Rates

    NASA Astrophysics Data System (ADS)

    Sun, Zi-Jian; Wang, Li-Li

    The dynamic damage evolution for PP/PA blends with different compatibilizers is studied in high strain rates from two different approaches, namely by determining the unloading elastic modulus of specimen experienced impact deformation and by combining the split Hopkinson pressure bar (SHPB) experimental technique with the back-propagation (BP) neural network. The results obtained by both approaches consistently show that a threshold strain ɛth exists for dynamic damage evolution, and both the damage evolution and ɛth are dependent on strain and strain rate. For non-linear visco-elastic materials, the damage evolution determined by the unloading elastic modulus provides an underestimation of real damage evolution.

  4. Investigating strength of materials at very high strain rates using magnetically driven expanding cylinders

    NASA Astrophysics Data System (ADS)

    Lovinger, Zev; Nemirovsky, Ron; Avriel, Eyal; Dorogoy, Avraham; Ashuach, Yehezkel; Rittel, Daniel

    2015-09-01

    Dynamic characterization of strength properties is done, in common practice by the means of a Split-Hopkinson Pressure Bar (also named Kolsky-Bar) apparatus. In such systems, strain rates are limited up to ˜ 5 ṡ 103 sec-1. For higher strain rates, the strain rate hardening is assumed to be the same as that measured at lower rates, with no direct measurement to validate the assumptions used for this extrapolation. In this work we are using a pulsed current generator (PCG) to create electro-magnetic (EM) driving forces on expanding cylinders. Most standard techniques for creating EM driving forces on cylinders or rings, as reported in the literature, reach strain rates of 1e3-1e4. Using our PCG, characterized by a fast rise time, we reach strain rates of ˜1e5, thus paving the way to a standard technique to measure strength at very high strain rates. To establish the experimental technique, we conducted a numerical study of the expanding cylinder set up using 2D hydrodynamic simulations to reach the desired high strain rates.

  5. Strain-rate/temperature behavior of high density polyethylene in compression

    NASA Technical Reports Server (NTRS)

    Clements, L. L.; Sherby, O. D.

    1978-01-01

    The compressive strain rate/temperature behavior of highly linear, high density polyethylene was analyzed in terms of the predictive relations developed for metals and other crystalline materials. For strains of 5 percent and above, the relationship between applied strain rate, dotted epsilon, and resulting flow stress, sigma, was found to be: dotted epsilon exp times (Q sub f/RT) = k'(sigma/sigma sub c) to the nth power; the left-hand side is the activation-energy-compensated strain rate, where Q sub f is activation energy for flow, R is gas constant, and T is temperature; k is a constant, n is temperature-independent stress exponent, and sigma/sigma sub c is structure-compensated stress. A master curve resulted from a logarithmic plot of activation-energy-compensated strain rate versus structure-compensated stress.

  6. Strain-energy release rate analysis of cyclic delamination growth in compressively loaded laminates

    NASA Technical Reports Server (NTRS)

    Whitcomb, J. D.

    1984-01-01

    Delamination growth in compressively loaded composite laminates was studied analytically and experimentally. The configuration used was a laminate with an across-the-width delamination. An approximate super-position stress analysis was developed to quantify the effects of various geometric, material, and load parameters on mode 1 and mode 2 strain energy release rates G sub 1 and G sub 2, respectively. Calculated values of G sub 1 and G sub 2 were then compared with measured cyclic delamination growth rates to determine the relative importance of G sub 1 and G sub 2. High growth rates were observed only when G sub 1 was large. However, slow growth was observed even when G sub 1 was negligibly small. This growth was apparently due to a large value of G sub 2.

  7. Strain energy release rate analysis of cyclic delamination growth in compressively loaded laminates

    NASA Technical Reports Server (NTRS)

    Whitcomb, J. D.

    1983-01-01

    Delamination growth in compressively loaded composite laminates was studied analytically and experimentally. The configuration used was a laminate with an across-the-width delamination. An approximate super-position stress analysis was developed to quantify the effects of various geometric, material, and load parameters on mode 2 and mode 2 strain energy release rates G sub/1 and G sub 2, respectively. Calculated values of G sub 1 and G sub 2 were then compared with measured cyclic delamination growth rates to determine the relative importance of G sub 1 and G sub 2. High growth rates were observed only when G sub 1 was large. However, slow growth was observed even when G sub 1 was negligibly small. This growth apparently was due to a large value of G sub 2.

  8. Strain rate dependence of the tensile properties of V-(4--5%)Cr-(4--5%)Ti irradiated in EBR-II and HFBR

    SciTech Connect

    Zinkle, S.J.; Snead, L.L.; Robertson, J.P.; Rowcliffe, A.F.

    1998-03-01

    Elevated temperature tensile tests performed on V-(405)Cr-(4-5)Ti indicate that the yield stress increases with increasing strain rate for irradiation and test temperatures near 200 C, and decreases with increasing strain rate for irradiation and test temperatures near 400 C. This observation is in qualitative agreement with the temperature-dependent strain rate effects observed on unirradiated specimens, and implies that some interstitial solute remains free to migrate in irradiated specimens. Additional strain rate data at different temperatures are needed.

  9. Development of intermediate and high strain rate experimentation and material modeling for viscoplastic metals

    NASA Astrophysics Data System (ADS)

    Whittington, Wilburn Ray

    This work presents a combined theoretical-experimental study of strain rate behavior in metals. The method is to experimentally calibrate and validate an Internal State Variable (ISV) constitutive model with a wide range of strain rate sensitivity. Therefore a practical apparatus and methodology for performing highly sought-after intermediate strain rate experimentation was created. For the first time in reported literature, the structure-property relations of Rolled Homogeneous Armor is quantified at the microscale and modeled with varying strain rates, temperatures, and stress states to capture plasticity and damage with a single set of constants that includes intermediate strain rates. A rolled homogeneous armor (RHA) was used as a material system to prove the methodology. In doing so, a newly implemented strain rate dependent nucleation parameter for RHA was implemented to transition the dominant damage mechanism from void growth to void nucleation as strain rate increased. The ISVs were utilized in finite element analysis for robust predictability of mechanical performance as well as predictability of microstructural evolution with regards to void size and number distribution. For intermediate strain rate experiments, robust load acquisition was achieved using a novel serpentine transmittal bar that allowed for long stress waves to traverse a short bar system; this system eliminated load- ringing that plagues servo-hydraulic systems. A direct hydraulic loading apparatus was developed to provide uniform strain rates throughout intermediate rate tests to improve on the current limitations of the state-of-the-art. Key recommendations on the advancement of predictive modeling of dynamic materials, as well as performing advanced dynamic experimentation, are elucidated.

  10. Strain and rate-dependent neuronal injury in a 3D in vitro compression model of traumatic brain injury

    PubMed Central

    Bar-Kochba, Eyal; Scimone, Mark T.; Estrada, Jonathan B.; Franck, Christian

    2016-01-01

    In the United States over 1.7 million cases of traumatic brain injury are reported yearly, but predictive correlation of cellular injury to impact tissue strain is still lacking, particularly for neuronal injury resulting from compression. Given the prevalence of compressive deformations in most blunt head trauma, this information is critically important for the development of future mitigation and diagnosis strategies. Using a 3D in vitro neuronal compression model, we investigated the role of impact strain and strain rate on neuronal lifetime, viability, and pathomorphology. We find that strain magnitude and rate have profound, yet distinctively different effects on the injury pathology. While strain magnitude affects the time of neuronal death, strain rate influences the pathomorphology and extent of population injury. Cellular injury is not initiated through localized deformation of the cytoskeleton but rather driven by excess strain on the entire cell. Furthermore we find that, mechanoporation, one of the key pathological trigger mechanisms in stretch and shear neuronal injuries, was not observed under compression. PMID:27480807

  11. Strain and rate-dependent neuronal injury in a 3D in vitro compression model of traumatic brain injury.

    PubMed

    Bar-Kochba, Eyal; Scimone, Mark T; Estrada, Jonathan B; Franck, Christian

    2016-01-01

    In the United States over 1.7 million cases of traumatic brain injury are reported yearly, but predictive correlation of cellular injury to impact tissue strain is still lacking, particularly for neuronal injury resulting from compression. Given the prevalence of compressive deformations in most blunt head trauma, this information is critically important for the development of future mitigation and diagnosis strategies. Using a 3D in vitro neuronal compression model, we investigated the role of impact strain and strain rate on neuronal lifetime, viability, and pathomorphology. We find that strain magnitude and rate have profound, yet distinctively different effects on the injury pathology. While strain magnitude affects the time of neuronal death, strain rate influences the pathomorphology and extent of population injury. Cellular injury is not initiated through localized deformation of the cytoskeleton but rather driven by excess strain on the entire cell. Furthermore we find that, mechanoporation, one of the key pathological trigger mechanisms in stretch and shear neuronal injuries, was not observed under compression. PMID:27480807

  12. Strain and rate-dependent neuronal injury in a 3D in vitro compression model of traumatic brain injury

    NASA Astrophysics Data System (ADS)

    Bar-Kochba, Eyal; Scimone, Mark T.; Estrada, Jonathan B.; Franck, Christian

    2016-08-01

    In the United States over 1.7 million cases of traumatic brain injury are reported yearly, but predictive correlation of cellular injury to impact tissue strain is still lacking, particularly for neuronal injury resulting from compression. Given the prevalence of compressive deformations in most blunt head trauma, this information is critically important for the development of future mitigation and diagnosis strategies. Using a 3D in vitro neuronal compression model, we investigated the role of impact strain and strain rate on neuronal lifetime, viability, and pathomorphology. We find that strain magnitude and rate have profound, yet distinctively different effects on the injury pathology. While strain magnitude affects the time of neuronal death, strain rate influences the pathomorphology and extent of population injury. Cellular injury is not initiated through localized deformation of the cytoskeleton but rather driven by excess strain on the entire cell. Furthermore we find that, mechanoporation, one of the key pathological trigger mechanisms in stretch and shear neuronal injuries, was not observed under compression.

  13. Strain rate response of a Ni-Ti shape memory alloy after hydrogen charging

    NASA Astrophysics Data System (ADS)

    Gamaoun, Fehmi; Hassine, Tarak; Bouraoui, Tarak

    2014-01-01

    In this work, we investigate the susceptibility of Ni-Ti superelastic wires to the strain rates during tensile testing after hydrogen charging. Cathodic hydrogen charging is performed at a current density of 10 A/m² during 2-12 h in 0.9% NaCl solution and aged for 24 h at room temperature. Specimens underwent one cycle of loading-unloading reaching a stress value of 700 MPa. During loading, strain rates from 10-6 to 5 × 10-2 s-1 have been achieved. After 8 h of hydrogen charging, an embrittlement has been detected in the tensile strain rate range of 10-6 to 10-4 s-1. In contrast, no embrittlement has been detected for strain rates of 10-3 s-1 and higher. However, after 12 h of hydrogen charging and 24 h of annealing at room temperature, the embrittlement occurs in the beginning of the austenite-martensite transformation for all the studied strain rate values. These results show that for a range of critical amounts of diffused hydrogen, the embrittlement of the Ni-Ti superelastic alloy strongly depends on the strain rate during the tensile test. Moreover, it has been shown that this embrittlement occurs for low values of strain rates rather than the higher ones. This behaviour is attributed to the interaction between the diffused hydrogen and growth of the martensitic domain.

  14. EXPERIMENTAL TESTS OF VANADIUM STRENGTH MODELS AT HIGH PRESSURES AND STRAIN RATES

    SciTech Connect

    Park, H; Barton, N R; Becker, R C; Bernier, J V; Cavallo, R M; Lorenz, K T; Pollaine, S M; Remington, B A; Rudd, R E

    2010-03-02

    Experimental results showing significant reductions from classical in the Rayleigh-Taylor (RT) instability growth rate due to high pressure material strength or effective lattice viscosity in metal foils are presented. On the Omega Laser in the Laboratory for Laser Energetics, University of Rochester, target samples of polycrystalline vanadium are compressed and accelerated quasi-isentropically at {approx}1 Mbar pressures, while maintaining the samples in the solid-state. Comparison of the results with constitutive models for solid state strength under these conditions show that the measured RT growth is substantially lower than predictions using existing models that work well at low pressures and long time scales. High pressure, high strain rate data can be explained by the enhanced strength due to a phonon drag mechanism, creating a high effective lattice viscosity.

  15. Dynamics of a competing two-strain SIS epidemic model on complex networks with a saturating incidence rate

    NASA Astrophysics Data System (ADS)

    Yang, Junyuan; Li, Chun-Hsien

    2016-05-01

    This paper studies a two-strain SIS epidemic model with a competing mechanism and a saturating incidence rate on complex networks. This type of incidence rate can be used to reflect the crowding effect of the infective individuals. We first obtain the associated reproduction numbers for each of the two strains which determine the existence of the boundary equilibria. The stability of the disease-free and boundary equilibria are further examined. Besides this, we also show that the two competing strains can coexist under certain conditions. Interestingly, the saturating incidence rate can have specific effects on not only the stability of the boundary equilibria, but also the existence of the coexistence equilibrium. Numerical simulations are presented to support the theoretical results.

  16. Coseismic Damage Generation in Fault Zones by Successive High Strain Rate Loading Experiments

    NASA Astrophysics Data System (ADS)

    Aben, F. M.; Doan, M. L.; Renard, F.; Toussaint, R.; Reuschlé, T.; Gratier, J. P.

    2014-12-01

    Damage zones of active faults control both resistance to rupture and transport properties of the fault. Hence, knowing the rock damage's origin is important to constrain its properties. Here we study experimentally the damage generated by a succession of dynamic loadings, a process mimicking the stress history of a rock sample located next to an active fault. A propagating rupture generates high frequency stress perturbations next to its tip. This dynamic loading creates pervasive damage (pulverization), as multiple fractures initiate and grow simultaneously. Previous single loading experiments have shown a strain rate threshold for pulverization. Here, we focus on conditions below this threshold and the dynamic peak stress to constrain: 1) if there is dynamic fracturing at these conditions and 2) if successive loadings (cumulative seismic events) result in pervasive fracturing, effectively reducing the pulverization threshold to milder conditions. Monzonite samples were dynamically loaded (strain rate > 50 s-1) several times below the dynamic peak strength, using a Split Hopkinson Pressure Bar apparatus. Several quasi-static experiments were conducted as well (strain rate < 10-5-s). Samples loaded up to stresses above the quasi-static uniaxial compressive strength (qsUCS) systematically fragmented or pulverized after four successive loadings. We measured several damage proxies (P-wave velocity, porosity), that show a systematic increase in damage with each load. In addition, micro-computed tomography acquisition on several damage samples revealed the growth of a pervasive fracture network between ensuing loadings. Samples loaded dynamically below the qsUCS failed along one fracture after a variable amount of loadings and damage proxies do not show any a systematic trend. Our conclusions is that milder dynamic loading conditions, below the dynamic peak strength, result in pervasive dynamic fracturing. Also, successive loadings effectively lower the pulverization

  17. Microstructure and nanohardness distribution in a polycrystalline Zn deformed by high strain rate impact

    SciTech Connect

    Dirras, G.; Ouarem, A.; Couque, H.; Gubicza, J.; Szommer, P.; Brinza, O.

    2011-05-15

    Polycrystalline Zn with an average grain size of about 300 {mu}m was deformed by direct impact Hopkinson pressure bar at a velocity of 29 m/s. An inhomogeneous grain structure was found consisting of a center region having large average grain size of 20 {mu}m surrounded by a fine-grained rim with an average grain size of 6 {mu}m. Transmission electron microscopy investigations showed a significant dislocation density in the large-grained area while in the fine-grained rim the dislocation density was negligible. Most probably, the higher strain yielded recrystallization in the outer ring while in the center only recovery occurred. The hardening effect of dislocations overwhelms the smaller grain size strengthening in the center part resulting in higher nanohardness in this region than in the outer ring. - Graphical Abstract: (a): EBSD micrograph showing the initial microstructure of polycrystalline Zn that was subsequently submitted to high strain rate impact. (b): an inhomogeneous grain size refinement was obtained which consists of a central coarse-grained area, surrounded by a fine-grained recrystallized rim. The black arrow points to the disc center. Research Highlights: {yields} A polycrystalline Zn specimen was submitted to high strain rate impact loading. {yields} Inhomogeneous grain refinement occurred due to strain gradient in impacted sample. {yields} A fine-grained recrystallized rim surrounded the coarse-grained center of specimen. {yields} The coarse-grained center exhibited higher hardness than the fine-grained rim. {yields} The higher hardness of the center was caused by the higher dislocation density.

  18. High Strain and Strain-Rate Behaviour of Ptfe/aluminuim/tungsten Mixtures

    NASA Astrophysics Data System (ADS)

    Addiss, John; Cai, Jing; Walley, Stephen; Proud, William; Nesterenko, Vitali

    2007-12-01

    Conventional drop-weight techniques were modified to accommodate low-amplitude force transducer signals from low-strength, cold isostatically pressed `heavy' composites of polytetrafluoroethylene, aluminum and tungsten (W). The failure strength, strain and the post-critical behavior of failed samples were measured for samples of different porosity and tungsten grain size. Unusual phenomenon of significantly higher strength (55 MPa) of porous composites (density 5.9 g/cm3) with small W particles (<1 μm) in comparison with strength (32 MPa) of dense composites (7.1 g/cm3) with larger W particles (44 μm) at the same volume content of components was observed. This is attributed to force chains created by a network of small W particles. Interrupted tests at different levels of strain revealed the mechanisms of fracture under dynamic compression.

  19. Strain-rate sensitivity of foam materials: A numerical study using 3D image-based finite element model

    NASA Astrophysics Data System (ADS)

    Sun, Yongle; Li, Q. M.; Withers, P. J.

    2015-09-01

    Realistic simulations are increasingly demanded to clarify the dynamic behaviour of foam materials, because, on one hand, the significant variability (e.g. 20% scatter band) of foam properties and the lack of reliable dynamic test methods for foams bring particular difficulty to accurately evaluate the strain-rate sensitivity in experiments; while on the other hand numerical models based on idealised cell structures (e.g. Kelvin and Voronoi) may not be sufficiently representative to capture the actual structural effect. To overcome these limitations, the strain-rate sensitivity of the compressive and tensile properties of closed-cell aluminium Alporas foam is investigated in this study by means of meso-scale realistic finite element (FE) simulations. The FE modelling method based on X-ray computed tomography (CT) image is introduced first, as well as its applications to foam materials. Then the compression and tension of Alporas foam at a wide variety of applied nominal strain-rates are simulated using FE model constructed from the actual cell geometry obtained from the CT image. The stain-rate sensitivity of compressive strength (collapse stress) and tensile strength (0.2% offset yield point) are evaluated when considering different cell-wall material properties. The numerical results show that the rate dependence of cell-wall material is the main cause of the strain-rate hardening of the compressive and tensile strengths at low and intermediate strain-rates. When the strain-rate is sufficiently high, shock compression is initiated, which significantly enhances the stress at the loading end and has complicated effect on the stress at the supporting end. The plastic tensile wave effect is evident at high strain-rates, but shock tension cannot develop in Alporas foam due to the softening associated with single fracture process zone occurring in tensile response. In all cases the micro inertia of individual cell walls subjected to localised deformation is found to

  20. Micro-Structural Response of DP 600 to High Strain Rate Deformation

    NASA Technical Reports Server (NTRS)

    Hamburg, Brian; Schneider, Judy; Jones, Stanley E.

    2008-01-01

    The object of this study was to investigate the micro-structural response of DP 600 subjected to high strain rate, ballistic impact tests. The ballistic tests were conducted using normal impact of a hardened steel penetrator into a 2 mm thick sheet of DP 600. The average strain rates produced from this test method are on the order of 10(exp 5)/s. Electron microscopy was used to investigate the microstructure before and after high strain rate deformation. A variation in material response was observed between tests conducted at 0.8 x 105 and 25 x 10(exp 5)/s.

  1. The Extinction of Low Strain Rate Diffusion Flames by a Suppressant

    NASA Technical Reports Server (NTRS)

    Hamins, A.; Yang, J.; Puri, I. K.

    1999-01-01

    This paper describes plans for an experimental and computational study on the structure and extinction of low strain rate diffusion flames by a suppressant added to the oxidizer stream. Stable low strain rate flames will be established through ground based reduced gravity experiments using the 2.2 s drop tower. A variety of agents will be investigated, including both physically and chemically acting agents (He, N2, CO2, and CF3Br) for flames burning methane and propane. A computational model of flame structure and extinction will be modified to include radiative losses, which is thought to be a significant heat loss mechanism at low strain rates.

  2. Three-dimensional geometry, strain rates and basement deformation mechanisms of thrust-bend folding

    NASA Astrophysics Data System (ADS)

    Wibberley, Christopher A. J.

    1997-03-01

    Models for thrust-bend folding of an isotropic medium are used to predict initial basement thrust sheet geometries and sub-surface thrust fault shapes from final basement thrust sheet structure. Predicted strains and strain rates from these models are compared with data on deformation fabrics in an example of a basement thrustbend fold in order to characterise the deformation response to thrust-bend folding. The Glencoul thrust sheet in the Moine Thrust Zone of north-west Scotland is restored to an initial thrust sheet geometry. Spatial and orientation distribution data of syn-emplacement fractures and cataclastic fault zones from within the Glencoul thrust sheet are then compared with the strain and strain rate histories predicted by thrust-bend folding models. A different set of cataclastic fault seams is demonstrated to have been generated at each frontal thrust bend. Cataclastic failure is restricted to portions of the thrust sheet that have moved over frontal bends with smaller radii of curvature. From model thrust-bend geometries and an assumed slip rate of 1 x 10 -10 ms -1, estimated minimum (critical) strain rates required for fracture failure of the Lewisian basement are 10 -11 to 10 -14 s -1 for shear strain rates and 10 -12 to 10 -15 s -1 for extensional strain rates.

  3. Response of Polypmeric Foams and ABS Plastics to High Strain Rate Loading

    NASA Astrophysics Data System (ADS)

    Dick, Richard; Chang, Peter; Fourney, William

    1999-06-01

    The split-Hopkinson pressure bar (SHPB) technique was utilized to obtain high strain rate response data for low-density foams and solid ABS and polypropylene plastics. General Motors provided the materials for this study. These materials are used in the interior panels of automobiles. Because the foams have a very low impedance, polycarbonate bars were used to acquire the strain rate data in the 100 to 1600 per second range. An aluminum SHPB was used to obtain the solid plastics data that covered strain rates of 1000 to 4000 pre second. The experimental data indicate that the foams over the test range are only slightly strain rate dependent while the polypropylene appears to be strain rate independent above 1000 per second and the ABS plastics are strain rate independent above 3000 per second. The projectile length was varied to provide a wide range of induced strains ranging from 10 to 70 per cent for the foams and up to 20 per cent for the plastic materials.

  4. Influence of strain rate and temperature on the mechanical behavior of beryllium

    SciTech Connect

    Blumenthal, W.R.; Carpenter, R.W.; Cannon, D.D.; Abeln, S.P.; Gray, G.T. III

    1997-07-01

    The compressive stress-strain response of three grades of beryllium were studied as a function of strain rate and temperature. Grades S2OOD, E, and F represent a historical perspective of beryllium processing from the 1960`s through 1990`s technology. The purpose of this study was to measure the mechanical behavior of beryllium over a range of deformation conditions for constitutive model development and to obtain microstructural evidence for deformation mechanisms. The compressive stress-strain response was found to be independent of grade and strongly dependent on the applied strain rate between 0.001 and 8000. The strain-hardening response displayed a moderate temperature dependence between 77 K and 873 K Because distinct yield was not observed, the intercept-stress from linear strain-hardening fits was analyzed and was found to be only weakly dependent on strain rate and temperature above ambient. Microstructural examination of SHPB specimens revealed that twinning was extensive at strains between 7-22%. A SHPB sample deformed to over 20% strain contained both extensive twinning and grain boundary microcracking.

  5. Influence of strain aging on the strain-rate sensitivity of the flow stress

    SciTech Connect

    Schwarz, R.B.

    1982-01-01

    Previously published studies on the deformation kinetics of several fcc alloys, i.e. single crystals of Al-0.7% Mg, polycrystals of AlMg, Inconel 600, Inconel X750, NiCo, AuCu, and FeC, are cited, and two models are proposed to explain the reported observations. The calculations suggest that excess vacancies play an important role in the dynamic strain aging of the alloys and that an intermediate thermal annealing process should remove the vacancies. (BLM)

  6. Strain rate dependence of impact properties of sintered 316L stainless steel

    NASA Astrophysics Data System (ADS)

    Lee, Woei-Shyan; Lin, Chi-Feng; Liu, Tsung-Ju

    2006-12-01

    This paper uses a material testing system (MTS) and a compressive split-Hopkinson bar to investigate the impact behaviour of sintered 316L stainless steel at strain rates ranging from 10 -3 s -1 to 7.5 × 10 3 s -1. It is found that the true stress, the rate of work hardening and the strain rate sensitivity vary significantly as the strain rate increases. The flow behaviour of the sintered 316L stainless steel can be accurately predicted using a constitutive law based on Gurson's yield criterion and the flow rule proposed by Khan, Huang and Liang (KHL). Microstructural observations reveal that the degree of localized grain deformation increases, but the pore density and the grain size decrease, with increasing strain rate. Adiabatic shear bands associated with cracking are developed at strain rates higher than 5.6 × 10 3 s -1. The fracture surfaces exhibit ductile dimples. The depth and density of these dimples decrease with increasing strain rate.

  7. Mechanical response of porcine skin under compression from low to high strain rates

    NASA Astrophysics Data System (ADS)

    Bo, Chiara; Butler, Ben; Williams, Alun; Brown, Katherine; Proud, William

    2013-06-01

    Uniaxial compression experiments were performed on fresh porcine skin samples at different strain rates to study the stress-strain response. Low strain rate experiments were performed with an Instron 5566, while high strain rates were achieved using a Split Hopkinson Pressure Bar system. Magnesium bars and semiconductor strain gauges were used respectively to maximize the signal transmission from porcine skin to the output bar and to allow the signal measurement. Skin samples were harvested from different area of the animal to investigate the heterogeneity of such material. The experimental results showed that the mechanical response of skin in compression is strongly dependent on the strain rate of loading and on the location from which the samples were collected. Specimens collected from the rump showed a stiffer response compared to samples harvested from the thigh. Finally, a histological analysis of the samples post compression was carried out to examine the extent of tissue damage as a function of strain rate. This work is supported by the Atomic Weapons Establishment, UK and The Royal British Legion Centre for Blast Injury Studies at Imperial College London, UK.

  8. Physical mechanisms underlying the strain-rate-dependent mechanical behavior of kangaroo shoulder cartilage

    NASA Astrophysics Data System (ADS)

    Thibbotuwawa, Namal; Oloyede, Adekunle; Li, Tong; Singh, Sanjleena; Senadeera, Wijitha; Gu, YuanTong

    2015-09-01

    Due to anatomical and biomechanical similarities to human shoulder, kangaroo was chosen as a model to study shoulder cartilage. Comprehensive enzymatic degradation and indentation tests were applied on kangaroo shoulder cartilage to study mechanisms underlying its strain-rate-dependent mechanical behavior. We report that superficial collagen plays a more significant role than proteoglycans in facilitating strain-rate-dependent behavior of the kangaroo shoulder cartilage. By comparing the mechanical properties of degraded and normal cartilages, it was noted that proteoglycan and collagen degradation significantly compromised strain-rate-dependent mechanical behavior of the cartilage. Superficial collagen contributed equally to the tissue behavior at all strain-rates. This is different to the studies reported on knee cartilage and confirms the importance of superficial collagen on shoulder cartilage mechanical behavior. A porohyperelastic numerical model also indicated that collagen disruption would lead to faster damage of the shoulder cartilage than when proteoglycans are depleted.

  9. Influence of strain rate on the mechanical behaviour in tension of bovine cortical bone

    NASA Astrophysics Data System (ADS)

    Latella, C.; Dotta, M.; Forni, D.; Tesio, N.; Cadoni, E.

    2015-09-01

    The mechanical behaviour of bones when subjected to tension loading in a wide range of strain-rates is fundamental to develop protection systems. The paper presents the preliminary tests on the tensile behaviour of bovine cortical bone at medium and high strain rates. Two special apparatus, both installed at the DynaMat Laboratory of the University of Applied Sciences of Southern Switzerland, a Hydro-Pneumatic Machine and a Modified Hopkinson Bar respectively for medium and high strain-rate tests have been used. Flat shape specimens (having 10 mm of gauge length, 5 mm width and 3 mm thickness) have been obtained from 15 bovine femurs with the same age. The paper describes the preparation techniques of the samples and the experimental results obtained. The bovine cortical bone shown a quite important strain rate dependency.

  10. The high strain rate compressive response of Mg-Al alloy/fly Ash cenosphere composites

    NASA Astrophysics Data System (ADS)

    Luong, Dung D.; Gupta, Nikhil; Rohatgi, Pradeep K.

    2011-02-01

    The strain rate dependence of mechanical properties of AZ91D alloy composites filled with 5 wt.% hollow fly ash cenosphere is examined in the strain rate range of 630-1,203 s-1 using a split-Hopkinson pressure bar system. In addition, a test scheme is designed to study the intermediate strain rate response of the material. Addition of fly ash caused grain refinement and finer precipitates in the matrix alloy. Compared to the matrix alloy, the energy absorption is higher in AZ91D/fly ash cenosphere composites at comparable strain rates. In addition, the yield strength is found to be about 19-41% higher in the composites containing fly ash cenospheres.

  11. The mechanisms of plastic strain accommodation during the high strain rate collapse of corrugated Ni-Al laminate cylinders

    NASA Astrophysics Data System (ADS)

    Olney, K. L.; Chiu, P. H.; Higgins, A.; Serge, M.; Weihs, T. P.; Fritz, G. M.; Stover, A. K.; Benson, D. J.; Nesterenko, V. F.

    2014-09-01

    The Thick-Walled Cylinder method was used on corrugated Ni-Al reactive laminates to examine how their mesostructures accommodate large strain, high strain rate plastic deformation and to examine the potential for intermetallic reaction initiation due to mechanical stimuli. Three main mesoscale mechanisms of large plastic strain accommodation were observed in addition to the bulk distributed uniform plastic flow: (a) the extrusion of wedge-shaped regions into the interior of the cylinder along planes of easy slip provided by angled layers, (b) the development of trans-layer shear bands in the layers with orientation close to radial and (c) the cooperative buckling of neighbouring layers perpendicular to the radius. These mesoscale mechanisms acted to block the development of periodic patterns of multiple, uniformly distributed, shear bands that have been observed in all previously examined solid homogeneous materials and granular materials. The high-strain plastic flow within the shear bands resulted in the dramatic elongation and fragmentation of Ni and Al layers. The quenched reaction between Al and Ni was observed inside these trans-layer shear bands and in a number of the interfacial extruded wedge-shaped regions. The reaction initiated in these spots did not ignite the bulk of the material, demonstrating that these mesostructured Ni-Al laminates are able to withstand high-strain, high-strain rate deformation without reaction. Numerical simulations of the explosively collapsed samples were performed using the digitized geometry of corrugated laminates and predictions of the final, deformed mesostructures agree with the observed deformation patterns.

  12. Materials design and processings for industrial high-strain-rate superplastic forming

    SciTech Connect

    Hosokawa, H.; Higashi, K.

    2000-07-01

    The optimum materials design in microstructural control could be developed for the high-strain-rate superplastic materials in the industrial scale. In the present work, it is reported that the high-performance-engine pistons with near-net-shape can be fabricated by the superplastic forging technology in the high-strain-rate superplastic PM Al-Si based alloy, which is produced by using this optimum materials design.

  13. Longitudinal Strain and Strain Rate Abnormalities Precede Invasive Diagnosis of Transplant Coronary Artery Vasculopathy in Pediatric Cardiac Transplant Patients.

    PubMed

    Zoeller, Bridget B; Miyamoto, Shelley D; Younoszai, Adel K; Landeck, Bruce F

    2016-04-01

    Transplant coronary artery vasculopathy (TCAV) is the primary cause of late graft loss in pediatric heart transplant recipients. TCAV is diagnosed using angiography or intravascular ultrasound; however, noninvasive methods remain elusive. We sought to define patterns of myocardial mechanics in patients with TCAV and to determine whether this can detect TCAV before invasive methods. In this retrospective study, we queried our heart transplant database to identify all recipients with TCAV since 2006 (n = 41). Echoes were reviewed from the last normal catheterization and at TCAV diagnosis, and from time-matched transplant controls (n = 33) without TCAV. Peak global circumferential and longitudinal strain and systolic and diastolic strain rate (SSR and DSR) of the left ventricle were derived using velocity vector imaging. T tests were used to compare both groups longitudinally and between groups at both time points. Longitudinal strain, SSR, and DSR were diminished in the TCAV group compared to the transplant control group at both time points. No differences were found across time points in either group. Retrospective modeling using a longitudinal strain cutoff of 15 % on echoes 2 years prior to TCAV diagnosis predicted development or exclusion of TCAV with sensitivity of 53 %, specificity of 89 % with an area under the curve of 0.8. Decreases in longitudinal strain measurements demonstrate that alterations in myocardial mechanics occur in patients with TCAV at least 2 years prior to invasive diagnosis. These early changes may be due to microvascular disease. This modality could aid in earlier treatment and intervention for this challenging problem .

  14. High Strain Rate Characterization of Plastics and Foams Using Polymeric Split Hopkinson Bar

    NASA Astrophysics Data System (ADS)

    Sawas, Omar; Brar, N. S.

    1997-07-01

    High strain rate and high/low temperature response of engineered plastics and foams is relevant and important for the design and development of fighter aircraft canopies, submarine interiors and automobile exterior and interior systems. The mechanical impedance of conventional split Hopkinson bar materials (aluminum or steel) is extremely large compared to those of plastic or foam specimens. To overcome this difficulty of impedance mismatch we have developed the Polymeric Split Hopkinson Bar (PSHB). A viscoelastic model for cast acrylic bar material, which relates stresses and strains as well as particle velocity and strain, is developed to account for the wave dispersion along the bar. The model is verified by comparing the stress strain data on 1100 aluminum and polycarbonate specimens obtained using PSHB and conventional aluminum SHB. Stress-strain data at a strain rate of 103/s on low strength polyurethane foam (density = 0.57 g/cm3) following this technique show that the foam has a recoverable compressive strain of 0.4 at a stress of 2.9 MPa. High strain rate (2x102-2x103/s) data on polycarbonate, generic elastomer, and styrofoam will also be presented.

  15. Physics of friction and strain rate localization in synthetic fault gouge

    NASA Astrophysics Data System (ADS)

    Sleep, Norman H.; Richardson, Eliza; Marone, Chris

    2000-11-01

    Data on synthetic fault gouge previously collected by Richardson and Marone [1999] were compared with the predictions of a unified theory for rate- and state-dependent friction compiled by Sleep [1997]. The theory treats the gouge as a continuum one-dimensional fluid sheared between parallel plates. It is predicted that the strain rate localized into a shear band of width called Wss during steady state sliding from the nominal width of the gouge zone Wnom. The critical displacement during velocity stepping tests is predicted to be Wss ɛint, where ɛint is the critical strain, an intrinsic material property. It is predicted that the strain rate for renewed sliding after holds delocalizes to a width Wnew which is greater than Wss and for long holds approaches the full gouge zone width Wnom. The displacement for recovery of the shear traction to its steady state value is predicted to be Wnewɛint, which for long holds is much greater than the critical displacement obtained by velocity stepping. Only the macroscopic effects of this process could be studied using the laboratory data in hand. Compaction during the hold and the difference between peak shear traction upon restart and the steady state shear traction during sliding (healing) were measured. To simulate more complex normal traction variations on real faults, the normal traction was varied sinusoidally about its previous value during some holds. The theory reasonably predicts the observed relationship between healing and compaction and healing versus hold time. It predicts the slip needed for recovery of shear traction following holds but poorly predicts the shear traction versus time during recovery. We attribute this failure to the fact that the laboratory gouge is a heterogeneous three-dimensional substance. Qualitatively, the delocalized width Wnew varies with position within the gouge plane, and slip is required for localized shear to organize in three dimensions. As strain rate was not observed as a

  16. Transformation plasticity at high strain rate in magnesia-partially-stabilized zirconia

    SciTech Connect

    Rogers, W.P. . Dept. of Mechanical Engineering); Nemat-Nasser, S.

    1990-01-01

    Transformation plasticity in magnesia- partially-stabilized zirconia (Mg-PSZ) is studied using a split Hopkinson pressure bar modified for ceramic materials. Axial and transverse strains are measured under uniaxial compressive loading at a strain rate of 250/s. The transformation yield stress is found to increase from 900 MPa under quasi-static loading to 1.2 GPa at high strain rate. Post-yield deformation is characterized by shear and volumetric plastic strains up to 1.2%. During unloading, the axial and transverse plastic strains are partially recovered while the volume is conserved. Axially oriented microcracks are observed but they do not contribute significantly to plastic deformation in Mg-PSZ.

  17. Yielding of tantalum at strain rates up to 109 s-1

    NASA Astrophysics Data System (ADS)

    Crowhurst, Jonathan C.; Armstrong, Michael R.; Gates, Sean D.; Zaug, Joseph M.; Radousky, Harry B.; Teslich, Nick E.

    2016-08-01

    We have used a 45 μJ laser pulse to accelerate the free surface of fine-grained tantalum films up to peak velocities of ˜1.2 km s-1. The films had thicknesses of ˜1-2 μm and in-plane grain widths of ˜75-150 nm. Using ultrafast interferometry, we have measured the time history of the velocity of the surface at different spatial positions across the accelerated region. The initial part of the histories (assumed to correspond to the "elastic precursor" observed previously) exhibited measured strain rates of ˜0.6 to ˜3.2 × 109 s-1 and stresses of ˜4 to ˜22 GPa. Importantly, we find that elastic amplitudes exhibit little variation with strain rate for a constant peak surface velocity, even though, via covariation of the strain rate with peak surface velocity, they vary with strain rate. Furthermore, by comparison with data obtained at lower strain rates, we find that amplitudes are much better predicted by peak velocities rather than by either strain rate or sample thickness.

  18. Micromechanics-Based Permeability Evolution in Brittle Materials at High Strain Rates

    NASA Astrophysics Data System (ADS)

    Perol, Thibaut; Bhat, Harsha S.

    2016-08-01

    We develop a micromechanics-based permeability evolution model for brittle materials at high strain rates (≥ 100 s^{-1}). Extending for undrained deformation the mechanical constitutive description of brittle solids, whose constitutive response is governed by micro-cracks, we now relate the damage-induced strains to micro-crack aperture. We then use an existing permeability model to evaluate the permeability evolution. This model predicts both the percolative and connected regime of permeability evolution of Westerly Granite during triaxial loading at high strain rate. This model can simulate pore pressure history during earthquake coseismic dynamic ruptures under undrained conditions.

  19. A method for calculating strain energy release rate based on beam theory

    NASA Technical Reports Server (NTRS)

    Sun, C. T.; Pandey, R. K.

    1993-01-01

    The Timoshenko beam theory was used to model cracked beams and to calculate the total strain energy release rate. The root rotation of the beam segments at the crack tip were estimated based on an approximate 2D elasticity solution. By including the strain energy released due to the root rotations of the beams during crack extension, the strain energy release rate obtained using beam theory agrees very well with the 2D finite element solution. Numerical examples were given for various beam geometries and loading conditions. Comparisons with existing beam models were also given.

  20. Improved method for calculating strain energy release rate based on beam theory

    NASA Technical Reports Server (NTRS)

    Sun, C. T.; Pandey, R. K.

    1994-01-01

    The Timoshenko beam theory was used to model cracked beams and to calculate the total strain-energy release rate. The root rotations of the beam segments at the crack tip were estimated based on an approximate two-dimensional elasticity solution. By including the strain energy released due to the root rotations of the beams during crack extension, the strain-energy release rate obtained using beam theory agrees very well with the two-dimensional finite element solution. Numerical examples were given for various beam geometries and loading conditions. Comparisons with existing beam models were also given.

  1. Impact comminution of solids due to local kinetic energy of high shear strain rate: I. Continuum theory and turbulence analogy

    NASA Astrophysics Data System (ADS)

    Bažant, Zdeněk P.; Caner, Ferhun C.

    2014-03-01

    The modeling of high velocity impact into brittle or quasibrittle solids is hampered by the unavailability of a constitutive model capturing the effects of material comminution into very fine particles. The present objective is to develop such a model, usable in finite element programs. The comminution at very high strain rates can dissipate a large portion of the kinetic energy of an impacting missile. The spatial derivative of the energy dissipated by comminution gives a force resisting the penetration, which is superposed on the nodal forces obtained from the static constitutive model in a finite element program. The present theory is inspired partly by Grady's model for expansive comminution due to explosion inside a hollow sphere, and partly by analogy with turbulence. In high velocity turbulent flow, the energy dissipation rate gets enhanced by the formation of micro-vortices (eddies) which dissipate energy by viscous shear stress. Similarly, here it is assumed that the energy dissipation at fast deformation of a confined solid gets enhanced by the release of kinetic energy of the motion associated with a high-rate shear strain of forming particles. For simplicity, the shape of these particles in the plane of maximum shear rate is considered to be regular hexagons. The particle sizes are assumed to be distributed according to the Schuhmann power law. The condition that the rate of release of the local kinetic energy must be equal to the interface fracture energy yields a relation between the particle size, the shear strain rate, the fracture energy and the mass density. As one experimental justification, the present theory agrees with Grady's empirical observation that, in impact events, the average particle size is proportional to the (-2/3) power of the shear strain rate. The main characteristic of the comminution process is a dimensionless number Ba (Eq. (37)) representing the ratio of the local kinetic energy of shear strain rate to the maximum possible

  2. High speed imaging for material parameters calibration at high strain rate

    NASA Astrophysics Data System (ADS)

    Sasso, M.; Fardmoshiri, M.; Mancini, E.; Rossi, M.; Cortese, L.

    2016-05-01

    To describe the material behaviour at high strain rates dynamic experimental tests are necessary, and appropriate constitutive models are to be calibrated accordingly. A way to achieve this is through an inverse procedure, based on the minimization of an error function calculated as the difference between experimental and numerical data coming from Finite Element analysis. This approach, widely used in the literature, has a heavy computational cost associated with the minimization process that requires, for each variation of the material model parameters, the execution of FE calculations. In this work, a faster but yet effective calibration procedure is studied Experimental tests were performed on an aluminium alloy AA6061-T6, by means of a direct tension-compression Split Hopkinson bar. A fast camera with a resolution of 192 × 128 pixels and capable of a sample rate of 100,000 fps captured images of the deformation process undergone by the samples during the tests. The profile of the sample obtained after the image binarization and processing, was postprocessed to derive the deformation history; afterwards it was possible to calculate the true stress and strain, and carry out the inverse calibration by analytical computations. The results of this method were compared with the ones coming from the Finite Element approach.

  3. Transient x-ray diffraction with simultaneous imaging under high strain-rate loading

    SciTech Connect

    Fan, D.; E, J. C.; Zhao, F.; Luo, S. N.; Lu, L.; Li, B.; Qi, M. L.; Sun, T.; Fezzaa, K.; Chen, W.

    2014-11-15

    Real time, in situ, multiframe, diffraction, and imaging measurements on bulk samples under high and ultrahigh strain-rate loading are highly desirable for micro- and mesoscale sciences. We present an experimental demonstration of multiframe transient x-ray diffraction (TXD) along with simultaneous imaging under high strain-rate loading at the Advanced Photon Source beamline 32ID. The feasibility study utilizes high strain-rate Hopkinson bar loading on a Mg alloy. The exposure time in TXD is 2–3 μs, and the frame interval is 26.7–62.5 μs. Various dynamic deformation mechanisms are revealed by TXD, including lattice expansion or compression, crystal plasticity, grain or lattice rotation, and likely grain refinement, as well as considerable anisotropy in deformation. Dynamic strain fields are mapped via x-ray digital image correlation, and are consistent with the diffraction measurements and loading histories.

  4. LS-DYNA Implementation of Polymer Matrix Composite Model Under High Strain Rate Impact

    NASA Technical Reports Server (NTRS)

    Zheng, Xia-Hua; Goldberg, Robert K.; Binienda, Wieslaw K.; Roberts, Gary D.

    2003-01-01

    A recently developed constitutive model is implemented into LS-DYNA as a user defined material model (UMAT) to characterize the nonlinear strain rate dependent behavior of polymers. By utilizing this model within a micromechanics technique based on a laminate analogy, an algorithm to analyze the strain rate dependent, nonlinear deformation of a fiber reinforced polymer matrix composite is then developed as a UMAT to simulate the response of these composites under high strain rate impact. The models are designed for shell elements in order to ensure computational efficiency. Experimental and numerical stress-strain curves are compared for two representative polymers and a representative polymer matrix composite, with the analytical model predicting the experimental response reasonably well.

  5. The High-Strain Rate Loading of Structural Biological Materials

    NASA Astrophysics Data System (ADS)

    Proud, W. G.; Nguyen, T.-T. N.; Bo, C.; Butler, B. J.; Boddy, R. L.; Williams, A.; Masouros, S.; Brown, K. A.

    2015-10-01

    The human body can be subjected to violent acceleration as a result of explosion caused by military ordinance or accident. Blast waves cause injury and blunt trauma can be produced by violent impact of objects against the human body. The long-term clinical manifestations of blast injury can be significantly different in nature and extent to those suffering less aggressive insult. Similarly, the damage seen in lower limbs from those injured in explosion incidents is in general more severe than those falling from height. These phenomena increase the need for knowledge of the short- and long-term effect of transient mechanical loading to the biological structures of the human body. This paper gives an overview of some of the results of collaborative investigation into blast injury. The requirement for time-resolved data, appropriate mechanical modeling, materials characterization and biological effects is presented. The use of a range of loading platforms, universal testing machines, drop weights, Hopkinson bars, and bespoke traumatic injury simulators are given.

  6. Strain-rate dependence of the compressive properties of normal and carbon-fiber-reinforced bone cement.

    PubMed

    Saha, S; Pal, S

    1983-11-01

    Normal and carbon-fiber-reinforced (1 wt. %) bone cement samples were tested in compression at various strain rates. Both the compressive strength and proportional limit increased in general with increasing strain rate. Similar strain-rate sensitivity was also shown by the carbon-fiber-reinforced bone cement. The mechanical properties, namely the modulus of elasticity, the proportional limit, and the compressive strength of the carbon-fiber-reinforced bone cement showed highly significant positive correlations with the strain rate. PMID:6654926

  7. Static and dynamic strain energy release rates in toughened thermosetting composite laminates

    NASA Technical Reports Server (NTRS)

    Cairns, Douglas S.

    1992-01-01

    In this work, the static and dynamic fracture properties of several thermosetting resin based composite laminates are presented. Two classes of materials are explored. These are homogeneous, thermosetting resins and toughened, multi-phase, thermosetting resin systems. Multi-phase resin materials have shown enhancement over homogenous materials with respect to damage resistance. The development of new dynamic tests are presented for composite laminates based on Width Tapered Double Cantilevered Beam (WTDCB) for Mode 1 fracture and the End Notched Flexure (ENF) specimen. The WTDCB sample was loaded via a low inertia, pneumatic cylinder to produce rapid cross-head displacements. A high rate, piezo-electric load cell and an accelerometer were mounted on the specimen. A digital oscilloscope was used for data acquisition. Typical static and dynamic load versus displacement plots are presented. The ENF specimen was impacted in three point bending with an instrumented impact tower. Fracture initiation and propagation energies under static and dynamic conditions were determined analytically and experimentally. The test results for Mode 1 fracture are relatively insensitive to strain rate effects for the laminates tested in this study. The test results from Mode 2 fracture indicate that the toughened systems provide superior fracture initiation and higher resistance to propagation under dynamic conditions. While the static fracture properties of the homogeneous systems may be relatively high, the apparent Mode 2 dynamic critical strain energy release rate drops significantly. The results indicate that static Mode 2 fracture testing is inadequate for determining the fracture performance of composite structures subjected to conditions such as low velocity impact. A good correlation between the basic Mode 2 dynamic fracture properties and the performance is a combined material/structural Compression After Impact (CAI) test is found. These results underscore the importance of

  8. High strain rate mechanical properties of IM7/8551-7 graphite epoxy composite

    SciTech Connect

    Powers, B.M.; Vinson, J.R.; Hall, I.W.

    1995-12-31

    Polymer matrix composites offer excellent mechanical properties such as high specific strength and stiffness which make them attractive for many naval, aerospace and automotive structural components. Although they are candidate materials for many applications where high strain rate loading is probable, little is known of the material responses to shock loading for most composite materials. Because mechanical properties vary significantly with strain rate, the use of static properties in the analysis and design of structures which undergo dynamic loadings can on one hand lead to a very conservative overweight design, or on the other hand can lead to designs which fail prematurely and unexpectedly. The use of dynamic material properties will ensure the design of composite structures which are weight efficient and structurally sound when they are subjected to dynamic loads. In this study, a Split Hopkinson Pressure Bar is used to obtain compressive mechanical properties of a unidirectional IM7/8551-7 graphite epoxy composite. For each of the three principal directions, the yield stress, yield strain, ultimate stress, ultimate strain, modulus of elasticity, elastic strain energy function and the total strain energy to failure are presented for strain rates varying from 49 sec{sup {minus}1} to 1430 sec{sup {minus}1}. The data from 72 tests are statistically analyzed, represented by equations, and discussed in some detail.

  9. Closing an open system: Pore pressure changes in permeable edifice rock at high strain rates

    NASA Astrophysics Data System (ADS)

    Heap, Michael J.; Wadsworth, Fabian B.

    2016-04-01

    A permeable or open system will react as a closed system if the rocks implicated are deformed on a timescale that precludes fluid movement. Closed system ("undrained") deformation therefore leads to a failure mode dependent change in pore pressure: microcracking (dilatant behaviour) and cataclastic pore collapse (compactant behaviour) will decrease and increase pore pressure, respectively. In the dilatant regime (i.e., in the shallow edifice, < 1 km depth), a decrease in pore pressure will serve to strengthen rock-a process termed dilatancy hardening. However, it is shown here, using undrained triaxial deformation experiments, that the high initial porosity and microcrack density of typical edifice-forming andesites prevent dilatancy hardening. This allows the rock proximal to the magma-filled conduit in the shallow edifice to remain weak during periods of unrest when high magma strain rates could be transferred to the adjacent country rock. Although the propensity for fracturing will likely reduce the structural integrity of the edifice, fracturing of the shallow edifice may improve the outgassing efficiency of the nearby magma-filled conduit. The increase in pore pressure during undrained deformation in the compactant regime (i.e., in the deep edifice, > 1 km depth) could lead to pore pressure embrittlement and fracturing. Indeed, the experiments of this study show that the pore pressure increases during progressive compaction in a closed system. However, the pore pressure is prevented from reaching the critical value required to promote a dilatant response (i.e., fracturing) for two reasons. First, the rate of compaction (i.e., porosity decrease) slows as the sample is deformed at a constant strain rate, a consequence of the decay in effective pressure. Second, the emergence of microcracking as the rock approaches the compactant-dilatant transition acts as a negative feedback and prevents the rock from transiting into the dilatant field. At this point, local

  10. A map of strain rate for Eastern Turkey, from InSAR and GPS data

    NASA Astrophysics Data System (ADS)

    Walters, R. J.; Parsons, B.; Wright, T. J.

    2013-12-01

    Tectonic deformation in Eastern Turkey is dominated by strain localisation on two major strike-slip faults; the North Anatolian Fault (NAF) and the East Anatolian Fault (EAF). Here we use Interferometric Synthetic Aperture Radar (InSAR) to map interseismic strain across the Eurasian-Arabian plate boundary zone in Eastern Turkey, covering both the NAF and the EAF. Most previous InSAR interseismic studies of the NAF have used only descending track data, and in these studies it was therefore necessary to assume purely horizontal, fault-parallel motion in modelling deformation. The slip rate of the EAF has been the focus of only a few geological and geodetic studies, and InSAR has not previously been used to measure interseismic strain accumulation across this fault. We construct ~400 Envisat interferograms on three descending and two ascending tracks in Eastern Turkey, covering both the NAF and EAF. We use these data to generate five line-of-sight velocity maps (ratemaps) using the PiRATE software package (Wang et al., GRL, 2009), which implements a multi-interferogram network approach in order to maximise spatial coverage and correct for orbital errors. We find that the five InSAR ratemaps agree best in overlapping regions when all interferograms are first corrected for atmospheric effects using model outputs from the ERA-Interim global atmospheric model (Jolivet et al., GRL, 2011). From these five overlapping ratemaps, we model elastic strain accumulation for both the NAF and EAF, and calculate slip rates of 20×3 mm/yr and 10×2 mm/yr respectively, with associated locking depths of 16×9 km and 13×4 km. We then use the ratemaps, together with a compilation of GPS data in the area, to calculate a velocity field for Eastern Turkey. We find that the velocity field derived from InSAR and GPS data significantly reduces the uncertainty of east-west velocities when compared with the velocity field derived from GPS data alone, and shows that strain is mainly localised

  11. Ductile strain rates measurements reveal continental crust long-term deformation modes

    NASA Astrophysics Data System (ADS)

    Boutonnet, E.; Leloup, P. H.; Sassier, C.; Gardien, V.; Ricard, Y.

    2012-04-01

    Any discussion on the long-term crustal rheology is hindered by our poor knowledge of deformation rates in the deep crust. These rates have only been estimated to be ≤10-15 and ≥10-13 s-1 in the "stable" and highly deforming zones respectively, and measured in a few peculiar cases. Because quartz ribbons are ubiquitous in continental shear zones, the quartz-strain-rate-metry (QRS) method, based on experimentally calibrated quartz piezometers and ductile flow laws, could provide deformation rates measurements in many geological contexts. However, the results are highly sensitive on the deformation temperature that is difficult to measure. Furthermore, results vary by three orders of magnitude depending on the chosen piezometer and rheological law. If recent technical progress allow measuring more precisely the deformation temperature, it is still not clear what is the most accurate piezometer - rheological law association. We solved that dilemma by comparing strain rates measured by the QRS method with a reference one measured with another method on the same outcrop of the Ailao Shan - Red River (ASRR) shear zone. At site C1, by combining dating of syntectonic dykes and measurements of their deformation, the strain rate is calculated between 3 and 4 x10-14 s-1 between 29 to 22 Ma, (Sassier et al., JGR, 2009). Quartz ribbons sampled in site C1 show large grains recrystallized by grain boundary migration (GBM), themselves recrystallized at lower temperature by sub-grain rotation (SGR). The mean recrystallized quartz grain size for the SGR event range between 74.0 and 79.3 μm. The associated stresses, measured with Shimizu (JSG, 2008) piezometer, range between 35.2 and 38.1 MPa. Conditions of deformation of P≈ 1.5 kbar and T≈ 430°C were inferred by combining several thermobarometers on quartz, such as TitaniQ, fluid inclusions microthermometry and crystallographic fabrics. The calculated strain rate with five flow laws and three piezometers range between 3

  12. Inverse methods for the mechanical characterization of materials at high strain rates

    NASA Astrophysics Data System (ADS)

    Hernandez, C.; Maranon, A.; Ashcroft, I. A.; Casas-Rodriguez, J. P.

    2012-08-01

    Mechanical material characterization represents a research challenge. Furthermore, special attention is directed to material characterization at high strain rates as the mechanical properties of some materials are influenced by the rate of loading. Diverse experimental techniques at high strain rates are available, such as the drop-test, the Taylor impact test or the Split Hopkinson pressure bar among others. However, the determination of the material parameters associated to a given mathematical constitutive model from the experimental data is a complex and indirect problem. This paper presents a material characterization methodology to determine the material parameters of a given material constitutive model from a given high strain rate experiment. The characterization methodology is based on an inverse technique in which an inverse problem is formulated and solved as an optimization procedure. The input of the optimization procedure is the characteristic signal from the high strain rate experiment. The output of the procedure is the optimum set of material parameters determined by fitting a numerical simulation to the high strain rate experimental signal.

  13. Earthquake potential and magnitude limits inferred from a geodetic strain-rate model for southern Europe

    NASA Astrophysics Data System (ADS)

    Rong, Y.; Bird, P.; Jackson, D. D.

    2016-04-01

    The project Seismic Hazard Harmonization in Europe (SHARE), completed in 2013, presents significant improvements over previous regional seismic hazard modeling efforts. The Global Strain Rate Map v2.1, sponsored by the Global Earthquake Model Foundation and built on a large set of self-consistent geodetic GPS velocities, was released in 2014. To check the SHARE seismic source models that were based mainly on historical earthquakes and active fault data, we first evaluate the SHARE historical earthquake catalogues and demonstrate that the earthquake magnitudes are acceptable. Then, we construct an earthquake potential model using the Global Strain Rate Map data. SHARE models provided parameters from which magnitude-frequency distributions can be specified for each of 437 seismic source zones covering most of Europe. Because we are interested in proposed magnitude limits, and the original zones had insufficient data for accurate estimates, we combine zones into five groups according to SHARE's estimates of maximum magnitude. Using the strain rates, we calculate tectonic moment rates for each group. Next, we infer seismicity rates from the tectonic moment rates and compare them with historical and SHARE seismicity rates. For two of the groups, the tectonic moment rates are higher than the seismic moment rates of the SHARE models. Consequently, the rates of large earthquakes forecast by the SHARE models are lower than those inferred from tectonic moment rate. In fact, the SHARE models forecast higher seismicity rates than the historical rates, which indicate that the authors of SHARE were aware of the potentially higher seismic activities in the zones. For one group, the tectonic moment rate is lower than the seismic moment rates forecast by the SHARE models. As a result, the rates of large earthquakes in that group forecast by the SHARE model are higher than those inferred from tectonic moment rate, but lower than what the historical data show. For the other two

  14. Distribution of energy storage rate in area of strain localization during tension of austenitic steel

    NASA Astrophysics Data System (ADS)

    Oliferuk, W.; Maj, M.; Zembrzycki, K.

    2015-01-01

    The present work is devoted to experimental determination of the energy storage rate in the area of strain localization. The experimental procedure involves two complementary techniques: i.e. infrared thermography (IRT) and visible light imaging. The results of experiments have shown that during the evolution of plastic strain localization the energy storage rate in some areas of the deformed specimen drops to zero. To interpret the decrease of the energy storage rate in terms of micro-mechanisms, microstructural observations using electron back scattered diffraction (EBSC) were performed.

  15. Large human YACs constructed in a rad52 strain show a reduced rate of chimerism

    SciTech Connect

    Haldi, M.; Perrot, V.; Saumier, M.

    1994-12-01

    Current YAC libraries are plagued by a high frequency of chimeras - that is, clones containing fragments from multiple genomic regions. Chimeras are thought to arise largely through recombination in the yeast host cell. If so, the use of recombination-deficient yeast strains, such as rad52 mutants, might be expected to alleviate the problem. Here, we report the construction of megabase-sized human YACs in the rad52 strain MHY5201 and the determination of their rate of chimerism by fluorescence in situ hybridization analysis. Examination of 48 YACs showed a rate of chimerism of at most 8%, whereas YACs constructed in the wildtype host AB1380 showed a rate of about 50%. These results show that it is possible to significantly decrease the rate of YAC chimerism through the use of appropriate yeast host strains. 27 refs., 3 figs., 3 tabs.

  16. Strain rate, temperature, and humidity on strength and moduli of a graphite/epoxy composite

    NASA Technical Reports Server (NTRS)

    Lifshitz, J. M.

    1981-01-01

    Results of an experimental study of the influence of strain rate, temperature and humidity on the mechanical behavior of a graphite/epoxy fiber composite are presented. Three principal strengths (longitudinal, transverse and shear) and four basic moduli (E1, E2, G12 and U12) of a unidirectional graphite/epoxy composite were followed as a function of strain rate, temperature and humidity. Each test was performed at a constant tensile strain rate in an environmental chamber providing simultaneous temperature and humidity control. Prior to testing, specimens were given a moisture preconditioning treatment at 60 C. Values for the matrix dominated moduli and strength were significantly influenced by both environmental and rate parameters, whereas the fiber dominated moduli were not. However, the longitudinal strength was significantly influenced by temperature and moisture content. A qualitative explanation for these observations is presented.

  17. Determination of forming limit diagram for tube hydroforming based on the strain rate change criterion

    NASA Astrophysics Data System (ADS)

    Hu, Guolin; Yang, Lianfa; Liu, Jianwei

    2013-12-01

    Tube hydroforming (THF) is an attractive manufacturing process in automotive industry, and forming limit diagram (FLD) is a significant strategy to assess the formability of THF. In present study, a method of predicting the FLD for THF is developed based on finite element (FE) simulation with the strain rate change criterion (SRCC) as a failure criteria of identify localized necking. FE simulations under various linear loading paths are carried out to obtain the strain information. The equivalent strain rates at potential fracturing and its adjacent nodes are calculated and utilized with SRCC to distinguish the onset of fracturing in FE simulation. The fracture strains at the two nodes under various linear loading paths are abstracted for establishing FLD. Tube hydo-bulging experiments under the linear loading paths have been conducted to verify the prediction method of FLD, and the results show that this prediction method bears good agreement with experimental data.

  18. Influence of strain rate and temperature on the mechanical behavior of beryllium

    SciTech Connect

    Blumenthal, W.R.; Abeln, S.P.; Cannon, D.D.; Gray, G.T. III; Carpenter, R.W.

    1998-07-01

    The compressive stress-strain response of three grades of beryllium were studied as a function of strain rate and temperature. Grades S200D, E, and F represent a historical perspective of beryllium processing from the 1960{close_quote}s through 1990{close_quote}s technology. The purpose of this study was to measure the mechanical behavior of beryllium over a range of deformation conditions for constitutive model development and to obtain microstructural evidence for deformation mechanisms. The compressive stress-strain response was found to be independent of grade and strongly dependent on the applied strain rate between 0.001 and 8000 s{sup {minus}1}. The strain-hardening response displayed a moderate temperature dependence between 77{degree}K and 873{degree}K. Microstructural examination of SHPB specimens revealed that twinning was extensive at strains above 7{percent}. A SHPB sample deformed to over 20{percent} strain contained both twinning and grain boundary microcracking. {copyright} {ital 1998 American Institute of Physics.}

  19. Influence of strain rate on the orientation dependence of microstructure in nickel single crystals

    NASA Astrophysics Data System (ADS)

    Zheng, X. H.; Zhang, H. W.; Huang, X.; Hansen, N.; Lu, K.

    2016-02-01

    The deformation microstructures of nickel single crystals (99.945 wt.%) during dynamic plastic deformation and quasi-static compression to a true strain of 0.20 were comparatively investigated. The deformation microstructures are orientation dependent, forming cell structure, slip plane aligned or not slip plane aligned extended boundaries. It is found that the orientation spread decreases, remains unchanged and becomes enhanced when loading along <0 0 1>, <0 1 1> and <1 1 1>, respectively, as strain rate increases.

  20. Slow Strain Rate Testing of Alloy 22 in Simulated Concentrated Ground Waters

    SciTech Connect

    King, K J; Wong, L L; Estill, J C; Rebak, R B

    2003-10-29

    The proposed engineering barriers for the high-level nuclear waste repository in Yucca Mountain include a double walled container and a detached drip shield. The candidate material for the external wall of the container is Alloy 22 (N06022). One of the anticipated degradation modes for the containers could be environmentally assisted cracking (EAC). The objective of the current research was to characterize the effect of applied potential and temperature on the susceptibility of Alloy 22 to EAC in simulated concentrated water (SCW) and other environments using the slow strain rate technique (SSRT). Results show that the temperature and applied potential have a strong influence on the susceptibility of Alloy 22 to suffer EAC in SCW solution. Limited results show that sodium fluoride solution is more detrimental than sodium chloride solution.

  1. Numerical analysis of high strain rate failure of electro-magnetically loaded steel sheets

    NASA Astrophysics Data System (ADS)

    Erice, Borja; Mohr, Dirk

    2015-09-01

    Electro-magnetic forces provide a potentially power full means in designing dynamic experiments with active control of the loading conditions. This article deals with the development of computational models to simulate the thermo-mechanical response of electro-magnetically loaded metallic structures. The model assumes linear electromagnetic constitutive equations and time-independent electric induction to estimate the Joule heating and the Lorentz forces. The latter are then taken into account when evaluating stress equilibrium. A thermo-visco-plastic model with Johnson-Cook type of temperature and strain rate dependence and combined Swift-Voce hardening is used to evaluate the material's thermo-mechanical response. As a first application, the model is used to analyse the effect of electro-magnetic loading on the ductility of advanced high strength steels.

  2. On the Strain Rate Sensitivity of Abs and Abs Plus Fused Deposition Modeling Parts

    NASA Astrophysics Data System (ADS)

    Vairis, A.; Petousis, M.; Vidakis, N.; Savvakis, K.

    2016-06-01

    In this work the effect of strain rate on the tensile strength of fused deposition modeling parts built with Acrylonitrile-butadiene-styrene (ABS) and ABS plus material is presented. ASTM D638-02a specimens were built with ABS and ABS plus and they were tested on a Schenck Trebel Co. tensile test machine at three different test speeds, equal, lower, and higher to the test speed required by the ASTM D638-02a standard. The experimental tensile strength results were compared and evaluated. The fracture surfaces of selected specimens were examined with a scanning electron microscope, to determine failure mode of the filament strands. It was found that, as the test speed increases, specimens develop higher tensile strength and have higher elastic modulus. Specimens tested in the highest speed of the experiment had on average about 10% higher elastic modulus and developed on average about 11% higher tensile strength.

  3. On the Strain Rate Sensitivity of Abs and Abs Plus Fused Deposition Modeling Parts

    NASA Astrophysics Data System (ADS)

    Vairis, A.; Petousis, M.; Vidakis, N.; Savvakis, K.

    2016-09-01

    In this work the effect of strain rate on the tensile strength of fused deposition modeling parts built with Acrylonitrile-butadiene-styrene (ABS) and ABS plus material is presented. ASTM D638-02a specimens were built with ABS and ABS plus and they were tested on a Schenck Trebel Co. tensile test machine at three different test speeds, equal, lower, and higher to the test speed required by the ASTM D638-02a standard. The experimental tensile strength results were compared and evaluated. The fracture surfaces of selected specimens were examined with a scanning electron microscope, to determine failure mode of the filament strands. It was found that, as the test speed increases, specimens develop higher tensile strength and have higher elastic modulus. Specimens tested in the highest speed of the experiment had on average about 10% higher elastic modulus and developed on average about 11% higher tensile strength.

  4. Experimental characterization and modelling of UO2 behavior at high temperatures and high strain rates

    NASA Astrophysics Data System (ADS)

    Salvo, Maxime; Sercombe, Jérôme; Ménard, Jean-Claude; Julien, Jérôme; Helfer, Thomas; Désoyer, Thierry

    2015-01-01

    This work presents an experimental characterization of uranium dioxide (UO2) in compression under Reactivity Initiated Accident (RIA) conditions. Pellet samples were tested at four temperatures (1100, 1350, 1550 and 1700 °C) and at a strain rate varying over 4 decades (10-4-10-3-10-2-10-1 /s). The experimental results show that the stress-strain curves cannot be fitted with a unique power law as it is the case at smaller strain rates (10-9-10-5 /s). A strain-hardening also appears in most of the tests. The microstructural observations show a pronounced evolution of the porosity at the pellet center during the tests. A hyperbolic sine model which accounts for volume variations (pore compressibility) was therefore proposed to describe the behavior of UO2 on a large range of temperatures (1100 - 1700 °C) and strain rates (10-9-10-1 /s). The Finite Element simulations of the compression tests lead to results (maximum stress, axial and hoop strain distribution, porosity distribution) in good agreement with the measurements. The model was then assessed on a database of more than two hundred creep tests.

  5. Application of high-speed photography to the study of high-strain-rate materials testing

    NASA Astrophysics Data System (ADS)

    Ruiz, D.; Harding, John; Noble, J. P.; Hillsdon, Graham K.

    1991-04-01

    There is a growing interest in material behaviour at strain rates greater than 104sec1, for instance in the design of aero-engine turbine blades. It is necessary therefore, to develop material testing techniques that give well-defined information on mechanical behaviour in this very high strain-rate regime. A number of techniques are available, including the expanding ring test1, a miniaturised compression Hopkinson bar technique using direct impact and the double-notch shear test3 which has been described by Nicholas4 as "one of the most promising for future studies in dynamic plasticity". However, although it is believed to be a good test for determining the flow stress at shear strain rates of 104sec and above, the design of specimen used makes an accurate determination of strain extremely difficult while, in the later stages of the test the deformation mode involves rotation as well as shear. If this technique is to be used, therefore, it is necessary to examine in detail the progressive deformation and state of stress within the specimen during the impact process. An attempt can then be made to assess how far the data obtained is a reliable measure of the specimen material response and the test can be calibrated. An extensive three stage analysis has been undertaken. In the first stage, reported in a previous paper5, the initial elastic behaviour was studied. Dynamic photoelastic experiments were used to support linear elastic numerical results derived by the finite element method. Good qualitative agreement was obtained between the photoelastic experiment and the numerical model and the principal source of error in the elastic region of the double-notch shear test was identified as the assumption that all deformation of the specimen is concentrated in the two shear zones. For the epoxy (photoelastic) specimen a calibration factor of 5.3 was determined. This factor represents the ratio between the defined (nominal) gauge length and the effective gauge length

  6. Development of a strain rate dependent material model of human cortical bone for computer-aided reconstruction of injury mechanisms.

    PubMed

    Asgharpour, Zahra; Zioupos, Peter; Graw, Matthias; Peldschus, Steffen

    2014-03-01

    Computer-aided methods such as finite-element simulation offer a great potential in the forensic reconstruction of injury mechanisms. Numerous studies have been performed on understanding and analysing the mechanical properties of bone and the mechanism of its fracture. Determination of the mechanical properties of bones is made on the same basis used for other structural materials. The mechanical behaviour of bones is affected by the mechanical properties of the bone material, the geometry, the loading direction and mode and of course the loading rate. Strain rate dependency of mechanical properties of cortical bone has been well demonstrated in literature studies, but as many of these were performed on animal bones and at non-physiological strain rates it is questionable how these will apply in the human situations. High strain-rates dominate in a lot of forensic applications in automotive crashes and assault scenarios. There is an overwhelming need to a model which can describe the complex behaviour of bone at lower strain rates as well as higher ones. Some attempts have been made to model the viscoelastic and viscoplastic properties of the bone at high strain rates using constitutive mathematical models with little demonstrated success. The main objective of the present study is to model the rate dependent behaviour of the bones based on experimental data. An isotropic material model of human cortical bone with strain rate dependency effects is implemented using the LS-DYNA material library. We employed a human finite element model called THUMS (Total Human Model for Safety), developed by Toyota R&D Labs and the Wayne State University, USA. The finite element model of the human femur is extracted from the THUMS model. Different methods have been employed to develop a strain rate dependent material model for the femur bone. Results of one the recent experimental studies on human femur have been employed to obtain the numerical model for cortical femur. A

  7. Development of a strain rate dependent material model of human cortical bone for computer-aided reconstruction of injury mechanisms.

    PubMed

    Asgharpour, Zahra; Zioupos, Peter; Graw, Matthias; Peldschus, Steffen

    2014-03-01

    Computer-aided methods such as finite-element simulation offer a great potential in the forensic reconstruction of injury mechanisms. Numerous studies have been performed on understanding and analysing the mechanical properties of bone and the mechanism of its fracture. Determination of the mechanical properties of bones is made on the same basis used for other structural materials. The mechanical behaviour of bones is affected by the mechanical properties of the bone material, the geometry, the loading direction and mode and of course the loading rate. Strain rate dependency of mechanical properties of cortical bone has been well demonstrated in literature studies, but as many of these were performed on animal bones and at non-physiological strain rates it is questionable how these will apply in the human situations. High strain-rates dominate in a lot of forensic applications in automotive crashes and assault scenarios. There is an overwhelming need to a model which can describe the complex behaviour of bone at lower strain rates as well as higher ones. Some attempts have been made to model the viscoelastic and viscoplastic properties of the bone at high strain rates using constitutive mathematical models with little demonstrated success. The main objective of the present study is to model the rate dependent behaviour of the bones based on experimental data. An isotropic material model of human cortical bone with strain rate dependency effects is implemented using the LS-DYNA material library. We employed a human finite element model called THUMS (Total Human Model for Safety), developed by Toyota R&D Labs and the Wayne State University, USA. The finite element model of the human femur is extracted from the THUMS model. Different methods have been employed to develop a strain rate dependent material model for the femur bone. Results of one the recent experimental studies on human femur have been employed to obtain the numerical model for cortical femur. A

  8. Peak strain magnitudes and rates in the tibia exceed greatly those in the skull: An in vivo study in a human subject

    PubMed Central

    Hillam, Richard A; Goodship, Allen E; Skerry, Tim M

    2015-01-01

    Bone mass and architecture are the result of a genetically determined baseline structure, modified by the effect of internal hormonal/biochemical regulators and the effect of mechanical loading. Bone strain is thought to drive a feedback mechanism to regulate bone formation and resorption to maintain an optimal, but not excessive mass and organisation of material at each skeletal location. Because every site in the skeleton has different functions, we have measured bone strains induced by physiological and more unusual activities, at two different sites, the tibia and cranium of a young human male in vivo. During the most vigorous activities, tibial strains were shown to exceed 0.2%, when ground reaction exceeded 5 times body weight. However in the skull the highest strains recorded were during heading a heavy medicine/exercise ball where parietal strains were up to 0.0192%. Interestingly parietal strains during more physiological activities were much lower, often below 0.01%. Strains during biting were not dependent upon bite force, but could be induced by facial contortions of similar appearance without contact between the teeth. Rates of strain change in the two sites were also very different, where peak tibial strain rate exceeded rate in the parietal bone by more than 5 fold. These findings suggest that the skull and tibia are subject to quite different regulatory influences, as strains that would be normal in the human skull would be likely to lead to profound bone loss by disuse in the long bones. PMID:26232812

  9. Peak strain magnitudes and rates in the tibia exceed greatly those in the skull: An in vivo study in a human subject.

    PubMed

    Hillam, Richard A; Goodship, Allen E; Skerry, Tim M

    2015-09-18

    Bone mass and architecture are the result of a genetically determined baseline structure, modified by the effect of internal hormonal/biochemical regulators and the effect of mechanical loading. Bone strain is thought to drive a feedback mechanism to regulate bone formation and resorption to maintain an optimal, but not excessive mass and organisation of material at each skeletal location. Because every site in the skeleton has different functions, we have measured bone strains induced by physiological and more unusual activities, at two different sites, the tibia and cranium of a young human male in vivo. During the most vigorous activities, tibial strains were shown to exceed 0.2%, when ground reaction exceeded 5 times body weight. However in the skull the highest strains recorded were during heading a heavy medicine/exercise ball where parietal strains were up to 0.0192%. Interestingly parietal strains during more physiological activities were much lower, often below 0.01%. Strains during biting were not dependent upon bite force, but could be induced by facial contortions of similar appearance without contact between the teeth. Rates of strain change in the two sites were also very different, where peak tibial strain rate exceeded rate in the parietal bone by more than 5 fold. These findings suggest that the skull and tibia are subject to quite different regulatory influences, as strains that would be normal in the human skull would be likely to lead to profound bone loss by disuse in the long bones.

  10. Measurement of the mechanical properties of car body sheet steels at high strain rates and non ambient temperature

    NASA Astrophysics Data System (ADS)

    Bleck, W.; Larour, P.

    2003-09-01

    Crash behaviour and light weight have become the major design criteria for car bodies. Modem high strength steels offer appropriate solutions for these requirements. The prediction of the crash behaviour in simulation programs requires the information on materials behaviour during dynamic testing. The reduction of the signal waviness and the inertia effects at strain rates above 50s^{-1} are major issues in dynamic tensile testing. Damping techniques or load measurement on the sample itself are the common way to reduce oscillations. Strain measurement from the piston displacement or from optical devices on the specimen itself are also compared. Advantages and drawbacks of those various measurement techniques are presented.

  11. Molecular Dynamics Simulation of High Strain-Rate Void Nucleation in Nanocrystalline Copper.

    NASA Astrophysics Data System (ADS)

    Belak, J.; Boercker, D. B.; Bales, G. S.; Glosli, J.

    1997-03-01

    Isotropic tension is simulated in nanoscale polycrystalline copper with 10nm grain sizes using large-scale molecular dynamics. The nanocrystalline copper is fabricated on the computer by growing randomly oriented grains from random positions in the simulations cell. Constant volume strain rates of 10^8 - 10^10 are considered for systems ranging from 10^5 - 10^6 atoms using an EAM interatomic potential for copper. The spacing between voids for room temperature simulations is found to scale approximately as l ~ 0.005 * Cs / dotɛ, where Cs is the sound speed and dotɛ is the strain rate. Below strain rates of about 10^9, only one void is observed to nucleate and grow in the simulation cell. Results are presented for several grain boundary orientations (textures) and compared to macroscopic nucleation and growth models.

  12. Exploration of mechanisms underlying the strain-rate-dependent mechanical property of single chondrocytes

    SciTech Connect

    Nguyen, Trung Dung; Gu, YuanTong

    2014-05-05

    Based on the characterization by Atomic Force Microscopy, we report that the mechanical property of single chondrocytes has dependency on the strain-rates. By comparing the mechanical deformation responses and the Young's moduli of living and fixed chondrocytes at four different strain-rates, we explore the deformation mechanisms underlying this dependency property. We found that the strain-rate-dependent mechanical property of living cells is governed by both of the cellular cytoskeleton and the intracellular fluid when the fixed chondrocytes are mainly governed by their intracellular fluid, which is called the consolidation-dependent deformation behavior. Finally, we report that the porohyperelastic constitutive material model which can capture the consolidation-dependent behavior of both living and fixed chondrocytes is a potential candidature to study living cell biomechanics.

  13. Simple formulas for strain-energy release rates with higher order and singular finite elements

    NASA Technical Reports Server (NTRS)

    Raju, I. S.

    1986-01-01

    A general finite element procedure for obtaining strain-energy release rates for crack growth in isotropic materials is presented. The procedure is applicable to two-dimensional finite element analyses and uses the virtual crack-closure method. The procedure was applied to non-singular 4-noded (linear), 8-noded (parabolic), and 12-noded (cubic) elements and to quarter-point and cubic singularity elements. Simple formulas for strain-energy release rates were obtained with this procedure for both non-singular and singularity elements. The formulas were evaluated by applying them to two mode I and two mixed mode problems. Comparisons with results from the literature for these problems showed that the formulas give accurate strain-energy release rates.

  14. Calculation of strain-energy release rates with higher order and singular finite elements

    NASA Technical Reports Server (NTRS)

    Raju, I. S.

    1987-01-01

    A general finite element procedure for obtaining strain-energy release rates for crack growth in isotropic materials is presented. The procedure is applicable to two-dimensional finite element analyses and uses the virtual crack-closure method. The procedure was applied to nonsingular 4-noded (linear), 8-noded (parabolic), and 12-noded (cubic) elements and to quarter-point and cubic singularity elements. Simple formulas for strain-energy release rates were obtained with this procedure for both nonsingular and singularity elements. The formulas were evaluated by applying them to two mode I and two mixed mode problems. Comparisons with results from the literature for these problems showed that the formulas give accurate strain-energy release rates.

  15. Quantifying velocity, strain rate and stress distribution in coalescing salt sheets for safer drilling

    NASA Astrophysics Data System (ADS)

    Weijermars, R.; van Harmelen, A.

    2015-03-01

    Reaching sub-salt hydrocarbon targets in the deeper part of the Gulf of Mexico requires drilling through a salt canopy. The suture zones in the salt canopy are potential drilling hazards due to anomalous pressure behaviour of entrapped sediments. The Pólya vector field of coalescing salt sheets inside the canopy is used to explain suture formation and distinguish between upright and inclined suture contacts. Our analytical models, based on complex potentials, provide exact solutions for multiple source flows as they compete for space when spreading into the viscous continuum of the salt canopy. The velocity gradient tensor yields the strain rate tensor, which is used to map the principal strain rate magnitude inside the canopy. Quantification of one of the principal strain rates is sufficient because the plane deformation assumption ensures the two principal strain rates are equal in magnitude (but of opposite sign); the third principal dimension can have neither strain nor deviatoric stress. Visualization of the locations where the principal stress vanishes or peaks (with highs and lows) is useful for pre-drilling plans because such peaks must be avoided and the stress-free locations provide the safer drilling sites. A case study-of the Walker Ridge region-demonstrates the practical application of our new method.

  16. Strain-rate and temperature dependent material properties of Agar and Gellan Gum used in biomedical applications.

    PubMed

    Schiavi, Alessandro; Cuccaro, Rugiada; Troia, Adriano

    2016-01-01

    Agar and Gellan Gum are biocompatible polymers extensively used in several fields of tissue engineering research (e.g. tissue replacement, tissue support, tissue mimicking), due to their mechanical behaviour effectively representative of actual biological tissues. Since mechanical properties of artificial tissues are related to biocompatibility and functionality of medical implants and significantly influence adhesion, growth and differentiation of cells in tissue-engineering scaffolds, an accurate characterization of Young׳s modulus and relaxation time processes is needed. In this study, the strain-rate and temperature dependent material properties of Agarose and one among the numerous kind of Gellan Gum commercially available, known as Phytagel(®), have been investigated. Nine hydrogel samples have been realized with different mechanical properties: the first one Agar-based as a reference material, the further eight samples Gellan Gum based in which the effect of dispersed solid particles like kieselguhr and SiC, as enhancing mechanical properties factors, have been investigated as a function of concentration. Stress-strain has been investigated in compression and relaxation time has been evaluated by means of the Kohlrausch-Williams-Watts time decay function. Mechanical properties have been measured as a function of temperature between 20 °C and 35 °C and at different strain rates, from ~10(-3)s(-1) and ~10(-2)s(-1) (or deformation rate from ~0.01 mms(-1) to ~0.1 mms(-1)). From experimental data, the combined temperature and strain-rate dependence of hydrogels Young׳s modulus is determined on the basis of a constitutive model. In addition to a dependence of Young׳s modulus on temperature, a remarkable influence of strain-rate has been observed, especially in the sample containing solid particles; in same ranges of temperature and strain-rate, also relaxation time variations have been monitored in order to identify a possible dependence of damping

  17. Modeling ductile metals under large strain, pressure and high strain rates incorporating damage and microstructure evolution

    NASA Astrophysics Data System (ADS)

    Iannitti, Gianluca; Bonora, Nicola; Ruggiero, Andrew; Dichiaro, Simone

    2011-06-01

    In this work, a constitutive modeling that couples plasticity, grain size evolution (due to plastic deformation and dynamic recrystallization) and ductile damage has been developed. The effect of grain size on the material yield stress (Hall-Petch) and on the melting temperature has been considered. The model has been used to investigate computationally the behaviour of high purity copper in dynamic tensile extrusion test (DTE). An extensive numerical simulation work, using implicit finite element code with direct integration, has been performed and the results have been compared with available experimental data. The major finding is that the proposed model is capable to predict most of the observed features such as the increase of material ductility with the decreasing average grain size, the overall number and size of fragments and the average grain size distribution in the fragment trapped into the dime.

  18. Modeling ductile metals under large strain, pressure and high strain rate incorporating damage and microstructure evolution

    NASA Astrophysics Data System (ADS)

    Iannitti, Gianluca; Bonora, Nicola; Ruggiero, Andrew; Dichiaro, Simone

    2012-03-01

    In this work, a constitutive modeling that couples plasticity, grain size evolution (due to plastic deformation and dynamic recrystallization) and ductile damage has been developed. The effect of grain size on the material yield stress (Hall-Petch) and on the melting temperature has been considered. The model has been used to investigate computationally the behavior of high purity copper in dynamic tensile extrusion test (DTE). An extensive numerical simulation work, using implicit finite element code with direct integration, has been performed and the results have been compared with available experimental data. The major finding is that the proposed model is capable to predict most of the observed features such as the increase of material ductility with the decreasing average grain size, the overall number and size of fragments and the average grain size distribution in the fragment trapped into the dime.

  19. Strain rate sensitivity of nanoindentation creep in an AlCoCrFeNi high-entropy alloy

    NASA Astrophysics Data System (ADS)

    Jiao, Z. M.; Wang, Z. H.; Wu, R. F.; Qiao, J. W.

    2016-09-01

    Creep behaviors of an AlCoCrFeNi high-entropy alloy with the body-centered cubic structure were investigated by nanoindentation. The enhanced strain gradient induced by higher strain rate leads to decreased strain rate sensitivity during creep process. The present alloy exhibits excellent creep resistance, mainly due to its large entropy of mixing and highly distorted lattice structure.

  20. Material Properties and Constitutive Modeling of Infant Porcine Cerebellum Tissue in Tension at High Strain Rate

    PubMed Central

    Li, Kui; Zhao, Hui; Liu, Wenjun; Yin, Zhiyong

    2015-01-01

    Background The mechanical characterization of infant porcine cerebellum tissue in tension at high strain rate is crucial for modeling traumatic cerebellum injury, which is in turn helpful for understanding the biomechanics of such injuries suffered in traffic accidents. Material and Method In this study, the infant porcine cerebellum tissue was given three loading velocities, ie, 2s-1, 20s-1 and 100s-1 with up to 30% strain to investigate the tensile properties. At least six tensile tests for each strain rate were validly performed. Fung, Gent, Ogden and exponential models were applied to fit the constitutive equations, so as to obtain material parameters from the experimental data. Results The Lagrange stress of infant porcine cerebellum tissue in tension appeared to be no more than 3000Pa at each loading velocity. More specifically, the Lagrange stress at 30% strain was (393.7±84.4)Pa, (928.3±56.3)Pa and (2582.4±282.2)Pa at strain rates of 2s-1, 20s-1 and 100s-1, respectively. Fung (0.833≤R2≤0.924), Gent (0.797≤R2≤0.875), Ogden (0.859≤R2≤0.944) and exponential (0.930≤R2≤0.972) models provided excellent fitting to experimental data up to 30% strain. Conclusions The infant cerebellum tissue shows a stiffer response with increase of the loading speed, indicating a strong strain-rate sensitivity. This study will enrich the knowledge on the material properties of infant brain tissue, which may augment the biofidelity of finite element model of human pediatric cerebellum. PMID:25830545

  1. Energy absorption at high strain rate of glass fiber reinforced mortars

    NASA Astrophysics Data System (ADS)

    Fenu, Luigi; Forni, Daniele; Cadoni, Ezio

    2015-09-01

    In this paper, the dynamic behaviour of cement mortars reinforced with glass fibers was studied. The influence of the addition of glass fibers on energy absorption and tensile strength at high strain-rate was investigated. Static tests in compression, in tension and in bending were first performed. Dynamic tests by means of a Modified Hopkinson Bar were then carried out in order to investigate how glass fibers affected energy absorption and tensile strength at high strain-rate of the fiber reinforced mortar. The Dynamic Increase Factor (DIF) was finally evaluated.

  2. Modeling of Final Structure Obtained Under High Strain-Rate Deformation

    SciTech Connect

    Majta, J.; Zurek, A.K.

    1999-01-01

    This paper discusses results of experimental research and a model implementation of the hot deformation process in the two-phase region under high strain rate. Hot compression tests were employed to determine the behavior of deformed microalloyed steel over a range of strain rates (1 x 10{sup -3} s{sup -1} - 2.5 x 10{sup 3} s{sup -1}) and temperatures (650 C - 850 C). The thermomechanical history of the material is consequently integrated in the simulation and compared with the experimental results.

  3. In vivo vascular wall shear rate and circumferential strain of renal disease patients.

    PubMed

    Park, Dae Woo; Kruger, Grant H; Rubin, Jonathan M; Hamilton, James; Gottschalk, Paul; Dodde, Robert E; Shih, Albert J; Weitzel, William F

    2013-02-01

    This study measures the vascular wall shear rate at the vessel edge using decorrelation based ultrasound speckle tracking. Results for nine healthy and eight renal disease subjects are presented. Additionally, the vascular wall shear rate and circumferential strain during physiologic pressure, pressure equalization and hyperemia are compared for five healthy and three renal disease subjects. The mean and maximum wall shear rates were measured during the cardiac cycle at the top and bottom wall edges. The healthy subjects had significantly higher mean and maximum vascular wall shear rate than the renal disease subjects. The key findings of this research were that the mean vascular wall shear rates and circumferential strain changes between physiologic pressure and hyperemia that was significantly different between healthy and renal disease subjects.

  4. High Strain Rate Compression of Martensitic NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Qiu, Ying; Young, Marcus L.; Nie, Xu

    2015-09-01

    The compressive response of martensitic NiTi shape memory alloys (SMAs) under high strain rate (1200 s-1) was investigated on a modified Kolsky (Split Hopkinson) compression bar. The single-loading momentum trapping system ensures precise deformation control (1.4, 1.8, 3.0, 4.8, and 9.6 % strain) and single loading during dynamic compression. With increasing strain, the phase transformation peaks shift toward lower temperatures, while the intensities of these peaks decrease and eventually disappear completely at strains above 7 %, where the onset of plastic deformation of reoriented martensite occurs. All transformation peaks are recoverable after deformation simply by annealing at 873 K (600 °C) for 30 min, except those peaks corresponding to strains above 7 % (e.g., 9.6 %) which return upon annealing, but at a lower temperature. XRD results showed the variation of the strongest diffraction peak from (1bar{1}1) to (111) crystal plane before and after high strain rate compression.

  5. Adhesive-Bonded Composite Joint Analysis with Delaminated Surface Ply Using Strain-Energy Release Rate

    NASA Technical Reports Server (NTRS)

    Chadegani, Alireza; Yang, Chihdar; Smeltzer, Stanley S. III

    2012-01-01

    This paper presents an analytical model to determine the strain energy release rate due to an interlaminar crack of the surface ply in adhesively bonded composite joints subjected to axial tension. Single-lap shear-joint standard test specimen geometry with thick bondline is followed for model development. The field equations are formulated by using the first-order shear-deformation theory in laminated plates together with kinematics relations and force equilibrium conditions. The stress distributions for the adherends and adhesive are determined after the appropriate boundary and loading conditions are applied and the equations for the field displacements are solved. The system of second-order differential equations is solved to using the symbolic computation tool Maple 9.52 to provide displacements fields. The equivalent forces at the tip of the prescribed interlaminar crack are obtained based on interlaminar stress distributions. The strain energy release rate of the crack is then determined by using the crack closure method. Finite element analyses using the J integral as well as the crack closure method are performed to verify the developed analytical model. It has been shown that the results using the analytical method correlate well with the results from the finite element analyses. An attempt is made to predict the failure loads of the joints based on limited test data from the literature. The effectiveness of the inclusion of bondline thickness is justified when compared with the results obtained from the previous model in which a thin bondline and uniform adhesive stresses through the bondline thickness are assumed.

  6. Growth rate regulation of rRNA content of a marine Synechococcus (cyanobacterium) strain

    SciTech Connect

    Binder, B.J.; Liu, Y.C.

    1998-09-01

    The relationship between growth rate and rRNA content in a marine Synechococcus strain was examined. A combination of flow cytometry and whole-cell hybridization with fluorescently labeled 16S rRNA-targeted oligonucleotide probes was used to measure the rRNA content of Synechococcus strain WH8101 cells grown at a range of light-limited growth rates. The sensitivity of this approach was sufficient for the analysis of rRNA even in very slowly growing Synechococcus cells. The relationship between growth rate and cellular rRNA content comprised three phases: (1) at low growth rates, rRNA cell{sup {minus}1} remained approximately constant; (2) at intermediate rates, rRNA cell{sup {minus}1} increased proportionally with growth rate; and (3) at the highest, light-saturated rates, rRNA cell{sup {minus}1} dropped abruptly. Total cellular RNA was well correlated with the probe-based measure of rRNA and varied in a similar manner with growth rate. Mean cell volume and rRNA concentration were related to growth rate in a manner similar to rRNA cell{sup {minus}1}, although the overall magnitude linear increase in ribosome efficiency with increasing growth rate, which is consistent with the prevailing prokaryotic model at low growth rates. Taken together, these results support the notion that measurements of cellular rRNA content might be useful for estimating in situ growth rates in natural Synechococcus populations.

  7. A method for intermediate strain rate compression testing and study of compressive failure mechanism of Mg-Al-Zn alloy

    NASA Astrophysics Data System (ADS)

    Gupta, Nikhil; Luong, Dung D.; Rohatgi, Pradeep K.

    2011-05-01

    Obtaining meaningful information from the test results is a challenge in the split-Hopkinson pressure bar (SHPB) test method if the specimen does not fail during the test. Although SHPB method is now widely used for high strain rate testing, this limitation has made it difficult to use it for characterization of materials in the intermediate strain rate range (typically 10-1000 s-1). In the present work, a method is developed to characterize materials in the intermediate strain rate range using SHPB setup. In this method, the specimen is repeatedly tested under compression at a given strain rate until failure is achieved. The stress-strain graphs obtained from each test cycle are used to plot the master stress-strain graph for that strain rate. This method is used to study the strain rate dependence of compressive response of a Mg-Al-Zn alloy in the intermediate strain rate range. A remarkable difference is observed in the failure mechanism of the alloy under quasi-static and intermediate strain rate compression. Matrix cracking is the main failure mechanism under quasi-static compression, whereas shattering of intermetallic precipitates, along with plastic deformation of the matrix, is discovered to become prominent as the strain rate is increased.

  8. High strain rate characterization of low-density low-strength materials

    NASA Astrophysics Data System (ADS)

    Sawas, Omar

    The Split Hopkinson Bar (SHB) is a reliable experimental technique for measuring high strain rate properties of high-strength, ductile materials. Attempts to apply the SHB in measurement on more compliant materials, such as polymers and foams, are limited by the maximum achievable strain and high noise-to-signal ratios. This work introduces an all-polymeric split Hopkinson bar (APSHB) experiment, which overcomes these limitations. The proposed method uses polymeric pressure bars to achieve a closer impedance match between the pressure bars and the specimen material, thus providing both low signal-to-noise ratio data and a longer input pulse for higher maximum strain. The APSHB requires very careful data reduction procedures because of the viscoelastic behavior of the incident and transmitter pressure bars. The APSHB produces high-quality stress-strain data for a variety of compliant materials, including polycarbonate, elastomer, polyurethane, and styrofoam.

  9. Strain rate-dependent deformation and strength modeling of a polymer matrix composite utilizing a micromechanics approach

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert Keith

    1999-11-01

    Potential gas turbine applications will expose polymer matrix composites to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under extreme conditions. Specifically, analytical methods designed for these applications must have the capability of properly capturing the strain rate sensitivities and nonlinearities that are present in the material response. The Ramaswamy-Stouffer constitutive equations, originally developed to analyze the viscoplastic deformation of metals, have been modified to simulate the nonlinear deformation response of ductile, crystalline polymers. The constitutive model is characterized and correlated for two representative ductile polymers, Fiberite 977-2 and PEEK, and the computed results correlate well with experimental values. The polymer constitutive equations are implemented in a mechanics of materials based composite micromechanics model to predict the nonlinear, rate dependent deformation response of a composite ply. Uniform stress and uniform strain assumptions are applied to compute the effective stresses of a composite unit cell from the applied strains. The micromechanics equations are successfully verified for two polymer matrix composites, IM7/977-2 and AS4/PEEK. The ultimate strength of a composite ply is predicted with the Hashin failure criteria that were implemented in the composite micromechanics model. The failure stresses of the two composite material systems are accurately predicted for a variety of fiber orientations and strain rates. The composite deformation model is implemented in LS-DYNA, a commercially available transient dynamic explicit finite element code. The matrix constitutive equations are converted into an incremental form, and the model is implemented into LS-DYNA through the use of a user defined material subroutine. The deformation response of a bulk polymer and a polymer matrix composite are predicted by finite element analyses. The results

  10. High strain rate behavior of alloy 800H at high temperatures

    NASA Astrophysics Data System (ADS)

    Shafiei, E.

    2016-05-01

    In this paper, a new model using linear estimation of strain hardening rate vs. stress, has been developed to predict dynamic behavior of alloy 800H at high temperatures. In order to prove the accuracy and competency of the presented model, Johnson-Cook model pertaining modeling of flow stress curves was used. Evaluation of mean error of flow stress at deformation temperatures from 850 °C to 1050 °C and at strain rates of 5 S-1 to 20 S-1 indicates that the predicted results are in a good agreement with experimentally measured ones. This analysis has been done for the stress-strain curves under hot working condition for alloy 800H. However, this model is not dependent on the type of material and can be extended for any similar conditions.

  11. Determination of surfaces of constant inelastic strain rate at elevated temperature

    NASA Technical Reports Server (NTRS)

    Battiste, R. L.; Ball, S. J.

    1986-01-01

    An experimental effort to perform special exploratory multiaxial deformation tests on tubular specimens of type 316 stainless steel at 650 C (1200 F) is described. One test specimen was subjected to a time-independent torsional shear strain test history, and surfaces of constant inelastic strain rate (SCISRs) in an axial/torsional stress space were measured at various predetermined points during the test. A second specimen was subjected to a 14-week time-dependent (creep-recovery-creep periods) torsional shear stress histogram SCISRs determinations made at 17 points during the test. The tests were conducted in a high temperature, computer controlled axial/torsional test facility using high-temperature multiaxial extensometer. The effort was successful, and for the first time the existence of surfaces of constant inelastic strain rate was experimentally demonstrated.

  12. Mechanical Characterization of Immature Porcine Brainstem in Tension at Dynamic Strain Rates

    PubMed Central

    Zhao, Hui; Yin, Zhiyong; Li, Kui; Liao, Zhikang; Xiang, Hongyi; Zhu, Feng

    2016-01-01

    Background Many brain injury cases involve pediatric road traffic accidents, and among these, brainstem injury causes disastrous outcomes. A thorough understanding of the tensile characterization of immature brainstem tissue is crucial in modeling traumatic brain injury sustained by children, but limited experimental data in tension is available for the immature brain tissue at dynamic strain rates. Material/Methods We harvested brainstem tissue from immature pigs (about 4 weeks old, and at a developmental stage similar to that of human toddlers) as a byproduct from a local slaughter house and very carefully prepared the samples. Tensile tests were performed on specimens at dynamic strain rates of 2/s, 20/s, and 100/s using a biological material instrument. The constitutive models, Fung, Ogden, Gent, and exponential function, for immature brainstem tissue material property were developed for the recorded experimental data using OriginPro® 8.0 software. The t test was performed for infinitesimal shear modules. Results The curves of stress-versus-stretch ratio were convex in shape, and inflection points were found in all the test groups at the strain of about 2.5%. The average Lagrange stress of the immature brainstem specimen at the 30% strain at the strain rates of 2, 20, and 100/s was 273±114, 515±107, and 1121±197 Pa, respectively. The adjusted R-Square (R2) of Fung, Ogden, Gent, and exponential model was 0.820≤R2≤0.933, 0.774≤R2≤0.940, 0.650≤R2≤0.922, and 0.852≤R2≤0.981, respectively. The infinitesimal shear modulus of the strain energy functions showed a significant association with the strain rate (p<0.01). Conclusions The immature brainstem is a rate-dependent material in dynamic tensile tests, and the tissue becomes stiffer with increased strain rate. The reported results may be useful in the study of brain injuries in children who sustain injuries in road traffic accidents. Further research in more detail should be performed in the

  13. Localisation of shear fracture networks in anisotropic materials: influence of strain rate and material strength

    NASA Astrophysics Data System (ADS)

    Gomez-Rivas, E.; Griera, A.

    2009-04-01

    This contribution presents an experimental study of deformation localisation and the formation of fracture networks in elastoviscoplastic layered materials under pure shear boundary conditions. The mechanical properties of the analogue mixtures, which are made of plasticine, have been used to analyse the transition from models in which deformation is accommodated by homogeneous viscous flow to systems controlled by a few active faults. Two series of experiments have been studied: (a) the same material was deformed at different strain rates and (b) four materials with different mechanical properties were deformed at a fixed strain rate. The results show that strain rate and viscous ductility define a change on the degree of deformation localisation and the geometry of fracture networks. The increase of deformation also produces changes on the mechanical behaviour of the systems and the type of deformation. Localisation of fracture networks is enhanced when strain rate is increased. Moreover, there is a progressive increment in the relationship between fracture displacement and fracture length related to the strain rate applied to the system. This experimental observation is also corroborated by a series of simple finite element linear elastoviscous simulations. In these models, a horizontal inclusion within a matrix simulates a pre-existing fracture. The displacement along this fracture is tracked at all times using some selected nodes located at the two walls. The results indicate that there is a dependency of fracture displacements on the strain rate. A deviation between shear strains registered by fractures and the one applied by the boundary conditions is also detected, especially at low strain. The degree of localisation and the nucleation of shear fractures also depend strongly on the viscous ductility and strength of the analogue material. The raise of the material stiffness causes an increase of the length of fractures and displacements along them. This fact

  14. Strain rate hardening: a hidden but critical mechanism for biological composites?

    PubMed

    Chintapalli, Ravi Kiran; Breton, Stephanie; Dastjerdi, Ahmad Khayer; Barthelat, Francois

    2014-12-01

    Natural materials such as nacre, bone, collagen and spider silk boast unusual combinations of stiffness, strength and toughness. Behind this performance is a staggered microstructure, which consists of stiff and elongated inclusions embedded in a softer and more deformable matrix. The micromechanics of deformation and failure associated with this microstructure are now well understood at the "unit cell" level, the smallest representative volume for this type of material. However, these mechanisms only translate to high performance if they propagate throughout large volumes, an important condition which is often overlooked. Here we present, for the first time, a model which captures the conditions for either spreading of deformations or localization, which determines whether a staggered composite is brittle or deformable at the macroscale. The macroscopic failure strain for the material was calculated as function of the viscoplastic properties of the interfaces and the severity of the defect. As expected, larger strains at failure can be achieved when smaller defects are present within the material, or with more strain hardening at the interface. The model also shows that strain rate hardening is a powerful source of large deformations for the material as well, a result we confirmed and validated with tensile experiments on glass-polydimethylsiloxane (PDMS) nacre-like staggered composites. An important implication is that natural materials, largely made of rate-dependent materials, could rely on strain rate hardening to tolerate initial defects and damage to maintain their functionality. Strain rate hardening could also be harnessed and optimized in bio-inspired composites in order to maximize their overall performance. PMID:25174668

  15. Strain rate hardening: a hidden but critical mechanism for biological composites?

    PubMed

    Chintapalli, Ravi Kiran; Breton, Stephanie; Dastjerdi, Ahmad Khayer; Barthelat, Francois

    2014-12-01

    Natural materials such as nacre, bone, collagen and spider silk boast unusual combinations of stiffness, strength and toughness. Behind this performance is a staggered microstructure, which consists of stiff and elongated inclusions embedded in a softer and more deformable matrix. The micromechanics of deformation and failure associated with this microstructure are now well understood at the "unit cell" level, the smallest representative volume for this type of material. However, these mechanisms only translate to high performance if they propagate throughout large volumes, an important condition which is often overlooked. Here we present, for the first time, a model which captures the conditions for either spreading of deformations or localization, which determines whether a staggered composite is brittle or deformable at the macroscale. The macroscopic failure strain for the material was calculated as function of the viscoplastic properties of the interfaces and the severity of the defect. As expected, larger strains at failure can be achieved when smaller defects are present within the material, or with more strain hardening at the interface. The model also shows that strain rate hardening is a powerful source of large deformations for the material as well, a result we confirmed and validated with tensile experiments on glass-polydimethylsiloxane (PDMS) nacre-like staggered composites. An important implication is that natural materials, largely made of rate-dependent materials, could rely on strain rate hardening to tolerate initial defects and damage to maintain their functionality. Strain rate hardening could also be harnessed and optimized in bio-inspired composites in order to maximize their overall performance.

  16. Influence of compressibility on the Lagrangian statistics of vorticity-strain-rate interactions.

    PubMed

    Danish, Mohammad; Sinha, Sawan Suman; Srinivasan, Balaji

    2016-07-01

    The objective of this study is to investigate the influence of compressibility on Lagrangian statistics of vorticity and strain-rate interactions. The Lagrangian statistics are extracted from "almost" time-continuous data sets of direct numerical simulations of compressible decaying isotropic turbulence by employing a cubic spline-based Lagrangian particle tracker. We study the influence of compressibility on Lagrangian statistics of alignment in terms of compressibility parameters-turbulent Mach number, normalized dilatation-rate, and flow topology. In comparison to incompressible turbulence, we observe that the presence of compressibility in a flow field weakens the alignment tendency of vorticity toward the largest strain-rate eigenvector. Based on the Lagrangian statistics of alignment conditioned on dilatation and topology, we find that the weakened tendency of alignment observed in compressible turbulence is because of a special group of fluid particles that have an initially negligible dilatation-rate and are associated with stable-focus-stretching topology. PMID:27575211

  17. Influence of compressibility on the Lagrangian statistics of vorticity-strain-rate interactions.

    PubMed

    Danish, Mohammad; Sinha, Sawan Suman; Srinivasan, Balaji

    2016-07-01

    The objective of this study is to investigate the influence of compressibility on Lagrangian statistics of vorticity and strain-rate interactions. The Lagrangian statistics are extracted from "almost" time-continuous data sets of direct numerical simulations of compressible decaying isotropic turbulence by employing a cubic spline-based Lagrangian particle tracker. We study the influence of compressibility on Lagrangian statistics of alignment in terms of compressibility parameters-turbulent Mach number, normalized dilatation-rate, and flow topology. In comparison to incompressible turbulence, we observe that the presence of compressibility in a flow field weakens the alignment tendency of vorticity toward the largest strain-rate eigenvector. Based on the Lagrangian statistics of alignment conditioned on dilatation and topology, we find that the weakened tendency of alignment observed in compressible turbulence is because of a special group of fluid particles that have an initially negligible dilatation-rate and are associated with stable-focus-stretching topology.

  18. Influence of compressibility on the Lagrangian statistics of vorticity-strain-rate interactions

    NASA Astrophysics Data System (ADS)

    Danish, Mohammad; Sinha, Sawan Suman; Srinivasan, Balaji

    2016-07-01

    The objective of this study is to investigate the influence of compressibility on Lagrangian statistics of vorticity and strain-rate interactions. The Lagrangian statistics are extracted from "almost" time-continuous data sets of direct numerical simulations of compressible decaying isotropic turbulence by employing a cubic spline-based Lagrangian particle tracker. We study the influence of compressibility on Lagrangian statistics of alignment in terms of compressibility parameters—turbulent Mach number, normalized dilatation-rate, and flow topology. In comparison to incompressible turbulence, we observe that the presence of compressibility in a flow field weakens the alignment tendency of vorticity toward the largest strain-rate eigenvector. Based on the Lagrangian statistics of alignment conditioned on dilatation and topology, we find that the weakened tendency of alignment observed in compressible turbulence is because of a special group of fluid particles that have an initially negligible dilatation-rate and are associated with stable-focus-stretching topology.

  19. Inverse correlation between longevity and developmental rate among wild C. elegans strains

    PubMed Central

    Jung, Juyoung; Park, Sangsoon; Cabatbat, Josephine Jill T.; Kim, Pan-Jun; Lee, Seung-Jae V.

    2016-01-01

    Genetic studies using model organisms have shown that many long-lived mutants display impaired fitness, such as reduced fecundity and delayed development. However, in several wild animals, the association between longevity and fitness does not seem to be inevitable. Thus, the relationship between longevity and fitness in wild organisms remains inconclusive. Here, we determined the correlation between lifespan and fitness, developmental rate and brood size, by using 16 wild-derived C. elegans strains originated from various geographic areas. We found a negative correlation between lifespan and developmental rate. In contrast, we did not find such negative correlation between longevity and developmental rate among the individuals of C. elegans strains. These data imply that polymorphic genetic variants among wild isolates determine resource allocation to longevity and developmental rate. PMID:27193830

  20. TRP 9904 - Constitutive Behavior of High Strength Multiphase Sheel Steel Under High Strain Rate Deformation

    SciTech Connect

    David Matlock; John Speer

    2005-03-31

    The focus of the research project was to systematically assess the strain rate dependence of strengthening mechanisms in new advanced high strength sheet steels. Data were obtained on specially designed and produced Duel Phase and TRIP steels and compared to the properties of automotive steels currently in use.

  1. Heart wall motion analysis by dynamic 3D strain rate imaging from tissue Doppler echocardiography

    NASA Astrophysics Data System (ADS)

    Hastenteufel, Mark; Wolf, Ivo; de Simone, Raffaele; Mottl-Link, Sibylle; Meinzer, Hans-Peter

    2002-04-01

    The knowledge about the complex three-dimensional (3D) heart wall motion pattern, particular in the left ventricle, provides valuable information about potential malfunctions, e.g., myocardial ischemia. Nowadays, echocardiography (cardiac ultrasound) is the predominant technique for evaluation of cardiac function. Beside morphology, tissue velocities can be obtained by Doppler techniques (tissue Doppler imaging, TDI). Strain rate imaging (SRI) is a new technique to diagnose heart vitality. It provides information about the contraction ability of the myocardium. Two-dimensional color Doppler echocardiography is still the most important clinical method for estimation of morphology and function. Two-dimensional methods leads to a lack of information due to the three-dimensional overall nature of the heart movement. Due to this complex three-dimensional motion pattern of the heart, the knowledge about velocity and strain rate distribution over the whole ventricle can provide more valuable diagnostic information about motion disorders. For the assessment of intracardiac blood flow three-dimensional color Doppler has already shown its clinical utility. We have developed methods to produce strain rate images by means of 3D tissue Doppler echocardiography. The tissue Doppler and strain rate images can be visualized and quantified by different methods. The methods are integrated into an interactively usable software environment, making them available in clinical everyday life. Our software provides the physician with a valuable tool for diagnosis of heart wall motion.

  2. Strain-rate dependent shear viscosity of the Gaussian core model fluid.

    PubMed

    Ahmed, Alauddin; Mausbach, Peter; Sadus, Richard J

    2009-12-14

    Nonequilibrium molecular dynamics simulations are reported for the shear viscosity of the Gaussian core model (GCM) fluid over a wide range of densities, temperatures and strain rates. A transition from Newtonian and non-Newtonian behavior is observed in all cases for sufficiently high strain rates. On the high-density side of the solid region where re-entrant melting occurs, the shear viscosity decreases significantly when the density is increased at constant temperature and Newtonian behavior persists until very high strain rates. This behavior, which is attributed to particle overlap, is in contrast to the monotonic increase in shear viscosity with density observed for the Lennard-Jones potential. Contrary to the behavior of normal fluids, the viscosity is observed to increase with increasing temperatures at high densities. This reflects a peculiarity of the GCM, namely the approach to the "infinite-density ideal-gas limit." The behavior is also consistent with viscosity measurements of cationic surfactant solutions. In contrast to other potentials, the shear viscosities for the Gaussian core potential at low to moderate strain rates are obtained with modest statistical uncertainties. Zero shear viscosities extrapolated from the nonequilibrium simulations are in good agreement with equilibrium Green-Kubo calculations.

  3. Stress corrosion cracking of alloy 600 using the constant strain rate test

    SciTech Connect

    Bulischeck, T. S.; van Rooyen, D.

    1980-01-01

    The most recent corrosion problems experienced in nuclear steam generators tubed with Inconel alloy 600 is a phenomenon labeled ''denting''. Denting has been found in various degrees of severity in many operating pressurized water reactors. Laboratory investigations have shown that Inconel 600 exhibits intergranular SCC when subjected to high stresses and exposed to deoxygenated water at elevated temperatures. A research project was initiated at Brookhaven National Laboratory in an attempt to improve the qualitative and quantitative understanding of factors influencing SCC in high temperature service-related environments. An effort is also being made to develop an accelerated test method which could be used to predict the service life of tubes which have been deformed or are actively denting. Several heats of commercial Inconel 600 tubing were procured for testing in deaerated pure and primary water at temperatures from 290 to 365/sup 0/C. U-bend type specimens were used to determine crack initiation times which may be expected for tubes where denting has occurred but is arrested and provide baseline data for judging the accelerating effects of the slow strain rate method. Constant extension rate tests were employed to determine the crack velocities experienced in the crack propagation stage and predict failure times of tubes which are actively denting. 8 refs., 17 figs., 5 tabs.

  4. Accuracy of heart strain rate calculation derived from Doppler tissue velocity data

    NASA Astrophysics Data System (ADS)

    Santos, Andres; Ledesma-Carbayo, Maria J.; Malpica, Norberto; Desco, Manuel; Antoranz, Jose C.; Marcos-Alberca, Pedro; Garcia-Fernandez, Miguel A.

    2001-05-01

    Strain Rate (SR) Imaging is a recent imaging technique that provides information about regional myocardial deformation by measuring local compression and expansion rates. SR can be obtained by calculating the local in-plane velocity gradients along the ultrasound beam from Doppler Tissue velocity data. However, SR calculations are very dependent on the image noise and artifacts, and different calculation algorithms may provide inconsistent results. This paper compares techniques to calculate SR. 2D Doppler Tissue Images (DTI) are acquired with an Acuson Sequoia scanner. Noise was measured with the aid of a rotating phantom. Processing is performed on polar coordinates. For each image, after removal of black spot artifacts by a selective median filter, two different SR calculation methods have been implemented. In the first one, SR is computed as the discrete velocity derivative, and noise is reduced with a variable-width gaussian filter. In the second method a smoothing cubic spine is calculated for every scan line according to the noise level and the derivative is obtained from an analytical expression. Both methods have been tested with DTI data from synthetic phantoms and normal volunteers. Results show that noise characteristics, border effects and the adequate scale are critical to obtain meaningful results.

  5. Spatial and Temporal Variations in Strain Rates in the Western Transverse Ranges, California

    NASA Astrophysics Data System (ADS)

    Marshall, S. T.; Funning, G. J.; Owen, S. E.

    2012-12-01

    We determine the spatial and temporal variations in strain rates in the Transverse Ranges of southern California by combing data from 52 continuous GPS sites in the Plate Boundary Observatory network with InSAR time series. To characterize periodic seasonal motions in the GPS time series, phases and amplitudes of annual and semiannual motions are estimated for each GPS station. We remove these seasonal terms, and then perform Principal Component Analysis on the residual time series to remove common-mode errors. We find that seasonal GPS motions are not strongly dependent on local substrate geology. To quantify the spatial patterns of deformation in greater detail than GPS can provide, we use a persistent scatterer InSAR (PSI) data set comprised of 23 ENVISAT ASAR scenes. The PSI data were derived using the software package, StaMPS [Hooper et al. 2004]. The PSI data show potential anthropogenic subsidence in the Oxnard/Ventura area as well as at a location just south of the Oak Ridge. A highly localized zone of subsidence is also present along the Ventura Avenue anticline, where ongoing petroleum extraction is occurring. Comparison of the InSAR and the GPS projected into the InSAR line of sight, shows general agreement. The relative lack of significant non-tectonic motions in the western Transverse Ranges is in stark contrast to the nearby Los Angeles basin where anthropogenic motions dominate many InSAR scenes. To determine the local tectonic deformation rates, we remove strain associated with the nearby San Andreas fault using a rectangular dislocation model. Direct inversion of the GPS velocities into a triangulated network with variable strain/rotation rates produces a generalized map of variations in tectonic strain rates. The strain rate map shows the largest strain rates to be near the central Ventura basin with rates generally decreasing westward towards the Santa Barbara Channel. To determine compatible regional fault slip rates, we use a forward mechanical

  6. Compressive viscoelasticity of freshly excised mouse skin is dependent on specimen thickness, strain level and rate.

    PubMed

    Wang, Yuxiang; Marshall, Kara L; Baba, Yoshichika; Lumpkin, Ellen A; Gerling, Gregory J

    2015-01-01

    Although the skin's mechanical properties are well characterized in tension, little work has been done in compression. Here, the viscoelastic properties of a population of mouse skin specimens (139 samples from 36 mice, aged 5 to 34 weeks) were characterized upon varying specimen thickness, as well as strain level and rate. Over the population, we observed the skin's viscoelasticity to be quite variable, yet found systematic correlation of residual stress ratio with skin thickness and strain, and of relaxation time constants with strain rates. In particular, as specimen thickness ranged from 211 to 671 μm, we observed significant variation in both quasi-linear viscoelasticity (QLV) parameters, the relaxation time constant (τ1 = 0.19 ± 0.10 s) and steady-state residual stress ratio (G∞ = 0.28 ± 0.13). Moreover, when τ1 was decoupled and fixed, we observed that G∞ positively correlated with skin thickness. Second, as steady-state stretch was increased (λ∞ from 0.22 to 0.81), we observed significant variation in both QLV parameters (τ1 = 0.26 ± 0.14 s, G∞ = 0.47 ± 0.17), and when τ1 was fixed, G∞ positively correlated with stretch level. Third, as strain rate was increased from 0.06 to 22.88 s-1, the median time constant τ1 varied from 1.90 to 0.31 s, and thereby negatively correlated with strain rate. These findings indicate that the natural range of specimen thickness, as well as experimental controls of compression level and rate, significantly influence measurements of skin viscoelasticity.

  7. The chemical and mechanical behaviors of polymer / reactive metal systems under high strain rates

    NASA Astrophysics Data System (ADS)

    Shen, Yubin

    As one category of energetic materials, impact-initiated reactive materials are able to release a high amount of stored chemical energy under high strain rate impact loading, and are used extensively in civil and military applications. In general, polymers are introduced as binder materials to trap the reactive metal powders inside, and also act as an oxidizing agent for the metal ingredient. Since critical attention has been paid on the metal / metal reaction, only a few types of polymer / reactive metal interactions have been studied in the literature. With the higher requirement of materials resistant to different thermal and mechanical environments, the understanding and characterization of polymer / reactive metal interactions are in great demand. In this study, PTFE (Polytetrafluoroethylene) 7A / Ti (Titanium) composites were studied under high strain rates by utilizing the Taylor impact and SHPB tests. Taylor impact tests with different impact velocities, sample dimensions and sample configurations were conducted on the composite, equipped with a high-speed camera for tracking transient images during the sudden process. SHPB and Instron tests were carried out to obtain the stress vs. strain curves of the composite under a wide range of strain rates, the result of which were also utilized for fitting the constitutive relations of the composite based on the modified Johnson-Cook strength model. Thermal analyses by DTA tests under different flow rates accompanied with XRD identification were conducted to study the reaction mechanism between PTFE 7A and Ti when only heat was provided. Numerical simulations on Taylor impact tests and microstructural deformations were also performed to validate the constitutive model built for the composite system, and to investigate the possible reaction mechanism between two components. The results obtained from the high strain rate tests, thermal analyses and numerical simulations were combined to provide a systematic study on

  8. Compressive Viscoelasticity of Freshly Excised Mouse Skin Is Dependent on Specimen Thickness, Strain Level and Rate

    PubMed Central

    Wang, Yuxiang; Marshall, Kara L.; Baba, Yoshichika; Lumpkin, Ellen A.; Gerling, Gregory J.

    2015-01-01

    Although the skin’s mechanical properties are well characterized in tension, little work has been done in compression. Here, the viscoelastic properties of a population of mouse skin specimens (139 samples from 36 mice, aged 5 to 34 weeks) were characterized upon varying specimen thickness, as well as strain level and rate. Over the population, we observed the skin’s viscoelasticity to be quite variable, yet found systematic correlation of residual stress ratio with skin thickness and strain, and of relaxation time constants with strain rates. In particular, as specimen thickness ranged from 211 to 671 μm, we observed significant variation in both quasi-linear viscoelasticity (QLV) parameters, the relaxation time constant (τ1 = 0.19 ± 0.10 s) and steady-state residual stress ratio (G∞ = 0.28 ± 0.13). Moreover, when τ1 was decoupled and fixed, we observed that G∞ positively correlated with skin thickness. Second, as steady-state stretch was increased (λ∞ from 0.22 to 0.81), we observed significant variation in both QLV parameters (τ1 = 0.26 ± 0.14 s, G∞ = 0.47 ± 0.17), and when τ1 was fixed, G∞ positively correlated with stretch level. Third, as strain rate was increased from 0.06 to 22.88 s−1, the median time constant τ1 varied from 1.90 to 0.31 s, and thereby negatively correlated with strain rate. These findings indicate that the natural range of specimen thickness, as well as experimental controls of compression level and rate, significantly influence measurements of skin viscoelasticity. PMID:25803703

  9. Transform method for laser speckle strain-rate measurements in biological tissues and biomaterials

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, Sean J.

    1999-03-01

    Laser speckle strain measurements in biological tissues and some synthetic biomaterials, such as translucent dental composites and ceramics, are often complicated by the physical properties of the materials. For example, speckles generated by illuminating soft biological tissue with laser light are subject to rapid decorrelation due to the Brownian movement of water and scattering particles in the tissues and to cellular motions. In addition, the penetration of the laser beam into the tissue or translucent biomaterial results in multiple scattering and a complete depolarization of the speckle field. This may complicate the evaluation of the strain field when a force is applied to the material because the speckle pattern shift is providing information from the surface of the material as well as from the bulk sample, where the strains may or may not be the same as on the surface. This paper presents a variation of a speckle processing scheme originally called the `Transform Method' for evaluating both surface and bulk strain rates and total strains in biological tissues and translucent biomaterials. The method is not a correlation-based technique, but instead relies upon 2D frequency transforms of time series of 1D speckle pattern records stacked into 2D arrays. The method is insensitive to speckle field depolarization and, compared to correlation-based techniques, is relatively insensitive to speckle decorrelation. Strain rates and total in-plane strains were measured in both hard (cortical bone) and soft (artery segments) biological tissues and in translucent biomaterials (dental ceramics). Potential applications to medical diagnostics and biomaterials science are also discussed.

  10. Flow and failure of an aluminium alloy from low to high temperature and strain rate

    NASA Astrophysics Data System (ADS)

    Sancho, Rafael; Cendón, David; Gálvez, Francisco

    2015-09-01

    The mechanical behaviour of an aluminium alloy is presented in this paper. The study has been carried out to analyse the flow and failure of the aluminium alloy 7075-T73. An experimental study has been planned performing tests of un-notched and notched tensile specimens at low strain rates using a servo-hydraulic machine. High strain rate tests have been carried out using the same geometry in a Hopkinson Split Tensile Bar. The dynamic experiments at low temperature were performed using a cryogenic chamber, and the high temperature ones with a furnace, both incorporated to the Hopkinson bar. Testing temperatures ranged from - 50 ∘C to 100 ∘C and the strain rates from 10-4 s-1 to 600 s-1. The material behaviour was modelled using the Modified Johnson-Cook model and simulated using LS-DYNA. The results show that the Voce type of strain hardening is the most accurate for this material, while the traditional Johnson-Cook is not enough accurate to reproduce the necking of un-notched specimens. The failure criterion was obtained by means of the numerical simulations using the analysis of the stress triaxiality versus the strain to failure. The diameters at the failure time were measured using the images taken with an image camera, and the strain to failure was computed for un-notched and notched specimens. The numerical simulations show that the analysis of the evolution of the stress triaxiality is crucial to achieve accurate results. A material model using the Modified Johnson-Cook for flow and failure is proposed.

  11. Strain effects on oxygen transport in tetragonal zirconium dioxide

    SciTech Connect

    Xian-Ming Bai; Yongfeng Zhang; Michael R. Tonks

    2013-11-01

    Temperature accelerated dynamics and molecular dynamics simulations are used to investigate the strain effects on oxygen interstitial and vacancy migration in tetragonal zirconium dioxide. At zero external strain, the anisotropic migration mechanisms of oxygen defects are characterized. At non-zero strains, both the crystal structure and defect migration barriers are modified by strain. Under compressive strains, the defect migration barrier increases with the increasing strain for both interstitials and vacancies. The crystal structure transforms from a tetragonal to a nearly cubic fluorite structure. Accordingly, the defect migration becomes nearly isotropic. Under dilative strains, the migration barrier first decreases then increases with increasing strain for both types of defects. The tetragonal phase transforms to a lower symmetry structure that is close to the orthorhombic phase. In turn, the defect migration becomes highly anisotropic. Under both compressive and dilative strains, interstitials respond to strain more strongly than vacancies. At small dilative strains, an oxygen interstitial has comparable diffusivity to a vacancy, suggesting that both types of defects can contribute to oxygen transport, if they are present. Although currently no previous result is available to validate oxygen interstitial diffusion behavior, the trend of strain effects on oxygen vacancy diffusion is in good agreement with available experimental and theoretical studies in the literature.

  12. Planar Strain-Rate-Free Diffusion Flames: Initiation, Properties, and Extinction

    NASA Technical Reports Server (NTRS)

    Fendell, Francis; Gokoglu, Suleyman; Rungaldier, Harald; Schultz, Donald

    1999-01-01

    An effectively strain-rate-free diffusion flame constitutes the most vigorous laminar combustion of initially unmixed reactive gases. Such a diffusion flame is characterized by a relatively long residence time and by a relatively large characteristic length scale. If such a flame were also planar, providing high symmetry, it would be particularly suitable for experimental and theoretical investigations of key combustion phenomena, such as multicomponent diffusion, chemical kinetics, and soot inception, growth, and oxidation. Unfortunately, a planar strain-rate-free diffusion flame is highly disrupted in earth-gravity (e.g., in a counterflow-diffusion-flame apparatus) because of the very rapid onset (approx. 100 ms) of gravity-induced instability. Accordingly, a specially dedicated apparatus was designed, fabricated, and initially checked out for the examination of a planar strain-rate-free diffusion flame in microgravity. Such a diffusion flame may be formed within a hollowed-out squat container (initially configured as 25 cm x 25 cm x 9 cm), with isothermal, noncatalytic, impervious walls. At test initiation, a thin metallic sheet (approx. 1 mm in thickness) that separates the internal volume into two equal portions, each of dimensions 25 cm x 25 cm x 4.5 cm, is withdrawn, by uniform translation (approx. 50 cm/s) in its own plane, through a tightly fitting slit in one side wall. Thereupon, diluted fuel vapor (initially confined to one half-volume of the container) gains access to diluted oxygen (initially with the same pressure, density, and temperature as the fuel, but initially confined to the other half-volume). After a brief delay (approx. 10 ms), to permit limited but sufficient-for-flammability diffusional interpenetration of fuel vapor and oxidizer, burning is initiated by discharge of a line igniter, located along that side wall from which the trailing edge of the separator withdraws. The ignition spawns a triple-flame propagation across the 25 cm x 25 cm

  13. The response of polymethyl methacrylate (PMMA) subjected to large strains, high strain rates, high pressures, a range in temperatures, and variations in the intermediate principal stress

    NASA Astrophysics Data System (ADS)

    Holmquist, T. J.; Bradley, J.; Dwivedi, A.; Casem, D.

    2016-05-01

    This article presents the response of polymethyl methacrylate (PMMA) subjected to large strains, high strain rates, high pressures, a range in temperatures, and variations in the intermediate principal stress. Laboratory data from the literature, and new test data provided here, are used in the evaluation. The new data include uniaxial stress compression tests (at various strain rates and temperatures) and uniaxial stress tension tests (at low strain rates and ambient temperatures). The compression tests include experiments at ˙ɛ = 13,000 s-1, significantly extending the range of known strain rate data. The observed behavior of PMMA includes the following: it is brittle in compression at high rates, and brittle in tension at all rates; strength is dependent on the pressure, strain, strain rate, temperature, and the intermediate principal stress; the shear modulus increases as the pressure increases; and it is highly compressible. Also presented are novel, high velocity impact tests (using high-speed imaging) that provide insight into the initiation and evolution of damage. Lastly, computational constitutive models for pressure, strength, and failure are presented that provide responses that are in good agreement with the laboratory data. The models are used to compute several ballistic impact events for which experimental data are available.

  14. Effect of low dose rate radiation on cell growth kinetics.

    PubMed Central

    Gregg, E C; Yau, T M; Kim, S C

    1979-01-01

    Experimental determinations were made of cell number as a function of time for two strains of L5178Y mammalian cells maintained continuously in various environments of radiation. One strain possessed a shoulder in its dose response curve whereas the other did not. Neither strain showed any significant difference in growth rate for interdivision doses on the order of the median lethal dose or less delivered continuously at a low dose rate or pulsed every 4 h at a high instantaneous dose rate. It was also shown that large numbers of dead cells have little effect on growth rate and that these dead cells last as discrete entities for many days. A simple theory of growth rate in the presence of radiation is presented, and the agreement with the observations implies that there is no effect of any sublethal low dose rate radiation received in one generation on the growth rate or radiation sensitivity of the succeeding generation. Further analysis of the data also showed that for the no-shoulder cells at 37 degrees C, tritiated water had a relative biological effect close to unity for cell sterilization. PMID:262446

  15. Convergence of strain energy release rate components for edge-delaminated composite laminates

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Crews, J. H., Jr.; Aminpour, M. A.

    1988-01-01

    Strain energy release rates for edge delaminated composite laminates were obtained using quasi 3 dimensional finite element analysis. The problem of edge delamination at the -35/90 interfaces of an 8-ply composite laminate subjected to uniform axial strain was studied. The individual components of the strain energy release rates did not show convergence as the delamination tip elements were made smaller. In contrast, the total strain energy release rate converged and remained unchanged as the delamination tip elements were made smaller and agreed with that calculated using a classical laminated plate theory. The studies of the near field solutions for a delamination at an interface between two dissimilar isotropic or orthotropic plates showed that the imaginary part of the singularity is the cause of the nonconvergent behavior of the individual components. To evaluate the accuracy of the results, an 8-ply laminate with the delamination modeled in a thin resin layer, that exists between the -35 and 90 plies, was analyzed. Because the delamination exists in a homogeneous isotropic material, the oscillatory component of the singularity vanishes.

  16. Convergence of strain energy release rate components for edge-delaminated composite laminates

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Crews, J. H., Jr.; Aminpour, M. A.

    1987-01-01

    Strain energy release rates for edge delaminated composite laminates were obtained using quasi 3 dimensional finite element analysis. The problem of edge delamination at the -35/90 interfaces of an 8-ply composite laminate subjected to uniform axial strain was studied. The individual components of the strain energy release rates did not show convergence as the delamination tip elements were made smaller. In contrast, the total strain energy release rate converged and remained unchanged as the delamination tip elements were made smaller and agreed with that calculated using a classical laminated plate theory. The studies of the near field solutions for a delamination at an interface between two dissimilar isotropic or orthotropic plates showed that the imaginary part of the singularity is the cause of the nonconvergent behavior of the individual components. To evaluate the accuracy of the results, an 8-ply laminate with the delamination modeled in a thin resin layer, that exists between the -35 and 90 plies, was analyzed. Because the delamination exists in a homogeneous isotropic material, the oscillatory component of the singularity vanishes.

  17. Intermediate Strain-Rate Loading Experiments - Technique and Applications to Ceramics

    SciTech Connect

    Chhabildas, L.C.; Reinhart, W.D.

    1999-08-16

    A new test methodology is described which allows access to loading rates that lie between split Hopkinson bar and shock-loading techniques. Gas gun experiments combined with velocity interferometry techniques have been used to experimentally determine the intermediate strain-rate loading behavior of Coors AD995 alumina and Cercom silicon-carbide rods. Graded-density materials have been used as impactors; thereby eliminating the tension states generated by the radial stress components during the loading phase. Results of these experiments demonstrate that the time-dependent stress pulse generated during impact allows an efficient transition from the initial uniaxial strain loading to a uniaxial stress state as the stress pulse propagates through the rod. This allows access to intermediate loading rates over 5 x 10{sup 3}/s to a few times 10{sup 4}/s.

  18. High Strain Rate Deformation Modeling of a Polymer Matrix Composite. Part 2; Composite Micromechanical Model

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Stouffer, Donald C.

    1998-01-01

    Recently applications have exposed polymer matrix composite materials to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under these extreme conditions. In this second paper of a two part report, a three-dimensional composite micromechanical model is described which allows for the analysis of the rate dependent, nonlinear deformation response of a polymer matrix composite. Strain rate dependent inelastic constitutive equations utilized to model the deformation response of a polymer are implemented within the micromechanics method. The deformation response of two representative laminated carbon fiber reinforced composite materials with varying fiber orientation has been predicted using the described technique. The predicted results compare favorably to both experimental values and the response predicted by the Generalized Method of Cells, a well-established micromechanics analysis method.

  19. High Strain Rate Deformation Modeling of a Polymer Matrix Composite. Part 1; Matrix Constitutive Equations

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Stouffer, Donald C.

    1998-01-01

    Recently applications have exposed polymer matrix composite materials to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under these extreme conditions. In this first paper of a two part report, background information is presented, along with the constitutive equations which will be used to model the rate dependent nonlinear deformation response of the polymer matrix. Strain rate dependent inelastic constitutive models which were originally developed to model the viscoplastic deformation of metals have been adapted to model the nonlinear viscoelastic deformation of polymers. The modified equations were correlated by analyzing the tensile/ compressive response of both 977-2 toughened epoxy matrix and PEEK thermoplastic matrix over a variety of strain rates. For the cases examined, the modified constitutive equations appear to do an adequate job of modeling the polymer deformation response. A second follow-up paper will describe the implementation of the polymer deformation model into a composite micromechanical model, to allow for the modeling of the nonlinear, rate dependent deformation response of polymer matrix composites.

  20. The role of reactant unmixedness, strain rate, and length scale on premixed combustor performance

    SciTech Connect

    Samuelsen, S.; LaRue, J.; Vilayanur, S.

    1995-10-01

    Lean premixed combustion provides a means to reduce pollutant formation and increase combustion efficiency. However, fuel-air mixing is rarely uniform in space and time. This nonuniformity in concentration will lead to relative increases in pollutant formation and decreases in combustion efficiency. The nonuniformity of the concentration at the exit of the premixer has been defined by Lyons (1981) as the {open_quotes}unmixedness.{close_quotes} Although turbulence properties such as length scales and strain rate are known to effect unmixedness, the exact relationship is unknown. Evaluating this relationship and the effect of unmixedness in premixed combustion on pollutant formation and combustion efficiency are an important part of the overall goal of US Department of Energy`s Advanced Turbine Systems (ATS) program and are among the goals of the program described herein. The information obtained from ATS is intended to help to develop and commercialize gas turbines which have (1) a wide range of operation/stability, (2) a minimal amount of pollutant formation, and (3) high combustion efficiency. Specifically, with regard to pollutants, the goals are to reduce the NO{sub x} emissions by at least 10%, obtain less than 20 PPM of both CO and UHC, and increase the combustion efficiency by 5%.

  1. Polymer-Ion Interaction Weakens the Strain-Rate Dependence of Extension-Induced Crystallization for Poly(ethylene oxide).

    PubMed

    Hu, Tingting; Tian, Nan; Ali, Sarmad; Wang, Zhen; Chang, Jiarui; Huang, Ningdong; Li, Liangbin

    2016-03-01

    The crystallization of poly(ethylene oxide) (PEO)-sodium iodine (NaI) composites is investigated by differential scanning calorimetry (DSC), extensional rheology, and in situ small-angle X-ray scattering (SAXS) with the aim of demonstrating versatile roles played by polymer-ion interactions. In the isothermal quiescent crystallization process, a decrease in the crystal growth rate is observed for PEO-NaI and is attributed to slow chain movement caused by the coordination between cations and polymer. In situ SAXS on extensional flow-induced crystallization (FIC) exhibits enhanced kinetics and orientation for both PEO and PEO-NaI with increasing strain rate. However, an overall weaker strain-rate dependence of FIC is observed for PEO-NaI, which can be interpreted as a synergistic consequence of promoted nucleation under flow and impeded crystal growth by polymer-ion interaction. A possible microscopic mechanism is proposed to account for the experimental observation based on the formation of transient cross-linking points in PEO-NaI and their influence on the entanglement network of polymer under various flow fields. The disclosed strain-rate dependence and various ion effects on the behavior of PEO-salt composites contribute to a comprehensive understanding of polymer-ion solid polyelectrolytes. PMID:26822166

  2. Doppler-derived myocardial systolic strain rate is a strong index of left ventricular contractility

    NASA Technical Reports Server (NTRS)

    Greenberg, Neil L.; Firstenberg, Michael S.; Castro, Peter L.; Main, Michael; Travaglini, Agnese; Odabashian, Jill A.; Drinko, Jeanne K.; Rodriguez, L. Leonardo; Thomas, James D.; Garcia, Mario J.

    2002-01-01

    BACKGROUND: Myocardial fiber strain is directly related to left ventricular (LV) contractility. Strain rate can be estimated as the spatial derivative of velocities (dV/ds) obtained by tissue Doppler echocardiography (TDE). The purposes of the study were (1) to determine whether TDE-derived strain rate may be used as a noninvasive, quantitative index of contractility and (2) to compare the relative accuracy of systolic strain rate against TDE velocities alone. METHODS AND RESULTS: TDE color M-mode images of the interventricular septum were recorded from the apical 4-chamber view in 7 closed-chest anesthetized mongrel dogs during 5 different inotropic stages. Simultaneous LV volume and pressure were obtained with a combined conductance-high-fidelity pressure catheter. Peak elastance (Emax) was determined as the slope of end-systolic pressure-volume relationships during caval occlusion and was used as the gold standard of LV contractility. Peak systolic TDE myocardial velocities (Sm) and peak (epsilon'(p)) and mean (epsilon'(m)) strain rates obtained at the basal septum were compared against Emax by linear regression. Emax as well as TDE systolic indices increased during inotropic stimulation with dobutamine and decreased with the infusion of esmolol. A stronger association was found between Emax and epsilon'(p) (r=0.94, P<0.01, y=0.29x+0.46) and epsilon'(m) (r=0.88, P<0.01) than for Sm (r=0.75, P<0.01). CONCLUSIONS: TDE-derived epsilon'(p) and epsilon'(m) are strong noninvasive indices of LV contractility. These indices appear to be more reliable than S(m), perhaps by eliminating translational artifact.

  3. Morphology and mycelial growth rate of Pleurotus spp. strains from the Mexican mixtec region.

    PubMed

    Guadarrama-Mendoza, P C; del Toro, G Valencia; Ramírez-Carrillo, R; Robles-Martínez, F; Yáñez-Fernández, J; Garín-Aguilar, M E; Hernández, C G; Bravo-Villa, G

    2014-01-01

    Two native Pleurotus spp. strains (white LB-050 and pale pink LB-051) were isolated from rotten tree trunks of cazahuate (Ipomoea murucoides) from the Mexican Mixtec Region. Both strains were chemically dedikaryotized to obtain their symmetrical monokaryotic components (neohaplonts). This was achieved employing homogenization time periods from 60 to 65 s, and 3 day incubation at 28 °C in a peptone-glucose solution (PGS). Pairing of compatible neohaplonts resulted in 56 hybrid strains which were classified into the four following hybrid types: (R(1-n)xB(1-n), R(1-n)xB(2-1), R(2-n)xB(1-n) and R(2-n)xB(2-1)). The mycelial growth of Pleurotus spp. monokaryotic and dikaryotic strains showed differences in texture (cottony or floccose), growth (scarce, regular or abundant), density (high, regular or low), and pigmentation (off-white, white or pale pink). To determine the rate and the amount of mycelium growth in malt extract agar at 28 °C, the diameter of the colony was measured every 24 h until the Petri dish was completely colonized. A linear model had the best fit to the mycelial growth kinetics. A direct relationship between mycelial morphology and growth rate was observed. Cottony mycelium presented significantly higher growth rates (p < 0.01) in comparison with floccose mycelium. Thus, mycelial morphology can be used as criterion to select which pairs must be used for optimizing compatible-mating studies. Hybrids resulting from cottony neohaplonts maintained the characteristically high growth rates of their parental strains with the hybrid R(1-n)xB(1-n) being faster than the latter. PMID:25477920

  4. Morphology and mycelial growth rate of Pleurotus spp. strains from the Mexican mixtec region.

    PubMed

    Guadarrama-Mendoza, P C; del Toro, G Valencia; Ramírez-Carrillo, R; Robles-Martínez, F; Yáñez-Fernández, J; Garín-Aguilar, M E; Hernández, C G; Bravo-Villa, G

    2014-01-01

    Two native Pleurotus spp. strains (white LB-050 and pale pink LB-051) were isolated from rotten tree trunks of cazahuate (Ipomoea murucoides) from the Mexican Mixtec Region. Both strains were chemically dedikaryotized to obtain their symmetrical monokaryotic components (neohaplonts). This was achieved employing homogenization time periods from 60 to 65 s, and 3 day incubation at 28 °C in a peptone-glucose solution (PGS). Pairing of compatible neohaplonts resulted in 56 hybrid strains which were classified into the four following hybrid types: (R(1-n)xB(1-n), R(1-n)xB(2-1), R(2-n)xB(1-n) and R(2-n)xB(2-1)). The mycelial growth of Pleurotus spp. monokaryotic and dikaryotic strains showed differences in texture (cottony or floccose), growth (scarce, regular or abundant), density (high, regular or low), and pigmentation (off-white, white or pale pink). To determine the rate and the amount of mycelium growth in malt extract agar at 28 °C, the diameter of the colony was measured every 24 h until the Petri dish was completely colonized. A linear model had the best fit to the mycelial growth kinetics. A direct relationship between mycelial morphology and growth rate was observed. Cottony mycelium presented significantly higher growth rates (p < 0.01) in comparison with floccose mycelium. Thus, mycelial morphology can be used as criterion to select which pairs must be used for optimizing compatible-mating studies. Hybrids resulting from cottony neohaplonts maintained the characteristically high growth rates of their parental strains with the hybrid R(1-n)xB(1-n) being faster than the latter.

  5. Morphology and mycelial growth rate of Pleurotus spp. strains from the Mexican mixtec region

    PubMed Central

    Guadarrama-Mendoza, P.C.; del Toro, G. Valencia; Ramírez-Carrillo, R.; Robles-Martínez, F.; Yáñez-Fernández, J.; Garín-Aguilar, M.E.; Hernández, C.G.; Bravo-Villa, G.

    2014-01-01

    Two native Pleurotus spp. strains (white LB-050 and pale pink LB-051) were isolated from rotten tree trunks of cazahuate (Ipomoea murucoides) from the Mexican Mixtec Region. Both strains were chemically dedikaryotized to obtain their symmetrical monokaryotic components (neohaplonts). This was achieved employing homogenization time periods from 60 to 65 s, and 3 day incubation at 28 °C in a peptone-glucose solution (PGS). Pairing of compatible neohaplonts resulted in 56 hybrid strains which were classified into the four following hybrid types: (R1-nxB1-n, R1-nxB2-1, R2-nxB1-n and R2-nxB2-1). The mycelial growth of Pleurotus spp. monokaryotic and dikaryotic strains showed differences in texture (cottony or floccose), growth (scarce, regular or abundant), density (high, regular or low), and pigmentation (off-white, white or pale pink). To determine the rate and the amount of mycelium growth in malt extract agar at 28 °C, the diameter of the colony was measured every 24 h until the Petri dish was completely colonized. A linear model had the best fit to the mycelial growth kinetics. A direct relationship between mycelial morphology and growth rate was observed. Cottony mycelium presented significantly higher growth rates (p < 0.01) in comparison with floccose mycelium. Thus, mycelial morphology can be used as criterion to select which pairs must be used for optimizing compatible-mating studies. Hybrids resulting from cottony neohaplonts maintained the characteristically high growth rates of their parental strains with the hybrid R1-nxB1-n being faster than the latter. PMID:25477920

  6. Strain-rate Dependence of Power-law Creep and Folding of Rocks

    NASA Astrophysics Data System (ADS)

    Ord, A.; Hobbs, B. E.

    2011-12-01

    Kocks (1987) proposed how the kinetics of deformation associated with different stress levels results in different shear stress-shear strain rate behaviours, with a cross-over or threshold from thermally activated dislocation motion at low stresses to viscous glide at some critical shear stress. Cordier (pers. comm.; Carrez et al., 2010) clarified this transition at least for MgO through atomistic, single dislocation and Dislocation Dynamics calculations. These studies indicate that the power-law relations observed experimentally for deforming rocks may be different for geological strain-rates, in that rate laws may become relatively strain-rate insensitive at low strain-rates. This transition from power law behaviour with relatively small values of the stress exponent, N, (N = 1 to 5) to large values of N (N = 5 to 20) has important implications for the development of localised behaviour during deformation as has been demonstrated at the other end of the spectrum for high stresses by Schmalholz and Fletcher (2011). Since localisation of fold systems arises from softening of the tangential viscosity, large values of N mean that little softening occurs with changes in strain rate, and sinusoidal folds are expected. There is therefore a critical range of N-values where localised, natural looking, folds develop. We explore the implications for folding of linear viscous single layers embedded in power-law viscous materials with N that varies with the stress level. The strain-rate dependence of the power law parameters results in strongly localised, aperiodic folding as opposed to the fold styles that arise from the linear Biot theory of folding. Also developed are axial plane shear fabrics. These structures resemble natural ones more than those that arise from simple Newtonian viscous or power-law behaviour with constant N. The results show that new studies of folded rocks and associated axial plane structures in the field may give important information on the

  7. The effect of muscle fatigue on in vivo tibial strains.

    PubMed

    Milgrom, Charles; Radeva-Petrova, Denitsa R; Finestone, Aharon; Nyska, Meir; Mendelson, Stephen; Benjuya, Nisim; Simkin, Ariel; Burr, David

    2007-01-01

    Stress fracture is a common musculoskeletal problem affecting athletes and soldiers. Repetitive high bone strains and strain rates are considered to be its etiology. The strain level necessary to cause fatigue failure of bone ex vivo is higher than the strains recorded in humans during vigorous physical activity. We hypothesized that during fatiguing exercises, bone strains may increase and reach levels exceeding those measured in the non-fatigued state. To test this hypothesis, we measured in vivo tibial strains, the maximum gastrocnemius isokinetic torque and ground reaction forces in four subjects before and after two fatiguing levels of exercise: a 2km run and a 30km desert march. Strains were measured using strain-gauged staples inserted percutaneously in the medial aspect of their mid-tibial diaphysis. There was a decrease in the peak gastrocnemius isokinetic torque of all four subjects' post-march as compared to pre-run (p=0.0001), indicating the presence of gastrocnemius muscle fatigue. Tension strains increased 26% post-run (p=0.002, 95 % confidence interval (CI) and 29% post-march (p=0.0002, 95% CI) as compared to the pre-run phase. Tension strain rates increased 13% post-run (p=0.001, 95% CI) and 11% post-march (p=0.009, 95% CI) and the compression strain rates increased 9% post-run (p=0.0004, 95% CI) and 17% post-march (p=0.0001, 95% CI). The fatigue state increases bone strains well above those recorded in rested individuals and may be a major factor in the stress fracture etiology.

  8. Mechanical characterization of brain tissue in compression at dynamic strain rates.

    PubMed

    Rashid, Badar; Destrade, Michel; Gilchrist, Michael D

    2012-06-01

    Traumatic brain injury (TBI) occurs when local mechanical load exceeds certain tolerance levels for brain tissue. Extensive research has been done previously for brain matter experiencing compression at quasistatic loading; however, limited data is available to model TBI under dynamic impact conditions. In this research, an experimental setup was developed to perform unconfined compression tests and stress relaxation tests at strain rates ≤90/s. The brain tissue showed a stiffer response with increasing strain rates, showing that hyperelastic models are not adequate. Specifically, the compressive nominal stress at 30% strain was 8.83 ± 1.94, 12.8 ± 3.10 and 16.0 ± 1.41 kPa (mean ± SD) at strain rates of 30, 60 and 90/s, respectively. Relaxation tests were also conducted at 10%-50% strain with the average rise time of 10 ms, which can be used to derive time dependent parameters. Numerical simulations were performed using one-term Ogden model with initial shear modulus μ(o)=6.06±1.44, 9.44 ± 2.427 and 12.64 ± 1.227 kPa (mean ± SD) at strain rates of 30, 60 and 90/s, respectively. A separate set of bonded and lubricated tests were also performed under the same test conditions to estimate the friction coefficient μ, by adopting combined experimental-computational approach. The values of μ were 0.1 ± 0.03 and 0.15 ± 0.07 (mean ± SD) at 30 and 90/s strain rates, respectively, indicating that pure slip conditions cannot be achieved in unconfined compression tests even under fully lubricated test conditions. The material parameters obtained in this study will help to develop biofidelic human brain finite element models, which can subsequently be used to predict brain injuries under impact conditions. PMID:22520416

  9. Slow Strain Rate Tensile Testing to Assess the Ability of Superalloys to Resist Environment-Assisted Intergranular Cracking

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Telesman, Jack; Banik, Anthony; McDevitt, Erin

    2014-01-01

    Intergranular fatigue crack initiation and growth due to environmental degradation, especially at notched features, can often limit the fatigue life of disk superalloys at high temperatures. For clear comparisons, the effects of alloy composition on cracking in air needs to be understood and compared separately from variables associated with notches and cracks such as effective stress concentration, plastic flow, stress relaxation, and stress redistribution. The objective of this study was to attempt using simple tensile tests of specimens with uniform gage sections to compare the effects of varied alloy composition on environment-assisted cracking of several powder metal and cast and wrought superalloys including ME3, LSHR, Udimet 720, ATI 718Plus alloy, Haynes 282, and Inconel 740. Slow and fast strain-rate tensile tests were found to be a useful tool to compare propensities for intergranular surface crack initiation and growth. The effects of composition and heat treatment on tensile fracture strain and associated failure modes were compared. Environment interactions were determined to often limit ductility, by promoting intergranular surface cracking. The response of various superalloys and heat treatments to slow strain rate tensile testing varied substantially, showing that composition and microstructure can significantly influence environmental resistance to cracking.

  10. Using Google Earth to Explore Strain Rate Models of Southern California

    NASA Astrophysics Data System (ADS)

    Richard, G. A.; Bell, E. A.; Holt, W. E.

    2007-12-01

    A series of strain rate models for the Transverse Ranges of southern California were developed based on Quaternary fault slip data and geodetic data from high precision GPS stations in southern California. Pacific-North America velocity boundary conditions are applied for all models. Topography changes are calculated using the model dilatation rates, which predict crustal thickness changes under the assumption of Airy isostasy and a specified rate of crustal volume loss through erosion. The models were designed to produce graphical and numerical output representing the configuration of the region from 3 million years ago to 3 million years into the future at intervals of 50 thousand years. Using a North American reference frame, graphical output for the topography and faults and numerical output for locations of faults and points on the crust marked by the locations on cities were used to create data in KML format that can be used in Google Earth to represent time intervals of 50 thousand years. As markers familiar to students, the cities provide a geographic context that can be used to quantify crustal movement, using the Google Earth ruler tool. By comparing distances that markers for selected cities have moved in various parts of the region, students discover that the greatest amount of crustal deformation has occurred in the vicinity of the boundary between the North American and Pacific plates. Students can also identify areas of compression or extension by finding pairs of city markers that have converged or diverged, respectively, over time. The Google Earth layers also reveal that faults that are not parallel to the plate boundary have tended to rotate clockwise due to the right lateral motion along the plate boundary zone. KML TimeSpan markup was added to two versions of the model, enabling the layers to be displayed in an automatic sequenced loop for a movie effect. The data is also available as QuickTime (.mov) and Graphics Interchange Format (.gif

  11. Room temperature strain rate sensitivity in precursor derived HfO{sub 2}/Si-C-N(O) ceramic nanocomposites

    SciTech Connect

    Sujith, Ravindran; Kumar, Ravi

    2014-01-15

    Investigation on the room temperature strain rate sensitivity using depth sensing nanoindentation is carried out on precursor derived HfO{sub 2}/Si-C-N(O) ceramic nanocomposite sintered using pulsed electric current sintering. Using constant load method the strain rate sensitivity values are estimated. Lower strain rate sensitivity of ∼ 3.7 × 10{sup −3} is observed and the limited strain rate sensitivity of these ceramic nanocomposites is explained in terms of cluster model. It is concluded that presence of amorphous Si-C-N(O) clusters are responsible for the limited flowability in these ceramics.

  12. Beyond linear elasticity: jammed solids at finite shear strain and rate.

    PubMed

    Boschan, Julia; Vågberg, Daniel; Somfai, Ellák; Tighe, Brian P

    2016-06-28

    The shear response of soft solids can be modeled with linear elasticity, provided the forcing is slow and weak. Both of these approximations must break down when the material loses rigidity, such as in foams and emulsions at their (un)jamming point - suggesting that the window of linear elastic response near jamming is exceedingly narrow. Yet precisely when and how this breakdown occurs remains unclear. To answer these questions, we perform computer simulations of stress relaxation and shear start-up tests in athermal soft sphere packings, the canonical model for jamming. By systematically varying the strain amplitude, strain rate, distance to jamming, and system size, we identify characteristic strain and time scales that quantify how and when the window of linear elasticity closes, and relate these scales to changes in the microscopic contact network. PMID:27212139

  13. The temperature and strain rate dependence of the flow stress of single crystal NiAl deformed along <110>

    SciTech Connect

    Maloy, S.A.; Gray, G.T. III

    1995-12-31

    Single crystal NiAl and Ni-49.75Al-0.25Fe have been deformed along <110> at temperatures of 77, 298 and 773K and strain rates of 0.001/s, and 2000/s. The flow stress of <110> NiAl is rate and temperature sensitive. The 0.25 at.% Fe addition resulted in a small increase in flow stress at strain rates of 0.001 and 0.1/s at 298 and 77K. A significant decrease in the work hardening rate is observed after deformation at 77K and a strain rate of 2000/s. Coarse [110] slip traces are observed after deformation at a strain rate of 2000/s at 77K, while no slip traces were observed after deformation under all other conditions. TEM observations reveal distinct [110] slip bands after deformation at 77K and a strain rate of 2000/s.

  14. Shear avalanches in metallic glasses under nanoindentation: Deformation units and rate dependent strain burst cut-off

    SciTech Connect

    Bian, X. L.; Wang, G.; Gao, Y. L.; Zhai, Q. J.; Chan, K. C.; Ren, J. L.

    2013-09-02

    Indented metallic glasses at the nanoscale deform via strain bursts. Conventional continuum descriptions are not appropriate for such highly stochastic, intermittent deformations. In this study, after a statistical analysis of strain bursts in five metallic glasses, the dependence of the cut-off of the strain burst size on deformation units and loading rate is established. For soft metallic glasses with smaller deformation units, cut-off of the strain burst size truncates the scale-free behavior at larger strain burst sizes. For hard metallic glasses, scale-free behavior occurs in a wide range of strain burst sizes.

  15. An Evaluation of Constitutive Laws and their Ability to Predict Flow Stress over Large Variations in Temperature, Strain, and Strain Rate Characteristic of Friction Stir Welding

    NASA Astrophysics Data System (ADS)

    Kuykendall, Katherine

    2011-07-01

    Constitutive laws commonly used to model friction stir welding have been evaluated, both qualitatively and quantitatively, and a new application of a constitutive law which can be extended to materials commonly used in FSW is presented. Existing constitutive laws have been classified as path-dependent or path-independent. Path-independent laws have been further classified according to the physical phenomena they capture: strain hardening, strain rate hardening, and/or thermal softening. Path-dependent laws can track gradients in temperature and strain rate characteristic to friction stir welding; however, path-independent laws cannot. None of the path-independent constitutive laws evaluated has been validated over the full range of strain, strain rate, and temperature in friction stir welding. Holding all parameters other than constitutive law constant in a friction stir weld model resulted in temperature differences of up to 21%. Varying locations for maximum temperature difference indicate that the constitutive laws resulted in different temperature profiles. The Sheppard and Wright law is capable of capturing saturation but incapable of capturing strain hardening with errors as large as 57% near yield. The Johnson-Cook law is capable of capturing strain hardening; however, its inability to capture saturation causes over-predictions of stress at large strains with errors as large as 37% near saturation. The Kocks and Mecking model is capable of capturing strain hardening and saturation with errors less than 5% over the entire range of plastic strain. The Sheppard and Wright and Johnson-Cook laws are incapable of capturing transients characteristic of material behavior under interrupted temperature or strain rate. The use of a state variable in the Kocks and Mecking law allows it to predict such transients. Constants for the Kocks and Mecking model for AA 5083, AA 3004, and Inconel 600 were determined from Atlas of Formability data. Constants for AA 5083 and AA

  16. Plastic flow and failure in HY100, HY130 and AF1410 alloy steels under high strain rate and impact loading conditions

    NASA Astrophysics Data System (ADS)

    Rajendran, A. M.; Last, H. R.; Garrett, R. K., Jr.

    1995-03-01

    This report presents the results from impact experiments, constitutive/failure modeling, and metallurgical failure analyses for three steels: HY100, HY130, and AF1410. The main objectives of this effort are: (1) to obtain fundamental engineering data in terms of stress-strain curves up to failure at different temperatures and strain rates, (2) to evaluate the observed differences in the macroscopic behaviors through microscopic metallurgical studies, and (3) to describe the flow and failure behaviors using already available material strength and spall models. The high strain rate and impact experiments considered are the split Hopkinson bar (SHB) and the planar plate impact tests, respectively. In addition, the baseline data include quasi-static (QS) tests at low strain rates. The QS and SHB data provide stress-strain curves at different strain rates and temperatures. The experimental data illustrate the effects of two important loading parameters (strain rate and temperature) on the flow and failure behaviors of HY100, HY130, and AF1410 steels.

  17. Numerical implementation of a crystal plasticity model with dislocation transport for high strain rate applications

    NASA Astrophysics Data System (ADS)

    Mayeur, Jason R.; Mourad, Hashem M.; Luscher, Darby J.; Hunter, Abigail; Kenamond, Mark A.

    2016-05-01

    This paper details a numerical implementation of a single crystal plasticity model with dislocation transport for high strain rate applications. Our primary motivation for developing the model is to study the influence of dislocation transport and conservation on the mesoscale response of metallic crystals under extreme thermo-mechanical loading conditions (e.g. shocks). To this end we have developed a single crystal plasticity theory (Luscher et al (2015)) that incorporates finite deformation kinematics, internal stress fields caused by the presence of geometrically necessary dislocation gradients, advection equations to model dislocation density transport and conservation, and constitutive equations appropriate for shock loading (equation of state, drag-limited dislocation velocity, etc). In the following, we outline a coupled finite element–finite volume framework for implementing the model physics, and demonstrate its capabilities in simulating the response of a [1 0 0] copper single crystal during a plate impact test. Additionally, we explore the effect of varying certain model parameters (e.g. mesh density, finite volume update scheme) on the simulation results. Our results demonstrate that the model performs as intended and establishes a baseline of understanding that can be leveraged as we extend the model to incorporate additional and/or refined physics and move toward a multi-dimensional implementation.

  18. The Interaction of Dislocations and Radiation-Induced Obstacles at High-Strain Rate

    SciTech Connect

    Young, J A; Wirth, B D; Robach, J; Robertson, I

    2003-07-14

    Improved understanding of the plastic deformation of metals during high strain rate shock loading is key to predicting their resulting material properties. This paper presents the results of molecular dynamics simulations that identify the deformation modes of aluminum over a range of applied shear stresses and examines the interaction between dislocations and irradiation induced obstacles. These simulations show that while super-sonic dislocation motion can occur during impact loading, the finite dimensions of the materials render this motion transient. Larger applied loads do not stabilize supersonic dislocations, but instead lead an alternate deformation mode, namely twinning. Finally, the atomistic mechanisms that underlie the observed changes in the mechanical properties of metals as a function of irradiation are examined. Specifically, simulations of the interactions between moving edge dislocations and nanometer-sized helium bubbles provide insight into increases of the critical shear stresses but also reveal the effect of internal gas pressure on the deformation mode. The information gained in these studies provides fundamental insight into materials behavior, as well as important inputs for multi-scale models of materials deformation.

  19. Strain rate behaviour of multi-phase and complex-phase steels for automotive applications

    NASA Astrophysics Data System (ADS)

    Cadoni, E.; Singh, N. K.; Singha, M. K.; Gupta, N. K.

    2012-08-01

    A combined study on the mechanical behaviour of multi-phase 800 high yield strength steel (MP800HY) and complex-phase 800 steel (CP800) is carried out under tensile loads in the strain rate range from 0.001s-1 to 750s-1. Quasi-static (0.001s-1) tests are performed on electromechanical machine, whereas, medium (5s-1 and 25s-1) and high strain rate (250s-1, 500s-1 and 750s-1) experiments are conducted on hydro-pneumatic machine (HPM) and modified Hopkinson bar (MHB) setup respectively. The thermal softening behaviors of the materials are investigated at quasi-static condition and the materials' m-parameters of the existing Johnson-Cook model are imposed in authors' previous work. Thereafter, the predicted flow stress by Johnson-Cook model has been compared with the experimental results.

  20. The Dynamic Tensile Behavior of Railway Wheel Steel at High Strain Rates

    NASA Astrophysics Data System (ADS)

    Jing, Lin; Han, Liangliang; Zhao, Longmao; Zhang, Ying

    2016-10-01

    The dynamic tensile tests on D1 railway wheel steel at high strain rates were conducted using a split Hopkinson tensile bar (SHTB) apparatus, compared to quasi-static tests. Three different types of specimens, which were machined from three different positions (i.e., the rim, web and hub) of a railway wheel, were prepared and examined. The rim specimens were checked to have a higher yield stress and ultimate tensile strength than those web and hub specimens under both quasi-static and dynamic loadings, and the railway wheel steel was demonstrated to be strain rate dependent in dynamic tension. The dynamic tensile fracture surfaces of all the wheel steel specimens are cup-cone-shaped morphology on a macroscopic scale and with the quasi-ductile fracture features on the microscopic scale.

  1. High Strain-Rate Response of High Purity Aluminum at Temperatures Approaching Melt

    SciTech Connect

    Grunschel, S E; Clifton, R J; Jiao, T

    2010-01-28

    High-temperature, pressure-shear plate impact experiments were conducted to investigate the rate-controlling mechanisms of the plastic response of high-purity aluminum at high strain rates (10{sup 6} s{sup -1}) and at temperatures approaching melt. Since the melting temperature of aluminum is pressure dependent, and a typical pressure-shear plate impact experiment subjects the sample to large pressures (2 GPa-7 GPa), a pressure-release type experiment was used to reduce the pressure in order to measure the shearing resistance at temperatures up to 95% of the current melting temperature. The measured shearing resistance was remarkably large (50 MPa at a shear strain of 2.5) for temperatures this near melt. Numerical simulations conducted using a version of the Nemat-Nasser/Isaacs constitutive equation, modified to model the mechanism of geometric softening, appear to capture adequately the hardening/softening behavior observed experimentally.

  2. Effect of strain on thermoelectric power of suspended graphene

    SciTech Connect

    Vaidya, R. G.; Sankeshwar, N. S. Mulimani, B. G.

    2013-12-04

    Thermoelectric power, S, of suspended graphene in the presence of strain is investigated. The electrons are considered to be scattered by in-plane and flexural phonons. The dominant contribution to S of non-strained and strained suspended graphene (SG) is found to be from the phonon drag component, S{sub g} for T < 90K. For T > 150 K contribution from diffusion thermopower becomes important. The effect of strain is found to be suppress S{sub d} and to alter its behavior, the effect being larger at higher temperatures.

  3. Short communication: Antiproliferative effect of 8 different Lactobacillus strains on K562 cells.

    PubMed

    Tuo, Yanfeng; Jiang, Shujuan; Qian, Fang; Mu, Guangqing; Liu, Peng; Guo, Yuanji; Ma, Changlu

    2015-01-01

    Some strains of Lactobacillus genus have antiproliferative activities against cancer cells. However, until now, the exact effector molecules of Lactobacillus strains with anticancer activity have not been identified. The aim of the present study was to explore which fraction of the Lactobacillus cells exerts the highest antiproliferative effect. For this purpose, the heat-killed bacterial cells, bacterial cell wall extract, and genomic DNA of 8 Lactobacillus strains were prepared to assess their antiproliferative activities against human myeloid leukemia cell lines K562. The heat-killed bacterial cells of the 8 lactobacilli strains exerted antiproliferative effect on K562 cells, and the inhibition rates exerted by the heat-killed bacterial cells of the strains G15AL, M5AL, SB31AL, SB5AL, and T3AL were significantly higher than those exerted by the cell walls and genomic DNA of the strains. The bacterial DNA of G15AL exerted higher antiproliferative effect on K562 cells. The exact effector molecules and the effect mechanism of the strains should be further explored for the application of these strains as probiotic strains or bioactive probiotic molecules.

  4. Biologically inspired crack delocalization in a high strain-rate environment.

    PubMed

    Knipprath, Christian; Bond, Ian P; Trask, Richard S

    2012-04-01

    Biological materials possess unique and desirable energy-absorbing mechanisms and structural characteristics worthy of consideration by engineers. For example, high levels of energy dissipation at low strain rates via triggering of crack delocalization combined with interfacial hardening by platelet interlocking are observed in brittle materials such as nacre, the iridescent material in seashells. Such behaviours find no analogy in current engineering materials. The potential to mimic such toughening mechanisms on different length scales now exists, but the question concerning their suitability under dynamic loading conditions and whether these mechanisms retain their energy-absorbing potential is unclear. This paper investigates the kinematic behaviour of an 'engineered' nacre-like structure within a high strain-rate environment. A finite-element (FE) model was developed which incorporates the pertinent biological design features. A parametric study was carried out focusing on (i) the use of an overlapping discontinuous tile arrangement for crack delocalization and (ii) application of tile waviness (interfacial hardening) for improved post-damage behaviour. With respect to the material properties, the model allows the permutation and combination of a variety of different material datasets. The advantage of such a discontinuous material shows notable improvements in sustaining high strain-rate deformation relative to an equivalent continuous morphology. In the case of the continuous material, the shockwaves propagating through the material lead to localized failure while complex shockwave patterns are observed in the discontinuous flat tile arrangement, arising from platelet interlocking. The influence of the matrix properties on impact performance is investigated by varying the dominant material parameters. The results indicate a deceleration of the impactor velocity, thus delaying back face nodal displacement. A final series of FE models considered the

  5. Biologically inspired crack delocalization in a high strain-rate environment

    PubMed Central

    Knipprath, Christian; Bond, Ian P.; Trask, Richard S.

    2012-01-01

    Biological materials possess unique and desirable energy-absorbing mechanisms and structural characteristics worthy of consideration by engineers. For example, high levels of energy dissipation at low strain rates via triggering of crack delocalization combined with interfacial hardening by platelet interlocking are observed in brittle materials such as nacre, the iridescent material in seashells. Such behaviours find no analogy in current engineering materials. The potential to mimic such toughening mechanisms on different length scales now exists, but the question concerning their suitability under dynamic loading conditions and whether these mechanisms retain their energy-absorbing potential is unclear. This paper investigates the kinematic behaviour of an ‘engineered’ nacre-like structure within a high strain-rate environment. A finite-element (FE) model was developed which incorporates the pertinent biological design features. A parametric study was carried out focusing on (i) the use of an overlapping discontinuous tile arrangement for crack delocalization and (ii) application of tile waviness (interfacial hardening) for improved post-damage behaviour. With respect to the material properties, the model allows the permutation and combination of a variety of different material datasets. The advantage of such a discontinuous material shows notable improvements in sustaining high strain-rate deformation relative to an equivalent continuous morphology. In the case of the continuous material, the shockwaves propagating through the material lead to localized failure while complex shockwave patterns are observed in the discontinuous flat tile arrangement, arising from platelet interlocking. The influence of the matrix properties on impact performance is investigated by varying the dominant material parameters. The results indicate a deceleration of the impactor velocity, thus delaying back face nodal displacement. A final series of FE models considered the

  6. Determination of the ductile-brittle transition temperature from the microplastic-strain rate

    NASA Astrophysics Data System (ADS)

    Andreev, A. K.; Solntsev, Yu. P.

    2008-04-01

    The possibility of the determination of the tendency of cast and deformed steels to brittle fracture using the temperature dependence of the small-plastic-strain rate is studied. The temperature corresponding to the maximum in this curve is found to indicate an abrupt decrease in the steel plasticity, which makes it possible to interpret it as the ductile-brittle transition temperature depending only on the structure of a material.

  7. Biologically inspired crack delocalization in a high strain-rate environment.

    PubMed

    Knipprath, Christian; Bond, Ian P; Trask, Richard S

    2012-04-01

    Biological materials possess unique and desirable energy-absorbing mechanisms and structural characteristics worthy of consideration by engineers. For example, high levels of energy dissipation at low strain rates via triggering of crack delocalization combined with interfacial hardening by platelet interlocking are observed in brittle materials such as nacre, the iridescent material in seashells. Such behaviours find no analogy in current engineering materials. The potential to mimic such toughening mechanisms on different length scales now exists, but the question concerning their suitability under dynamic loading conditions and whether these mechanisms retain their energy-absorbing potential is unclear. This paper investigates the kinematic behaviour of an 'engineered' nacre-like structure within a high strain-rate environment. A finite-element (FE) model was developed which incorporates the pertinent biological design features. A parametric study was carried out focusing on (i) the use of an overlapping discontinuous tile arrangement for crack delocalization and (ii) application of tile waviness (interfacial hardening) for improved post-damage behaviour. With respect to the material properties, the model allows the permutation and combination of a variety of different material datasets. The advantage of such a discontinuous material shows notable improvements in sustaining high strain-rate deformation relative to an equivalent continuous morphology. In the case of the continuous material, the shockwaves propagating through the material lead to localized failure while complex shockwave patterns are observed in the discontinuous flat tile arrangement, arising from platelet interlocking. The influence of the matrix properties on impact performance is investigated by varying the dominant material parameters. The results indicate a deceleration of the impactor velocity, thus delaying back face nodal displacement. A final series of FE models considered the

  8. Hardness and phase analysis of IN 718 deformed at high strain rate.

    PubMed

    Renhof, L; Guder, S; Werner, E

    2004-06-01

    Specimens of the nickel base alloy IN 718 deformed at high strain rate (approximately 10 s(-1)), as realized in a screw press, have higher strength than parts forged conventionally in a hydraulic press. Microstructure analyses in light and transmission electron microscopes reveal the precipitation of very small Ni(3)Nb particles (gamma"-phase) to be the reason for the increased hardness. Several processing routes are discussed and analyzed in relation to the TTT-diagram of IN 718.

  9. GNSS strain rate patterns and their application to investigate geodynamical credibility of the GNSS velocities

    NASA Astrophysics Data System (ADS)

    Araszkiewicz, Andrzej; Figurski, Mariusz

    2015-04-01

    The potential that lies in the use of GNSS measurements for crustal deformation studies have already noticed in the beginning of the first of such a system (GPS). Today thanks to the development of satellite positioning techniques it is possible to detect displacement on the Earth surface with an accuracy less than 1 cm. With long-term observations we can determine the velocities even more accurately. Growing demand in the last years for GNSS applications, both for scientific and civil use, meant that new networks of the reference stations were created. Such a dense GNSS networks allow to conduct research in the field of crust deformation at a higher spatial resolution than before. In Europe most of the research focuses on Mediterranean regions, where we can monitor events resulting from the tectonic plates collision. But even in Central Europe we can see effect of Africa push. In our research we focused on Polish territory, where in the past 5 years a nearly 300 reference stations were established. With minimal movements that have been observed in Poland, a key issue in this type of research is to determine the geodynamic reliability of the estimated stations velocities. While the long-term observations enable us to determine the very accurate velocities, it hard to indicate how reliably they reflect actual tectonic movements is. In this paper we proposed a method for testing the reliability of stations velocities based on the strain rate field analysis. The method is based on the analysis of the distribution of the rate of deformation tensor components obtained for triangular elements built on the basis of assessed station. The paper presents the results of numerical simulations and initial use of the method for the Polish network of reference stations: ASG-EUPOS

  10. Some influences of rock strength and strain rate on propagation of rock avalanches

    NASA Astrophysics Data System (ADS)

    Bowman, Elisabeth; Rait, Kim

    2016-04-01

    Rock avalanches are extreme and destructive mass movements in which large volumes of rock (typically >1 million cubic metres) travel at high speeds, covering large distances, and the occurrence of which is highly unpredictable. The "size effect" in rock avalanches, whereby those with larger volumes produce greater spreading efficiency (as defined by an increase in normalised runout) or lower farboschung angle (defined as the tangent of the ratio of fall height to runout length), is well known. Studies have shown that rock strength is a controlling factor in the mobility of rock avalanches - that is, mass movements involving lower strength rock are generally found to produce greater mobility as evidenced by the spread of deposits or low farboschung angle. However, there are conflicting ideas as to how and why this influence is manifested. This paper discusses different theories of rock comminution in light of numerical simulations of rock clasts undergoing normal and shear induced loading, experimental work on rock avalanche behaviour, and dynamic fracture mechanics. In doing so, we introduce the idea of thresholds of strain rate for the production of dynamic fragmentation (as opposed to pseudo-static clast crushing) that are based, inter alia, on static rock strength. To do this, we refer to data from physical models using rock analogue materials, field data on chalk cliff collapses, and field statistics from documented rock avalanches. The roles of normal and shear loading and loading rate within a rock avalanche are examined numerically using 3D Discrete Element Method models of rock clasts loaded to failure. Results may help to reconcile the observations that large rock avalanches in stronger materials tend not to fragment as much as those in weaker materials and also possess lower mobility, while small cliff collapses (typically > 1000 cubic metres) in weak chalk can exhibit rock avalanche-like behaviour at much smaller volumes.

  11. Ultrahigh strain-rate bending of copper nanopillars with laser-generated shock waves

    SciTech Connect

    Colorado, H. A.; Navarro, A.; Prikhodko, S. V.; Yang, J. M.; Ghoniem, N.; Gupta, V.

    2013-12-21

    An experimental study to bend FIB-prepared cantilevered single crystal Cu nanopillars of several hundred nanometers in diameter and length at ultrahigh strain rate is presented. The deformation is induced by laser-generated stress waves, resulting in local strain rates exceeding 10{sup 7} s{sup −1}. Loading of nano-scale Cu structures at these extremely short loading times shows unique deformation characteristics. At a nominal stress value of 297 MPa, TEM examination along with selected area electron diffraction characterization revealed that twins within the unshocked Cu pillars interacted with dislocations that nucleated from free surfaces of the pillars to form new subgrain boundaries. MD simulation results were found to be consistent with the very low values of the stress required for dislocation activation and nucleation because of the extremely high surface area to volume ratio of the nanopillars. Specifically, simulations show that the stress required to nucleate dislocations at these ultrahigh strain rates is about one order of magnitude smaller than typical values required for homogeneous nucleation of dislocation loops in bulk copper single crystals under quasi-static conditions.

  12. Molecular Dynamics Simulation of High Strain-Rate Void Nucleation and Growth in Copper

    NASA Astrophysics Data System (ADS)

    Belak, J.; Boercker, D. B.; Bales, G. S.; Glosli, J.

    1997-07-01

    Isotropic tension is simulated in nanoscale polycrystalline copper with 10nm grain sizes using large-scale molecular dynamics. The nanocrystalline copper is fabricated on the computer by growing randomly oriented grains from random positions in the simulations cell. Constant volume strain rates of 10^8 - 10^10 are considered for systems ranging from 10^5 - 10^6 atoms using an EAM interatomic potential for copper. The spacing between voids for room temperature simulations is found to scale approximately as l ~ 0.005 * Cs / dotɛ, where Cs is the sound speed and dotɛ is the strain rate. Below strain rates of about 10^9, only one void is observed to nucleate and grow in the simulation cell. The growth of small voids is simulated by cutting a void out of the simulation cells and repeating the isotropic expansion. Results are presented for several grain boundary orientations (textures) and void sizes and compared to macroscopic models.

  13. Hopkinson bar techniques for the intermediate strain rate testing of bovine cortical bone

    PubMed Central

    Cloete, T. J.; Paul, G.; Ismail, E. B.

    2014-01-01

    Detailed knowledge of the dynamic viscoelastic properties of bone is required to understand the mechanisms of macroscopic bone fracture in humans, and other terrestrial mammals, during impact loading events (e.g. falls, vehicle accidents, etc.). While the dynamic response of bone has been studied for several decades, high-quality data remain limited, and it is only within the last decade that techniques for conducting dynamic compression tests on bone at near-constant strain rates have been developed. Furthermore, there appears to be a lack of published bone data in the intermediate strain rate (ISR) range (i.e. 1–100 s−1), which represents a regime in which many dynamic bone fractures occur. In this paper, preliminary results for the dynamic compression of bovine cortical bone in the ISR regime are presented. The results are obtained using two Hopkinson-bar-related techniques, namely the conventional split Hopkinson bar arrangement incorporating a novel cone-in-tube striker design, and the recently developed wedge bar apparatus. The experimental results show a rapid transition in the strain rate sensitive behaviour of bovine cortical bone in the ISR range. Finally, a new viscoelastic model is proposed that captures the observed transition behaviour. PMID:24711493

  14. A fault-based model for crustal deformation, fault slip-rates and off-fault strain rate in California

    USGS Publications Warehouse

    Zeng, Yuehua; Shen, Zheng-Kang

    2016-01-01

    We invert Global Positioning System (GPS) velocity data to estimate fault slip rates in California using a fault‐based crustal deformation model with geologic constraints. The model assumes buried elastic dislocations across the region using Uniform California Earthquake Rupture Forecast Version 3 (UCERF3) fault geometries. New GPS velocity and geologic slip‐rate data were compiled by the UCERF3 deformation working group. The result of least‐squares inversion shows that the San Andreas fault slips at 19–22  mm/yr along Santa Cruz to the North Coast, 25–28  mm/yr along the central California creeping segment to the Carrizo Plain, 20–22  mm/yr along the Mojave, and 20–24  mm/yr along the Coachella to the Imperial Valley. Modeled slip rates are 7–16  mm/yr lower than the preferred geologic rates from the central California creeping section to the San Bernardino North section. For the Bartlett Springs section, fault slip rates of 7–9  mm/yr fall within the geologic bounds but are twice the preferred geologic rates. For the central and eastern Garlock, inverted slip rates of 7.5 and 4.9  mm/yr, respectively, match closely with the geologic rates. For the western Garlock, however, our result suggests a low slip rate of 1.7  mm/yr. Along the eastern California shear zone and southern Walker Lane, our model shows a cumulative slip rate of 6.2–6.9  mm/yr across its east–west transects, which is ∼1  mm/yr increase of the geologic estimates. For the off‐coast faults of central California, from Hosgri to San Gregorio, fault slips are modeled at 1–5  mm/yr, similar to the lower geologic bounds. For the off‐fault deformation, the total moment rate amounts to 0.88×1019  N·m/yr, with fast straining regions found around the Mendocino triple junction, Transverse Ranges and Garlock fault zones, Landers and Brawley seismic zones, and farther south. The overall California moment rate is 2.76×1019

  15. Correlation between strain rate sensitivity and α relaxation of metallic glasses

    NASA Astrophysics Data System (ADS)

    Zhang, M.; Wang, Y. J.; Dai, L. H.

    2016-07-01

    An inherent correlation between the strain rate sensitivity and α relaxation of metallic glasses (MGs) is observed. This correlation can be attributed to the secondary term which incorporates the nonaffine displacements of atoms in the analytical expression of the elastic modulus of amorphous solids. The observed correlation supports the proposition that stress and temperature play equivalent role in the glass transition of MGs. Besides, an ideal liquid state of MGs is observed in the supercooled liquid region when they are deformed below a critical loading rate. This observation would benefit the application of MGs in the fabrication of micro parts for MEMS (Micro Electro-Mechanical Systems).

  16. High-strain-rate compression and fracture of B sub 4 C-aluminum cermets

    SciTech Connect

    Blumenthal, W.R.

    1990-01-01

    The compressive behavior of liquid-metal infiltrated boron carbide-aluminum cermets were studied as a function of strain rate, composition, and microstructure. Hopkinson split pressure bar (HSPB) and quasi-static compression tests were conducted using dumb-bell-shaped specimens. Results showed cermet compressive strength to be independent of loading rate. Strength was also found to be independent of the aluminum alloy used to infiltrate pre-sintered 65 vol % B{sub 4}C pre-forms. compositions with the smallest phase size displayed the best strength and ductility. 18 refs., 4 figs.

  17. Rate dependent stress-strain behavior of advanced polymer matrix composites

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.

    1991-01-01

    The formulation of an elastic/viscoplastic constitutive model which was used to predict the measured behavior of graphite/thermoplastic and graphite/bismaleimide composite materials at elevated temperature is described. The model incorporates the concepts of overstress and effective strain/strain to provide a simple formulation which was able to account for material behavior under monotonic tension or compression loads over a temperature range of 23 to 200 C. Observed behavior such as stress relaxation and steady state creep, in off-axis tension and compression tests, were predicted by the model. Material constants required by the model were extracted from simple off-axis test data.

  18. High Strain Rate Testing of Rocks using a Split-Hopkinson-Pressure Bar

    NASA Astrophysics Data System (ADS)

    Zwiessler, Ruprecht; Kenkmann, Thomas; Poelchau, Michael; Nau, Siegfried; Hess, Sebastian

    2016-04-01

    Dynamic mechanical testing of rocks is important to define the onset of rate dependency of brittle failure. The strain rate dependency occurs through the propagation velocity limit (Rayleigh wave speed) of cracks and their reduced ability to coalesce, which, in turn, significantly increases the strength of the rock. We use a newly developed pressurized air driven Split-Hopkinson-Pressure Bar (SHPB), that is specifically designed for the investigation of high strain rate testing of rocks, consisting of several 10 to 50 cm long strikers and bar components of 50 mm in diameter and 2.5 meters in length each. The whole set up, composed of striker, incident- and transmission bar is available in aluminum, titanium and maraging steel to minimize the acoustic impedance contrast, determined by the change of density and speed of sound, to the specific rock of investigation. Dynamic mechanical parameters are obtained in compression as well as in spallation configuration, covering a wide spectrum from intermediate to high strain rates (100-103 s-1). In SHPB experiments [1] one-dimensional longitudinal compressive pulses of diverse shapes and lengths - formed with pulse shapers - are used to generate a variety of loading histories under 1D states of stress in cylindrical rock samples, in order to measure the respective stress-strain response at specific strain rates. Subsequent microstructural analysis of the deformed samples is aimed at quantification fracture orientation, fracture pattern, fracture density, and fracture surface properties as a function of the loading rate. Linking mechanical and microstructural data to natural dynamic deformation processes has relevance for the understanding of earthquakes, landslides, impacts, and has several rock engineering applications. For instance, experiments on dynamic fragmentation help to unravel super-shear rupture events that pervasively pulverize rocks up to several hundred meters from the fault core [2, 3, 4]. The dynamic, strain

  19. High Strain Rate Testing of Rocks using a Split-Hopkinson-Pressure Bar

    NASA Astrophysics Data System (ADS)

    Zwiessler, Ruprecht; Kenkmann, Thomas; Poelchau, Michael; Nau, Siegfried; Hess, Sebastian

    2016-04-01

    Dynamic mechanical testing of rocks is important to define the onset of rate dependency of brittle failure. The strain rate dependency occurs through the propagation velocity limit (Rayleigh wave speed) of cracks and their reduced ability to coalesce, which, in turn, significantly increases the strength of the rock. We use a newly developed pressurized air driven Split-Hopkinson-Pressure Bar (SHPB), that is specifically designed for the investigation of high strain rate testing of rocks, consisting of several 10 to 50 cm long strikers and bar components of 50 mm in diameter and 2.5 meters in length each. The whole set up, composed of striker, incident- and transmission bar is available in aluminum, titanium and maraging steel to minimize the acoustic impedance contrast, determined by the change of density and speed of sound, to the specific rock of investigation. Dynamic mechanical parameters are obtained in compression as well as in spallation configuration, covering a wide spectrum from intermediate to high strain rates (100-103 s‑1). In SHPB experiments [1] one-dimensional longitudinal compressive pulses of diverse shapes and lengths - formed with pulse shapers - are used to generate a variety of loading histories under 1D states of stress in cylindrical rock samples, in order to measure the respective stress-strain response at specific strain rates. Subsequent microstructural analysis of the deformed samples is aimed at quantification fracture orientation, fracture pattern, fracture density, and fracture surface properties as a function of the loading rate. Linking mechanical and microstructural data to natural dynamic deformation processes has relevance for the understanding of earthquakes, landslides, impacts, and has several rock engineering applications. For instance, experiments on dynamic fragmentation help to unravel super-shear rupture events that pervasively pulverize rocks up to several hundred meters from the fault core [2, 3, 4]. The dynamic

  20. GPS Velocity and Strain Rate Fields in Southwest Anatolia from Repeated GPS Measurements.

    PubMed

    Erdoğan, Saffet; Sahin, Muhammed; Tiryakioğlu, Ibrahim; Gülal, Engin; Telli, Ali Kazım

    2009-01-01

    Southwestern Turkey is a tectonically active area. To determine kinematics and strain distribution in this region, a GPS network of sixteen stations was established. We have used GPS velocity field data for southwest Anatolia from continuous measurements covering the period 2003 to 2006 to estimate current crustal deformation of this tectonically active region. GPS data were processed using GAMIT/GLOBK software and velocity and strain rate fields were estimated in the study area. The measurements showed velocities of 15-30 mm/yr toward the southwest and strain values up to 0.28-8.23×10(-8). Results showed that extension has been determined in the Burdur-Isparta region. In this study, all of strain data reveal an extensional neotectonic regime through the northeast edge of the Isparta Angle despite the previously reported compressional neotectonic regime. Meanwhile, results showed some small differences relatively with the 2006 model of Reilinger et al. As a result, active tectonic movements, in agreement with earthquake fault plane solutions showed important activity. PMID:22573998