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.

Earthquake potential in California-Nevada implied by correlation of strain rate and seismicity

USGS Publications Warehouse

Zeng, Yuehua; Petersen, Mark D.; Shen, Zheng-Kang

2018-01-01

Rock mechanics studies and dynamic earthquake simulations show that patterns of seismicity evolve with time through (1) accumulation phase, (2) localization phase, and (3) rupture phase. We observe a similar pattern of changes in seismicity during the past century across California and Nevada. To quantify these changes, we correlate GPS strain rates with seismicity. Earthquakes of M > 6.5 are collocated with regions of highest strain rates. By contrast, smaller magnitude earthquakes of M ≥ 4 show clear spatiotemporal changes. From 1933 to the late 1980s, earthquakes of M ≥ 4 were more diffused and broadly distributed in both high and low strain rate regions (accumulation phase). From the late 1980s to 2016, earthquakes were more concentrated within the high strain rate areas focused on the major fault strands (localization phase). In the same time period, the rate of M > 6.5 events also increased significantly in the high strain rate areas. The strong correlation between current strain rate and the later period of seismicity indicates that seismicity is closely related to the strain rate. The spatial patterns suggest that before the late 1980s, the strain rate field was also broadly distributed because of the stress shadows from previous large earthquakes. As the deformation field evolved out of the shadow in the late 1980s, strain has refocused on the major fault systems and we are entering a period of increased risk for large earthquakes in California.

Earthquake Potential in California-Nevada Implied by Correlation of Strain Rate and Seismicity

NASA Astrophysics Data System (ADS)

Zeng, Yuehua; Petersen, Mark D.; Shen, Zheng-Kang

2018-02-01

Rock mechanics studies and dynamic earthquake simulations show that patterns of seismicity evolve with time through (1) accumulation phase, (2) localization phase, and (3) rupture phase. We observe a similar pattern of changes in seismicity during the past century across California and Nevada. To quantify these changes, we correlate GPS strain rates with seismicity. Earthquakes of M > 6.5 are collocated with regions of highest strain rates. By contrast, smaller magnitude earthquakes of M ≥ 4 show clear spatiotemporal changes. From 1933 to the late 1980s, earthquakes of M ≥ 4 were more diffused and broadly distributed in both high and low strain rate regions (accumulation phase). From the late 1980s to 2016, earthquakes were more concentrated within the high strain rate areas focused on the major fault strands (localization phase). In the same time period, the rate of M > 6.5 events also increased significantly in the high strain rate areas. The strong correlation between current strain rate and the later period of seismicity indicates that seismicity is closely related to the strain rate. The spatial patterns suggest that before the late 1980s, the strain rate field was also broadly distributed because of the stress shadows from previous large earthquakes. As the deformation field evolved out of the shadow in the late 1980s, strain has refocused on the major fault systems and we are entering a period of increased risk for large earthquakes in California.

Influences of strain rate on yield strength aluminum alloys

NASA Astrophysics Data System (ADS)

Rizal, Samsul; Firdaus, Hamdani Teuku; Thaib, Razali; Homma, Hiroomi

2005-04-01

The simulation of aircraft has often been performing by implementing finite element code on supercomputers. The reliability an accuracy of simulation depends mainly on the material model as well as on structural model used in calculations. Consequently, an accurate knowledge of mechanical behavior of materials under impact loading is essential for safety performance evaluation of structure. Impact tension tests on specimens for aircrafts and automotive structural applications are conduct by means of the split Hopkinson bar apparatus. Small specimens having diameter 4 mm are use in the test. Tensile stress-strain relations at strain rates of 102 s-1 to over 103 s-1 are present and compared with those obtained at quasi-static strain rates. The limitations on the applicability of apparatus are also discusses. The other importance of the reference of strain, while studying void growth in elastic-viscoplastic material, is emphasized. In the present paper, a simplified plane-symmetrical two-dimensional finite element model for a SHPB with a plate specimen made of an elastic material is first established. The used of strain gage mounted at the specimens to be monitored strain during the course of impact test. Comparisons may then be made between the numerical predicted and experimentally observed of load and a specimen strain. This report also describes the apparatus and instrumentation, and also be discusses the advantages and limitations of experimental technique. Fractograph is taken by scanning electron microscope on the center of the specimens for judgment of the fracture mechanism and strain rates influences on the materials.

Strain rate dependent calcite microfabric evolution - an experiment carried out by nature

NASA Astrophysics Data System (ADS)

Rogowitz, A.; Huet, B.; Grasemann, B.; Habler, G.

2013-12-01

evidence for grain size sensitive deformation mechanisms at smaller grain sizes (3.6 μm) consistent with experimental observations and determined flaw laws. Although mylonitic layers evolve at high (10^-10 s^-1) and intermediate strain rates (10^-11 s^-1) by SGR recrystallization we observe variations in texture leading to the assumption that at varying strain rates different gliding systems were active. The results of this study are compared with experimental data, closing the gap between experimental and natural geological strain rates.

High strain rate deformation and fracture of the magnesium alloy Ma2-1 under shock wave loading

NASA Astrophysics Data System (ADS)

Garkushin, G. V.; Kanel', G. I.; Razorenov, S. V.

2012-05-01

This paper presents the results of measurements of the dynamic elastic limit and spall strength under shock wave loading of specimens of the magnesium alloy Ma2-1 with a thickness ranging from 0.25 to 10 mm at normal and elevated (to 550°C) temperatures. From the results of measurements of the decay of the elastic precursor of a shock compression wave, it has been found that the plastic strain rate behind the front of the elastic precursor decreases from 2 × 105 s-1 at a distance of 0.25 mm to 103 s-1 at a distance of 10 mm. The plastic strain rate in a shock wave is one order of magnitude higher than that in the elastic precursor at the same value of the shear stress. The spall strength of the alloy decreases as the solidus temperature is approached.

Rheology of arc dacite lavas: experimental determination at low strain rates

NASA Astrophysics Data System (ADS)

Avard, Geoffroy; Whittington, Alan G.

2012-07-01

Andesitic-dacitic volcanoes exhibit a large variety of eruption styles, including explosive eruptions, endogenous and exogenous dome growth, and kilometer-long lava flows. The rheology of these lavas can be investigated through field observations of flow and dome morphology, but this approach integrates the properties of lava over a wide range of temperatures. Another approach is through laboratory experiments; however, previous studies have used higher shear stresses and strain rates than are appropriate to lava flows. We measured the apparent viscosity of several lavas from Santiaguito and Bezymianny volcanoes by uniaxial compression, between 1,109 and 1,315 K, at low shear stress (0.085 to 0.42 MPa), low strain rate (between 1.1 × 10-8 and 1.9 × 10-5 s-1), and up to 43.7 % total deformation. The results show a strong variability of the apparent viscosity between different samples, which can be ascribed to differences in initial porosity and crystallinity. Deformation occurs primarily by compaction, with some cracking and/or vesicle coalescence. Our experiments yield apparent viscosities more than 1 order of magnitude lower than predicted by models based on experiments at higher strain rates. At lava flow conditions, no evidence of a yield strength is observed, and the apparent viscosity is best approached by a strain rate- and temperature-dependent power law equation. The best fit for Santiaguito lava, for temperatures between 1,164 and 1,226 K and strain rates lower than 1.8 × 10-4 s-1, is log {η_{{app}}} = - 0.738 + 9.24 × {10^3}{/}T(K) - 0.654 \\cdot log dot{\\varepsilon } where η app is apparent viscosity and dot{\\varepsilon } is strain rate. This equation also reproduced 45 data for a sample from Bezymianny with a root mean square deviation of 0.19 log unit Pa s. Applying the rheological model to lava flow conditions at Santiaguito yields calculated apparent viscosities that are in reasonable agreement with field observations and suggests that

High Strain Rate Tensile Testing of Silver Nanowires: Rate-Dependent Brittle-to-Ductile Transition.

PubMed

Ramachandramoorthy, Rajaprakash; Gao, Wei; Bernal, Rodrigo; Espinosa, Horacio

2016-01-13

The characterization of nanomaterials under high strain rates is critical to understand their suitability for dynamic applications such as nanoresonators and nanoswitches. It is also of great theoretical importance to explore nanomechanics with dynamic and rate effects. Here, we report in situ scanning electron microscope (SEM) tensile testing of bicrystalline silver nanowires at strain rates up to 2/s, which is 2 orders of magnitude higher than previously reported in the literature. The experiments are enabled by a microelectromechanical system (MEMS) with fast response time. It was identified that the nanowire plastic deformation has a small activation volume (<10b(3)), suggesting dislocation nucleation as the rate controlling mechanism. Also, a remarkable brittle-to-ductile failure mode transition was observed at a threshold strain rate of 0.2/s. Transmission electron microscopy (TEM) revealed that along the nanowire, dislocation density and spatial distribution of plastic regions increase with increasing strain rate. Furthermore, molecular dynamic (MD) simulations show that deformation mechanisms such as grain boundary migration and dislocation interactions are responsible for such ductility. Finally, the MD and experimental results were interpreted using dislocation nucleation theory. The predicted yield stress values are in agreement with the experimental results for strain rates above 0.2/s when ductility is pronounced. At low strain rates, random imperfections on the nanowire surface trigger localized plasticity, leading to a brittle-like failure.

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.

The Microstructure Evolution of Dual-Phase Pipeline Steel with Plastic Deformation at Different Strain Rates

NASA Astrophysics Data System (ADS)

Ji, L. K.; Xu, T.; Zhang, J. M.; Wang, H. T.; Tong, M. X.; Zhu, R. H.; Zhou, G. S.

2017-07-01

Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10-5, 1.25 × 10-4, 2.5 × 10-3, and 1.25 × 10-2 s-1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10-3 s-1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10-5 s-1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10-3 s-1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.

TRIP effect in austenitic-martensitic VNS9-Sh steel at various strain rates

NASA Astrophysics Data System (ADS)

Terent'ev, V. F.; Slizov, A. K.; Prosvirnin, D. V.

2016-10-01

The mechanical properties of austenitic-martensitic VNS9-Sh (23Kh15N5AM3-Sh) steel are studied at a static strain rate from 4.1 × 10-5 to 17 × 10-3 s-1 (0.05-20 mm/min). It is found that, as the strain rate increases, the ultimate tensile strength decreases and the physical yield strength remains unchanged (≈1400 MPa). As the strain rate increases, the yield plateau remains almost unchanged and the relative elongation decreases continuously. Because of high microplastic deformation, the conventional yield strength is lower than the physical yield strength over the entire strain rate range under study. The influence of the TRIP effect on the changes in the mechanical properties of VNS9-Sh steel at various strain rates is discussed.

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.

Effect of strain rate and dislocation density on the twinning behavior in Tantalum

DOE PAGES

Florando, Jeffrey N.; El-Dasher, Bassem S.; Chen, Changqiang; ...

2016-04-28

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 10 3/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 ofmore » 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. Additionally, 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.« less

Effect of strain rate on bake hardening response of BH220 steel

NASA Astrophysics Data System (ADS)

Das, Anindya; Tarafder, Soumitro; Sivaprasad, S.; Chakrabarti, Debalay

2015-09-01

This study aims at understanding the bake hardening ability of ultra low carbon BH220 steel at different strain rates. The as-received material has been pre-strained to four different levels and then deformed in tension under (a) as pre-strained state and (b) after baking at 170 ∘C for 20 minutes, at three different strain rates of 0.001, 0.1 and 100/s. In both the conditions, yield stress increased with pre-strain and strain rate, but bake hardening ability was found to decrease when strain rate was increased. The strain rate sensitivity of the material was also found to decrease with bake hardening. Generation of dislocation forests and their subsequent immobility during baking treatment enables them to act as long range obstacles during further deformation. At higher strain rates, less amount of dislocations are produced which can interact with themselves and produce hardening, because of which bake hardening ability and the strain rate drops. A dislocation based strengthening model, as proposed by Larour et al. 2011 [7], was used to predict the yield stress values obtained at different conditions. The equation produced excellent co-relation with the experimental data.

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.

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

Complete genome sequence of Rhodospirillum rubrum type strain (S1).

PubMed

Munk, A Christine; Copeland, Alex; Lucas, Susan; Lapidus, Alla; Del Rio, Tijana Glavina; Barry, Kerrie; Detter, John C; Hammon, Nancy; Israni, Sanjay; Pitluck, Sam; Brettin, Thomas; Bruce, David; Han, Cliff; Tapia, Roxanne; Gilna, Paul; Schmutz, Jeremy; Larimer, Frank; Land, Miriam; Kyrpides, Nikos C; Mavromatis, Konstantinos; Richardson, Paul; Rohde, Manfred; Göker, Markus; Klenk, Hans-Peter; Zhang, Yaoping; Roberts, Gary P; Reslewic, Susan; Schwartz, David C

2011-07-01

Rhodospirillum rubrum (Esmarch 1887) Molisch 1907 is the type species of the genus Rhodospirillum, which is the type genus of the family Rhodospirillaceae in the class Alphaproteobacteria. The species is of special interest because it is an anoxygenic phototroph that produces extracellular elemental sulfur (instead of oxygen) while harvesting light. It contains one of the most simple photosynthetic systems currently known, lacking light harvesting complex 2. Strain S1(T) can grow on carbon monoxide as sole energy source. With currently over 1,750 PubMed entries, R. rubrum is one of the most intensively studied microbial species, in particular for physiological and genetic studies. Next to R. centenum strain SW, the genome sequence of strain S1(T) is only the second genome of a member of the genus Rhodospirillum to be published, but the first type strain genome from the genus. The 4,352,825 bp long chromosome and 53,732 bp plasmid with a total of 3,850 protein-coding and 83 RNA genes were sequenced as part of the DOE Joint Genome Institute Program DOEM 2002.

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

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

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} tomore » 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.« less

Moisture Effects on the High Strain-Rate Behavior of Sand (Preprint)

DTIC Science & Technology

2008-04-01

1986) used a conventional SHPB to evaluate a single short pressure pulse traveling through long specimens of 20/40 dry sand, 50/80 dry sand...constant strain-rate within the specimen. In a conventional SHPB experiment, e.g., on dry sand by Veyera (1994), the incident pulse is nearly...strain-rate of 400 s-1. The sand specimen confined in a hardened steel tube, had a dry density of 1.50 g/cm3 with moisture contents varied from 3% to 20

Dynamic tensile fracture of mortar at ultra-high strain-rates

NASA Astrophysics Data System (ADS)

Erzar, B.; Buzaud, E.; Chanal, P.-Y.

2013-12-01

During the lifetime of a structure, concrete and mortar may be exposed to highly dynamic loadings, such as impact or explosion. The dynamic fracture at high loading rates needs to be well understood to allow an accurate modeling of this kind of event. In this work, a pulsed-power generator has been employed to conduct spalling tests on mortar samples at strain-rates ranging from 2 × 104 to 4 × 104 s-1. The ramp loading allowed identifying the strain-rate anytime during the test. A power law has been proposed to fit properly the rate-sensitivity of tensile strength of this cementitious material over a wide range of strain-rate. Moreover, a specimen has been recovered damaged but unbroken. Micro-computed tomography has been employed to study the characteristics of the damage pattern provoked by the dynamic tensile loading.

Temperature and strain rate dependent behavior of polymer separator for Li-ion batteries

DOE PAGES

Kalnaus, Sergiy; Wang, Yanli; Li, Jianlin; ...

2018-03-07

Safe performance of advanced Li-ion batteries relies on integrity of the separator membrane which prevents contact between electrodes of opposite polarity. Current work provides detailed study of mechanical behavior of such membrane. Temperature and strain rate sensitivity of the triple-layer polypropylene (PP)/polyethylene (PE)/polypropylene (PP) porous separator for Li-ion batteries was studied experimentally under controlled temperatures of up to 120° (393 K), and strain rates (from 1∙10-4s-1 to 0.1s-1). Digital image correlation was used to study strain localization in separator under load. The results show significant dependence of mechanical properties on temperature, with the yield stress decreasing by 30% and elasticmore » modulus decreasing by a factor of two when the temperature is increased from 20 °C to 50 °C. The strain rate strengthening also decreased with higher temperatures while the temperature softening remained independent of the applied strain rate. Application of temperature creates long lasting changes in mechanical behavior of separator as was revealed by performing experiments after the annealing. Such delayed effect of temperature application appears to have directional dependence. The results demonstrate complex behavior of polymer separator which needs to be considered in proper safety assessments of Li-ion batteries.« less

Temperature and strain rate dependent behavior of polymer separator for Li-ion batteries

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

Kalnaus, Sergiy; Wang, Yanli; Li, Jianlin

Safe performance of advanced Li-ion batteries relies on integrity of the separator membrane which prevents contact between electrodes of opposite polarity. Current work provides detailed study of mechanical behavior of such membrane. Temperature and strain rate sensitivity of the triple-layer polypropylene (PP)/polyethylene (PE)/polypropylene (PP) porous separator for Li-ion batteries was studied experimentally under controlled temperatures of up to 120° (393 K), and strain rates (from 1∙10-4s-1 to 0.1s-1). Digital image correlation was used to study strain localization in separator under load. The results show significant dependence of mechanical properties on temperature, with the yield stress decreasing by 30% and elasticmore » modulus decreasing by a factor of two when the temperature is increased from 20 °C to 50 °C. The strain rate strengthening also decreased with higher temperatures while the temperature softening remained independent of the applied strain rate. Application of temperature creates long lasting changes in mechanical behavior of separator as was revealed by performing experiments after the annealing. Such delayed effect of temperature application appears to have directional dependence. The results demonstrate complex behavior of polymer separator which needs to be considered in proper safety assessments of Li-ion batteries.« less

THE EFFECT OF STRAIN RATE ON FRACTURE TOUGHNESS OF HUMAN CORTICAL BONE: A FINITE ELEMENT STUDY

PubMed Central

Ural, Ani; Zioupos, Peter; Buchanan, Drew; Vashishth, Deepak

2011-01-01

Evaluating the mechanical response of bone under high loading rates is crucial to understanding fractures in traumatic accidents or falls. In the current study, a computational approach based on cohesive finite element modeling was employed to evaluate the effect of strain rate on fracture toughness of human cortical bone. Two-dimensional compact tension specimen models were simulated to evaluate the change in initiation and propagation fracture toughness with increasing strain rate (range: 0.08 to 18 s−1). In addition, the effect of porosity in combination with strain rate was assessed using three-dimensional models of microcomputed tomography-based compact tension specimens. The simulation results showed that bone’s resistance against the propagation of fracture decreased sharply with increase in strain rates up to 1 s−1 and attained an almost constant value for strain rates larger than 1 s−1. On the other hand, initiation fracture toughness exhibited a more gradual decrease throughout the strain rates. There was a significant positive correlation between the experimentally measured number of microcracks and the fracture toughness found in the simulations. Furthermore, the simulation results showed that the amount of porosity did not affect the way initiation fracture toughness decreased with increasing strain rates, whereas it exacerbated the same strain rate effect when propagation fracture toughness was considered. These results suggest that strain rates associated with falls lead to a dramatic reduction in bone’s resistance against crack propagation. The compromised fracture resistance of bone at loads exceeding normal activities indicates a sharp reduction and/or absence of toughening mechanisms in bone during high strain conditions associated with traumatic fracture. PMID:21783112

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

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

Florando, Jeffrey N., E-mail: florando1@llnl.gov; Swift, Damian C.; Barton, Nathan R.

2016-04-15

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{sup −4}/s to 10{sup 3}/s under uniaxial stress conditions, and under laser-induced shock-loading conditions. In this study, twinning was observed at 77 K at strain rates from 1/s to 10{sup 3}/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 givenmore » 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.« less

Using strain rates to forecast seismic hazards

USGS Publications Warehouse

Evans, Eileen

2017-01-01

One essential component in forecasting seismic hazards is observing the gradual accumulation of tectonic strain accumulation along faults before this strain is suddenly released as earthquakes. Typically, seismic hazard models are based on geologic estimates of slip rates along faults and historical records of seismic activity, neither of which records actively accumulating strain. But this strain can be estimated by geodesy: the precise measurement of tiny position changes of Earth’s surface, obtained from GPS, interferometric synthetic aperture radar (InSAR), or a variety of other instruments.

Dynamic Behavior of AA2519-T8 Aluminum Alloy Under High Strain Rate Loading in Compression

NASA Astrophysics Data System (ADS)

Olasumboye, A. T.; Owolabi, G. M.; Odeshi, A. G.; Yilmaz, N.; Zeytinci, A.

2018-06-01

In this study, the effects of strain rate on the dynamic behavior, microstructure evolution and hence, failure of the AA2519-T8 aluminum alloy were investigated under compression at strain rates ranging from 1000 to 3500 s-1. Cylindrical specimens of dimensions 3.3 mm × 3.3 mm (L/D = 1) were tested using the split-Hopkinson pressure bar integrated with a digital image correlation system. The microstructure of the alloy was assessed using optical and scanning electron microscopes. Results showed that the dynamic yield strength of the alloy is strain rate dependent, with the maximum yield strength attained by the material being 500 MPa. The peak flow stress of 562 MPa was attained by the material at 3500 s-1. The alloy also showed a significant rate of strain hardening that is typical of other Al-Cu alloys; the rate of strain hardening, however, decreased with increase in strain rate. It was determined that the strain rate sensitivity coefficient of the alloy within the range of high strain rates used in this study is approximately 0.05 at 0.12 plastic strain; a more significant value than what was reported in literature under quasi-static loading. Micrographs obtained showed potential sites for the evolution of adiabatic shear band at 3500 s-1, with a characteristic circular-shaped surface profile comprising partially dissolved second phase particles in the continuous phase across the incident plane of the deformed specimen. The regions surrounding the site showed little or no change in the size of particles. However, the constituent coarse particles were observed as agglomerations of fractured pieces, thus having a shape factor different from those contained in the as-received alloy. Since the investigated alloy is a choice material for military application where it can be exposed to massive deformation at high strain rates, this study provides information on its microstructural and mechanical responses to such extreme loading condition.

Dynamic Behavior of AA2519-T8 Aluminum Alloy Under High Strain Rate Loading in Compression

NASA Astrophysics Data System (ADS)

Olasumboye, A. T.; Owolabi, G. M.; Odeshi, A. G.; Yilmaz, N.; Zeytinci, A.

2018-02-01

In this study, the effects of strain rate on the dynamic behavior, microstructure evolution and hence, failure of the AA2519-T8 aluminum alloy were investigated under compression at strain rates ranging from 1000 to 3500 s-1. Cylindrical specimens of dimensions 3.3 mm × 3.3 mm (L/D = 1) were tested using the split-Hopkinson pressure bar integrated with a digital image correlation system. The microstructure of the alloy was assessed using optical and scanning electron microscopes. Results showed that the dynamic yield strength of the alloy is strain rate dependent, with the maximum yield strength attained by the material being 500 MPa. The peak flow stress of 562 MPa was attained by the material at 3500 s-1. The alloy also showed a significant rate of strain hardening that is typical of other Al-Cu alloys; the rate of strain hardening, however, decreased with increase in strain rate. It was determined that the strain rate sensitivity coefficient of the alloy within the range of high strain rates used in this study is approximately 0.05 at 0.12 plastic strain; a more significant value than what was reported in literature under quasi-static loading. Micrographs obtained showed potential sites for the evolution of adiabatic shear band at 3500 s-1, with a characteristic circular-shaped surface profile comprising partially dissolved second phase particles in the continuous phase across the incident plane of the deformed specimen. The regions surrounding the site showed little or no change in the size of particles. However, the constituent coarse particles were observed as agglomerations of fractured pieces, thus having a shape factor different from those contained in the as-received alloy. Since the investigated alloy is a choice material for military application where it can be exposed to massive deformation at high strain rates, this study provides information on its microstructural and mechanical responses to such extreme loading condition.

Effect of Strain Rate on Hot Ductility Behavior of a High Nitrogen Cr-Mn Austenitic Steel

NASA Astrophysics Data System (ADS)

Wang, Zhenhua; Meng, Qing; Qu, Minggui; Zhou, Zean; Wang, Bo; Fu, Wantang

2016-03-01

18Mn18Cr0.6N steel specimens were tensile tested between 1173 K and 1473 K (900 °C and 1200 °C) at 9 strain rates ranging from 0.001 to 10 s-1. The tensile strained microstructures were analyzed through electron backscatter diffraction analysis. The strain rate was found to affect hot ductility by influencing the strain distribution, the extent of dynamic recrystallization and the resulting grain size, and dynamic recovery. The crack nucleation sites were primarily located at grain boundaries and were not influenced by the strain rate. At 1473 K (1200 °C), a higher strain rate was beneficial for grain refinement and preventing hot cracking; however, dynamic recovery appreciably occurred at 0.001 s-1 and induced transgranular crack propagation. At 1373 K (1100 °C), a high extent of dynamic recrystallization and fine new grains at medium strain rates led to good hot ductility. The strain gradient from the interior of the grain to the grain boundary increased with decreasing strain rate at 1173 K and 1273 K (900 °C and 1000 °C), which promoted hot cracking. Grain boundary sliding accompanied grain rotation and did not contribute to hot cracking.

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

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.

Dynamic tensile fracture of mortar at ultra-high strain-rates

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

Erzar, B., E-mail: benjamin.erzar@cea.fr; Buzaud, E.; Chanal, P.-Y.

2013-12-28

During the lifetime of a structure, concrete and mortar may be exposed to highly dynamic loadings, such as impact or explosion. The dynamic fracture at high loading rates needs to be well understood to allow an accurate modeling of this kind of event. In this work, a pulsed-power generator has been employed to conduct spalling tests on mortar samples at strain-rates ranging from 2 × 10{sup 4} to 4 × 10{sup 4} s{sup −1}. The ramp loading allowed identifying the strain-rate anytime during the test. A power law has been proposed to fit properly the rate-sensitivity of tensile strength of thismore » cementitious material over a wide range of strain-rate. Moreover, a specimen has been recovered damaged but unbroken. Micro-computed tomography has been employed to study the characteristics of the damage pattern provoked by the dynamic tensile loading.« less

Effect of high strain rates on peak stress in a Zr-based bulk metallic glass

NASA Astrophysics Data System (ADS)

Sunny, George; Yuan, Fuping; Prakash, Vikas; Lewandowski, John

2008-11-01

The mechanical behavior of Zr41.25Ti13.75Cu12.5Ni10Be22.5 (LM-1) has been extensively characterized under quasistatic loading conditions; however, its mechanical behavior under dynamic loading conditions is currently not well understood. A Split-Hopkinson pressure bar (SHPB) and a single-stage gas gun are employed to characterize the mechanical behavior of LM-1 in the strain-rate regime of 102-105/s. The SHPB experiments are conducted with a tapered insert design to mitigate the effects of stress concentrations and preferential failure at the specimen-insert interface. The higher strain-rate plate-impact compression-and-shear experiments are conducted by impacting a thick tungsten carbide (WC) flyer plate with a sandwich sample comprising a thin bulk metallic glass specimen between two thicker WC target plates. Specimens employed in the SHPB experiments failed in the gage-section at a peak stress of approximately 1.8 GPa. Specimens in the high strain-rate plate-impact experiments exhibited a flow stress in shear of approximately 0.9 GPa, regardless of the shear strain-rate. The flow stress under the plate-impact conditions was converted to an equivalent flow stress under uniaxial compression by assuming a von Mises-like material behavior and accounting for the plane strain conditions. The results of these experiments, when compared to the previous work conducted at quasistatic loading rates, indicate that the peak stress of LM-1 is essentially strain rate independent over the strain-rate range up to 105/s.

Dynamic Response of AA2519 Aluminum Alloy under High Strain Rates

NASA Astrophysics Data System (ADS)

Olasumboye, Adewale Taiwo

Like others in the AA2000 series, AA2519 is a heat-treatable Al-Cu alloy. Its excellent ballistic properties and stress corrosion cracking resistance, combined with other properties, qualify it as a prime candidate for armored vehicle and aircraft applications. However, available data on its high strain-rate response remains limited. In this study, AA2519 aluminum alloy was investigated in three different temper conditions: T4, T6, and T8, to determine the effects of heat treatment on the microstructure and dynamic deformation behavior of the material at high strain rates ranging within 1000 ≤ epsilon ≤ 4000 s-1. Split Hopkinson pressure bar integrated with digital image correlation system was used for mechanical response characterization. Optical microscopy and scanning electron microscopy were used to assess the microstructure of the material after following standard metallographic specimen preparation techniques. Results showed heterogeneous deformation in the three temper conditions. It was observed that dynamic behavior in each condition was dependent on strength properties due to the aging type controlling the strengthening precipitates produced and initial microstructure. At 1500 s -1, AA2519-T6 exhibited peak dynamic yield strength and flow stress of 509 and 667 MPa respectively, which are comparable with what were observed in T8 condition at higher rate of 3500 s-1 but AA2519-T4 showed the least strength and flow stress properties. Early stress collapse, dynamic strain aging, and higher susceptibility to shear band formation and fracture were observed in the T6 condition within the selected range of high strain rates. The alloy's general mode of damage evolution was by dispersoid particle nucleation, shearing and cracking.

Mechanical Properties of Transgenic Silkworm Silk Under High Strain Rate Tensile Loading

NASA Astrophysics Data System (ADS)

Chu, J.-M.; Claus, B.; Chen, W.

2017-12-01

Studies have shown that transgenic silkworm silk may be capable of having similar properties of spider silk while being mass-producible. In this research, the tensile stress-strain response of transgenic silkworm silk fiber is systematically characterized using a quasi-static load frame and a tension Kolsky bar over a range of strain-rates between 10^{-3} and 700/s. The results show that transgenic silkworm silk tends to have higher overall ultimate stress and failure strain at high strain rate (700/s) compared to quasi-static strain rates, indicating rate sensitivity of the material. The failure strain at the high strain rate is higher than that of spider silk. However, the stress levels are significantly below that of spider silk, and far below that of high-performance fiber. Failure surfaces are examined via scanning electron microscopy and reveal that the failure modes are similar to those of spider silk.

High-strain-rate superplasticity of the Al-Zn-Mg-Cu alloys with Fe and Ni additions

NASA Astrophysics Data System (ADS)

Kotov, A. D.; Mikhaylovskaya, A. V.; Borisov, A. A.; Yakovtseva, O. A.; Portnoy, V. K.

2017-09-01

During high-strain-rate superplastic deformation, superplasticity indices, and the microstructure of two Al-Zn-Mg-Cu-Zr alloys with additions of nickel and iron, which contain equal volume fractions of eutectic particles of Al3Ni or Al9FeNi, have been compared. It has been shown that the alloys exhibit superplasticity with 300-800% elongations at the strain rates of 1 × 10-2-1 × 10-1 s-1. The differences in the kinetics of alloy recrystallization in the course of heating and deformation at different temperatures and rates of the superplastic deformation, which are related to the various parameters of the particles of the eutectic phases, have been found. At strain rates higher than 4 × 10-2, in the alloy with Fe and Ni, a partially nonrecrystallized structure is retained up to material failure and, in the alloy with Ni, a completely recrystallized structure is formed at rates of up to 1 × 10-1 s-1.

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

DOE PAGES

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, s 2, 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 s 2 tangential to the shear layer. The extensive and compressive principal strain rates, s 1 and s 3, 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 s 1¯-s 2¯ plane and orthogonal to s 3¯.« less

Strain rate dependency of bovine trabecular bone under impact loading at sideways fall velocity.

PubMed

Enns-Bray, William S; Ferguson, Stephen J; Helgason, Benedikt

2018-05-03

There is currently a knowledge gap in scientific literature concerning the strain rate dependent properties of trabecular bone at intermediate strain rates. Meanwhile, strain rates between 10 and 200/s have been observed in previous dynamic finite element models of the proximal femur loaded at realistic sideways fall speeds. This study aimed to quantify the effect of strain rate (ε̇) on modulus of elasticity (E), ultimate stress (σ u ), failure energy (U f ), and minimum stress (σ m ) of trabecular bone in order to improve the biofidelity of material properties used in dynamic simulations of sideways fall loading on the hip. Cylindrical cores of trabecular bone (D = 8 mm, L gauge  = 16 mm, n = 34) from bovine proximal tibiae and distal femurs were scanned in µCT (10 µm), quantifying apparent density (ρ app ) and degree of anisotropy (DA), and subsequently impacted within a miniature drop tower. Force of impact was measured using a piezoelectric load cell (400 kHz), while displacement during compression was measured from high speed video (50,000 frames/s). Four groups, with similar density distributions, were loaded at different impact velocities (0.84, 1.33, 1.75, and 2.16 m/s) with constant kinetic energy (0.4 J) by adjusting the impact mass. The mean strain rates of each group were significantly different (p < 0.05) except for the two fastest impact speeds (p = 0.09). Non-linear regression models correlated strain rate, DA, and ρ app with ultimate stress (R 2  = 0.76), elastic modulus (R 2  = 0.63), failure energy (R 2  = 0.38), and minimum stress (R 2  = 0.57). These results indicate that previous estimates of σ u could be under predicting the mechanical properties at strain rates above 10/s. Copyright © 2018 Elsevier Ltd. All rights reserved.

Variation of strain rate sensitivity index of a superplastic aluminum alloy in different testing methods

NASA Astrophysics Data System (ADS)

Majidi, Omid; Jahazi, Mohammad; Bombardier, Nicolas; Samuel, Ehab

2017-10-01

The strain rate sensitivity index, m-value, is being applied as a common tool to evaluate the impact of the strain rate on the viscoplastic behaviour of materials. The m-value, as a constant number, has been frequently taken into consideration for modeling material behaviour in the numerical simulation of superplastic forming processes. However, the impact of the testing variables on the measured m-values has not been investigated comprehensively. In this study, the m-value for a superplastic grade of an aluminum alloy (i.e., AA5083) has been investigated. The conditions and the parameters that influence the strain rate sensitivity for the material are compared with three different testing methods, i.e., monotonic uniaxial tension test, strain rate jump test and stress relaxation test. All tests were conducted at elevated temperature (470°C) and at strain rates up to 0.1 s-1. The results show that the m-value is not constant and is highly dependent on the applied strain rate, strain level and testing method.

Influence of strain rate and temperature on the mechanical behavior of iron aluminide-based alloys

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

Gray, G.T.

Iron aluminides are receiving increasing attention as potential high temperature structural materials due to their excellent oxidation and sulfidation resistance. Although the influence of strain rate on the microstructure/property relationships of pure iron and a variety of iron alloys and steels has been extensively studied, the effect of strain rate on the stress-strain and deformation response of iron aluminides remains poorly understood. In this paper the influence of strain rate, varied between 0.001 and 10{sup 4} s{sup {minus}1}, and temperature, between 77 & 1073{degree}K, on the mechanical behavior of Fe-40Al-0.1B and Fe-16.12Al-5.44Cr-0.11Zr-0.13C-1.07Mo-006Y, called FAP-Y, (both in at.%) is presented. Themore » rate sensitivity and work hardening of Fe-40Al and the disordered alloy based on Fe-16% Al are discussed as a function of strain rate and temperature.« less

Complete genome sequence of Rhodospirillum rubrum type strain (S1T)

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

Munk, Christine; Copeland, A; Lucas, Susan

2011-01-01

Rhodospirillum rubrum (Esmarch 1887) Molisch 1907 is the type species of the genus Rho- dospirillum, which is the type genus of the family Rhodospirillaceae in the class Alphaproteo- bacteria. The species is of special interest because it is an anoxygenic phototroph that pro- duces extracellular elemental sulfur (instead of oxygen) while harvesting light. It contains one of the most simple photosynthetic systems currently known, lacking light harvesting complex 2. Strain S1T can grow on carbon monoxide as sole energy source. With currently over 1,750 PubMed entries, R. rubrum is one of the most intensively studied microbial species, in partic- ularmore » for physiological and genetic studies. Next to R. centenum strain SW, the genome se- quence of strain S1T is only the second genome of a member of the genus Rhodospirillum to be published, but the first type strain genome from the genus. The 4,352,825 bp long chro- mosome and 53,732 bp plasmid with a total of 3,850 protein-coding and 83 RNA genes were sequenced as part of the DOE Joint Genome Institute Program DOEM 2002.« less

Bauschinger effect in haynes 230 alloy: Influence of strain rate and temperature

NASA Astrophysics Data System (ADS)

Thakur, Aniruddha; Vecchio, Kenneth S.; Nemat-Nasser, Sia

1996-07-01

Quasistatic and dynamic Bauschinger behavior in HAYNES 230 alloy is examined. At low strain rate (10-3/s), the as- received 230 alloy does not show a drop in flow stress, i.e., no Bauschinger effect is displayed. At high strain rate (103/s), a drop in flow stress of 240 MPa was observed upon stress reversal. In contrast, the precipitation- strengthened condition exhibited a Bauschinger effect in both low and high strain rate stress-reversal experiments. The magnitude of the Bauschinger effect was found to increase with increasing strain rate, forward strain, and decreasing temperature. The substructure evolution accompanying the forward loading cycles was investigated by transmission electron microscopy and is related to the back stresses that developed. The increased Bauschinger stress drop observed at high strain rate and/or low temperature was correlated to an increased degree of planar slip under these conditions.

Strain rate effects on mechanical properties of fiber composites, part 3

NASA Technical Reports Server (NTRS)

Daniel, I. M.; Liber, T.

1976-01-01

An experimental investigation was conducted to determine the strain rate effects in fiber composites. Unidirectional composite specimens of boron/epoxy, graphite/epoxy, S-glass/epoxy and Kevlar/epoxy were tested to determine longitudinal, transverse and intralaminar (in-plane) shear properties. In the Longitudinal direction the Kevlar/epoxy shows a definite increase in both modulus and strength with strain rate. In the transverse direction, a general trend toward higher strength with strain rate is noticed. The intralaminar shear moduli and strengths of boron/epoxy and graphite/epoxy show a definite rise with strain rate.

Microstructure characterization of 316L deformed at high strain rates using EBSD

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

Yvell, K., E-mail: kyv@du.se

2016-12-15

Specimens from split Hopkinson pressure bar experiments, at strain rates between ~ 1000–9000 s{sup −1} at room temperature and 500 °C, have been studied using electron backscatter diffraction. No significant differences in the microstructures were observed at different strain rates, but were observed for different strains and temperatures. Size distribution for subgrains with boundary misorientations > 2° can be described as a bimodal lognormal area distribution. The distributions were found to change due to deformation. Part of the distribution describing the large subgrains decreased while the distribution for the small subgrains increased. This is in accordance with deformation being heterogeneousmore » and successively spreading into the undeformed part of individual grains. The variation of the average size for the small subgrain distribution varies with strain but not with strain rate in the tested interval. The mean free distance for dislocation slip, interpreted here as the average size of the distribution of small subgrains, displays a variation with plastic strain which is in accordance with the different stages in the stress-strain curves. The rate of deformation hardening in the linear hardening range is accurately calculated using the variation of the small subgrain size with strain. - Highlights: •Only changes in strain, not strain rate, gave differences in the microstructure. •A bimodal lognormal size distribution was found to describe the size distribution. •Variation of the subgrain fraction sizes agrees with models for heterogeneous slip. •Variation of subgrain size with strain describes part of the stress strain curve.« less

Duplex PCR for differentiation of the vaccine strain Brucella suis S2 and B. suis biovar 1 from other strains of Brucella spp.

PubMed

Nan, Wenlong; Tan, Pengfei; Wang, Yong; Xu, Zouliang; Mao, Kairong; Peng, Daxin; Chen, Yiping

2014-09-01

Immunisation with attenuated Brucella spp. vaccines prevents brucellosis, but may also interfere with diagnosis. In this study, a duplex PCR was developed to distinguish Brucella suis vaccine strain S2 from field strains of B. suis biovar 1 and other Brucella spp. The PCR detected 60 fg genomic DNA of B. suis S2 or biovar 1 field strains and was able to distinguish B. suis S2 and wild-type strains of B. suis biovar 1 among 76 field isolates representing all the common species and biovars, as well as four vaccine strains, of Brucella. Copyright © 2014 Elsevier Ltd. All rights reserved.

The young's modulus of 1018 steel and 67061-T6 aluminum measured from quasi-static to elastic precursor strain-rates

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

Rae, Philip J; Trujillo, Carl; Lovato, Manuel

2009-01-01

The assumption that Young's modulus is strain-rate invariant is tested for 6061-T6 aluminium alloy and 1018 steel over 10 decades of strain-rate. For the same billets of material, 3 quasi-static strain-rates are investigated with foil strain gauges at room temperature. The ultrasonic sound speeds are measured and used to calculate the moduli at approximately 10{sup 4} s{sup -1}. Finally, ID plate impact is used to generate an elastic pre-cursor in the alloys at a strain-rate of approximately 10{sup 6} s{sup -1} from which the longitudinal sound speed may be obtained. It is found that indeed the Young's modulus is strain-ratemore » independent within the experimental accuracy.« less

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

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.

Strain rate effect on fault slip and rupture evolution: Insight from meter-scale rock friction experiments

NASA Astrophysics Data System (ADS)

Xu, Shiqing; Fukuyama, Eiichi; Yamashita, Futoshi; Mizoguchi, Kazuo; Takizawa, Shigeru; Kawakata, Hironori

2018-05-01

We conduct meter-scale rock friction experiments to study strain rate effect on fault slip and rupture evolution. Two rock samples made of Indian metagabbro, with a nominal contact dimension of 1.5 m long and 0.1 m wide, are juxtaposed and loaded in a direct shear configuration to simulate the fault motion. A series of experimental tests, under constant loading rates ranging from 0.01 mm/s to 1 mm/s and under a fixed normal stress of 6.7 MPa, are performed to simulate conditions with changing strain rates. Load cells and displacement transducers are utilized to examine the macroscopic fault behavior, while high-density arrays of strain gauges close to the fault are used to investigate the local fault behavior. The observations show that the macroscopic peak strength, strength drop, and the rate of strength drop can increase with increasing loading rate. At the local scale, the observations reveal that slow loading rates favor generation of characteristic ruptures that always nucleate in the form of slow slip at about the same location. In contrast, fast loading rates can promote very abrupt rupture nucleation and along-strike scatter of hypocenter locations. At a given propagation distance, rupture speed tends to increase with increasing loading rate. We propose that a strain-rate-dependent fault fragmentation process can enhance the efficiency of fault healing during the stick period, which together with healing time controls the recovery of fault strength. In addition, a strain-rate-dependent weakening mechanism can be activated during the slip period, which together with strain energy selects the modes of fault slip and rupture propagation. The results help to understand the spectrum of fault slip and rock deformation modes in nature, and emphasize the role of heterogeneity in tuning fault behavior under different strain rates.

Influence of strain rate on the structure/property behavior of the alpha-2 alloy Ti-24.5Al-10.5Nb-1.5Mo

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

Gray, G.T. III; Hong, Sun Ig; Marquardt, B.J.

Preliminary dislocation g{center_dot}b analysis revealed that following room temperature deformation at low strain rate the majority of the dislocations are a-dislocations lying on basal planes, 2nd order pyramidal (a/2 + c) slip on [1211], and 1st order pyramidal a-slip on [1011]. Increasing the rate of deformation at room temperature to 6000 s{sup {minus}1} is seen to result in increased a-slip on prism planes and a decreased amount of basal slip. At high-strain-rates and elevated temperatures the substructure was seen to be generally similar to that observed following high-rate deformation at room temperature except for an increased amount of basal slipmore » and a somewhat higher incidence of 2nd order pyramidal slip. The defect generation and the rate sensitivity of Ti-24.5Al-10.5Nb-1.5Mo are discussed as a function of strain rate and temperature and contrasted to that observed in conventional titanium alloys and TiAl.« less

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.

Material properties of rat middle cerebral arteries at high strain rates.

PubMed

Bell, E David; Converse, Matthew; Mao, Haojie; Unnikrishnan, Ginu; Reifman, Jaques; Monson, Kenneth L

2018-03-19

Traumatic brain injury (TBI), resulting from either impact- or non-impact blast-related mechanisms, is a devastating cause of death and disability. The cerebral blood vessels, which provide critical support for brain tissue in both health and disease, are commonly injured in TBI. However, little is known about how vessels respond to traumatic loading, particularly at rates relevant to blast. To better understand vessel responses to trauma, the objective of this project was to characterize the high-rate response of passive cerebral arteries. Rat middle cerebral arteries were isolated and subjected to high-rate deformation in the axial direction. Vessels were perfused at physiological pressures and stretched to failure at strain rates ranging from approximately 100 to 1300 s-1. Although both in vivo stiffness and failure stress increased significantly with strain rate, failure stretch did not depend on rate.

Effect of axial tibial torque direction on ACL relative strain and strain rate in an in vitro simulated pivot landing.

PubMed

Oh, Youkeun K; Kreinbrink, Jennifer L; Wojtys, Edward M; Ashton-Miller, James A

2012-04-01

Anterior cruciate ligament (ACL) injuries most frequently occur under the large loads associated with a unipedal jump landing involving a cutting or pivoting maneuver. We tested the hypotheses that internal tibial torque would increase the anteromedial (AM) bundle ACL relative strain and strain rate more than would the corresponding external tibial torque under the large impulsive loads associated with such landing maneuvers. Twelve cadaveric female knees [mean (SD) age: 65.0 (10.5) years] were tested. Pretensioned quadriceps, hamstring, and gastrocnemius muscle-tendon unit forces maintained an initial knee flexion angle of 15°. A compound impulsive test load (compression, flexion moment, and internal or external tibial torque) was applied to the distal tibia while recording the 3D knee loads and tibofemoral kinematics. AM-ACL relative strain was measured using a 3 mm DVRT. In this repeated measures experiment, the Wilcoxon signed-rank test was used to test the null hypotheses with p < 0.05 considered significant. The mean (±SD) peak AM-ACL relative strains were 5.4 ± 3.7% and 3.1 ± 2.8% under internal and external tibial torque, respectively. The corresponding mean (± SD) peak AM-ACL strain rates reached 254.4 ± 160.1%/s and 179.4 ± 109.9%/s, respectively. The hypotheses were supported in that the normalized mean peak AM-ACL relative strain and strain rate were 70 and 42% greater under internal than under external tibial torque, respectively (p = 0.023, p = 0.041). We conclude that internal tibial torque is a potent stressor of the ACL because it induces a considerably (70%) larger peak strain in the AM-ACL than does a corresponding external tibial torque. Copyright © 2011 Orthopaedic Research Society.

Strain, strain rate, and the force frequency relationship in patients with and without heart failure.

PubMed

Mak, Susanna; Van Spall, Harriette G C; Wainstein, Rodrigo V; Sasson, Zion

2012-03-01

The aim of this study was to examine the effect of heart rate (HR) on indices of deformation in adults with and without heart failure (HF) who underwent simultaneous high-fidelity catheterization of the left ventricle to describe the force-frequency relationship. Right atrial pacing to control HR and high-fidelity recordings of left ventricular (LV) pressure were used to inscribe the force-frequency relationship. Simultaneous two-dimensional echocardiographic imaging was acquired for speckle-tracking analysis. Thirteen patients with normal LV function and 12 with systolic HF (LV ejection fraction, 31 ± 13%) were studied. Patients with HF had depressed isovolumic contractility and impaired longitudinal strain and strain rate. HR-dependent increases in LV+dP/dt(max), the force-frequency relationship, was demonstrated in both groups (normal LV function, baseline to 100 beats/min: 1,335 ± 296 to 1,564 ± 320 mm Hg/sec, P < .0001; HF, baseline to 100 beats/min: 970 ± 207 to 1,083 ± 233 mm Hg/sec, P < .01). Longitudinal strain decreased significantly (normal LV function, baseline to 100 beats/min: 18.0 ± 3.5% to 10.8 ± 6.0%, P < .001; HF: 9.4 ± 4.1% to 7.5 ± 3.4%, P < .01). The decrease in longitudinal strain was related to a decrease in LV end-diastolic dimensions. Strain rate did not change with right atrial pacing. Despite the inotropic effect of increasing HR, longitudinal strain decreases in parallel with stroke volume as load-dependent indices of ejection. Strain rate did not reflect the modest HR-related changes in contractility; on the other hand, the use of strain rate for quantitative stress imaging is also less likely to be confounded by chronotropic responses. Copyright © 2012 American Society of Echocardiography. Published by Mosby, Inc. All rights reserved.

A Geodetic Strain Rate Model for the East African Rift System.

PubMed

Stamps, D S; Saria, E; Kreemer, C

2018-01-15

Here we describe the new Sub-Saharan Africa Geodetic Strain Rate Model v.1.0 (SSA-GSRM v.1.0), which provides fundamental constraints on long-term tectonic deformation in the region and an improved seismic hazards assessment in Sub-Saharan Africa. Sub-Saharan Africa encompasses the East African Rift System, the active divergent plate boundary between the Nubian and Somalian plates, where strain is largely accommodated along the boundaries of three subplates. We develop an improved geodetic strain rate field for sub-Saharan Africa that incorporates 1) an expanded geodetic velocity field, 2) redefined regions of deforming zones guided by seismicity distribution, and 3) updated constraints on block rotations. SSA-GSRM v.1.0 spans longitudes 22° to 55.5° and latitudes -52° to 20° with 0.25° (longitude) by 0.2° (latitude) spacing. For plates/sub-plates, we assign rigid block rotations as constraints on the strain rate calculation that is determined by fitting bicubic Bessel splines to a new geodetic velocity solution for an interpolated velocity gradient tensor field. We derive strain rates, velocities, and vorticity rates from the velocity gradient tensor field. A comparison with the Global Geodetic Strain Rate model v2.1 reveals regions of previously unresolved spatial heterogeneities in geodetic strain rate distribution, which indicates zones of elevated seismic risk.

Flow behavior of Ti-24Al-11Nb at high strain rates

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

Harbison, L.S.; Koss, D.A.; Bourcier, R.J.

The deformation and crack initiation behavior of Ti-24Al-11Nb has been examined over a temperature range of 298 to 923 K and for strain rates from 10{sup {minus}4}/s to 10{sup 2}/s. Tests performed in compression indicate much lower strain hardening at 10{sup 2}/s than at either 10{sup {minus}1}/s or 10{sup {minus}4}/s at all temperatures. Associated with this behavior is the occurrence of non-uniform, localized deformation bands at 10{sup 2}/s. An analysis indicates that adiabatic deformation conditions predominate at 10{sup 2}/s and that these result in adiabatic softening. Furthermore, as a result of non-uniform deformation and adiabatic heating, this Ti{sub 3}-Al-based alloymore » is actually more resistant to strain-induced microcrack initiation at 10{sup 2}/s than at 10{sup {minus}4}/s during room temperature testing. 16 refs., 7 figs.« less

Dynamic mechanical characterization of aluminum: analysis of strain-rate-dependent behavior

NASA Astrophysics Data System (ADS)

Rahmat, Meysam

2018-05-01

A significant number of materials show different mechanical behavior under dynamic loads compared to quasi-static (Salvado et al. in Prog. Mater. Sci. 88:186-231, 2017). Therefore, a comprehensive study of material dynamic behavior is essential for applications in which dynamic loads are dominant (Li et al. in J. Mater. Process. Technol. 255:373-386, 2018). In this work, aluminum 6061-T6, as an example of ductile alloys with numerous applications including in the aerospace industry, has been studied under quasi-static and dynamic tensile tests with strain rates of up to 156 s^{-1}. Dogbone specimens were designed, instrumented and tested with a high speed servo-hydraulic load frame, and the results were validated with the literature. It was observed that at a strain rate of 156 s^{-1} the yield and ultimate strength increased by 31% and 33% from their quasi-static values, respectively. Moreover, the failure elongation and fracture energy per unit volume also increased by 18% and 52%, respectively. A Johnson-Cook model was used to capture the behavior of the material at different strain rates, and a modified version of this model was presented to enhance the capabilities of the original model, especially in predicting material properties close to the failure point. Finally, the fracture surfaces of specimens tested under quasi-static and dynamic loads were compared and conclusions about the differences were drawn.

Strain rate dependent calcite microfabric evolution at natural conditions

NASA Astrophysics Data System (ADS)

Rogowitz, Anna; Grasemann, Bernhard; Huet, Benjamin; Habler, Gerlinde

2014-05-01

Crystal plastic deformational behaviour of calcite has been the focus of many experimental studies. Different strain rates, pressure and temperature conditions have been addressed to investigate a wide range of deformation regimes. However, a direct comparison with natural fault rocks remains difficult because of extreme differences between experimental and natural strain rates. A flanking structure developed in almost pure calcite marble on Syros (Cyclades, Greece). Due to rotation of a planar feature (crack) a heterogeneous strain field in the surrounding area occurred resulting in different strain domains and the formation of the flanking structure. Assuming that deformation was active continuously during the development of the flanking structure, the different strain domains correspond to different strain-rate domains. The outcrop thus represents the final state of a natural experiment and gives us a great opportunity to get natural constraints on strain rate dependent deformation behaviour of calcite. Comparing the microfabrics in the 1 to 2.5 cm thick shear zone and the surrounding host rocks, which formed under the same metamorphic conditions but with different strain rates, is the central focus of this study. Due to the extreme variation in strain and strain rate, different microstructures and textures can be observed corresponding to different deformation mechanisms. With increasing strain rate we observe a change in dominant deformation mechanism from dislocation glide to dislocation creep and finally diffusion creep. Additionally, a change from subgrain rotation to bulging recrystallization can be observed in the dislocation creep regime. Crystallographic preferred orientations (CPO) and the grade of intracrystalline deformation were measured on a FEI Quanta 3D FEG instrument equipped with an EDAX Digiview IV EBSD camera. At all strain rates clear CPOs developed leading to the assumption that calcite preferentially deforms within the dislocation creep

Constant strain rate and peri-implant bone modeling: an in vivo longitudinal micro-CT analysis.

PubMed

De Smet, Els; Jaecques, Siegfried V N; Wevers, Martine; Sloten, Jos Vander; Naert, Ignace E

2013-06-01

Strain, frequency, loading time, and strain rate, among others, determine mechanical parameters in osteogenic loading. We showed a significant osteogenic effect on bone mass (BM) by daily peri-implant loading at 1.600µε.s(-1) after 4 weeks. To study the peri-implant osteogenic effect of frequency and strain in the guinea pig tibia by in vivo longitudinal micro-computed tomography (CT) analysis. One week after implant installation in both hind limb tibiae, one implant was loaded daily for 10' during 4 weeks, while the other served as control. Frequencies (3, 10, and 30Hz) and strains varied alike in the three series to keep the strain rate constant at 1.600µε.s(-1) . In vivo micro-CT scans were taken of both tibiae: 1 week after implantation but before loading (v1) and after 2 (v2) and 4 weeks (v3) of loading as well as postmortem (pm). BM (BM (%) bone-occupied area fraction) was calculated as well as the difference between test and control sides (delta BM) RESULTS: All implants (n=78) were clinically stable at 4 weeks. Significant increase in BM was measured between v1 and v2 (p<.0001) and between v1 and v3 (p<.0001). A significant positive effect of loading on delta BM was observed in the distal peri-implant marrow 500 Region of Interest already 2 weeks after loading (p=.01) and was significantly larger (11%) in series 1 compared with series 2 (p=.006) and 3 (p=.016). Within the constraints of constant loading time and strain rate, the effect of early implant loading on the peri-implant bone is strongly dependent on strain and frequency. This cortical bone model has shown to be most sensitive for high force loading at low frequency. © 2011 Wiley Periodicals, Inc.

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

Flow and fracture behavior of aluminum alloy 6082-T6 at different tensile strain rates and triaxialities.

PubMed

Chen, Xuanzhen; Peng, Yong; Peng, Shan; Yao, Song; Chen, Chao; Xu, Ping

2017-01-01

This study aims to investigate the flow and fracture behavior of aluminum alloy 6082-T6 (AA6082-T6) at different strain rates and triaxialities. Two groups of Charpy impact tests were carried out to further investigate its dynamic impact fracture property. A series of tensile tests and numerical simulations based on finite element analysis (FEA) were performed. Experimental data on smooth specimens under various strain rates ranging from 0.0001~3400 s-1 shows that AA6082-T6 is rather insensitive to strain rates in general. However, clear rate sensitivity was observed in the range of 0.001~1 s-1 while such a characteristic is counteracted by the adiabatic heating of specimens under high strain rates. A Johnson-Cook constitutive model was proposed based on tensile tests at different strain rates. In this study, the average stress triaxiality and equivalent plastic strain at facture obtained from numerical simulations were used for the calibration of J-C fracture model. Both of the J-C constitutive model and fracture model were employed in numerical simulations and the results was compared with experimental results. The calibrated J-C fracture model exhibits higher accuracy than the J-C fracture model obtained by the common method in predicting the fracture behavior of AA6082-T6. Finally, the Scanning Electron Microscope (SEM) of fractured specimens with different initial stress triaxialities were analyzed. The magnified fractographs indicate that high initial stress triaxiality likely results in dimple fracture.

Flow and fracture behavior of aluminum alloy 6082-T6 at different tensile strain rates and triaxialities

PubMed Central

Chen, Xuanzhen; Peng, Shan; Yao, Song; Chen, Chao; Xu, Ping

2017-01-01

This study aims to investigate the flow and fracture behavior of aluminum alloy 6082-T6 (AA6082-T6) at different strain rates and triaxialities. Two groups of Charpy impact tests were carried out to further investigate its dynamic impact fracture property. A series of tensile tests and numerical simulations based on finite element analysis (FEA) were performed. Experimental data on smooth specimens under various strain rates ranging from 0.0001~3400 s-1 shows that AA6082-T6 is rather insensitive to strain rates in general. However, clear rate sensitivity was observed in the range of 0.001~1 s-1 while such a characteristic is counteracted by the adiabatic heating of specimens under high strain rates. A Johnson-Cook constitutive model was proposed based on tensile tests at different strain rates. In this study, the average stress triaxiality and equivalent plastic strain at facture obtained from numerical simulations were used for the calibration of J-C fracture model. Both of the J-C constitutive model and fracture model were employed in numerical simulations and the results was compared with experimental results. The calibrated J-C fracture model exhibits higher accuracy than the J-C fracture model obtained by the common method in predicting the fracture behavior of AA6082-T6. Finally, the Scanning Electron Microscope (SEM) of fractured specimens with different initial stress triaxialities were analyzed. The magnified fractographs indicate that high initial stress triaxiality likely results in dimple fracture. PMID:28759617

High-rate operant behavior in two mouse strains: a response-bout analysis.

PubMed

Johnson, Joshua E; Pesek, Erin F; Newland, M Christopher

2009-06-01

Operant behavior sometimes occurs in bouts characterized by an initiation rate, within-bout response rate, and bout length. The generality of this structure was tested using high-rate nose-poking in mice. Reinforcement of short interresponse times produced high response rates while a random-interval schedule held reinforcement rates constant. BALB/c mice produced bouts that were more frequent, longer, and contained a higher within-bout rate of responding (nine nose-pokes/s) than did the C57BL/6 mice (five nose-pokes/s). Adding a running wheel decreased total nose-pokes and bout length, and increased bout-initiation rate. Free-feeding reduced nose-poking by decreasing bout-initiation rate. Photoperiod reversal decreased bout-initiation rate but not total nose-poke rate. Despite strain differences in bout structure, both strains responded similarly to the interventions. The three bout measures were correlated with overall rate but not with each other. Log-survival analyses provided independent descriptors of the structure of high-rate responding in these two strains.

Deformation twinning: Influence of strain rate

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

Gray, G.T. III

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 shockmore » 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.« less

Influence of Strain Rate on Heat Release under Quasi-Static Stretching of Metals. Experiment

NASA Astrophysics Data System (ADS)

Zimin, B. A.; Sventitskaya, V. E.; Smirnov, I. V.; Sud'enkov, Yu. V.

2018-04-01

The paper presents the results of experimental studies of energy dissipation during a quasi-static stretching of metals and alloys at room temperature. The strain rates varied in the range of 10-3-10-2 s-1. Samples of M1 copper, AZ31B magnesium alloy, BT6 titanium, 12Cr18Ni10Ti steel, and D16AM aluminum alloy were analyzed. The experimental results demonstrated a significant dependence of the heat release on the strain rate in the absence of its influence on stress-strain diagrams for all the metals studied in this range of strain rates. The correlation of the changes in the character of heat release with the processes of structural transformations at various stages of plastic flow is shown on the qualitative level. A difference in the nature of the processes of heat release in materials with different ratios of the plasticity and strength is noted.

Mechanical Characterization of Immature Porcine Brainstem in Tension at Dynamic Strain Rates.

PubMed

Zhao, Hui; Yin, Zhiyong; Li, Kui; Liao, Zhikang; Xiang, Hongyi; Zhu, Feng

2016-01-21

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. 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. 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). 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 future.

Characterization of a New Fully Recycled Carbon Fiber Reinforced Composite Subjected to High Strain Rate Tension

NASA Astrophysics Data System (ADS)

Meftah, H.; Tamboura, S.; Fitoussi, J.; BenDaly, H.; Tcharkhtchi, A.

2017-08-01

The aim of this study is the complete physicochemical characterization and strain rate effect multi-scale analysis of a new fully recycled carbon fiber reinforced composites for automotive crash application. Two composites made of 20% wt short recycled carbon fibers (CF) are obtained by injection molding. The morphology and the degree of dispersion of CF in the matrixes were examined using a new ultrasonic method and SEM. High strain tensile behavior up to 100 s-1 is investigated. In order to avoid perturbation due to inertial effect and wave propagation, the specimen geometry was optimized. The elastic properties appear to be insensitive to the strain rate. However, a high strain rate effect on the local visco-plasticity of the matrix and fiber/matrix interface visco-damageable behavior is emphasized. The predominant damage mechanisms evolve from generalized matrix local ductility at low strain rate regime to fiber/matrix interface debonding and fibers pull-out at high strain rate regime.

Characterization of a New Fully Recycled Carbon Fiber Reinforced Composite Subjected to High Strain Rate Tension

NASA Astrophysics Data System (ADS)

Meftah, H.; Tamboura, S.; Fitoussi, J.; BenDaly, H.; Tcharkhtchi, A.

2018-06-01

The aim of this study is the complete physicochemical characterization and strain rate effect multi-scale analysis of a new fully recycled carbon fiber reinforced composites for automotive crash application. Two composites made of 20% wt short recycled carbon fibers (CF) are obtained by injection molding. The morphology and the degree of dispersion of CF in the matrixes were examined using a new ultrasonic method and SEM. High strain tensile behavior up to 100 s-1 is investigated. In order to avoid perturbation due to inertial effect and wave propagation, the specimen geometry was optimized. The elastic properties appear to be insensitive to the strain rate. However, a high strain rate effect on the local visco-plasticity of the matrix and fiber/matrix interface visco-damageable behavior is emphasized. The predominant damage mechanisms evolve from generalized matrix local ductility at low strain rate regime to fiber/matrix interface debonding and fibers pull-out at high strain rate regime.

High-resolution surface velocity and strain rate mapping across the Alpine-Himalayan belt using InSAR and GNSS data

NASA Astrophysics Data System (ADS)

Weiss, J. R.; Walters, R. J.; Wright, T. J.; Hussain, E.; González, P. J.; Hooper, A. J.

2017-12-01

Accurate and high-resolution measurements of interseismic crustal velocity and the strain-rate fields derived from these measurements are an important input for the assessment of earthquake hazard. However, most strain-rate estimation methods and associated seismicity forecasts rely heavily on Global Navigation Satellite System (GNSS) networks with sparse and heterogeneous spatial coverage, limiting both accuracy and resolution. Interferometric Synthetic Aperture Radar (InSAR) provides remotely-sensed observations of surface motion, with accuracy comparable to GNSS data, and with a spatial resolution of a few tens of meters. The recently launched Sentinel-1 (S1) radar satellites can measure deformation at the tectonic-plate scale and across slowly straining regions where earthquake hazard is poorly characterised. We are producing large-scale crustal velocity and strain-rate fields for the Alpine-Himalayan belt (AHB) by augmenting global GNSS data compilations with InSAR-derived surface velocities. We are also systematically processing S1 interferograms for the AHB and these products are freely available to the geoscience community. We focus on the Anatolian microplate, where we have used both Envisat and S1 data to measure crustal velocity. We address some of the challenges associated with merging the complementary geodetic datasets including reference-frame issues, treatment of uncertainties, and comparison of different velocity/strain-rate inversion methods. We use synthetic displacement fields to illustrate how inclusion of InSAR can aid in identifying features such as unmapped active faults and fault segments that are creeping. From our preliminary results for Anatolia, we investigate the spatial distribution of strain and variation of strain rates during the seismic cycle.

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.

Physical nature of strain rate sensitivity of metals and alloys at high strain rates

NASA Astrophysics Data System (ADS)

Borodin, E. N.; Gruzdkov, A. A.; Mayer, A. E.; Selyutina, N. S.

2018-04-01

The role of instabilities of plastic flow at plastic deformation of various materials is one of the important cross-disciplinary problems which is equally important in physics, mechanics and material science. The strain rate sensitivities under slow and high strain rate conditions of loading have different physical nature. In the case of low strain rate, the sensitivity arising from the inertness of the defect structures evolution can be expressed by a single parameter characterizing the plasticity mechanism. In our approach, this is the value of the characteristic relaxation time. In the dynamic case, there are additional effects of “high-speed sensitivity” associated with the micro-localization of the plastic flow near the stress concentrators. In the frames of mechanical description, this requires to introduce additional strain rate sensitivity parameters, which is realized in numerous modifications of Johnson–Cook and Zerilli–Armstrong models. The consideration of both these factors is fundamental for an adequate description of the problems of dynamic deformation of highly inhomogeneous metallic materials such as steels and alloys. The measurement of the dispersion of particle velocities on the free surface of a shock-loaded material can be regarded as an experimental expression of the effect of micro-localization. This is also confirmed by our results of numerical simulation of the propagation of shock waves in a two-dimensional formulation and analytical estimations.

Comparison of epoxy-based encapsulating materials over temperature and strain rate

NASA Astrophysics Data System (ADS)

Khan, Amnah S.; Wilgeroth, James; Balzer, Jens; Proud, William G.

2017-01-01

The highly insulating, adhesive and bonding properties of thermosetting epoxies, their ability to be injection moulded in an uncured state, as well as their presence in a wide number of composites, has resulted in their widespread use in both electrical and aerospace applications. There is thus a need to understand the compressive response of epoxies over the range of temperatures likely to be experienced within their working environment. The effects of varying strain rates and temperatures on an epoxy resin (Scotchcast 8) and an epoxy-based syntactic foam (Stycast 1090) were investigated. The samples were studied from -20 °C to +80 °C over a range of strain rates (10-4 - 10+3 s-1). Stress-strain data was obtained, with further analysis from high-speed images. Dynamic Mechanical Analysis (DMA) was also performed on the two materials. Data obtained from these experiments demonstrated key differences in the behaviour of the two materials, forming a basis for comparison with numerical simulations.

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

Rearrangements of mycoreovirus 1 S1, S2 and S3 induced by the multifunctional protein p29 encoded by the prototypic hypovirus Cryphonectria hypovirus 1 strain EP713.

PubMed

Tanaka, Toru; Sun, Liying; Tsutani, Kouhei; Suzuki, Nobuhiro

2011-08-01

Mycoreovirus 1 (MyRV1), a member of the family Reoviridae possessing a genome consisting of 11 dsRNA segments (S1-S11), infects the chestnut blight fungus and reduces its virulence (hypovirulence). Studies have previously demonstrated reproducible induction of intragenic rearrangements of MyRV1 S6 (S6L: almost full-length duplication) and S10 (S10ss: internal deletion of three-quarters of the ORF), mediated by the multifunctional protein p29 encoded by the prototype hypovirus, Cryphonectria hypovirus 1 (CHV1) strain EP713, of the family Hypoviridae with ssRNA genomes. The current study showed that CHV1 p29 also induced rearrangements of the three largest MyRV1 segments, S1, S2 and S3, which encode structural proteins. These rearranged segments involved in-frame extensions of almost two-thirds of the ORFs (S1L, S2L and S3L, respectively), which is rare for a reovirus rearrangement. MyRV1 variants carrying S1L, S2L or S3L always contained S10ss (MyRV1/S1L+S10ss2, MyRV1/S2L+S10ss2 or MyRV1/S3L+S10ss2). Levels of mRNAs for the rearranged and co-existing unaltered genome segments in fungal colonies infected with each of the MyRV1 variants appeared to be comparable to those for the corresponding normal segments in wild-type MyRV1-infected colonies, suggesting that the rearranged segments were fully competent for packaging and transcription. Protein products of the rearranged segments were detectable in fungal colonies infected with S2L MyRV1/S2L+S10ss2 and S3L MyRV1/S3L+S10ss2, whilst S1L-encoded protein remained undetectable. S1L, S2L and S3L were associated with enhancement of the aerial hyphae growth rate. This study has provided additional examples of MyRV1 intragenic rearrangements induced by p29, and suggests that normal S1, S2 and S3 are required for the symptoms caused by MyRV1.

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

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

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 ofmore » 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.« less

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

Strain Rate Effect on Tensile Flow Behavior and Anisotropy of a Medium-Manganese TRIP Steel

NASA Astrophysics Data System (ADS)

Alturk, Rakan; Hector, Louis G.; Matthew Enloe, C.; Abu-Farha, Fadi; Brown, Tyson W.

2018-06-01

The dependence of the plastic anisotropy on the nominal strain rate for a medium-manganese (10 wt.% Mn) transformation-induced plasticity (TRIP) steel with initial austenite volume fraction of 66% (balance ferrite) has been investigated. The material exhibited yield point elongation, propagative instabilities during hardening, and austenite transformation to α'-martensite either directly or through ɛ-martensite. Uniaxial strain rates within the range of 0.005-500 s-1 along the 0°, 45°, and 90° orientations were selected based upon their relevance to automotive applications. The plastic anisotropy ( r) and normal anisotropy ( r n) indices corresponding to each direction and strain rate were determined using strain fields obtained from stereo digital image correlation systems that enabled both quasistatic and dynamic measurements. The results provide evidence of significant, orientation-dependent strain rate effects on both the flow stress and the evolution of r and r n with strain. This has implications not only for material performance during forming but also for the development of future strain-rate-dependent anisotropic yield criteria. Since tensile data alone for the subject medium-manganese TRIP steel do not satisfactorily determine the microstructural mechanisms responsible for the macroscopic-scale behavior observed on tensile testing, additional tests that must supplement the mechanical test results presented herein are discussed.

Strain Rate Effect on Tensile Flow Behavior and Anisotropy of a Medium-Manganese TRIP Steel

NASA Astrophysics Data System (ADS)

Alturk, Rakan; Hector, Louis G.; Matthew Enloe, C.; Abu-Farha, Fadi; Brown, Tyson W.

2018-04-01

The dependence of the plastic anisotropy on the nominal strain rate for a medium-manganese (10 wt.% Mn) transformation-induced plasticity (TRIP) steel with initial austenite volume fraction of 66% (balance ferrite) has been investigated. The material exhibited yield point elongation, propagative instabilities during hardening, and austenite transformation to α'-martensite either directly or through ɛ-martensite. Uniaxial strain rates within the range of 0.005-500 s-1 along the 0°, 45°, and 90° orientations were selected based upon their relevance to automotive applications. The plastic anisotropy (r) and normal anisotropy (r n) indices corresponding to each direction and strain rate were determined using strain fields obtained from stereo digital image correlation systems that enabled both quasistatic and dynamic measurements. The results provide evidence of significant, orientation-dependent strain rate effects on both the flow stress and the evolution of r and r n with strain. This has implications not only for material performance during forming but also for the development of future strain-rate-dependent anisotropic yield criteria. Since tensile data alone for the subject medium-manganese TRIP steel do not satisfactorily determine the microstructural mechanisms responsible for the macroscopic-scale behavior observed on tensile testing, additional tests that must supplement the mechanical test results presented herein are discussed.

Strain rate effects for spallation of concrete

NASA Astrophysics Data System (ADS)

Häussler-Combe, Ulrich; Panteki, Evmorfia; Kühn, Tino

2015-09-01

Appropriate triaxial constitutive laws are the key for a realistic simulation of high speed dynamics of concrete. The strain rate effect is still an open issue within this context. In particular the question whether it is a material property - which can be covered by rate dependent stress strain relations - or mainly an effect of inertia is still under discussion. Experimental and theoretical investigations of spallation of concrete specimen in a Hopkinson Bar setup may bring some evidence into this question. For this purpose the paper describes the VERD model, a newly developed constitutive law for concrete based on a damage approach with included strain rate effects [1]. In contrast to other approaches the dynamic strength increase is not directly coupled to strain rate values but related to physical mechanisms like the retarded movement of water in capillary systems and delayed microcracking. The constitutive law is fully triaxial and implemented into explicit finite element codes for the investigation of a wide range of concrete structures exposed to impact and explosions. The current setup models spallation experiments with concrete specimen [2]. The results of such experiments are mainly related to the dynamic tensile strength and the crack energy of concrete which may be derived from, e.g., the velocity of spalled concrete fragments. The experimental results are compared to the VERD model and two further constitutive laws implemented in LS-Dyna. The results indicate that both viscosity and retarded damage are required for a realistic description of the material behaviour of concrete exposed to high strain effects [3].

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

Determination of Strain Rate Sensitivity of Micro-struts Manufactured Using the Selective Laser Melting Method

NASA Astrophysics Data System (ADS)

Gümrük, Recep; Mines, R. A. W.; Karadeniz, Sami

2018-03-01

Micro-lattice structures manufactured using the selective laser melting (SLM) process provides the opportunity to realize optimal cellular materials for impact energy absorption. In this paper, strain rate-dependent material properties are measured for stainless steel 316L SLM micro-lattice struts in the strain rate range of 10-3 to 6000 s-1. At high strain rates, a novel version of the split Hopkinson Bar has been developed. Strain rate-dependent materials data have been used in Cowper-Symonds material model, and the scope and limit of this model in the context of SLM struts have been discussed. Strain rate material data and the Cowper-Symonds model have been applied to the finite element analysis of a micro-lattice block subjected to drop weight impact loading. The model output has been compared to experimental results, and it has been shown that the increase in crush stress due to impact loading is mainly the result of strain rate material behavior. Hence, a systematic methodology has been developed to investigate the impact energy absorption of a micro-lattice structure manufactured using additive layer manufacture (SLM). This methodology can be extended to other micro-lattice materials and configurations, and to other impact conditions.

High Strain Rate and Shock-Induced Deformation in Metals

NASA Astrophysics Data System (ADS)

Ravelo, Ramon

2012-02-01

Large-scale non-equilibrium molecular Dynamics (MD) simulations are now commonly used to study material deformation at high strain rates (10^9-10^12 s-1). They can provide detailed information-- such as defect morphology, dislocation densities, and temperature and stress profiles, unavailable or hard to measure experimentally. Computational studies of shock-induced plasticity and melting in fcc and bcc single, mono-crystal metals, exhibit generic characteristics: high elastic limits, large directional anisotropies in the yield stress and pre-melting much below the equilibrium melt temperature for shock wave propagation along specific crystallographic directions. These generic features in the response of single crystals subjected to high strain rates of deformation can be explained from the changes in the energy landscape of the uniaxially compressed crystal lattice. For time scales relevant to dynamic shock loading, the directional-dependence of the yield strength in single crystals is shown to be due to the onset of instabilities in elastic-wave propagation velocities. The elastic-plastic transition threshold can accurately be predicted by a wave-propagation stability analysis. These strain-induced instabilities create incipient defect structures, which can be quite different from the ones, which characterize the long-time, asymptotic state of the compressed solid. With increase compression and strain rate, plastic deformation via extended defects gives way to amorphization associated with the loss in shear rigidity along specific deformation paths. The hot amorphous or (super-cooled liquid) metal re-crystallizes at rates, which depend on the temperature difference between the amorphous solid and the equilibrium melt line. This plastic-amorphous transition threshold can be computed from shear-waves stability analyses. Examples from selected fcc and bcc metals will be presented employing semi-empirical potentials of the embedded atom method (EAM) type as well as

On the use of a split Hopkinson pressure bar in structural geology: High strain rate deformation of Seeberger sandstone and Carrara marble under uniaxial compression

NASA Astrophysics Data System (ADS)

Zwiessler, Ruprecht; Kenkmann, Thomas; Poelchau, Michael H.; Nau, Siegfried; Hess, Sebastian

2017-04-01

There is increasing evidence that seismogenic fractures can propagate faster than the shear wave velocity of the surrounding rocks. Strain rates within the tip region of such super-shear earthquake ruptures can reach deformation conditions similar to impact processes, resulting in rock pulverization. The physical response of brittle rocks at high strain rates changes dramatically with respect to quasi-static conditions. Rocks become stiffer and their strength increases. A measure for the dynamic behavior of a rock and its strain dependency is the dynamic increase factor (DIF) which is the ratio of the dynamic compressive strength to the quasi-static uniaxial compressive strength. To investigate deformation in the high strain rate regime experimentally, we introduce the split Hopkinson pressure bar technology to the structural geology community, a method that is frequently used by rock and impact engineers. We measure the stress-strain response of homogeneous, fine-grained Seeberger sandstone and Carrara marble in uniaxial compression at strain rates ranging from 10+1 to 10+2 s-1 with respect to tangent modulus and dynamic uniaxial compressive strength. We present full stress-strain response curves of Seeberger sandstone and Carrara marble at high strain rates and an evaluation method to determine representative rates of deformation. Results indicate a rate-dependent elastic behavior of Carrara marble where an average increase of ∼18% could be observed at high strain rates of about 100 s-1. DIF reaches a factor of 2.2-2.4. Seeberger sandstone does not have a rate-dependent linear stress-strain response at high strain rates. Its DIF was found to be about 1.6-1.7 at rates of 100 s-1. The onset of dynamic behavior is accompanied with changes in the fracture pattern from single to multiple fractures to pervasive pulverization for increasing rates of deformation. Seismogenic shear zones and their associated fragment-size spectra should be carefully revisited in the

Assessment of a miniature four-roll mill and a cross-slot microchannel for high-strain-rate stagnation point flows

NASA Astrophysics Data System (ADS)

Akbaridoust, Farzan; Philip, Jimmy; Marusic, Ivan

2018-04-01

Stagnation point flows have been widely used to study the deformation and break-up of objects in two-dimensional pure straining flows. Here, we report a systematic study of the characterisation of stagnation point flows in two devices, a miniature Taylor’s four-roll mill and a cross-slot microchannel. The aim of the study is to find the best platform suitable for investigating the effect of strain rate on the mechanical properties of waterborne microorganisms. Using micro-PIV, the velocity field and the strain rates in both devices were measured at different flow rates and compared with an ideal hyperbolic stagnation point flow. The cross-slot microchannel was found to be a better experimental device than the miniature four-roll mill for the purpose of confining micron-sized objects in a controlled stagnation point flow. This is mainly due to the difficulty of maintaining a fixed location for the stagnation point within one micron in the miniature four-roll mill and achieving high strain rates beyond 10 s-1 . However, with no moving parts, the cross-slot microchannel was found to maintain a steady flow, with the stagnation point varying less than one micron at a cross-junction of 400× 400~μm2 , and was able to reach uniform strain rates up to 140 s-1 .

Effect of Strengthening Mechanism on Strain-Rate Related Tensile Properties of Low-Carbon Sheet Steels for Automotive Application

NASA Astrophysics Data System (ADS)

Das, Anindya; Biswas, Pinaki; Tarafder, S.; Chakrabarti, D.; Sivaprasad, S.

2018-05-01

In order to ensure crash resistance of the steels used in automotive components, the ensile deformation behavior needs to be studied and predicted not only under quasi-static condition, but also under dynamic loading rates. In the present study, tensile tests have been performed on four different automobile grade sheet steels, namely interstitial free steel, dual-phase 600 and 800, and a carbon manganese steel over the strain rate regime of 0.001-800/s. Apart from the variation in strength (which always increased with strain rate), the effect of strengthening mechanism on strain rate sensitivity and strain hardening behavior has been evaluated. Strain rate sensitivity was found to increase at high-strain rate regime for all the steels. Contribution of solid solution hardening on strain rate sensitivity at lower plastic strains was found to be higher compared to dislocation strengthening and second-phase hardening. However, precipitation hardening coupled with solid solution hardening produced the highest strain rate sensitivity, in C-Mn-440 steel at high strain rates. Different strain-rate-sensitive models which take into account the change in yield stress and strain hardening behavior with strain rate for ductile materials were used to predict the flow behavior of these sheet steels at strain rates up to 800/s.

High strain-rate soft material characterization via inertial cavitation

NASA Astrophysics Data System (ADS)

Estrada, Jonathan B.; Barajas, Carlos; Henann, David L.; Johnsen, Eric; Franck, Christian

2018-03-01

Mechanical characterization of soft materials at high strain-rates is challenging due to their high compliance, slow wave speeds, and non-linear viscoelasticity. Yet, knowledge of their material behavior is paramount across a spectrum of biological and engineering applications from minimizing tissue damage in ultrasound and laser surgeries to diagnosing and mitigating impact injuries. To address this significant experimental hurdle and the need to accurately measure the viscoelastic properties of soft materials at high strain-rates (103-108 s-1), we present a minimally invasive, local 3D microrheology technique based on inertial microcavitation. By combining high-speed time-lapse imaging with an appropriate theoretical cavitation framework, we demonstrate that this technique has the capability to accurately determine the general viscoelastic material properties of soft matter as compliant as a few kilopascals. Similar to commercial characterization algorithms, we provide the user with significant flexibility in evaluating several constitutive laws to determine the most appropriate physical model for the material under investigation. Given its straightforward implementation into most current microscopy setups, we anticipate that this technique can be easily adopted by anyone interested in characterizing soft material properties at high loading rates including hydrogels, tissues and various polymeric specimens.

Microstructure dependence of dynamic fracture and yielding in aluminum and an aluminum alloy at strain rates of 2 × 106 s-1 and faster

NASA Astrophysics Data System (ADS)

Dalton, D. A.; Worthington, D. L.; Sherek, P. A.; Pedrazas, N. A.; Quevedo, H. J.; Bernstein, A. C.; Rambo, P.; Schwarz, J.; Edens, A.; Geissel, M.; Smith, I. C.; Taleff, E. M.; Ditmire, T.

2011-11-01

Experiments investigating fracture and resistance to plastic deformation at fast strain rates (>106 s-1) were performed via laser ablation on thin sheets of aluminum and aluminum alloys. Single crystal high purity aluminum (Al-HP) and a single crystal 1100 series aluminum alloy (AA1100) were prepared to investigate the role of impurity particles. Specimens of aluminum alloy +3 wt. % Mg (Al+3Mg) at three different grain sizes were also studied to determine the effect of grain size. In the present experiments, high purity aluminum (Al-HP) exhibited the highest spall strength over 1100 series aluminum alloy (AA1100) and Al+3Mg. Fracture characterization and particle analysis revealed that fracture was initiated in the presence of particles associated with impurity content in the AA1100 and at both grain boundaries and particles in Al+3Mg. The Al+3Mg specimens exhibited the greatest resistance to plastic deformation likely resulting from the presence of magnesium atoms. The Al-HP and AA1100, both lacking a strengthening element such as Mg, were found to have the same Hugoniot elastic limit (HEL) stress. Within the single crystal specimens, orientation effects on spall strength and HEL stress appear to be negligible. Although the fracture character shows a trend with grain size, no clear dependence of spall strength and HEL stress on grain size was measured for the Al+3Mg. Hydrodynamic simulations show how various strength and fracture models are insufficient to predict material behavior at fast strain rates, and a revised set of Tuler-Butcher coefficients for spall are proposed.

High-Strain Rate Failure Modeling Incorporating Shear Banding and Fracture

DTIC Science & Technology

2017-11-22

High Strain Rate Failure Modeling Incorporating Shear Banding and Fracture The views, opinions and/or findings contained in this report are those of...SECURITY CLASSIFICATION OF: 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 13. SUPPLEMENTARY NOTES 12. DISTRIBUTION AVAILIBILITY STATEMENT 6. AUTHORS...Report as of 05-Dec-2017 Agreement Number: W911NF-13-1-0238 Organization: Columbia University Title: High Strain Rate Failure Modeling Incorporating

Effects of Strain Rate and Temperature on the Mechanical Properties of Medium Manganese Steels

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

Rana, Radhakanta; Matlock, David K; Speer, John G

2016-11-16

The effects of temperature (-60 to 100 °C) and strain rate (0.002 to 0.2 s-1) on the properties of Al-alloyed 7 and 10 wt-% Mn steels containing 34.8 and 57.3 vol-% austenite respectively were evaluated by tensile tests in isothermal liquid baths. The tensile strengths of both medium Mn steels increased with a decrease in temperature owing to the decreased austenite stability with a decrease in temperature. At lower temperatures the strength of the 10MnAl steel was highest, a consequence of the higher strain hardening rate caused by more austenite transformation to martensite with deformation. The resulting properties are assessedmore » with a consideration of the effects of strain rate and deformation on adiabatic heating which was observed to be as high as 95o C.« less

A New Global Geodetic Strain Rate Model

NASA Astrophysics Data System (ADS)

Kreemer, C. W.; Klein, E. C.; Blewitt, G.; Shen, Z.; Wang, M.; Chamot-Rooke, N. R.; Rabaute, A.

2012-12-01

As part of the Global Earthquake Model (GEM) effort to improve global seismic hazard models, we present a new global geodetic strain rate model. This model (GSRM v. 2) is a vast improvement on the previous model from 2004 (v. 1.2). The model is still based on a finite-element type approach and has deforming cells in between the assumed rigid plates. While v.1.2 contained ~25,000 deforming cells of 0.6° by 0.5° dimension, the new models contains >136,000 cells of 0.25° by 0.2° dimension. We redefined the geometries of the deforming zones based on the definitions of Bird (2003) and Chamot-Rooke and Rabaute (2006). We made some adjustments to the grid geometry at places where seismicity and/or GPS velocities suggested the presence of deforming areas where those previous studies did not. As a result, some plates/blocks identified by Bird (2003) we assumed to deform, and the total number of plates and blocks in GSRM v.2 is 38 (including the Bering block, which Bird (2003) did not consider). GSRM v.1.2 was based on ~5,200 GPS velocities, taken from 86 studies. The new model is based on ~17,000 GPS velocities, taken from 170 studies. The GPS velocity field consists of a 1) ~4900 velocities derived by us for CPS stations publicly available RINEX data and >3.5 years of data, 2) ~1200 velocities for China from a new analysis of all CMONOC data, and 3) velocities published in the literature or made otherwise available to us. All studies were combined into the same reference frame by a 6-parameter transformation using velocities at collocated stations. Because the goal of the project is to model the interseismic strain rate field, we model co-seismic jumps while estimating velocities, ignore periods of post-seismic deformation, and exclude time-series that reflect magmatic and anthropogenic activity. GPS velocities were used to estimate angular velocities for most of the 38 rigid plates and blocks (the rest being taken from the literature), and these were used as boundary

Texture studies of hot compressed near alpha titanium alloy (IMI 834) at 1000°C with different strain rates

NASA Astrophysics Data System (ADS)

Kodli, B. K.; Saxena, K. K.; Dey, S. R.; Pancholi, V.; Bhattacharjee, A.

2015-04-01

IMI 834 Titanium alloy is a near alpha (hcp) titanium alloy used for high temperature applications with the service temperature up to 600°C. Generally, this alloy is widely used in gas turbine engine applications such as low pressure compressor discs. For these applications, good fatigue and creep properties are required, which have been noticed better in a bimodal microstructure, containing 15-20% volume fraction of primary alpha grains (αp) and remaining bcc beta (β) grains transformed secondary alpha laths (αs). The bimodal microstructure is achieved during processing of IMI 834 in the high temperature α+β region. The major issue of bimodal IMI 834 during utilization is its poor dwell fatigue life time caused by textured macrozones. Textured macrozone is the spatial accumulation of similar oriented grains in the microstructure generated during hot processing in the high temperature α+β region. Textured macrozone can be mitigated by controlling the hot deformation with certain strain rate under stable plastic conditions having β grains undergoing dynamic recrystallization. Hence, a comprehensive study is required to understand the deformation behavior of α and β grains at different strain rates in that region. Hot compression tests up to 5°% strain of the samples are performed with five different strain rates i.e. 10-3 s-1, 10-2 s-1, 10-1 s-1, 1 s-1 and 10 s-1 at 1000°C using Gleeble 3800. The resultant bimodal microstructure and the texture studies of primary alpha grains (αp) and secondary alpha laths (αs) are carried out using scanning electron microscopy (SEM)-electron back scattered diffraction (EBSD) method.

Stereospecific oxidation of (R)- and (S)-1-indanol by naphthalene dioxygenase from Pseudomonas sp. strain NCIB 9816-4.

PubMed Central

Lee, K; Resnick, S M; Gibson, D T

1997-01-01

A recombinant Escherichia coli strain which expresses naphthalene dioxygenase (NDO) from Pseudomonas sp. strain NCIB 9816-4 oxidized (S)-1-indanol to trans-(1S,3S)-indan-1,3-diol (95.5%) and (R)-3-hydroxy-1-indanone (4.5%). The same cells oxidized (R)-1-indanol to cis-1,3-indandiol (71%), (R)-3-hydroxy-1-indanone (18.2%), and cis-1,2,3-indantriol (10.8%). Purified NDO oxidized (S)-1-indenol to both syn- and anti-2,3-dihydroxy-1-indanol. PMID:9143136

Stereospecific oxidation of (R)- and (S)-1-indanol by naphthalene dioxygenase from Pseudomonas sp. strain NCIB 9816-4.

PubMed

Lee, K; Resnick, S M; Gibson, D T

1997-05-01

A recombinant Escherichia coli strain which expresses naphthalene dioxygenase (NDO) from Pseudomonas sp. strain NCIB 9816-4 oxidized (S)-1-indanol to trans-(1S,3S)-indan-1,3-diol (95.5%) and (R)-3-hydroxy-1-indanone (4.5%). The same cells oxidized (R)-1-indanol to cis-1,3-indandiol (71%), (R)-3-hydroxy-1-indanone (18.2%), and cis-1,2,3-indantriol (10.8%). Purified NDO oxidized (S)-1-indenol to both syn- and anti-2,3-dihydroxy-1-indanol.

The Features of Fracture Behavior of an Aluminum-Magnesium Alloy AMg6 Under High-Rate Straining

NASA Astrophysics Data System (ADS)

Skripnyak, N. V.

2015-09-01

The results of investigation of fracture dynamics of rolled sheet specimens of an AMg6 alloy are presented for the range of strain rates from 10-3 to 103 s-1. It is found out that the presence of nanostructured surface layers on the thin AMg6 rolled sheets results in improved strength characteristics within the above range of strain rates. A modified model of a deforming medium is proposed to describe the plastic flow and fracture of the AMg6 alloy.

Deformation and spallation of a magnesium alloy under high strain rate loading

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

Wang, M.; Lu, L.; Li, C.

2016-04-01

We investigate deformation and damage of a magnesium alloy, AZ91, under high strain rate (similar to 10(5) s(-1)) loading via planar impact. The soft-recovered specimens are examined with electron back-scatter diffraction (EBSD). EBSD analysis reveals three types of twinning: {1012} extension, {10 (1) over bar1} contraction, and {10 (1) over bar1}-{10 (1) over bar2) double twinning, and their number density increases with increasing impact velocity. The extension twins dominate contraction and double twins in size and number. Dislocation densities of the recovered specimens are evaluated with x-ray diffraction, and increase with increasing impact velocity. X-ray tomography is used to resolvemore » three-dimensional microstructure of shock-recovered samples. The EBSD and tomography results demonstrate that the second phase, Mg17Al12, plays an important role in both deformation twinning and tensile cracking. Deformation twinning appears to be a common mechanism in deformation of magnesium alloys at low, medium and high strain rates, in addition to dislocation motion. (C) 2016 Elsevier B.V. All rights reserved.« less

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.

Large Strain Behaviour of ZEK100 Magnesium Alloy at Various Strain Rates

NASA Astrophysics Data System (ADS)

Lévesque, Julie; Kurukuri, Srihari; Mishra, Raja; Worswick, Michael; Inal, Kaan

A constitutive framework based on a rate-dependent crystal plasticity theory is employed to simulate large strain deformation in hexagonal closed-packed metals that deform by slip and twinning. The model allows the twinned zones and the parent matrix to rotate independently. ZEK100 magnesium alloy sheets which significant texture weakening compared to AZ31 sheets are investigated using the model. There is considerable in-plane anisotropy and tension compression asymmetry in the flow behavior of ZEK100. Simulations of uniaxial tension in different directions at various strain rates and the accompanying texture evolution are performed and they are in very good agreement with experimental measurements. The effect of strain rate on the activation of the various slip systems and twinning show that differences in the strain rate dependence of yield stress and Rvalues in ZEK100 have their origin in the activation of different deformation mechanisms.

Strain rate orientations near the Coso Geothermal Field

NASA Astrophysics Data System (ADS)

Ogasa, N. T.; Kaven, J. O.; Barbour, A. J.; von Huene, R.

2016-12-01

Many geothermal reservoirs derive their sustained capacity for heat exchange in large part due to continuous deformation of preexisting faults and fractures that permit permeability to be maintained. Similarly, enhanced geothermal systems rely on the creation of suitable permeability from fracture and faults networks to be viable. Stress measurements from boreholes or earthquake source mechanisms are commonly used to infer the tectonic conditions that drive deformation, but here we show that geodetic data can also be used. Specifically, we quantify variations in the horizontal strain rate tensor in the area surrounding the Coso Geothermal Field (CGF) by analyzing more than two decades of high accuracy differential GPS data from a network of 14 stations from the University of Nevada Reno Geodetic Laboratory. To handle offsets in the data, from equipment changes and coseismic deformation, we segment the data, perform a piecewise linear fit and take the average of each segment's strain rate to determine secular velocities at each station. With respect to North America, all stations tend to travel northwest at velocities ranging from 1 to 10 mm/yr. The nearest station to CGF shows anomalous motion compared to regional stations, which otherwise show a coherent increase in network velocity from the northeast to the southwest. We determine strain rates via linear approximation using GPS velocities in Cartesian reference frame due to the small area of our network. Principal strain rate components derived from this inversion show maximum extensional strain rates of 30 nanostrain/a occur at N87W with compressional strain rates of 37nanostrain/a at N3E. These results generally align with previous stress measurements from borehole breakouts, which indicate the least compressive horizontal principal stress is east-west oriented, and indicative of the basin and range tectonic setting. Our results suggest that the CGF represents an anomaly in the crustal deformation field, which

Dynamic High-temperature Testing of an Iridium Alloy in Compression at High-strain Rates: Dynamic High-temperature Testing

DOE PAGES

Song, B.; Nelson, K.; Lipinski, R.; ...

2014-08-21

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-strain -rate performance are needed for understanding high-speed impacts in severe 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. In our study, we analyzed the difficulties encountered in high-temperature Kolsky bar testing of thin iridium alloy specimens in compression. We made appropriate modifications using themore » current high-temperature Kolsky bar technique in order to obtain reliable compressive stress–strain response of an iridium alloy at high-strain rates (300–10 000 s -1) and temperatures (750 and 1030°C). The compressive stress–strain response of the iridium alloy showed significant sensitivity to both strain rate and temperature.« less

Relationships of left ventricular strain and strain rate to wall stress and their afterload dependency.

PubMed

Murai, Daisuke; Yamada, Satoshi; Hayashi, Taichi; Okada, Kazunori; Nishino, Hisao; Nakabachi, Masahiro; Yokoyama, Shinobu; Abe, Ayumu; Ichikawa, Ayako; Ono, Kota; Kaga, Sanae; Iwano, Hiroyuki; Mikami, Taisei; Tsutsui, Hiroyuki

2017-05-01

Whether and how left ventricular (LV) strain and strain rate correlate with wall stress is not known. Furthermore, it is not determined whether strain or strain rate is less dependent on the afterload. In 41 healthy young adults, LV global peak strain and systolic peak strain rate in the longitudinal direction (LS and LSR, respectively) and circumferential direction (CS and CSR, respectively) were measured layer-specifically using speckle tracking echocardiography (STE) before and during a handgrip exercise. Among all the points before and during the exercise, all the STE parameters significantly correlated linearly with wall stress (LS: r = -0.53, p < 0.01, LSR: r = -0.28, p < 0.05, CS in the inner layer: r = -0.72, p < 0.01, CSR in the inner layer: r = -0.47, p < 0.01). Strain more strongly correlated with wall stress than strain rate (r = -0.53 for LS vs. r = -0.28 for LSR, p < 0.05; r = -0.72 for CS vs. r = -0.47 for CSR in the inner layer, p < 0.05), whereas the interobserver variability was similar between strain and strain rate (longitudinal 6.2 vs. 5.2 %, inner circumferential 4.8 vs. 4.7 %, mid-circumferential 7.9 vs. 6.9 %, outer circumferential 10.4 vs. 9.7 %), indicating that the differences in correlation coefficients reflect those in afterload dependency. It was thus concluded that LV strain and strain rate linearly and inversely correlated with wall stress in the longitudinal and circumferential directions, and strain more strongly depended on afterload than did strain rate. Myocardial shortening should be evaluated based on the relationships between these parameters and wall stress.

Strain rate effects in stress corrosion cracking

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

Parkins, R.N.

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 maymore » 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.« less

Interseismic strain and rotation rates in the northeast Mojave domain, eastern California

USGS Publications Warehouse

Savage, J.C.; Svarc, J.L.; Prescott, II W.

2004-01-01

The northeast Mojave domain, a type locality for bookshelf faulting, is a region of east striking, left-lateral faults in the northeast comer of the Mojave block, a block otherwise dominated by ??N40??W striking, right-lateral faults. Paleomagnetic evidence suggests that blocks within the domain have rotated clockwise about a vertical axis as much as 60?? since 12.8 Ma [Schermer et al., 1996]. In 1994, and again in 2002, the U.S. Geological Survey surveyed an array of 14 geodetic monuments distributed across the northeast Mojave domain. The 2002 survey results were adjusted to remove the coseismic offsets imposed by the nearby Hector Mine earthquake (16 October 1999, Mw = 7.1). The adjusted deformation across the array appears to be uniform and can be approximated by the principal strain rates ??:1 = 28.9 ?? 9.1 N77.2??W ?? 4.8?? and ??2 = -48.2 ?? 8.9 N12.8??E ?? 4.8?? nstrain yr-1; extension reckoned positive, and quoted uncertainties are standard deviations. That strain accumulation could be released by slip . on faults striking N32??W but not by bookshelf faulting on the east striking faults alone. The vertical axis rotation rate of the northeast Mojave domain as a whole relative to fixed North America is 71.0 ?? 6.4 nrad yr-1 (4.07?? ?? 0.37?? Myr-1) clockwise, about twice the maximum tenser shear strain rate. The observed rotation rate acting over 12.8 Myr would produce'a clockwise rotation of 52.1?? ?? 4.7??, exclusive of possible coseismic rotations. That rotation is in rough agreement with the paleomagnetic rotation accumulated in the individual fault blocks within the northeast Mojave domain since 12.8 Ma.

Dynamic Mechanical Response of Biomedical 316L Stainless Steel as Function of Strain Rate and Temperature

PubMed Central

Lee, Woei-Shyan; Chen, Tao-Hsing; Lin, Chi-Feng; Luo, Wen-Zhen

2011-01-01

A split Hopkinson pressure bar is used to investigate the dynamic mechanical properties of biomedical 316L stainless steel under strain rates ranging from 1 × 103 s−1 to 5 × 103 s−1 and temperatures between 25°C and 800°C. The results indicate that the flow stress, work-hardening rate, strain rate sensitivity, and thermal activation energy are all significantly dependent on the strain, strain rate, and temperature. For a constant temperature, the flow stress, work-hardening rate, and strain rate sensitivity increase with increasing strain rate, while the thermal activation energy decreases. Catastrophic failure occurs only for the specimens deformed at a strain rate of 5 × 103 s−1 and temperatures of 25°C or 200°C. Scanning electron microscopy observations show that the specimens fracture in a ductile shear mode. Optical microscopy analyses reveal that the number of slip bands within the grains increases with an increasing strain rate. Moreover, a dynamic recrystallisation of the deformed microstructure is observed in the specimens tested at the highest temperature of 800°C. PMID:22216015

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.

Echocardiographic strain and strain-rate imaging: a new tool to study regional myocardial function.

PubMed

D'hooge, Jan; Bijnens, Bart; Thoen, Jan; Van de Werf, Frans; Sutherland, George R; Suetens, Paul

2002-09-01

Ultrasonic imaging is the noninvasive clinical imaging modality of choice for diagnosing heart disease. At present, two-dimensional ultrasonic grayscale images provide a relatively cheap, fast, bedside method to study the morphology of the heart. Several methods have been proposed to assess myocardial function. These have been based on either grayscale or motion (velocity) information measured in real-time. However, the quantitative assessment of regional myocardial function remains an important goal in clinical cardiology. To do this, ultrasonic strain and strain-rate imaging have been introduced. In the clinical setting, these techniques currently only allow one component of the true three-dimensional deformation to be measured. Clinical, multidimensional strain (rate) information can currently thus only be obtained by combining data acquired using different transducer positions. Nevertheless, given the appropriate postprocessing, the clinical value of these techniques has already been shown. Moreover, multidimensional strain and strain-rate estimation of the heart in vivo by means of a single ultrasound acquisition has been shown to be feasible. In this paper, the new techniques of ultrasonic strain rate and strain imaging of the heart are reviewed in terms of definitions, data acquisition, strain-rate estimation, postprocessing, and parameter extraction. Their clinical validation and relevance will be discussed using clinical examples on relevant cardiac pathology. Based on these examples, suggestions are made for future developments of these techniques.

Effect of strain on evolution of dynamic recrystallization in Nb-1 wt%Zr-0.1 wt%C alloy at 1500 and 1600 °C

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

Behera, A.N.

Uniaxial compression tests were carried out on Nb-1 wt%Zr-0.1 wt%C alloy at temperature of 1500 and 1600 °C and strain rate of 0.1 s{sup −1} to study the evolution of dynamic recrystallization with strain. Electron back scatter diffraction was used to quantify the microstructural evolution. Nb-1Zr-0.1C alloy showed a necklace structure at a strain of 0.9 when deformed at 1500 °C and at strain of 0.6 when deformed at 1600 °C, both at strain rate of 0.1 s{sup −1}. This suggested the occurrence of dynamic recrystallization. At 1500 °C and strain of 0.9 the local average misorientation and the grainmore » orientation spread was low confirming the presence of dynamic recrystallization at this deformation condition. At both 1500 and 1600 °C and all measured strains the recrystallized grains had a strong fiber component of <001>. - Highlights: • Necklace formation of dynamically recrystallized grains occurred at strain of 0.6 and 0.9 for 1500 and 1600 °C, respectively. • Equiaxed microstructures were seen with increase in strain for both 1500 and 1600 °C. • At large strains the predominant recrystallized texture evolved to <001> pole.« less

Microstructure and Strain Rate-Dependent Tensile Deformation Behavior of Fiber Laser-Welded Butt Joints of Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Liu, Yang; Dong, Danyang; Han, Zhiqiang; Yang, Zhibin; Wang, Lu; Dong, Qingwei

2018-05-01

The microstructure and tensile deformation behavior of the fiber laser-welded similar and dissimilar dual-phase (DP) steel joints over a wide range of strain rates from 10-3 to 103 s-1 were investigated for the further applications on the lightweight design of vehicles. The high strain rate dynamic tensile deformation process and full-field strain distribution of the base metals and welded joints were examined using the digital image correlation method and high-speed photography. The strain rate effects on the stress-strain responses, tensile properties, deformation, and fracture behavior of the investigated materials were analyzed. The yield stress (YS) and ultimate tensile strength (UTS) of the dissimilar DP780/DP980 welded joints were lying in-between those of the DP780 and DP980 base metals, and all materials exhibited positive strain rate dependence on the YS and UTS. Owing to the microstructure heterogeneity, the welded joints showed relatively lower ductility in terms of total elongation (TE) than those of the corresponding base metals. The strain localization started before the maximum load was reached, and the strain localization occurred earlier during the whole deformation process with increasing strain rate. As for the dissimilar welded joint, the strain localization tended to occur in the vicinity of the lowest hardness value across the welded joint, which was in the subcritical HAZ at the DP780 side. As the strain rate increased, the typical ductile failure characteristic of the investigated materials did not change.

Microstructure and Strain Rate-Dependent Tensile Deformation Behavior of Fiber Laser-Welded Butt Joints of Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Liu, Yang; Dong, Danyang; Han, Zhiqiang; Yang, Zhibin; Wang, Lu; Dong, Qingwei

2018-04-01

The microstructure and tensile deformation behavior of the fiber laser-welded similar and dissimilar dual-phase (DP) steel joints over a wide range of strain rates from 10-3 to 103 s-1 were investigated for the further applications on the lightweight design of vehicles. The high strain rate dynamic tensile deformation process and full-field strain distribution of the base metals and welded joints were examined using the digital image correlation method and high-speed photography. The strain rate effects on the stress-strain responses, tensile properties, deformation, and fracture behavior of the investigated materials were analyzed. The yield stress (YS) and ultimate tensile strength (UTS) of the dissimilar DP780/DP980 welded joints were lying in-between those of the DP780 and DP980 base metals, and all materials exhibited positive strain rate dependence on the YS and UTS. Owing to the microstructure heterogeneity, the welded joints showed relatively lower ductility in terms of total elongation (TE) than those of the corresponding base metals. The strain localization started before the maximum load was reached, and the strain localization occurred earlier during the whole deformation process with increasing strain rate. As for the dissimilar welded joint, the strain localization tended to occur in the vicinity of the lowest hardness value across the welded joint, which was in the subcritical HAZ at the DP780 side. As the strain rate increased, the typical ductile failure characteristic of the investigated materials did not change.

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.

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.

a Study on Strain Rate Effect in Collision Analysis of Rolling STOCK

NASA Astrophysics Data System (ADS)

Kim, Seung Rok; Koo, Jeong Seo

In this paper, the strain rate effect of energy absorption members in rolling stock is studied using the virtual testing model (VTM) for Korean high speed train (KHST). The VTM of KHST was simulated for two different strain rate conditions. The VTM is composed of FE models for structures, and nonlinear spring/damper models for dynamic components. To simplify numerical model for the full rake KHST, the first three units consist of full flexible multi-body dynamic models, and the remainder does 1-D spring/damper/mass models. To evaluate the strain rate effect of KHST, the crash simulation was performed under the accident scenario for a collision with a rigid mass of 15 tons at 110kph. The numerical results show that the overall crash response of the train is not largely affected as much as expected, but individual components have some different deformations according to strain rate. The deformation of the front end structure without strain rate effect is larger than that with it. However, the deformation of the rear end structure without strain rate effect is smaller than that with it. Finally, the intrusion of the driver's cabin is overestimated for no strain rate effect when compared to the case with it.

Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing.

PubMed

Bazant, Zdenek P; Caner, Ferhun C

2013-11-26

Although there exists a vast literature on the dynamic comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the -2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the -1/3 power of this rate. A dimensionless indicator of the comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow.

Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing

PubMed Central

Bažant, Zdeněk P.; Caner, Ferhun C.

2013-01-01

Although there exists a vast literature on the dynamic comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the −2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the −1/3 power of this rate. A dimensionless indicator of the comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow. PMID:24218624

Interactive Web Interface to the Global Strain Rate Map Project

NASA Astrophysics Data System (ADS)

Meertens, C. M.; Estey, L.; Kreemer, C.; Holt, W.

2004-05-01

An interactive web interface allows users to explore the results of a global strain rate and velocity model and to compare them to other geophysical observations. The most recent model, an updated version of Kreemer et al., 2003, has 25 independent rigid plate-like regions separated by deformable boundaries covered by about 25,000 grid areas. A least-squares fit was made to 4900 geodetic velocities from 79 different geodetic studies. In addition, Quaternary fault slip rate data are used to infer geologic strain rate estimates (currently only for central Asia). Information about the style and direction of expected strain rate is inferred from the principal axes of the seismic strain rate field. The current model, as well as source data, references and an interactive map tool, are located at the International Lithosphere Program (ILP) "A Global Strain Rate Map (ILP II-8)" project website: http://www-world-strain-map.org. The purpose of the ILP GSRM project is to provide new information from this, and other investigations, that will contribute to a better understanding of continental dynamics and to the quantification of seismic hazards. A unique aspect of the GSRM interactive Java map tool is that the user can zoom in and make custom views of the model grid and results for any area of the globe selecting strain rate and style contour plots and principal axes, observed and model velocity fields in specified frames of reference, and geologic fault data. The results can be displayed with other data sets such Harvard CMT earthquake focal mechanisms, stress directions from the ILP World Stress Map Project, and topography. With the GSRM Java map tool, the user views custom maps generated by a Generic Mapping Tool (GMT) server. These interactive capabilities greatly extend what is possible to present in a published paper. A JavaScript version, using pre-constructed maps, as well as a related information site have also been created for broader education and outreach access

Engineering the Transformation Strain in LiMn y Fe 1–y PO 4 Olivines for Ultrahigh Rate Battery Cathodes

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

Ravnsbæk, Dorthe B.; Xiang, Kai; Xing, Wenting

2016-04-13

Alkali ion intercalation compounds used as battery electrodes often exhibit first-order phase transitions during electro-chemical cycling, accompanied by significant transformation strains. Despite 30 years of research into the behavior of such compounds, the relationship between transformation strain and electrode performance, especially the rate at which working ions (e.g., Li) can be intercalated and deintercalated, is still absent. In this work, we use the LiMn yFe 1-yPO 4 system for a systematic study, and measure using operando synchrotron radiation powder X-ray diffraction (SR-PXD) the dynamic strain behavior as a function of the Mn content (y) in powders of similar to 50more » nm average diameter. The dynamically produced strain deviates significantly from what is expected from the equilibrium phase diagrams and demonstrates metastability but nonetheless spans a wide range from 0 to 8 vol % with y. For the first time, we show that the discharge capacity at high C-rates (20-50C rate) varies in inverse proportion to the transformation strain, implying that engineering electrode materials for reduced strain can be used to maximize the power capability of batteries.« less

Strain rate effects on reinforcing steels in tension

NASA Astrophysics Data System (ADS)

Cadoni, Ezio; Forni, Daniele

2015-09-01

It is unquestionable the fact that a structural system should be able to fulfil the function for which it was created, without being damaged to an extent disproportionate to the cause of damage. In addition, it is an undeniable fact that in reinforced concrete structures under severe dynamic loadings, both concrete and reinforcing bars are subjected to high strain-rates. Although the behavior of the reinforcing steel under high strain rates is of capital importance in the structural assessment under the abovementioned conditions, only the behaviour of concrete has been widely studied. Due to this lack of data on the reinforcing steel under high strain rates, an experimental program on rebar reinforcing steels under high strain rates in tension is running at the DynaMat Laboratory. In this paper a comparison of the behaviour in a wide range of strain-rates of several types of reinforcing steel in tension is presented. Three reinforcing steels, commonly proposed by the European Standards, are compared: B500A, B500B and B500C. Lastly, an evaluation of the most common constitutive laws is performed.

Simultaneous Presence of PrtH and PrtH2 Proteinases in Lactobacillus helveticus Strains Improves Breakdown of the Pure αs1-Casein▿ †

PubMed Central

Sadat-Mekmene, L.; Jardin, J.; Corre, C.; Mollé, D.; Richoux, R.; Delage, M.-M.; Lortal, S.; Gagnaire, V.

2011-01-01

Lactobacillus helveticus can possess one or two cell envelope proteinases (CEPs), called PrtH2 and PrtH. The aim of this work was to explore the diversity of 15 strains of L. helveticus, isolated from various origins, in terms of their proteolytic activities and specificities on pure caseins or on milk casein micelles. CEP activity differed 14-fold when the strains were assayed on a synthetic substrate, but no significant differences were detected between strains possessing one or two CEPs. No correlation was observed between the proteolytic activities of the strains and their rates of acidification in milk. The kinetics of hydrolysis of purified αs1- and β-casein by L. helveticus whole cells was monitored using Tris-Tricine sodium dodecyl sulfate (SDS) electrophoresis, and for four strains, the peptides released were identified using mass spectrometry. While rapid hydrolysis of pure β-casein was observed for all strains, the hydrolysis kinetics of αs1-casein was the only criterion capable of distinguishing between the strains based on the number of CEPs. Fifty-four to 74 peptides were identified for each strain. When only PrtH2 was present, 22 to 30% of the peptides originated from αs1-casein. The percentage increased to 41 to 49% for strains in which both CEPs were expressed. The peptide size ranged from 6 to 33 amino acids, revealing a broad range of cleavage specificities, involving all classes of amino acids (Leu, Val, Ala, Ile, Glu, Gln, Lys, Arg, Met, and Pro). Regions resistant to proteolysis were identified in both caseins. When strains were grown in milk, a drastic reduction in the number of peptides was observed, reflecting changes in accessibility and/or peptide assimilation during growth. PMID:21037305

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.

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

DOE PAGES

Song, Bo; Sanborn, Brett

2018-05-07

In this paper, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that eithermore » constant engineering or constant true strain rate is attained during the experiment.« less

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

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

Song, Bo; Sanborn, Brett

In this paper, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that eithermore » constant engineering or constant true strain rate is attained during the experiment.« less

Dynamic Brazilian Test of Rock Under Intermediate Strain Rate: Pendulum Hammer-Driven SHPB Test and Numerical Simulation

NASA Astrophysics Data System (ADS)

Zhu, W. C.; Niu, L. L.; Li, S. H.; Xu, Z. H.

2015-09-01

The tensile strength of rock subjected to dynamic loading constitutes many engineering applications such as rock drilling and blasting. The dynamic Brazilian test of rock specimens was conducted with the split Hopkinson pressure bar (SHPB) driven by pendulum hammer, in order to determine the indirect tensile strength of rock under an intermediate strain rate ranging from 5.2 to 12.9 s-1, which is achieved when the incident bar is impacted by pendulum hammer with different velocities. The incident wave excited by pendulum hammer is triangular in shape, featuring a long rising time, and it is considered to be helpful for achieving a constant strain rate in the rock specimen. The dynamic indirect tensile strength of rock increases with strain rate. Then, the numerical simulator RFPA-Dynamics, a well-recognized software for simulating the rock failure under dynamic loading, is validated by reproducing the Brazilian test of rock when the incident stress wave retrieved at the incident bar is input as the boundary condition, and then it is employed to study the Brazilian test of rock under the higher strain rate. Based on the numerical simulation, the strain-rate dependency of tensile strength and failure pattern of the Brazilian disc specimen under the intermediate strain rate are numerically simulated, and the associated failure mechanism is clarified. It is deemed that the material heterogeneity should be a reason for the strain-rate dependency of rock.

Experimental Study and Modelling of Poly (Methyl Methacrylate) and Polycarbonate Compressive Behavior from Low to High Strain Rates

NASA Astrophysics Data System (ADS)

El-Qoubaa, Z.; Colard, L.; Matadi Boumbimba, R.; Rusinek, A.

2018-06-01

This paper concerns an experimental investigation of Polycarbonate and Poly (methyl methacrylate) compressive behavior from low to high strain rates. Experiments were conducted from 0.001/s to ≈ 5000/s for PC and from 0.001/s to ≈ 2000/s for PMMA. The true strain-stress behavior is established and analyzed at various stain rates. Both PC and PMMA mechanical behavior appears as known, to be strain rate and temperature dependent. The DSGZ model is selected for modelling the strain-stress curves while the yield stress is reproduced using the cooperative model and a modified Eyring equation based on Eyring first process theory. All the three models predictions are in agreement with experiments performed on PC and PMMA.

Experimental Study and Modelling of Poly (Methyl Methacrylate) and Polycarbonate Compressive Behavior from Low to High Strain Rates

NASA Astrophysics Data System (ADS)

El-Qoubaa, Z.; Colard, L.; Matadi Boumbimba, R.; Rusinek, A.

2018-03-01

This paper concerns an experimental investigation of Polycarbonate and Poly (methyl methacrylate) compressive behavior from low to high strain rates. Experiments were conducted from 0.001/s to ≈ 5000/s for PC and from 0.001/s to ≈ 2000/s for PMMA. The true strain-stress behavior is established and analyzed at various stain rates. Both PC and PMMA mechanical behavior appears as known, to be strain rate and temperature dependent. The DSGZ model is selected for modelling the strain-stress curves while the yield stress is reproduced using the cooperative model and a modified Eyring equation based on Eyring first process theory. All the three models predictions are in agreement with experiments performed on PC and PMMA.

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

Strain rate sensitivity of the tensile strength of two silicon carbides: experimental evidence and micromechanical modelling.

PubMed

Zinszner, Jean-Luc; Erzar, Benjamin; Forquin, Pascal

2017-01-28

Ceramic materials are commonly used to design multi-layer armour systems thanks to their favourable physical and mechanical properties. However, during an impact event, fragmentation of the ceramic plate inevitably occurs due to its inherent brittleness under tensile loading. Consequently, an accurate model of the fragmentation process is necessary in order to achieve an optimum design for a desired armour configuration. In this work, shockless spalling tests have been performed on two silicon carbide grades at strain rates ranging from 10 3 to 10 4  s -1 using a high-pulsed power generator. These spalling tests characterize the tensile strength strain rate sensitivity of each ceramic grade. The microstructural properties of the ceramics appear to play an important role on the strain rate sensitivity and on the dynamic tensile strength. Moreover, this experimental configuration allows for recovering damaged, but unbroken specimens, giving unique insight on the fragmentation process initiated in the ceramics. All the collected data have been compared with corresponding results of numerical simulations performed using the Denoual-Forquin-Hild anisotropic damage model. Good agreement is observed between numerical simulations and experimental data in terms of free surface velocity, size and location of the damaged zones along with crack density in these damaged zones.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'. © 2016 The Author(s).

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

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.

Stress Orientations and Strain Rates in the Upper Plate of a `Locked' subduction zone, at southernmost North Island, New Zealand

NASA Astrophysics Data System (ADS)

Evanzia, D. A. D.; Lamb, S. H.; Savage, M. K.

2017-12-01

The southern North Island, New Zealand is located at the southern Hikurangi Margin, where the Pacific Plate is obliquely subducting westward underneath the Australian Plate. The orientations of the principle stresses in the overriding plate are determined from microseismic focal mechanisms detected and located using the temporary SAHKE and permanent GeoNet seismic array operating during 2009-2010. The microseismic earthquakes are located with the NonLinLoc method, using a New Zealand specific 3D velocity model; only those earthquakes located above the modelled subduction plate interface are used. Strain rate parameters calculations are calculated using cGPS velocities from 56 stations located from the central North Island to the northernmost South Island, New Zealand. In the region west of the Tararua-range-bounding Wairarapa fault (the Western region), the orientations of stresses indicate a normal regime (S1: vertical; S2 & S3: horizontal), with SHmax trending ENE. In the Central Basin region (east of the Wairarapa fault) the orientations of the stresses indicate a reverse regime (S3: vertical; S1 & S2: horizontal), with SHmax orientated NW. The low seismicity rates in the Eastern region make the results unreliable. There is a distinct difference between the strain rate and vorticity on either side the Wairarapa fault. Strain rate and vorticity rates increase west and decreased east of the Wairarapa; this correlates well with the pattern of observed seismicity. The southern North Island is predominately contracting, except for a region on the West coast, where some expansion is occurs. This pattern of expansion in the West and contraction in the center of the study area, calculated from cGPS, is similar the stress inversion results calculated from focal mechanisms. These similarities suggest that the present stress and strain rates are collinear, as occurs in isotropic media.

Isolation of endosulfan sulfate-degrading Rhodococcus koreensis strain S1-1 from endosulfan contaminated soil and identification of a novel metabolite, endosulfan diol monosulfate

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

Ito, Koji; Kawashima, Fujimasa; Organochemicals Division, National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki, 305-8604

2016-05-13

An aerobic endosulfan sulfate-degrading bacterium, Rhodococcus koreensis strain S1-1, was isolated from soil to which endosulfan had been applied annually for more than 10 years until 2008. The strain isolated in this work reduced the concentration of endosulfan sulfate (2) from 12.25 μM to 2.11 μM during 14 d at 30 °C. Using ultra performance liquid chromatography-electrospray ionization-mass spectroscopy (UPLC-ESI-MS), a new highly water-soluble metabolite possessing six chlorine atoms was found to be endosulfan diol monosulfate (6), derived from 2 by hydrolysis of the cyclic sulfate ester ring. The structure of 6 was elucidated by chemical synthesis of the candidate derivatives and by HR-MSmore » and UPLC-MS analyses. Therefore, it was suggested that the strain S1-1 has a new metabolic pathway of 2. In addition, 6 was expected to be less toxic among the metabolites of 1 because of its higher water-solubility. -- Highlights: •A novel endosulfan sulfate-degrading bacterium was isolated and named strain S1-1. •Strain S1-1 degraded endosulfan sulfate into a novel metabolite endosulfan diol monosulfate. •Endosulfan diol monosulfate showed higher polarity than other known metabolites of endosulfan. •We proposed the plausible metabolic pathway of endosulfan in terms of organic chemistry.« less

Shrinkage strain-rates of dental resin-monomer and composite systems.

PubMed

Atai, Mohammad; Watts, David C; Atai, Zahra

2005-08-01

The purpose of this study was to investigate the shrinkage strain rate of different monomers, which are commonly used in dental composites and the effect of monomer functionality and molecular mass on the rate. Bis-GMA, TEGDMA, UDMA, MMA, HEMA, HPMA and different ratios of Bis-GMA/TEGDMA were mixed with Camphorquinone and Dimethyl aminoethyle methacrylate as initiator system. The shrinkage strain of the samples photopolymerised at Ca. 550 mW/cm2 and 23 degrees C was measured using the bonded-disk technique of Watts and Cash (Meas. Sci. Technol. 2 (1991) 788-794), and initial shrinkage-strain rates were obtained by numerical differentiation. Shrinkage-strain rates rose rapidly to a maximum, and then fell rapidly upon vitrification. Strain and initial strain rate were dependent upon monomer functionality, molecular mass and viscosity. Strain rates were correlated with Bis-GMA in Bis-GMA/TEGDMA mixtures up to 75-80 w/w%, due to the higher molecular mass of Bis-GMA affecting termination reactions, and then decreased due to its higher viscosity affecting propagation reactions. Monofunctional monomers exhibited lower rates. UDMA, a difunctional monomer of medium viscosity, showed the highest shrinkage strain rate (P < 0.05). Shrinkage strain rate, related to polymerization rate, is an important factor affecting the biomechanics and marginal integrity of composites cured in dental cavities. This study shows how this is related to monomer molecular structure and viscosity. The results are significant for the production, optimization and clinical application of dental composite restoratives.

The Effect of Strain Rate on the Evolution of Plane Wakes Subjected to Irrotational Strains

NASA Technical Reports Server (NTRS)

Rogers, Michael M.; Merriam, Marshal (Technical Monitor)

1996-01-01

Direct numerical simulations of time-evolving turbulent plane wakes developing in the presence of irrotational plane strain applied at three different strain rates have been generated. The strain geometry is such that the flow is compressed in the streamwise direction and expanded in the cross-stream direction with the spanwise direction being unstrained. This geometry is the temporally evolving analogue of a spatially evolving wake in an adverse pressure gradient. A pseudospectral numerical method with up to 16 million modes is used to solve the equations in a reference frame moving with the irrotational strain. The initial condition for each simulation is taken from a previous turbulent self-similar plane wake direct numerical simulation at a velocity deficit Reynolds number, Re, of about 2,000. Although the evolutions of many statistics are nearly collapsed when plotted against total strain, there are some differences owing to the different strain rate histories. The impact of strain-rate on the wake spreading rate, the peak velocity deficit, the Reynolds stress profiles, and the flow structure is examined.

Tensile characterisation of the aorta across quasi-static to blast loading strain rates

NASA Astrophysics Data System (ADS)

Magnus, Danyal; Proud, William; Haller, Antoine; Jouffroy, Apolline

2017-06-01

The dynamic tensile failure mechanisms of the aorta during Traumatic Aortic Injury (TAI) are poorly understood. In automotive incidents, where the aorta may be under strains of the order of 100/s, TAI is the second largest cause of mortality. In these studies, the proximal descending aorta is the most common site where rupture is observed. In particular, the transverse direction is most commonly affected due to the circumferential orientation of elastin, and hence the literature generally concentrates upon axial samples. This project extends these dynamic studies to the blast loading regime where strain-rates are of the order of 1000/s. A campaign of uniaxial tensile experiments are conducted at quasi-static, intermediate (drop-weight) and high (tensile Split-Hopkinson Pressure Bar) strain rates. In each case, murine and porcine aorta models are considered and the extent of damage assessed post-loading using histology. Experimental data will be compared against current viscoelastic models of the aorta under axial stress. Their applicability across strain rates will be discussed. Using a multi-disciplinary approach, the conditions applied to the samples replicate in vivo conditions, employing a blood simulant-filled tubular specimen surrounded by a physiological solution.

Shock structures at ultrahigh strain rates: what can they tell us about material behavior on very fast time scales?

NASA Astrophysics Data System (ADS)

Crowhurst, Jonathan

2013-06-01

In recent years, techniques based on table-top laser systems have shown promise for investigating dynamic material behavior at high rates of both compressive and tensile strain. Common to these techniques is a laser pulse that is used in some manner to rapidly deliver energy to the sample; while the energy itself is often comparatively very small, the intensity can be made high by tightly focusing the pump light. In this way pressures or stresses can be obtained that are sufficiently large to have relevance to a wide range of basic and applied fields. Also, when combined with established ultrafast diagnostics these experiments provide very high time resolution which is particularly desirable when studying, for example shock waves, in which the time for the material to pass from undisturbed to fully compressed (the ``rise time'') can be extremely short (order 10 ps or less) even at fairly small peak stresses. Since much of the most interesting physics comes into play during this process it is important to be able to adequately resolve the shock rise. In this context I will discuss our measurements on aluminum and iron thin films and compare the results with known behavior observed at lower strain rates. Specifically, for aluminum, I will compare our assumed steady wave data at strain rates of up to 1010 s-1 to literature data up to ~107 s-1 and show that the well-known fourth power scaling relation of strain rate to shock stress is maintained even at these very high strain rates. For iron, I will show how we have used our nonsteady data (up to ~109 s-1) to infer a number of important properties of the alpha to epsilon polymorphic transition: 1. The transition can occur on the tens of ps time scale at sufficiently high strain rates and corresponding very large deviatoric stresses, and 2, most of the material appears to transform at a substantially higher stress than the nominal value usually inferred from shock wave experiments of about 13 GPa. This work was

Constitutive equations for multiphase TRIP steels at high rates of strain

NASA Astrophysics Data System (ADS)

van Slycken, J.; Verleysen, P.; Degrieck, J.; Bouquerel, J.

2006-08-01

Multiphase TRansformation Induced Plasticity (TRIP) steels show an excellent combination of high strength and high strain values, making them ideally suited for use in vehicle body structures. A complex synergy of three different phases (ferrite, bainite and austenite) on the one hand, and the meta-stable character of the austenite on the other hand, give the material indeed a high energy absorption potential. The knowledge and understanding of the dynamic behaviour of these sheet steels is essential to investigate the impact-dynamic characteristics of the structures. Therefore split Hopkinson tensile tests are performed in a strain rate range of 500 to 2000 s-1. Three TRIP steel grades with a different Al and Si content were studied. The experimental results show that these steels preserve their excellent shock-absorbing properties in dynamic conditions. The typical high strain rate loading conditions and the complex behaviour of TRIP steels offer a unique investigation opportunity. This behaviour can be described with phenomenological material models that can be used for numerical simulations of car crashes. The Johnson-Cook model, a frequently used model in finite element codes, is well-suited to describe the dynamic behaviour of the investigated TRIP steels. This model is compared to the Rusinek-Klepaczko model.

Constant strain accumulation rate between major earthquakes on the North Anatolian Fault.

PubMed

Hussain, Ekbal; Wright, Tim J; Walters, Richard J; Bekaert, David P S; Lloyd, Ryan; Hooper, Andrew

2018-04-11

Earthquakes are caused by the release of tectonic strain accumulated between events. Recent advances in satellite geodesy mean we can now measure this interseismic strain accumulation with a high degree of accuracy. But it remains unclear how to interpret short-term geodetic observations, measured over decades, when estimating the seismic hazard of faults accumulating strain over centuries. Here, we show that strain accumulation rates calculated from geodetic measurements around a major transform fault are constant for its entire 250-year interseismic period, except in the ~10 years following an earthquake. The shear strain rate history requires a weak fault zone embedded within a strong lower crust with viscosity greater than ~10 20  Pa s. The results support the notion that short-term geodetic observations can directly contribute to long-term seismic hazard assessment and suggest that lower-crustal viscosities derived from postseismic studies are not representative of the lower crust at all spatial and temporal scales.

Effects of the Strain Rate and Temperature on the Microstructural Evolution of Twin-Rolled Cast Wrought AZ31B Alloys Sheets

NASA Astrophysics Data System (ADS)

Rodriguez, A. K.; Kridli, G.; Ayoub, G.; Zbib, H.

2013-10-01

This article investigates the effects of the strain rate and temperature on the microstructural evolution of twin-rolled cast wrought AZ31B sheets. This was achieved through static heating and through tensile test performed at strain rates from 10-4 to 10-1 s-1 and temperatures between room temperature (RT) and 300 °C. While brittle fracture with high stresses and limited elongation was observed at the RT, ductile behavior was obtained at higher temperatures with low strain rates. The strain rate sensitivity and activation energy calculations indicate that grain boundary diffusion and lattice diffusion are the two rate-controlling mechanisms at warm and high temperatures, respectively. An analysis of the evolution of the microstructure provided some indications of the most probable deformation mechanisms in the material: twinning operates at lower temperatures, and dynamic recrystallization dominates at higher temperatures. The static evolution of the microstructure was also studied, proving a gradual static grain growth of the AZ31B with annealing temperature and time.

Effect of strain rate and notch geometry on tensile properties and fracture mechanism of creep strength enhanced ferritic P91 steel

NASA Astrophysics Data System (ADS)

Pandey, Chandan; Mahapatra, M. M.; Kumar, Pradeep; Saini, N.

2018-01-01

Creep strength enhanced ferritic (CSEF) P91 steel were subjected to room temperature tensile test for quasi-static (less than 10-1/s) strain rate by using the Instron Vertical Tensile Testing Machine. Effect of different type of notch geometry, notch depth and angle on mechanical properties were also considered for different strain rate. In quasi-static rates, the P91 steel showed a positive strain rate sensitivity. On the basis of tensile data, fracture toughness of P91 steel was also calculated numerically. For 1 mm notch depth (constant strain rate), notch strength and fracture toughness were found to be increased with increase in notch angle from 45° to 60° while the maximum value attained in U-type notch. Notch angle and notch depth has found a minute effect on P91 steel strength and fracture toughness. The fracture surface morphology was studied by field emission scanning electron microscopy (FESEM).

vacA s1m1 genotype and cagA EPIYA-ABC pattern are predominant among Helicobacter pylori strains isolated from Mexican patients with chronic gastritis.

PubMed

Atrisco-Morales, Josefina; Martínez-Santos, Verónica I; Román-Román, Adolfo; Alarcón-Millán, Judit; De Sampedro-Reyes, José; Cruz-Del Carmen, Iván; Martínez-Carrillo, Dinorah N; Fernández-Tilapa, Gloria

2018-03-01

Virulent genotypes of Helicobacter pylori vacA s1m1/cagA + /babA2 + have been associated with severe gastric diseases. VacA, CagA and BabA are polymorphic proteins, and their association with the disease is allele-dependent. The aims of this work were: (i) to determine the prevalence of H. pylori by type of chronic gastritis; (ii) to describe the frequency of cagA, babA2 and vacA genotypes in strains from patients with different types of chronic gastritis; (iii) to characterize the variable region of cagA alleles. A total of 164 patients with chronic gastritis were studied. Altogether, 50 H. pylori strains were isolated, and the status of cagA, babA2 and vacA genotypes was examined by PCR. cagA EPIYA segment identification was performed using PCR and sequencing of cagA fragments of six randomly selected strains.Results/Key findings. The overall prevalence of H. pylori was 30.5 %. Eighty percent of the isolated strains were vacA s1m1, and the cagA and babA2 genes were detected in 74 and 32 % of the strains, respectively. The most frequent genotypes were vacA s1m1/cagA + /babA2 - and vacA s1m1/cagA + /babA2 + , with 40 % (20/50) and 28 % (14/50), respectively. In cagA + , the most frequent EPIYA motif was -ABC (78.4 %), and EPIYA-ABCC and -ABCCC motifs were found in 10.8 % of the strains. A modified EPIYT-B motif was found in 66.6 % of the sequenced strains. H. pylori strains carrying vacA s1m1, cagA + and babA2 - genotypes were the most prevalent in patients with chronic gastritis from the south of Mexico. In the cagA + strains, the EPIYA-ABC motif was the most common.

vacA s1m1 genotype and cagA EPIYA-ABC pattern are predominant among Helicobacter pylori strains isolated from Mexican patients with chronic gastritis

PubMed Central

Atrisco-Morales, Josefina; Martínez-Santos, Verónica I.; Román-Román, Adolfo; Alarcón-Millán, Judit; De Sampedro-Reyes, José; Cruz-del Carmen, Iván; Martínez-Carrillo, Dinorah N.; Fernández-Tilapa, Gloria

2018-01-01

Purpose Virulent genotypes of Helicobacter pylori vacA s1m1/cagA+/babA2+ have been associated with severe gastric diseases. VacA, CagA and BabA are polymorphic proteins, and their association with the disease is allele-dependent. The aims of this work were: (i) to determine the prevalence of H. pylori by type of chronic gastritis; (ii) to describe the frequency of cagA, babA2 and vacA genotypes in strains from patients with different types of chronic gastritis; (iii) to characterize the variable region of cagA alleles. Methodology A total of 164 patients with chronic gastritis were studied. Altogether, 50 H. pylori strains were isolated, and the status of cagA, babA2 and vacA genotypes was examined by PCR. cagA EPIYA segment identification was performed using PCR and sequencing of cagA fragments of six randomly selected strains. Results/Key findings The overall prevalence of H. pylori was 30.5 %. Eighty percent of the isolated strains were vacA s1m1, and the cagA and babA2 genes were detected in 74 and 32 % of the strains, respectively. The most frequent genotypes were vacA s1m1/cagA+/babA2- and vacA s1m1/cagA+/babA2+, with 40 % (20/50) and 28 % (14/50), respectively. In cagA+, the most frequent EPIYA motif was -ABC (78.4 %), and EPIYA-ABCC and -ABCCC motifs were found in 10.8 % of the strains. A modified EPIYT-B motif was found in 66.6 % of the sequenced strains. Conclusion H. pylori strains carrying vacA s1m1, cagA+ and babA2- genotypes were the most prevalent in patients with chronic gastritis from the south of Mexico. In the cagA+ strains, the EPIYA-ABC motif was the most common. PMID:29458667

A New Global Geodetic Strain Rate Model

NASA Astrophysics Data System (ADS)

Kreemer, C.; Blewitt, G.; Klein, E. C.; Shen, Z.; Wang, M.; Estey, L.; Wier, S.

2013-12-01

As part of the Global Earthquake Model (GEM) effort to improve global seismic hazard models, we present a new global geodetic strain rate model. This model (GSRM v. 2) is a vast improvement on the previous model from 2004 (v. 1.2). The model is still based on a finite-element type approach and has deforming cells in between the assumed rigid plates. The new model contains ~144,700 cells of 0.25° by 0.2° dimension. We redefined the geometries of the deforming zones based on the definitions of Bird (2003) and Chamot-Rooke and Rabaute (2006). We made some adjustments to the grid geometry at places where seismicity and/or GPS velocities suggested either the presence of deforming areas or a rigid block where those previous studies did not. GSRM v.2 includes 50 plates and blocks, including many not considered by Bird (2003). The new GSRM model is based on over 20,700 horizontal geodetic velocities at over 17,000 unique locations. The GPS velocity field consists of a 1) Over 6500 velocities derived by the University of Nevada, Reno, for CGPS stations for which >2.5 years of RINEX data are available until April 2013, 2) ~1200 velocities for China from a new analysis of all data from the Crustal Movement Network of China (CMONOC), and 3) about 13,000 velocities from 212 studies published in the literature or made otherwise available to us. Velocities from all studies were combined into the same reference frame by a 6-parameter transformation using velocities at collocated stations. We model co-seismic jumps while estimating velocities, ignore periods of post-seismic deformation, and exclude time-series that reflect magmatic and anthropogenic activity. GPS velocities were used to estimate angular velocities for 36 of the 50 rigid plates and blocks (the rest being taken from the literature), and these were used as boundary conditions in the strain rate calculations. For the strain rate calculations we used the method of Haines and Holt. In order to fit the data equally well

Strain Rate Dependency of Fracture Toughness, Energy Release Rate and Geomechanical Attributes of Select Indian Shales

NASA Astrophysics Data System (ADS)

Mahanta, B.; Vishal, V.; Singh, T. N.; Ranjith, P.

2016-12-01

In addition to modern improved technology, it requires detailed understanding of rock fractures for the purpose of enhanced energy extraction through hydraulic fracturing of gas shales and geothermal energy systems. The understanding of rock fracture behavior, patterns and properties such as fracture toughness; energy release rate; strength and deformation attributes during fracturing hold significance. Environmental factors like temperature, pressure, humidity, water vapor and experimental condition such as strain rate influence the estimation of these properties. In this study, the effects of strain rates on fracture toughness, energy release rate as well as geomechanical properties like uniaxial compressive strength, Young's modulus, failure strain, tensile strength, and brittleness index of gas shales were investigated. In addition to the rock-mechanical parameters, the fracture toughness and the energy release rates were measured for three different modes viz. mode I, mixed mode (I-II) and mode II. Petrographic and X-ray diffraction (XRD) analyses were performed to identify the mineral composition of the shale samples. Scanning electron microscope (SEM) analyses were conducted to have an insight about the strain rate effects on micro-structure of the rock. The results suggest that the fracture toughness; the energy release rate as well as other geomechanical properties are a function of strain rates. At high strain rates, the strength and stiffness of shale increases which in turn increases the fracture toughness and the energy release rate of shale that may be due to stress redistribution during grain fracturing. The fracture toughness and the strain energy release rates for all the modes (I/I-II/II) are comparable at lower strain rates, but they vary considerably at higher strain rates. In all the cases, mode I and mode II fracturing requires minimum and maximum applied energy, respectively. Mode I energy release rate is maximum, compared to the other modes.

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.

Strain Rate and Stress Relaxation Effects on Pressuremeter Testing in Clays

DTIC Science & Technology

1992-03-01

CHARACTERISTICS OF KAOLINITE AND GROUND SILICA 245 APPENDIX E COMPUTER PROGRAMS ....................... 248 0 0 0 0 0 0 0 iv LIST OF TABLES Table Page 3.1 A...Comparison of Three Types of Boundary Conditions in a Multiaxial Cubical Test Apparatus ................... 37 3.2 Properties of the Kaolinite and Kaolin...to 0.01 %/min Versus Strain Rate for Kaolinite Clay ................... 102 4.3 Shear Strength Normalized with Respect to 0.01 %/min Versus Strain Rate

Effects of strain rate and surface cracks on the mechanical behaviour of Balmoral Red granite.

PubMed

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

2017-01-28

This work presents a systematic study on the effects of strain rate and surface cracks on the mechanical properties and behaviour of Balmoral Red granite. The tensile behaviour of the rock was studied at low and high strain rates using Brazilian disc samples. Heat shocks were used to produce samples with different amounts of surface cracks. The surface crack patterns were analysed using optical microscopy, and the complexity of the patterns was quantified by calculating the fractal dimensions of the patterns. The strength of the rock clearly drops as a function of increasing fractal dimensions in the studied strain rate range. However, the dynamic strength of the rock drops significantly faster than the quasi-static strength, and, because of this, also the strain rate sensitivity of the rock decreases with increasing fractal dimensions. This can be explained by the fracture behaviour and fragmentation during the dynamic loading, which is more strongly affected by the heat shock than the fragmentation at low strain rates.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'. © 2016 The Author(s).

Tissue Doppler, strain, and strain rate echocardiography for the assessment of left and right systolic ventricular function

PubMed Central

Pellerin, D; Sharma, R; Elliott, P; Veyrat, C

2003-01-01

Tissue Doppler (TDE), strain, and strain rate echocardiography are emerging real time ultrasound techniques that provide a measure of wall motion. They offer an objective means to quantify global and regional left and right ventricular function and to improve the accuracy and reproducibility of conventional echocardiography studies. Radial and longitudinal ventricular function can be assessed by the analysis of myocardial wall velocity and displacement indices, or by the analysis of wall deformation using the rate of deformation of a myocardial segment (strain rate) and its deformation over time (strain). A quick and easy assessment of left ventricular ejection fraction is obtained by mitral annular velocity measurement during a routine study, especially in patients with poor endocardial definition or abnormal septal motion. Strain rate and strain are less affected by passive myocardial motion and tend to be uniform throughout the left ventricle in normal subjects. This paper reviews the underlying principles of TDE, strain, and strain rate echocardiography and discusses currently available quantification tools and clinical applications. PMID:14594870

ITS1/5.8S/ITS2, a Good Marker for Initial Classification of Shiitake Culinary-Medicinal Lentinus edodes (Agaricomycetes) Strains in China.

PubMed

Song, Xiao-Xia; Zhao, Yan; Song, Chun-Yan; Li, Chuan-Hua; Song, Ying; Chen, Ming-Jie; Bao, Da-Peng; Tan, Qi

2018-01-01

China is home to rich wild and cultivated strains of Lentinus edodes, an important edible and medicinal mushroom. Artificial selection of L. edodes has a long history, and the widely cultivated strains belong to populations different from those of most wild strains. Internal transcribed spacer (ITS) regions have been used as good markers to identify L. edodes populations. But because ITS regions exhibit incomplete concerted evolution, the use of an ITS to identify L. edodes populations has been questioned. The objective of this study was to determine whether the ITS region is suitable for identifying L. edodes populations and which populations the widely cultivated strains and the most wild strains belong to by investigating intraindividual and differential ITS polymorphisms between 44 cultivars and 44 wild strains of L. edodes in China. Intraindividual ITS polymorphism is common in L. edodes strains, and most strains possessed 2 different ITS sequences, which came from their heterokaryons. The genetic polymorphisms of ITS1, 5.8S, and ITS2 in L. edodes strains are distinct. All strains were divided into one 5.8S type (5.8S-A), 2 ITS1 types (ITS1-A and ITS1-B), and 2 ITS2 types (ITS2-A and ITS2-B), which were subdivided into 2 branches (ITS2-A1 and ITS2-A2; ITS2-B1 and ITS2-B2). ITS1/5.8S/ITS2 could be used as a good marker in preliminary classification of L. edodes strains in China. It not only exhibited classified information of ITS1, 5.8S, and ITS2 for each strain at the same time, it also indicated whether the strain was heterozygous. The 44 cultivated strains were mainly the A/A/A1 type, and the 44 wild strains were mainly the A/A/A2 and other mixed types.

Electron Excitation Rate Coefficients for Transitions from the IS21S Ground State to the 1S2S1,3S and 1S2P1,3P0 Excited States of Helium

NASA Astrophysics Data System (ADS)

Aggarwal, K. M.; Kingston, A. E.; McDowell, M. R. C.

1984-03-01

The available experimental and theoretical electron impact excitation cross section data for the transitions from the 1s2 1S ground state to the 1s2s 1,3S and 1s2p 1,3P0 excited states of helium are assessed. Based on this assessed data, excitation rate coefficients are calculated over a wide electron temperature range below 3.0×106K. A comparison with other published results suggests that the rates used should be lower by a factor of 2 or more.

Pressure-strain-rate events in homogeneous turbulent shear flow

NASA Technical Reports Server (NTRS)

Brasseur, James G.; Lee, Moon J.

1988-01-01

A detailed study of the intercomponent energy transfer processes by the pressure-strain-rate in homogeneous turbulent shear flow is presented. Probability density functions (pdf's) and contour plots of the rapid and slow pressure-strain-rate show that the energy transfer processes are extremely peaky, with high-magnitude events dominating low-magnitude fluctuations, as reflected by very high flatness factors of the pressure-strain-rate. A concept of the energy transfer class was applied to investigate details of the direction as well as magnitude of the energy transfer processes. In incompressible flow, six disjoint energy transfer classes exist. Examination of contours in instantaneous fields, pdf's and weighted pdf's of the pressure-strain-rate indicates that in the low magnitude regions all six classes play an important role, but in the high magnitude regions four classes of transfer processes, dominate. The contribution to the average slow pressure-strain-rate from the high magnitude fluctuations is only 50 percent or less. The relative significance of high and low magnitude transfer events is discussed.

Strain rate sensitivity of autoclaved aerated concrete from quasi-static regime to shock loading

NASA Astrophysics Data System (ADS)

Mespoulet, Jérôme; Plassard, Fabien; Hereil, Pierre Louis

2015-09-01

The quasi-static mechanical behavior of autoclaved aerated concrete is well-known and can be expressed as a function of its density. There are however not much studies dealing with its dynamic behavior and its damping ability when subjected to a mechanical shock or a blast. This study presents experimental results obtained at the Shock Physics Laboratory of THIOT INGENIERIE company. The test specimens are made of YTONG(TM ) cellular concrete with porosity in the range of 75 to 80%. Experimental tests cover a large strain rate amplitude (higher than 104 s-1) for specimens up to 250 mm. They were carried out with a small compression press and with two facilities dedicated to dynamic material characterization: JUPITER dynamic large press (2 MN, 3 ms rising time) and TITAN multi-caliber single-stage gas gun. Results in un-confined conditions show an increase of the compressive strength when strain rate increases (45% increase at 5.102 s-1) but dynamic tests induce damage early in the experiment. This competition between dynamic strength raise and specimen fracture makes the complete compaction curve determination not to be done in unconfined dynamic condition. A 25% increase of the compressive strength has been observed between unconfined and confined condition in Q.S. regime.

Utilization of Dimethyl Sulfide as a Sulfur Source with the Aid of Light by Marinobacterium sp. Strain DMS-S1

PubMed Central

Fuse, Hiroyuki; Takimura, Osamu; Murakami, Katsuji; Yamaoka, Yukiho; Omori, Toshio

2000-01-01

Strain DMS-S1 isolated from seawater was able to utilize dimethyl sulfide (DMS) as a sulfur source only in the presence of light in a sulfur-lacking medium. Phylogenetic analysis based on 16S ribosomal DNA genes indicated that the strain was closely related to Marinobacterium georgiense. The strain produced dimethyl sulfoxide (DMSO), which was a main metabolite, and small amounts of formate and formaldehyde when grown on DMS as the sole sulfur source. The cells of the strain grown with succinate as a carbon source were able to use methyl mercaptan or methanesulfonate besides DMS but not DMSO or dimethyl sulfone as a sole sulfur source. DMS was transformed to DMSO primarily at wavelengths between 380 and 480 nm by heat-stable photosensitizers released by the strain. DMS was also degraded to formaldehyde in the presence of light by unidentified heat-stable factors released by the strain, and it appeared that strain DMS-S1 used the degradation products, which should be sulfite, sulfate, or methanesulfonate, as sulfur sources. PMID:11097944

Variability of hydrolysis of β-, αs1-, and αs2-caseins by 10 strains of Streptococcus thermophilus and resulting bioactive peptides.

PubMed

Miclo, Laurent; Roux, Emeline; Genay, Magali; Brusseaux, Emilie; Poirson, Chantal; Jameh, Nawara; Perrin, Clarisse; Dary, Annie

2012-01-18

Milk proteins contain numerous potential bioactive peptides, which may be released by digestive proteases or by the proteolytic system of lactic acid bacteria during food processing. The capacity of Streptococcus thermophilus to generate peptides, especially bioactive peptides, from bovine caseins was investigated. Strains expressing various levels of the cell envelope proteinase, PrtS, were incubated with α(s1)-, α(s2)-, or β-casein. Analysis of the supernatants by LC-ESI-MS/MS showed that the β-casein was preferentially hydrolyzed, followed by α(s2)-casein and then α(s1)-casein. Numbers and types of peptides released were strain-dependent. Hydrolysis appeared to be linked with the accessibility of different casein regions by protease. Analysis of bonds hydrolyzed in the region 1-23 of α(s1)-casein suggests that PrtS is at least in part responsible for the peptide production. Finally, among the generated peptides, 13 peptides from β-casein, 5 from α(s2)-casein, and 2 from α(s1)-casein have been reported as bioactive, 15 of them being angiotensin-converting enzyme inhibitors.

Effect of Strain Rates on the Compressive Response of Neck Rubber From Humanetics HIII 50th Percentile Male Dummy Under Different Loading Sequences

DTIC Science & Technology

2013-02-01

diene monomer ( EPDM ) rubber under high-rate uniaxial compression using an SHPB (5). Additionally, Song and Chen used a strain energy-based function to...describe a one-dimensional constitutive relation to describe the high strain rate behavior of the EPDM rubber , which agreed with the experimental...intermediate rate to about 6 MPa at 500 s -1 . This behavior and rate dependence was similar to the EPDM rubber studied by Chen and Zhang (2), which

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.

The influence of the region of interest width on two-dimensional speckle tracking-based measurements of strain and strain rate.

PubMed

Spriestersbach, Hendrik; Oh-Icí, Darach; Schmitt, Boris; Berger, Felix; Schmitz, Lothar

2015-01-01

There are significant variations in the published normal values of two-dimensional speckle tracking-derived strain and strain rate. These occur even when authors use the same software. To measure strain, the operator creates a region of interest (ROI) to define the myocardium to be analyzed. The purpose of this study was to test the hypothesis that measurements vary significantly with the chosen ROI width. In 20 healthy subjects (11 males, mean age 17.6 ± 6.18 years) an apical four-chamber view (4CH) and parasternal short-axis view (SAX) were analyzed. Initially ROI width was set automatically by the software. Two subsequent measurements were obtained from each cine loop by choosing the ROI width one step narrower and one step wider than the automatic ROI width. The mean differences between the measurements of narrower and automatic ROI and between automatic and wider ROI were -1.8 ± 0.7% and -0.9 ± 0.5% for global longitudinal strain (SL), -2.2 ± 0.6% and -1.7 ± 0.7% for global circumferential strain (SC), -0.10 ± 0.06/sec and -0.07 ± 0.06/sec for global longitudinal strain rate (SrL), and -0.15 ± 0.09/sec and -0.12 ± 0.07/sec for global circumferential strain rate (SrC) (all P < 0.000). This corresponds to a relative difference to the mean of both measurements of -4.4 to -11.0%. Layer-specific myocardial deformation and curvature dependency lead to an inverse correlation between the chosen ROI width and strain and strain rate measurements. Just one step of ROI-width change leads to a significant bias. Precise ROI-width definition is essential but technical factors limit its feasibility. © 2014, Wiley Periodicals, Inc.

The response of equine cortical bone to loading at strain rates experienced in vivo by the galloping horse.

PubMed

Evans, G P; Behiri, J C; Vaughan, L C; Bonfield, W

1992-03-01

The behaviour of cortical bone under load is strain rate-dependent, i.e. it is dependent on the rate at which the load is applied. This is particularly relevant in the galloping horse since the strain rates experienced by the bone are far in excess of those recorded for any other species. In this study the effect of strain rates between 0.0001 and 1 sec-1 on the mechanical properties of equine cortical bone were assessed. Initially, increasing strain rates resulted in increased mechanical properties. Beyond a critical value, however, further increases in strain rate resulted in lower strain to failure and energy absorbing capacity. This critical rate occurred around 0.1 sec-1 which is within the in vivo range for a galloping racehorse. Analysis of the stress-strain curves revealed a transition in the type of deformation at this point from pseudo-ductile to brittle. Bones undergoing brittle deformation are more likely to fail under load, leading to catastrophic fracture and destruction of the animal.

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2.

PubMed

Lloyd, David; Liu, Xinghui; Christopher, Jason W; Cantley, Lauren; Wadehra, Anubhav; Kim, Brian L; Goldberg, Bennett B; Swan, Anna K; Bunch, J Scott

2016-09-14

We demonstrate the continuous and reversible tuning of the optical band gap of suspended monolayer MoS2 membranes by as much as 500 meV by applying very large biaxial strains. By using chemical vapor deposition (CVD) to grow crystals that are highly impermeable to gas, we are able to apply a pressure difference across suspended membranes to induce biaxial strains. We observe the effect of strain on the energy and intensity of the peaks in the photoluminescence (PL) spectrum and find a linear tuning rate of the optical band gap of 99 meV/%. This method is then used to study the PL spectra of bilayer and trilayer devices under strain and to find the shift rates and Grüneisen parameters of two Raman modes in monolayer MoS2. Finally, we use this result to show that we can apply biaxial strains as large as 5.6% across micron-sized areas and report evidence for the strain tuning of higher level optical transitions.

Feasibility and reproducibility of a standard protocol for 2D speckle tracking and tissue Doppler-based strain and strain rate analysis of the fetal heart.

PubMed

Crispi, Fàtima; Sepulveda-Swatson, Eduardo; Cruz-Lemini, Monica; Rojas-Benavente, Juan; Garcia-Posada, Raul; Dominguez, Jesus Maria; Sitges, Marta; Bijnens, Bart; Gratacós, Eduard

2012-01-01

Assessment of cardiac function in the fetal heart is challenging because of its small size and high heart rate, restricted physical access to the fetus, and impossibility of fetal ECG recording. We aimed to standardize the acquisition and postprocessing of fetal echocardiography for deformation analysis and to assess its feasibility, reproducibility, and correlation for longitudinal strain and strain rate measurements by tissue Doppler imaging (TDI) and 2D speckle tracking (2D-strain) during pregnancy. Echocardiography was performed in 56 fetuses. 2D and color TDI in apical or basal four-chamber views were recorded for subsequent analysis. Caution was taken to achieve a frame rate >70 Hz for speckle tracking and >150 Hz for TDI analysis. For each acquisition, 7.5 s of noncompressed data were stored in cine loop format and analyzed offline. Since fetal ECG information is by definition not available, aortic valve closure was marked from aortic flow and the onset of each cardiac cycle was manually indicated in the 2D images. Sample volume length was standardized at the minimum size. Two observers measured the left and right ventricular peak systolic longitudinal strain and strain-rate. Strain and strain rate measurements were feasible in 93% of the TDI and 2D-strain acquisitions. The mean time spent on analyzing TDI images was 18 min, with an intraclass agreement coefficient of 0.86 (95% CI 0.77-0.92), 0.83 (95% CI 0.72-0.90), 0.96 (95% CI 0.93-0.98), and 0.86 (95% CI 0.76-0.92) for basal left and right free wall peak systolic strain and strain rate, respectively. Agreement between observers using tissue Doppler also showed high reliability. The mean time spent for 2D-strain analysis was 15 min, with an intraclass agreement coefficient of 0.97 (95% CI 0.95-0.98), 0.94 (95% CI 0.89-0.96), 0.96 (95% CI 0.93-0.98), and 0.84 (95% CI 0.73-0.90) for basal left and right free wall peak systolic strain and strain rate, respectively. Agreement between observers also showed a

Feasibility and reproducibility of feature-tracking-based strain and strain rate measures of the left ventricle in different diseases and genders.

PubMed

Maceira, Alicia M; Tuset-Sanchis, Luis; López-Garrido, Miguel; San Andres, Marta; López-Lereu, M Pilar; Monmeneu, Jose V; García-González, M Pilar; Higueras, Laura

2018-05-01

The measurement of myocardial deformation by strain analysis is an evolving tool to quantify regional and global myocardial function. To assess the feasibility and reproducibility of myocardial strain/strain rate measurements with magnetic resonance feature tracking (MR-FT) in healthy subjects and in patient groups. Prospective study. Sixty patients (20 hypertensives with left ventricular (LV) hypertrophy (H); 20 nonischemic dilated cardiomyopathy (D); 20 ischemic heart disease (I); as well as 20 controls (C) were included, 10 men and 10 women in each group. A 1.5T MR protocol including steady-state free precession (SSFP) cine sequences in the standard views and late enhancement sequences. LV volumes, mass, global and regional radial, circumferential, and longitudinal strain/strain rate were measured using CVI42 software. The analysis time was recorded. Intraobserver and interobserver agreement and intraclass correlation coefficients (ICC) were obtained for reproducibility assessment as well as differences according to gender and group of pertinence. Strain/strain rate analysis could be achieved in all subjects. The average analysis time was 14 ± 3 minutes. The average intraobserver ICC was excellent (ICC >0.90) for strain and good (ICC >0.75) for strain rate. Reproducibility of strain measurements was good to excellent (ICC >0.75) for all groups of subjects and both genders. Reproducibility of strain measurements was good for basal segments (ICC >0.75) and excellent for middle and apical segments (ICC >0.90). Reproducibility of strain rate measurements was moderate for basal segments (ICC >0.50) and good for middle and apical segments. MR-FT for strain/strain rate analysis is a feasible and highly reproducible technique. CVI42 FT analysis was equally feasible and reproducible in various pathologies and between genders. Better reproducibility was seen globally for middle and apical segments, which needs further clarification. 3 Technical Efficacy Stage 2 J

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.

Influence of strain rate on indentation response of porcine brain.

PubMed

Qian, Long; Zhao, Hongwei; Guo, Yue; Li, Yuanshang; Zhou, Mingxing; Yang, Liguo; Wang, Zhiwei; Sun, Yifan

2018-06-01

Knowledge of brain tissue mechanical properties may be critical for formulating hypotheses about some specific diseases mechanisms and its accurate simulations such as traumatic brain injury (TBI) and tumor growth. Compared to traditional tests (e.g. tensile and compression), indentation shows superiority by virtue of its pinpoint and nondestructive/quasi-nondestructive. As a viscoelastic material, the properties of brain tissue depend on the strain rate by definition. However most efforts focus on the aspect of velocity in the field of brain indentation, rather than strain rate. The influence of strain rate on indentation response of brain tissue is taken little attention. Further, by comparing different results from literatures, it is also obvious that strain rate rather than velocity is more appropriate to characterize mechanical properties of brain. In this paper, to systematically characterize the influence of strain rate, a series of indentation-relaxation tests n = 210) are performed on the cortex of porcine brain using a custom-designed indentation device. The mechanical response that correlates with indenter diameters, depths of indentation and velocities, is revealed for the indentation portion, and elastic behavior of brain tissue is analyzed as the function of strain rate. Similarly, a linear viscoelastic model with a Prony series is employed for the indentation-relaxation portion, wherein the brain tissue shows more viscous and responds more quickly with increasing strain rate. Understanding the effect of strain rate on mechanical properties of brain indentation may be far-reaching for brain injury biomechanics and accurate simulations, but be important for bridging between indentation results of different literatures. Copyright © 2018 Elsevier Ltd. All rights reserved.

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.

Spherical nanoindentation stress-strain analysis, Version 1

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

Weaver, Jordan S.; Turner, David; Miller, Calvin

Nanoindentation is a tool that allows the mechanical response of a variety of materials at the nano to micron length scale to be measured. Recent advances in spherical nanoindentation techniques have allowed for a more reliable and meaningful characterization of the mechanical response from nanoindentation experiments in the form on an indentation stress-strain curve. This code base, Spin, is written in MATLAB (The Mathworks, Inc.) and based on the analysis protocols developed by S.R. Kalidindi and S. Pathak [1, 2]. The inputs include the displacement, load, harmonic contact stiffness, harmonic displacement, and harmonic load from spherical nanoindentation tests in themore » form of an Excel (Microsoft) spreadsheet. The outputs include indentation stress-strain curves and indentation properties as well their variance due to the uncertainty of the zero-point correction in the form of MATLAB data (.mat) and figures (.png). [1] S. Pathak, S.R. Kalidindi. Spherical nanoindentation stress–strain curves, Mater. Sci. Eng R-Rep 91 (2015). [2] S.R. Kalidindi, S. Pathak. Determination of the effective zero-point and the extraction of spherical nanoindentation stress-strain curves, Acta Materialia 56 (2008) 3523-3532.« less

Noninvasive detection of intimal xanthoma using combined ultrasound, strain rate and photoacoustic imaging.

PubMed

Graf, Iulia M; Kim, Seungsoo; Wang, Bo; Smalling, Richard; Emelianov, Stanislav

2012-03-01

The structure, composition and mechanics of carotid artery are good indicators of early progressive atherosclerotic lesions. The combination of three imaging modalities (ultrasound, strain rate and photoacoustic imaging) which could provide corroborative information about the named arterial properties could enhance the characterization of intimal xanthoma. The experiments were performed using a New Zealand white rabbit model of atherosclerosis. The aorta excised from an atherosclerotic rabbit was scanned ex vivo using the three imaging techniques: (1) ultrasound imaging of the longitudinal section: standard ultrasound B-mode (74Hz frame rate); (2) strain rate imaging: the artery was flushed with blood and a 1.5Hz physiologic pulsation was induced, while the ultrasound data were recorded at higher frame rate (296Hz); (3) photoacoustic imaging: the artery was irradiated with nanosecond pulsed laser light of low fluence in the 1210-1230nm wavelength range and the photoacoustic data was recorded at 10Hz frame rate. Post processing algorithms based on cross-correlation and optical absorption variation were implemented to derive strain rate and spectroscopic photoacoustic images, respectively. Based on the spatio-temporal variation in displacement of different regions within the arterial wall, strain rate imaging reveals differences in tissue mechanical properties. Additionally, spectroscopic photoacoustic imaging can spatially resolve the optical absorption properties of arterial tissue and identify the location of lipid pools. The study demonstrates that ultrasound, strain rate and photoacoustic imaging can be used to simultaneously evaluate the structure, the mechanics and the composition of atherosclerotic lesions to improve the assessment of plaque vulnerability. Copyright © 2011 Elsevier B.V. All rights reserved.

Compressive strain induced dynamical stability of monolayer 1T-MX2 (M  =  Mo, W; X  =  S, Se)

NASA Astrophysics Data System (ADS)

Li, Xiaoyong; Wu, Musheng; Xu, Bo; Liu, Ruifan; Ouyang, Chuying

2017-11-01

The lattice dynamical properties of 1T-MX2 (M  =  Mo, W; X  =  S, Se) under different strains were studied by using density functional perturbation theory method. Our results show that all MX2 with 1T phase in our calculations are dynamical instable under zero strain or tensile strain as obvious imaginary frequencies (soft modes) exist. When 3% biaxial compressive strains are applied, the imaginary frequencies remain except that the absolute values of maximum imaginary frequency decrease. With the increase of compressive strain to be 6%, 1T-MoS2, 1T-MoSe2, 1T-WS2 become stable, whereas 1T-WSe2 has small imaginary frequencies. When biaxial compressive strain reaches 9%, all 1T-MX2 are dynamical stable without imaginary frequencies in the phonon dispersion curves. Energy band structures show that all 1T-MX2 are metallic, regardless of zero strain or compressive strain. Therefore, compressive strain could be a practical approach to enhance the stability of 1T-MX2 while maintaining the metallic property.

Microstructural and strain rate effects on plastic deformation in aluminum 2219-T87

NASA Astrophysics Data System (ADS)

Rincon, Carlos D.

A fundamental investigation has been conducted on the effects of microstructure and strain rate on the plastic deformation of theta-prime-strengthened 2219 aluminum. The motivation for this work is based upon a previous study which showed inhomogeneous and locally extreme work hardening in the HAZ regions in VPPA 2219-T87 butt welds. This strongly suggests that the HAZ microstructure plays a major role in the deformation and fracture process in precipitation hardened aluminum alloy 2219. Tensile specimens of the weld joint exhibited more rapid work hardening in the heat-affected-zone (HAZ) at higher strain levels. Microhardness contour maps for these welds illustrated that late stage deformation was concentrated in two crossing bands at about 45sp° to the tensile axis. The width of the deformation bands and the ultimate tensile strength seemed to be dictated by the amount of work hardening in the HAZ. In this study, three different heat treatments were used to produce samples with different particle sizes and particle spacings, but all hardened by copper aluminide precipitates of the thetasp' structure. The heat treatments were categorized as being (A) as-received T87 condition, (B) T87 condition aged at approximately 204sp°C for 3 hours and (C) T87 over-aged at 204sp°C for 7 days. Uniaxial tensile tests consisted of two sets of experiments: (1) three heat treatments (A, B, and C) at two strain rates (0.02 minsp{-1} and 0.2 minsp{-1}) and (2) three heat treatments that were interrupted at select stress-strain levels (0.8% and 2% total strain) during the tensile tests at strain rate equal to 0.02 minsp{-1} at room temperature. Furthermore, a detailed transmission electron microscopy (TEM) study demonstrates the microstructural development during tensile deformation. The Voce equation of strain-hardening provides a slightly better fit to the tensile curves than the Ludwik-Hollomon equation. At higher strains, localized areas showed strain fields around thetasp

Forming limit curves of DP600 determined in high-speed Nakajima tests and predicted by two different strain-rate-sensitive models

NASA Astrophysics Data System (ADS)

Weiß-Borkowski, Nathalie; Lian, Junhe; Camberg, Alan; Tröster, Thomas; Münstermann, Sebastian; Bleck, Wolfgang; Gese, Helmut; Richter, Helmut

2018-05-01

Determination of forming limit curves (FLC) to describe the multi-axial forming behaviour is possible via either experimental measurements or theoretical calculations. In case of theoretical determination, different models are available and some of them consider the influence of strain rate in the quasi-static and dynamic strain rate regime. Consideration of the strain rate effect is necessary as many material characteristics such as yield strength and failure strain are affected by loading speed. In addition, the start of instability and necking depends not only on the strain hardening coefficient but also on the strain rate sensitivity parameter. Therefore, the strain rate dependency of materials for both plasticity and the failure behaviour is taken into account in crash simulations for strain rates up to 1000 s-1 and FLC can be used for the description of the material's instability behaviour at multi-axial loading. In this context, due to the strain rate dependency of the material behaviour, an extrapolation of the quasi-static FLC to dynamic loading condition is not reliable. Therefore, experimental high-speed Nakajima tests or theoretical models shall be used to determine the FLC at high strain rates. In this study, two theoretical models for determination of FLC at high strain rates and results of experimental high-speed Nakajima tests for a DP600 are presented. One of the theoretical models is the numerical algorithm CRACH as part of the modular material and failure model MF GenYld+CrachFEM 4.2, which is based on an initial imperfection. Furthermore, the extended modified maximum force criterion considering the strain rate effect is also used to predict the FLC. These two models are calibrated by the quasi-static and dynamic uniaxial tensile tests and bulge tests. The predictions for the quasi-static and dynamic FLC by both models are presented and compared with the experimental results.

Effects of Strain Rate on Compressive Properties in Bimodal 7075 Al-SiCp Composite

NASA Astrophysics Data System (ADS)

Lee, Hyungsoo; Choi, Jin Hyeok; Jo, Min Chul; Jo, Ilguk; Lee, Sang-Kwan; Lee, Sunghak

2018-07-01

A 7075 Al alloy matrix composite reinforced with SiC particulates (SiCps) whose sizes were 10 and 30 μm, i.e., a bimodal Al-SiCp composite, was made by a liquid pressing process, and its quasi-static and dynamic compressive properties were evaluated by using a universal testing machine and a split Hopkinson pressure bar, respectively. Mg-Si-, Al-Fe-, and Cu-rich intermetallic compounds existed inside the Al matrix, but might not deteriorate compressive properties because of their low volume fraction (about 2.6%) which was much lower than that of SiCp. The dynamic compressive strength was higher than the quasi-static strength, and was higher in the specimen tested at 2800 s-1 than in the specimen tested at 1400 s-1 according to the strain-rate hardening. For explaining the strain data, the blocking extent of crack propagation by the Al matrix was quantitatively examined. The melting of Al matrix occurred by adiabatic heating was favorable for the improvement in compressive strain because it favorably worked for activating the shear band formation and for blocking the crack propagation, thereby leading to the excellent compressive strain (10.9-11.6%) as well as maximum compressive strength (1057-1147 MPa). Thus, the present bimodal 7075 Al-SiCp composite provides a promise for new applications to high-performance armor plates.

Effects of Strain Rate on Compressive Properties in Bimodal 7075 Al-SiCp Composite

NASA Astrophysics Data System (ADS)

Lee, Hyungsoo; Choi, Jin Hyeok; Jo, Min Chul; Jo, Ilguk; Lee, Sang-Kwan; Lee, Sunghak

2018-03-01

A 7075 Al alloy matrix composite reinforced with SiC particulates (SiCps) whose sizes were 10 and 30 μm, i.e., a bimodal Al-SiCp composite, was made by a liquid pressing process, and its quasi-static and dynamic compressive properties were evaluated by using a universal testing machine and a split Hopkinson pressure bar, respectively. Mg-Si-, Al-Fe-, and Cu-rich intermetallic compounds existed inside the Al matrix, but might not deteriorate compressive properties because of their low volume fraction (about 2.6%) which was much lower than that of SiCp. The dynamic compressive strength was higher than the quasi-static strength, and was higher in the specimen tested at 2800 s-1 than in the specimen tested at 1400 s-1 according to the strain-rate hardening. For explaining the strain data, the blocking extent of crack propagation by the Al matrix was quantitatively examined. The melting of Al matrix occurred by adiabatic heating was favorable for the improvement in compressive strain because it favorably worked for activating the shear band formation and for blocking the crack propagation, thereby leading to the excellent compressive strain (10.9-11.6%) as well as maximum compressive strength (1057-1147 MPa). Thus, the present bimodal 7075 Al-SiCp composite provides a promise for new applications to high-performance armor plates.

Ultrastructure and Development of Pasteuria sp. (S-1 strain), an Obligate Endoparasite of Belonolaimus longicaudatus (Nemata: Tylenchida).

PubMed

Giblin-Davis, R M; Williams, D S; Wergin, W P; Dickson, D W; Hewlett, T E; Bekal, S; Becker, J O

2001-12-01

Pasteuria sp., strain S-1, is a gram-positive, obligate endoparasitic bacterium that uses the phytoparasitic sting nematode, Belonolaimus longicaudatus, as its host in Florida. The host attachment of S-1 appears to be specific to the genus Belonolaimus with development occurring only in juveniles and adults of B. longicaudatus. This bacterium is characterized from other described species of Pasteuria using ultrastructure of the mature endospore. Penetration, development, and sporogenesis were elucidated with TEM, LTSEM, and SEM and are similar to other nematode-specific Pasteuria. Recent analysis of 16S rDNA sequence homology confirms its congeneric ranking with other Pasteuria species and strains from nematodes and cladocerans, and corroborates ultrastructural, morphological, morphometric, and host-range evidence suggesting separate species status.

Differentiation of Strains of Infectious Bovine Rhinotracheitis Virus by Neutralization Kinetics with Late 19S Rabbit Antibodies

PubMed Central

Potgieter, Leon N. D.; Maré, C. John

1974-01-01

Two vaccine, two respiratory (infectious bovine rhinotracheitis [IBR]), and two genital (infectious pustular vulvovaginitis [IPV]) strains of infectious bovine rhinotracheitis virus were compared by neutralization kinetics using late 19S antibody (AB). The two vaccine strains were indistinguishable from one another, but were neutralized far more rapidly than the other four strains when either anti-IBR or anti-IPV 19S AB was used. The two IPV strains were indistinguishable from one another, but were neutralized significantly more rapidly than the two IBR strains when anti-IBR 19S AB was used. The 2 IBR strains were neutralized at a similar rate with the latter globulin preparation. Almost identical results were obtained with anti-IPV 19S AB, except that one IPV strain was neutralized at a rate similar to the IBR strains. However, when early and late rabbit 7S AB were used, IBR strains could not be distinguished from IPV strains by neutralization kinetics. Preliminary experiments indicated that both early and late 19S rabbit antibodies neutralized the homologous strain more rapidly than the heterologous strain, but the difference was more noticeable with late 19S AB. It was also determined that neutralization of IBR-IPV virus by specific early and late 19S rabbit AB and early 7S rabbit AB was markedly enhanced by guinea pig complement. Neutralization of this virus by late 7S AB, however, was only slightly enhanced by complement. These results suggest that vaccine strains of IBR-IPV virus may be distinguished by neutralization kinetics with late 19S rabbit AB, and that genital and respiratory strains may possibly also be distinguishable with some 19S AB preparations. Images PMID:4372173

Strain rates estimated by geodetic observations in the Borborema Province, Brazil

NASA Astrophysics Data System (ADS)

Marotta, Giuliano Sant'Anna; França, George Sand; Monico, João Francisco Galera; Bezerra, Francisco Hilário R.; Fuck, Reinhardt Adolfo

2015-03-01

The strain rates for the Borborema Province, located in northeastern Brazil, were estimated in this study. For this purpose, we used GNSS tracking stations with a minimum of two years data. The data were processed using the software GIPSY, version 6.2, provided by the JPL of the California Institute of Technology. The PPP method was used to process the data using the non-fiducial approach. Satellite orbits and clock were supplied by the JPL. Absolute phase center offsets and variations for both the receiver and the satellite antennaes were applied, together with ambiguity resolution; corrections of the first and second order effects of the ionosphere and troposphere models adopting the VMF1 mapping function; 10° elevation mask; FES2004 oceanic load model and terrestrial tide WahrK1 PolTid FreqDepLove OctTid. From a multi annual solution, involving at least 2 years of continuous data, the coordinates and velocities as well as their accuracies were estimated. The strain rates were calculated using the Delaunay triangulation and the Finite Element Method. The results show that the velocity direction is predominantly west and north, with maximum variation of 4.0 ± 1.5 mm/year and 4.1 ± 0.5 mm/year for the x and y components, respectively. The highest strain values of extension and contraction were 0.109552 × 10-6 ± 3.65 × 10-10/year and -0.072838 × 10-6 ± 2.32 × 10-10/year, respectively. In general, the results show that the highest strain and variation of velocity values are located close to the Potiguar Basin, region that concentrates seismic activities of magnitudes of up to 5.2 mb. We conclude that the contraction direction of strain is consistent with the maximum horizontal stress derived from focal mechanism and breakout data. In addition, we conclude that the largest strain rates occur around the Potiguar Basin, an area already recognized as one of the major sites of seismicity in intraplate South America.

Early Assessment of Right Ventricular Function in Systemic Lupus Erythematosus Patients using Strain and Strain Rate Imaging.

PubMed

Luo, Runlan; Cui, Hongyan; Huang, Dongmei; Sun, Lihua; Song, Shengda; Sun, Mengyao; Li, Guangsen

2018-06-11

Right ventricular function is a crucial factor of the prognosis of systemic lupus erythematosus (SLE). To evaluate the right ventricular function in SLE patients with different degrees of pulmonary hypertension (PH) by strain and strain rate imaging. A total of 102 SLE patients and 30 healthy volunteers were studied between October 2015 and May 2016. Patients were divided into three groups according to pulmonary artery systolic pressure (PASP) estimated by echocardiography: group control (A); PASP ≤ 30 mmHg (group B, n = 37); PASP 30-50 mmHg (mild PH; group C, n = 34); and PASP ≥ 50 mmHg (moderate-to-severe PH; group D, n = 31). Longitudinal peak systolic strain (ε) and strain rate (SR), including systolic strain rate (SRs), early diastolic strain rate (SRe) and late diastolic strain rate (SRa) were measured in the basal, middle and apical segments of the right ventricular free wall in participants by two-dimensional speckle tracking echocardiography (2D-STE) from the apical four-chamber view. A p < 0.05 was set for statistical significance. The parameters of ε, SRs, SRe, and SRa were significantly decreased in groups C and D compared with groups A and B. The ε of each segments was significantly lower in group D than in group C, while there were no differences in SRs, SRe and SRa between groups C and D. Strain and strain rate imaging could early detect the right ventricular dysfunction in SLE patients with PH, and provide important value for clinical therapy and prognosis of these patients. (Arq Bras Cardiol. 2018; [online].ahead print, PP.0-0).

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

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

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.

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.

Strain rate sensitivity of the tensile strength of two silicon carbides: experimental evidence and micromechanical modelling

NASA Astrophysics Data System (ADS)

Zinszner, Jean-Luc; Erzar, Benjamin; Forquin, Pascal

2017-01-01

Ceramic materials are commonly used to design multi-layer armour systems thanks to their favourable physical and mechanical properties. However, during an impact event, fragmentation of the ceramic plate inevitably occurs due to its inherent brittleness under tensile loading. Consequently, an accurate model of the fragmentation process is necessary in order to achieve an optimum design for a desired armour configuration. In this work, shockless spalling tests have been performed on two silicon carbide grades at strain rates ranging from 103 to 104 s-1 using a high-pulsed power generator. These spalling tests characterize the tensile strength strain rate sensitivity of each ceramic grade. The microstructural properties of the ceramics appear to play an important role on the strain rate sensitivity and on the dynamic tensile strength. Moreover, this experimental configuration allows for recovering damaged, but unbroken specimens, giving unique insight on the fragmentation process initiated in the ceramics. All the collected data have been compared with corresponding results of numerical simulations performed using the Denoual-Forquin-Hild anisotropic damage model. Good agreement is observed between numerical simulations and experimental data in terms of free surface velocity, size and location of the damaged zones along with crack density in these damaged zones. This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

Evaluation of serological cross-reactivity and cross-neutralization between the United States porcine epidemic diarrhea virus prototype and S-INDEL-variant strains.

PubMed

Chen, Qi; Thomas, Joseph T; Giménez-Lirola, Luis G; Hardham, John M; Gao, Qinshan; Gerber, Priscilla F; Opriessnig, Tanja; Zheng, Ying; Li, Ganwu; Gauger, Phillip C; Madson, Darin M; Magstadt, Drew R; Zhang, Jianqiang

2016-04-05

At least two genetically different porcine epidemic diarrhea virus (PEDV) strains have been identified in the United States (U.S. PEDV prototype and S-INDEL-variant strains). The current serological assays offered at veterinary diagnostic laboratories for detection of PEDV-specific antibody are based on the U.S. PEDV prototype strain. The objectives of this study were: 1) isolate the U.S. PEDV S-INDEL-variant strain in cell culture; 2) generate antisera against the U.S. PEDV prototype and S-INDEL-variant strains by experimentally infecting weaned pigs; 3) determine if the various PEDV serological assays could detect antibodies against the U.S. PEDV S-INDEL-variant strain and vice versa. A U.S. PEDV S-INDEL-variant strain was isolated in cell culture in this study. Three groups of PEDV-negative, 3-week-old pigs (five pigs per group) were inoculated orally with a U.S. PEDV prototype isolate (previously isolated in our lab), an S-INDEL-variant isolate or virus-negative culture medium. Serum samples collected at 0, 7, 14, 21 and 28 days post inoculation were evaluated by the following PEDV serological assays: 1) indirect fluorescent antibody (IFA) assays using the prototype and S-INDEL-variant strains as indicator viruses; 2) virus neutralization (VN) tests against the prototype and S-INDEL-variant viruses; 3) PEDV prototype strain whole virus based ELISA; 4) PEDV prototype strain S1-based ELISA; and 5) PEDV S-INDEL-variant strain S1-based ELISA. The positive antisera against the prototype strain reacted to and neutralized both prototype and S-INDEL-variant viruses, and the positive antisera against the S-INDEL-variant strain also reacted to and neutralized both prototype and S-INDEL-variant viruses, as examined by IFA antibody assays and VN tests. Antibodies against the two PEDV strains could be detected by all three ELISAs although detection rates varied to some degree. These data indicate that the antibodies against U.S. PEDV prototype and S-INDEL-variant strains

Modelling of Mechanical Behavior at High Strain Rate of Ti-6al-4v Manufactured By Means of Direct Metal Laser Sintering Technique

NASA Astrophysics Data System (ADS)

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

2017-06-01

In this work, the mechanical behavior of Ti-6Al-4V obtained by additive manufacturing technique was investigated, also considering the build direction. Dog-bone shaped specimens and Taylor cylinders were machined from rods manufactured by means of the EOSSINT M2 80 machine, based on Direct Metal Laser Sintering technique. Tensile tests were performed at strain rate ranging from 5E-4 s-1 to 1000 s-1 using an Instron electromechanical machine for quasistatic tests and a Direct-Tension Split Hopkinson Bar for dynamic tests. The mechanical strength of the material was described by a Johnson-Cook model modified to account for stress saturation occurring at high strain. Taylor cylinder tests and their corresponding numerical simulations were carried out in order to validate the constitutive model under a complex deformation path, high strain rates, and high temperatures.

Diversity of HIV-1 subtype C strains isolated in Romania.

PubMed

Paraschiv, Simona; Foley, Brian; Otelea, Dan

2011-03-01

Two unique aspects particularities of the HIV-1 epidemics in Romania are the high prevalence of subtype F1 strains and the large pediatric population infected in the late 1980s and early 1990s. During recent years, more infections with other subtypes have been seen in newly diagnosed patients. After subtype B, subtype C was the most frequent one. This subtype is prevalent in countries from sub-Saharan Africa and India, being responsible for half of the total HIV-1 infections in the world. We have identified 37 patients infected with subtype C, sequenced the reverse transcriptase and protease regions of their pol genes, and applied phylogenetic analyses to the sequences. We have also included 20 subtype F1 strains isolated from both teenagers (children at the time of diagnosis) and adults. The phylogenetic analysis was performed by using the PhyML method, the GTR (general time reversible) model of evolution and gamma distribution of variability of rates between sites, empirically calculated from the data. The epidemiological data indicates that the main route of transmission for the adult subjects was by heterosexual contact and a relatively small number of patients were possibly infected abroad. In three cases, blood transfusion prior to 1989 or surgical procedures at early ages were suspected to be the cause of the HIV infection and three other patients were most probably parenterally infected. The phylogenetic analyses showed that the Romanian C strains are very diverse overall, clustered in several groups characterized by common transmission route (transfusion/surgical procedures) or local geographical relatedness. The HIV-1 epidemics in Romania apparently followed different patterns for subtypes F and C. While subtype F1 seems to have been monoclonally introduced and extensively spread in the 80s, the subtype C strains, although present in the late 80s, failed to spread to the same extent. Copyright © 2010 Elsevier B.V. All rights reserved.

EFFECT OF AXIAL TIBIAL TORQUE DIRECTION ON ACL RELATIVE STRAIN AND STRAIN RATE IN AN IN VITRO SIMULATED PIVOT LANDING

PubMed Central

Oh, Youkeun K.; Kreinbrink, Jennifer L.; Wojtys, Edward M.; Ashton-Miller, James A.

2011-01-01

Anterior cruciate ligament (ACL) injuries most frequently occur under the large loads associated with a unipedal jump landing involving a cutting or pivoting maneuver. We tested the hypotheses that internal tibial torque would increase the anteromedial (AM) bundle ACL relative strain and strain rate more than would the corresponding external tibial torque under the large impulsive loads associated with such landing maneuvers. Twelve cadaveric female knees [mean (SD) age: 65.0 (10.5) years] were tested. Pretensioned quadriceps, hamstring and gastrocnemius muscle-tendon unit forces maintained an initial knee flexion angle of 15°. A compound impulsive test load (compression, flexion moment and internal or external tibial torque) was applied to the distal tibia while recording the 3-D knee loads and tibofemoral kinematics. AM-ACL relative strain was measured using a 3mm DVRT. In this repeated measures experiment, the Wilcoxon Signed-Rank test was used to test the null hypotheses with p<0.05 considered significant. The mean (± SD) peak AM-ACL relative strains were 5.4±3.7 % and 3.1±2.8 % under internal and external tibial torque, respectively. The corresponding mean (± SD) peak AM-ACL strain rates reached 254.4±160.1 %/sec and 179.4±109.9 %/sec, respectively. The hypotheses were supported in that the normalized mean peak AM-ACL relative strain and strain rate were 70% and 42% greater under internal than external tibial torque, respectively (p=0.023, p=0.041). We conclude that internal tibial torque is a potent stressor of the ACL because it induces a considerably (70%) larger peak strain in the AM-ACL than does a corresponding external tibial torque. PMID:22025178

Microstructural effects on ignition sensitivity in Ni/Al systems subjected to high strain rate impacts

NASA Astrophysics Data System (ADS)

Reeves, Robert; Mukasyan, Alexander; Son, Steven

2011-06-01

The effect of microstructural refinement on the sensitivity of the Ni/Al (1:1 at%) system to ignition via high strain rate impacts is investigated. The tested microstructures include compacts of irregularly convoluted lamellar structures with nanometric features created through high-energy ball milling (HEBM) of micron size Ni/Al powders and compacts of nanometric Ni and Al powders. The test materials were subjected to high strain rate impacts through Asay shear experiments powered by a light gas gun. Muzzle velocities up to 1.1 km/s were used. It was found that the nanometric powder exhibited a greater sensitivity to ignition via impact than the HEBM material, despite greater thermal sensitivity of the HEBM. A previously unseen fast reaction mode where the reaction front traveled at the speed of the input stress wave was also observed in the nanometric mixtures at high muzzle energies. This fast mode is considered to be a mechanically induced thermal explosion mode dependent on the magnitude of the traveling stress wave, rather than a self-propagating detonation, since its propagation rate decreases rapidly across the sample. A similar mode is not exhibited by HEBM samples, although local, nonpropagating reaction zones occur in shear bands formed during the impact event.

Microstructural effects on ignition sensitivity in Ni/Al systems subjected to high strain rate impacts

NASA Astrophysics Data System (ADS)

Reeves, Robert V.; Mukasyan, Alexander S.; Son, Steven

2012-03-01

The effect of microstructural refinement on the sensitivity of the Ni/Al (1:1 mol%) system to ignition via high strain rate impacts is investigated. The tested microstructures include compacts of irregularly convoluted lamellar structures with nanometric features created through high-energy ball milling (HEBM) of micron size Ni/Al powders and compacts of nanometric Ni and Al powders. The test materials were subjected to high strain rate impacts through Asay shear experiments powered by a light gas gun. Muzzle velocities up to 1.1 km/s were used. It was found that the nanometric powder exhibited a greater sensitivity to ignition via impact than the HEBM material, despite greater thermal sensitivity of the HEBM. A previously unseen fast reaction mode where the reaction front traveled at the speed of the input stress wave was also observed in the nanometric mixtures at high muzzle energies. This fast mode is considered to be a mechanically induced thermal explosion mode dependent on the magnitude of the traveling stress wave, rather than a self-propagating detonation, since its propagation rate decreases rapidly across the sample. A similar mode is not exhibited by HEBM samples, although local, nonpropagating reaction zones shear bands formed during the impact event are observed.

Modeling Strain Rate Effect of Heterogeneous Materials Using SPH Method

NASA Astrophysics Data System (ADS)

Ma, G. W.; Wang, X. J.; Li, Q. M.

2010-11-01

The strain rate effect on the dynamic compressive failure of heterogeneous material based on the smoothed particle hydrodynamics (SPH) method is studied. The SPH method employs a rate-insensitive elasto-plastic damage model incorporated with a Weibull distribution law to reflect the mechanical behavior of heterogeneous rock-like materials. A series of simulations are performed for heterogeneous specimens by applying axial velocity conditions, which induce different strain-rate loadings to the specimen. A detailed failure process of the specimens in terms of microscopic crack-activities and the macro-mechanical response are discussed. Failure mechanisms between the low and high strain rate cases are compared. The result shows that the strain-rate effects on the rock strength are mainly caused by the changing internal pressure due to the inertial effects as well as the material heterogeneity. It also demonstrates that the inertial effect becomes significant only when the induced strain rate exceeds a threshold, below which, the dynamic strength enhancement can be explained due to the heterogeneities in the material. It also shows that the dynamic strength is affected more significantly for a relatively more heterogeneous specimen, which coincides with the experimental results showing that the poor quality specimen had a relatively larger increase in the dynamic strength.

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

Tensile strength and failure mechanisms of tantalum at extreme strain rates

NASA Astrophysics Data System (ADS)

Hahn, Eric; Fensin, Saryu; Germann, Timothy; Meyers, Marc

Non-equilibrium molecular dynamics simulations are used to probe the tensile response of monocrystalline, bicrystalline, and nanocrystalline tantalum over six orders of magnitude of strain rate. Our analysis of the strain rate dependence of strength is extended to over nine orders of magnitude by bridging the present simulations to recent laser-driven shock experiments. Tensile strength shows a power-law dependence with strain rate over this wide range, with different relationships depending on the initial microstructure and active deformation mechanism. At high strain rates, multiple spall events occur independently and continue to occur until communication occurs by means of relaxation waves. Temperature plays a significant role in the reduction of spall strength as the initial shock required to achieve such large strain rates also contributes to temperature rise, through pressure-volume work as well as visco-plastic heating, which leads to softening and sometimes melting upon release. At ultra-high strain rates, those approaching or exceeding the atomic vibrational frequency, spall strength saturates at the ultimate cohesive strength of the material. UC Research Laboratories Grant (09-LR-06-118456-MEYM); Department of Energy NNSA/SSAP (DE-NA0002080); DOE ASCR Exascale Co-design Center for Materials in Extreme Environments.

Human Lumbar Spine Creep during Cyclic and Static Flexion: Creep Rate, Biomechanics, and Facet Joint Capsule Strain

PubMed Central

Little, Jesse S.; Khalsa, Partap S.

2005-01-01

There is a high incidence of low back pain (LBP) associated with occupations requiring sustained and/or repetitive lumbar flexion (SLF and RLF, respectively), which cause creep of the viscoelastic tissues. The purpose of this study was to determine the effect of creep on lumbar biomechanics and facet joint capsule (FJC) strain. Specimens were flexed for 10 cycles, to a maximum 10 Nm moment at L5-S1, before, immediately after, and 20 min after a 20-min sustained flexion at the same moment magnitude. The creep rates of SLF and RLF were also measured during each phase and compared to the creep rate predicted by the moment relaxation rate function of the lumbar spine. Both SLF and RLF resulted in significantly increased intervertebral motion, as well as significantly increased FJC strains at the L3-4 to L5-S1 joint levels. These parameters remained increased after the 20-min recovery. Creep during SLF occurred significantly faster than creep during RLF. The moment relaxation rate function was able to accurately predict the creep rate of the lumbar spine at the single moment tested. The data suggest that SLF and RLF result in immediate and residual laxity of the joint and stretch of the FJC, which could increase the potential for LBP. PMID:15868730

Assessment of strain and strain rate by two-dimensional speckle tracking in mice: comparison with tissue Doppler echocardiography and conductance catheter measurements.

PubMed

Ferferieva, V; Van den Bergh, A; Claus, P; Jasaityte, R; La Gerche, A; Rademakers, F; Herijgers, P; D'hooge, J

2013-08-01

This study was designed in order to compare the strain and strain rate deformation parameters assessed by speckle tracking imaging (STI) with those of tissue Doppler imaging (TDI) and conductance catheter measurements in chronic murine models of left ventricular (LV) dysfunction. Twenty-four male C57BL/6J mice were assigned to wild-type (n = 8), myocardial infarction (n = 8) and transaortic constriction (n = 8) groups. Echocardiographic and conductance measurements were simultaneously performed at rest and during dobutamine infusion (5 µg/kg/min) in all animals 10 weeks post-surgery. The LV circumferential strain (Scirc) and the strain rate (SRcirc) were derived from grey scale and tissue Doppler data at frame rates of 224 and 375 Hz, respectively. Scirc and SRcirc by TDI/STI correlated well with the preload recruitable stroke work (PRSW) (r = -0.64 and -0.71 for TDI; r = -0.46 and -0.50 for STI, P < 0.05). Both modalities showed a good agreement with respect to Scirc and SRcirc (r = 0.60 and r = 0.63, P < 0.05). During stress, however, TDI-estimated Scirc and SRcirc values were predominantly higher than those measured by STI (P < 0.05). The similarity of Scirc and SRcirc measurements with respect to the STI/TDI data was examined by the Bland-Altman analysis. In mice, the STI- and TDI-derived strain and strain rate deformation parameters relate closely to intrinsic myocardial function. At low heart rate-to-frame rate ratios (HR/FR), both STI and TDI are equally acceptable for assessing the LV function non-invasively in these animals. At HR/FR (e.g. dobutamine challenge), however, these methods cannot be used interchangeably as STI underestimates S and SR at high values.

High-rate deformation and fracture of steel 09G2S

NASA Astrophysics Data System (ADS)

Balandin, Vl. Vas.; Balandin, Vl. Vl.; Bragov, A. M.; Igumnov, L. A.; Konstantinov, A. Yu.; Lomunov, A. K.

2014-11-01

The results of experimental and theoretical studies of steel 09G2S deformation and fracture laws in a wide range of strain rates and temperature variations are given. The dynamic deformation curves and the ultimate characteristics of plasticity in high-rate strain were determined by the Kolsky method in compression, extension, and shear tests. The elastoplastic properties and spall strength were studied by using the gaseous gun of calibre 57 mm and the interferometer VISAR according to the plane-wave experiment technique. The data obtained by the Kolsky method were used to determine the parameters of the Johnson-Cook model which, in the framework of the theory of flow, describes how the yield surface radius depends on the strain, strain rate, and temperature.

Advanced Nanoindentation Testing for Studying Strain-Rate Sensitivity and Activation Volume

NASA Astrophysics Data System (ADS)

Maier-Kiener, Verena; Durst, Karsten

2017-11-01

Nanoindentation became a versatile tool for testing local mechanical properties beyond hardness and modulus. By adapting standard nanoindentation test methods, simple protocols capable of probing thermally activated deformation processes can be accomplished. Abrupt strain-rate changes within one indentation allow determining the strain-rate dependency of hardness at various indentation depths. For probing lower strain-rates and excluding thermal drift influences, long-term creep experiments can be performed by using the dynamic contact stiffness for determining the true contact area. From both procedures hardness and strain-rate, and consequently strain-rate sensitivity and activation volume can be reliably deducted within one indentation, permitting information on the locally acting thermally activated deformation mechanism. This review will first discuss various testing protocols including possible challenges and improvements. Second, it will focus on different examples showing the direct influence of crystal structure and/or microstructure on the underlying deformation behavior in pure and highly alloyed material systems.

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

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

Coriton, Bruno Rene Leon; Frank, Jonathan H.

2016-08-10

The effects of combustion on the strain rate field are investigated in turbulent premixed CH 4/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 ofmore » heat 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

A numerical and experimental study of temperature effects on deformation behavior of carbon steels at high strain rates

NASA Astrophysics Data System (ADS)

Pouya, M.; Winter, S.; Fritsch, S.; F-X Wagner, M.

2017-03-01

Both in research and in the light of industrial applications, there is a growing interest in methods to characterize the mechanical behavior of materials at high strain rates. This is particularly true for steels (the most important structural materials), where often the strain rate-dependent material behavior also needs to be characterized in a wide temperature range. In this study, we use the Finite Element Method (FEM), first, to model the compressive deformation behavior of carbon steels under quasi-static loading conditions. The results are then compared to experimental data (for a simple C75 steel) at room temperature, and up to testing temperatures of 1000 °C. Second, an explicit FEM model that captures wave propagation phenomena during dynamic loading is developed to closely reflect the complex loading conditions in a Split-Hopkinson Pressure Bar (SHPB) - an experimental setup that allows loading of compression samples with strain rates up to 104 s-1 The dynamic simulations provide a useful basis for an accurate analysis of dynamically measured experimental data, which considers reflected elastic waves. By combining numerical and experimental investigations, we derive material parameters that capture the strain rate- and temperature-dependent behavior of the C75 steel from room temperature to 1000 °C, and from quasi-static to dynamic loading.

Initial reaction(s) in biotransformation of CL-20 is catalyzed by salicylate 1-monooxygenase from Pseudomonas sp. strain ATCC 29352.

PubMed

Bhushan, Bharat; Halasz, Annamaria; Spain, Jim C; Hawari, Jalal

2004-07-01

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) (C(6)H(6)N(12)O(12)), a future-generation high-energy explosive, is biodegradable by Pseudomonas sp. strain FA1 and Agrobacterium sp. strain JS71; however, the nature of the enzyme(s) involved in the process was not understood. In the present study, salicylate 1-monooxygenase, a flavin adenine dinucleotide (FAD)-containing purified enzyme from Pseudomonas sp. strain ATCC 29352, biotransformed CL-20 at rates of 0.256 +/- 0.011 and 0.043 +/- 0.003 nmol min(-1) mg of protein(-1) under anaerobic and aerobic conditions, respectively. The disappearance of CL-20 was accompanied by the release of nitrite ions. Using liquid chromatography/mass spectrometry in the negative electrospray ionization mode, we detected a metabolite with a deprotonated mass ion [M - H](-) at 345 Da, corresponding to an empirical formula of C(6)H(6)N(10)O(8), produced as a result of two sequential N denitration steps on the CL- 20 molecule. We also detected two isomeric metabolites with [M - H](-) at 381 Da corresponding to an empirical formula of C(6)H(10)N(10)O(10). The latter was a hydrated product of the metabolite C(6)H(6)N(10)O(8) with addition of two H(2)O molecules, as confirmed by tests using (18)O-labeled water. The product stoichiometry showed that each reacted CL-20 molecule produced about 1.7 nitrite ions, 3.2 molecules of nitrous oxide, 1.5 molecules of formic acid, and 0.6 ammonium ion. Diphenyliodonium-mediated inhibition of salicylate 1-monooxygenase and a comparative study between native, deflavo, and reconstituted enzyme(s) showed that FAD site of the enzyme was involved in the biotransformation of CL-20 catalyzed by salicylate 1-monooxygenase. The data suggested that salicylate 1-monooxygenase catalyzed two oxygen-sensitive single-electron transfer steps necessary to release two nitrite ions from CL-20 and that this was followed by the secondary decomposition of this energetic chemical.

Burkholderia cenocepacia Strain CEIB S5-1, a Rhizosphere-Inhabiting Bacterium with Potential in Bioremediation

PubMed Central

Martínez-Ocampo, Fernando; Lozano-Aguirre Beltrán, Luis Fernando; Hernández-Mendoza, Armando; Rojas-Espinoza, Luis Enrique; Popoca-Ursino, Elida Carolina; Ortiz-Hernández, María Laura; Sánchez-Salinas, Enrique; Ramos Quintana, Fernando

2015-01-01

Burkholderia cenocepacia is considered an opportunistic pathogen from humans and may cause disease in plants. A bioprospection from a plaguicide-contaminated agricultural field in Mexico identified several methyl parathion-degrading bacteria. Here, we report the draft genome sequence of B. cenocepacia strain CEIB S5-1, which gave us clues into ecological biodiversity. PMID:25744996

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

Role of luxS in Stress Tolerance and Adhesion Ability in Lactobacillus plantarum KLDS1.0391

PubMed Central

Jia, Fang-Fang; Zheng, Hui-Qi; Sun, Si-Rui; Pang, Xue-Hui; Liang, Yu; Shang, Jia-Cui; Zhu, Zong-Tao

2018-01-01

Lactobacillus plantarum, a probiotic, has a high survival rate and high colonization ability in the gastrointestinal tract. Tolerance to the gastrointestinal environment and adhesion to intestinal epithelial cells by some Lactobacillus species (excluding L. plantarum) are related to luxS/AI-2. Here, the role of luxS in tolerance to simulated digestive juice (SDJ) and adhesion to Caco-2 cells by L. plantarum KLDS1.0391 (hereafter, KLDS1.0391) was investigated. The KLDS1.0391 luxS mutant strain was constructed by homologous recombination. When luxS was deleted, acid and bile salt tolerance and survival rates in SDJ significantly decreased (p < 0.05 for all). The ability of the luxS deletion strain to adhere to Caco-2 cells was markedly lower than that of the wild-type strain (p < 0.05). The ability of the luxS mutant strain to adhere (competition, exclusion, and displacement) to Escherichia coli ATCC 25922 was significantly lower than that of the wild-type strain (p < 0.05 for all). A significant decrease was noted only in the exclusion adhesion inhibition of the luxS mutant strain to Salmonella typhimurium ATCC 14028 (p < 0.05). These results indicate that the luxS gene plays an important role in the gastrointestinal environment tolerance and adhesion ability of KLDS1.0391. PMID:29651434

Near-Isogenic Cry1F-Resistant Strain of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Investigate Fitness Cost Associated With Resistance in Brazil.

PubMed

Horikoshi, Renato J; Bernardi, Oderlei; Bernardi, Daniel; Okuma, Daniela M; Farias, Juliano R; Miraldo, Leonardo L; Amaral, Fernando S A; Omoto, Celso

2016-04-01

Field-evolved resistance to Cry1F maize in Spodoptera frugiperda (J.E. Smith) populations in Brazil was reported in 2014. In this study, to investigate fitness costs, we constructed a near-isogenic S. frugiperda-resistant strain (R-Cry1F) using Cry1F-resistant and Cry1F-susceptible strains sharing a close genetic background. A near-isogenic R-Cry1F strain was obtained by eight repeated backcrossings, each followed by sib-mating and selection among resistant and susceptible strains. Fitness cost parameters were evaluated by comparing the biological performance of resistant, susceptible, and heterozygous strains on artificial diet. Fitness parameters monitored included development time and survival rates of egg, larval, pupal, and egg-to-adult periods; sex ratio; adult longevity; timing of preoviposition, oviposition, and postoviposition; fecundity; and fertility. A fertility life table was also calculated. The near-isogenic R-Cry1F strain showed lower survival rate of eggs (32%), when compared with Sus and reciprocal crosses (41 and 55%, respectively). The number of R-Cry1F insects that completed the life cycle was reduced to ∼25%, compared with the Sus strain with ∼32% reaching the adult stage. The mean generation time (T) of R-Cry1F strain was ∼2 d shorter than R-Cry1F♂×Sus♀ and Sus strains. The reproductive parameters of R-Cry1F strain were similar to the Sus strain. However, fewer females were produced by R-Cry1F strain than R-Cry1F♀×Sus♂ and more females than R-Cry1F♂×Sus♀. In summary, no relevant fitness costs are observed in a near-isogenic Cry1F-resistant strain of S. frugiperda, indicating stability of resistance to Cry1F protein in Brazilian populations of this species in the absence of selection pressure.

Effects of strain rate, mixing ratio, and stress-strain definition on the mechanical behavior of the polydimethylsiloxane (PDMS) material as related to its biological applications.

PubMed

Khanafer, Khalil; Duprey, Ambroise; Schlicht, Marty; Berguer, Ramon

2009-04-01

Tensile tests on Polydimethylsiloxane (PDMS) materials were conducted to illustrate the effects of mixing ratio, definition of the stress-strain curve, and the strain rate on the elastic modulus and stress-strain curve. PDMS specimens were prepared according to the ASTM standards for elastic materials. Our results indicate that the physiological elastic modulus depends strongly on the definition of the stress-strain curve, mixing ratio, and the strain rate. For various mixing ratios and strain rates, true stress-strain definition results in higher stress and elastic modulus compared with engineering stress-strain and true stress-engineering strain definitions. The elastic modulus increases as the mixing ratio increases up-to 9:1 ratio after which the elastic modulus begins to decrease even as the mixing ratio continues to increase. The results presented in this study will be helpful to assist the design of in vitro experiments to mimic blood flow in arteries and to understand the complex interaction between blood flow and the walls of arteries using PDMS elastomer.

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium

PubMed Central

Thorgersen, Michael P.; Lancaster, W. Andrew; Rajeev, Lara; Ge, Xiaoxuan; Vaccaro, Brian J.; Poole, Farris L.; Arkin, Adam P.; Mukhopadhyay, Aindrila

2016-01-01

ABSTRACT Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC had an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. IMPORTANCE Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Herein, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. While other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U(IV) bound by an

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium

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

Thorgersen, Michael P.; Lancaster, W. Andrew; Rajeev, Lara

Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC hadmore » an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Here in this paper, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. Finally, while other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium.

PubMed

Thorgersen, Michael P; Lancaster, W Andrew; Rajeev, Lara; Ge, Xiaoxuan; Vaccaro, Brian J; Poole, Farris L; Arkin, Adam P; Mukhopadhyay, Aindrila; Adams, Michael W W

2017-02-15

Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC had an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Herein, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. While other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U(IV) bound by an S-layer complex

Diversity and Ecophysiology of New Isolates of Extremely Acidophilic CS2-Converting Acidithiobacillus Strains

PubMed Central

Smeulders, Marjan J.; Pol, Arjan; Zandvoort, Marcel H.; Jetten, Mike S. M.

2013-01-01

Biofiltration of industrial carbon disulfide (CS2)-contaminated waste air streams results in the acidification of biofilters and therefore reduced performance, high water use, and increased costs. To address these issues, we isolated 16 extremely acidophilic CS2-converting Acidithiobacillus thiooxidans strains that tolerated up to 6% (vol/vol) sulfuric acid. The ecophysiological properties of five selected strains (2Bp, Sts 4-3, S1p, G8, and BBW1) were compared. These five strains had pH optima between 1 (2Bp) and 2 (S1p). Their affinities for CS2 ranged between 80 (G8) and 130 (2Bp) μM. Strains S1p, G8, and BBW1 had more hydrophobic cell surfaces and produced less extracellular polymeric substance than did strains 2Bp and Sts 4-3. All five strains converted about 80% of the S added as CS2 to S0 when CS2 was supplied in excess. The rate of S0 consumption varied between 7 (Sts 4-3) and 63 (S1p) nmol O2 min−1 ml culture−1. Low S0 consumption rates correlated partly with low levels of cell attachment to externally produced S0 globules. During chemostat growth, the relative amount of CS2 hydrolase in the cell increased with decreasing growth rates. This resulted in more S0 accumulation during CS2 overloads at low growth rates. Intermittent interruptions of the CS2 supply affected all five strains. Strains S1p, G8, and BBW1 recovered from 24 h of starvation within 4 h, and strains 2Bp and Sts 4-3 recovered within 24 h after CS2 was resupplied. We recommend the use of mixtures of Acidithiobacillus strains in industrial biofilters. PMID:23995926

Experimental and numerical investigation of strain rate effect on low cycle fatigue behaviour of AA 5754 alloy

NASA Astrophysics Data System (ADS)

Kumar, P.; Singh, A.

2018-04-01

The present study deals with evaluation of low cycle fatigue (LCF) behavior of aluminum alloy 5754 (AA 5754) at different strain rates. This alloy has magnesium (Mg) as main alloying element (Al-Mg alloy) which makes this alloy suitable for Marines and Cryogenics applications. The testing procedure and specimen preparation are guided by ASTM E606 standard. The tests are performed at 0.5% strain amplitude with three different strain rates i.e. 0.5×10-3 sec-1, 1×10-3 sec-1 and 2×10-3 sec-1 thus the frequency of tests vary accordingly. The experimental results show that there is significant decrease in the fatigue life with the increase in strain rate. LCF behavior of AA 5754 is also simulated at different strain rates by finite element method. Chaboche kinematic hardening cyclic plasticity model is used for simulating the hardening behavior of the material. Axisymmetric finite element model is created to reduce the computational cost of the simulation. The material coefficients used for “Chaboche Model” are determined by experimentally obtained stabilized hysteresis loop. The results obtained from finite element simulation are compared with those obtained through LCF experiments.

High Strain Rate Material Behavior

DTIC Science & Technology

1985-12-01

data. iii Mr. Dennis Paisely conducted the single plate impact test. Mr. Danny Yaziv is responsible for developing the double flyer plate technique and...neck developed . The sharp rise in the flow stress is due to the increased strain-rates during necking. The maximum observed value of effective stress...for the material modeling. Computer programs and special purpose subroutines were developed to use the Bodner-Partom model in the STEALTH finite

Deformation mechanisms of antigorite and strain localization during dehydration

NASA Astrophysics Data System (ADS)

Proctor, B.; Hirth, G.

2012-12-01

Antigorite, the high temperature and pressure serpentine polytype, is thought to exist along subduction zones between the mantle wedge and the subducting oceanic crust (e.g., Wada et al., 2008). Understanding how the rheology of antigorite changes with depth along the slab may be key to understanding seismicity along the upper plate boundary (e.g., Hacker et al., 2003). To explore this phenomenon we are conducting constant strain rate general shear experiments on antigorite-rich serpentinite at shear strain rates of 5*10^-7/s to 10^-5/s, confining pressures from 1-2 GPa and temperatures from 400-700°C. We are using microstructural observations to constrain deformation mechanisms and investigate conditions where strain localization occurs. In some experiments we employ either strain rate stepping or temperature ramping to examine the stress dependence of viscosity (i.e., determine stress exponent) and syntectonic reaction during heating. The results of our general shear experiments suggest the rheologic behavior of antigorite varies significantly with changes in temperature and pressure, similar to previous work in axial compression (e.g., Chernak and Hirth, 2010). At 400°C and 1GPa confining pressure antigorite deforms initially via steady-state ductile flow with strengths as high as 1.4 GPa at a strain rate of 10^-5/s. With increasing strain we observe weakening events that correlate with the development of shear fractures within the sample. At 2GPa pressure, the flow strength of antigorite increases to ~1.8 GPa at 10^-6/s and deformation is distributed at low strain. Strain rate stepping at these conditions suggests a very weak strain rate dependence on strength with a 5-10% change in stress for an order of magnitude strain rate step. At 700C and 1 GPa, above the thermal stability of antigorite, the steady-state strength is ~120 MPa at 10^-5/s. In these samples olivine becomes the dominant phase as antigorite progressively reacts to olivine and pyroxene. At the

Ferromagnetic properties of Mn-doped HfS2 monolayer under strain

NASA Astrophysics Data System (ADS)

Ma, Xu; Zhao, Xu; Wu, Ninghua; Xin, Qianqian; Liu, Xiaomeng; Wang, Tianxing; Wei, Shuyi

2017-12-01

Using the first-principles calculations, we investigated electronic and magnetic properties of Mn-doped HfS2 monolayer for 4% and 8% Mn concentration. We study the strain tuning of electronic and magnetic properties of 4% Mn-doped HfS2 monolayer firstly. Our results show that the Mn-doped HfS2 monolayer is magnetic nanomaterial without strain. It keeps this character until the compressive strain comes to -8%, and the magnetism disappear with lager compressive strain. With the increasing tensile strain, the doped system transforms from semiconductor to half-metallic when the tensile strain is equivalent to or greater than 5%. The largest half-metallic gap is 1.307 eV at 5% tensile strain and the magnetic moment always keeps about 3μB, which indicates that Mn-doped HfS2 monolayer can be a candidate for superior half-metallic namomaterial. Furthermore, we find two Mn dopants couple ferromagnetically via antiferromagnetic (AFM) p-d exchange interaction at the environment of 8% concentration. It keeps the properties of magnetic semiconductor under two Mn-doped configurations with different Mn-Mn separations. Our studies predict Mn-doped HfS2 monolayer under strain to be candidates for dilute magnetic semiconductors.

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.

Global stability analysis of two-strain epidemic model with bilinear and non-monotone incidence rates

NASA Astrophysics Data System (ADS)

Baba, Isa Abdullahi; Hincal, Evren

2017-05-01

In this article we studied an epidemic model consisting of two strains with different types of incidence rates; bilinear and non-monotone. The model consists of four equilibrium points: disease-free equilibrium, endemic with respect to strain 1, endemic with respect to strain 2, and endemic with respect to both strains. The global stability analysis of the equilibrium points was carried out through the use of Lyapunov functions. Two basic reproduction ratios R 1 0 and R 2 0 are found, and we have shown that if both are less than one, the disease dies out, and if both are greater than one epidemic occurs. Furthermore, epidemics occur with respect to any strain with a basic reproduction ratio greater than one and disease dies out with respect to any strain with a basic reproduction ratio less than one. It was also shown that any strain with highest basic reproduction ratio will automatically outperform the other strain, thereby eliminating it. Numerical simulations were carried out to support the analytic result and to show the effect of the parameter k in the non-monotone incidence rate, which describes the psychological effect of general public towards infection.

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.

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.

Prospective Evaluation of the Global Earthquake Activity Rate Model (GEAR1) Earthquake Forecast: Preliminary Results

NASA Astrophysics Data System (ADS)

Strader, Anne; Schorlemmer, Danijel; Beutin, Thomas

2017-04-01

The Global Earthquake Activity Rate Model (GEAR1) is a hybrid seismicity model, constructed from a loglinear combination of smoothed seismicity from the Global Centroid Moment Tensor (CMT) earthquake catalog and geodetic strain rates (Global Strain Rate Map, version 2.1). For the 2005-2012 retrospective evaluation period, GEAR1 outperformed both parent strain rate and smoothed seismicity forecasts. Since 1. October 2015, GEAR1 has been prospectively evaluated by the Collaboratory for the Study of Earthquake Predictability (CSEP) testing center. Here, we present initial one-year test results of the GEAR1, GSRM and GSRM2.1, as well as localized evaluation of GEAR1 performance. The models were evaluated on the consistency in number (N-test), spatial (S-test) and magnitude (M-test) distribution of forecasted and observed earthquakes, as well as overall data consistency (CL-, L-tests). Performance at target earthquake locations was compared between models using the classical paired T-test and its non-parametric equivalent, the W-test, to determine if one model could be rejected in favor of another at the 0.05 significance level. For the evaluation period from 1. October 2015 to 1. October 2016, the GEAR1, GSRM and GSRM2.1 forecasts pass all CSEP likelihood tests. Comparative test results show statistically significant improvement of GEAR1 performance over both strain rate-based forecasts, both of which can be rejected in favor of GEAR1. Using point process residual analysis, we investigate the spatial distribution of differences in GEAR1, GSRM and GSRM2 model performance, to identify regions where the GEAR1 model should be adjusted, that could not be inferred from CSEP test results. Furthermore, we investigate whether the optimal combination of smoothed seismicity and strain rates remains stable over space and time.

The Microstructural Evolution and Mechanical Properties of Zr-Based Metallic Glass under Different Strain Rate Compressions

PubMed Central

Chen, Tao-Hsing; Tsai, Chih-Kai

2015-01-01

In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD) and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10−3 to 5.1 × 103 s−1 and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB) and an MTS tester. An in situ transmission electron microscope (TEM) nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles. PMID:28788034

Growth rates of three geographically separated strains of the ichthyotoxic Prymnesium parvum (Prymnesiophyceae) in response to six different pH levels

NASA Astrophysics Data System (ADS)

Lysgaard, Maria L.; Eckford-Soper, Lisa; Daugbjerg, Niels

2018-05-01

Continued anthropogenic carbon emissions are expected to cause a decline in global average pH of the oceans to a projected value of 7.8 by the end of the century. Understanding how harmful algal bloom (HAB) species will respond to lowered pH levels will be important when predicting future HAB events and their ecological consequences. In this study, we examined how manipulated pH levels affected the growth rate of three strains of Prymnesium parvum from North America, Denmark and Japan. Triplicate strains were grown under pH conditions ranging from 6.6 to 9.1 to simulate plausible future levels. Different tolerances were evident for all strains. Significantly higher growth rates were observed at pH 6.6-8.1 compared to growth rates at pH 8.6-9.1 and a lower pH limit was not observed. The Japanese strain (NIES-1017) had the highest maximum growth rate of 0.39 divisions day-1 at pH 6.6 but a low tolerance (0.22 divisions day-1) to high levels (pH 9.1) with growth declining markedly after pH 7.6. The Danish (SCCAP K-0081) and North American (UTEX LB 2797) strains had maximum growth rates of 0.26 and 0.35 divisions day-1, respectively between pH 6.6-8.1. Compared to the other two strains the Danish strain had a statistically lower growth rate across all pH treatments. Strain differences were either attributed to their provenance or the length of time the strain had been in culture.

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

A Combined Precipitation, Yield Stress, and Work Hardening Model for Al-Mg-Si Alloys Incorporating the Effects of Strain Rate and Temperature

NASA Astrophysics Data System (ADS)

Myhr, Ole Runar; Hopperstad, Odd Sture; Børvik, Tore

2018-05-01

In this study, a combined precipitation, yield strength, and work hardening model for Al-Mg-Si alloys known as NaMo has been further developed to include the effects of strain rate and temperature on the resulting stress-strain behavior. The extension of the model is based on a comprehensive experimental database, where thermomechanical data for three different Al-Mg-Si alloys are available. In the tests, the temperature was varied between 20 °C and 350 °C with strain rates ranging from 10-6 to 750 s-1 using ordinary tension tests for low strain rates and a split-Hopkinson tension bar system for high strain rates, respectively. This large span in temperatures and strain rates covers a broad range of industrial relevant problems from creep to impact loading. Based on the experimental data, a procedure for calibrating the different physical parameters of the model has been developed, starting with the simplest case of a stable precipitate structure and small plastic strains, from which basic kinetic data for obstacle limited dislocation glide were extracted. For larger strains, when work hardening becomes significant, the dynamic recovery was linked to the Zener-Hollomon parameter, again using a stable precipitate structure as a basis for calibration. Finally, the complex situation of concurrent work hardening and dynamic evolution of the precipitate structure was analyzed using a stepwise numerical solution algorithm where parameters representing the instantaneous state of the structure were used to calculate the corresponding instantaneous yield strength and work hardening rate. The model was demonstrated to exhibit a high degree of predictive power as documented by a good agreement between predictions and measurements, and it is deemed well suited for simulations of thermomechanical processing of Al-Mg-Si alloys where plastic deformation is carried out at various strain rates and temperatures.

Effects of Recovery Behavior and Strain-Rate Dependence of Stress-Strain Curve on Prediction Accuracy of Thermal Stress Analysis During Casting

NASA Astrophysics Data System (ADS)

Motoyama, Yuichi; Shiga, Hidetoshi; Sato, Takeshi; Kambe, Hiroshi; Yoshida, Makoto

2017-06-01

Recovery behavior (recovery) and strain-rate dependence of the stress-strain curve (strain-rate dependence) are incorporated into constitutive equations of alloys to predict residual stress and thermal stress during casting. Nevertheless, few studies have systematically investigated the effects of these metallurgical phenomena on the prediction accuracy of thermal stress in a casting. This study compares the thermal stress analysis results with in situ thermal stress measurement results of an Al-Si-Cu specimen during casting. The results underscore the importance for the alloy constitutive equation of incorporating strain-rate dependence to predict thermal stress that develops at high temperatures where the alloy shows strong strain-rate dependence of the stress-strain curve. However, the prediction accuracy of the thermal stress developed at low temperatures did not improve by considering the strain-rate dependence. Incorporating recovery into the constitutive equation improved the accuracy of the simulated thermal stress at low temperatures. Results of comparison implied that the constitutive equation should include strain-rate dependence to simulate defects that develop from thermal stress at high temperatures, such as hot tearing and hot cracking. Recovery should be incorporated into the alloy constitutive equation to predict the casting residual stress and deformation caused by the thermal stress developed mainly in the low temperature range.

On strain and stress in living cells

NASA Astrophysics Data System (ADS)

Cox, Brian N.; Smith, David W.

2014-11-01

in detail. However, estimates can be inferred from the known relative velocities of the cells' centers of mass. When averaged over a volume comparable to the cell size, representative values of the strain are, to order of magnitude, ɛ0≈0.1 and γ0≈0.1. The shape distortions of cells seen, for example, in Fig. 1c, imply peak strains in minor segments of a cell of magnitude unity, ɛ0≈1 and γ0≈1; these values represent the upper bound of plausible values and are included for discussion of the extremes of attainable strain energy rates.Given the strain magnitudes, the strain rates follow from the fact that a cell switches from one contacting neighbor in the adjacent row to the next in approximately 0.25 d, during which motion the strains might vary from zero to their maximum values and back again. Thus the most probable shear strain rate is inferred to be γ˙0=10-6 s-1 and the most probable tensile strain rate is inferred to be ɛ˙0≈10-6 s-1, with high bounds γ˙0=10-5 s-1 and ɛ˙0=10-5 s-1.

Analysis of High Precision GPS Time Series and Strain Rates for the Geothermal Play Fairway Analysis of Washington State Prospects Project

DOE Data Explorer

Michael Swyer

2015-02-22

Global Positioning System (GPS) time series from the National Science Foundation (NSF) Earthscope’s Plate Boundary Observatory (PBO) and Central Washington University’s Pacific Northwest Geodetic Array (PANGA). GPS station velocities were used to infer strain rates using the ‘splines in tension’ method. Strain rates were derived separately for subduction zone locking at depth and block rotation near the surface within crustal block boundaries.

Deletion of JJJ1 improves acetic acid tolerance and bioethanol fermentation performance of Saccharomyces cerevisiae strains.

PubMed

Wu, Xuechang; Zhang, Lijie; Jin, Xinna; Fang, Yahong; Zhang, Ke; Qi, Lei; Zheng, Daoqiong

2016-07-01

To improve tolerance to acetic acid that is present in lignocellulosic hydrolysates and affects bioethanol production by Saccharomyces cerevisiae. Saccharomyces cerevisiae strains with improved tolerance to acetic acid were obtained through deletion of the JJJ1 gene. The lag phase of the JJJ1 deletion mutant BYΔJJJ1 was ~16 h shorter than that of the parent strain, BY4741, when the fermentation medium contained 4.5 g acetic acid/l. Additionally, the specific ethanol production rate of BYΔJJJ1 was increased (0.057 g/g h) compared to that of the parent strain (0.051 g/g h). Comparative transcription and physiological analyses revealed higher long chain fatty acid, trehalose, and catalase contents might be critical factors responsible for the acetic acid resistance of JJJ1 knockout strains. JJJ1 deletion improves acetic acid tolerance and ethanol fermentation performance of S. cerevisiae.

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.

Degradation of 1,2-Dibromoethane by Mycobacterium sp. Strain GP1

PubMed Central

Poelarends, Gerrit J.; van Hylckama Vlieg, Johan E. T.; Marchesi, Julian R.; Freitas Dos Santos, Luisa M.; Janssen, Dick B.

1999-01-01

The newly isolated bacterial strain GP1 can utilize 1,2-dibromoethane as the sole carbon and energy source. On the basis of 16S rRNA gene sequence analysis, the organism was identified as a member of the subgroup which contains the fast-growing mycobacteria. The first step in 1,2-dibromoethane metabolism is catalyzed by a hydrolytic haloalkane dehalogenase. The resulting 2-bromoethanol is rapidly converted to ethylene oxide by a haloalcohol dehalogenase, in this way preventing the accumulation of 2-bromoethanol and 2-bromoacetaldehyde as toxic intermediates. Ethylene oxide can serve as a growth substrate for strain GP1, but the pathway(s) by which it is further metabolized is still unclear. Strain GP1 can also utilize 1-chloropropane, 1-bromopropane, 2-bromoethanol, and 2-chloroethanol as growth substrates. 2-Chloroethanol and 2-bromoethanol are metabolized via ethylene oxide, which for both haloalcohols is a novel way to remove the halide without going through the corresponding acetaldehyde intermediate. The haloalkane dehalogenase gene was cloned and sequenced. The dehalogenase (DhaAf) encoded by this gene is identical to the haloalkane dehalogenase (DhaA) of Rhodococcus rhodochrous NCIMB 13064, except for three amino acid substitutions and a 14-amino-acid extension at the C terminus. Alignments of the complete dehalogenase gene region of strain GP1 with DNA sequences in different databases showed that a large part of a dhaA gene region, which is also present in R. rhodochrous NCIMB 13064, was fused to a fragment of a haloalcohol dehalogenase gene that was identical to the last 42 nucleotides of the hheB gene found in Corynebacterium sp. strain N-1074. PMID:10094681

Degradation of 1,2-dibromoethane by Mycobacterium sp. strain GP1.

PubMed

Poelarends, G J; van Hylckama Vlieg, J E; Marchesi, J R; Freitas Dos Santos, L M; Janssen, D B

1999-04-01

The newly isolated bacterial strain GP1 can utilize 1, 2-dibromoethane as the sole carbon and energy source. On the basis of 16S rRNA gene sequence analysis, the organism was identified as a member of the subgroup which contains the fast-growing mycobacteria. The first step in 1,2-dibromoethane metabolism is catalyzed by a hydrolytic haloalkane dehalogenase. The resulting 2-bromoethanol is rapidly converted to ethylene oxide by a haloalcohol dehalogenase, in this way preventing the accumulation of 2-bromoethanol and 2-bromoacetaldehyde as toxic intermediates. Ethylene oxide can serve as a growth substrate for strain GP1, but the pathway(s) by which it is further metabolized is still unclear. Strain GP1 can also utilize 1-chloropropane, 1-bromopropane, 2-bromoethanol, and 2-chloroethanol as growth substrates. 2-Chloroethanol and 2-bromoethanol are metabolized via ethylene oxide, which for both haloalcohols is a novel way to remove the halide without going through the corresponding acetaldehyde intermediate. The haloalkane dehalogenase gene was cloned and sequenced. The dehalogenase (DhaAf) encoded by this gene is identical to the haloalkane dehalogenase (DhaA) of Rhodococcus rhodochrous NCIMB 13064, except for three amino acid substitutions and a 14-amino-acid extension at the C terminus. Alignments of the complete dehalogenase gene region of strain GP1 with DNA sequences in different databases showed that a large part of a dhaA gene region, which is also present in R. rhodochrous NCIMB 13064, was fused to a fragment of a haloalcohol dehalogenase gene that was identical to the last 42 nucleotides of the hheB gene found in Corynebacterium sp. strain N-1074.

Strain rate and shear stress at the grain scale generated during near equilibrium antigorite dehydration

NASA Astrophysics Data System (ADS)

Padrón-Navarta, José Alberto; Tommasi, Andréa; Garrido, Carlos J.; Mainprice, David; Clément, Maxime

2016-04-01

has not been previously reported and offers an unique opportunity to estimate a lower bound for the strain rates and local shear stresses generated during the grain growth and coeval compaction. Estimated values based on experimental creep rates on pyroxene aggregates [3] result in strain rates in the order of 10-12 to 10-13 s-1 and shear stresses of 60-70 MPa. Lower shear stress values (20-40 MPa) are retrieved using the thermodynamic model clinoenstatite inversion of Coe [4] in combination with the hydrostatic high-pressure experimental data on the stability of low clinoenstatite (P21/c). These data suggest that, under low deviatoric stress, fluid extraction and compaction near equilibrium in natural systems are only marginally higher than the strain rate of the solid matrix. These observations support the relatively long residence time of fluids in dehydration fronts and the necessity to further explore and quantify the feedback between mineral grain growth and fluid migration. [1] Connolly (2010) Elements 6(3):165-172; [2] Padrón-Navarta et al. (2015). Contrib Miner Petrol 169:35 [3] Raleigh et al. (1971). J Geophys Res 76(17): 4011-4022; [4] Coe (1970). Contrib Miner Petrol 26(3):247-264

Initial Reaction(s) in Biotransformation of CL-20 Is Catalyzed by Salicylate 1-Monooxygenase from Pseudomonas sp. Strain ATCC 29352

PubMed Central

Bhushan, Bharat; Halasz, Annamaria; Spain, Jim C.; Hawari, Jalal

2004-01-01

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) (C6H6N12O12), a future-generation high-energy explosive, is biodegradable by Pseudomonas sp. strain FA1 and Agrobacterium sp. strain JS71; however, the nature of the enzyme(s) involved in the process was not understood. In the present study, salicylate 1-monooxygenase, a flavin adenine dinucleotide (FAD)-containing purified enzyme from Pseudomonas sp. strain ATCC 29352, biotransformed CL-20 at rates of 0.256 ± 0.011 and 0.043 ± 0.003 nmol min−1 mg of protein−1 under anaerobic and aerobic conditions, respectively. The disappearance of CL-20 was accompanied by the release of nitrite ions. Using liquid chromatography/mass spectrometry in the negative electrospray ionization mode, we detected a metabolite with a deprotonated mass ion [M − H]− at 345 Da, corresponding to an empirical formula of C6H6N10O8, produced as a result of two sequential N denitration steps on the CL- 20 molecule. We also detected two isomeric metabolites with [M − H]− at 381 Da corresponding to an empirical formula of C6H10N10O10. The latter was a hydrated product of the metabolite C6H6N10O8 with addition of two H2O molecules, as confirmed by tests using 18O-labeled water. The product stoichiometry showed that each reacted CL-20 molecule produced about 1.7 nitrite ions, 3.2 molecules of nitrous oxide, 1.5 molecules of formic acid, and 0.6 ammonium ion. Diphenyliodonium-mediated inhibition of salicylate 1-monooxygenase and a comparative study between native, deflavo, and reconstituted enzyme(s) showed that FAD site of the enzyme was involved in the biotransformation of CL-20 catalyzed by salicylate 1-monooxygenase. The data suggested that salicylate 1-monooxygenase catalyzed two oxygen-sensitive single-electron transfer steps necessary to release two nitrite ions from CL-20 and that this was followed by the secondary decomposition of this energetic chemical. PMID:15240281

Analysis of the tensile stress-strain behavior of elastomers at constant strain rates. I - Criteria for separability of the time and strain effects

NASA Technical Reports Server (NTRS)

Hong, S. D.; Fedors, R. F.; Schwarzl, F.; Moacanin, J.; Landel, R. F.

1981-01-01

A theoretical analysis of the tensile stress-strain relation of elastomers at constant strain rate is presented which shows that the time and the stress effect are separable if the experimental time scale coincides with a segment of the relaxation modulus that can be described by a single power law. It is also shown that time-strain separability is valid if the strain function is linearly proportional to the Cauchy strain, and that when time-strain separability holds, two strain-dependent quantities can be obtained experimentally. In the case where time and strain effect are not separable, superposition can be achieved only by using temperature and strain-dependent shift factors.

Influence of strain rate and temperature on tensile properties and flow behaviour of a reduced activation ferritic-martensitic steel

NASA Astrophysics Data System (ADS)

Vanaja, J.; Laha, K.; Sam, Shiju; Nandagopal, M.; Panneer Selvi, S.; Mathew, M. D.; Jayakumar, T.; Rajendra Kumar, E.

2012-05-01

Tensile strength and flow behaviour of a Reduced Activation Ferritic-Martensitic (RAFM) steel (9Cr-1W-0.06Ta-0.22V-0.08C) have been investigated over a temperature range of 300-873 K at different strain rates. Tensile strength of the steel decreased with temperature and increased with strain rate except at intermediate temperatures. Negative strain rate sensitivity of flow stress of the steel at intermediate temperatures revealed the occurrence of dynamic strain ageing in the steel, even though no serrated flow was observed. The tensile flow behaviour of the material was well represented by the Voce strain hardening equation for all the test conditions. Temperature and strain rate dependence of the various parameters of Voce equation were interpreted with the possible deformation mechanisms. The equivalence between the saturation stress at a given strain rate in tensile test and steady state deformation rate at a given stress in creep test was found to be satisfied by the RAFM steel.

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

Dynamic Strain Aging of Nickel-Base Alloys 800H and 690

NASA Astrophysics Data System (ADS)

Moss, Tyler E.; Was, Gary S.

2012-10-01

The objective of the current investigation is to characterize the dynamic strain aging (DSA) behavior in alloys 800H and 690. Constant extension rate tests were conducted at strain rates in the range of 10-4 s-1 to 10-7 s-1and temperatures between 295 K and 673 K (22 °C and 400 °C), in an argon atmosphere. Maps for the occurrence of serrated flow as a function of strain rate and temperature were built for both alloys. The enthalpy of serrated flow appearance of alloy 800H was found to be 1.07 ± 0.30 eV.

Influence of oxygen concentration, fuel composition, and strain rate on synthesis of carbon nanomaterials

NASA Astrophysics Data System (ADS)

Hou, Shuhn-Shyurng; Huang, Wei-Cheng

2015-02-01

This paper investigates the influence of flame parameters including oxygen concentration, fuel composition, and strain rate on the synthesis of carbon nanomaterials in opposed-jet ethylene diffusion flames with or without rigid-body rotation. In the experiments, a mixture of ethylene and nitrogen was introduced from the upper burner; meanwhile, a mixture of oxygen and nitrogen was supplied from the lower burner. A nascent nickel mesh was used as the catalytic metal substrate to collect deposited materials. With non-rotating opposed-jet diffusion flames, carbon nanotubes (CNTs) were successfully produced for oxygen concentrations in the range of 21-50 % at a fixed ethylene concentration of 20 %, and for ethylene concentrations ranging from 14 to 24 % at a constant oxygen concentration of 40 %. With rotating opposed-jet diffusion flames, the strain rate was varied by adjusting the angular velocities of the upper and lower burners. The strain rate governed by flow rotation greatly affects the synthesis of carbon nanomaterials [i.e., CNTs and carbon nano-onions (CNOs)] either through the residence time or carbon sources available. An increase in the angular velocity lengthened the residence time of the flow and thus caused the diffusion flame to experience a decreased strain rate, which in turn produced more carbon sources. The growth of multi-walled CNTs was achieved for the stretched flames experiencing a higher strain rate [i.e., angular velocity was equal to 0 or 1 rotations per second (rps)]. CNOs were synthesized at a lower strain rate (i.e., angular velocity was in the range of 2-5 rps). It is noteworthy that the strain rate controlled by flow rotation greatly influences the fabrication of carbon nanostructures owing to the residence time as well as carbon source. Additionally, more carbon sources and higher temperature are required for the synthesis of CNOs compared with those required for CNTs (i.e., about 605-625 °C for CNTs and 700-800 °C for CNOs).

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.

Molecular dynamics simulations showing 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) membrane mechanoporation damage under different strain paths.

PubMed

Murphy, M A; Mun, Sungkwang; Horstemeyer, M F; Baskes, M I; Bakhtiary, A; LaPlaca, Michelle C; Gwaltney, Steven R; Williams, Lakiesha N; Prabhu, R K

2018-04-09

Continuum finite element material models used for traumatic brain injury lack local injury parameters necessitating nanoscale mechanical injury mechanisms be incorporated. One such mechanism is membrane mechanoporation, which can occur during physical insults and can be devastating to cells, depending on the level of disruption. The current study investigates the strain state dependence of phospholipid bilayer mechanoporation and failure. Using molecular dynamics, a simplified membrane, consisting of 72 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) phospholipids, was subjected to equibiaxial, 2:1 non-equibiaxial, 4:1 non-equibiaxial, strip biaxial, and uniaxial tensile deformations at a von Mises strain rate of 5.45 × 10 8 s -1 , resulting in velocities in the range of 1 to 4.6 m·s -1 . A water bridge forming through both phospholipid bilayer leaflets was used to determine structural failure. The stress magnitude, failure strain, headgroup clustering, and damage responses were found to be strain state-dependent. The strain state order of detrimentality in descending order was equibiaxial, 2:1 non-equibiaxial, 4:1 non-equibiaxial, strip biaxial, and uniaxial. The phospholipid bilayer failed at von Mises strains of .46, .47, .53, .77, and 1.67 during these respective strain path simulations. Additionally, a Membrane Failure Limit Diagram (MFLD) was created using the pore nucleation, growth, and failure strains to demonstrate safe and unsafe membrane deformation regions. This MFLD allowed representative equations to be derived to predict membrane failure from in-plane strains. These results provide the basis to implement a more accurate mechano-physiological internal state variable continuum model that captures lower length scale damage and will aid in developing higher fidelity injury models.

Strain rate dependent orthotropic properties of pristine and impulsively loaded porcine temporomandibular joint disk.

PubMed

Beatty, M W; Bruno, M J; Iwasaki, L R; Nickel, J C

2001-10-01

The purpose of this study was to characterize the tensile stress-strain behavior of the porcine temporomandibular joint (TMJ) disk with respect to collagen orientation and strain rate dependency. The apparent elastic modulus, ultimate tensile strength, and strain at maximum stress were measured at three elongation rates (0.5, 50, and 500 mm/min) for dumbbell-shaped samples oriented along either anteroposterior or mediolateral axes of the disks. In order to study the effects of impact-induced fissuring on the mechanical behavior, the same properties were measured along each orientation at an elongation rate of 500 mm/min for disks subjected to impulsive loads of 0.5 N. s. The results suggested a strongly orthotropic nature to the healthy pristine disk. The values for the apparent modulus and ultimate strength were 10-fold higher along the anteroposterior axis (p < or = 0.01), which represented the primary orientation of the collagen fibers. Strain rate dependency was evident for loading along the anteroposterior axis but not along the mediolateral axis. No significant differences in any property were noted between pristine and impulsively loaded disks for either orientation (p > 0.05). The results demonstrated the importance of choosing an orthotropic model for the TMJ disk to conduct finite element modeling, to develop failure criteria, and to construct tissue-engineered replacements. Impact-induced fissuring requires further study to determine if the TMJ disk is orthotropic with respect to fatigue.

The effect of strain rate on the evolution of microstructure in aluminium alloys.

PubMed

Leszczyńska-Madej, B; Richert, M

2010-03-01

Intensive deformations influence strongly microstructure. The very well-known phenomenon is the diminishing dimension of grain size by the severe plastic deformation (SPD) methods. The nanometric features of microstructure were discovered after the SPD deformation of various materials, such as aluminium alloys, iron and others. The observed changes depended on the kind of the deformed material, amount of deformation, strain rate, existence of different phases and stacking fault energy. The influence of the strain and strain rate on the microstructure is commonly investigated nowadays. It was found that the high strain rates activate deformation in shear bands, microbands and adiabatic shear bands. It was observed that bands were places of the nucleation of nanograins in the material deformed by SPD methods. In the work, the refinement of microstructure of the aluminium alloys influenced by the high strain rate was investigated. The samples were compressed by a specially designed hammer to the deformation of phi= 0/0.62 with the strain rate in the range of [Formula in text]. The highest reduction of microbands width with the increase of the strain was found in the AlCu4Zr alloy. The influence of the strain rate on the microstructure refinement indicated that the increase of the strain rate caused the reduction of the microbands width in the all investigated materials (Al99.5, AlCu4Zr, AlMg5, AlZn6Mg2.5CuZr). A characteristic feature of the microstructure of the compressed material was large density of the shear bands and microbands. It was found that the microbands show a large misorientation to the surrounds and, except Al99.5, the large density of dislocation.

Characteristic systolic waveform of left ventricular longitudinal strain rate in patients with hypertrophic cardiomyopathy.

PubMed

Okada, Kazunori; Kaga, Sanae; Mikami, Taisei; Masauzi, Nobuo; Abe, Ayumu; Nakabachi, Masahiro; Yokoyama, Shinobu; Nishino, Hisao; Ichikawa, Ayako; Nishida, Mutsumi; Murai, Daisuke; Hayashi, Taichi; Shimizu, Chikara; Iwano, Hiroyuki; Yamada, Satoshi; Tsutsui, Hiroyuki

2017-05-01

We analyzed the waveform of systolic strain and strain-rate curves to find a characteristic left ventricular (LV) myocardial contraction pattern in patients with hypertrophic cardiomyopathy (HCM), and evaluated the utility of these parameters for the differentiation of HCM and LV hypertrophy secondary to hypertension (HT). From global strain and strain-rate curves in the longitudinal and circumferential directions, the time from mitral valve closure to the peak strains (T-LS and T-CS, respectively) and the peak systolic strain rates (T-LSSR and T-CSSR, respectively) were measured in 34 patients with HCM, 30 patients with HT, and 25 control subjects. The systolic strain-rate waveform was classified into 3 patterns ("V", "W", and "√" pattern). In the HCM group, T-LS was prolonged, but T-LSSR was shortened; consequently, T-LSSR/T-LS ratio was distinctly lower than in the HT and control groups. The "√" pattern of longitudinal strain-rate waveform was more frequently seen in the HCM group (74 %) than in the control (4 %) and HT (20 %) groups. Similar but less distinct results were obtained in the circumferential direction. To differentiate HCM from HT, the sensitivity and specificity of the T-LSSR/T-LS ratio <0.34 and the "√"-shaped longitudinal strain-rate waveform were 85 and 63 %, and 74 and 80 %, respectively. In conclusion, in patients with HCM, a reduced T-LSSR/T-LS ratio and a characteristic "√"-shaped waveform of LV systolic strain rate was seen, especially in the longitudinal direction. The timing and waveform analyses of systolic strain rate may be useful to distinguish between HCM and HT.

Predictions of High Strain Rate Failure Modes in Layered Aluminum Composites

NASA Astrophysics Data System (ADS)

Khanikar, Prasenjit; Zikry, M. A.

2014-01-01

A dislocation density-based crystalline plasticity formulation, specialized finite-element techniques, and rational crystallographic orientation relations were used to predict and characterize the failure modes associated with the high strain rate behavior of aluminum layered composites. Two alloy layers, a high strength alloy, aluminum 2195, and an aluminum alloy 2139, with high toughness, were modeled with representative microstructures that included precipitates, dispersed particles, and different grain boundary distributions. Different layer arrangements were investigated for high strain rate applications and the optimal arrangement was with the high toughness 2139 layer on the bottom, which provided extensive shear strain localization, and the high strength 2195 layer on the top for high strength resistance The layer thickness of the bottom high toughness layer also affected the bending behavior of the roll-bonded interface and the potential delamination of the layers. Shear strain localization, dynamic cracking, and delamination are the mutually competing failure mechanisms for the layered metallic composite, and control of these failure modes can be used to optimize behavior for high strain rate applications.

Cyclic strain rate effects in fatigued face-centred and body-centred cubic metals

NASA Astrophysics Data System (ADS)

Mughrabi, Haël

2013-09-01

The present work deals mainly with the effect and the use of strain rate and temperature changes during cyclic deformation as a means to obtain valuable information on the thermally activated dislocation glide processes, based on the assessment of reversible changes of the thermal effective stress and of transient changes of the athermal stress. The importance of closed-loop testing in true plastic strain control with constant cyclic plastic strain rate throughout the cycle is explained and emphasized, especially with respect to the case of strain rate sensitive materials. Stress responses of face-centred cubic and body-centred cubic (bcc) metals to cyclic strain rate changes are presented to illustrate that the deformation modes of these two classes of materials differ characteristically at temperatures below that the so-called knee temperature of bcc metals. When such tests are performed in cyclic saturation, the temperature and strain rate dependence of bcc metals can be measured very accurately on one and the same specimen, permitting a thorough analysis of thermal activation.

Forming Ganymede’s grooves at smaller strain: Toward a self-consistent local and global strain history for Ganymede

USGS Publications Warehouse

Bland, Michael T.; McKinnon, W. B.

2015-01-01

The ubiquity of tectonic features formed in extension, and the apparent absence of ones formed in contraction, has led to the hypothesis that Ganymede has undergone global expansion in its past. Determining the magnitude of such expansion is challenging however, and extrapolation of locally or regionally inferred strains to global scales often results in strain estimates that exceed those based on global constraints. Here we use numerical simulations of groove terrain formation to develop a strain history for Ganymede that is generally consistent at local, regional, and global scales. These simulations reproduce groove-like amplitudes, wavelengths, and average slopes at modest regional extensions (10–15%). The modest strains are more consistent with global constraints on Ganymede’s expansion. Yet locally, we also find that surface strains can be much larger (30–60%) in the same simulations, consistent with observations of highly-extended impact craters. Thus our simulations satisfy both the smallest-scale and largest-scale inferences of strain on Ganymede. The growth rate of the topography is consistent with (or exceeds) predictions of analytical models, and results from the use of a non-associated plastic rheology that naturally permits localization of brittle failure (plastic strain) into linear fault-like shear zones. These fault-like zones are organized into periodically-spaced graben-like structures with stepped, steeply-dipping faults. As in previous work, groove amplitudes and wavelengths depend on both the imposed heat flux and surface temperature, but because our brittle strength increases with depth, we find (for the parameters explored) that the growth rate of topography is initially faster for lower heat flows. We observe a transition to narrow rifting for higher heat flows and larger strains, which is a potential pathway for breakaway margin or band formation.

Cometabolic Degradation of Naproxen by Planococcus sp. Strain S5.

PubMed

Domaradzka, Dorota; Guzik, Urszula; Hupert-Kocurek, Katarzyna; Wojcieszyńska, Danuta

Naproxen is a non-steroidal anti-inflammatory drug frequently detected in the influent and effluent of sewage treatment plants. The Gram-positive strain Planococcus sp. S5 was able to remove approximately 30 % of naproxen after 35 days of incubation in monosubstrate culture. Under cometabolic conditions, with glucose or phenol as a growth substrate, the degradation efficiency of S5 increased. During 35 days of incubation, 75.14 ± 1.71 % and 86.27 ± 2.09 % of naproxen was degraded in the presence of glucose and phenol, respectively. The highest rate of naproxen degradation observed in the presence of phenol may be connected with the fact that phenol is known to induce enzymes responsible for aromatic ring cleavage. The activity of phenol monooxygenase, naphthalene monooxygenase, and hydroxyquinol 1,2-dioxygenase was indicated in Planococcus sp. S5 culture with glucose or phenol as a growth substrate. It is suggested that these enzymes may be engaged in naproxen degradation.

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.

Atypical transitions in material response during constant strain rate, hot deformation of austenitic steel

NASA Astrophysics Data System (ADS)

Borah, Utpal; Aashranth, B.; Samantaray, Dipti; Kumar, Santosh; Davinci, M. Arvinth; Albert, Shaju K.; Bhaduri, A. K.

2017-10-01

Work hardening, dynamic recovery and dynamic recrystallization (DRX) occurring during hot working of austenitic steel have been extensively studied. Various empirical models describe the nature and effects of these phenomena in a typical framework. However, the typical model is sometimes violated following atypical transitions in deformation mechanisms of the material. To ascertain the nature of these atypical transitions, researchers have intentionally introduced discontinuities in the deformation process, such as interrupting the deformation as in multi-step rolling and abruptly changing the rate of deformation. In this work, we demonstrate that atypical transitions are possible even in conventional single-step, constant strain rate deformation of austenitic steel. Towards this aim, isothermal, constant true strain rate deformation of austenitic steel has been carried out in a temperature range of 1173-1473 K and strain rate range of 0.01-100 s-1. The microstructural response corresponding to each deformation condition is thoroughly investigated. The conventional power-law variation of deformation grain size (D) with peak stress (σp) during DRX is taken as a typical model and experimental data is tested against it. It is shown that σp-D relations exhibit an atypical two-slope linear behaviour rather than a continuous power law relation. Similarly, the reduction in σp with temperature (T) is found to consist of two discrete linear segments. In practical terms, the two linear segments denote two distinct microstructural responses to deformation. As a consequence of this distinction, the typical model breaks down and is unable to completely relate microstructural evolution to flow behaviour. The present work highlights the microstructural mechanisms responsible for this atypical behavior and suggests strategies to incorporate the two-slope behaviour in the DRX model.

Saccharomyces cerevisiae FLO1 Gene Demonstrates Genetic Linkage to Increased Fermentation Rate at Low Temperatures

PubMed Central

Deed, Rebecca C.; Fedrizzi, Bruno; Gardner, Richard C.

2017-01-01

Low fermentation temperatures are of importance to food and beverage industries working with Saccharomyces cerevisiae. Therefore, the identification of genes demonstrating a positive impact on fermentation kinetics is of significant interest. A set of 121 mapped F1 progeny, derived from a cross between haploid strains BY4716 (a derivative of the laboratory yeast S288C) and wine yeast RM11-1a, were fermented in New Zealand Sauvignon Blanc grape juice at 12.5°. Analyses of five key fermentation kinetic parameters among the F1 progeny identified a quantitative trait locus (QTL) on chromosome I with a significant degree of linkage to maximal fermentation rate (Vmax) at low temperature. Independent deletions of two candidate genes within the region, FLO1 and SWH1, were constructed in the parental strains (with S288C representing BY4716). Fermentation of wild-type and deletion strains at 12.5 and 25° confirmed that the genetic linkage to Vmax corresponds to the S288C version of the FLO1 allele, as the absence of this allele reduced Vmax by ∼50% at 12.5°, but not at 25°. Reciprocal hemizygosity analysis (RHA) between S288C and RM11-1a FLO1 alleles did not confirm the prediction that the S288C version of FLO1 was promoting more rapid fermentation in the opposing strain background, suggesting that the positive effect on Vmax derived from S288C FLO1 may only provide an advantage in haploids, or is dependent on strain-specific cis or trans effects. This research adds to the growing body of evidence demonstrating the role of FLO1 in providing stress tolerance to S. cerevisiae during fermentation. PMID:28143947

Transcriptional analysis of four family 4 P450s in a Puerto Rico strain of Aedes aegypti (Diptera: Culicidae) compared with an Orlando strain and their possible functional roles in permethrin resistance.

PubMed

Reid, William R; Thornton, Anne; Pridgeon, Julia W; Becnel, James J; Tang, Fang; Estep, Alden; Clark, Gary G; Allan, Sandra; Liu, Nannan

2014-05-01

A field strain of Aedes aegypti (L.) was collected from Puerto Rico in October 2008. Based on LD50 values by topical application, the Puerto Rico strain was 73-fold resistant to permethrin compared with a susceptible Orlando strain. In the presence of piperonyl butoxide, the resistance of Puerto Rico strain of Ae. aegypti was reduced to 15-fold, suggesting that cytochrome P450-mediated detoxification is involved in the resistance of the Puerto Rico strain to permethrin. To determine the cytochrome P450s that might play a role in the resistance to permethrin, the transcriptional levels of 164 cytochrome P450 genes in the Puerto Rico strain were compared with that in the Orlando strain. Of the 164 cytochrome P450s, 33 were significantly (P < 0.05) up-regulated, including cytochrome P450s in families four, six, and nine. Multiple studies have investigated the functionality of family six and nine cytochrome P450s, therefore, we focused on the up-regulated family 4 cytochrome P450s. To determine whether up-regulation of the four cytochrome P450s had any functional role in permethrin resistance, transgenic Drosophila melanogaster Meigen lines overexpressing the four family 4 P450 genes were generated, and their ability to survive exposure to permethrin was evaluated. When exposed to 5 microg per vial permethrin, transgenic D. melanogaster expressing CYP4D24, CYP4H29, CYP4J15v1, and CYP4H33 had a survival rate of 60.0 +/- 6.7, 29.0 +/- 4.4, 64.4 +/- 9.7, and 11.0 +/- 4.4%, respectively. However, none of the control flies survived the permethrin exposure at the same concentration. Similarly, none of the transgenic D. melanogaster expressing CYP4J15v1 or CYP4H33 ?5 survived when they were exposed to permethrin at 10 microg per vial. However, transgenic D. melanogaster expressing CYP4D24 and CYP4H29 had a survival rate of 37.8 +/- 4.4 and 2.2 +/- 2.2%, respectively. Taken together, our results suggest that CYP4D24 might play an important role in cytochrome P450-mediated

Fracture in Westerly granite under AE feedback and constant strain rate loading: Nucleation, quasi-static propagation, and the transition to unstable fracture propagation

USGS Publications Warehouse

Thompson, B.D.; Young, R.P.; Lockner, D.A.

2006-01-01

New observations of fracture nucleation are presented from three triaxial compression experiments on intact samples of Westerly granite, using Acoustic Emission (AE) monitoring. By conducting the tests under different loading conditions, the fracture process is demonstrated for quasi-static fracture (under AE Feedback load), a slowly developing unstable fracture (loaded at a 'slow' constant strain rate of 2.5 ?? 10-6/s) and an unstable fracture that develops near instantaneously (loaded at a 'fast' constant strain rate of 5 ?? 10-5/s). By recording a continuous ultrasonic waveform during the critical period of fracture, the entire AE catalogue can be captured and the exact time of fracture defined. Under constant strain loading, three stages are observed: (1) An initial nucleation or stable growth phase at a rate of ??? 1.3 mm/s, (2) a sudden increase to a constant or slowly accelerating propagation speed of ??? 18 mm/s, and (3) unstable, accelerating propagation. In the ??? 100 ms before rupture, the high level of AE activity (as seen on the continuous record) prevented the location of discrete AE events. A lower bound estimate of the average propagation velocity (using the time-to-rupture and the existing fracture length) suggests values of a few m/s. However from a low gain acoustic record, we infer that in the final few ms, the fracture propagation speed increased to 175 m/s. These results demonstrate similarities between fracture nucleation in intact rock and the nucleation of dynamic instabilities in stick slip experiments. It is suggested that the ability to constrain the size of an evolving fracture provides a crucial tool in further understanding the controls on fracture nucleation. ?? Birkha??user Verlag, Basel, 2006.

Repeatability of strain magnitude and strain rate measurements in the periodontal ligament using fibre Bragg gratings: An ex vivo study in a swine model.

PubMed

Romanyk, Dan L; Guan, Raymond; Major, Paul W; Dennison, Christopher R

2017-03-21

Measurement of periodontal ligament (PDL) strain in an ex vivo or in vivo setting of a complete tooth-PDL-bone complex (TPBC) has yet to be achieved in the literature. The objective of this study was to investigate inter- and intra-TPBC PDL strain measurement using fibre Bragg grating (FBG) strain sensors. Second and third premolars from the left and the right side of four swine mandibles were removed to yield sixteen TPBC samples. Samples were secured in a miniature load-frame equipped with a digital actuator used to apply apical-directed displacement to the tooth. The same tooth on left and right sides of the mouth were exposed to the same loading condition over ten trials allowing for comparisons in a split-mouth study. Displacements of 0.2 and 0.3mm were considered along with displacement rates of 0.025, 0.05, and 0.1mm/s, yielding six loading combinations. Hypothesis testing between left and right teeth revealed FBGs did not always measure the same strain between left and right TPBCs. For all strain measures, the average coefficient of variation (CV) (all data collected) was 2.16 (range: 0.274-10.71). For repeated measures in single TPBCs, the minimum CV ranged from 0.037 to 0.449, and generally coincided with the time of maximum strain measured over the test duration. Based on the findings of this study, it is suggested that FBGs can provide repeatable ex vivo strain measures in the PDL of complete TPBCs. Copyright © 2017 Elsevier Ltd. All rights reserved.

High Strain-Rate and Temperature Effects on the Response of Composites

NASA Technical Reports Server (NTRS)

Gilat, Amos

2004-01-01

The objective of the research is to expand the experimental study of the effect of strain rate on mechanical response (deformation and failure) of epoxy resins and carbon fibers/epoxy matrix composites, to include elevated temperature tests. The experimental data provide the information needed for NASA scientists for the development of a nonlinear, strain rate and temperature dependent deformation and strength models for composites that can subsequently be used in design. This year effort was directed into the development and testing of the epoxy resin at elevated temperatures. Two types of epoxy resins were tested in shear at high strain rates of about 700 per second and elevated temperatures of 50 and 80 C. The results show that the temperature significantly affects the response of epoxy.

Major effect of inherited rheology weakening in the crust and mantle on continental intraplate strain and seismicity rates

NASA Astrophysics Data System (ADS)

Gueydan, Frédéric; Mazzotti, Stephane

2017-04-01

Stable Continental Regions (SCR, i.e., intraplate) are commonly viewed as non-deforming and very high resistance lithosphere domains, except in localized regions of higher strain and seismicity rates that often related to fossilized tectonic zones acting as weaker domains (e.g., Rhine Graben, New Madrid). Two main categories of models have been proposed to explain strain concentration in SCR: Local stress concentration (fault intersection, erosion pulse, …) and local lithosphere weakness (high geotherm, mantle anisotropy, …). In order to test the respective role of these various parameters of the stress - rheology - strain relationship, we propose a simple 1D model to quantify first-order continental strain rate variations using laboratory and field-based rheology laws for the crust and mantle. In particular, we include new strain-weakening rheologies in order to simulate tectonic heritage. Within the framework of near-failure equilibrium between tectonic forces and strain rates, we show that inherited rheology weakening plays a fundamental role in allowing for and explaining strain and seismicity concentration in intraplate weak zones. A comparison with empirical strain rate estimations in SCR and intraplate weak zones shows that inherited weakening rheologies can increase local strain rates by as much as three orders of magnitude, about one to two orders higher than that permitted by other processes such as stress concentration, thermal anomaly, etc.

Microstructure and critical strain of dynamic recrystallization of 6082 aluminum alloy in thermal deformation

NASA Astrophysics Data System (ADS)

Ren, W. W.; Xu, C. G.; Chen, X. L.; Qin, S. X.

2018-05-01

Using high temperature compression experiments, true stress true strain curve of 6082 aluminium alloy were obtained at the temperature 460°C-560°C and the strain rate 0.01 s-1-10 s-1. The effects of deformation temperature and strain rate on the microstructure are investigated; (‑∂lnθ/∂ε) ‑ ε curves are plotted based on σ-ε curve. Critical strains of dynamic recrystallization of 6082 aluminium alloy model were obtained. The results showed lower strain rates were beneficial to increase the volume fraction of recrystallization, the average recrystallized grain size was coarse; High strain rates are beneficial to refine average grain size, the volume fraction of dynamic recrystallized grain is less than that by using low strain rates. High temperature reduced the dislocation density and provided less driving force for recrystallization so that coarse grains remained. Dynamic recrystallization critical strain model and thermal experiment results can effectively predict recrystallization critical point of 6082 aluminium alloy during thermal deformation.

Rotation and strain rate of Sulawesi from geometrical velocity field

NASA Astrophysics Data System (ADS)

Sarsito, D. A.; Susilo, Simons, W. J. F.; Abidin, H. Z.; Sapiie, B.; Triyoso, W.; Andreas, H.

2017-07-01

One of methods that can be used to determine the tectonic deformation status is rate estimation from geometric rotation and strain using quantitative velocity data from GPS observations. Microplate Sulawesi region located in the zone of triple junction (Eurasia, Australia and Philippine Sea Plates) has very complex tectonic and seismic condition, which is why become very important to know its recent deformation status in order to study neo-tectonic and disaster mitigation. Deformation rate quantification is estimated in two parameters: rotation and geodetic strain rate of each GPS station Delaunay triangle in the study area. The analysis in this study is not done using the grids since there is no rheological information at location that can be used as the interpolation-extrapolation constraints. Our analysis reveals that Sulawesi is characterized by rapid rotation in several different domains and compression-strain pattern that varies depending on the type and boundary conditions of microplate. This information is useful for studying neo tectonic deformation status and earthquake disaster mitigation.

Biodegradation of buprofezin by Rhodococcus sp. strain YL-1 isolated from rice field soil.

PubMed

Li, Chao; Zhang, Ji; Wu, Zhi-Guo; Cao, Li; Yan, Xin; Li, Shun-Peng

2012-03-14

A buprofezin-degrading bacterium, YL-1, was isolated from rice field soil. YL-1 was identified as Rhodococcus sp. on the basis of the comparative analysis of 16S rDNA sequences. The strain could use buprofezin as the sole source of carbon and nitrogen for growth and was able to degrade 92.4% of 50 mg L(-1) buprofezin within 48 h in liquid culture. During the degradation of buprofezin, four possible metabolites, 2-tert-butylimino-3-isopropyl-1,3,5-thiadiazinan-4-one, N-tert-butyl-thioformimidic acid formylaminomethyl ester, 2-isothiocyanato-2-methyl-propane, and 2-isothiocyanato-propane, were identified using gas chromatography-mass spectrometry (GC-MS) analysis. The catechol 2,3-dioxygenase activity was strongly induced during the degradation of buprofezin. A novel microbial biodegradation pathway for buprofezin was proposed on the basis of these metabolites. The inoculation of soils treated with buprofezin with strain YL-1 resulted in a higher degradation rate than that observed in noninoculated soils, indicating that strain YL-1 has the potential to be used in the bioremediation of buprofezin-contaminated environments.

[Screening and optimization of cholesterol conversion strain].

PubMed

Fan, Dan; Xiong, Bingjian; Pang, Cuiping; Zhu, Xiangdong

2014-10-04

Bacterial strain SE-1 capable of transforming cholesterol was isolated from soil and characterized. The transformation products were identified. Fermentation conditions were optimized for conversion. Cholesterol was used as sole carbon source to isolate strain SE-1. Morphology, physiological and biochemical characteristics of strain SE-1 were studied. 16S rRNA gene was sequenced and subjected to phylogenetic analysis. Fermentation supernatants were extracted with chloroform, the transformation products were analyzed by silica gel thin layer chromatography and Sephadex LH20. Their structures were identified by 1H-NMR and 13C-NMR. Fermentation medium including carbon and nitrogen, methods of adding substrates and fermentation conditions for Strain SE-1 were optimized. Strain SE-1 was a Gram-negative bacterium, exhibiting the highest homologs to Burkholderia cepacia based on the physiological analysis. The sequence analysis of 16S rRNA gene of SE-1 strain and comparison with related Burkholderia show that SE-1 strain was very close to B. cepacia (Genbank No. U96927). The similarity was 99%. The result of silica gel thin layer chromatography shows that strain SE-1 transformed cholesterol to two products, 7beta-hydroxycholesterol and the minor product was 7-oxocholesterol. The optimum culture conditions were: molasses 5%, (NH4 )2SO4 0.3%, 4% of inoculation, pH 7.5 and 36 degrees C. Under the optimum culture condition, the conversion rate reached 34.4% when concentration of cholesterol-Tween 80 was 1 g/L. Cholesterol 7beta-hydroxylation conversion rate under optimal conditions was improved by 20.8%. Strain SE-1 isolated from soil is capable of converting cholesterol at lab-scale.

A Novel Saccharomyces cerevisiae Killer Strain Secreting the X Factor Related to Killer Activity and Inhibition of S. cerevisiae K1, K2 and K28 Killer Toxins.

PubMed

Melvydas, Vytautas; Bružauskaitė, Ieva; Gedminienė, Genovaitė; Šiekštelė, Rimantas

2016-09-01

It was determined that Kx strains secrete an X factor which can inhibit all known Saccharomyces cerevisiae killer toxins (K1, K2, K28) and some toxins of other yeast species-the phenomenon not yet described in the scientific literature. It was shown that Kx type yeast strains posess a killer phenotype producing small but clear lysis zones not only on the sensitive strain α'1 but also on the lawn of S. cerevisiae K1, K2 and K28 type killer strains at temperatures between 20 and 30 °C. The pH at which killer/antikiller effect of Kx strain reaches its maximum is about 5.0-5.2. The Kx yeast were identified as to belong to S. cerevisiae species. Another newly identified S. cerevisiae killer strain N1 has killer activity but shows no antikilller properties against standard K1, K2 and K28 killer toxins. The genetic basis for Kx killer/antikiller phenotype was associated with the presence of M-dsRNA which is bigger than M-dsRNA of standard S. cerevisiae K1, K2, K28 type killer strains. Killer and antikiller features should be encoded by dsRNA. The phenomenon of antikiller (inhibition) properties was observed against some killer toxins of other yeast species. The molecular weight of newly identified killer toxins which produces Kx type strains might be about 45 kDa.

Tunable magnetic coupling in Mn-doped monolayer MoS2 under lattice strain

NASA Astrophysics Data System (ADS)

Miao, Yaping; Huang, Yuhong; Bao, Hongwei; Xu, Kewei; Ma, Fei; Chu, Paul K.

2018-05-01

First-principles calculations are conducted to study the electronic and magnetic states of Mn-doped monolayer MoS2 under lattice strain. Mn-doped MoS2 exhibits half-metallic and ferromagnetic (FM) characteristics in which the majority spin channel exhibits metallic features but there is a bandgap in the minority spin channel. The FM state and the total magnetic moment of 1 µ B are always maintained for the larger supercells of monolayer MoS2 with only one doped Mn, no matter under tensile or compressive strain. Furthermore, the FM state will be enhanced by the tensile strain if two Mo atoms are substituted by Mn atoms in the monolayer MoS2. The magnetic moment increases up to 0.50 µ B per unit cell at a tensile strain of 7%. However, the Mn-doped MoS2 changes to metallic and antiferromagnetic under compressive strain. The spin polarization of Mn 3d orbitals disappears gradually with increasing compressive strain, and the superexchange interaction between Mn atoms increases gradually. The results suggest that the electronic and magnetic properties of Mn-doped monolayer MoS2 can be effectively modulated by strain engineering providing insight into application to electronic and spintronic devices.

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

2016-11-01

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.

Development of a Low Strain-Rate Gun Propellant Bed Compression Test and its Use in Evaluating Mechanical Response

DTIC Science & Technology

2016-09-01

heuristics, die and propellant geometries from similar facilities reported in the literature [2,3] and the DST Group design .  bed* (mm) φbed...compliance curves from the experimental data. In UNCLASSIFIED DST- Group -TR-3291 UNCLASSIFIED 18 Figure 13, the red axial compliance traces were...UNCLASSIFIED DST- Group -TR-3291 UNCLASSIFIED 46 At a test temperature of -60˚C, the equivalent strain rates are within the 10 to 500 s-1 given in

Effects of Adiabatic Heating on the High Strain Rate Deformation of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Sorini, Chris; Chattopadhyay, Aditi; Goldberg, Robert K.

2017-01-01

Polymer matrix composites (PMCs) are increasingly being used in aerospace structures that are expected to experience complex dynamic loading conditions throughout their lifetime. As such, a detailed understanding of the high strain rate behavior of the constituents, particularly the strain rate, temperature, and pressure dependent polymer matrix, is paramount. In this paper, preliminary efforts in modeling experimentally observed temperature rises due to plastic deformation in PMCs subjected to dynamic loading are presented. To this end, an existing isothermal viscoplastic polymer constitutive formulation is extended to model adiabatic conditions by incorporating temperature dependent elastic properties and modifying the components of the inelastic strain rate tensor to explicitly depend on temperature. It is demonstrated that the modified polymer constitutive model is capable of capturing strain rate and temperature dependent yield as well as thermal softening associated with the conversion of plastic work to heat at high rates of strain. The modified constitutive model is then embedded within a strength of materials based micromechanics framework to investigate the manifestation of matrix thermal softening, due to the conversion of plastic work to heat, on the high strain rate response of a T700Epon 862 (T700E862) unidirectional composite. Adiabatic model predictions for high strain rate composite longitudinal tensile, transverse tensile, and in-plane shear loading are presented. Results show a substantial deviation from isothermal conditions; significant thermal softening is observed for matrix dominated deformation modes (transverse tension and in-plane shear), highlighting the importance of accounting for the conversion of plastic work to heat in the polymer matrix in the high strain rate analysis of PMC structures.

Two groups of S-layer proteins, SLP1s and SLP2s, in Bacillus thuringiensis co-exist in the S-layer and in parasporal inclusions.

PubMed

Zhou, Zhou; Peng, Donghai; Zheng, Jinshui; Guo, Gang; Tian, Longjun; Yu, Ziniu; Sun, Ming

2011-05-01

We screened four B. thuringiensis strains whose parasporal inclusions contained the S-layer protein (SLP), and cloned two slp genes from each strain. Phylogenetic analysis indicated these SLPs could be divided into two groups, SLP1s and SLP2s. To confirm whether SLPs were present in the S-layer or as a parasporal inclusion, strains CTC and BMB1152 were chosen for further study. Western blots with whole-cell associated proteins from strains CTC and BMB1152 in the vegetative phase showed that SLP1s and SLP2s were constituents of the S-layer. Immunofluorescence utilizing spore-inclusion mixtures of strains CTC and BMB1152 in the sporulation phase showed that SLP1s and SLP2s were also constituents of parasporal inclusions. When heterogeneously expressed in the crystal negative strain BMB171, four SLPs from strains CTC and BMB1152 could also form parasporal inclusions. This temporal and spatial expression is not an occasional phenomenon but ubiquitous in B. thuringiensis strains.

Influence of methanol/sorbitol co-feeding rate on pAOX1 induction in a Pichia pastoris Mut+ strain in bioreactor with limited oxygen transfer rate.

PubMed

Carly, F; Niu, H; Delvigne, F; Fickers, P

2016-04-01

High Pichia pastoris biomass density could be obtained using high co-feeding rate of methanol and sorbitol in a fed-batch or continuous culture, while further higher feeding rate finally leads to oxygen limitation in bioreactor. In the literature, there is lack of report about AOX1 promoter regulation with regard to dissolved oxygen level (DO). Therefore, in this work, chemostat cultures were performed to investigate the cell growth, metabolism and regulation of the AOX1 promoter (pAOX1) regarding co-feeding rate of optimized methanol/sorbitol mixture (methanol fraction 0.60 C-mol/C-mol) using a P. pastoris Mut+/pAOX1-lacZ strain. The oxygen transfer rates (OTR) in bioreactor were kept in the range of typical values of large bioreactor, i.e., 4-8 g/(L h) if DO equals 30 % saturation or 5-10 g/(L h) if DO nears zero. For DO >0, an increase of the carbon fed led to an increase of pAOX1 induction. By contrast, when dissolved oxygen was completely depleted, methanol accumulated, causing a 30 % decrease of pAOX1 induction. However, this decrease is more likely to be lined to methanol accumulation than to low level of dissolved oxygen (<4 % DO). Methanol/sorbitol co-feeding allowed cells to adapt to oxygen transient limitations that often occur at industrial scale with reduced effect on pAOX1 induction. The optimal feeding rate tested here was 6.6 mmol C (DCW h)(-1) at an OTR of 8.28 g O2(L h)(-1) with over fivefold pAOX1 induction (probably directly associated with target protein productivity) compared with previous work.

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

NASA Astrophysics Data System (ADS)

Polyzois, Ioannis

For years high strength steels and alloys have been widely used by the military for making armor plates. Advances in technology have led to the development of materials with improved resistance to penetration and deformation. Until recently, the behavior of these materials under high strain rates and large strains has been primarily based on laboratory testing using the Split Hopkinson Pressure Bar apparatus. With the advent of sophisticated computer programs, computer modeling and finite element simulations are being developed to predict the deformation behavior of these metals for a variety of conditions similar to those experienced during combat. In the present investigation, a modified direct impact Split Hopkinson Pressure Bar apparatus was modeled using the finite element software ABAQUS 6.8 for the purpose of simulating high strain rate compression of specimens of three armor materials: maraging steel 300, high hardness armor (HHA), and aluminum alloy 5083. These armor materials, provided by the Canadian Department of National Defence, were tested at the University of Manitoba by others. In this study, the empirical Johnson-Cook visco-plastic and damage models were used to simulate the deformation behavior obtained experimentally. A series of stress-time plots at various projectile impact momenta were produced and verified by comparison with experimental data. The impact momentum parameter was chosen rather than projectile velocity to normalize the initial conditions for each simulation. Phenomena such as the formation of adiabatic shear bands caused by deformation at high strains and strain rates were investigated through simulations. It was found that the Johnson-Cook model can accurately simulate the behavior of body-centered cubic (BCC) metals such as steels. The maximum shear stress was calculated for each simulation at various impact momenta. The finite element model showed that shear failure first occurred in the center of the cylindrical specimen and

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.

Resolution of enantiopure (S)-1-(1-napthyl) ethanol from racemic mixture by a novel Bacillus cereus isolate.

PubMed

Ranjan, Preeti; Pandey, Ashok; Binod, Parameswaran

2017-09-01

Chiral intermediates have wide application and high demand in pharmaceutical, agricultural, and other biotechnological industries for the preparation of bulk drug substances or fine chemicals. (S)-1-(1-napthyl) ethanol is an important synthetic intermediate of mevinic acid analog and a potential inhibitor of 3-hydroxy methyl glutaryl coenzyme A reductase enzymes which is rate limiting for cholesterol synthesis. The present study focuses on the resolution of (RS)-1-(1-napthyl) ethanol using whole cell biotransformation approach. The screening of microbial strains for the specific conversion were performed by the enrichment techniques using (RS)-1-(1-napthyl) ethanol. Evaluation of resolution, i.e., the enantioselective conversion of (R)-1-(1-napthyl) ethanol into 1-acetonapthone and production of (S)-1-(1-napthyl) ethanol with high purity were carried out. Among the isolates, a novel strain Bacillus cereus WG3 was found to be potent for the resolution and conversion of (S)-1-(1-napthyl) ethanol. This strain showed 86% conversion of (R)-1-(1-napthyl) ethanol and 95% yield of S-1-(1-napthyl) ethanol with 80% ee after 24 h. Further, the optimization of biotransformation reactions was carried out and the optimal parameters were found to be pH 7.0 and temperature 30 °C. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of Loading Rate and Orientation on the Compressive Response of Human Cortical Bone

DTIC Science & Technology

2014-05-01

use thereof. Destroy this report when it is no longer needed. Do not return it to the originator. Army Research Laboratory Aberdeen Proving...quasi-static (0.001/s), intermediate (1/s), and dynamic (1000–2000/s) strain rates using a split-Hopkinson pressure bar to determine the strain rate...6 Figure 5. Strain rate and strain histories of human cortical bone specimen at high rate using bar signals

Creating a Strain Relief Loop during S1 Transforaminal Lead Placement for Dorsal Root Ganglion Stimulation for Foot Pain: A Technical Note.

PubMed

van Velsen, Valery; van Helmond, Noud; Chapman, Kenneth B

2018-04-01

Chronic neuropathic pain is often refractory to conventional medical treatments and leads to significant disability and socio-economic burden. Dorsal root ganglion (DRG) stimulation has recently emerged as a treatment for persistent neuropathic pain, but creating a strain relief loop at the S1 level has thus far been a challenging technical component of DRG lead placement. We describe a refined technique for strain relief loop formation at the S1 level using a transforaminal approach that we employed in a 45-year-old patient with intractable foot pain. We successfully placed a strain relief loop in the sacral space in a predictable and easily reproducible manner using a transforaminal anchorless approach. The patient experienced a decrease in visual analog pain score (85%), and improvement in function during the trial period, and proceeded with permanent implantation. The described sacral transforaminal strain relief loop formation technique appears to be a more reliable and predictable technique of DRG lead placement in the sacrum than those previously documented. © 2017 World Institute of Pain.

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.

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

Microstructural change in electroformed copper liners of shaped charges upon plastic deformation at ultra-high strain rate

NASA Astrophysics Data System (ADS)

Tian, W. H.; Hu, S. L.; Fan, A. L.; Wang, Z.

2002-01-01

Transmission electron microscopy (TEM) observations were carried out for examining the as-formed and post-deformed microstructures in a variety of electroformed copper liners of shaped charges. The deformation was carried out at an ultra-high strain rate. Specifically, the electron backscattering Kikuchi pattern (EBSP) technique was utilized to examine the micro-texture of these materials. TEM observations revealed that these electroformed copper liners of shaped charges have a grain size of about 1-3 mum, EBSP analysis demonstrated that the as-grown copper liners of shaped charges exhibit a l 10) fiber micro-texture which is parallel to the normal direction of the surface of the liners of shaped charges. Having undergone plastic deformation at ultra-high strain rate (10(7) s(-1)), the specimens which were recovered from the copper slugs were found to have grain size of the same order as that before deformation. EBSP analysis revealed that the (110) fiber texture existed in the as-formed copper liners disappears in the course of deformation. TEM examination results indicate that dynamic recovery and recrystallization play a significant role in this deformation process.

Calving laws and strain rates: a comparison between modelled relationships and observations from InSAR velocity maps from across Greenland.

NASA Astrophysics Data System (ADS)

Lea, James; Nick, Faezeh; Benn, Douglas; Kirchner, Nina

2017-04-01

Calving is a major mechanism of cryospheric ice mass loss and a significant contributor to global sea level change, though it is currently poorly understood as a process. Longitudinal strain rate is often cited as a first order control on calving, however multiple different calving laws (not always including the strain rate) have been used to represent this in numerical models of ice sheets. This study seeks to investigate how (1) different calving laws within a 1D flowline model predict strain rate will evolve within increasing terminus thickness for steady state and transient simulations, and (2) how these relationships compare with observed strains (derived from MEaSUREs Greenland InSAR velocity maps; Joughin et al., 2010 [updated 2016]) and depths (from BedMachine v.2 subglacial topography data; Morlighem et al., 2014). We identify that systematic relationships with terminus thickness exist for height above buoyancy, waterline and full-depth crevasse calving laws amongst others for both steady state and transient simulations. However, analysis of observed near-terminus strain rates for multiple Greenlandic glaciers using a variety of metrics (with a range of bed depths predicted by BedMachine) does not reproduce the shape or magnitude of any of these modelled relationships. Relationships between strain rate and depth derived from simple 1D model simulations therefore cannot be realistically compared to current real-world observations. This suggests that the magnitude of observed strain rates at an individual point, or area-averaged conditions near a real-world terminus are not meaningful in determining the potential for calving when taken in isolation. To improve understanding of first/second order calving processes, future modelling work should therefore look to analyse how/if the distribution of strain across the terminus region impacts calving as part of 2D-planform/3D models.

Effects of polyaluminum chloride and lanthanum-modified bentonite on the growth rates of three Cylindrospermopsis raciborskii strains

PubMed Central

van Oosterhout, Frank; Becker, Vanessa; Attayde, José Luiz; Lürling, Miquel

2018-01-01

In tropical and subtropical lakes, eutrophication often leads to nuisance blooms of Cylindrospermopsis raciborskii. In laboratory experiments, we tested the combined effects of flocculant polyaluminum chloride (PAC) and lanthanum-modified bentonite (LMB) on the sinking and growth rates of three C. raciborskii strains. We tested the hypothesis that the combination of PAC and LMB would (1) effectively sink C. raciborskii in a test tube experiment and (2) impair C. raciborskii growth, irrespective of the biomass of the inoculum (bloom) and the strain in the growth experiment. We tested the recommended (LMB1) and a three-times higher dose of LMB (LMB3). The combined addition of PAC and LMB enhanced the sedimentation of all C. raciborskii strains. Moreover, both the PAC and LMB doses decreased the phosphate concentration. PAC and LMB1 decreased the growth rate of all strains, but the efficacy depended on the biomass and strain. The combined addition of PAC and LMB3 inhibited the growth of all strains independently of the biomass and strain. We conclude that a low dose of PAC in combination with the recommended dose of LMB decreases C. raciborskii blooms and that the efficiency of the technique depends on the biomass of the bloom. A higher dose of LMB is needed to obtain a more efficient control of C. raciborskii blooms. PMID:29614118

Effects of polyaluminum chloride and lanthanum-modified bentonite on the growth rates of three Cylindrospermopsis raciborskii strains.

PubMed

Araújo, Fabiana; van Oosterhout, Frank; Becker, Vanessa; Attayde, José Luiz; Lürling, Miquel

2018-01-01

In tropical and subtropical lakes, eutrophication often leads to nuisance blooms of Cylindrospermopsis raciborskii. In laboratory experiments, we tested the combined effects of flocculant polyaluminum chloride (PAC) and lanthanum-modified bentonite (LMB) on the sinking and growth rates of three C. raciborskii strains. We tested the hypothesis that the combination of PAC and LMB would (1) effectively sink C. raciborskii in a test tube experiment and (2) impair C. raciborskii growth, irrespective of the biomass of the inoculum (bloom) and the strain in the growth experiment. We tested the recommended (LMB1) and a three-times higher dose of LMB (LMB3). The combined addition of PAC and LMB enhanced the sedimentation of all C. raciborskii strains. Moreover, both the PAC and LMB doses decreased the phosphate concentration. PAC and LMB1 decreased the growth rate of all strains, but the efficacy depended on the biomass and strain. The combined addition of PAC and LMB3 inhibited the growth of all strains independently of the biomass and strain. We conclude that a low dose of PAC in combination with the recommended dose of LMB decreases C. raciborskii blooms and that the efficiency of the technique depends on the biomass of the bloom. A higher dose of LMB is needed to obtain a more efficient control of C. raciborskii blooms.

Isolation and characterization of butachlor-catabolizing bacterial strain Stenotrophomonas acidaminiphila JS-1 from soil and assessment of its biodegradation potential.

PubMed

Dwivedi, S; Singh, B R; Al-Khedhairy, A A; Alarifi, S; Musarrat, J

2010-07-01

Isolation, characterization and assessment of butachlor-degrading potential of bacterial strain JS-1 in soil. Butachlor-degrading bacteria were isolated using enrichment culture technique. The morphological, biochemical and genetic characteristics based on 16S rDNA sequence homology and phylogenetic analysis confirmed the isolate as Stenotrophomonas acidaminiphila strain JS-1. The strain JS-1 exhibited substantial growth in M9 mineral salt medium supplemented with 3.2 mmol l(-1) butachlor, as a sole source of carbon and energy. The HPLC analysis revealed almost complete disappearance of butachlor within 20 days in soil at a rate constant of 0.17 day(-1) and half-life (t((1/2))) of 4.0 days, following the first-order rate kinetics. The strain JS-1 in stationary phase of culture also produced 21.0 microg ml(-1) of growth hormone indole acetic acid (IAA) in the presence of 500 microg ml(-1) of tryptophan. The IAA production was stimulated at lower concentrations of butachlor, whereas higher concentrations above 0.8 mmol l(-1) were found inhibitory. The isolate JS-1 characterized as Stenotrophomonas acidaminiphila was capable of utilizing butachlor as sole source of carbon and energy. Besides being an efficient butachlor degrader, it substantially produces IAA. The bacterial strain JS-1 has a potential for butachlor remediation with a distinctive auxiliary attribute of plant growth stimulation.

Solid-state experiments at high pressure and strain rates

NASA Astrophysics Data System (ADS)

Kalantar, D. H.

1999-11-01

We are developing experiments on intense laser facilities to study shock compressed metal foils in the solid state. At high pressure, Rayleigh-Taylor induced perturbation growth can be reduced by the strength of the material. [1] We use this to characterize the strength of the metal foils accelerated at high pressure in the solid state. In our experiments, Al and Cu foils are compressed and accelerated with staged shocks using a temporally shaped x-ray drive that is generated in a Nova laser hohlraum target. [2] The peak pressures exceed 1 Mbar (100 GPa), and strain rates are very high, 10^7-10^9 s-1. The instability growth is observed by x-ray radiography. To probe the state of the material under compression and to demonstrate that it remains solid, we are using the dynamic Bragg diffraction technique. [3] This technique has been demonstrated on the Nova laser [4] using Si crystals shocked to 200-500 kbar. Additionally, we have observed diffraction from Cu crystals that are shocked to 100-200 kbar by direct laser irradiation on the Trident and OMEGA lasers. Compressions of up to a 10in the crystal lattice spacing have been observed. We will present the results of our work to develop these high pressure solid-state hydrodynamics experiments. 1. J. F. Barnes et al, J. Appl. Phys. 45, 727 (1974); A. I. Lebedev et al , Proc. 4th IWPCTM, 29 March-1 April, 1993, p. 81. 2. D. H. Kalantar et al., to appear in Int. J. of Impact Eng. (1999). 3. R. R. Whitlock and J. S. Wark, Phys. Rev. B 52, 8 (1995). 4. D. H. Kalantar et al, Rev. Sci. Instrum. 70, 629 (1999).

Effects of Temperature and Strain Rate on Tensile Deformation Behavior of 9Cr-0.5Mo-1.8W-VNb Ferritic Heat-Resistant Steel

NASA Astrophysics Data System (ADS)

Guo, Xiaofeng; Weng, Xiaoxiang; Jiang, Yong; Gong, Jianming

2017-09-01

A series of uniaxial tensile tests were carried out at different strain rate and different temperatures to investigate the effects of temperature and strain rate on tensile deformation behavior of P92 steel. In the temperature range of 30-700 °C, the variations of flow stress, average work-hardening rate, tensile strength and ductility with temperature all show three temperature regimes. At intermediate temperature, the material exhibited the serrated flow behavior, the peak in flow stress, the maximum in average work-hardening rate, and the abnormal variations in tensile strength and ductility indicates the occurrence of DSA, whereas the sharp decrease in flow stress, average work-hardening rate as well as strength values, and the remarkable increase in ductility values with increasing temperature from 450 to 700 °C imply that dynamic recovery plays a dominant role in this regime. Additionally, for the temperature ranging from 550 to 650 °C, a significant decrease in flow stress values is observed with decreasing in strain rate. This phenomenon suggests the strain rate has a strong influence on flow stress. Based on the experimental results above, an Arrhenius-type constitutive equation is proposed to predict the flow stress.

[Genetic Characterization of Hemagglutinin on Measles Virus Epidemic Strain Genotype H1a in Liaoning Province (China) from 1997 to 2014].

PubMed

Wang, Yan; Ma, Yan; Xu, Xiaoting; Hao, Shuang; Han, Yue; Yao, Wenqing; Zhao, Zhuo

2015-07-01

To wished to characterize the hemagglutinin (H) gene of the measles virus epidemic strain H1a in Liaoning Province (China) from 1997-2014 to provide a basis for the control and elimination of measles. All 63 measles virus strains were the H1a genotype. Fragments of the H gene (1854 nucleotides) and nucleoprotein (N) gene (450 nucleotides) were amplified by reverse transcription-polymerase chain reaction (RT-PCR) and the PCR products sequenced and analyzed. Phylogenetic-trees were constructed with reference strains of the genotype-H measles virus downloaded from GenBank, including Chinese measles virus strains isolated in 1993-1994 and the vaccine reference strains S-191 and C-47. Sixty-three strains of the measles virus in 1997-2014 belonged to genotype H1a. The mean evolutionary rate for gene N-450 was higher than that for the H gene. All 63 strains of the measles virus were mutated from: serine (Ser S) to asparagine (Asn N) in the 240th amino acid; arginine (Arg R) to glycine (Gly G) in the 243th; and tyrosine (Tyr Y) to Asn N in the 481th amino acid. All measles virus strains in cluster 2 were mutated from proline (Pro P) to leucine (Leu L) in the 397th amino acid. The other neutralization sites showed no apparent difference when comparing the nucleotides/amino acids of the H gene of S191 vaccine strains.

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