low strain rate
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2021 ◽  
Vol 902 ◽  
pp. 15-19
Author(s):  
Jin Wang ◽  
Yang Wang ◽  
Zi Ran Li

The compressive behavior of ME20M alloy along rolling direction (RD) at a wide strain rates under low temperatures is investigated in this paper. Compressive stress-strain results reveal that the effect of strain rate on yield strength and flow stress is not obvious, especially at low temperatures. Moreover, the temperature plays an important role in compressive responses. SEM observations indicate that brittle fracture is the main fracture mode at low strain rate, and ductile fracture occurs in the failure of the alloy at high strain rate.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
John P. Pappachen ◽  
Rajesh Sathiyaseelan ◽  
Param K. Gautam ◽  
Sanjit Kumar Pal

AbstractThe possibility of a major earthquake like 2015 Gorkha–Nepal or even greater is anticipated in the Garhwal–Kumaun region in the Central Seismic Gap of the NW Himalaya. The interseismic strain-rate from GPS derived crustal velocities show multifaceted strain-rate pattern in the region and are classified into four different strain-rate zones. Besides compressional, we identified two NE–SW orienting low strain rate (~ 20 nstrain/a) zones; namely, the Ramganga-Baijro and the Nainital-Almora, where large earthquakes can occur. These zones have surface locking widths of ~ 72 and ~ 75 km respectively from the Frontal to the Outer Lesser Himalaya, where no significant surface rupture and associated large earthquakes were observed for the last 100 years. However, strain reducing extensional deformation zone that appears sandwiched between the low strain-rate zones pose uncertainties on the occurences of large earthquakes in the locked zone. Nevertheless, such zone acts as a conduit to transfer strain from the compressional zone (> 100 nstrain/a) to the deforming frontal active fault systems. We also observed a curvilinear surface strain-rate pattern in the Chamoli cluster and explained how asymmetric crustal accommodation processes at the northwest and the southeast edges of the Almora Klippe, cause clockwise rotational couple on the upper crust moving over the MHT.


Author(s):  
Yi Zhang ◽  
Liang Qiao ◽  
Junming Fan ◽  
Shifeng Xue ◽  
PY Ben Jar

Plastic deformation of polyethylene in uniaxial and biaxial loading conditions is studied using molecular dynamics simulation. Effects of tensile strain rates from 1 × 105 to 1 × 109 s−1, and mass density in the range of 0.923–0.926 g/cm3 on mechanical behaviour and microstructure evolution are examined. Two biaxial tensile deformation modes are considered. One is through simultaneous stretching in both the x and y directions and the other sequential stretching, firstly in the x-direction and then in the y-direction while strain in the x-direction remains constant. Tangent modulus and yield stress that are determined using the stress–strain curves from the molecular dynamics simulation show a strong dependence on the deformation mode, strain rate and mass density, and all are in good agreement with results from the experimental testing, including fracture behaviour which is ductile at a low strain rate but brittle at a high strain rate. Furthermore, the study suggests that the stress–strain curves under uniaxial tension and simultaneous biaxial tension at a relatively low strain rate contain four distinguishable regions, for elastic, yield, strain softening and strain hardening, respectively, whereas under sequential biaxial tension, stress increases monotonically with the increase of strain, without noticeable yielding, strain softening or strain hardening behaviour. The molecular dynamics simulation also suggests that an increase in the strain rate enhances the possibility of cavitation. Under simultaneous biaxial tension, with the strain rate increasing from 1 × 106 to 1 × 109 s−1, the molecular dynamics simulation shows that polyethylene failure changes from a local to a global phenomenon, accompanied by a decrease of the void size and increase of uniformity in the void distribution. Under sequential biaxial tension, on the other hand, the density of the cavities is clearly reduced.


Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1517
Author(s):  
Hailong Yi ◽  
Yifan Zhang ◽  
Renyi Xie ◽  
Mengyuan Bi ◽  
Daixiu Wei

High entropy alloys (HEAs) containing multi-principal metallic constituents have attracted much attention. A good understanding of their hot-deformation behavior and recrystallization mechanism is the prerequisite for microstructures tuning and for optimizing mechanical performance. Here, the flow behavior and recrystallization mechanism of the N-doped and C-doped face-centered cubic phase HEAs are produced at high temperatures by hot-compression at 1123–1273 K, with strain rates of 0.1–0.001 s−1. Constitutive equations were successfully constructed to reveal flow behavior, and stress-strain curves were predicted using strain compensated polynomial functions. Discontinuous and continuous dynamic recrystallization proceeded concurrently when compressed at a low temperature and high strain rate, whereas discontinuous recrystallization, which occurs at primary grain boundaries, became predominant at a high temperature and low strain rate, significantly contributing to the refinement and homogenization of the grains. For this reason, a relatively high temperature and a low strain rate, in which the recrystallized grains exhibit equiaxed morphology and very weak texture, are more suitable for refining grains. The average size of the grains was approximately 10 μm. This study sheds light on grain optimization and mechanical properties through thermomechanical processing.


2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Fengjiao Guan ◽  
Guanjun Zhang ◽  
Xiaohang Jia ◽  
Xiaopeng Deng

Craniocerebral injury has been a research focus in the field of injury biomechanics. Although experimental endeavors have made certain progress in characterizing the material behavior of the brain, the temperature dependency of brain mechanics appears to be inconclusive thus far. To partially address this knowledge gap, the current study measured the brain material behavior via unconstrained uniaxial compression tests under low strain rate (0.0083 s-1) and high strain rate (0.83 s-1) at four different sample temperatures (13°C, 20°C, 27°C, and 37°C). Each group has 9~12 samples. One-way analysis of variance method was used to study the influence of sample temperature on engineering stress. The results show that the effect of sample temperature on the mechanical properties of brain tissue is significant under the high strain rate, especially at low temperature (13°C), in which the hardening of the brain tissue is very obvious. At the low strain rate, no temperature dependency of brain mechanics is noted. Therefore, the current results highlight that the temperature of the brain sample should be ensured to be in accordance with the living subject when studying the biomechanical response of living tissue.


Author(s):  
Yifan Yin ◽  
Stefan Wiemer ◽  
Edi Kissling ◽  
Federica Lanza ◽  
Antonio P. Rinaldi ◽  
...  

ABSTRACT Crustal earthquakes in low-strain-rate regions are rare in the human life span but can generate disastrous consequences when they occur. Such was the case in the Canterbury earthquake sequence that began in 2010 and eventually led to almost 200 fatalities. Our study explores this earthquake sequence’s origins by producing an enhanced earthquake catalog in the Canterbury Plains and Otago, South Island, New Zealand. We investigate seismicity rate changes from 2005 to before the 2010 Mw 7.2 Darfield earthquake. During this time, major subduction-zone earthquakes, such as the 2009 Mw 7.8 Dusky Sound earthquake, created measurable coseismic and postseismic strain in the region. We use template matching to expand the catalog of earthquakes in the region, and use a support vector machine classifier to remove false positives and poor detections. We then compare the newly obtained seismicity rates with the coseismic and postseismic crustal strain fields, and find that seismicity rate and crustal strain are positively correlated in the low-stress, low-seismicity region of the northern Canterbury Plains. In contrast, near fast-moving plate-boundary faults, the seismicity rate changes rise without much change in the strain rate. Our analysis reveals a substantial seismicity rate decrease in the western rupture area of the Darfield earthquake, which we infer to be an effect of coseismic and postseismic deformation caused by the Dusky Sound earthquake. We show in low-strain-rate regions, stress perturbation of a few kPas creates substantial seismicity rate change. However, the implication that such seismic quiescence is responsible for the nucleation of the Darfield earthquake requires further studies.


Author(s):  
F. M. F. Serafim ◽  
I. N. A. Oguocha ◽  
A. G. Odeshi ◽  
R. Evitts ◽  
R. J. Gerspacher ◽  
...  

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