Stress-strain and strain rate responses of precracked charpy specimens under dynamic loading

1992 ◽  
Vol 55 (3) ◽  
pp. R49-R53
Author(s):  
Junshan Lin ◽  
Mingjing Tu
Keyword(s):  
Strain Rate ◽  
Dynamic Loading ◽  
Stress Strain ◽  
Strain And Strain Rate

scholarly journals Evolution of specimen strain rate in split Hopkinson bar test

2019 ◽  
Vol 233 (13) ◽  
pp. 4667-4687 ◽  
Author(s):  
Hyunho Shin ◽  
Jong-Bong Kim
Keyword(s):  
Strain Rate ◽  
Rate Equation ◽  
Constant Strain Rate ◽  
Strain Curve ◽  
Hopkinson Bar ◽  
Stress Strain ◽  
Split Hopkinson Bar ◽  
Specimen Diameter ◽  
Strain And Strain Rate ◽  
Split Hopkinson

The specimen strain rate in the split Hopkinson bar (SHB) test has been formulated based on a one-dimensional assumption. The strain rate is found to be controlled by the stress and strain of the deforming specimen, geometry (the length and diameter) of specimen, impedance of bar, and impact velocity. The specimen strain rate evolves as a result of the competition between the rate-increasing and rate-decreasing factors. Unless the two factors are balanced, the specimen strain rate generally varies (decreases or increases) with strain (specimen deformation), which is the physical origin of the varying nature of the specimen strain rate in the SHB test. According to the formulated strain rate equation, the curves of stress–strain and strain rate–strain are mutually correlated. Based on the correlation of these curves, the strain rate equation is verified through a numerical simulation and experiment. The formulated equation can be used as a tool for verifying the measured strain rate–strain curve simultaneously with the measured stress–strain curve. A practical method for predicting the specimen strain rate before carrying out the SHB test has also been presented. The method simultaneously solves the formulated strain rate equation and a reasonably estimated constitutive equation of specimen to generate the anticipated curves of strain rate–strain and stress–strain in the SHB test. An Excel® program to solve the two equations is provided. The strain rate equation also indicates that the increase in specimen stress during deformation (e.g., work hardening) plays a role in decreasing the slope of the strain rate–strain curve in the plastic regime. However, according to the strain rate equation, the slope of the strain rate–strain curve in the plastic deformation regime can be tailored by controlling the specimen diameter. Two practical methods for determining the specimen diameter to achieve a nearly constant strain rate are presented.

scholarly journals Estimation of Stress-Strain behavior of polyethylene terephthalate (PET) at different strain rates by Artificial Neural Network under simultaneous stretch scenario

2021 ◽  
Author(s):  
Fei Teng ◽  
Gary Menary ◽  
Savko Malinov ◽  
Shiyong Yan
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Strain Rate ◽  
Strain Rates ◽  
Stress Strain ◽  
Strain Behavior ◽  
Strain And Strain Rate ◽  
Artificial Neural ◽  
Artificial Neural Network Ann ◽  
High Degree

In this paper, an Artificial Neural Network (ANN) is used to predict the stress-strain behavior of PET at conditions relevant to Stretch Blow Moulding i.e. Large equibiaxial deformation at elevated temperature and high strain rate. The input vectors considered are temperature, strain, and strain rate with a corresponding output parameter of stress. In the present work, a feed-forward back backpropagation algorithm was used to train the ANN. The ANN is able to approximate the relationship between stress and strain at various strain rates & temperatures to a high degree of accuracy for all conditions tested.

Stress, strain and strain-rate cemented carbide properties determined with a fem-supported evaluation of impact test imprints

2021 ◽  
Vol 94 ◽  
pp. 105384
Author(s):  
Antonios Bouzakis ◽  
Georgios Skordaris ◽  
Konstantinos-Dionysios Bouzakis ◽  
Mehmet-Gökhan Gökcen ◽  
Apostolos Boumpakis ◽  
...  
Keyword(s):  
Strain Rate ◽  
Impact Test ◽  
Cemented Carbide ◽  
Stress Strain ◽  
Strain And Strain Rate

An Empirical Creep Law From a Single Test

1962 ◽  
Vol 84 (2) ◽  
pp. 236-238
Author(s):  
Iain Finnie
Keyword(s):  
Strain Rate ◽  
Creep Test ◽  
Constant Load ◽  
Constant Stress ◽  
Single Test ◽  
Creep Tests ◽  
Stress Strain ◽  
Strain And Strain Rate ◽  
Single Constant

A method is described by which an empirical creep law, relating stress, strain, and strain rate, may be obtained from a single constant-load creep test. An example to illustrate the method is given, and the empirical creep law is compared with the results of several constant stress creep tests.

Effects of Foot Strike and Step Frequency on Achilles Tendon Stress During Running

2016 ◽  
Vol 32 (4) ◽  
pp. 365-372 ◽  
Author(s):  
Michael Lyght ◽  
Matthew Nockerts ◽  
Thomas W. Kernozek ◽  
Robert Ragan
Keyword(s):  
Strain Rate ◽  
Achilles Tendon ◽  
Musculoskeletal Model ◽  
Stress And Strain ◽  
Step Frequency ◽  
Stress Strain ◽  
Strain And Strain Rate ◽  
Subject Specific ◽  
Foot Strike ◽  
Crosssectional Area

Achilles tendon (AT) injuries are common in runners. The AT withstands high magnitudes of stress during running which may contribute to injury. Our purpose was to examine the effects of foot strike pattern and step frequency on AT stress and strain during running utilizing muscle forces based on a musculoskeletal model and subject-specific ultrasound-derived AT crosssectional area. Nineteen female runners performed running trials under 6 conditions, including rearfoot strike and forefoot strike patterns at their preferred cadence, +5%, and –5% preferred cadence. Rearfoot strike patterns had less peak AT stress (P < .001), strain (P < .001), and strain rate (P < .001) compared with the forefoot strike pattern. A reduction in peak AT stress and strain were exhibited with a +5% preferred step frequency relative to the preferred condition using a rearfoot (P < .001) and forefoot (P=.005) strike pattern. Strain rate was not different (P > .05) between step frequencies within each foot strike condition. Our results suggest that a rearfoot pattern may reduce AT stress, strain, and strain rate. Increases in step frequency of 5% above preferred frequency, regardless of foot strike pattern, may also lower peak AT stress and strain.

scholarly journals Experimental Study on Damage and Failure of Coal-Pillar Dams in Coal Mine Underground Reservoir under Dynamic Load

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Qiangling Yao ◽  
Liqiang Yu ◽  
Ning Chen ◽  
Weinan Wang ◽  
Qiang Xu
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Strain Rate ◽  
Water Content ◽  
Dynamic Loading ◽  
Coal Pillar ◽  
Strain Curve ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Underground Reservoir

The stability of coal-pillar dams in underground hydraulic engineering works is affected not only by long-term water erosion but also by dynamic loading induced, for example, by roof breaking or fault slipping. In this paper, the water absorption characteristics of coal samples from western China were studied by nondestructive immersion tests, and a high-speed camera was used to monitor SHPB tests on samples of varying water content and subjected to various strain rates. Besides, the coal-pillar dam is numerically simulated based on the experimental data and the actual engineering conditions. The results show that, given low strain rate and high water content, the compaction stage accounts for most of the stress-strain curve, whereas the elastic stage accounts for only a relatively small fraction of the stress-strain curve. The dynamic compressive strength and elastic modulus follow exponential and logarithmic functions of strain rate, respectively, exhibiting a significant positive correlation. As the water content increases, the dynamic elastic modulus increases almost linearly, and the compressive strength decreases gradually. Under the same impact load, samples with greater water content fail more rapidly, and the failure is exacerbated by the propagation of parallel cracks to staggered cracks. The average size of coal fragments decreases linearly with increasing strain rate and water content. Simulations indicate that dynamic loading increases the stress concentration on both sides of the dam and expands the high-stress area and plastic zone. The results provide guidance for designing waterproof coal pillars and underground reservoir dams.

The Biomechanical Determinants of Concussion: Finite Element Simulations to Investigate Tissue-Level Predictors of Injury During Sporting Impacts to the Unprotected Head

2015 ◽  
Vol 31 (4) ◽  
pp. 264-268 ◽  
Author(s):  
Declan A. Patton ◽  
Andrew S. McIntosh ◽  
Svein Kleiven
Keyword(s):  
Finite Element ◽  
Corpus Callosum ◽  
Strain Rate ◽  
Tissue Level ◽  
Von Mises Stress ◽  
Tolerance Limits ◽  
Stress Strain ◽  
Head Impacts ◽  
Strain And Strain Rate ◽  
Von Mises

Biomechanical studies of concussions have progressed from qualitative observations of head impacts to physical and numerical reconstructions, direct impact measurements, and finite element analyses. Supplementary to a previous study, which investigated maximum principal strain, the current study used a detailed finite element head model to simulate unhelmeted concussion and no-injury head impacts and evaluate the effectiveness of various tissue-level brain injury predictors: strain rate, product of strain and strain rate, cumulative strain damage measure, von Mises stress, and intracranial pressure. Von Mises stress was found to be the most effective predictor of concussion. It was also found that the thalamus and corpus callosum were brain regions with strong associations with concussion. Tentative tolerance limits for tissue-level predictors were proposed in an attempt to broaden the understanding of unhelmeted concussions. For the thalamus, tolerance limits were proposed for a 50% likelihood of concussion: 2.24 kPa, 24.0 s−1, and 2.49 s−1 for von Mises stress, strain rate, and the product of strain and strain rate, respectively. For the corpus callosum, tolerance limits were proposed for a 50% likelihood of concussion: 3.51 kPa, 25.1 s−1, and 2.76 s−1 for von Mises stress, strain rate, and the product of strain and strain rate, respectively.

scholarly journals Rock Failure Analysis under Dynamic Loading Based on a Micromechanical Damage Model

2018 ◽  
Vol 4 (11) ◽  
pp. 2801 ◽  
Author(s):  
Mohammad Hosein Ahmadi ◽  
Hamed Molladavoodi
Keyword(s):  
Compressive Strength ◽  
Strain Rate ◽  
Dynamic Loading ◽  
Damage Model ◽  
Dynamic Crack ◽  
Stress Strain ◽  
Micro Cracks ◽  
Proposed Model ◽  
Micromechanical Damage ◽  
Micromechanical Damage Model

A micromechanical constitutive damage model accounting for micro-crack interactions was developed for brittle failure of rock materials under compressive dynamic loading. The proposed model incorporates pre-existing flaws and micro-cracks that have same size with specific orientation. Frictional sliding on micro-cracks leading to inelastic deformation is very influential mechanism resulting in damage occurrence due to nucleation of wing-crack from both sides of pre-existing micro-cracks. Several homogenization schemes including dilute, Mori-Tanaka, self-consistence, Ponte-Castandea & Willis are usually implemented for up-scaling of micro-cracks interactions. In this study the Self-Consistent homogenization Scheme (SCS) was used in the developed damage model in which each micro-crack inside the elliptical inclusion surrounded by homogenized matrix experiences a stress field different from that acts on isolated cracks. Therefore, the difference between global stresses acting on rock material and local stresses experienced by micro-crack inside inclusion yields stress intensity factor (SIF) at the cracks tips which are utilized in the formulation of the dynamic crack growth criterion. Also the damage parameter was defined in term of crack density parameter. The developed model was programmed and used as a separate and new constitutive model in the commercial finite difference software (FLAC). The dynamic uniaxial compressive strength test of a brittle rock was simulated numerically and the simulated stress-strain curves under different imposed strain rates were compared each other. The analysis results show a very good strain rate dependency especially in peak and post-elastic region. The proposed model predicts a macroscopic stress-strain relation and a peak stress (compressive strength) with an associated transition strain rate beyond which the compressive strength of the material becomes highly strain rate sensitive. Also the damage growth process was studied by using the proposed micromechanical damage model and scale law was plotted to distinguish the dynamic and quasi-dynamic loading boundary. Results also show that as the applied strain rate increases, the simulated peak strength increases and the damage evolution becomes slower with strain increment.

Analytical Formulation of a Rate and Temperature Dependent Stress-Strain Relation

1979 ◽  
Vol 101 (3) ◽  
pp. 254-257 ◽  
Author(s):  
A. Merzer ◽  
S. R. Bodner
Keyword(s):  
Plastic Strain ◽  
Strain Rate ◽  
Uniaxial Stress ◽  
Plastic Strain Rate ◽  
Isotropic Hardening ◽  
Stress Strain ◽  
Rate Dependent ◽  
Strain Relation ◽  
Strain And Strain Rate ◽  
Stress Strain Relation

The equation for plastic strain rate in the Bodner-Partom viscoplastic formulation is integrated under conditions of uniaxial stress, constant plastic strain rate, and isotropic hardening to give an analytical expression for the stress as a function of plastic strain and strain rate. Temperature dependence is introduced which leads to a general relationship between stress, strain, strain rate, and temperature. The resulting equation indicates an asymptotic saturation stress whose dependence on strain rate and temperature appears to agree with experimental results. Strain hardening given by the analytical equation also seems to be consistent with experiments. A possible new definition of yield stress is a consequence of the rate dependent stress-strain relation.

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