Effect of Strain Rate on the Dynamic Hardness in Metals

2007 ◽  
Vol 129 (4) ◽  
pp. 505-512 ◽  
Author(s):  
Amin H. Almasri ◽  
George Z. Voyiadjis
Keyword(s):  
Strain Rate ◽  
Experimental Results ◽  
Strain Rates ◽  
Rate Dependency ◽  
Dynamic Hardness ◽  
Loading Rates ◽  
Hardening Law ◽  
Dislocation Densities ◽  
Indentation Tests ◽  
Good Agreement

Traditionally, the hardness of materials is determined from indentation tests at low loading rates (static). However, considerably less work has been conducted in studying the dynamic hardness of materials using relatively high loading rates. In the present work, two models are used to predict strain rate dependency in hardness. The first model is a power law expression that is based on the dependence of the yield stress on the strain rate. This model is relatively simple in implementation, and it is quite easy to determine its parameters from simple uniaxial experiments. The second model is a micromechanical based model using Taylor’s hardening law. It utilizes the behavior of dislocation densities at high strain rates in metals in order to relate dynamic hardness to strain rates. The latter model also accounts for any changes in temperature that could exist. A finite element is also run and compared with the two models proposed in this work. Results from both models are compared with available experimental results for oxygen-free high-conductivity copper and 1018 cold rolled steel, and both models show reasonably good agreement with the experimental results.

scholarly journals A Strain Rate-Dependent Damage Evolution Model for Concrete Based on Experimental Results

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Bin Xu ◽  
Xiaoyan Lei ◽  
P. Wang ◽  
Hui Song
Keyword(s):  
Strain Rate ◽  
Uniaxial Compression ◽  
Damage Evolution ◽  
Damage Model ◽  
Evolution Model ◽  
Experimental Results ◽  
Strain Rates ◽  
Compression Tests ◽  
Stress Strain ◽  
Actual Damage

There are various definitions of damage variables from the existing damage models. The calculated damage value by the current methods still could not well correspond to the actual damage value. Therefore, it is necessary to establish a damage evolution model corresponding to the actual damage evolution. In this paper, a strain rate-sensitive isotropic damage model for plain concrete is proposed to describe its nonlinear behavior. Cyclic uniaxial compression tests were conducted on concrete samples at three strain rates of 10−3s−1, 10−4s−1, and 10−5s−1, respectively, and ultrasonic wave measurements were made at specified strain values during the loading progress. A damage variable was defined using the secant and initial moduli, and concrete damage evolution was then studied using the experimental results of the cyclic uniaxial compression tests conducted at the different strain rates. A viscoelastic stress-strain relationship, which considered the proposed damage evolution model, was presented according to the principles of irreversible thermodynamics. The model results agreed well with the experiment and indicated that the proposed damage evolution model can accurately characterize the development of macroscopic mechanical weakening of concrete. A damage-coupled viscoelastic constitutive relationship of concrete was recommended. It was concluded that the model could not only characterize the stress-strain response of materials under one-dimensional compressive load but also truly reflect the degradation law of the macromechanical properties of materials. The proposed damage model will advance the understanding of the failure process of concrete materials.

Strain Rate Effect on Shear Behavior of Open-Graded Aggregates

2017 ◽  
Vol 2655 (1) ◽  
pp. 64-70 ◽  
Author(s):  
Thomas Gebrenegus ◽  
Jennifer E. Nicks ◽  
Michael T. Adams
Keyword(s):  
Strain Rate ◽  
Axial Strain ◽  
Shear Behavior ◽  
Strain Rate Effect ◽  
Rate Effect ◽  
Strength Parameter ◽  
Strain Rates ◽  
Rate Dependency ◽  
Confining Stress ◽  
Dilation Angle

Despite their wide application as construction materials in various earthworks built by state and local transportation agencies, the role of physical and mechanical factors in the strength and deformation behavior of crushed, manufactured open-graded aggregates (OGAs) is not well studied. In this investigation, the strain rate dependency of strength–deformation behaviors of two commonly employed crushed aggregates with small (12.7 mm) and large (38.1 mm) sizes is investigated. A 150-mm diameter triaxial testing device was used to conduct a drained compression test at five strain rates, ranging from 0.000083%/s to 0.0083%/s. To evaluate the significance of confining stress and density on the effect of strain rates, the shear tests were conducted at 34 kPa and 207 kPa effective confining stress levels, with the samples compacted at loose (30%) and dense (95%) relative densities. The peak friction angle, maximum dilation angle, secant modulus, and axial strain at which the aggregates started to dilate were determined to evaluate the strain rate effect on the shear behavior of OGAs. The results demonstrate that within the imposed quasistatic strain rate ranges, only the dilation angle showed an increasing trend with the increase in strain rate, whereas other extracted strength parameters were less sensitive to strain rate for both OGAs tested. Hence, the selection of strain rates according to ASTM specifications is appropriate for conducting strength parameter tests, used by practitioners for the design of geotechnical structures, on OGAs under quasistatic conditions.

scholarly journals Recording Wire Strainmeters on the Barnes Ice Cap, Baffin Island, Canada

1978 ◽  
Vol 20 (83) ◽  
pp. 409-423 ◽  
Author(s):  
K. Evans ◽  
D.J. Goodman ◽  
G. Holdsworth
Keyword(s):  
Strain Rate ◽  
Periodic Variation ◽  
Strain Rates ◽  
Baffin Island ◽  
Rate Data ◽  
Rapid Acquisition ◽  
Ice Cap ◽  
Good Agreement

AbstractThe report describes an experiment to evaluate the use of geophysical (Cambridge-type) wire strainmeters for the rapid acquisition of strain-rate data and to compare strains on a large ice mass over gauge distances of 5 m, 50 m, and 1 km.Three continuously recording wire strainmeters were installed at the centre of two separate arrays of strain poles 10.6 km and 19.5 km from the ice divide on the Barnes Ice Cap. Data was collected between 24 April and 15 May 1976. The 1 km strain arrays had previously been measured in 1974 and 1975. The results show good agreement between the strainmeter data and the larger strain arrays at the 10.6 km site but differ at the 19.5 km site. When the daily means are calculated for the strainmeters at the 19.5 km site, the strain-rates show a possible periodic variation with an apparent period ofabout 11 d. Since there appears to be no direct correlation between the strainmeter signal and either temperature or pressure, the result is assumed to represent real varying strain within the ice.

Tensile Behavior of Ti-5Al-2.5Sn Alloy at Low Temperatures and High Strain Rates

2019 ◽  
Vol 794 ◽  
pp. 135-141
Author(s):  
Bin Zhang ◽  
Yang Wang
Keyword(s):  
Strain Rate ◽  
Strain Hardening ◽  
Low Temperatures ◽  
High Strain ◽  
Testing Temperature ◽  
Tensile Behavior ◽  
Experimental Results ◽  
Strain Rates ◽  
Increasing Temperature ◽  
Strain Hardening Rate

The mechanical responses of Ti-5Al-2.5Sn alloy at low temperatures were investigated under quasi-static and dynamic tensile loads using MTS system and SHTB system, respectively. Tensile stress-strain curves were obtained over the temperature range of 153 to 298K and the rate range of 0.001 to 1050 s-1. Experimental results indicate that the tensile behavior of Ti-5Al-2.5Sn alloy is dependent on strain rate and temperature. Yield stress and flow stress increase with increasing strain rate and decrease with increasing temperature. Results also indicate that strain hardening rate of Ti-5Al-2.5Sn alloy is lower at high strain rate, while strain hardening rate varies little with testing temperature. The Khan-Huang-Liang constitutive model was chosen to characterize the tensile responses of Ti-5Al-2.5Sn alloy at low temperatures and different strain rates. The model results coincide well with the experimental results within the tested temperature and rate ranges.

Simulation of Fracture Behavior of Elastomer Modified Polypropylene Based on Elastoviscoplastic Constitutive Equation With Craze and Tensile Softening Law

2005 ◽  
Author(s):  
Hiroyuki Mae
Keyword(s):  
Constitutive Equation ◽  
Crack Propagation ◽  
Strain Rate ◽  
Fracture Behavior ◽  
Experimental Results ◽  
Experimental Result ◽  
Load Displacement ◽  
Macroscopic Crack ◽  
Tensile Softening ◽  
Good Agreement

The strong strain-rate dependence, neck propagation and craze evolution characterize the large plastic deformation and fracture behavior of polymer. In the latest study, Kobayashi, Tomii and Shizawa suggested the elastoviscoplastic constitutive equation based on craze evolution and annihilation and then applied it to the plane strain issue of polymer. In the previous study, the author applied their suggested elastoviscoplastic constitutive equation with craze effect to the three dimensional shell issue and then showed that the load displacement history was in good agreement with the experimental result including only microscopic crack such as craze. For the future industrial applications, the macroscopic crack had to be taken into account. For instance, an airbag deployment simulation needed the macroscopic crack prediction. Thus, the main objective of this study was to propose the tensile softening equation and then add it to the elastoviscoplastic constitutive equation with craze effect so that the load displacement history could be roughly simulated during the macroscopic crack propagation. The tested material in this study was the elastomer blended polypropylene used in the interior and exterior of automobiles. First, the material properties were obtained based on the tensile test results at wide range of strain rates: 10−4 – 102 (1/sec). Next, the fast compact tension test was conducted and then the tensile softening parameters were fixed. Then, the fast bending test and the dart impact test were carried out in order to obtain the load displacement history and also observe the macroscopic crack propagation at high strain rate. Finally, the fracture behavior was simulated and then compared with the experimental results. It was shown that the predictions of the constitutive equation with the proposed tensile softening equation were in good agreement with the experimental results.

scholarly journals Effect of loading rate on tensile and fracture behavior of AA2050-T84 alloy at high temperature

2021 ◽  
Vol 2070 (1) ◽  
pp. 012163
Author(s):  
Nagaraj Ekabote ◽  
Krishnaraja G Kodancha
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
Tensile Tests ◽  
Rate Variation ◽  
Strain Rates ◽  
Rate Dependency ◽  
Commercial Aircraft ◽  
Fracture Failure ◽  
Load Rate ◽  
Increased Susceptibility

Abstract AA2050-T84 alloy is commonly used in the fabrication of modern commercial aircraft wing parts. Load and temperature variation during aircraft take-off, flight, and landing at different environmental conditions is substantial. Mechanical properties variation of AA2050-T84 alloy at sub-zero and room temperatures are significant and well documented in the literature. In the present work, at a high temperature of 200°C, the effect of load rate variation on tensile and fracture properties of AA2050-T84 alloy are experimentally and numerically studied. The load rates represented in strain rates were applied at 0.01, 0.1, and 1s−1. Experimental tensile tests exhibited the positive strain rate dependency on the yield and ultimate strength of the alloy. 2D numerical elastic-plastic fracture analysis was carried out using Abaqus 6.14. Similar to tensile results, the fracture parameters dependency on strain rates was witnessed. Overall, higher strain rate causes the increased susceptibility of fracture failure with the increase in yield stress of the material.

Tensile Behavior of Unidirectional Carbon Reinforced Composites for Aerospace Structures under Varying Strain Rates

2015 ◽  
Vol 798 ◽  
pp. 357-361 ◽  
Author(s):  
Haris A. Khan ◽  
Mehr Nigar ◽  
Imran Ali Chaudhry
Keyword(s):  
Strain Rate ◽  
Volume Fraction ◽  
Testing Machine ◽  
Tensile Modulus ◽  
Failure Behavior ◽  
Strain Rates ◽  
Loading Rates ◽  
Matrix Volume ◽  
Versus Strain ◽  
Fiber Reinforced Laminates

This paper focuses on progressive damage investigation and failure analysis of carbon fiber reinforced laminates under varying strain rates in tensile mode. Samples specimen prepared for experiments were made from unidirectional ply with 70/30 fiber-matrix volume fraction and cross-ply (0°-90°) balanced stacking. These laminates were subjected to uniaxial longitudinal tensile loading in a Universal Testing Machine (UTM) with varying strain rates. Results acquired from the experiments were used to plot stress versus strain curves for different strain rates. These plots were subsequently analyzed to investigate the effect of varying loading rates on the mechanical properties and failure behavior of these composites. Experimental data revealed a considerable increase in the tensile strength with increasing strain rate. The tensile modulus and strain to failure were also found to exhibit slight increase with the increasing strain rate.

Crushing and Flowing Characteristics of Lightweight Foamed Concrete under Different Loading Rates and Temperatures

2013 ◽  
Vol 535-536 ◽  
pp. 569-573
Author(s):  
Wei Guo Guo ◽  
Jian Jun Wang ◽  
Guang Liang Li ◽  
Ya Jie Shi
Keyword(s):  
Strain Rate ◽  
Testing Machine ◽  
Strain Rate Range ◽  
Deformation And Failure ◽  
Loading Rates ◽  
Electric Driving ◽  
Strength Based ◽  
Foamed Concrete ◽  
Three Stages ◽  
Good Agreement

Lightweight foamed concrete is one kind of new and important runway arresting materials for airplanes and other vehicles. To study its crushing and flowing behavior under different loading rates, an electric-driving screw testing machine, and an Instron VHS 8800 higher strain-rate testing machine are used. Crushing mechanical characteristics, and deformation and failure mode with the density of 0.20g/ccm are systematically analysed, while crushing strain-rate range from 0.001/s to about 102/s. Results show this foamed concrete suffers three stages of deformation during loading, namely elastic region, crushing plateau region and densification region; and it presents very low shear strength. Based on testing results, a phenomenological model is established, and comparing model predictions with experimental results, a good agreement is obtained.

Measurement on Strain Rate Sensitivity Properties of Rice Husk (Rh)/Linear Low Density Polyethylene (Lldpe) Composites under Various Loading Rates

2015 ◽  
Vol 754-755 ◽  
pp. 77-82
Author(s):  
Mohd Firdaus Omar ◽  
Nur Suhaili Abdul Wahab ◽  
Hazizan Md. Akil ◽  
Zainal Arifin Ahmad ◽  
N.Z. Noriman
Keyword(s):  
Strain Rate ◽  
Thermal Activation ◽  
Testing Machine ◽  
Rate Sensitivity ◽  
Applied Strain ◽  
Strain Rates ◽  
Static Compression ◽  
Loading Rates ◽  
Compression Properties ◽  
Great Dependency

In this study, LLDPE/RH composites were tested under various strain rate loadings (0.001/s, 0.01/s and 0.1/s) using the universal testing machine. Static compression properties of LLDPE/RH composites with different filler contents of 5 wt%, 10 wt%, 15 wt%,20 wt% and, 30 wt% RH were investigated. Results show that the yield stress, ultimate compressive strength and the rigidity properties of LLDPE/RH composites were strongly affected by both filler contents and strain rate loadings. Apart from that, the rate of sensitivity of LLDPE/RH show great dependency towards applied strain rate, where it was increased with increasing strain rates. Unfortunately, the thermal activation values show contrary trend. Visually, from the post damage analysis, the results show that applied strain rates affected the deformation behavior of tested LLDPE/RH composites.

scholarly journals A Method of Determining the Strain-Rate Tensor at the Surface of a Glacier

1959 ◽  
Vol 3 (25) ◽  
pp. 409-419 ◽  
Author(s):  
J. F. Nye
Keyword(s):  
Strain Rate ◽  
Least Squares Method ◽  
Strain Tensor ◽  
Rate Of Change ◽  
Principal Strain ◽  
Strain Rate Tensor ◽  
Strain Rates ◽  
Principal Stresses ◽  
Independent Components ◽  
Good Agreement

AbstractThe rate of strain tensor at a point on the surface of a glacier may be determined by setting up a number of stakes in a pattern and measuring the rate of change of the distances between them. A suitable pattern consists of four stakes at the corners of a square with one stake at the center. Five such patterns were used on Austerdalsbreen, Norway, in August 1956. The problem is to deduce the best values of the 3 independent components of the strain-rate tensor from the 8 measured quantities, and, for this purpose, a least-squares method, invented by Bond for the analogous problem in crystal physics, is used. The principal strain-rates are found to within about ±0.005 yr.−1and their directions relative to the stake system to within about ±0.5°. The directions and magnitudes of the principal stresses are then deduced from Glen’s flow law and a suitable general theory. The directions of the principal strain-rates are in good agreement with the directions of the crevasses, but the experiment is inconclusive on the question of the magnitude of the stress needed to form a crevasse.

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