Dislocation Mechanics of Extremely High Rate Deformations in Iron and Tantalum

2021 ◽  
pp. 1-30
Author(s):  
Mu'Tasem Shehadeh ◽  
Pascale El Ters ◽  
Ronald W. Armstrong ◽  
Werner Arnold
Keyword(s):  
Strain Rate ◽  
Weak Shock ◽  
Rate Sensitivity ◽  
High Rate ◽  
Dislocation Dynamic ◽  
Dislocation Generation ◽  
High Deformation ◽  
Rate Analysis ◽  
Dislocation Mechanics ◽  
Dynamic Plasticity

Abstract High strain rate simulations were performed using the multiscale dislocation dynamic plasticity (MDDP) method to calculate different rise times and load durations in mimicking high deformation rate shock or isentropic (ramp) testing of a-iron and tantalum crystals. Focus for both types of loading on both materials was on the inter-relationship between the (dislocation-velocity-related) strain rate sensitivity and the (time-dependent) evolution of dislocation density. The computations are compared with model thermal activation strain rate analysis (TASRA), phonon drag and dislocation generation predictions. The overall comparison of simulated tests and previous experimental measurements shows that the imposition of a rise time even as small as 0.2 ns preceding plastic relaxation via the MDDP method is indicative of relatively weak shock behavior.

scholarly journals Strain rate and thermal softening effects in shear testing of AA7075-T6 sheet

2018 ◽  
Vol 183 ◽  
pp. 02037 ◽  
Author(s):  
Taamjeed Rahmaan ◽  
Ping Zhou ◽  
Cliff Butcher ◽  
Michael J. Worswick
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Rate Sensitivity ◽  
Thermal Conditions ◽  
Shear Loading ◽  
Image Correlation ◽  
High Rate ◽  
Strain Rates ◽  
Shear Testing ◽  
Plane Shear

Shear tests were performed at strain rates ranging from quasi-static (0.01 s-1) to 500 s-1 for AA7075-T6 sheet metal alloy at room temperature. A miniature sized shear specimen was used in this work to perform high strain rate shear testing. Digital image correlation (DIC) techniques were employed to measure the strains in the experiments. At maximum in-plane shear strains greater than 20%, the AA7075-T6 alloy demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the AA7075-T6 alloy showed mild positive rate sensitivity. The strain to localization (using the Zener-Holloman criterion), measured using the DIC technique, decreased with strain rate in shear loading. The strain at complete failure, however, exhibited an increase at the highest strain rate (500 s-1). The current work also focused on characterization of the thermal conditions occurring during high rate loading in shear with in situ high speed thermal imaging. Experimental results from the highest strain rate (500 s-1) tests showed a notable increase in temperature within the specimen gauge region as a result of the conversion of plastic deformation energy into heat.

Influence of Precipitate Phase on the Strain Rate Sensitivity of Mg-Gd-Y Alloy

2011 ◽  
Vol 311-313 ◽  
pp. 792-797
Author(s):  
Fan Zhang ◽  
Cheng Wen Tan ◽  
Hong Nian Cai
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Dynamic Strain ◽  
Precipitate Phase ◽  
Aged Condition ◽  
Dislocation Generation ◽  
Peak Aged Condition ◽  
Athermal Component ◽  
Peak Aged

Supersaturated Mg-Gd-Y alloy followed by aging at 225 °C with different times were subjected to quais-static and dynamic strain rates to determine the influence of precipitate phase β′ on the strain rate sensitivity of magnesium alloy. Strain rate sensitivity (SRS) decreases with the increase of the size of β′. SRS decreases from initial condition to peak-aged condition due to the β′ increases the athermal component of flow stress. On the other hand, the influence of precipitate interfaces on dislocation generation and storage mechanisms may be responsible for the decrease of SRS from peak-aged to over-aged condition.

High Rate Superplastic Deformation Mechanisms in IN90211 Mechanically Alloyed Aluminum

1990 ◽  
Vol 196 ◽  
Author(s):  
Thomas R. Bieler ◽  
Amiya K. Mukherjee
Keyword(s):  
Strain Rate ◽  
Superplastic Deformation ◽  
Rate Sensitivity ◽  
High Rate ◽  
Temperature Dependent ◽  
Mechanically Alloyed ◽  
Rate Limiting Step ◽  
Orowan Stress ◽  
Apparent Strain ◽  
Rate Limiting

ABSTRACTIN90211 has exhibited superplastic elongations above 500% at high homologous temperatures (0.76–0.82 Tm). A high strain rate and flow stress for optimum elongation was measured (1–5/sec, 20–60 MPa, 425–485 °C). The apparent strain rate sensitivity of m≈0.25 differs from the usual m≈0.5 observations of superplastic deformation. An analysis of the data at several strains indicates a highly temperature dependent threshold stress is present, with either a n=2 or n=3 assumption for the stress exponent. The magnitude of the threshold stresses in IN90211 are smaller than usually observed in a dispersion strengthened matrix (1–20% instead of ≈50% of the Orowan stress). Experimental evidence from creep experiments supports the n=3 deformation mechanism as the rate limiting step of deformation.

High Strain Rate Behaviour of Aluminium Alloy Sheet

2006 ◽  
Vol 519-521 ◽  
pp. 139-146 ◽  
Author(s):  
Michael J. Worswick ◽  
R. Smerd ◽  
C.P. Salisbury ◽  
S. Winkler ◽  
David J. Lloyd
Keyword(s):  
Strain Rate ◽  
Rate Sensitivity ◽  
Alloy Sheet ◽  
High Rate ◽  
Mild Strain ◽  
Elongation To Failure ◽  
Split Hopkinson ◽  
Constitutive Response ◽  
Reduction In Area ◽  
Rate Behaviour

This paper presents results from quasi-static and high rate tensile testing of three aluminum sheet alloys, AA5754, AA5182 and AA6111, all of which are candidates for replacing mild steel in automotive bodies. Tests were performed at quasi-static rates using an Instron apparatus and at strain rates of 600 to 1500 s-1 using a tensile split Hopkinson bar. Additionally, an in-depth investigation was performed to determine the levels of damage within the materials and its sensitivity to strain rate. The constitutive response of all of the aluminum alloys tested showed only mild strain rate sensitivity. Dramatic increases in the elongation to failure were observed with increases in strain rate as well as greater reduction in area. Additionally, the level of damage was seen to increase with strain rate.

The effects of strain and strain rate on residual microstructures in copper

1986 ◽  
Vol 44 ◽  
pp. 420-421
Author(s):  
M. F. Stevens ◽  
P. S. Follansbee
Keyword(s):  
Strain Rate ◽  
Applied Stress ◽  
Threshold Stress ◽  
Rate Sensitivity ◽  
Viscous Drag ◽  
Strain Rates ◽  
Strain And Strain Rate ◽  
Threshold Strength ◽  
Mechanism Transition ◽  
Intrinsic Strength

The strain rate sensitivity of a variety of materials is known to increase rapidly at strain rates exceeding ∼103 sec-1. This transition has most often in the past been attributed to a transition from thermally activated guide to viscous drag control. An important condition for imposition of dislocation drag effects is that the applied stress, σ, must be on the order of or greater than the threshold stress, which is the flow stress at OK. From Fig. 1, it can be seen for OFE Cu that the ratio of the applied stress to threshold stress remains constant even at strain rates as high as 104 sec-1 suggesting that there is not a mechanism transition but that the intrinsic strength is increasing, since the threshold strength is a mechanical measure of intrinsic strength. These measurements were made at constant strain levels of 0.2, wnich is not a guarantee of constant microstructure. The increase in threshold stress at higher strain rates is a strong indication that the microstructural evolution is a function of strain rate and that the dependence becomes stronger at high strain rates.

A Study on the Flow Behavior of 42CrMo Steel under Hot Compression by Thermal Physical Simulations

2010 ◽  
Vol 108-111 ◽  
pp. 494-499
Author(s):  
Ying Tong ◽  
Guo Zheng Quan ◽  
Gang Luo ◽  
Jie Zhou
Keyword(s):  
Strain Rate ◽  
Flow Behavior ◽  
Rate Sensitivity ◽  
Strain Hardening Exponent ◽  
Forming Process ◽  
Material Parameters ◽  
Basic Model ◽  
42Crmo Steel ◽  
Plastic Forming ◽  
Physical Simulations

This work was focused on the compressive deformation behavior of 42CrMo steel at temperatures from 1123K to 1348K and strain rates from 0.01s-1 to 10s-1 on a Gleeble-1500 thermo-simulation machine. The true stress-strain curves tested exhibit peak stresses at small strains, after them the flow stresses decrease monotonically until high strains, showing a dynamic flow softening. And the stress level decreases with increasing deformation temperature and decreasing strain rate. The values of strain hardening exponent n, and the strain rate sensitivity exponent m were calculated the method of multiple linear regression, the results show that the two material parameters are not constants, but changes with temperature and strain rate. Then the two variable material parameters were introduced into Fields-Backofen equation amended. Thus the constitutive mechanical discription of 42CrMo steel which can accurately describe the relationships among flow stress, temperature, strain rate, strain offers the basic model for plastic forming process simulation.

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