The Effect of Strain-Rate Upon the Tensile Deformation of Materials

1975 ◽  
Vol 97 (2) ◽  
pp. 151-155 ◽  
Author(s):  
R. G. Davies ◽  
C. L. Magee
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
High Speed ◽  
Tensile Deformation ◽  
Rate Sensitivity ◽  
Al Alloys ◽  
Reinforced Plastics ◽  
Strain Behavior ◽  
Static Testing ◽  
Dynamic Factors

The tensile strength of seventeen engineering materials including steels, Al alloys, and fiber-reinforced plastics, has been determined at strain-rates from 10−3 to 103 sec−1. Variable effects on the stress-strain behavior were found in the different materials with the Al alloys showing minimal strain-rate sensitivity and the plastics highest. All results exhibit a logarithmic dependence of flow stress on strain-rate and thus the dynamic factors (ratio of dynamic to low rate or quasi-static strengths) are as dependent upon changes in quasi-static testing speed (∼1 in./min (0.42 mm/s) as they are to changes at high speed (50,000 in./min or 50 mph (22.35 m/s). No significant influence of strain-rate on elongation or reduction in area has been found for any of the materials. Steels, which comprise the majority of the presently investigated materials, exhibit a higher rate sensitivity for yielding than for higher strain deformation. It is shown that the flow stress results for these steels leads to an internally consistent scheme when (1) strength level and (2) strengthening mechanisms are properly accounted for.

Dynamic Tensile Tests of Auto-Body Steel Sheets with the Variation of Temperature

2006 ◽  
Vol 116-117 ◽  
pp. 259-262 ◽  
Author(s):  
Hee Jong Lee ◽  
Jung Han Song ◽  
Hoon Huh
Keyword(s):  
Flow Stress ◽  
Tensile Test ◽  
Strain Rate ◽  
Mechanical Behavior ◽  
High Speed ◽  
Mechanical Response ◽  
Rate Sensitivity ◽  
Tensile Tests ◽  
Static State ◽  
Steel Sheets

This paper is concerned with the thermo-mechanical behavior of steel sheet for an autobody including the temperature dependent strain-rate sensitivity. Tensile tests have been carried out with the high strength steel sheets such as SPRC35R, SPRC45E and TRIP60. The tensile tests were performed with the variation of the strain-rates from 0.001/s to 200/s and with the variation of environmental temperatures from -40 to 200. The thermo-mechanical response at the quasi-static state is obtained with the static tensile test and the one at the intermediate strain-rate is obtained with the high speed tensile test. Both the strain-rate and the temperature sensitivity of the flow stress are calculated for the quantitative evaluation of thermo-mechanical behavior of steel sheets. The results demonstrate that as the strain-rate increases, the variation of the flow stress becomes more dependent on the temperature. The results also indicate that the material properties of SPRC35R are more sensitive to the strain-rate and the temperature than those of SPRC45E and TRIP60.

A Simple Constitutive Model for Prediction of Single-Peak Flow Curves Under Hot Working Conditions

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Roxana Baktash ◽  
Hamed Mirzadeh
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Peak Flow ◽  
Rate Sensitivity ◽  
Peak Strain ◽  
Flow Curves ◽  
Hollomon Parameter ◽  
Proposed Model ◽  
Stress Coefficient ◽  
Hollomon Equation

The hot flow stress of a typical stainless steel was modeled by the Hollomon equation, a modified form of the Hollomon equation, and another modified form based on the Fields–Backofen equation. The coupled effect of the deformation temperature and strain rate was also taken into account in the proposed formulae by consideration of the Zener–Hollomon parameter or dependency of the constants on temperature. The modified Fields–Backofen equation was found to be appropriate for prediction of flow stress, in which the incorporation of peak strain and consideration of temperature dependencies of the strain rate sensitivity and the stress coefficient were found to be beneficial. Moreover, the simplicity of the proposed model justifies its applicability for expressing hot flow stress characterizing dynamic recrystallization (DRX).

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.

Bulge Test Characterization of Static Softening and Dynamic Instabilities in Foils of an Al-Based Alloy

2001 ◽  
Vol 695 ◽  
Author(s):  
Miroslav Cieslar ◽  
Ayatollah Karimi ◽  
Jean-Luc Martin
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Cell Structure ◽  
Rate Sensitivity ◽  
Bulge Test ◽  
Large Strains ◽  
Subgrain Structure ◽  
Free Standing ◽  
Strain Behavior ◽  
Bulge Testing

ABSTRACTEffects of recovery and recrystallization on subsequent stress – strain behavior were studied in foils of non-age hardenable Al based alloy. A bulge testing device for mechanical testing of thin free standing films and foils, enabling the detection of large strains, was employed. The bulge tester was used at RT both for the predeformation of the foil in the biaxial mode and also for the study of softening after subsequent one-step annealing. Three stages of strength drop as a function of the annealing temperature were observed between RT and 590°C. The contribution of different annealing processes to the softening was established using transmission electron microscopy. It was found that below 200°C only redistribution of dislocations inside dislocation cells and refinement of the cell structure occurred. Between 200°C and 380°C the formation of a subgrain structure was observed. The softening process is terminated as partial recrystallization takes place at higher annealing temperatures. Dynamic interaction of solutes with dislocations was revealed during prestraining as well as poststraining of foils. This effect resulted in the appearance of a negative strain rate sensitivity and dynamic instabilities after appropriate prestraining and annealing conditions. The above results show that bulge testing of Al foils allows to study the successive annealing stages by measuring the most important macroscopic parameters of plastic deformation (yield stress, work hardening rate, ductility, strain rate sensitivity, etc.). These stages could be related to the microstructure evolution.

Tensile Deformation Behavior of 5A90 Al-Li Alloy Sheet at Elevated Temperature

2011 ◽  
Vol 66-68 ◽  
pp. 70-75 ◽  
Author(s):  
Gao Shan Ma ◽  
Song Yang Zhang ◽  
Han Ying Wang ◽  
Min Wan
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Deformation Behavior ◽  
Tensile Deformation ◽  
Alloy Sheet ◽  
Hot Forming ◽  
Uniaxial Tensile ◽  
Sensitivity Index ◽  
Tensile Deformation Behavior ◽  
Increasing Temperature

Uniaxial tensile deformation behavior of 5A90 aluminium-lithium alloy sheet is investigated in the hot forming with the temperature range of 200-450°C and strain rate range of 0.3×10-3-0.2×10-1s-1. It is found that the flow stress of 5A90 Al-Li alloy in uniaxial tension increase with increasing strain rate and decrease with increasing temperature, however, the tendency of total elongation is just the reverse, and the optimum forming temperature is 400°C. The strain rate sensitivity index (m-value) remarkably increases with increasing temperature for a given strain rate. It is shown that 5A90 Al-Li alloy sheet displays the sensitivity to the strain rate at elevated temperatures. For a given strain rate, the strain hardening index (n-value) decreases with increasing temperature, whereas the n-value increases above 350°C. The constitutive equation of stress, strain and strain rate for 5A90 Al-Li alloy at any temperature is obtained by fitting the experimental data, which gave a good flow stress model for the FEM simulation of hot forming.

The strain-rate sensitivity of the hardness in indentation creep

2007 ◽  
Vol 22 (4) ◽  
pp. 926-936 ◽  
Author(s):  
A.A. Elmustafa ◽  
S. Kose ◽  
D.S. Stone
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Hertzian Contact ◽  
Indentation Creep ◽  
Proportionality Factor ◽  
Element Analysis ◽  
Elastic Deformations ◽  
The Relationship

Finite element analysis is used to simulate indentation creep experiments with a cone-shaped indenter. The purpose of the work is to help identify the relationship between the strain-rate sensitivity of the hardness, νH, and that of the flow stress, νσ in materials for which elastic deformations are significant. In general, νH differs from νσ, but the ratio νH/νσ is found to be a unique function of H/E* where H is the hardness and E* is the modulus relevant to Hertzian contact. νH/νσ approaches 1 for small H/E*, 0 for large H/E*, and is insensitive to work hardening. The trend in νH/νσ as a function of H/E* can be explained based on a generalized analysis of Tabor’s relation in which hardness is proportional to the flow stress H = k × σeff and in which the proportionality factor k is a function of σeff/E*.

scholarly journals Strain Rate Sensitivity of Alloys 800H and 617

2013 ◽  
Author(s):  
J. K. Wright ◽  
J. A. Simpson ◽  
R. N. Wright ◽  
L. J. Carroll ◽  
T. L. Sham
Keyword(s):  
High Temperature ◽  
Flow Stress ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Temperature Limit ◽  
Applied Strain ◽  
Alloy 800H ◽  
Alloy 617 ◽  
Temperature Heat

The flow stress of many materials is a function of the applied strain rate at elevated temperature. The magnitude of this effect is captured by the strain rate sensitivity parameter “m”. The strain rate sensitivity of two face–center cubic solid solution alloys that are proposed for use in high temperature heat exchanger or steam generator applications, Alloys 800H and 617, has been determined as a function of temperature over that range of temperatures relevant for these applications. In addition to determining the strain rate sensitivity, it is important for nuclear design within Section III of the ASME Boiler and Pressure Vessel Code to determine temperature below which the flow stress is not affected by the strain rate. This temperature has been determined for both Alloy 800H and Alloy 617. At high temperature the strain rate sensitivity of the two alloys is significant and they have similar m values. For Alloy 617 the temperature limit below which little or no strain rate sensitivity is observed is approximately 700°C. For Alloy 800H this temperature is approximately 650°C.

Strain Rate Dependence of the Flow Stress and Work-Hardening of Single Crystals of NI3(Al,Hf)B

1994 ◽  
Vol 364 ◽  
Author(s):  
S. S. Ezz ◽  
Y. Q. Sun ◽  
P. B. Hirsch
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Yield Stress ◽  
Strain Rate Sensitivity ◽  
Work Hardening ◽  
Room Temperature ◽  
Rate Sensitivity ◽  
Controlling Mechanism

AbstractThe strain rate sensitivity ß of the flow stress τ is associated with workhardening and β=(δτ/δln ε) is proportional to the workhardening increment τh = τ - τy, where τy is the strain rate independent yield stress. The temperature dependence of β/τh reflects changes in the rate controlling mechanism. At intermediate and high temperatures, the hardening correlates with the density of [101] dislocations on (010). The nature of the local obstacles at room temperature is not established.

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