scholarly journals A Modified Eyring Equation for Modeling Yield and Flow Stresses of Metals at Strain Rates Ranging from 10−5to 5 × 104 s−1

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Ramzi Othman
Keyword(s):  
Constitutive Equation ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Large Strain ◽  
Rate Sensitivity ◽  
Industrial Applications ◽  
Strain Rate Range ◽  
Strain Rates ◽  
Wide Range ◽  
Large Strain Rate

In several industrial applications, metallic structures are facing impact loads. Therefore, there is an important need for developing constitutive equations which take into account the strain rate sensitivity of their mechanical properties. The Johnson-Cook equation was widely used to model the strain rate sensitivity of metals. However, it implies that the yield and flow stresses are linearly increasing in terms of the logarithm of strain rate. This is only true up to a threshold strain rate. In this work, a three-constant constitutive equation, assuming an apparent activation volume which decreases as the strain rate increases, is applied here for some metals. It is shown that this equation fits well the experimental yield and flow stresses for a very wide range of strain rates, including quasi-static, high, and very high strain rates (from 10−5to 5 × 104 s−1). This is the first time that a constitutive equation is showed to be able to fit the yield stress over a so large strain rate range while using only three material constants.

The Background to Superplastic Forming and Opportunities Arising from New Developments

2020 ◽  
Vol 306 ◽  
pp. 1-8
Author(s):  
Terence G. Langdon
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
High Strain ◽  
Rate Sensitivity ◽  
Superplastic Forming ◽  
Industrial Applications ◽  
Superplastic Flow ◽  
Dislocation Glide ◽  
Wide Range ◽  
Historical Developments

The occurrence of superplastic flow in metals has a long history but it is only over the last three or four decades that it was recognized that this process provides an opportunity for fabricating complex parts, especially curved panels, that may be used in a wide range of industrial applications. In practice, this use is dependent upon the high strain rate sensitivity of ~0.5 which is an inherent feature of true superplastic flow but in practice excellent forming may be achieved also through the use of metals deforming within the range of dislocation glide where the strain rate sensitivity is close to 0.3. New possibilities have arisen over the last two decades with the demonstrations that exceptionally refined microstructures, usually within the submicrometer or even the nanometer range, may be prepared from a wide range of commercial alloys through the application of severe plastic deformation in which the material is subjected to a very high strain without any significant changes in the overall dimensions of the sample. This presentation examines these historical developments and describes the new processing procedures that provide new opportunities within the field of superplastic forming.

scholarly journals Tensile Behavior of Polyetheretherketone over a Wide Range of Strain Rates

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Zakaria El-Qoubaa ◽  
Ramzi Othman
Keyword(s):  
Constitutive Equation ◽  
Strain Rate ◽  
Volume Change ◽  
Axial Strain ◽  
Rate Sensitivity ◽  
Tensile Behavior ◽  
Image Correlation ◽  
Strain Rates ◽  
Wide Range ◽  
The Impact

Polyetheretherketone (PEEK) is used in several engineering applications where it has to bear impact loads. Nevertheless, the tensile behavior has only been studied in the quasi-static range of loading rates. To address the lack of data in the impact strain rate range, the tensile mechanical behavior of PEEK is investigated at room temperature over a large range of strain rates (from 0.001 to 1000/s). The macroscopic volume change is studied under uniaxial tension using digital image correlation (DIC) method, showing a significant dilatation that reaches 16% at a logarithmic axial strain of 40%. The true stress-strain behavior is therefore established based on the measured volume change. Elsewhere, the yield stress shows a significant sensitivity to strain rate. Besides, a new constitutive equation is proposed to take into account the increase in strain rate sensitivity at high strain rates. It assumes an apparent activation volume which decreases as the strain rate increases. The new constitutive equation gives similar results when compared to the Ree-Eyring equation. However, only three material constants are to be identified and are physically interpreted.

Enhanced tensile ductility in an electrodeposited nanocrystalline copper

2008 ◽  
Vol 23 (8) ◽  
pp. 2238-2244 ◽  
Author(s):  
Guoyong Wang ◽  
Zhonghao Jiang ◽  
Hanzhuo Zhang ◽  
Jianshe Lian
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Activation Volume ◽  
Large Strain ◽  
Rate Sensitivity ◽  
Uniaxial Tensile ◽  
Strain Rates ◽  
Strain Rate Change ◽  
Perfect Plasticity

A fully dense nanocrystalline (nc) Cu with mean grain size of 72 nm and a broad grain size distribution was synthesized by electrodeposition. Uniaxial tensile tests were done at different strain rates and room temperature. A very high strength of 1.04 G was obtained at strain rate of 0.1 s−1. The nearly perfect plasticity with a large strain of close to 20% was displayed at specific low strain rates of 4 × 10−5 to 10−4 s−1. With increasing strain rate, the nearly perfect plasticity disappeared. Strain rate sensitivity and activation volume of the nc Cu were estimated from the flow stress at a fixed strain of 1% and a strain rate change (jump) test. It was deduced from the high strain rate sensitivity exponent of 0.08 and small activation volume of 12b3 that both dislocation and grain boundary activities would take place in this nc Cu, which explained the nearly perfect plasticity observed in the tensile test.

scholarly journals Low Temperature Strain Rate Sensitivity of Titanium Alloys

2016 ◽  
Vol 258 ◽  
pp. 570-573 ◽  
Author(s):  
Héloise Vigié ◽  
Thalita de Paula ◽  
Martin Surand ◽  
Bernard Viguier
Keyword(s):  
Strain Rate ◽  
Titanium Alloys ◽  
Strain Rate Sensitivity ◽  
Constant Strain Rate ◽  
Rate Sensitivity ◽  
Tensile Tests ◽  
Industrial Applications ◽  
Sustained Load ◽  
Dwell Fatigue ◽  
Wide Range

Titanium alloys are widely used in many industrial applications such as in aeronautics due to their combination of good mechanical properties, excellent corrosion resistance and low density. The mechanical behaviour of titanium alloys is known to exhibit a peculiar dependence on both deformation temperature and strain rate. Titanium alloys show significant room temperature creep and they are very sensitive to dwell fatigue and sustained load cracking. This behaviour is related to the viscosity of plastic deformation in titanium alloys, which can be represented by a strain rate sensitivity (SRS) parameter. The present study aims to compare the tensile behavior of two different titanium alloys, Ti-6Al-4V and β21S, which exhibit dissimilar microstructures. Results of tensile tests, performed under constant strain rate and including strain rate changes, are reported in terms of flow stress, ductility and SRS over a wide range of temperatures.

DYNAMIC TENSILE PROPERTIES OF IRON AND STEELS FOR A WIDE RANGE OF STRAIN RATES AND STRAIN

2008 ◽  
Vol 22 (09n11) ◽  
pp. 1255-1262 ◽  
Author(s):  
NOBUSATO KOJIMA ◽  
HIROYUKI HAYASHI ◽  
TERUMI YAMAMOTO ◽  
KOJI MIMURA ◽  
SHINJI TANIMURA
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Large Strain ◽  
Strain Rate Range ◽  
Block Type ◽  
Strain Rates ◽  
Viscous Term ◽  
Rate Range ◽  
Wide Range ◽  
True Fracture

The tensile stress-strain curves of iron and a variety of steels, covering a wide range of strength level, over a wide strain rate range on the order of 10−3 ~ 103 s −1, were obtained systematically by using the Sensing Block Type High Speed Material Testing System (SBTS, Saginomiya). Through intensive analysis of these results, the strain rate sensitivity of the flow stress for the large strain region, including the viscous term at high strain rates, the true fracture strength and the true fracture strain were cleared for the material group of the ferrous metals. These systematical data may be useful to develop a practical constitutive model for computer codes, including a fracture criterion for simulations of the dynamic behavior in crash worthiness studies and of work-pieces subjected to dynamic plastic working for a wide strain rate range.

Local Investigations of the Mechanical Properties of Ultrafine Grained Metals by Nanoindentations

2006 ◽  
Vol 503-504 ◽  
pp. 31-36 ◽  
Author(s):  
Johannes Mueller ◽  
Karsten Durst ◽  
Dorothea Amberger ◽  
Matthias Göken
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Room Temperature ◽  
Rate Sensitivity ◽  
Strain Rates ◽  
Fcc Metals ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Indentation Strain

The mechanical properties of ultrafine-grained metals processed by equal channel angular pressing is investigated by nanoindentations in comparison with measurements on nanocrystalline nickel with a grain size between 20 and 400 nm produced by pulsed electrodeposition. Besides hardness and Young’s modulus measurements, the nanoindentation method allows also controlled experiments on the strain rate sensitivity, which are discussed in detail in this paper. Nanoindentation measurements can be performed at indentation strain rates between 10-3 s-1 and 0.1 s-1. Nanocrystalline and ultrafine-grained fcc metals as Al and Ni show a significant strain rate sensitivity at room temperature in comparison with conventional grain sized materials. In ultrafine-grained bcc Fe the strain rate sensitivity does not change significantly after severe plastic deformation. Inelastic effects are found during repeated unloading-loading experiments in nanoindentations.

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