Elastic and pseudoviscous properties of coal under quasi-static and impact loadings

1984 ◽  
Vol 21 (2) ◽  
pp. 203-212 ◽  
Author(s):  
J. R. Klepaczko ◽  
T. R. Hsu ◽  
M. N. Bassim
Keyword(s):  
Strain Rate ◽  
Elastic Properties ◽  
Viscoelastic Properties ◽  
Viscoelastic Model ◽  
Rate Sensitivity ◽  
Bedding Plane ◽  
Strain Rates ◽  
Compression Tests ◽  
Wide Range ◽  
Coefficient Of Viscosity

An investigation of the elastic and viscoelastic properties of Nova Scotia coal was carried out over a wide range of strain rates (quasi-static to impact). High resolution stress–strain diagrams for the coal were obtained from compression tests for the lower and medium strain rates up to [Formula: see text] and with the split Hopkinson bar technique for the high strain rate region up to [Formula: see text].The elastic properties of the coal showed a moderate rate sensitivity at low and moderate strain rates.Above the strain rate [Formula: see text] both Young's modulus and the stress level of microcracking initiation σf0isplayed extreme rate sensitivity and was found to be a linear function of strain rate. The associated coefficient of viscosity perpendicular to the bedding plane was η* = 3.08 × 104 Pa∙s.The viscoelastic model so determined can be used to assess the elastic properties of coal at even higher strain rates, a situation that is similar to an explosive loading. Keywords: coal, strain rates, dynamic, viscoelastic properties.

Strain-Rate Effect on the Tensile Behaviour of High Strength Alloys

2011 ◽  
Vol 82 ◽  
pp. 124-129 ◽  
Author(s):  
Ezio Cadoni ◽  
Matteo Dotta ◽  
Daniele Forni ◽  
Stefano Bianchi
Keyword(s):  
Strain Rate ◽  
Rate Sensitivity ◽  
High Strength ◽  
Constitutive Law ◽  
Tensile Behaviour ◽  
Strain Rates ◽  
Cross Sectional ◽  
Split Hopkinson Tensile Bar ◽  
Wide Range ◽  
First Results

In this paper the first results of the mechanical characterization in tension of two high strength alloys in a wide range of strain rates are presented. Different experimental techniques were used for different strain rates: a universal machine, a Hydro-Pneumatic Machine and a JRC-Split Hopkinson Tensile Bar. The experimental research was developed in the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. An increase of the stress at a given strain increasing the strain-rate from 10-3 to 103 s-1, a moderate strain-rate sensitivity of the uniform and fracture strain, a poor reduction of the cross-sectional area at fracture with increasing the strain-rate were shown. Based on these experimental results the parameters required by the Johnson-Cook constitutive law were determined.

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.

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.

Superplastic Forming Properties of TIMETAL®54M (Ti-5%Al-4%V-0.6%Mo-0.4%Fe) Sheets

2010 ◽  
Vol 433 ◽  
pp. 311-317 ◽  
Author(s):  
Yoji Kosaka ◽  
Phani Gudipati
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Rate Sensitivity ◽  
Superplastic Forming ◽  
Total Elongation ◽  
Grain Boundary Sliding ◽  
Strain Rates ◽  
Wide Range ◽  
Boundary Sliding ◽  
Annealed Sheet

Superplastic forming (SPF) properties of TIMETAL54M (Ti-5Al-4V-0.6Mo-0.4Fe, or Ti-54M) sheet were investigated. A total elongation of Ti-54M exceeds 500% at temperatures between 750°C and 850°C at a strain rate of 10-3/S. Values of strain rate sensitivity (m-value) measured by jump strain rate tests are 0.45 ~0.6 in a temperature range of 730°C to 900°C at a strain arte of 5 x 10-4/S or 1 x 10-4/S. Flow stress of the alloy is 20 ~ 40% lower than that of Ti-6Al-4V (Ti-64) mill annealed sheet. The observation of microstructure after the tests revealed the indication of grain boundary sliding in a wide range of temperatures and strain rates.

scholarly journals Dynamic perforation and compression tests of PMMA for a wide range of temperatures - experimental and preliminary numerical analysis

2018 ◽  
Vol 183 ◽  
pp. 02055 ◽  
Author(s):  
Maciej Klosak ◽  
Alexis Rusinek ◽  
Tomasz Jankowiak ◽  
Zakaria El Qoubba ◽  
Rodrigue Matadi Boumbimba ◽  
...  
Keyword(s):  
Strain Rate ◽  
High Performance ◽  
Experimental Tests ◽  
Fe Model ◽  
Strain Rates ◽  
Stress Evolution ◽  
Compression Tests ◽  
Wide Range ◽  
Model Predictions ◽  
Key Factor

Experimental tests were carried out on poly(Methyl Methacrylate) (PMMA) in order to define its mechanical behaviour over a wide range of temperature. To reach high strain rate, perforation tests were performed within a wide range of temperatures using a high-performance oven, from room temperature to 130 °C, above the glass transition temperature Tg. In addition, the results were confronted with compression tests previously obtained. Based on experiments, the temperature transition between fragile and ductile was defined. The material became fully ductile above 118 °C inducing no cracking and debris during the perforation process. The yield stress evolution as function of strain rate for various temperatures was modelled by using the cooperative model. The model predictions were in agreement with experimental data. Two material models developed by Richeton and Nasraoui were analysed, the latter was then implemented into the FE model to simulate perforation tests for a wide range of temperatures and strain rates. It was observed that the coupling strain rate-temperature is a key factor to predict the structure behaviour not only in terms of material behaviour but also in terms of dynamic failure.

The Temperature Dependence of the Mechanical Properties of Gamma TiAl

1994 ◽  
Vol 364 ◽  
Author(s):  
B. Viguier ◽  
J. Bonneville ◽  
K. J. Hemker ◽  
J. L. Martin
Keyword(s):  
Mechanical Properties ◽  
Flow Stress ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Dislocation Motion ◽  
Compression Tests ◽  
Wide Range

AbstractMechanical properties of a polycrystalline single phased γ Ti47Al51Mn2 alloy were studied by compression tests in a wide range of temperature (100 K - 1300 K). We report, in this paper, the temperature dependence of both the flow stress and its strain rate sensitivity. These dependencies show the existence of three temperature domains corresponding to different dislocation motion mechanisms. The temperature dependence of the flow stress strain rate sensitivity is compared with values measured in single crystals1.

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.

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