Stress-strain temperature effects

The first two terms on the right-hand side of equation [12.6] are viscoelastic terms proposed by Schapery, where e represents uniaxial kinematic (or total) strain at time t, o is the Cauchy stress at time t, is the instantaneous compliance and AD(r[i ) is a transient creep compliance function. The factor g defines stress and temperature effects on the instantaneous elastic compliance and is a measure of state dependent reduction (or increase) in stiffness. Transient compliance factor gi has a similar meaning, operating on the creep compliance component. The factor gj accounts for the influence of loading rate on creep. The function i ) represents a reduced timescale parameter defined by ... 

Thus, finally, the stress-strain-temperature history of an element of material can be simulated as it is strained, from a specified initial temperature, at a constant rate. The strain rate chosen should not unduly influence the result, but should be representatively high . At each instant (he material properties are corrected, using the Eyring-Haward-Thackray extrapolation, to account for the effect of increasing temperature. 

Heat. Personal monitoring of the environmental conditions which impose a heat stress on a worker is impractical, so fixed station measurement of such parameters as wet bulb globe temperature are usually made (see Temperature measurements). These stations are carefully selected so that the results, plus worker location and workload data, can be combined to yield an overall heat stress estimate. Heat strain, the effect on the human, can be estimated from core body temperature, but this is usually only a research tool. 

Fig. 3. Effect of temperature and strain rate on stress—strain diagram of Ti—5% Al—2.5% Sn where A—E correspond to the strain rates 1.6x10, ...

The effect of temperature on PSF tensile stress—strain behavior is depicted in Figure 4. The resin continues to exhibit useful mechanical properties at temperatures up to 160°C under prolonged or repeated thermal exposure. PES and PPSF extend this temperature limit to about 180°C. The dependence of flexural moduli on temperature for polysulfones is shown in Figure 5 with comparison to other engineering thermoplastics. 

Figure 10.5. Effect of polymer density, testing rate and temperature on the shape of the stress-strain...

Figure 10.6. Effect of temperature on the tensile stress-strain curve for polyethylene. (Low-density polymer -0.92g/cm . MFI = 2.) Rate of extension 190% per minute ...

Fig. 1.3 Effect of material temperature on stress-strain behaviour of plastics...

As a starting point it is useful to plot the relationship between shear stress and shear rate as shown in Fig. 5.1 since this is similar to the stress-strain characteristics for a solid. However, in practice it is often more convenient to rearrange the variables and plot viscosity against strain rate as shown in Fig. 5.2. Logarithmic scales are common so that several decades of stress and viscosity can be included. Fig. 5.2 also illustrates the effect of temperature on the viscosity of polymer melts. 

This effect was estimated from the experimental comparison of the stress-strain properties in three sample series which were brought to different phase contents by means of heat treatment. All samples were hydrogen-alloyed to a = 0.35 at T = 1053 K, then furnace cooled. Before straining, samples of the first series were maintained at the test temperature for 0.5 h. Series 2 samples were heated to the j9-phase, T = 1163 K, for 15 min, then cooled to the test temperature and treated like series 1 samples. The phase content in the third series was equilibrated by heating to 1163 K and slow cooling to 903 K before the test temperature was fixed. 

Chul Kim, U. R. and van Rooyen, D., Strain rate and temperature effects on the stress corrosion cracking of Inconel 600 steam generator tubing in the (PWR) primary water conditions , Proc. 2nd Int. Conf. on Environmental Degradation of Materials in Nuclear Power Systems-VIalet Reactors, Monterey, USA, 9-12 Sept. 1985, American Nuclear Society, pp. 448-55 (1986)... 

Avoiding structural failure can depend in part on the ability to predict performance of materials. When required designers have developed sophisticated computer methods for calculating stresses in complex structures using different materials. These computational methods have replaced the oversimplified models of materials behavior relied upon previously. The result is early comprehensive analysis of the effects of temperature, loading rate, environment, and material defects on structural reliability. This information is supported by stress-strain behavior data collected in actual materials evaluations. 

Consequently, changing the temperature or the strain rate of a TP may have a considerable effect on its observed stress-strain behavior. At lower temperatures or higher strain rates, the stress-strain curve of a TP may exhibit a steeper initial slope and a higher yield stress. In the extreme, the stress-strain curve may show the minor deviation from initial linearity and the lower failure strain characteristic of a brittle material. 

Test rate and property The test rate or cross-head rate is the speed at which the movable cross-member of a testing machine moves in relation to the fixed cross-member. The speed of such tests is typically reported in cm/min. (in./min.). An increase in strain rate typically results in an increase yield point and ultimate strength. Figure 2-14 provides examples of the different test rates and temperatures on basic tensile stress-strain behaviors of plastics where (a) is at different testing rates per ASTM D 638 for a polycarbonate, (b) is the effects of tensile test-... 

It should be recognized that tensile properties would most likely vary with a change of speed of the pulling jaws and with variation in the atmospheric conditions. Figure 2-14 shows the variation in a stress-strain curve when the speed of testing is altered also shown are the effects of temperature changes on the stress-strain curves. When the speed of pulling force is increased, the material reacts like brittle material when the temperature is increased, the material reacts like ductile material. 

Effect of Temperature on the Stress-Strain Behavior of X-8 at 0.1 ihch/inch/min. .. P 424... 

Fig 6 Effect of temperature on the stress-strain behavior of OGK at 0.1 inch/inch/min... 

In TPE, the hard domains can act both as filler and intermolecular tie points thus, the toughness results from the inhibition of catastrophic failure from slow crack growth. Hard domains are effective fillers above a volume fraction of 0.2 and a size <100 nm [200]. The fracture energy of TPE is characteristic of the materials and independent of the test methods as observed for rubbers. It is, however, not a single-valued property and depends on the rate of tearing and test temperature [201]. The stress-strain properties of most TPEs have been described by the empirical Mooney-Rivlin equation... 

Figure 12 shows the stress-strain curves of IER at various temperatures. A strain-induced reinforcing effect is not observed at temperatures above -10 °C. This fact may be due to network inhomogeneities caused by imperfect crosslinking. 

Temperature. The effect of temperature on the stress-strain isotherms is of particular importance with regard to the... 

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