Effect of strain rate and temperature

This result suggests that, except at very low strain rates and high temperatures where the molecular chains have complete mobility, the fracture process is dominated by viscoelastic effects. Bueche [146] has treated this problem theoretically and obtained the observed form of the dependence of tensile strength on strain rate and temperature. Later theories have attempted to obtain the time dependence for both tensile strength and ultimate strain, or the time to break at a constant strain rate [147,148]. 

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The effects of strain rate and temperature are correlated, and can be modeled (Kinloch and Young, 1983, Kinloch, 1985). For different temperatures and strain rates, GIc and the time to failure, tf, were measured. Using the time-temperature superposition principle, shift factors (aT) applicable to the time to failure tf, were determine. Shift factors plotted against (T — Tg) are independent of the type of test used (Fig. 12.14). The construction of a typical master curve GIc versus tf/aT is shown in Fig. 12.15 (Hunston et al., 1984). The value of GIc may be predicted for any strain rate/temperature combination. This model can also be applied to rubber-modified epoxies (See chapter 13). 

George J, Thomas S, Bhagawan SS (1999) Effects of strain rate and temperature on tensile failure of pineapple fiber reinforced polyethylene composites. J Thermoplast Compos Mater 12 443 64... 

Not unlike the case of superplastic ceramics, ductility and strength relations are influenced by strain rate. The conditions of the experiment must be above the DBT to observe plastic flow, which is different for various ceramics. An illustration of the effect of strain rate and temperature on the strain (ductility) at some stress level can be seen in monolithic Si-C-N. Silicon-nitride-based ceramics are quite promising candidates for mechanical applications at elevated temperatures. Specimens were prepared by hot isostatic pressure (henceforth HIP) of pyrolyzed powder compact at 1500 °C and 950 MPa, without any sintering additives. These compression tests were conducted at temperatures from 1400 to 1700 °C in a nitrogen atmosphere with a servo-hydraulic-type testing machine at constant crosshead speed in an induction heating furnace. In Fig. 2.5, stress-strain curves... 

Microplasticity Effects under Cyclic Loading at Low Temperatures. Microplasticity effects under monotonic loading have been reported in the literature for single-and polycrystaUine Mo and Ta [1.171,174] information regarding effects of strain rate and temperature on the cyclic stress-strain response is given in [1.140,170]. Most experiments on cyclic stress-strain behavior have... 

We have already seen that the effect of pressure is to raise the temperature of various visco-elastic transitions in the polymer. It is also clear that in many cases the polymer at the sliding interface is subjected to enormous shear strains so that, in effect, the frictional process involves the shear strength of the polymer rather than some "smal1-strain" viscoelastic property. We may, therefore, ask how far the shear strength of a polymer is determined by contact pressure and other variables. Bahadur has discussed some of the data which he has obtained on the effect of strain-rate and temperature. Here we describe the effect of pressure. Thin films of polymer were deposited on a smooth glass surface and a hemi-spherical... 

Plumbridge, W.J. Gagg, C.R. Effect of strain rate and temperature on the stress-strain response of solder alloys. J. Mater. Sci. Mater. Electron. July 1999,10 (5/6), 461-468. 

Hence, a complete model for viscosity of a reacting polymer must contain the effects of strain rate, 7, temperature, T, and degree of cure, c, such as... 

J. Fembock, R. Stickler, A. Vinckier The effect of strain rate and heating rate on the tensile behavior of W and W—Th02 between room temperature and 1400 °C, Proc. 11th Plansee Seminar, Vol.1 (Plansee... 

In a series of articles by Salem [20-22], based on the results of the study of the effect of strain rate and draw temperature on the crystallization of PET, it was shown that the crystallization curves at different strain rates and temperatures could be superimposed by using a shift factor. This strain rate/draw-time superposition can be used to predict the degree of crystallinity at any strain rate and temperature. 

Increasing strain rate and increasing complexity of the stress system have the effect of decreasing ductility. Two tests of mechanical properties, the tensile and the impact test, are used to measure the effect of strain rate and stress complexity on ductility. The tensile test involves unidirectional stresses applied at comparatively slow rates. The impact test applies stresses in several directions at rapid rates. At a given temperature, a material may exhibit considerable ductility in the tensile test but not in the impact test. 

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)... 

The effect of strain rate, sy at - 50 °C and 50 °C is shown in Fig. 16. Qualitatively, increasing the strain rate is analogous to decreasing temperature (the temperature and strain rate dependencies of the stress-strain curve shapes are summarised in Fig. 17). However, it is worth noting that an equivalence temperature-strain rate does not apply over the whole stress-strain curve. 

To take into consideration these non-Newtonian effects, it is common to use a viscosity which is a function of the strain rate and temperature to calculate the stress tensor in eqn. (2.42)... 

Analysis of these effects is difficult and time consuming. Much recent work has utilized two-dimensional, finite-difference computer codes which require as input extensive material properties, e.g., yield and failure criteria, and constitutive laws. These codes solve the equations of motion for boundary conditions corresponding to given impact geometry and velocities. They have been widely and successfully used to predict the response of metals to high rate impact (2), but extension of this technique to polymeric materials has not been totally successful, partly because of the necessity to incorporate rate effects into the material properties. In this work we examined the strain rate and temperature sensitivity of the yield and fracture behavior of a series of rubber-modified acrylic materials. These materials have commercial and military importance for impact protection since as much as a twofold improvement in high rate impact resistance can be achieved with the proper rubber content. The objective of the study was to develop rate-sensitive yield and failure criteria in a form which could be incorporated into the computer codes. Other material properties (such as the influence of a hydrostatic pressure component on yield and failure and the relaxation spectra necessary to define viscoelastic wave propagation) are necssary before the material description is complete, but these areas will be left for later papers. 

It is certain that the relaxation behavior of filled rubbers at large strains involves numerous complications beyond the phenomena of linear viscoelasticity in unfilled amorphous polymers. Breakdown of filler structure, strain amplification, failure of the polymer-filler bond, scission of highly extended network chains and changes in network chain configuration probably all play important roles in certain ranges of time, strain rate, and temperature. A clear understanding of the interplay of these effects is not yet at hand. 

The strain rates and temperatures prevailing in abrasion are very different from those used in routine laboratory testing of tensile or tear strength. Because of friction, local temperatures may far exceed those of the test track or of the bulk of the rubber (229-230). Even at small sliding velocities the effective strain rate is very large, as small volume elements of rubber are deformed repeatedly to high strains by the many surface... 

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