Stress-strain-time

The theory relating stress, strain, time and temperature of viscoelastic materials is complex. For many practical purposes it is often better to use an ad hoc system known as the pseudo-elastic design approach. This approach uses classical elastic analysis but employs time- and temperature-dependent data obtained from creep curves and their derivatives. In outline the procedure consists of the following steps ... 

Stress-strain-time data are usually presented as creep curves of strain versus log time. Sets of such curves, seen in Fig. 2-27, can be produced by smoothing and interpolating data on a computer. These data may also be presented in other ways, to facilitate the selection of information to meet specific design requirements. Sections may be taken t... 

Fig. 2-37 Tensile stress-strain-time correlation resulting from creep for PC.

These equations should fully describe the stress-strain-time relationship for the materials over the full range of response. However, the range over which such linear behaviour is observed is invariably limited. Usually large stresses and strains or short times cause deviations from Equations 1.4 or 1.5. 

Infrared spectroscopy has been used to study molecular deformation processes in polymers as a function of stress, strain, time and temperature. Wool has summarized... 

In this general approach to viscoelasticity, appropriate models are constructed for the interpretation of the stress-strain-time behavior of a polymer. Then, values of Young s modulus G of the elastic elements and the viscosities i] of the viscous elements are used to characterize and predict the general behavior of the material. 

Figure 1.2 Highlighting load-time/viscoelasticity of plastics (1) stress-strain-time in creep and (2) strain-stress-time in stress relaxation.

Stress-Strain-Time Diagrams, Including Failure Envelopes, for High-Density Polyethylenes of Different Molecular Weight... 

The properties of high performance building sealants have been studied as a function of four variables stress, strain, time and temperature, using tensile tests. By time-temperature superposition the number of variables can be reduced to three and the material properties characterized in a three-dimensional coordinate system. For sealants the projection of the failure points to this system in the log strain versus log time plane is sufficient for characterization. Further simplification can be made depending on the properties of the various types of sealant. 

Stiffness properties of RPs are used (as with other materials) for the usual purpose of estimating stresses and strains in a structural design, and to predict buckling capacity under compressive loads. Also, stiffhess properties of individual plies of a layered flat plate approach may be used for the calculation of overall stiffiiess and strength properties. The relationship between stress and strain of unreinforced or RPs varies firom viscous to elastic. Most RPs, particularly RTSs are intermediate between viscous and elastic. The type of plastic, stress, strain, time, temperature, and environment all influence the degree of their viscoelasticity. 

Hirst, T.J. 1968. The influence of compositionalfactorson the stress-strain-time behavior of soils. PhD Thesis, University of California, Berkeley, CA. 

Singh, A., and Mitchell, J.K. 1968. A general stress-strain-time function for soil. Journal of Soil Mechanics and Foundations Division, 94(1) 21-46. 

Suspensions and emulsions are non-Newtonian Iluids. From a practical point of view, having to deal with non-Newtonian fluids means that viscosity is not enough to describe their response to deformation. This property no longer depends on temperature alone but on many other factors such as shear rate, shear stress, strain, time, and measuring geometry. Under shear conditions, the flow response is now called apparent viscosity and it is defined as... 

Hobbs, D. W. (1970). Stress-Strain-Time Behaviour of a Number of Coal Measure Rocks. International Journal of Rock Mechanics and Mining Sciences, 7, 149. doi 10.1016/0148-9062(70)90009-4... 

Figure 3.35 3-D thermomechanical cycle in terms of stress strain time for different stress relaxation times with pre-strain levels of 10% and 30%. Source [51] Reproduced with permission from Elsevier...

The extremely nonlinear behaviors for the entire thermomechanical cycle, including a three-step glassy temperature programming process and one-step heating recovery in both the stress-strain-time view and stress-strain-temperature view, are shown in Figure 3.38 (a) and (b). 

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