Elasto-plastic region

Elasto-Plastic Region - The deformation range from formation of the first plastic hinge up to formation of the final plastic hinge (i.e. ultimate capacity). 

The dependence of mechanical behavior on constitution in Zr02-Ni system results from the variation of microstructure and its distribution. In the regions rich in Ni or PSZ, the mechanical performance is controlled by continuous matrix component and displays elasto-plastic or linear elastic characteristics, respectively. The non-linear elastic behavior at 60 vol% PSZ is related to the connectivity transition of matrix component. 

While the existing approaches (such as the model of Qi and Boyce) often provide a good description of polyurethane tensile curves, th typically treat hard and soft phase volume fractions as adjustable (fitting) parameters. In a fully predictive theory, one needs to combine the Qi-Boyce or similar framework with a thermodynamic model to predict hard and soft phase volume fractions, as we discussed in the previous section. Below, we illustrate how one can build such a theory and obtain a qualitative, if not quantitative, agreement with experiment. We start from a micromechanical model of Figure 2.7. The initial value of Vfj (volume fi action of the elastically active regions of the percolated hard phase) is determined on the basis of thermodynamic considerations and the percolation model, as described in the previous section. We assume that each elastically active region of the har d phase can be described as an elasto-plastic material ... 

It is generally easy to find the yield stress of metals because there is usually a clear transition between elastic and plastic behavior. However, for polymers, the elastic region may not be linear and it is difficult to find the value of the stress corresponding to the initial yielding. Various authors have proposed methodologies to find the yield stress. Young and Lovell (1991) state that the exact position of the yield point is very difficult to estimate and so, they define yield as the maximum point on the stress-strain curve. This procedure is valid when the adhesive behaves elasto-plastically. For strain hardening adhesives, it is convenient to take the... 

Material nonlinearity may be hyperelastic or elasto-plastic. The difference between the behavior of an elastic and elasto-plastic material is seen on unloading as in the former case the unloading path coincides with the loading path whereas in the latter case a different unloading path results in permanent deformation when the load has been removed. Elasto-plastic behavior is characterized by a linear region up to the yield point, after which soflening behavior is seen. Hyperelastic materials such as elastomers exhibit nonlinear elastic response for even large strains. 

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