First-principle stress criterion

The first-principle stress (FPS) criterion simply assumes that only the first-principle stress 0/ is taken into account. The FPS criterion [3, 4] reads ... 

As one can see, both PC and HDPE in the first from the indicated regions have the values calculated according to the Eq. (10.28) larger than 2.7, that is, they are subjected to ductile fracture according to the criterion (10.29). For PC this threshold d value is reached at the expense of small values Pj (or that is the consequence of devitrificated amorphous phase availability for the latter attesting temperature T= 293 K. For PVC the value V in principle allows ductile fracture, proceeding from the Eq. (4.51), but (or small values result to the fact, that samples are broken down either by brittle mode or immediately beyond yield stress. For PMMA the small values (or are typical and, as consequence, small values d, indicating quasibrittle fracture, that is, 2.0 < <7 < 2.5 [6]. 

When a complex joint is to be introduced in a structure, the ideal situation is to test that specific joint. However, this approach is very expensive. Before real joints or prototypes are built, the designer should first come up with a good prediction of the failure load based, among other things, on the basic mechanical properties of the adhesive. The basic properties can mean the elastic properties, such as the Young s modulus and the Poisson s ratio in case the analysis is linear elastic. However, for the more realistic theoretical methods that take into account the nonlinear behavior of the adhesive, the yield stress, the ultimate stress, and the failure strain are necessary. The stress-strain curve of adhesives is necessary for designing adhesive joints in order to compute the stress distribution and apply a suitable failure criterion based on continuum mechanics principles. 

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