Stresses, fracture under multiaxial

Although relatively few studies have been made of the fracture of elastomers under complex stress conditions, some general conclusions can be drawn regarding fracture under specific combined-stress states, as follows. 

Failure in simple shear is still more complex. An approximate treatment for an interfadal crack, starting at one edge, yields a relation analogous to 

Here the constant k is 0.4 initially and then varies between 0.2 and 1.0 as the crack length increases [31]. 

FIGURE 7 Expansion of a cavity under a triaxial tension. 

The critical stress predicted by Eq. (14) depends only on the elastic modulus and not at all on the strength of the elastomer. In agreement with this, cavitation stresses in bonded rubber blocks under tension (Figs. 8 and 9) [35], and near rigid inclusions, at points where a triaxial tension is set up (Figs. 

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A polymer is more likely to fail by brittle fracture under uniaxial tension than under uniaxial compression. Lesser and Kody [164] showed that the yielding of epoxy-amine networks subjected to multiaxial stress states can be described with the modified van Mises criterion. It was found to be possible to measure a compressive yield stress (Gcy) for all of their networks, while the networks with the smallest Mc values failed by brittle fracture and did not provide measured values for the tensile yield stress (Gty) [23,164-166]. Crawford and Lesser [165] showed that Gcy and Gty at a given temperature and strain rate were related by Equation 11.43. 

These statistical approaches can not be applied directly to the experimental results in this study, because the fracture was occurred under biaxial stress in Disk-on-Rod tests and Piston-on-Ring tests. The statistical approaches for multiaxial stress state have been studied by several investigators. In order to determine the suitable equivalent stress more precisely, further investigation is needed for the widely variable stress states. However, it is considered that uniaxial statistical approach by eqs. (2) (5) are available for the comparison of the critical stress for maincrack formation under... 

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