This paper represents the authors’ contribution to Part B of the Second World-Wide Failure Exercise. The paper provides a comparison between the ‘blind’ theoretical predictions, based on Puck’s failure theory, and experimental data for 12 test cases, covering failure of isotropic material, unidirectional laminae and multi-directional laminates under three-dimensional states of stress. The theoretical and experimental results were, in general, in good agreement and no new calibration has been made to the predictions presented in Part A of WWFE-II. Some of the tubular specimens were re-analysed using finite element analysis and that shows that their shape had some effects on the correlation observed between the theory and the experiments. The paper has confirmed the applicability and the capability of the Puck failure criteria to deal with three-dimensional load cases. The paper highlighted the need to further develop physically-based extension of the theory to cater for some of the challenges associated with (a) modelling of large deformation and progressive damage under three-dimensional stresses and (b) closing the open envelopes under certain biaxial and triaxial stresses.

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The objectives of this article are to apply Puck’s failure criteria to predict the failure of 12 test problems, proposed in Part A of the second World-Wide Failure Exercise. These problems include a polymer material, various unidirectional laminae and three multi-directional laminates under a variety of 3D stress loadings. The implementation was carried out through a commercial finite element code where material nonlinearities, due to material behaviour under shear and transverse and through-thickness loadings and due to post failure damage, were taken into account. This is the first time where the critertion has been stretched to its limits. Some of the challenges found include the need to determine the fracture angle of action plane under 3D stresses and the treatment of the strengthening effects on the nonlinear stress strain curves when a lamina is subjected to combined compressive stresses in both the transverse and through-thickness directions. The successful methodology developed here will be used to analyse the effects of boundary conditions in Part B of the second World-Wide Failure Exercise to improve correlation with experimental results for the test problems.

To evaluate mechanical properties by means of nanoindentation, information on the contact area is crucial. However, the contact area is not directly accessible in experiments and is usually calculated according to the Oliver and Pharr procedure, which turned out to be unsatisfying when applied to viscoelastic materials like polymers. In this study, complementary in situ indentation testing and finite element analysis (FEA) were performed on silicone elastomers. Through this combination of techniques, several individual error sources in the conventional contact area determination have been identified and quantified. For shallow penetrations, contact areas after Oliver and Pharr were up to 40% smaller than the in situ testing results; for larger penetrations, the contact size was overestimated by approximately 6%. The deviations of the resulting mechanical properties were approximately 10%. Viscoelastic effects could be captured if dynamic indentation testing was performed.

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