An experimental and numerical study to evaluate the crack path under mixed mode loading on pvc foams

Being able to provide outstanding performances under out-of-plane loading, sandwich structures offer great flexibility for the design of lightweight structural systems. However, they can be affected by macroscopic and microscopic damages, which may trigger catastrophic failure modes. As a consequence, a detailed understanding of the propagation of macro-cracks in the core as well as of delamination phenomena at face-to-core interfaces are aspects of great computational interest. Moreover, linking sophisticated numerical models with the measurement of the mechanical properties of materials is fundamental in view of actual engineering applications. The elastic and fracture characterization of the core is particularly relevant because its cracking strongly reduces the capacity of the sandwich structures to carry out loads. To this end, PVC foams typically used as inner core in structural application are investigated over a range of foam densities. Firstly, the elastic properties of foams under compressive uni-axial loading are measured using the full-field methodology. Subsequently, Asymmetric Semi-Circular Bend (ASCB) specimens are tested varying the position of supports to generate all range of mixed fracture modes. Finally, some of the mostly recognized fracture criterions have been considered, and their capability to compute the crack propagation angles in PVC foams have been evaluated. The parameters experimentally determined have been used to test the accuracy of the response provided by a numerical model developed by the authors.