Crack growth behavior of a biomedical polymer-ceramic interpenetrating scaffolds composite in the subcritical regimen

•Quasi-static, static and cyclic test were performed for a polymer-infiltrated ceramic material.•A bi-modal defect size distribution dominated the fracture behavior at higher size-scales.•We demonstrated the absence of a degrading frictional term necessary for an R-curve effect. We subjected a commercial dental composite formed by interconnecting polymer-ceramic scaffolds to extensive quasi-static, static and cyclic experiments under biaxial flexure. By this we meant to obtain static and cyclic subcritical crack growth exponents that, based on established relationships describing the degradation of frictional bridging mechanisms, challenging the notion of a suggested R-curve behavior. By exploring the fracture statistics of specimens with increasing effective volumes and effective areas, we demonstrated the presence of a bi-modal defect size distribution in disaccord with the Weibull behavior across length scales. Lifetime distributions seemed to follow the strength distributions, and were used to derive crack growth velocity diagrams for combined levels of applied stress. Ultimately, the claim of an R-curve behavior could not be supported based on the absence of any significant cyclic fatigue effect, i.e. bridging degradation.