Experimental and theoretical investigation of mixed-mode I/II and I/III fracture behavior of PUR foams using a novel strain-based criterion

•Investigating the mixed-mode fracture behavior of Polyurethane foam.•Using the recently developed edge notch disc bend specimen for Polyurethane foam.•Comparing the test data to various fracture criteria predictions.•A newly developed criterion gives better estimations than more commonly known ones. Brittle fracture in Polyurethane (PUR) foam is experimentally and theoretically investigated under mixed-mode I/II and I/III loading conditions. Original test data are generated to examine different criteria in prediction of the mixed-mode fracture behavior of PUR foam. To this end, edge notched disc bend (ENDB) specimen which has been proven to be a suitable test configuration for such loading conditions is used, and subsequently, fracture angles and fracture toughness values are obtained experimentally. Three different fracture criteria, including minimum strain energy density (SED), maximum principal stress (MPS), and the recently introduced strain-based criterion called ECD-SN – which is established based on considering an effective critical distance – are considered to theoretically estimate the fracture behavior of PUR foam. A comparison between the experimental and theoretical results revealed that the ECD-SN criterion gives a better prediction both for the fracture angles and the mixed-mode fracture toughness of PUR foam. The results indicated that considering effective critical distance instead of the traditional approach, which assumes the critical distance is constant as a material property and independent of the loading mode, can considerably increase the accuracy of the theoretical estimation.