Polyurethane foams crush in compression and have a brittle fracture in tension, so their failure could be evaluated based on Linear Elastic Fracture Mechanics. Fracture toughness in mixed mode loading is of particular interest because foam cracking weakens the structure's capacity for carrying loads. The mixed mode fracture of three closed cell rigid polyurethane foams with densities: 100, 145 and 300 kg/m3 are experimentally investigated. Mixed mode fracture tests are performed using a single edge cracked specimen and a mixed mode loading device. The advantages of this specimen are the simple geometry and the ability to produce full range of mixed modes, from pure mode I to pure mode II, only by changing the loading direction. Fracture criteria based on the cellular topology and tensile strength of the solid material is assessed. It is found that the density of foams is the most important parameter influencing the fracture toughness. The crack propagation angles are also determined on the fractured specimens.
Keywords: mixed mode fracture, polyurethane foams, fracture toughness, asymmetric semi-circular bend specimen