Abstract
Off-axis angle dependence in fracture energy of a strip-biaxially stretched poly (ethylene terephthalate) film with single edge-crack has been studied by the essential work of fracture (EWF) method. In order to part the total fracture energy into initial local deformation energy at the ligament zone and following net fracture energy, we unloaded to zero force after yielding and reloaded to fracture. The load-unload-reload process enabled to consider the reduction of thickness at the ligament zone by the initial local deformation. From the viewpoint that the EWF method is the conventional method to divide a total energy density into areal one and volumetric one, we applied the method to the local deformation energy as well as to the fracture one and got informative results. The stretched film has clear anisotropy. We analyzed the anisotropy curves of modulus and yield stress and also checked the crack opening displacement about the cut-off samples at various off-axis angles from stretching direction to transverse one, and concluded that the evaluated values by the EWF method can be compared each other. Then the off-axis angle dependence of the evaluated value was considered. As a result, the total fracture energy showed the anisotropy as the maximum value 235.1±50.1kJ/m2 at stretched direction and the minimum one 30.3±5.3 kJ/m2 at transverse direction. The total non-essential work also showed the maximum value 38.1±8.3MJ/m3 and the minimum one 2.1±1.9MJ/m3.
