3D study of the competitions between shear yielding and crazing for a variable thickness on ductile polymers

The influence of the thickness in mode I fracture tests is investigated with extensive 3D finite elements calculations. A realistic constitutive law for the bulk is used. Failure by crazing is described with a cohesive model. A transition from ductile tearing to fracture by crazing is observed with increasing thickness. Ductile tearing takes place for thin samples even if possible crazing is allowed. Crazing takes place for thick samples with a noticeable difference in the load level for craze initiation to that for crack propagation. The consequence on the appropriate geometry for the estimation of the minimum toughness is discussed.