| A new mechanistic approach is applied to characterizing toughness of low-density polyethylene (LDPE) in ductile fracture, introduced in double-edge-notched tensile (DENT) test. Three mechanisms were involved in the new approach, i.e. fracture surface formation, necking and shear plastic deformation. This is different from the original essential work of fracture (EWF) method, as the latter does not consider the shear plastic deformation. The specific energy density for the fracture surface formation, determined from the new approach, was found to be about 12% higher than that from the original EWF method, and the specific energy density for necking is close to that determined from simple tensile test. The closeness of specific energy density for necking between DENT and simple tensile tests provides some support to validity of the new approach in characterizing fracture behavior of polyethylene when accompanied by large plastic deformation and necking. Ultra-high-molecular-weight polyethylene (UHMWPE) was also characterized using DENT test. However, it was found that its fracture behavior cannot be described using the original EWF method, and since necking does not occur, nor by the new mechanistic approach. As a result, a modified EWF method was developed. To justify validity of the modified EWF method, a formulation of energy balance equation was established, from which a nonlinear trend line was used to determine the fracture toughness. This study indicates that the original EWF method cannot be used to deal with the involvement of a significant amount of plastic deformation involved in the fracture process, for characterizing fracture behavior of UHMWPE. |
