The damage and failure mechanisms in polyethylene are investigated using a circumferentially notched tensile specimen subject to constant rate displacement conditions. The fracture process can be quantified, independent of the bulk deformation, using a local traction-separation relation. The study found that the mechanisms of deformation under quasi-static test speeds depend on the degree of crack tip constraint in addition to rate. This dependency can lead to contrasting deformation-failure behavior between different grades of polyethylene and hence the overall energy dissipation process. Based on this approach, both gross and subtle differences in the fracture behavior between the grades were readily detected and differentiated. In general, the damage mechanisms changed from a brittle mode under conditions of high constraint to a ductile mode as the level of constraint is reduced.