In this work, the Gurson–Tvergaard–Needleman model, commonly used for metallic materials, is applied to the failure of a polymeric material – specifically a polyethylene carbon monoxide copolymer, which is an enhanced photodegradable material. Gurson–Tvergaard–Needleman model parameters for this material are obtained using the Nelder–Mead simplex method when correlating experimental and numerical results of both tensile and fracture specimens. Results show that the Gurson–Tvergaard–Needleman model can also be used for polymeric materials with selection of proper parameters that are quite different from the ones proposed for metallic materials.