Validation of a small punch testing technique to characterize the mechanical behaviour of ultra-high-molecular-weight polyethylene.

The small punch or miniaturized disc bend test has been used successfully to characterize the ductility and fracture resistance of metals and ceramics with specimens measuring 0.5 mm in thickness. This study was performed to demonstrate the feasibility of performing small punch tests on implant grade ultra-high-molecular-weight polyethylene (UHMWPE). Large-deformation finite element simulations were developed and validated to explore the hypothesis that the macroscopic constitutive behaviour of UHMWPE may be inferred from a miniature specimen testing technique which can be used to characterize the ductility and work to failure for UHMWPE. The load-displacement curve was insensitive to cyclic preconditioning of the test specimen and only mildly sensitive to the loading rate. Furthermore, the initial slope of the small punch load-displacement curve was used to determine the elastic modulus of the UHMWPE with the help of the inverse finite element method. The ultimate goal of this research is to develop the capability to perform local measurements of material tensile and static fracture properties in as-manufactured, as-sterilized and as-retrieved UHMWPE components.