The effect of specimen thickness on the mechanical behavior of UHMWPE characterized by the small punch test

The small punch test has been validated for Ultra High Molecular Weight Polyethylene (UHMWPE) in ASTM F 2183-02. Because only a limited volume of material may be available from retrieved components, reducing the specimen size may increase the number of test specimens. It is unknown if the reduction in specimen thickness will affect the small punch metrics. Therefore, the goal of this study was to examine the relationship between the small punch specimen thickness and the test metrics. Ram extruded GUR 1050 UHMWPE was used to make 5 small punch specimens (diameter 6.35 mm) for each of four different thicknesses: 0.25 mm, 0.33 mm, 0.43 mm, and 0.5 mm. Specimens were tested following ASTM F 2183-02. Power law-based scaling relationships were observed between normalized specimen thickness and the normalized peak load, ultimate load, and work-to-failure of the small punch test (R-2 = 0.99, R-2= 0.99, and R-2=0.94, respectively). A nearly cubic relationship was observed between the normalized specimen thickness and the normalized initial stiffness, which was proportional to the elastic modulus of the UHMWPE, and was predicted based on beam theory (R-2 =0.99). The results of this study provide indication of a reliable means for normalizing small punch test measurements to account for variations in specimen thickness.