Mechanical properties testing small punch

This chapter reviews the development and application of miniature specimen mechanical testing techniques, based on the small punch test, to the characterization of UHMWPE components for total joint replacement. The development of the small punch test as applied to UHMWPE was motivated by two clinically relevant and related problems the relationship between process and system variables and polymer degradation, and the relationship between mechanical properties and the ensuing wear of the arthroplasty bearing. To a first order approximation, the polymer degradation problem was motivated by mechanical failure of tibial plateau bearings, and the wear problem was motivated by the clinical need to reduce the prevalence of small-particle mediated late-onset osteolysis in total hip arthroplasty systems. 

Low oxidation (OI < 1) For ASTM oxidation index values of less than 1, it is very difficult to demonstrate a negative correlation with mechanical properties from retrievals, regardless of whether they are measured using miniature tension tests or small punch tests [16, 22, 34]. For this reason, oxidation indices of less than 1 may be considered relatively low, and despite evidence of early oxidative changes, it is unlikely that these changes have yet had a substantial negative impact on mechanical behavior. 

In summary, over the past decade the small punch test has been extensively developed to perniit direct assay of the mechanical properties of orthopedic UHMWPE bearings. 

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