Miniature specimen mechanical testing

Kurtz S.M., C.W. Jewett, J.R. Foulds, and A.A. Edidin. 1999. Miniature specimen mechanical testing technique scaled to articulating surface of polyethylene components for total joint arthroplasty. J Biomed Mater Res 48(1) 75-81. 

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. 

Mechanical testing of miniature specimens— as opposed to bulk lai specimens— is attractive when the need arises to directly probe the properties of a specific component rather than a generic material. Testing of miniature specimens obtained directly from a specific structure becomes paramount when evidence suggests that the properties of the material under consideration are known to change over time. In such cases, tirere can be no assurance that assays of supposedly equivalent material, aged in a similar manner, will have any fidelity to individual components of interest. 

How, then, are we to interpret values in the literature for in vivo oxidation in retrievals Current studies of mechanical behavior in shelf aged components and retrievals, whether based on miniature uniaxial tensile specimens or the small punch test, exhibit considerable variability and scatter, even when oxidation values are measured directly from the miniature specimens themselves. Consequently, published data for the relationship between in vivo oxidation and mechanical behavior are necessarily statistical in... 

An extensive discussion of polymer fractography can be found in other studies (Kausch 1978, 1983 Plummer 2007). There are three different sources for fractured specimens (1) deformation of the sample and fracture after testing in standard mechanical testing devices, such as tension, compression, or bending tests, impact test, etc. (2) in situ deformation and fracture of microsamples by special miniature testing devices during observation in the microscope ... 

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