Numerous testing regimes have been used in vitro to assess the fatigue behaviour of acrylic bone cements. While some attempts have been made to introduce an optimal protocol that measures the fatigue life of bone cement under similar stress conditions to those exist in vivo, the effects of specific testing variables such as test specimen specification and stress parameters are still questionable. These factors can be important since inconsistency in results have been reported regarding the precise effects of other variables such as the mixing method of cement components and the resultant porosity. For a given series of testing variables; namely, specimen cross sectional shape, surface production method and stress type and level (herein collectively termed testing regime), this study investigates the effect of each variable on both the fatigue life and the fatigue crack propagation properties (fatigue behaviour) of bone cement. Testing was constantly performed in 37˚C saline under stress-controlled conditions at a frequency of 3Hz (2Hz for the CT specimens). All specimens were produced after vacuum mixing of the cement components and soaked in 37˚C saline for 1- 6 weeks. Specimens were manufactured with two cross sectional shapes: rectangular (ISO 527-2) and circular (ASTM F2118), using two production methods: direct moulding or machining. Two different bone cements were used: SmartSet GHV and CMW1. For each specimen type, at least 10 specimens were fatigued to failure at a maximum stress of 20 MPa applying either fully reversed tension-compression (R= –1) or tension-tension (R= 0.1) loading, followed by Weibull analysis. For the fully reversed loading only, at least 5 specimens were tested for each group at other three levels: ±12.5, ±15 and ±30 MPa and the four stresses were compared using S-N curves. Behaviour of fatigue cracks were assessed based on the cyclic stress-strain responses. CT specimens were used to measure the crack growth rates in the two cements. The findings of this study have emphasised the important role of the set of a testing regime variables included in testing and identified the influence of each testing variable on the fatigue behaviour of bone cement. Machining of test specimens and applying high stress levels, in particular, can lead to irrelevant findings when considering the in vivo conditions, depending also on the cement composition. While these “inappropriate” testing variables can be considered as possible reasons for the variations in fatigue results reported in previous work, it is suggested to consider the effects of these variables in future work.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:646734 |
| Date | January 2015 |
| Creators | Sheafi, Emadeddin A. Mansur |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/6250/ |
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