Defect-induced microcrack formation in cemented femoral stem model

Acoustic emission (AE) was used to monitor the progressive fatigue damage process in the cement mantles of two cemented femur stem constructs with naturally occurring defects. After the fatigue tests, morphological features of the defects were investigated using an environmental scanning microscope. It showed that the regions with no visible defects were mainly microcracks free, whereas the regions with large defects were the major resources that generate microcracks. There were two types of microcracks; Type I and Type II, whose positions were known and unknown, respectively. The microstructural investigations of the defects and the areas in the vicinity of the defects suggested their categorization into stable and unstable. Two essential differences between these types were, first, both the cumulative microcrack activity energy (U) and its growth rate were considerably greater in the case of a stable defect than that for an unstable defect. The differences in the various AE measures were a consequence of the difference in the defect morphologies - a stable defect extended almost through the thickness of the cement mantle and had an oval shape, while an unstable defect did not extend through the thickness of the cement mantle and had a sharp tip. It was noticed, interestingly, that the accumulative energy-time relationships revealed that stable and unstable microcrack curves had observed convex, and concave shapes, correspondingly, which are consistent with theoretical results in calculus analysis