Measurement of non-linear microcrack accumulation rates in polymethylmethacrylate bone cement under cyclic loading

Damage accumulation in the cement mantle used to fixate bone prosthesis is one failure scenario for joint reconstruction. It can be described as the p henomenon of numerous microcracks initiating and propagating within the mat erial. Microcracks grow in the cement mantle causing it to gradually lose i ts mechanical integrity, leading to loosening of the prosthesis. In this st udy microcracking within acrylic bone cement was quantified over the course of a fatigue test. Identification of new cracks and the growth of pre-exis ting cracks was monitored at intervals during fatigue testing of five speci mens at a mean cyclic stress of 7.5 MPa. Given these measurements, an avera ge damage evolution curve was derived for acrylic bone cement. It was obser ved that the initiation sites for microcracks were the pore perimeters; the refore, the number of microcracks present in a sample is dependent on poros ity. Variability was found within the results and the majority of the varia bility was accounted for by the difference in the porosity of each sample. Results have identified non-linear damage evolution. On a simplified level a power law equation can be used to describe the damage evolution process. (C) 1999 Kluwer Academic Publishers.