THE EFFECTS OF CENTRIFUGATION AND TITANIUM FIBER REINFORCEMENT ON FATIGUE FAILURE MECHANISMS IN POLY(METHYL METHACRYLATE) BONE-CEMENT

The contributions to fatigue resistance in poly(methyl methacrylate) b one cement (PMMA) by centrifugation and titanium fiber addition were s tudied. Three modified bone cements were tested: porosity reduced ceme nt (C-PMMA); titanium (Ti) fiber-reinforced cement (R-PMMA), using a n ovel method to incorporate fibers; and porosity reduced and Ti fiber-r einforced cement (C-R-PMMA). Specimens of untreated bone cement (PMMA) were included as controls. Non-notched and notched specimens were cyc lically loaded in fully reversed bending. For the non-notched specimen s, at all stress levels, C-R-PMMA had significantly greater fatigue li fe than either C-PMMA or R-PMMA (except C-PMMA at 30 MPa). R-PMMA had lower fatigue life than the control at 30 MPa (nominal maximum stress) , but higher fatigue life at 20 and 15 MPa. At both 20 and 15 MPa, the re was no statistical difference between the fatigue lives of C-PMMA a nd R-PMMA. Fractography revealed that, at 30 MPa, characteristics of r apid fracture predominated. At 20 and 15 MPa, in contrast, almost the entire fracture surface showed the characteristic fatigue morphology, indicating that subcritical crack growth was predominant. For the notc hed specimens, C-PMMA showed greater life than PMMA at the highest str ess intensity, but the lifetimes converged with decreasing stress inte nsity. In contrast, the lifetimes for PMMA and R-PMMA diverged with de creasing stress intensity. The effect of centrifugation appeared to be strongest at higher stress intensities, and diminished with decreasin g stress intensity. The reinforcing effect of Ti fiber addition increa sed the notched fatigue life at high initial stress intensities, and t he reinforcing effect increased with decreased stress intensity. In bo th the non-notched and notched fatigue experiments, the combination of porosity reduction and Ti fiber reinforcement (C-R-PMMA) led to subst antial improvements in fatigue life at each stress and stress intensit y level, suggesting that Ti fiber reinforcement and porosity reduction effects are additive. Fiber reinforcement affects the fatigue crack p ropagation phase of failure in bone cement, enhancing the fatigue crac k propagation resistance. Pore reduction may affect fatigue crack init iation as well as fatigue crack propagation resistance. (C) 1995 John Wiley & Sons, Inc.