Fatigue crack propagation rates in PMMA bone cement cannot be reduced to a single power law
✍ Scribed by Amos Race; Kenneth A. Mann
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 256 KB
- Volume
- 86B
- Category
- Article
- ISSN
- 1552-4973
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✦ Synopsis
Abstract
Cement mantles around metallic implants have pre‐existing flaws (shrinkage induced cracks, laminations, and endosteal surface features) and their fatigue failure is related to the fatigue crack propagation (FCP) rate of bone cement. We estimated the relevant in vivo range of cyclic stress intensity factor (Δ__K__) around a generic femoral stem (0–1 MPa √m) and determined that previous FCP data did not adequately cover this range of Δ__K__. Vacuum‐mixed standard bone cement was machined into ASTM E647 standard compact notched tension specimens. These were subject to sinusoidal loading (R = 0.1) at 5 Hz in 37°C DI water, covering a Δ__K__ range of 0.25–1.5 MPa √m (including a decreasing Δ__K__ protocol). FCP‐rate data is normally reduced to a power‐law fit relating crack growth rate (d__a__/d__n__) to Δ__K__. However, a substantial discontinuity was observed in our data at around Δ__K__ = 1, so two power‐law fits were used. Over the physiologically plausible range of Δ__K__, cracks grew at a rate of 2.9 E −8 × Δ__K__^2.6^ m/cycle. Our data indicated that FCP‐rates for 0.5 > Δ__K__ > 0.3 MPa √m are between 10 E −8 and 10 E −8 m/cycle, 1 or 2 orders of magnitude greater than predicted by extrapolating from previous models based on higher Δ__K__ data. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008