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Fatigue crack propagation rates in PMMA bone cement cannot be reduced to a single power law
Author(s) -
Race Amos,
Mann Kenneth A.
Publication year - 2008
Publication title -
journal of biomedical materials research part b: applied biomaterials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.665
H-Index - 108
eISSN - 1552-4981
pISSN - 1552-4973
DOI - 10.1002/jbm.b.31016
Subject(s) - materials science , cement , bone cement , composite material , discontinuity (linguistics) , power law , fracture mechanics , fracture toughness , tension (geology) , ultimate tensile strength , mathematical analysis , statistics , mathematics
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