![]() However, there has been little work on the S-N fatigue behavior of PEEK in the presence of a stress concentration. There have been some reports in the literature on the fatigue crack propagation behavior of PEEK, and also on the stress-life (S-N) behavior. However, since devices used in clinical situations will experience cyclic loading the fatigue behavior of PEEK in the presence of stress concentrations is of clinical interest. We have previously reported on the monotonic behavior of unfilled PEEK in the presence of stress concentrations (generically referred to as notches). Īll of these unfilled PEEK devices have design stress concentrations and/or undergo multiaxial loading conditions. An artificial disc fabricated entirely from unfilled PEEK (NUBAC intradiscal arthroplasty device for the lumbar spine by Pioneer Surgical Technology, Marquette, MI) is currently in an international multi–center prospective clinical trial with 225 of these devices implanted since December 2004. Medtronic Sofamor Danek have launched the CD Horizon Legacy PEEK pedicle-based, posterior rod for use as a dynamic stabilization system for the spine. Since the 1990s unfilled PEEK has been used in both cervical and lumbar spinal cages in vertebral fusion surgeries with considerable clinical success. This has the benefit that the mechanical properties of the material can be tailored by altering the composite formulation. Another reason that PEEK is of interest is that both carbon fiber reinforced (CFR) and hydroxyapatite (HA) filled and/or HA coated PEEK have been developed. In addition to high strength, unfilled PEEK has several attractive properties: transparency to X-rays, no artifacts created in CT images, and excellent biocompatibility. Poly(ether-ether-ketone) (PEEK), is a semicrystalline polymer that has an approximate crystallinity of 30-35% and a Tg of 143☌. Additional analysis was conducted to estimate the percent of the lifetime spent in crack initiation vs propagation, and it was found that the specimens spent the majority of the time in the crack initiation phase. Fractographic analysis via SEM further elucidated the potential fracture micromechanisms. It was found that the majority of the loading was elastic in nature, and that there was only a small portion on the lifetime where there was a detectable change in structural behavior prior to gross fracture. This work examines both stress-life (SN) fatigue behavior and the fracture behavior of unfilled PEEK under tension tension loading in circumferentially grooved round bar specimens with different elastic stress concentration factors. All of the orthopaedic applications contain stress concentrations (notches) in their design however, little work has been done to examine the fatigue behavior of PEEK in the presence of a notch. Poly(ether-ether-ketone) (PEEK) has been used as a load bearing orthopaedic implant material with clinical success.
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