[Publications]

Abstract

The purpose of this study was to investigate the fracture surfaces produced by uniaxial tensile fracture of medical grade PEEK with and without the presence of a stress concentration. Spine and orthopedic components contain stress-risers, thus it is of interest to determine the notch sensitivity behavior of PEEK.

The PEEK material used in this study was OPTIMA LT1 (Invibio, Inc.). Specimens were pre-conditioned in a 37C PBS bath for 8 weeks. 3 tensile specimen geometries were evaluated: unnotched cylindrical dog-bone (D=8mm); and 2 circumferentially grooved (Ushape) dog-bone. 6-10 specimens were tested in each geometry/rate group. Monotonic testing to failure was conducted at 2 displacement rates (6mm/min and 30mm/min) at 37C. Significant necking occurred in the unnotched specimens with propagation of the neck sometimes extending throughout the entire specimen. In contrast, the notched specimens behaved in a brittle manner. Notching caused a significant reduction (p < 0.05) in the true axial fracture stress with increasing severity causing a significant reduction between the two notch geometries (rate held constant). Increasing the rate of extension resulted in a small but significant increase in the true axial stress at fracture in each geometric condition (p < 0.05).

In this study, PEEK demonstrated significant notch sensitivity (reduction in fracture stress) in tension and a transition from ductile to brittle fracture micromechanisms.The finding that PEEK notch weakens in tension supports the need for careful consideration of the location and severity of notch risers in joint replacement and other orthopaedic components.

Acknowledgements: NIH AR47192; Wilbert J. Austin Chair; Invibio, Inc.; NIH GM07250; NIH AR07505