Plane-Strain Fracture Toughness and Tensile Testing of a Piezoelectric Composite for Spinal Fusion

Abstract

A novel piezoelectric spinal fusion device has been shown to improve spinal fusion. The mechanical properties of this novel piezoelectric material are important for the integrity of the device. To characterize the mechanical properties of the piezoelectric material, a uniaxial tensile test and a plane-strain fracture toughness test used to determine the mechanical integrity of the material. The specific materials investigated were a pure layered stack made of piezoelectric discs and piezoelectric discs stacked with intermediate compliant layers. Results of tensile testing were inconclusive. Stress concentrations around the layers and the brittle nature of the material caused early failure. Results of fracture toughness were unreliable due to a flaw in the experimental procedure. Theoretical calculations were performed to determine the potential fracture toughness of the material, resulting in a higher fracture toughness for the piezoelectric discs stacked with intermediate compliant layers as compared to the pure layered piezoelectric discs. Additional fracture toughness testing yielded preliminary fracture toughness values. A single sample with compliant layers had a higher fracture toughness than a single sample without the compliant layers. However, additional work with a larger sample size needs to be performed to determine statistical significance.