In vitro simulation of in vivo dynamic micromechanical failure of structural composite biomaterials

Concern exists whether fiber reinforced plastics can be developed with sufficient fatigue strength for long term use in structural orthopaedic application. The fiber/matrix interfacial bond is an important governing factor in the fracture behavior of composite materials. The goal of this research was to characterize the fatigue behavior of the fiber/matrix interfacial bond in candidate FRP composite biomaterial systems in simulated in vivo environments.; A miniature mechanical test machine was developed (and patented) to characterize the fracture behavior of the fiber/matrix interfacial bond. The fiber/matrix combinations selected for study were carbon fiber/polysulfone (CF/PSF), carbon fiber/polycarbonate (CF/PC), Kevlar 49 fiber/polysulfone (K49/PSF), and Kevlar 49 fiber/polycarbonate (K49/PC). The interface was characterized in terms of both ultimate and dynamic fatigue strength in three separate environments (37{dollar}spcirc{dollar}C dry air, saline, and inflammatory exudate) utilizing a single fiber pull-out test method.; Test results show the CF interfaces to possess greater ultimate bond strength (UBS) and fatigue strength (FS) than the K49 interfaces with each matrix type. The PC and PSF matrix interfacial bond strengths were found to be approximately equivalent for a given fiber type. The UBS and FS were found to be significantly decreased by both saline and exudate exposure with no significant difference being found in the saline and exudate environments. The fatigue results show a linear relationship between applied shear stress and the logarithm of fatigue life (cycles to failure) for each FRP system. SEM photographs of the site of debonding reveal that bond failure occurred primarily by adhesive failure at the interface in the UBS test while fatigue debonding occurred by a mixture of both adhesive and matrix cohesive failure.; Methods have been successfully developed for the dynamic fatigue characterization of the fiber/matrix interfacial bond utilizing a single fiber pull-out test. Interfacial bond ultimate and fatigue strength characterization in simulated in vivo environments should prove useful for the development of fatigue resistant FRP composite biomaterials for long term structural orthopaedic implant use.