Microindentation-based experiments and modeling to examine rate-dependent crack nucleation in cartilage

Guebum Han¹, Corinne R. Henak^1,2, Melih Eriten¹

¹Department of Mechanical Engineering, ²Department of Biomedical Engineering, University of Wisconsin, Madison, WI

ghan28@wisc.edu

Abstract

Introduction: Articular cartilage exhibits rate-dependent mechanical characteristics, which originate from poroelasticity (fluid-solid frictional interaction) and intrinsic viscoelasticity of the solid matrix (collagen fibrils and proteoglycans). The aim of this study is to investigate rate-dependent crack nucleation in cartilage. Method: Rate-dependent cartilage fracture behavior was examined by performing microindentation tests at different loading rates (1 m/s, 300 m/s, and 600 m/s). Critical load, critical displacement, and total work required for nucleation were determined. A fiber-reinforced poroviscoelastic finite element model provided insight into rate-dependent behavior of crack nucleation. Results: Critical load, critical displacement, and total work generally decreased with increasing loading rate; the effect of loading rate was more dominant in critical displacement rather than critical load. A fiber-reinforced poroviscoelastic model could reproduce the effect of loading rate on force-displacement curves. Discussion: Experimental results demonstrated that crack nucleation in cartilage was rate dependent. Finite element results suggested that this rate dependency was from the combination of poroelasticity and intrinsic viscoelasticity. Also, finite element results suggest that nucleation was induced by tensile stresses localized at the indenter tip. The findings of this study extend current knowledge of failure mechanisms in cartilage.