During the last decade, functionally modulus graded materials have been proposed for use in artificial joints. Compared to single-layer materials, the transition of modulus within the functionally-modulus graded materials was reduced at a macroscopic level, however, finite modulus mismatches still exist within the materials. The long-term function of these bearings is dependent on the ability to withstand the strains or stresses developed at these interfaces due to the finite modulus mismatch. This paper investigates the use of moire interferometry to study the viscoelastic strain distributions within and across the interfaces of multi-layer elastomeric samples, which were fabricated as simple models for functionally modulus-graded materials. While this technique has been widely used to study the strain distribution in rigid materials and composites, this paper represents the first report of its application to soft viscoelastic polymers above their glass transition temperature. The results obtained clearly demonstrate that moire interferometry can be successfully applied to study the viscoelastic strain distribution in the field of low modulus elastomeric materials. In the fringe patterns, large strain concentrations were observed at the interface between the top, stiffer SG60 layer and the softer middle, SG85 layer, within graded EG60/SG85/EG60 samples that exceeded the local yield strains. A high value and high gradient of residual strain ε{sub}y was observed within the material, very close to the interface, that could potentially result in the local failure of the material.
展开▼
