The purpose of this investigation is to refine previously published data (Woo et al., 1976) on the nonhomogeneous and directional tensile properties of articular cartilage by using the large deformation theory of elasticity. Normal articular cartilage of the bovine humeral joint provided the test specimen source. The specimens were of a standardized dumb-bell shape, 250–325 μm thick, taken from the surface, middle and deep zones, at 0°, 45° and 90° from the axis of the surface split line. During tensile testing the longitudinal stretch, lateral contraction and thickness reduction of the specimens were measured, from which nonlinear stress-strain relationships were obtained. With the measurement of the deformation in three directions, the volume change (or water loss) and a nonlinear stress-volume loss relationship of articular cartilage during tensile stretch were also determined.

The results showed significant differences between Eulerian stress (expressed in deformed cross-sectional area) and Lagrangian stress (expressed in original cross-sectional area). However, the trends of stiffness characteristics between 0°, 45° and 90° specimens taken from the same zone, or surface, middle and deep zone specimens taken from the same direction, were similar to those obtained previously (Woo et al., 1976). It is suggested that the current experimental methodology be extended to study the properties of other soft biological materials.