Mechanical properties of cracked articular cartilage under uniaxial creep and cyclic tensile loading.

Cracks may change the mechanical properties of articular cartilage, and further lead to early osteoarthritis. The study aimed to probe the mechanical properties of cracked cartilage under uniaxial tensile loading. The fracture process of cracked cartilage can be divided into two stages, namely crack-tip blunting stage and crack growth stage. The creep strain of cracked cartilage increases rapidly and then slowly with time, and it is well predicted by the nonlinear viscoelastic creep model. Compared with intact cartilage, cracked cartilage shows larger creep strain. During cyclic loading, the mean strain, degree of necking and crack-tip blunting of cracked cartilage increase with the increase of peak stress, while they decrease with the increase of loading frequency. The crack-tip morphology shows that cyclic loading has induced irreversible deformation in cartilage with a large number of collagen fibrils yielding, and further damaged the collagen fibril network of cartilage. However, no obvious crack growth is observed under the testing conditions.