Biphasic poroviscoelastic simulation of the unconfined compression of articular cartilage: II - Effect of variable strain rates

This study investigated the abilities of the linear biphasic poroviscoelast ic (BPVE) model and the linear biphasic poroelastic (BPE) model to simulate the effect of variable ramp strain rates on the unconfined compression str ess relaxation response of articular cartilage. Curve fitting of experiment al data showed that the BPVE model was able to successfully account for the ramp strain rate-dependent viscoelastic behavior of articular cartilage un der unconfined compression, while the BPE model was able to account for the complete viscoelastic response at a slow strain rate, but only the long-te rm viscoelastic response at faster strain rates. We concluded that the shor t-term viscoelastic behavior of articular cartilage, when subjected to a fa st ramp strain rate, is primarily governed by a fluid flow-independent (int rinsic) viscoelastic mechanism, whereas the long-term viscoelastic behavior is governed by a fluid flow-dependent (biphasic) viscoelastic mechanism. F urthermore, a linear viscoelastic representation of the solid stress was fo und to be a valid model assumption for the simulation of ramp strain rate-d ependent relaxation behaviors of articular cartilage within the range of ra mp strain rates investigated.