
Computational modelling of articular cartilage 225
where E
fr
is the tensile modulus of the brillar matrix in the radial direction,
which increases with the radial strain. Consequently, the pressure is a non-
linear function of the compressive strain. Noting that the brillar stress is
zero in the direction of compression, that is,
, the instantaneous axial
stress is determined by substituting Equations [7.28] into [7.27]:
r
[7.29]
Therefore, the effective compressive modulus at the instantaneous
response is:
+
[7.30]
Here E and ν must be consider ...