Prediction of Rubber Fatigue Life under Multiaxial Loading

The process of fatigue failure of rubbers is generally described by two phases: crack initiation and crack propagation. This study concerns the crack initiation in such materials submitted to a cyclical loading. Concerning this aspect, either criteria based upon maximum stretch or strain energy density have been developed in the literature [

1

,

2

,

3

]. More recently, a parameter predicting the onset of primary crack and its probable orientation has been introduced by Mars [

4

,

5

]. This criterion is based on the so-called “cracking strain energy density (CSED)” Wc and postulate that crack initition will occur in the plane in which the value of Wc is a maximum. The cracking strain energy density parameter represents only the portion of strain energy density available to initiate a crack in a given plane. It is defined incrementally as the dot product of traction vector with

$$ \vec \sigma $$

the strain increment vector

$$ d\vec \varepsilon $$

on this material plane (figure 1):

(1)

$$ dW_c = \vec \sigma .d\vec \varepsilon = (\vec r^T .\mathop \sigma \limits^ \approx ).(d\mathop \varepsilon \limits^ \approx .\vec r) $$