STATIC fatigue of rubber is defined by the authors as a progressive breakdown under the influence of a static load, whereas dynamic fatigue is defined as the progressive loss of strength due to successive cycles of stress. The static fatigue life is the time required for rupture under a static load.
Test data presented on the tension static fatigue of rubber indicate that the static fatigue lives of the samples are functions of the stresses acting on them; that the static fatigue lives fall off rapidly with increasing stresses; and that the dependents of static fatigue life on the stress is a function of the stock, among other things.
Curves of reduction of tensile due to static fatigue show that the tensiles of samples under load actually decrease and that the decrease is greater, the greater the time under load.
Referring to the effect of degree of cure, the data indicate that resistance to static fatigue decreases as degree of cure is increased beyond a certain optimum value which varies with the stock.
Other data show that large flow during cure in a particular region reduces the static fatigue resistance of that region in comparison with the remainder of the body of the stock; and that lateral pressure is highly beneficial in increasing the static fatigue lives of bonded rubber parts used in shear.