Multiaxial fatigue of rubber

Rubber components subjected to fluctuating loads often fail due to the nucleation and growth of defects or cracks. The prevention of such failures depends upon an understanding of the mechanics underlying the failure process. In particular, there is a great need for predicting the effects of complex loading histories on the fatigue life of rubber parts.; This work explores the nucleation and growth of cracks in filled, natural rubber. Several aspects of the fatigue process are explored: the evolution of stress-strain behavior with load cycles, the fatigue life and failure plane associated with the nucleation of visible cracks, and their subsequent growth. Both uniaxial and multiaxial aspects are considered, as well as the effects of R ratio (nonzero minimum load).; New experiments included fatigue crack nucleation tests over a wide range of load histories arising from combined axial and twist deformations of a short, thin-walled, cylindrical rubber specimen bonded between rigid mounting rings, including both proportional and non-proportional loading. The ability of existing multiaxial equivalence criteria (maximum principal strain, strain energy density, octahedral shear strain) to predict fatigue behavior is explored, and a new equivalence criterion is proposed, the Cracking Energy Density. Cracking Energy Density represents the portion of the strain energy density that is available to be released by virtue of crack growth on a given material plane. New models are also proposed for R > 0 fatigue crack growth behavior, for identifying the critical material failure plane, and for relating distributed flaw growth to the evolution of stress-strain behavior with cycles. Theoretical considerations are also introduced relating to the applicability of various fatigue life analysis approaches. New analyses of existing data from the literature were also conducted as part of this work.; Finally, a multiaxial analysis approach is recommended for rubber that appears most likely to result in accurate fatigue life predictions for the widest range of multiaxial strain histories, based on uniaxial material characterization tests. Instances in which other approaches may be adequate are also noted.