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Many factors are known to influence the mechanical fatigue life of rubber components. Four major categories of factors are reviewed here: the effects of mechanical loading history, environmental effects, effects of rubber formulation, and effects due to dissipative aspects of the constitutive response of rubber. For each category, primary factors are described, and existing literature is presented and reviewed. Rubber's fatigue behavior is extremely sensitive to both the maximum and minimum cyclic load limits. Other aspects of the mechanical load history are also discussed, including the effects of static loaded periods (“annealing”), load sequence, multiaxiality, frequency, and loading waveform. Environmental factors can affect both the short and long term fatigue behavior of rubber. The effects of temperature, oxygen, ozone, and static electrical charges are reviewed. A great range of behavior is available by proper manipulation of formulation and processing variables. Effects of elastomer type, filler type and volume fraction, antidegradants, curatives, and vulcanization are discussed. The role of dissipative constitutive behavior in the improvement of fatigue properties of rubber is also reviewed. Four distinct dissipative mechanisms are identified, and their effects on fatigue behavior are described.

This paper describes a new model for predicting multiaxial fatigue crack initiation in rubber. The work is motivated by a need to predict crack initiation life in tires, based on strain histories obtained via finite element analysis. The new model avoids the need to explicitly include cracks in the finite element model, and applies when the cracks are small compared to the strain gradient. The model links the far-field strain state to the energy release rate of an assumed intrinsic flaw. This is accomplished through a new parameter, the cracking energy density. The cracking energy density is the portion of the total elastic strain energy density that is available to be released on a given material plane. The model includes an algorithm to select the material plane which minimizes the life prediction for a given strain history. The consequences of the theory for simple strain histories are presented, as well as predictions for more complicated histories. The theory is compared with published data, and with new results from recent combined axial/torsion fatigue experiments.

Rubber parts in service often experience complex strain histories that can cause mechanical failure. The ability to predict the effects of complex strain histories on fatigue life is therefore a critical need. This paper presents recent results of cyclic, combined tension/torsion fatigue experiments, and compares them with predictions based on a new parameter, the Cracking Energy Density. The Cracking Energy Density is the stored elastic energy density that is available to a crack on a given material plane, and can be calculated for an arbitrarily complex strain history. The ability of Cracking Energy Density to predict the fatigue life and cracking plane is evaluated for both in-phase and out-of-phase histories of combined axial and shear strain.

This work explores the monotonic and cyclic behaviors of filled, natural rubber. Results of stress-strain experiments conducted under stress states of simple, planar, and equibiaxial tension are presented. The ability of hyperelastic models to capture the observed response, as well as recent developments in constitutive modeling of filled rubber such as the consequences of the Mullins effect, are discussed. Monotonic and cyclic multiaxial experiments were also conducted using a short, thin-walled, cylindrical specimen subjected to a wide range of combined axial and twist displacements. Experiments included pure axial tension, pure torsion, combined loading in which the axial and torsion displacements varied proportionally, and combined loading in which the axial and torsion displacements varied non-proportionally (phase between axial and torsion channels of ϕ=0 deg, 90 deg, 180 deg). Results from these tests are presented and discussed, including evolution of stress-strain behavior with load cycles, and the effects of a short period of initial overloading on the subsequent evolution of the stress-strain response.

Rubber components subjected to fluctuating loads often fail due to nucleation and the growth of defects or cracks. The prevention of such failures depends upon an understanding of the mechanics underlying the failure process. This investigation explores the nucleation and growth of cracks in filled natural rubber. Both fatigue macro‐crack nucleation as well as fatigue crack growth experiments were conducted using simple tension and planar tension specimens, respectively. Crack nucleation as well as crack growth life prediction analysis approaches were used to correlate the experimental data. Several aspects of the fatigue process, such as failure mode and the effects of R ratio (minimum strain) on fatigue life, are also discussed. It is shown that a small positive R ratio can have a significant beneficial effect on fatigue life and crack growth rate, particularly at low strain range.

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A B S T R A C T Fatigue experiments were conducted with an axial-torsion specimen covering a wide range of stretch biaxiality and a range of fatigue lives between 10 3 and 2 × 10 6 cycles. These experiments include combined torsion-compression, pure torsion, combined torsiontension and pure axial tension. Both in-phase and out-of-phase combinations of axial and torsion loading were considered. The multiaxial fatigue experiments described provide empirical evidence from which an understanding of the mechanics of the fatigue process in rubber can be developed. Each of the four equivalence parameters described in Part I has been applied to the axial-torsion fatigue experiments described in this paper (Part II). These results provide the basis for an analysis of the effects of multiaxial loading on fatigue life, and an assessment of the degree to which the various equivalence parameters are able to rationalize the results in a unified way. For the combined axial and shear strain histories in this study, the maximum principal strain criterion gave the best correlation to fatigue life. Strain energy density gave the worst correlation. The cracking energy density criterion was generally found to give good correlation of fatigue crack nucleation lives from combined axial-torsion tests. Because it provides a plane-specific analysis, this criterion appears to be particularly well suited for use in crack nucleation analyses of multiaxial strain histories.Keywords axial-torsion fatigue tests of rubber; correlation of multiaxial fatigue data of rubber. N O M E N C L A T U R EB = stretch biaxiality ratio E, E ij = Green-Lagrange strain tensor, components F = fatigue crack growth exponent G = shear modulus of linear elasticity, energy release rate H = specimen gage section height I 1 , I 2 , I 3 = stretch tensor invariants N , N f = cycles, cycles to failure N f,W , N f,WC = cycles to failure according to strain energy density criterion, according to cracking energy density criterion P, P a , P m = axial loads, amplitude, mean r = coefficient of correlation R = specimen outside gage section radius, minimum to maximum ratio R θ , R W , R WC = minimum to maximum twist displacement ratio θ min /θ max , strain energy density ratio W min /W max , cracking energy density ratio W C,min /W C,max t = time Correspondence: A. Fatemi.