Multiaxial fatigue of rubber: Part II: experimental observations and life predictions

Abstract

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.

Prediction of rubber fatigue life under multiaxial loading

“…Establishing a multiaxial criterion of fatigue crack nucleation requires a large set of data like that recently reported in the literature by Mars and Fatemi 20 . So, for our tested material, these results require to be enriched by experimental data basis which explores a wide range of strain states including, for example equibiaxial tension or simple shear fatigue tests.…”

Fatigue life prediction of vulcanized natural rubber under proportional and non‐proportional loading

“…However, for an incompressible material, the maximum principal strain always satisfies ɛ 1 > 0. The octahedral shear strain criterion makes a prediction that is roughly similar to the principal strain criterion for rubber 6,19 . In the meantime the octahedral shear strain always satisfies γ oct > 0.…”

“…The CED was recently introduced by Mars and Fatemi 6,19 . CED represents a part of the total SED available to initiate a crack in given plane, with critical plane characteristics.…”

Overview of Experimental Studies on Strength Problem of Rubber Material

“…Mars and Fatemi [23] are the pioneers in the field of rubber multiaxial fatigue, and carried out a series of fatigue tests of filled type of natural vulcanized rubber under proportional and non proportional loading path. The results show that rubber cracks are nucleation and expansion of a certain plane under multiaxial fatigue.…”