We investigate the use of cohesive theories of fracture, in conjunction with the explicit resolution of the near-tip plastic fields and the enforcement of closure as a contact constraint, for the purpose of fatigue-life prediction. An important characteristic of the cohesive laws considered here is that they exhibit unloading-reloading hysteresis. This feature has the important consequence of preventing shakedown and allowing for steady crack growth. Our calculations demonstrate that the theory is capable of a unified treatment of long cracks under constant-amplitude loading, short cracks and the effect of overloads, without ad hoc corrections or tuning.

A Cohesive model of fatigue crack growth

A literature survey on fatigue analysis approaches for rubber

An extension of the celebrated Paris law for crack propagation is given to take into account some of the deviations from the power-law regime in a simple manner using the Wohler SN curve of the material, suggesting a more general ''unified law''. In particular, using recent proposals by the first author, the stress intensity factor K(a) is replaced with a suitable mean over a material/structural parameter length scale Da, the ''fracture quantum''. In practice, for a Griffith crack, this is seen to correspond to increasing the effective crack length of Da, similarly to the Dugdale strip-yield models. However, instead of including explicitly information on cyclic plastic yield, short-crack behavior, crack closure, and all other detailed information needed to eventually explain the SN curve of the material, we include directly the SN curve constants as material property. The idea comes as a natural extension of the recent successful proposals by the first author to the static failure and to the infinite life envelopes. Here, we suggest a dependence of this fracture ''quantum'' on the applied stress range level such that the correct convergence towards the Wohler-like regime is obtained. Hence, the final law includes both Wohler's and Paris' material constants, and can be seen as either a generalized Wohler's SN curve law in the presence of a crack or a generalized Paris' law for cracks of any size. r 2006 Elsevier Ltd. All rights reserved.

https://staff.polito.it/alberto.carpinteri/papers/CARPINTERI_2006_N.407_JMPS.pdf

R. G. Forman

Papers

Numerical Analysis of Crack Propagation in Cyclic-Loaded Structures

Closure to “Discussion of ‘Numerical Analysis of Crack Propagation in Cyclic-Loaded Structures’” (1967, ASME J. Basic Eng., 89, pp. 463–464)