Effect of crack closure on non-linear crack tip parameters

Abstract

Crack closure concept has been widely used to explain different issues of fatigue crack propagation. However, some authors have questioned the relevance of crack closure and have proposed alternative concepts. The main objective here is to check the effectiveness of crack closure concept by linking the contact of crack flanks with non-linear crack tip parameters. Accordingly, 3D-FE numerical models with and without contact were developed for a wide range of loading scenarios and the crack tip parameters usually linked to fatigue crack growth, namely range of cyclic plastic strain, crack tip opening displacement, size of reversed plastic zone and total plastic dissipation per cycle were investigated. It was demonstrated that: (i) LEFM concepts are applicable to the problem under study; (ii) the crack closure phenomenon has a great influence on crack tip parameters decreasing their values; (iii) the ΔKeff concept is able to explain the variations of crack tip parameters produced by the contact of crack flanks; and (iv) the analysis of remote compliance is the best numerical parameter to quantify the crack opening level. Therefore the crack closure concept seems to be valid. Additionally, the curves of crack tip parameters against stress intensity factor range obtained without contact may be seen as master curves.

Fatigue crack growth modelling based on CTOD for the 7050‐T6 alloy

“…In authors' opinion, the linear elastic Δ K parameter needs to be replaced by nonlinear crack tip parameters (NLP), able to quantify effectively the crack tip plastic deformation which is supposed to control FCG rate (FCGR). Antunes et al used nonlinear parameters to validate the crack closure concept and to identify the best crack closure parameter. The effect of physical parameters like thickness, stress state, specimen geometry and/or overloads is naturally accommodated by the nonlinear parameters.…”

“…The link between NLP and da/dN has been exploited in literature using theoretical models and empirical relations . The NLP parameters identified in the literature review made by Antunes et al are the range of cyclic plastic strain, the size of reversed plastic zone, the total plastic dissipation per cycle and the crack opening displacement (COD). Note that these NLP, and also the J integral, usually replace K when the LEFM is no longer valid .…”

A study of overload effect on fatigue crack propagation using EBSD, FIB–DIC and FEM methods

“…Another mechanism, perhaps the most important to mention in the context of crack retardation, is the crack closure effect [5]. An OL causes plastic deformation at the crack tip, and produces excess material just ahead of it.…”

Numerical analysis of fatigue crack growth using a plastically dissipated energy factor based model

“…6 However, it is also pointed out that crack closure does not include the effect of the portion of the load cycle below the opening load, which is expected to affect crack growth. 7…”