Methods for the prediction of fatigue delamination growth in composites and adhesive bonds – A critical review

Abstract

An overview is given of the development of methods for the prediction of fatigue driven delamination growth over the past 40 years. Four categories of methods are identified: stress/strain-based models, fracture mechanics based models, cohesive-zone models, and models using the extended finite element method. It is highlighted that most models are phenomenological, based on the observed macro-scale behaviour of test specimens. It is suggested that a more physics based approach, focusing on elucidating the mechanisms involved, is needed to come to a full understanding of the problem of delamination growth.

Delamination growth in polymer-matrix fibre composites and the use of fracture mechanics data for material characterisation and life prediction

“…This phenomenon, i.e. that when plotting da/dN as a function of ∆(K 2 ) tests at low R ratios appear to be more severe than tests at high R ratios, also follows from the crack growth data presented in [67] and, as previously remarked is also seen from plotting delamination growth as a function of ∆G, see [17,18,43]. Therefore, it is best to follow the natural extension of the original Paris hypothesis [22,24] and relate da/dN to ∆√G (or �G max ), rather than to ∆G or G max or alternatively, as first suggested in [61,62] to Δ√W rather than by ΔW.…”

“…Here it should be recalled that, when originally formulating the equations for crack growth, Paris argued that, since Irwin [20,21] had shown that the stress-intensity factor, K, uniquely characterises the near tip stress field, then the rate of FCG should be a function of ΔK and K max [22,23]. In [24] [2,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][55]. (Where ∆√G is given by (�G max -�G min ); and G min is the minimum value of the energy release-rate in a fatigue cycle.…”

“…The use of Mode I DCB tests is the most common approach employed to characterise delamination growth as a function of the energy release-rate, G [2,4,5,19,26,[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][76][77][78]. However, a major problem with this method is the large retardation that can develop due to fibres bridging the delamination [4,5,13,14,36,42,49].…”

“…However, the logical extension of Paris' growth law to composites is to express da/dN as a function of �G max and/or ∆√G. Indeed, as shown in [17,43] expressing da/dN as a function of ∆G often leads to the anomalous conclusion that, for a given ∆G, increasing the mean stress level reduces the delamination growth rate. This anomaly is removed if da/dN is expressed as a function of ∆√G, see [17,43].…”

“…Indeed, as shown in [17,43] expressing da/dN as a function of ∆G often leads to the anomalous conclusion that, for a given ∆G, increasing the mean stress level reduces the delamination growth rate. This anomaly is removed if da/dN is expressed as a function of ∆√G, see [17,43]. A further illustration of how expressing da/dN as a function of ∆G conflicts with the original Paris formulation is given in the Appendix.…”