Application and discussion of various crack closure models to predict fatigue crack growth in 6061-T651 aluminium alloy

On the Link between Plastic Wake Induced Crack Closure and the Fatigue Threshold

“…Several possible forms of this (scaling) function U(R) are discussed in [50][51][52][53][54][55][56]59]. Here it should be noted that in [47] the function U was only a function of R. (A brief discussion of this statement is given in Appendix A) In such cases it thus follows from Equation (2) and from the facts that (a) if as per Elber [47] U(R) is only a function of R rather than of both ∆K and K max ; (b) and, if as per [47] for a given value of R the function U(R) has a fixed (constant) value; then if each R ratio dependent da/dN versus ∆K curve is to collapse onto a single da/dN versus ∆K eff curve by merely multiplying (each value of) ∆K by the function U(R), then Equation (2) can be rewritten in the form:…”

“…It is this process that is commonly refered to as "plastic wake induced crack closure. At this point, it should be mentioned that, whilst, as discussed in [48][49][50][51][52][53], there are other forms of crack closure and other formulations that attempt to account for this effect, this paper only addresses Elber's [46,47] original formulation and not the larger cross-section of formulations that are summarised in [52].…”

“…As outlined in [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] variants of this approach are now widely used to model the growth of long cracks in conventionally manufactured metals. However, it should also be noted that it has recently been suggested [65] that R ratio effects on the growth of long cracks can be interpreted as a reflection of the effect of the environment on the crack tip region rather than crack closure per se.…”

Microstructural investigation and model of fatigue short crack in EH36 steels

“…Based on the toughening theory, Dai et al 10 took the crack closure and PZ at crack tip into account and then proposed the plasticity‐correction ΔK ( ΔK pe ) to describe SC propagation. Crack closure also acts a significant role in the SC propagation, which can be ascribed to the compressive PZ caused by constant cyclic loading stress, affecting the crack growth, particularly for PSC 11–13 . For solving this problem, Newman et al 14 considered the crack closure and residual plastic deformation during crack growth, then modified the Elber model, 15 proposing the effective ΔK ( ΔK eff ) to describe da/dN of PSC in several alloys.…”

“…Crack closure also acts a significant role in the SC propagation, which can be ascribed to the compressive PZ caused by constant cyclic loading stress, affecting the crack growth, particularly for PSC. [11][12][13] For solving this problem, Newman et al 14 considered the crack closure and residual plastic deformation during crack growth, then modified the Elber model, 15 proposing the effective ΔK (ΔK eff ) to describe da/dN of PSC in several alloys. A model of the plastic deformation of the fracture surface asperities at the crack tip was developed to relate the crushing of the asperities to crack closure and da/dN.…”