Crack growth from naturally occurring material discontinuities under constant amplitude and operational loads

Crack growth in a naturally corroded bridge steel

“…This hypothesis is subsequently confirmed experimentally. As such, the present paper suggests that not only is the da/dN versus Δ K curve for bridge steels similar to that seen for the high‐strength aerospace steels D6ac and 4340 but also the methodology developed to assess the growth of small sub mm cracks in aerospace materials is applicable to cracks that initiate and grow from natural corrosion in a bridge steel.…”

“…Furthermore, for small cracks in operational structure, the very existence of a fatigue threshold is questioned in . Hence, as first shown in and discussed more in detail in , the behaviour of cracks that arise and grow naturally can often be approximated by a Paris‐like crack growth equation. For mild steels, this observation was first shown in for BS4360‐43A.…”

Composite repairs to bridge steels demystified

“…However, as noted in ASTM 647-13a any analysis/design (repair assessment) of a composite repair to an operational structure should use valid da/dN versus ΔK small crack data. This is particularly important since as explained in [34,35] even for materials that, for long cracks, exhibit crack closure effects the small crack da/dN versus ΔK curve is essentially R ratio and crack closure free. Hence, crack closure based analysis of CFRP repairs to bridge steels, which as we have seen above exhibit little crack closure even if the crack is long, is inapplicable 5 .…”

“…The physical reason for this 7 formulation is that, as explained in [49,50], the growth of cracks that initiate from small naturally occurring material discontinuities behave, as explained by 4 Nevertheless limited crack growth was observed in operational aircraft. 5 Here it should be noted that it is now know that for a range of materials tested under a range of operational load spectra the growth of cracks that initiate and grow from small naturally occurring material discontinuities can be accurately computed using the R ratio independent da/dN versus ΔK small crack relationship and setting closure effects to zero [27,28,[34][35][36][37]. 6 This is also referred to as exponential crack growth.…”

Local Monte Carlo Method for Fatigue Analysis of Coarse-Grained Metals with a Nanograined Surface Layer

“…Currently, fracture mechanics tools coupled with valid small crack growth equations can well compute the life of structural members with complex shapes under variable amplitude load spectra [2,[51][52][53][54][55][56][57]. At present, it is not a trivial task for the numerical model based on the cohesive finite element method and Monte Carlo method to accurately compute the fatigue crack growth history of realistic 3D structures under complex load histories.…”