Crack closure effects on fatigue damage ahead of crack tips

Verification of the ΔKeff hypothesis along the fatigue crack path in thin and thick Al specimens

“…In fact, PICC can justify many load sequence effects in FCG, such as delays or arrests after overloads (OL), attenuation of OL-induced delay effects after subsequent underloads, and FCG threshold sensitivity to R, which can much affect fatigue life estimates under variable amplitude loads (VAL). Hence, it is not surprising that FCG models based on ΔK eff concepts still are very much used in practical applications [3][4]. However, although many experiments (including the data presented here) support the existence of PICC, see e.g.…”

Analytical modeling of fatigue crack growth in plastically pre‐strained steels

“…The energy concept, as proposed in Ferreira et al 13 and Tzamtzis and Kermanidis, 39 defines the critical number of cycles (Ν crit ) for failure of the material element at the crack tip, leading to incremental crack extension, and is based on the energy theories established in the early works by Morrow 18 and Sih. 19,23 For Masing material behavior, typical for the type of steels examined in the current research, 37 for the stabilized hysteresis loop of Figure 2 under a constant plastic strain range, the dissipated PSE per cycle (ΔW) can be expressed as 18…”

“…Furthermore, strain hardening has been acknowledged as an influential mechanism on fatigue crack growth by controlling the crack tip opening displacement. 13,[34][35][36] Fatigue crack growth models that incorporate the cyclic hardening behavior as the main mechanism controlling FCGR usually consider the CPZ as the process zone, where cyclic plastic deformation evolves. In the fatigue crack growth retardation model developed by Pantelakis et al, 34 a plastic strip zone at the crack tip is taken into consideration, where the material hardening effect is occurring.…”

“…As a consequence, the mechanical properties of the metal are affected, resulting in an increase in strength and a decrease in ductility 10–12 . Furthermore, the rate at which fatigue cracks propagate is influenced by various factors, including the applied fatigue loads (load range and history, stress ratio), geometry, microstructural aspects, environmental conditions, and other phenomena at the crack tip, such as the crack closure mechanism (e.g., plasticity‐induced crack closure) 13,14 . The microstructural changes in the material at the atomic (dislocation slip, twinning, and interaction) and microscale (grain elongation) levels, induced by plastic pre‐deformation, influence the conditions near the crack tip and plastic zone size/shape and hence the Stage II fatigue crack propagation rate.…”

Experimental Verification and Estimation of Fatigue Crack Growth Delay due to Single Overload

“…In this feld, the crack closure theory has drawn many attentions, which purports that a crack will not propagate unless the crack driving force is over a specifc point. However, the closure efect is still highly controversial since this efect cannot explain many of its peculiarities, such as high loading ratio conditions or high-strength steels [19][20][21][22][23]. Besides, many phenomenological delay models have also been proposed based on the following main hypotheses: (1) the crack length afected by overload is estimated by the plastic zone sizes, which are infuenced by loading conditions; (2) the crack length corresponding to the value of the FCG rate is relative to the plastic zone size.…”