Assessment of low cycle fatigue crack growth under mixed-mode loading conditions by using a cohesive zone model

Application of a Cohesive Zone Model for Simulating Fatigue Crack Growth from Moderate to High ΔK Levels of Inconel 718

“…For example, in [25], the combination use of (2) and the cohesive envelope of the exponential form are performed to simulate fatigue crack growth; however, this combination results in the contradictory damage evolution at δ n > δ 0 if a slightly larger value of σ f /σ max,0 is provided, and this problem can be solved by using (1). As mentioned above, the similar CCZM has been proposed to investigate the mixed mode fatigue crack growth in our previous simulations [29], the difference between these two models is that the current one does not introduce the monotonic damage, the material degradation under cyclic loadings is described uniformly by (2), and the monotonic damage is determined by the cohesive envelope implicitly. Actually, the combination of (1) and (2) has the capacity to simulate fatigue crack growth at the high ΔK levels, the applications need not be distinguished between monotonic damage and fatigue damage as introduced in [29], the key point in such simulations is the form of (1), and more details will be performed in Section 3.…”

“…Although the Paris-like behavior which corresponds to the moderate ΔK levels in Regime II can be predicted by using the aforementioned CCZMs [11,[22][23][24][25][26][27], this is not the advantage of CCZMs, since the Paris regime associated with SSY has already been described successfully according to the K-based models. In order to resolve the more challenging task that to simulate the high fatigue crack growth rates in Regime III of the metallic materials, a CCZM was proposed in our previous work [29] in which two damage variables were defined to represent monotonic damage and fatigue damage, respectively. In fact, it is not easy to distinguish these two different damage mechanisms in fatigue crack growth before the final rupture occurs; thus, it is better to describe the material damage evolution uniformly.…”

“…The simulations reveal that the novel cohesive envelope combined with one damage evolution equation can also be used to capture the accelerated fatigue crack growth behavior at the high ΔK levels, and there is no need to distinguish 11 International Journal of Aerospace Engineering between the monotonic damage and the fatigue damage as introduced in [29]. The crack growth behaviors are largely affected by the accumulative length d Σ and the cohesive endurance limit σ f ; meanwhile, the effects of the cyclic model parameters are also influenced by the monotonic model parameters, that is, cohesive energy and the initial cohesive strength as the ΔK level approaches the critical value corresponding to the fracture toughness.…”

Structural fatigue assessment of a fixed mono-pile platform

“…A concentrated mass is modeled on the topside to represent the weight of the equipment and other nonstructural installation, and the structure is fully fixed at a location six times the diameter of the pile, which is 6 m beneath the mudline. 33 The structure is modeled with steel as the material with Young's modulus of 210 GPa, Poisson ratio of 0.3, and the density of 7850 kg/m 3 . In general, the most important contribution to the fatigue damage comes from small-to-moderate sea states.…”

“…One of them is the fracture mechanics approach based on Paris crack propagation criterion, which is usually applied to predict the propagation life from initial crack or defect. 3 Another one is the traditional fatigue curve (S-N curve) method on the basis of Palmgren-Miner (P-M) linear damage hypothesis (the method used in this article) which is intended for application at the design stage. Due to the difference in the theoretical basis, the latter approach can be divided into three categories, namely, deterministic method, frequency-domain method (spectra based method), and time-domain method, respectively.…”