Fatigue Crack Propagation and History Effects Induced by Plasticity

Abstract

For security‐relevant components, a fracture mechanics assessment has to be carried out. When complex loading conditions are encountered, various problems arise. Among them the prediction of history effects induced by plasticity remains a difficult task and is the object of this paper. After an overload, for instance, plasticity‐induced crack closure is known to decelerate the crack growth. This effect is known to be related to residual stresses ahead of and behind the crack tip. Since residual stresses are related to the material stress–strain behavior, the overload effect may vary significantly from one material to another. Finite‐element (FE) methods are commonly employed to model plasticity and were shown to give very satisfactory results. However, if millions of cycles need to be modeled to predict the fatigue behavior of an industrial component, the method becomes computationally too expensive. By employing a multiscale approach, very precise analyses computed by FE methods can be brought to a global scale. The data generated using the FE method enables the identification of a global cyclic elastic‐plastic model for the crack tip region. Once this model is identified, it can be employed directly with no need of additional FE computations, resulting in fast computations. This method was employed so as to predict fatigue crack growth under variable amplitude fatigue in steels at room temperatures and correlates well with experimental data. It was also extended so as to model fatigue crack growth in a nickel base superalloy under non‐isothermal fatigue‐dwell conditions. At present, the method is being extended to mixed‐mode variable‐amplitude loading conditions.

A State‐of‐Art Review on Prediction Model for Fatigue Performance of Welded Joints via Data‐Driven Method

“…Fatigue fracture is the main failure pattern of engineering structures; thus, the study on fatigue performance of metallic materials has been a hot topic. [1][2][3] As shown in Figure 1, fatigue performance is affected by several factors (material type, service environment, temperature, stress range, residual stress, weld defects, weld geometry, plate thickness, stress ratio, welding method, joint type, loading type, etc.). [4][5][6][7][8][9][10][11][12][13][14][15][16][17] In addition, the mechanism of fatigue fracture contains a large number of nonlinear relationships and the influencing factors (IFs) that are difficult to describe quantitatively.…”