Fatigue of engineering structures under combined nonproportional loads: An overview

Abstract

Nonproportionality in fatigue is a matter of loading sequences acting on structures. In such loading cases, a life assessment‐based search of the initiation site is required. This means that for a variety of potential sites, their stress‐strain sequences must be determined and the corresponding fatigue lives have to be calculated. For the determination of local stress‐strain sequences, a superposition of the action of loads at all times for all potential sites must be performed. The superposition has not only to be performed at a particular time of a load reversal but also for a sufficiently large number of intermediate points in time. For the assessment of crack initiation under local nonproportional stress‐strain sequences, a multiaxial fatigue damage hypothesis must be specified. Due to the superiority with respect to accuracy, critical plane approaches are the favourite ones when dealing with nonproportional fatigue of ductile metals. For describing fatigue crack growth, the time sequences for the stress intensity factors corresponding to the 3 opening modes must be obtained by superposition. A mixed‐mode hypothesis must be applied to predict both the direction and the increment of crack growth at each crack front point. A first prediction trial should be based on an appropriate extension of the maximum tangential stress hypothesis. An application of a variant of the maximum shear stress hypothesis might be an amendment. Especially in the case of crack turning, the consideration of crack face contact is mandatory.

Plastic Zone Radius Criteria for Crack Propagation Angle Evaluated with Experimentally Obtained Displacement Fields

“…One can see in Figure 2 that the crack orientation of the PZ changes from perpend ular to the tensile stress, mode I, to parallel to the shear stress, mode II. Therefore, a rameter, M [9,28], is used to tell whether the crack growth is dominated by the tens mode or the shear mode, as shown in Equation ( 7). One can see in Figure 2 that the crack orientation of the PZ changes from perpendicular to the tensile stress, mode I, to parallel to the shear stress, mode II.…”

“…However, in the case of mixed-mode loading, factors such as plasticity [4], crack interlocking, crack rugosity [5], trapped debris [6], and crack tip vicinity to defects [7], among others, may affect the crack growth rate and crack path (CP). Thus, CP prediction is not entirely understood [1,2,4,5,[8][9][10]. According to [11], the more kinked the crack is, the more crack growth might be retarded.…”

A physics-guided modelling method of artificial neural network for multiaxial fatigue life prediction under irregular loading

“…With a quantity of uniaxial fatigue experimental data, the semi-empirical Basquin-Coffin-Manson (BCM) equation provides a widely accepted relationship between strain amplitude and fatigue life [4,5]. Based on the BCM equation, a series of fatigue damage parameters [6][7][8][9][10] derived from strain and stress characteristics are proposed to make an equivalent damage calculation to predict multiaxial fatigue life. Notably, some parameters are calculated through critical plane methods and have gained significant attention [9,11,12].…”

Observations and modelling of non-proportional mixed mode cyclic loading

“…4 before the contents are summarized. For a comprehensive access to the subjects of non-proportionality and mixed mode loading please see some recently published overview articles [6][7][8].…”