Improved computation method in residual life estimation of structural components

Abstract

This work considers the numerical computation methods and procedures for the fatigue crack growth predicting of cracked notched structural components. Computation method is based on fatigue life prediction using the strain energy density approach. Based on the strain energy density (SED) theory, a fatigue crack growth model is developed to predict the lifetime of fatigue crack growth for single or mixed mode cracks. The model is based on an equation expressed in terms of low cycle fatigue parameters. Attention is focused on crack growth analysis of structural components under variable amplitude loads. Crack growth is largely influenced by the effect of the plastic zone at the front of the crack. To obtain efficient computation model plasticity-induced crack closure phenomenon is considered during fatigue crack growth. The use of the strain energy density method is efficient for fatigue crack growth prediction under cyclic loading in damaged structural components. Strain energy density method is easy for engineering applications since it does not require any additional determination of fatigue parameters (those would need to be separately determined for fatigue crack propagation phase), and low cyclic fatigue parameters are used instead. Accurate determination of fatigue crack closure has been a complex task for years. The influence of this phenomenon can be considered by means of experimental and numerical methods. Both of these models are considered. Finite element analysis (FEA) has been shown to be a powerful and useful tool1,6 to analyze crack growth and crack closure effects. Computation results are compared with available experimental results. [Projekat Ministarstva nauke Republike Srbije, br. OI 174001]

Determination of Fatigue Crack Growth Trajectory and Residual Life under Mixed Modes

“…The minimum strain energy density theory, proposed by Sih [6], postulates that a crack propagates when the strain energy density at a critical distance reaches a minimum value. The numerical implementation of this theory can be seen in [9] to [15]. The maximum circumferential tensile stress theory was presented by Erdogan and Sih [6] based on the state of stress near the crack tip.…”

“…The first incorporates the methodologies that consider the stress or the strain as the fatigue crack growth driving force, e.g. the maximum tangential stress (MTS) criterion [6] and [7], the tangential stress factor and tangential strain factor [8], the maximum tangential strain criterion [9], etc. The second category contains the methodologies that recognize the material strain energy density as the fatigue crack growth driving force, e.g.…”

“…To this scope, the tendency of the elastic stress field to minimize the accumulated elastic strain energy (e.g. [9] to [15]) (not the energy density) is taken into account. The proposed methodology differs from the previous methodologies in the following points: a) The factor controlling the mixed-mode crack propagation is the accumulated energy, while in the above works [10] to [16] it is the accumulated energy density; and b) The criterion for the prediction of the path of the mixed-mode fatigue crack propagation is…”

Some aspects of computation methods in strength analysis of flight structures

“…In a lug-type joint, the lug is connected to a fork by a single bolt or pin. Generally, the structures which have the difficulty in applying the fail-safe design need the damage tolerance design (Edwards and Davenport 2006;Fielding 1999;Maksimovic 2012;Maksimovic K. еt al. 2011).…”

“…To determine residual life of damaged structural components two crack growth methods are used here: (1) conventional Forman`s crack growth method and (2) crack growth model based on the strain energy density method. The last method uses the low cycle fatigue properties in the crack growth model (Maksimovic 2012). In Figures 1 and 2 representative structure of helicopter and aircraft are shown in which presented computation procedures can be used.…”