Continuum approach to fatigue crack initiation and propagation in welded steel joints

Analysis of fatigue crack growth under spectrum loading – The UniGrow fatigue crack growth model

Two-dimensional elastic or elasto-plastic models dominate the current fatigue crack growth assessment and life prediction procedures for plate components with through-the-thickness cracks. However, as demonstrated in many theoretical and experimental papers, the stress field near the crack tip is always three-dimensional and, as a result, the fatigue crack front is not straight. It is normally curved towards the plate faces. Over the past few years there were a number of very careful numerical studies focusing on the evaluation of fatigue crack front shapes. However, the application of the direct numerical techniques to fatigue phenomena is a very tedious and time consuming process and, sometimes, it is quite ambiguous. In the current paper we develop a simplified method for the evaluation of the front shapes of through-the-thickness fatigue cracks. Further, we validate the developed method against experimental results, investigate the influence of various parameters on the crack front shapes at stable (steady-state) propagation and analyse the differences in the results of fatigue crack growth evaluation obtained with two- and three-dimensional approaches.

A simplified method for the evaluation of fatigue crack front shapes under mode I loading

This work proposes an improved mechanical driving force parameter for crack growth analysis. The proposed parameter investigates fatigue crack growth FCG under constant amplitude loading, considering the influence of residual stress distribution near the crack tip. A 2D FE Analysis is developed in order to compute the stress distribution in the vicinity of the crack tip with in the framework of elastic-plastic fracture mechanics (EPFM). Elastic stress intensity factors are computed using both analytical solution and the extended finite element method (XFEM). Residual stress intensity factors are determined using the weight function through numerical analysis. The authors estimate the residual fatigue crack growth life of 7075-T6 Aluminum alloy attachment lugs with single through-thickness crack under various loading conditions. Moreover, a comparison with the available experimental data is performed. It is proved that this improved mechanical parameter so-called residual-corrected stress intensity factor can better predict fatigue life with a greater accuracy compared with experimental results.

Prediction of fatigue life by crack growth analysis

Fatigue strength assessment of initial semi-elliptical cracks located at a hole

https://uwaterloo.ca/centre-advanced-materials-joining/sites/ca.centre-advanced-materials-joining/files/uploads/files/1_s_mikheevskiy_2012.pdf

Analysis of fatigue crack growth in an attachment lug based on the weight function technique and the UniGrow fatigue crack growth model

A generalised step-by-step procedure for fatigue crack growth analysis of structural components subjected to variable amplitude loading spectra has been presented. The method has been illustrated by analysing fatigue growth of a planar corner crack in an attachment lug made of Al7050-T7451 alloy. Stress intensity factors required for the fatigue crack growth analysis were calculated using the weight function method. In addition, so-called “load-shedding” effect was accounted for in order to determine appropriate magnitudes of the applied stress intensity factors. The rate of the load shedding was determined with the help of the FE method by funding the amount of the load transferred through the cracked ligament. The UniGrow fatigue crack growth model, based on the analysis the material stress-strain behaviour near the crack tip, has been used to simulate the fatigue crack growth under three variable amplitude loading spectra. The comparison between theoretical estimations and experimental data proved the ability of the UniGrow model to correctly predict fatigue crack growth behaviour of two-dimensional planar cracks under complex stress field and subjected to arbitrary variable amplitude loading. BASICS OF THE UNIGROW FATIGUE CRACK GROWTH MODEL The UniGrow fatigue crack growth model, proposed by Noroozi and Glinka [1], is based on the idea that the fatigue process near cracks and notches is governed by highly concentrated strains and stresses in the notch/crack tip region. Therefore, the fatigue crack growth can be subsequently considered as a process of successive crack increments resulting from material damage in the tip region. In addition the two parameter driving force postulated by Vasudevan et.al [2] was also incorporated. It was postulated that the real material can be modeled as a set of elementary particles or material blocks of a finite dimension, ρ*. The assumption of the elementary material block implies that the actual stress-strain and fatigue response of the material near the crack tip is such as the crack had a blunt tip with the radius of ρ*. Therefore, the usual notch stress-strain analysis techniques can by applied in order to determine

D. Algera

Papers

Analysis of fatigue crack growth in an attachment lug based on the weight function technique and the UniGrow fatigue crack growth model

Fatigue crack growth analysis of structural components – the UniGrow two-parameter driving force model