Analysis of Fatigue Crack-Propagation Behavior in Fillet-Welded T-Joints - Experimental-Observation of Crack-Growth Under Various Loading Conditions Helps to Develop Predictive Model (original) (raw)
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Analysis of fatigue crack propagation behavior in fillet welded T-joint
Engineering Fracture Mechanics, 1990
Using fatigue analysis, crack growth behavior in a two-dimensional welded T-joint was studied both numerically and experimentally. The geometric parameters were weld size, initial crack orientation and unsupported flange length. Crack growth direction was predicted using the minimum strain energy density factor theory. The model was compared with an inclined crack in a thin plate of finite width. The results show that even though the fillet size and initial crack orientation affected the crack growth in the early stage, the cracks tended to converge when they entered the far-field stress region. Using this observation shows the initial period of crack growth could be distinguished from the rest of the propagations. There was reasonable agreement between the predicted and the experimentally observed crack growth paths. A correlation between the crack growth rate and the driving force parameter range was obtained for a T-joint construction from hot-rolled AISI 1035 steel.
Dyna, 2014
In this paper a procedure based on the Finite Element Method and Linear Elastic Fracture Mechanics to obtain a mathematical model of crack propagation in transverse fillet welded joints is presented. We used ASTM-A36 steel plates and E6013 electrodes for the joints, using shielded metal arc welding (SMAW) as the welding process. The model uses a surface crack located in the weld toe. Differences of up to 41% in crack growth rates were found between cracks located 90% out of the bead mid plane with respect to the central crack. The straight and convex bead profiles were employed and according to the results there were no significant differences in fatigue life for both kinds of bead profiles. The results of the models were compared with conventional weld calculations and validated with experimental tests. The theoretical fatigue life values were within the statistical confidence interval for p=95%.
Fatigue crack growth of a double fillet weld
Computational Materials Science, 2008
The welded structures have a broad applicability, steel constructions, car industry, aeronautical, marine, pipelines, etc. These structures are generally subjected to cyclic requests. A simple existing defect after welding can generate a catastrophic fracture. This work studies the fatigue crack growth of a double fillet weld with the existence of a semi-elliptical crack. Two types of aluminum alloys are studied with knowing the alloy 2024 T351 and the 7075 T6. Crack growth analysis uses linear elastic fracture mechanics and related crack growth material properties to determine how fast a crack or crack-like defect will grow. Fracture mechanics is based on the concept of stress intensity (K) that describes the magnitude of both the stress and strain fields around a crack. It is computed from the stress range (Dr), and crack size (a) and crack shape (b). The effect on the fatigue life of the geometrical parameters of the crack (a/c ratio), the angle of inclination of the weld bead and the level of loading are studied. In order to predict the fatigue behavior of the welded structure, a constant amplitude loading is applied where the influence of the load ratio over the fatigue life is presented. A comparative study of fatigue crack growth of the cited aluminum alloys are detailed in order to show the effect of several parameters.
Effect of local geometrical variations on the fatigue strength of fillet welded joints
The goal of this investigation was to study the effect of local geometrical variations of the weld on the fatigue strength. Therefore the fatigue behaviour of non-load-carrying cruciform fillet welded joint under tensile loading has been studied parametrically. Several two-dimensional (2D) finite element models of the joint were analyzed using plane strain linear elastic fracture mechanics (LEFM) calculations in order to get the magnification function Mk. A maximum tangential stress criterion was used to predict the crack growth direction under mixed mode KI - KII conditions. The derived Mk solution was then applied both for continuous weld toe cracks and also for semi-elliptical toe cracks at the deepest point of the crack front. An experimental crack aspect ratio development curve was used for propagating semi-elliptical cracks. The as-welded condition was assumed with the result that no crack initiation period was considered and stress ranges were fully effective. The Paris crack...
Fatigue Analysis of Welded Joint for T-Shape Plate
International Journal of Analytical, Experimental and Finite Element Analysis, 2021
A fracture mechanics technique has been used to estimate the fatigue strength of welded joints, taking into consideration the fatigue behaviour of small fractures, in this study. An important use of this approach is to calculate the rate of crack propagation as a function of the difference between a force and the material threshold for crack propagation. For the assessment of the fatigue behaviour of notched steel plates, analytical fatigue models have been created. Outcomes have been compared with results of foreign economic activity in order to forecast service life.
Fatigue & Fracture of Engineering Materials & Structures, 2007
Residual stresses and weld defects play a major role in the fatigue behaviour of welded structures, so these effects need to be accounted for in a theoretical analysis. A simplified engineering procedure based on linear-elastic fracture mechanics is applied to estimate the fatigue behaviour, particularly the limit of endurance. Local geometrical irregularities and pre-existing flaws, which are typical for this kind of weld, are covered by an overall notch intensity factor instead of a specific stress intensity factor, so the initial flaw size is not needed explicitly in the analysis. The effect of residual stresses can be easily included. The cut-compliance method was applied to measure the residual stress distribution on the cross-section of the weld. A welded T-joint was used as a benchmark. Unexpectedly, compressive residual stresses were found to prevail in the root region. According to the analysis, they contribute to the endurance limit of the considered joint by about 50%. This result was confirmed by fatigue tests where a significant decrease in the fatigue strength after a post-weld stress relieving heat treatment was observed.
Fatigue Crack Propagation Life Calculation in Welded Joints
2009
The determination of fatigue strength of welded joint across the board hasbig draw to evaluate fatigue life of welded joints. In spite of considerable fatigue designdata which exist for welded joints in the recommendations, the studies for the effect ofcrack growth parameters C, m and initial crack length determinations of weldedstructures are still not clear and have not been discussed enough. Therefore, this paperaims to present procedures to find the FAT for welded geometries and determine initialcrack depth. The new recommended limits of FAT for new geometries not listed yet inrecommendations can be calculated according to backward calculations. Initial crackand crack growth parameter are determined
This work is part of a global study performed, among a research partnership between three industries and a research laboratory, on the development of a method which allows to better estimate the fatigue life of welded structures (armoured vehicles, ships, Floating Production Storage Off-loading units, wrecking cranes, cars …) submitted to variable loading conditions. The complexity of these structures has lead to adopt a multiscale approach, based on the use of finite element codes associated to various levels of modelling, going from the global cartography of damaged zones to the local calculation with cracks inserted in the models. The aim of this project is to develop an industrial process, avoiding successive re-meshing, being an efficient and easy tool to apply. It is also open enough to provide tools allowing the engineer to assess crack initiation, propagation until failure. The crack initiation is calculated by the use of a multi-axial fatigue damage criterion based on the local approach. Coupled with an extension of the Line Spring Method, multi-initiation of fatigue cracks in welds and through crack growth are then considered, in order to calculate the stress intensity factors for various loads and geometries. Furthermore, sets of tools were developed to predict crack bifurcation and take into account the influence of the loading history on fatigue crack growth, such as crack growth retardation effect, as a result of overloads. This approach is then applied to an overall aluminium welded structure experiment, which was designed to allow several cracks to initiate and propagate. Local micro-geometries and residual stresses were measured at weld toe, as needed for local stress calculations. Furthermore, a complete instrumentation and test of this welded structure allowed to determine precisely crack initiations and to follow crack propagation. The results are in good agreement with calculations and point out the industrial necessity to measure the local characteristics of welds and to control the quality for fatigue design.
Influence of crack on welded joint characteristics in different types of loads
Scientific Technical Review
The application of high strength steels in design of heavy duty welded structures requires data about properties in different loading conditions. Thanks to high yield stress the wall thickness can be reduced compared to mild structural steels, and accordingly welded joint cross-sections, welding consumables consumption and time for welded joints manufacturing will be minimized. This is of importance for pressurized equipment, but also for other industrial branches (cranes, excavator). Complete characterization of welded joint has to include data for parent metal, but also the properties for weld metal and the heat-affected-zone (HAZ) are necessary, at least in order to compare them with parent metal properties. This is of special importance because of heterogeneity structure in HAZ.
Determination of Some Parameters for Fatigue Life in Welded Joints Using Fracture Mechanics Method
Journal of Materials Engineering and Performance, 2010
In this work, the parameters stress intensity factor (SIF), initial and final crack lengths (a i and a f), crack growth parameters (C and m), and fatigue strength (FAT) are investigated. The determination of initial crack length seems to be the most serious factor in fatigue life and strength calculations for welded joints. A fracture mechanics approach was used in these calculations based on SIF which was calculated with the finite element method (FEM). The weld toe crack was determined to be equal to 0.1 mm, whereas the weld root crack’s length was varied depending on the degree of the weld penetration. These initial crack length values are applicable for all types of joints which have the same crack phenomenon. As based on the above calculated parameters, the new limits of FAT for new geometries which are not listed yet in recommendations can be calculated according to the current approach.