Fatigue Crack Propagation Life Calculation in Welded Joints (original) (raw)
Related papers
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.
Some Results on the Estimation of Fatigue Resistance of Welded Joints
Current fracture mechanics methods for fatigue assessment are based on long cracks behaviour, including those that consider thresholds for crack propagation. The present work aims at predicting the fatigue strength of welded joints by means of a fracture mechanics approach that takes into account the fatigue behaviour of short cracks. The methodology estimates the fatigue crack propagation rate as a function of the difference between the applied driving force (function of crack length) and the material threshold for crack propagation. The fatigue strength of butt-welded specimens transversely stressed was analysed. Experimental results from the literature were used for comparisons. Good estimations are obtained by using only the fatigue limit and the fatigue propagation threshold for long cracks that correspond to the base metal, and the applied crack driving force distribution along the crack path obtained from simple FE models. The influence of plate thickness, material and initia...
Fracture mechanics-based estimation of fatigue lives of welded joints
2013
The effects of the lack of penetration flaw and misalignment on fatigue life of cruciform welded joints made of low-alloy steel were studied experimentally and theoretically. It was found that two locations of fatigue fracture were possible under cyclic tension loading, depending on the relative magnitude of the misalignment. In the absence of misalignment, all fatigue failures occurred as a result of fatigue growth of cracks emanating from the weld root. In the presence of misalignment, fatigue life depended on the fatigue growth of cracks growing from the weld toe. It has been shown that the entire fatigue life can be modeled as a fatigue growth of cracks starting either from the weld toe or the weld root. The initial crack size was selected as a small crack characteristic for a given material, i.e., being dependent only on the material. The weight function method was used to calculate the required stress intensity factors.
Analytical vs Numerical Calculation of Fatigue Life for Different Welded Joint Regions
Tehnicki vjesnik - Technical Gazette, 2020
This research will show the analytical way of determining the remaining life of a welded joint with a fatigue crack initiated in its heat affected zone. The calculation will be divided into two stages, since the fatigue crack propagated through the heat affected zone, and then through the parent material. The analysis will be related to specimens with different fatigue properties taken into account for both regions. These calculations included a number of models, since different crack lengths were used for the heat affected zone and the parent material. There were three pairs of different HAZ vs PM fatigue crack lengths, always with the assumption that the total crack length is 5 mm, due to measuring range of the used measuring foils. The aim of this analysis was to apply method typically used in fracture mechanics in order to determine the number of cycles in a welded joint with an initiated fatigue crack, depending on a number of parameters. Obtained results were then compared to the results from the numerical analysis for the same cases. While the total number of cycles was mostly unaffected by these changes, some noticeable differences were observed between individual welded joint regions in question, the heat affected zone and the parent material.
Fatigue Life Prediction of Welded Joints?A Re-Assessment
Fatigue & Fracture of Engineering Materials and Structures, 1987
Fatigue life prediction of welded joints needs an accurate and exhaustive theoretical Fracture Mechanics characterization of weld toe crack propagation. The method proposed by Albrecht et al. leads rapidly to accurate solutions of the LEFM AK-parameter. However, non-LEFM short crack behavior within the notch (weld toe) plastic zone must be taken into account. Available information on notch fatigue is surveyed, and practical cases where short crack growth is likely to occur are identified. Based on an elastoplastic finite element analysis, the LEFM validity limits and errors resulting from the misuse of LEFM in fatigue life prediction are quantified.
A Review on Fatigue Life Estimation of Welded Joints
Metals are the most broadly utilized materials in designing structures, and a standout amongst the most well-known failure methods of metal structures is Failure due to fatigue. Although metal exhaustion has been considered for over 160 years, numerous issues still stay unsolved. In this article, a best in class survey of metal failure due to fatigue is done, with specific accentuation on the most recent improvements in fatigue life forecast techniques. The literature is reviewed by considering primarily the papers of previous 10– 15 years. All factors which affect the fatigue life of metal structures are grouped into following categories: material selection, crack initiation/propagation and different type of approaches used.
1991
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.
Determination of fatigue crack growth parameters in welded joint of HSLA steel
2011
The structural integrity and operational safety of welded pressure vessels primarily depends on the behaviour of weldments. In spite of all efforts in material production and improvements in welding techniques, including strict codes, requirements and directives, the crack occurrence in welded structures cannot be completely excluded. This is why fracture mechanics analysis is inevitable in the structural integrity assessment of all welded structures. Examples of practical application of fracture mechanics parameters in cracked pressure vessel structural integrity are considered. This paper shows the determination of parameters of the fatigue crack for constituents of welded joints produced of high strength low alloyed steel Nionikral-70 (yield strength 700 MPa). Results have shown that the position of notch and crack initiation affect the values of the stress intensity range of fatigue threshold ?Kth and parameters in the Paris' equation.
A simple expression to estimate the fatigue endurance of welded joints
MATEC Web of Conferences
A simple expression is proposed to estimate the fatigue endurance of welded joints that can be used to understand and analyze in a simple way the influence of the main geometrical, mechanical and material effects (weld geometry, local geometry, material properties, residual stresses and size of defects). The proposed expression was derived from the results of the analysis of the fatigue strength of welds studied by means of a fracture mechanics approach that takes into account the fatigue behavior of short cracks by using the resistance curve method. For that purpose numerical simulation of transversely stressed butt, T and cruciform joints were performed.