Fracture mechanics-based estimation of fatigue lives of welded joints (original) (raw)
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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.
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.
Fatigue Design of Cruciform Joints including V-notch Effect at the Weld Toe
Procedia Materials Science, 2014
The present paper proposes a new and more accurate fatigue life prediction model for fillet welded joints in steel subjected to constant amplitude loading. With the traditional fracture mechanics approach, the greatest difficulty when computing the fatigue life of a welded detail is to determine the initial crack size a 0 . The classical way to determine the stress intensity factor K (SIF) is by using the following formula a T a g K
Crack Propagation in Cruciform Welded Joints : Study of Modern Analysis
2011
This thesis is investigating how the effective notch method can be used for fatigue assessment of welded joints. The effective notch method is based on a finite element analysis where the joint is modeled with all notches fictitiously rounded with a radius of 1 mm. Analyses are performed on a cruciform fillet welded joint where parameters such as, load case, steel plate thickness and weld size, are varied. The achieved lifetime estimations are then compared to calculations with other fatigue assessment methods, linear elastic fracture mechanics and the nominal method. The goal is to draw conclusions about pros and cons of the effective notch method. The results are also compared to experimental fatigue tests performed on the same geometry. The results indicates that the effective notch method tends overestimating the lifetime, especially when the steel plate thickness is small. This leads to a non conservative method that is dangerous to use as guidance when designing. The estimations are though better when considering a toe crack then when considering a root crack.
Advanced Materials Research, 2015
Analysis of fracture toughness of high-strength low alloyed steel, Nionikral-70, welded joint constituencies, subjected to variable load is given in this paper, using two parameters. Crack initiation resistance is determined by testing of endurance limit and by designing of Wöhler curves. Crack propagation resistance is determined by testing of crack growth rate, and accordingly determination of Paris equation parameters. Analysis of fracture toughness is given based on testing results, comparing obtained values for base metal, weld metal and heat affected zone.
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...
Experimental examination of fatigue life of welded joint with stress concentration
Frattura ed Integrità Strutturale
This paper presents results of experimental examinations of stress concentration influence to fatigue life of butt welded joints with K-groove, produced from the most frequently used structural steel S355J2+N. One group of experiments comprised examinations carried out on the K-groove specimens with stress concentrators of edged notch type. Specimens with short cracks (limited length of initial crack), defined on the basis of the experience from fracture mechanics by the three points bending examinations, have been examined according to standard for the determination of S-N curve, and aimed to determine fatigue strengths for different lengths of initial crack and Relationship between fatigue strength and crack length. Other group of experiments comprised examinations of specimens with edge notch, prepared in accordance with ASTM E 399 for three points bending, in order to establish regularity between crack growth and range of exerted stress intensity factor aimed to determine resistance of welded joint to initial crack growth, namely fatigue threshold (ΔK th).
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.
Fatigue behavior of welded joints Part 2: Physical modeling of the fatigue process
Welding Journal, 2006
The fatigue process in fillet welded joints is discussed and modeled. As a first approximation, a pure fracture mechanics model was employed to describe the entire fatigue process. The model is calibrated to fit the crack growth measurements obtained from extensive testing on fillet weld joints where cracks emanate from the weld toes. Emphasis is laid on the choice of growth parameters in conjunction with a fictitious initial crack size distribution in order to obtain both reliable crack growth histories and predictions of the entire fatigue life. The model has its shortcomings in describing the damage evolution at low stress ranges due to the presence of a significant crack initiation period in this stress regime. As an alternative to the fracture mechanics model, a two-phase model (TPM) for the fatigue process was developed and calibrated. The number of cycles to crack initiation was modeled by a local strain approach using the Coffin-Manson equation, whereas the propagation phase...