Fillet-welded Joints Research Articles

Determination of welding deformation in fillet-welded joint by means of numerical simulation and comparison with experimental measurements

Fillet weld is the most common weld type used in the fabrication of structural members in shipbuilding, automobile and other industries. Fillet-welded joints usually suffer from various welding deformation patterns, such as longitudinal shrinkage, transverse shrinkage, angular distortion and longitudinal bending. Welding deformation has negative effects on fabrication accuracy, external appearance and various strengths of the welded structures. In this study, experiments are performed to investigate the characteristics of welding deformation in the fillet-welded joint. In order to precisely predict welding deformation by numerical method, a 3-D thermal elastic plastic finite element computational procedure is developed. The simulated results are in a good agreement with the experimental measurements. The influence on welding deformation of the flange thickness is investigated by experiment and numerical simulation. In addition, the generation mechanism of angular distortion is clarified through numerical simulation.

Preliminary Study of Improvement of Fatigue Properties of Welded Joints by Plasma Spray Process

The addition of a low modulus coating by a spray process was used to improve the fatigue properties of a fillet-welded joint. Fatigue tests were performed on TIG welded cruciform joints in 1Cr18Ni9Ti stainless steel under stress ratio R = 0, in the as welded, flame sprayed, and plasma sprayed conditions. These showed that the plasma spray process was effective in increasing the fatigue strength of the cruciform welded joints, but flame spraying was less effective. In particular, the fatigue strength of the as welded joints was increased by 26 % with plasma sprayed coating, but by only 10 % with the flame sprayed coating. The corresponding increases in fatigue life were 1.58~9.62 for the plasma sprayed specimens compared with 1.55~1.97 times for the flame sprayed specimens. Finite element stress analysis showed that the stress concentration factor at weld toe of the spray coated specimens was much decreased. It also confirmed that the stress perpendicular to the interface between the spray coating and base metal was greater than the adhesion strength of the flamed-sprayed coating, which resulted in the coating near the weld toe peeling off during the fatigue tests. As a result, the fatigue life of the flame sprayed specimens was lower than that of the plasma sprayed ones.

Assessment of fatigue strength of weld root in ship structure: an approximate procedure

The paper presents results of analysis of weld root-initiated crack growth conditions in a cruciform fillet-welded joint. The focus was on assessment of conditions for crack propagation in a boxing fillet-welded joint. An approximate procedure is developed which allows evaluating initial part of fatigue process in a boxing fillet-welded joint where the crack is controlled by the stress field emanated from the slit tip. The crack traversing the weld bead at the attachment ending is regarded as a design criterion. A comparison of simulated and experimental data is given which may be regarded favorable for the approach when the crack growth is controlled mostly by the elastic stress field in weld material.

Fatigue life assessment of load-carrying fillet-welded cruciform joints inclined to uniaxial cyclic loading

This study examines, the relationship between the direction of an applied stress cycle and the fatigue behaviour of load-carrying fillet-welded cruciform joints with weld root cracks, and presents the fatigue life assessment of the joints. Fatigue tests were performed on four sets of cruciform joints inclined at an angle of 0, 15, 30, or 45° to the normal direction of the uniaxial cyclic loading. Fatigue cracks propagated perpendicularly to the stress direction, and formed a flat plane or multiple propagation planes according to the inclination angles. The fatigue crack propagation rate may be estimated by only the mode I stress intensity factor of an inclined through crack assumed in this study. The fatigue life can be evaluated by the stress range at the weld throat in the normal direction to the inclined crack propagation, irrespective of difference in the inclination angle.

Fatigue behaviour of load-carrying, fillet-welded, cruciform joints with plates of different thickness

Large numbers of fillet-welded cruciform joints are extensively employed at the connection zones of steel structural members because of their superiority from consideration of ease of construction and economy. Where this welded cruciform joint becomes a load-carrying type, the fatigue fracture starting point will be either at the weld toe zone, the root zone or both, so the fatigue behaviour becomes complex. In particular, when root fracture takes place, the fatigue strength is low compared with other welded joints and also it is difficult to detect by means of non-destructive inspection at the initial stage of crack occurrence; consequently there are some cases where fatigue becomes a problem.

Fatigue strength evaluation of load-carrying cruciform fillet-welded joints made with mild steel plates of different thickness

This study examined the fatigue behavior of load-carrying cruciform fillet-welded joints made with mild steel plates of different thickness. Fatigue tests were carried out on four types of welded joint, made from two 6-, 9-, 14-, or 25-mm thick main plates and one 6- or 14-mm thick cross plate. The fatigue strength was also analyzed using linear elastic fracture mechanics on 34 parametric models simulating welded joints with different plate thicknesses. From the experimental and analytical results, the effects of the thickness ratio of the main plates and the change in cross plate thickness on fatigue strength were evaluated.

溶接材料の相変態挙動を利用した溶接継手の残留応力低減効果に関する検討―溶接時における温度・ミクロ組織・熱応力履歴の数値シミュレーションとその応用に関する研究 （第２報）―

Residual stress in welded joints by using a new weld metal with the property of low-temperature phase transformation is numerically analyzed. 10 % Nickel and 10 % Chromium are involved in the developed welding material for producing the property of martensitic phase transformation at a low temperature and for generating compressive residual stress. A fillet-welded joint between plate and stiffener is used for the numerical simulation of the thermal elastic-plastic finite-element analysis with coupling phase transformation effect. Moving heat source is considered by using the gradual deposition of the finite-element during welding process. Distribution of the computed residual stress mostly agrees with the measuring values by strain gauge. Compressive residual stress distributes in the weld metal for both longitudinal and transverse directions with weld line. The effects of the material of weld metal and welding pass sequence on residual stress are then investigated. Residual stresses on the weld toe and root are improved lower by using the low-temperature transformation weld wire than the conventional one, regardless of the sequence of welding deposition. It is found that the weld metal with property of low-temperature phase transformation is effective to reduce residual stress near weld metal.

Analysis of non-loading carrying fillet welds joint using SGBEM

Fatigue failure is probably the most common type of failure in welded construction. It is usually initiates at a stress concentration area within the structure. The fatigue behavior of non-load carrying cruciform fillet welded joint has been studied extensively using boundary element method. The symmetric boundary element method for multiple cracks problem is derived using Betti's reciprocal theorem in auxiliary fictitious state. High order element is proposed to solve the double integrals. The analysis demonstrates that symmetrical Galerkin boundary element method (SGBEM) can be used effectively for analyzing non-load carrying fillet welded cruciform joints containing any number of surface and embedded cracks. The stress intensity factor and the magnification factors Mk are analyzed. General formulation for this kind of fatigue life estimation is derived for engineering design purpose. The fatigue life estimate results are consistent with the code of practice and those of other researchers. This can provide a good method for engineering design under fatigue loading conditions.

Fatigue Strength of CP Grade 2 Titanium Fillet Welded Joint for Ship Structure

Titanium is suitable for the material of ship hull structures because of its high specific strength responding to highspeed demanding and high corrosion resistance in marine environment. In Japan, CP titanium plates have been already used for the structural members of fishing boats. However, there is no application of the structural members of merchant or government ships where the authorized standard is strict, because there is no suitable rule or recommendation for welded built-up titanium plate structures. Additionally, there is little research concerned with the fatigue strength of titanium fillet welded joints that are indispensable to ship structure. In this study, for promoting the development of titanium ships, the fatigue tests of butt-welded joints, transverse fillet welded joints and longitudinal fillet welded joints were carried out. As a result of mentioned above, the effectiveness of the fatigue strength of steel was investigated for designing on the safety judgment of titanium-welded joints. Good correlation was achieved between the fatigue test results obtained from three types of welded joint relevant to ships that fail from the weld toe, using a modified version of the equivalent stress defined in MIL-HDBK-5. Furthermore, similar results were obtained for base metal failure.

Effect of Grooving on Static Strength of Fillet Welded Joint for Ship Structure under Compressive Stress Condition applied by bending moment

Corrosion of structural members of ships is one of the main problems for ship safety.In this report effect of grooving on static strength of corroded fillet welded joints for ship structure is investigated with experimental result and FEM analysis. Four points bending test was conducted with half size model specimen of hold frame of Cape-size bulk carrier. It is mainly obtained that in case of grooving in compressive stress region applied by bending moment, at fillet welded joint, maximum load occurs at lateral deflection of web plate and grooving width and grooving depth effects maximum load. When the size of compressive stress region is small at grooving part of fillet welded joint effect of grooving on static strength is not observed.

A Study on Static Strength of Corroded Fillet Welded Joints for Ship Structures

Corrosion of structural members of ships is one of the main problems for ship safety. In this report static strength of corroded fillet welded joints for ship structure is investigated with experimental result using actual materials taken from old ships and corrosion-simulated specimens. Tensile strength, bending strength, parallel shear strength and normal shear strength of corroded fillet welded joints are obtained. Size-ratio of web-thickness to throat-thickness of weld-bead is an important factor for fracture mode, that is, web fracture and weld-bead fracture, of corroded fillet welded joints. And also failures of hold frames in bulk carriers are discussed with result of this study.

A probabilistic damage tolerance concept for welded joints. Part 1: data base and stochastic modelling

The present paper presents the necessary crack growth statistics and suggests stochastic models for a reliability analysis of the fatigue fracture of welded steel plate joints. The reliability levels are derived from extensive testing with fillet-welded joints for which the entire crack growth history has been measured, not only the final fatigue life. The statistics for the time to reach given crack depths are determined. Fracture-mechanics-derived crack growth curves are fitted to the measured experimental curves and the best fit defines the growth parameters involved for each test specimen. The derived statistics and distribution function for these parameters are used as variables in a Monte Carlo simulation (MCS). In addition a Markov model is developed as an alternative stochastic model. It is a Markov chain for which the discrete damage states are related to chosen crack depths in the material. This model works directly with the experimental time statistics. It is a “stochastic bulk approach” not involving any random variables or fracture mechanics modeling. Both models are fitted to the data base and scaled to in-service conditions. Both methods are compared and discussed. The aim is to provide data for the variables used in a MCS and to develop a Markov chain for fast reliability calculation, especially when predicting the most likely influence of numerous future inspections.

Residual Stress Reduction and Fatigue Strength Improvement by Controlling Welding Pass Sequences

The effects of residual stress on fatigue strength at a weld toe in a multi-pass fillet weld joint were evaluated. The residual stresses in the weld joints were varied by controlling the sequence of welding passes. The residual stress at the weld toe was 80 MPa in the specimen whose last welding pass was on the main plate side, but it was 170 MPa in the specimen whose last pass was on the attachment side. The fatigue strength was nearly the same at high stress amplitude for both specimens, but the fatigue strength of the specimen whose last weld pass on the main plate was higher than that of the other specimen at low stress amplitude. This difference is due to the magnitude of the initial residual stress and the relaxation of the residual stress under fatigue cycling. The effects of the residual stress were shown in a modified Goodman diagram, in which residual stress is treated as a mean stress. [S0094-4289(00)01701-1]

Fatigue crack initiation point in load carrying fillet-welded cruciform joints

Summary Load carrying fillet-welded cruciform joints have two fatigue crack initiation points. They are located in the weld toes and weld roots where high stress concentrations occur. Which of the two serves as the initiation point depends on the weld leg length, plate thickness, and weld penetration, and the mechanism concerned is easily understood. Some experimental results indicate that the fatigue crack initiation point is also affected by the magnitude of the stress range. The reason for this phenomenon remains rather obscure. To establish this reason, the present research study is intended to clarify the relationship between the stress range level and fatigue crack initiation point changes and to quantify the effects of the weld leg length and penetration depth on the fatigue crack initiation point. Fatigue tests of welded joint specimens, thermal elastic-plastic finite element method (FEM) analyses of welding residual stresses and fatigue crack propagation analyses considering the residual stress are performed.

Influence of Corrosion Wastage on the Fatigue Strength of Fillet Welded Joints

Fatigue tests on fillet welded joints were carried out using test specimens simulating reduced plate thickness and reduced fillet weld due to corrosion wastage to investigate the influence of corrosion wastage on the fatigue strength of fillet welded joints. The results of the tests and the related studies are summarized below.It was observed that in cruciform fillet welded joints, the tensile fatigue strength of test specimens with reduced plate thickness decreased considerably compa'red to the tensile fatigue strength of sound specimens. In side fillet welded joints, the shearing fatigue strength of test specimens with reduced plate thickness decreased considerably compared to the shearing fatigue strength of sound specimens. Stress analysis of test specimens was carried out using solid model. The maximum stress arised in the root of the fillet weld at the central part of the width of the plate in cruciform fillet welded joints, and also in the root of the fillet weld at the end of center side of the test specimen in side fillet welded joints. The position where the maximum stress arised almost coincided with the position where the crack occurred in fatigue tests.Rules related to thickness of web plate and leg length of fillet weld of hold frames in large bulk carriers were amended in view of the marine casualties to these ships. From the results of fatigue tests, it was concluded that considerable improvement may be anticipated, as a result of the amendments to rules, in the fatigue strength of fillet welded joints in which corrosion wastage has progressed.From the results of studies on measured data of plate thickness, it was observed that the variation in initiation life and progress rate of corrosion wastage in structural members of hull was considerable in several cases. Accordingly, it is very important to carry out timely maintenance after carefully studying and evaluating the status of corrosion wastage in order to prevent hull damage due to corrosion wastage.

Improvement of Fatigue Strength through Residual Stress Reduction by Controlling the Sequence of Welding Pass.

The effects of residual stress on fatigue strength at a weld toe in multi-pass fillet-welded joints were evaluated. The residual stresses in the specimen were varied by controlling the sequence of welding passes. The residual stress at the weld toe was 80 MPa in the specimen whose last welding pass was on the main plate, but it was 170 MPa in the specimen whose last pass was on the attachment. The fatigue strength of the specimens was nearly the same at high stress amplitude, but the fatigue strength of the specimen whose last welded pass on the main plate was larger than that of the other specimen at low stress amplitude. This difference is due to the magnitude of the initial residual stress and the relaxation of the residual stress under the cyclic loading. The effects of the residual stress were shown in the modified Goodman diagram, in which residual stress is treated as a mean stress.

すみ肉溶接継手の曲げ疲労強度に及ぼす板厚および残留応力の影響 : 荷重非伝達すみ肉溶接継手の曲げ疲労き裂の発生・進展に及ぼす板厚および残留応力の影響(第2報)

すみ肉溶接継手の曲げ疲労強度に及ぼす板厚および残留応力の影響 : 荷重非伝達すみ肉溶接継手の曲げ疲労き裂の発生・進展に及ぼす板厚および残留応力の影響(第2報)

Improvement of fatigue strength of fillet-welded joints by water jet treatment of weld toe region

Summary This paper describes an investigation of improvement of the fatigue strength of non-load-carrying cruciform fillet welded joints through the kinetic energy of an abrasive water jet being applied to the weld toe region at a nozzle travel speed of 30 cm/min. An FEM analysis, measurements of the residual stress and hardness in the toe region, and 0-tension fatigue tests of the fillet welds were performed to analyse fatigue strength improvement. Fatigue failures invariably occurred in the toe region. The results obtained may be summarised as follows: 1. Suitable water jet treatment makes the fatigue limit of the water jet treated joints (W07538, W05010, W10038-3, W07538-3, W10038, W07525 series) some 1.6–2.0 times (180–224 M Pa) better than that of corresponding as-welded joints to give an improvement effect next behind TIG dressing and hammer peening. 2. This fatigue strength improvement is attributable to a decrease in the tensile residual stress, a hardness increase, and a decrease in the stress concentration factor in the toe region depending on the water jet treatment conditions. 3. The single-pass W07538 and W05010 joints have the highest fatigue limit (around twice that of the as-welded joints). The stress concentration factor in the toe region being higher than that of the as-welded joints, however, suggests that the kinetic energy of the water jet was in these cases set too high. The overall improvement of the fatigue limit is due to the fact that water jet treatment increases the hardness and exerts a compressive residual stress effect on the joints. 4. The triple-pass W07538-3 and W10038-3 joints have a fatigue limit around 1.8 times that of the as-welded joints. This is due to the fact that the values of the maximum stress concentration factor Ktmax and maximum hardness HVmax produce more stable fatigue strength improvement conditions. The fatigue strength can also be expected to be improved by the hardness increase and compressive residual stress effect through a maximum three passes being concentrated in the toe region.

Estimation Method of Residual Stress Distribution and Fatigue Life Takaing the Effect of Welding Procedure Sequence into Consideration in Welded Build-up Structures

It is known that fatigue strength is affected by stress concentration depended on local shape of weld toe and welding residual stress. Fatigue strength of welded build-up structures decreases considerably because there are large tensile residual stresses and stress concentration at the fatigue crack initiation part in these structures.Authors showed that fatigue strength of the corner boxing joints and continuous fillet weld joints with load carrying girder increases very much by turning the tensile residual stress to compressive ones. Flame line heating on appropriate part enables to change the residual stress distribution. These results show that residual stress has a considerable influence on fatigue strength of welded build-up structures.Residual stress at the fatigue crack initiation part depends on welding procedure sequence near this part. Because the change of welding sequence means the change of thermal cycle given into this part by welding.The purpose of this paper makes clear the effect of welding procedure sequence on residual stress distribution and fatigue strength. Two different welding sequence specimens which have continuous fillet weld joints with load carrying girder were used. One of fatigue crack initiation part is the toe of final welding. The other is different part from final welding.Residual stress and fatigue life was investigated by using these specimens. Moreover, the estimation of residual stress distribution taking the welding sequence into consideration was carried out by using elastic finite element analysis based on inherent stress method.As a result of these investigations and analyses, it is clear that welding sequence has a considerable influence on residual stress distribution and that fatigue strength can be enhanced considerably by changing of welding sequence.

A study on cold cracking susceptibility in high strength steel fillet weld joints

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