• Proceedings of the KWS Conference
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• v.43
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• pp.275-277
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• 2004

Fictitious notch radius approach is based on the Neuter's microstructural support hypothesis which assumes that fatigue crack is governed by highly stressed volume of the material right on the weld toe area rather than the surface stress at a pin point of weld toe area. Variety of successes have been achieved in applying this methodology to the fatigue of welded joint, hence, it became one of recommended design procedure in IIW's recommendation as well as many ship classification societies. 1mm fictitious notch radius approach was applied to the various fatigue problems of welded joints in this study covering the effect of weld size, notch stress calculation for 3D geometry and low cycle fatigue problem. It was found that fictitious notch radius approach fumed out to be very effective and accurate in dealing with fatigue strength of welded joint.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.252-254
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• 2004

Fatigue life a box weldment was predicted with the stress concentration and residual stress using the equation reported. In order to change the stress concentration and residual stress of the box weldment, Post treatments such as smooth grinding of weld bead, weld toe grinding and hammer peening were applied. The fatigue life of the weldment after post treatment clearly increased, which is attributed to the reduction of stress concentration and/or introduction of compressive residual stress at the weld toe. The predicted fatigue life was a relatively good agreement with the experiment for a long fatigue life, while it was underestimated for a short fatigue life.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.4
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• pp.133-141
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• 1996

The mode of fatigue failure is depended on the characteristics of the fatigue crack initiated and propagated from the weld toe and the weld root in the load-carrying fillet welded joints. The characteristics of fatigue crack are deeply affected by the geometry of fillet and the stress range. The purpose of this study is to investigate critical weld size and stress range in order to occur toe failure under pulsating tension loading in the load-carrying fillet welded cruciform joints.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.396-398
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• 2005

At present, fatigue design of welded structures is primarily based on nominal stress or hot spot stress approach with a series of classified weld S-N curves. However, these methods are known to possess drawbacks, such as difficulty associated with defining proper nominal stress and the finite element sue sensitivity etc. Recently, a mesh-size insensitive structural stress definition is proposed by Battelle that gives a stress state at weld toe with relatively large mesh size. The structural stress definition is based on the elementary structural mechanics theory and provides an effective measure of a stress state in front of weld toe. As an experimental validation of the structural stress method in obtaining the fatigue strength of weldments, a series of experiment is carried out for various sizes of weldments. Based on the result from this study, it is expected to develop a more precise fatigue strength evaluation technique and to save time period required in the fatigue design of ship and offshore structures.

• Journal of Ocean Engineering and Technology
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• v.22 no.2
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• pp.58-64
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• 2008

Large-scale tests of welded tubular K-joint sunder balanced in-plane bending braces were carried out to observe the fatigue behavior of the API 2W Gr.60 steel plate produced by POSCO. Toe grinding and weld profiling were used to improve the fatigue life of a tubular K-joint. The effects of the steel grade and chord wall thickness on the fatigue life were also investigated. The present results were compared with the UK DEn design curve.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.3
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• pp.1-7
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• 1996

The stress concentration factor gives the significant effect the fatigue strength of welded joints. The model used herein is the type of the load carrying fillet welded cruciform joint with full or partial penetration. In order to obtain the stress concentration factor at the weld toe of fillet joint, the reasonable element size of the toe part is investigated and the stress analysis for the series models by FEM under tensile load is performed. On the basis of the calculation results, the estimated formulae for the stress concentration factor(Kt) at weld toe part of the fillet welded joint, which the effect of toe radius, flank angle and other parameters are taken into account, is derived.

• Journal of the Korean Institute of Gas
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• v.16 no.4
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• pp.16-22
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• 2012

The use of welding process has been increased for manufacture of machine, bridges, ships, gas facilities and so on together with development of welding technique. Accordingly, it has been needed to develop the welding methods considering higher productivity and safety design for manufacture of their welding structures. In this study, it was studied basically on characteristics of fatigue strength and fatigue life in full penetrated cruciform fillet weld zone in relation to material thickness, welding passes, loading direction and notch radius of toe zone. Most of fatigue failure occurred in toe zone of cruciform fillet weld joint. Fatigue strength and fatigue life are under the influence of stress concentration due to notch radius and flank angle of toe zone. The metal of toe zone annealed and diffused by multi-layer welding and acicular ferrite structure formed by the result improved fatigue strength and fatigue life.

• Journal of Welding and Joining
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• v.3 no.2
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• pp.52-63
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• 1985

Fillet welded joints, specially in ship structure, are well known the critical part where stress concentrate or crack initiates and grows. This paper is concerned with the study of the behavior of fatigue crack growth t the root and toe of load carrying cruciform fillet welded joints under three points bending by the determination of stress intensity factor from the J-Integral, using the Finite Element Method. The stress intensity factor was investigated in accordance to the variation of the weld size (H/Tp). weld penetration (a/W) and plate thickness (2a'/Tp). As mixed mode is occurred on account of shearing force under the three points bending, Stern's reciprocal theory is applied to confirm which mode is the major one. The main results may be summarized as follows 1) The calculation formula of the stress intensity factor at the both of root and toe of the joint was obtained to estimate the stress intensity factor in the arbitrary case. 2) The change of stress field around crack tip gives much influence on each other at the roof and toe as H/Tp decreases. 3) Mode I is a major mode under the three points bending.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.839-844
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• 2007

In order to reduce resultant stress of the connection detail of longitudinal and rib and floor beam, in this study, the parameter studies for the reinforcement details as the bulk head and the vertical rib were preformed with FE analysis. As the result, it was shown that reinforcement detail with the bulk head plate in longitudinal rig reduced generally the principal stress at the connection detail, but the stress concentration of the weld toe parts occurring fatigue crack increased. However, it was known that the reinforcement detail with the vertical rib in the rib is more effective than the bulk head plate of the reduction stress concentration in the weld toe parts.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.60-62
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• 2005

The purpose of this study is to evaluate the effect of spot heating on the fatigue strength at the weldment. To do this, the transitional behavior of residual stress at the weld toe induced by spot heating was identified using FEA and experiment. The amount and distribution of residual stress at the weld toe strongly depends on the locations of spot heating. Based on the results, the proper spot heating condition was established. The fatigue strength of the spot-heated specimen increases compared with as-welded specimen.