• Journal of Welding and Joining
• /
• 제12권1호
• /
• pp.102-115
• /
• 1994

This paper is to evaluate the fatigue strength of lap joints of materials applied to LNG carrier cargo containment of GAZ-TRANSPORT(GT) type, which was welded by manual and automatic TIG welding process. The thicknesses of lapped members were 1.5mm/1.5mm or 1.5mm/0.7mm in Invar to Invar joint, and 1.5mm/8.0mm in Invar to stainless steel joint, respectively. These lap joints were mainly applied to the membrance fabrication of GT-LNG carrier. Fatigue tests of Invar/Inar lap joints were conducted under the stress ratio R=0 at room temperature. The effect of mean stress and cumulative fatigue damage on the allowable stress of Invar lap joint was evaluated on the basis of test results. Fatigue test was also conducted on Inver/Stainless steel lap joints welded by automatic TIG process without filler metals. The fatigue test of the joint was carried out under the same conditions as those of Invar/invar lap joints. The fatigue strength of the joint welded without filler metal was comparable to those welded with filler metal quoted from reference. The fatigue strength of Invar/stainless steel lap joint was only dependent on the lap throat thickness, and not on the welding process. Based on test results, the applicability of TIG welding process without filler metal in Invar/stainless steel lap joint was reviewed by controlling welding variables to assure the valid throat thickness of lap joints.

• Steel and Composite Structures
• /
• 제4권5호
• /
• pp.355-365
• /
• 2004

A new reduction method of residual stress in welding joint is proposed where welded metals are shaken during welding. By an experiment using a small shaker, it can be shown that tensile residual stress near the bead is significantly reduced. Since tensile residual stress on the surface degrades fatigue strength for cumulative damage, the proposed method is effective to reduction of residual stress of welded joints. The effectiveness of the proposed method is demonstrated by the response analysis using one mass model with nonlinear springs.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.583-588
• /
• 2002

The purpose of the study is to evaluate fracture toughness on the Laser and the electron beam welded joints of high tensile steels (HT500, HT550, HT650) by using 3-point bend CTOD and Charpy impact test. WM (weld metal) CTOD tests have been carried out using two kinds of CTOD specimen, the Laser beam welding (108mm length, and 24mm width, and 12mm thickness) and the electron beam welding (l71mm length, and 38mm width, and 19mm thickness). WM Charpy impact specimen is a standard V-notch type, and the temperature of the experiment is changed from -45 to 20 degree of centigrade. FE-analysis is also performed in order to investigate the effect of stress-strain fields on fracture characteristics. Results of the standard V-notch Charpy test are influenced by strength mis-match effect and the absorbed energy vE depends on crack path, and The transition temperature of Laser beam welded joints is more higher than that of electron beam welded joints. Results of the 3-point bend test give low critical CTOD and the crack path is in the weld metal of al specimens. These results indicate fracture toughness characteristics of the welded joints and transition temperature of HT500 are similar both a Laser beam welded joint and an electron beam welded joint. But the fracture toughness and the transition temperature of the electron beam welded joints of HT550 and HT650 are higher than those o the Laser beam welded joints.

• Journal of Welding and Joining
• /
• 제12권1호
• /
• pp.80-93
• /
• 1994

The microstructure and fractography of the friction welded joint of Al to Cu have been investigated in order to understand the formation of intermetallic compounds and their effects on the failure in tensile test of the joint. The variation of welding pressure did not affect significantly the tensile strength of joint. However, the tensile strength of joint decreaed as welding time increased. The thickness of reaction layers of welded joints was several micro-meters and mainly composed of intermetallic compounds of $CuAl_2$, $Cu_9Al_4$ and Al+$CuAl_2$. The thickness of $CuAl_2$, $Cu_9Al_4$ was increased with welding time. However, $CuAl_2$ was gradually changed to $Cu_9Al_4$ which caused the decrease of tensile strength . Even though the morphology of fractured surfaces depended upon the welding time, the failure occurred along $CuAl_2$ intermetallic compound itself or between $CuAl_2$ and $Cu_9Al_4$ in most cases.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
• /
• pp.132.2-132.2
• /
• 2005

• International Journal of Korean Welding Society
• /
• 제5권1호
• /
• pp.60-65
• /
• 2005

In the field of welding the mechanical behavior of a welded structure under consideration may be predicted via heat transfer and welding residual stress analysis. Usually such numerical analyses are limited to small regular mesh models or test specimens. Nevertheless, there is very few strength assessment of the whole structure that includes the effect of welded residual stress. The present work is based on the specialized finite element codes for the calculation of nonlinear heat transfer details and residual stress including the external load on the welded RHS (Rectangular Hollow Section) T-joint connections of the whole structure. First the thermal history of the combined fillet and butt-welded T-joint equal width cold-formed RHS are calculated using nonlinear finite element analysis (FEA) considering the quarter model of the joint. Then using this thermal history the residual stress around the joints has been evaluated. To validity the FEA result, the calculated residual stresses were compared with the available experimental results. The residual stress obtained from the quarter model is mapped to the full model and then to the whole structure model using FEM codes. The results from the FEM codes were exported to the commercial package for visualization and further analysis applying loads and boundary conditions on the whole structure. The residual stress redistribution along with the external applied load is examined computationally.

• 한국안전학회지
• /
• 제29권6호
• /
• pp.28-33
• /
• 2014

Vibro ripper worked by high frequency vibration is developed to do rock fragmentation and work of ripper is the different concept with other existing breakers. The gear box-shank welded joint of vibro ripper is very important part to deliver vibromotive force to tooth, so this part should endure high frequency vibration environments. The purposes of this study are to choose the optimal welding conditions for fatigue strength. The conditions were made using three kind of shank materials and two kind of filler metals. Shank materials are Hadox-hituf, Posten80 and AR400, and filler metals are CSF-71T and CSF-81T. The fatigue test was conducted each condition. Fracture surface was observed to estimate fracture characteristics of welded joint using SEM.

• 대한기계학회논문집A
• /
• 제30권5호
• /
• pp.481-487
• /
• 2006

Spot-welding is a widely used manufacturing method for thin-sheet components, especially in mass-production industries such as the car industry. Automobiles are often constructed by multi-lap spot welding to secure the passenger from the accident, where optimisation of the welding conditions is a major economic consideration. This research is conducted to investigate weldability characteristics with various welding conditions on the 4-lap spot welded joint of structural steel sheets in automobile. The relationship between the tensile-shear strength and the indentation depth has been investigated to propose the optimum welding conditions. The welding current and the welding time have a greater effect on the welding characteristics than the electrode force. It was found that the electrode force has a relatively close relationship with the expulsion occurrence. The design curves for optimum welding are proposed for the 4-lap spot welded joint.

• 한국정밀공학회지
• /
• 제24권2호
• /
• pp.118-126
• /
• 2007

Most of materials receive forces in use so that the characteristics of materials must be considered in system design to prevent deformation or destruction. Mechanical properties of materials can be expressed as responsible level of material itself under the exterior operation. Main mechanical properties are strength, hardness, ductility and stiffness. Currently, among major measure facilities to measure the mechanical properties, advanced indentation technique has important use in industrial areas due to nondestructive and easy applications for mechanical tensile properties and evaluation of residual stress of materials. This study is to find the optimum experimental condition about residual stress advanced indentation technique for accurate analysis of the welded joint of steel materials through indentation load-depth curve obtained from cruciform specimen experiment. Optimum selection was applied to the welded joint of real steel materials to find out non-equi-biaxial stress state and the results were compared with general residual stress analyzing method fur verification.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.1103-1108
• /
• 2003

The fatigue strength of welded joint is influenced by the welding residual stress which is relaxed depending on local stress distributed in vicinity of stress raisers, eg. under cut, overlap and blow hole. To evaluate its fatigue life the geometry of the stress raisers and the welding residual stress should be taken into account. The several methods based on notch strain approach have been proposed in order to consider the two factors above mentioned. These methods, however, have shown considerable differences between analytical and experimental results. It is due to the fact that the amount of the relaxed welding residual stress evaluated by the cyclic stress-strain relationship do not correspond with that occurred in reality. In this paper the residual stress relaxation model based on experimental results was used in order to reduce the discrepancy of the estimated amount of the relaxed welding residual stress. Under an assumption of the superimposition of the relaxed welding residual stress and the local stress, a modified notch strain approach was proposed and verified to the cruciform welded joint.