• International Journal of Korean Welding Society
• /
• v.2 no.1
• /
• pp.57-61
• /
• 2002

This paper presents development of a SEC(Solar Energy Concentration) utilizing the concentrated solar beam radiation for joining engineering thermoplastics such as Acrylonitrile/Butadiene/Styrene(ABS), Polycarbonate(PC) and Polymethylmethacrylate (PMMA). In addition, to study the joining of the materials, necessary experimentation with applying primer was performed. Tensile tests were conducted to determine the bond strength achieved at the specimen Joint interface. Microscopic examinations of the fractured joints were performed in order to analyze the overall bond quality. Finally, the results in terms of bond strength achieved at the joint interface and energy consumed in the process was compared with those obtained with similar thermoplastic joining technique utilizing microwave energy.

• Journal of Welding and Joining
• /
• v.25 no.2
• /
• pp.43-48
• /
• 2007

Laser Transmission Joining (LTJ) of plastics is a process in which light of suitable wavelength is transmitted through a transparent substrate that is in contact with an absorbing one. In this paper, LTJ is investigated by preliminary experiments from the viewpoint of mechanical engineering. To understand transmitting characteristics of each polymer substrate, transmission rate, reflection rate and absorption coefficient of polymer are measured by using a laser power-meter. Characteristics of joining in the spot welding and seam welding are investigated by measuring the fracture load. Fracture load increases in accordance to the laser power and irradiation time. However, when the laser power is over 60W and irradiation time over 4seconds, fracture load decreases. This phenomenon is probably due to heat-softening of materials. Besides, cavities are generated at a joint by evaporation of water molecules, which can be suppressed by introduction of a gap between two substrates.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.12 no.1
• /
• pp.58-64
• /
• 2003

A mechanical press joining was investigated in ender for joining A1-5052 sheets for automobile body weight reduction. Static tensile and fatigue tests were conducted using tensile-shear specimens for evaluation of fatigue strength of the joint. During Tox joining process for A1-5052 plates, using the current sheet thickness and punch diameter, the optimal applied punching force was found to be 32 kN under the current joining condition. For the static tensile-shear experiment results, the fracture mode is classified into interface fracture mode, in which the neck area fractured due to influence of neck thickness, and pull-out fracture mode due to influence of plastic deformation of the joining area. And, during fatigue tests for the A1-5052 tensile shear specimens, interface failure mode occurred in the region of low cycle. The fatigue endurance limit approached to 6 percents of the maximum applied load, considering fatigue lifetime of $2.5\times10^6$ cycles.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.681-687
• /
• 2002

The cumulative, shrinkage plastic strains and their distributions in the weld joint after completion of the welding process determine welding-induced distortion. Although the weldment undergoes many complex physical and metallurgical changes during welding, only the material plastic temperature range and its cooling history below this temperature range influence the [mal state of the cumulative shrinkage plastic strains. In addition, for structural welds, these plastic strains are uniform, except in the arc start and stop regions, along the weld. Therefore, the plastic strain-based "inherent shrinkage model" is effective and accurate to describe welding-induced distortion. This paper presents the theoretical background and numerical verification of this root cause.

• Journal of Welding and Joining
• /
• v.27 no.5
• /
• pp.34-41
• /
• 2009

Thermal and mechanical characteristics in dissimilar SS400-STS304 steel weldment have been investigated by 3D thermal elastic-plastic analysis. Moreover, the influence of welding residual stresses on the mechanical behaviour of this welded joint, by applying superimposed external load (tension load) was determined. The residual stresses obtained by numerical simulation were compared with the experimentally measured results. The FE results were in good agreement with the measured values. The mechanical test (hardness, tensile test) and metallurgical analysis was carried out to ensure the weld integrity. Hence, possibility of applying SS400-STS304 dissimilar steels in industries has been established.

• Journal of Welding and Joining
• /
• v.21 no.7
• /
• pp.49-58
• /
• 2003

It has been well known that ductile fracture of steel is accelerated by triaxiality stresses. The characteristics of ductile crack initiation in steels are evaluate quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameter, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of geometrical heterogeneity and strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on critical condition to initiate ductile crack using two-parameter. Then, the crack initiation testing were conducted under static and dynamic loading. To evaluate the stress/strain state in the specimens especially under dynamic loading, thermal elastic-plastic dynamic FE-analysis considering the temperature rise was used. The result showed that the critical global strain to initiate ductile fracture in specimens with strength mismatch under various loading rate cu be estimated based on the local criterion, that is two-parameter criterion obtained on homogeneous specimens under static tension, by mean of FE-analysis taken into account accurately both strength mismatch and dynamic loading effects on stress/strain behavior.

• Journal of Welding and Joining
• /
• v.26 no.1
• /
• pp.56-62
• /
• 2008

In this paper, elastic and plastic adhesion index was very important in deciding adhesive characteristics and varying elastic and plastic index, dimensionless load and pull-off force were analyzed and simulated. Finally, using AFM, experimental surface roughness parameters of substrates and pull-off force between tip and substrates were produced. Using these values, pull-off forces were calculated and were compared with experimental pull-off forces. Through simulation and experiment, it was found that interaction of asperity also had very important influence on adhesive contact.

• Journal of Welding and Joining
• /
• v.21 no.4
• /
• pp.75-79
• /
• 2003

The welding distortion of a hull structure in the shipbuilding industry is inevitable at each assembly stage. This geometric inaccuracy caused by the welding distortion tends to preclude the introduction of automation and mechanization and needs the additional man-hours for the adjusting work at the following assembly stage. To overcome this problem, a distortion control method should be applied. For this purpose, it is necessary to develop an accurate prediction method which can explicitly account for the influence of various factors on the welding distortion. The validity of the prediction method must be also clarified through experiments. For the purpose of reducing the weld-induced bending deflection, this paper proposes the plastic counter-deforming method (PCDM) using the line heating as the optimum distortion control method. The validity of this method has been substantiated by a number of numerical simulations and actual measurements.

• Journal of Welding and Joining
• /
• v.8 no.4
• /
• pp.69-75
• /
• 1990

In this paper, ultimate compressive strength of TMCP 50HT steel plates (yield stress .sigma.$_{o}$=36kg/mm$^{2}$) with HAZ softening is studied. Finite element method formulated by the author is applied to analyze the elasto-plastic large deflection behaviour of the plates. The influence of HAZ softening breadth, welding direction and slenderness ratio on the ultimate compressive strength is investigated. The results obtained are summarized as 1) With the increasing of the HAZ softening breadth, early plasticity on the plates is formed and then the ultimate compressive strength is decreased, in which about 8% of the ultimate strength for the plate with h/t=4(h: HAZ softening breadth, t: plate thickness) was reduced comparing with no HAZ softening. 2) The large decrease of the ultimate strength for the case that the welding direction is normal to the loading direction is occurred than the case that the welding direction is parallel to the loading direction. 3) The influence of HAZ softening on the ultimate compressive strength is serious for thick plates, while it may be negligible for thin plates.s.

• Journal of Welding and Joining
• /
• v.23 no.3
• /
• pp.34-39
• /
• 2005

It is required for the steel materials used in the sour environment to have sufficient resistance to hydrogen induced cracking(HIC). For line pipe steels, HIC resistance could be varied during pipe making process due to the large plastic deformation applied in the thick-wall pipe. In order to figure out such effect, HIC tests were performed not only in the plate condition but in the pipe condition and their results were compared in terms of cracking ratio. Test results demonstrated a detrimental effect of plastic deformation to HIC resulting in a substantial increase in the cracking ratio after pipe forming process. All of the cracks found in the pipe material were located in the outer layer of pipe where the tensile strain was resulted during pipe forming stage. In order to understand the HIC resistance of the pipe but in the plate condition, it was suggested to pre-strain the plate to some extent before the HIC test.