• Journal of the korean Society of Automotive Engineers
• /
• v.13 no.5
• /
• pp.42-50
• /
• 1991

According as the members and inner and outer plates of the automobile body structure have been thinned their thickness and have become high strength, each part of the body structure has been put more severe stress condition. Therefore, it has been increasingly required to improve the fatigue strength of the spot welded structures. As one of the improving methods for such problem, the author had previously proposed the method of alleviating stress concentration at nugget edge of the spot weld part and improving its fatigue strength [1]. But, because fatigue strength of the spot welded lap joint is influenced by its geometrical and mechanical factors, welding condition and etc., there needs a quantitative and systematic estimation method of them. In this report, by considering nugget edge of the spot weld part of the spot welded lap joint subjected to tensile load to the ligament crack, fatigue strength of various spot welded lap joints was estimated with the stress intensity factor (S.I.F.) K which is fracture mechanical parameter. It is known that evaluation of fatigue strength of the spot welded lap joint by the stress intensity factor (S.I.F.) K is more effective than the maximum stress $(\sigma_{ymax}$) at edge of the spot weld part on the center line of width of the plate.

• Journal of Welding and Joining
• /
• v.15 no.1
• /
• pp.55-65
• /
• 1997

The stress intensity factor has been calculated for the cracked plate subjected to remote normal stress and reinforced with a plate by symmetric spot welding. The solution was based on displacement compatibility condition between the cracked sheet and the reinforcement plate. It is shown that the results from the derived equation for stress intensity factor were agreed with previous solutions. The reinforcement effect gets better as a joining spot is closer to the crack tip and the other joining spots become nearer to the crack surface.

• Journal of Ocean Engineering and Technology
• /
• v.11 no.3
• /
• pp.20-28
• /
• 1997

The fatigue crack propagation properties and fatigue life of two kinds of Al body panel for automobile were examined experimentally by using the plate specimen and the single spot welding specimen. The fatigue limit of spot welding specimens was lower than that of a plate specimen. The fatigue limit was similar in two kinds of spot welding specimen. The shape and size of crack propagation were observed and measured on beach mark of fracture surface. The crack propagation of surface crack specimen showed almost same tendency to that of a thick plate as almost semi-elliptical. In spot welding specimen, the fatigue crack occurred in inside surface of nugget area was almost semi-elliptical. The crack growth rate can be explained using equation of stress intensity factors.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.1 s.173
• /
• pp.38-51
• /
• 2000

The study on the mechanical behavior of a spot-welded specimen is largely divided into the quasi-static overload failure analysis and the fatigue failure prediction. The main issue in an overload analysis is to examine the critical loads, thereby providing a generalized overload failure criterion. As the welding spot forms a singular geometry of an external crack type, fatigue failure of spot-welded specimens can be evaluated by means of a fracture parameter. In this study, we first present the limit loads of 4 representative types of single spot-welded specimens in terms of the base metal yield strength and specimen geometries. Recasting the load vs. fatigue life relationships experimentally, obtained here, we then predict the fatigue life of spot-weld specimens with a single parameter denoted the equivalent stress intensity factor. This crack driving parameter is demonstrated to successfully describe the effects of specimen geometry and loading type in a comprehensive manner. The suggested fatigue life formula for a single spot weld can play a key, role in the design and assessment of spot-welded panel structures, in that the fatigue strength of multi-spots is eventually determined by the fatigue strength of each single spot.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.5
• /
• pp.20-27
• /
• 1998

According as the member of the automobile body structure have been thinned their thickness and have become high strength, each part of the body structure has been put more severe stress condition. And, because fatigue strength of the spot welded lap joint is influenced by its geometrical and mechanical factors, welding condition and etc., there needs a quantitative and systematic evaluation method for them. In this study, by considering nugget edge of the spot weld part of the IB-type spot welded lap joint under tension-shear load to the ligament crack. fatigue strength of various IB-type spot welded lap joints was estimated with the stress intensity factor(S.I.F.) KIII which is fracture mechanical parameter. We could find that fatigue strength evaluation of the IB-type spot welded lap joints by KIII is more effective than the maximum principal stress ($\sigma$1max) at edge of the spot weld obtained from FEM analysis.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.22 no.3
• /
• pp.569-578
• /
• 1998

The mode I and II stress intensity factors have been calculated theoretically for the cracked plate reinforced with a plate by symmetric spot welding under remote mixed mode loading. This is the extension of authors' previous work for the reinforced cracked plate under remote normal stress. Regardless of loading types, the reinforcement effect gets better as one joining spot is closer to the crack tip and the others are closer to the crack surface, and optimum number of the joining spots can be existed. For the present model, the remote loading parallel to crack surface produces the mode I stress intensity factor.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1997.10a
• /
• pp.140-145
• /
• 1997

In case of spot-welded joints, the fatigue cracks generally originate from the weld interfaces of the neighborhood nugget tips, and propagate toward the outer surfaces of the sheets. Generally, because fatigue crack was observed in nugget around, strain gage was attached at nugget zone. Accordingly, it was very difficult to detect the generation time of fatigue crack in spot-welded joints and to measure the propagation speed of fatigue crack. We developed the non-destructive method, according to which th fatigue crack propagation rate can be quantitatively estimated by utilizing information obtained from strain gages bonded on the electrode indentations of spot welds. The results measured by real crack were compared with the data which was measured by strain gauge method in fatigue testing. And so fatigue strength was evaluated by stress intensity factor. In this study behavior of fatigue crack propagation under repeated load were considered.

• Asian-Australasian Journal of Animal Sciences
• /
• v.19 no.10
• /
• pp.1404-1408
• /
• 2006

In order to investigate the genetic marker associated with economic performance in Hanwoo (Korean Brown Cattle), proteomic approach was used. Breeding values were estimated from performance tested steers. The top 20 and bottom 19 steers based on carcass weight (CW), eye muscle area (EMA), backfat thickness (BF) and marbling score (MS) evaluation for one progeny testing period was used. Meat samples dissected from longissimus dorsi muscles were taken from the slaughter house and analyzed for two-dimensional gel electrophoresis. A total of 102 significant spots out of total 146 on each gel were detected and compared with the reference gel (synthetic gel) to be evaluated. Four candidate spots for marbling score were identified: 205, 84, 204 and 198. The study confirmed the relationship between breeding values of economic traits of Hanwoo cattle and spot intensity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.05a
• /
• pp.39-42
• /
• 2004

In the present paper, a novel systematic method using the 2-D hybrid special finite elements containing an edge crack is employed to study the fracture behaviors of laser beam spot-welds in automotive structures. 2-D hybrid special finite elements each containing an edge crack can assure the high precision especially in the vicinity of crack tips and give a better description of its singularity with only one hybrid element surrounding one crack. Therefore, the numerical modeling of the laser beam spot-welds can be greatly simplified. Some numerical examples are provided to demonstrate the validity and versatility of the proposed method. All the lap-shear, lap-tension and angle clip specimens are analyzed and some useful fracture parameters (such as stress intensity factors, the initial direction of crack growth) are obtained simultaneously.

• Journal of the Korean Society of Industry Convergence
• /
• v.7 no.4
• /
• pp.349-354
• /
• 2004

The growth mode of the Si layers which were grown on Si(111) by using Ag as surfactant were investigated by intensity oscillations of the RHEED specular spot at the different temperatures. we found that the introduction of Ag as the surfactant alters the growth mode from a three-dimensional clustering mechanism to a two-dimensional layer-by-layer growth. In the growth of Si layers on Si(111) with a surfactant Ag, At $450^{\circ}C$, RHEED intensity oscillation was very stable and periodic from early stage of deposition to 32 ML. RHEED patterns during homoepitaxial growth at $450^{\circ}C$ was changed from $7{\times}7$ structure into ${\sqrt{3}}{\times}{\sqrt{3}}$ structures. Since the ${\sqrt{3}}{\times}{\sqrt{3}}$ structure include no stacking fault, the stacking fault layer seems to be reconstructed into normal stacking one at transition from the $7{\times}7$ structure to a ${\sqrt{3}}{\times}{\sqrt{3}}$ one. We also found that the number of the intensity oscillation of the specular spot for Si growth with a surfactant Ag was more than for Si growth without a surfactant. This result may be explained that the activation energy decrease for the surface diffusion of Si atoms due to segregation of the surfactant toward the growing surface.