• Journal of the Korean Geotechnical Society
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• v.16 no.6
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• pp.35-41
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• 2000

Residual stress is defined as a minimum stress with a large displacement of specimens and the residual stress after peak shear stress appears with displacement volume but there is no provision to select the residual stress. In the previous study, residual stress was recorded when the change of shear load is small in the condition of the strain more than 15%. But, in this study, hyperbolic function((No Abstract.see full/text), b=experimental constant) of soil test is adapted to joint of rock and the propriety is investigated. In a landslide and landsliding of artificial slope, wedge failure of tunnel with a large displacement, tests are simulated from peak stress to residual stress for safety analysis. But now. direct shear stress and triaxial compressive tests are usually performed to find out characteristics of shear stress about joint. Although these tests get a small displacement, that data of peak stress and residual stress are used for safety analysis. In this study, we tried to determine failure criteria for joints of rock using ring shear test machine. The residual stress following shear behavior was determined by the result of ring shear test and direct shear test. In conclusion, after comparing the results of the two test, we found that cohesion(c) and internal friction angle(ø) of ring shear test are 30% and 22% respectively of those of the direct shear test.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.2
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• pp.26-33
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• 1997

In this study effect of residual stress and its redistribution in weldment on the fatigue crack propagation was investigated. Fatigue tests were conducted by the center notched specimens machined with welded plate. The residual stress and its redistribution after the crack growth were measured by the magnetizing stress indicator and hole-drilling method. Fatigue crack propagation was estimated by the specimens having residual stress redistributed after the cracks growth and having the effects of crack closure. Crack growth rates were predicted and compared with experimental results. It had been found that the predicted crack propagation rates have a good agreement with experimental results when the redistribution of residual stress was considered.

• Journal of Welding and Joining
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• v.5 no.1
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• pp.73-80
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• 1987

During PWHT, it is well known that residual stress in weld HAZ is one of the reasons for PWHT embitterment. In case of static loading, it was experimentally found that fracture toughness of weld HAZ was dependant upon PWHT conditions. However, the effects of PWHT on fatigue behavior are not clearly verified. Therefore, in this paper, the effects of heating rate PWHT conditions and residual stress simulated in weld HAZ of Cr-Mo steel on fatigue crack propagation behavior were evaluated by fatigue Testing and SEM observation. The obtained results are summarized as follows; 1. Applied stress($10 Kgf/mm^2$) in weld HAZ during PWHT tneded to decrease fatigue strength and to increase fatigue crack growth rate. 2. Applied stress and slow heating rate of 60.deg. C/hr during PWHT contributed to precipitin of impurity elements as well as carbide, which promoted the fatigue crack growth. 3. Fatigue crack growth rate decreased at the heating rate of 220.deg. C/hr in contrast with 600.deg. C/hr and 60.deg. C/hr.

• Journal of Welding and Joining
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• v.10 no.4
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• pp.250-258
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• 1992

In order to clarify the mechanical behavior of welding crack and to evaluate the mechanical characteristics of welded parts in thick plate, it is very important to accurately predict the welding deformation and residual stress including transient state before welding. In this paper, the theory of a three-dimensional elasto-plastic problem for the analysis of mechanical phenomenon of welding joint on the plate is developed into an efficient and accurate method based on the finite element method, and then several examples are considered by using the proposed model. The results of numerical analyses are discussed in the viewpoint of the mechanical characteristics of the distribution of three-dimensional welding residual stresses, plastic strains and their production mechanism on the thick plate.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.2
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• pp.219-225
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• 2011

Silicone resin is recently used as encapsulant for high-power LED module due to its excellent thermal and optical properties. In the present investigation, finite element analysis of cure process was attempted to examine residual stress evolution behavior during silicone resin cure process which is composed of chemical curing and post-cooling. To model chemical curing of silicone, a cure kinetics equation was evaluated based on the measurement by differential scanning calorimeter. The evolutions of elastic modulus and chemical shrinkage during cure process were assumed as a function of the degree of cure to examine their effect on residual stress evolution. Finite element predictions showed how residual stress in cured silicone resin can be affected by elastic modulus and chemical shrinkage behavior. Finite element analysis is supposed to be utilized to select appropriate silicone resin or to design optimum cure process which brings about a minimum residual stress in encapsulant silicone resin.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1328-1336
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• 2004

According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt-welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.108-113
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• 2004

According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt~welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• Journal of the Korean Society of Safety
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• v.9 no.3
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• pp.13-21
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• 1994

Effects of tensile and compression residual stresses in the welded SS41 and A17075-76 on fatigue crack propagation behavior are investigated when a crack propagates from residual stresses region. We propose the fatigue crack growth equation on tensile and compression residual stresses in welded metal. The results obtained in this experimental study are summarized as follows . 1 ) A fatigue crack growth equation which applied fatigue fracture behavior of the welded metal is proposed. (equation omitted) where, $\alpha$, $\beta$, ${\gamma}$ and $\delta$ are constants, and R$_{eff}$ is effective stress ratio [R$_{eff}$=(Kmin+Kres)/(Kmax+Kres)], Kcf is critical fatigue stress intensity factor. The constants are obtained from nonlinear least square method. The relation between crack length and number of cycles obtained by integrating the fatigue crack growth rate equation is in agreement with the experimental data. 2) The experimental results confirmed that the cause of crack extension and retardation by residual stresses has relation to the phenomenon of crack closure. 3) The relaxing trend of residual stresses by the crack propagation was greater In case of compressive residual stress than that of tensile residual stress in the welded metal.tal.

• International Journal of Automotive Technology
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• v.7 no.1
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• pp.69-74
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• 2006

Residual stresses are introduced in aluminum cylinder head during quenching at the end of the T6 heat treatment process. Tensile residual stress resulted from quenching is detrimental to fatigue behavior of a cylinder head when it is overlapped with stresses of engine operation load. Quenching simulation has been performed to assess the distribution of residual stress in the cylinder head. Analysis revealed that in-homogeneous temperature distribution led to high tensile residual stress at the foot of the long intake port, where high stresses of engine operation load are expected. Measurements of residual stress have been followed and compared with the calculated results. Results successfully proved that high tensile residual stress, which was large enough to accelerate fatigue failure of the cylinder head, are formed during quenching process at the end of heat treatment at the same critical position. Effect of quenching parameters on the distribution of residual stress in cylinder head has been investigated by choosing different combination of heat treatment parameters. It was demonstrated that changes of quenching parameters led to more homogeneous temperature distribution during cooling and could reduce tensile residual stress at the critical region of the cylinder head used in this study.

• Journal of Ship and Ocean Technology
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• v.11 no.2
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• pp.26-33
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• 2007

For the assessment of the retardation of fatigue crack propagation behavior due to overload, new FE analysis algorithms considering compressive residual stress redistribution near crack tip was proposed in this paper. The size of plastic zone near crack tip was obtained by elasto-plastic analysis and it was compared with Irwin's equation. The amount of residual stress redistribution was assessed by subsequent elasto-plastic analysis, and the difference of residual stress distributions between constant amplitude load and overload was obtained. In the analysis of fatigue crack propagation, the applied SIF range was evaluated by ASTM E647, and the effect of residual stresses on crack propagation was considered using the effective SIF concept. The test results of crack propagations were compared with the predicted data obtained by the analysis.