• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.167-170
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• 2003

Thermal elastic-plastic analysis was performed to assess the initial residual stress distribution of welded joints considering temperature dependent material properties. The test model was the idealized boxing fillet specimen, frequently appeared in the joints of longitudinal and transverse members of ship structure. Residual stress relaxations due to external loads were analyzed by subsequent elastic-plastic analysis considering loading and unloading steps, and the characteristics of residual stress relaxations were discussed with the levels of external loads. Additionally, to define the fatigue life of crack initiation and propagation, the S-N data for each crack length were appraised.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.401-408
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• 2009

This study is performed to check the three dimensional characteristics of residual stress in the dissimilar metal weld. Although two dimensional analysis has been widely used for the assessment of weld residual stress, it has limitations to understand the stress distribution of the third direction. 3-D analysis was done to understand residual stress distribution of the welded plate. A simple butt-welded plate was considered to show the stress variation on all direction. A mock-up plate weldment was fabricated with SA-508 and F316L, which are widely used in nuclear power plants. The analysis results were validated with the measured values in the mock-up.

• Proceedings of the KWS Conference
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• 1999.05a
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• pp.233-236
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• 1999

The welding residual stress should be considered in fatigue stress analysis because it develope during the process of the electric resistance spot welding and it causes bad affect on the fatigue crack initiation and growth at nugget edge of spot welded points. Therefore the accurate estimation of residual stress is crucial. In this study, nonlinear finite element analysis on welding residual stress generated during the process of the spot welding was conducted, and their results were compared with the experimental data measured by X-ray diffraction method. From the results, it was found that welding residual stress existed as tension in the nugget center and as compression around the nugget edge.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.390-398
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• 2001

Welding process generates distortion and residual stress in the weldment due to rapid heating and cooling. Welding distortion and residual stress in the welded structure result in many troubles such as dimensional inaccuracies in assembling and safety problem during service. The accurate prediction of welding residual stress is thus very important to improve the quality of weldment and find the way to reduce itself. This paper suggests new analysis method to predict welding residual stress by considering solid phase transformation during welding process. Using the method, analysis is performed for medium and low carbon steel. The analysis result for medium carbon steel reveals that case considering phase transformation has compressive residual stress in contrast with the case neglecting phase transformation because of martensite formation. However, for the case of low carbon steel, residual stress shows little difference between the case considering phase transformation and the other case, because it has small transformation strain and recovers rapidly stress after phase transformation.

• The Journal of Korean Medicine
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• v.20 no.1 s.37
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• pp.44-51
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• 1999

Analysis of residual pesticides in herbal drugs was performed by GC-ECD and GC-MS. Especially, selected ion monitoring(SIM) technique was applied to increase the GC/MS sensitivity. Analysis of residual pesticides was determined sensitivity and selectively without any internal standard by setting the SIM technique to their characteristic fragments for quantitation ion and confirmation ion. The combination of two detector, GC-ECD and MS-SIM technique, is abailable for determining a multiclass residual pesticides in herbal drugs. The average recoveries through the method were $65.9%{\sim}99.7%$ in herbal drugs. The data of gas chromatographic analysis was compared with the limits of residual pesticides in herbal drugs and agricultural foods. 4. 4-DDT was detected above the limits to the residual pesticides in herbal drugs. Diazinon and EPN were detected, but the limits of residual pesticides were less than that of agricultural foods.

• International Journal of Korean Welding Society
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• v.1 no.2
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• pp.51-60
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• 2001

A prediction method for determining the welding residual stress by artificial neural network is proposed. A three-dimensional transient thermo-mechanical analysis has been performed for the $CO_2$ arc welding using the finite element method. The first part of numerical analysis performs a three-dimensional transient heat transfer analysis, and the second part then uses the results of the first part and performs a three-dimensional transient thermo-elastic-plastic analysis to compute transient and residual stresses in the weld. Data from the finite element method are used to train a back propagation neural network to predict the residual stress. Architecturally, the fully interconnected network consists of an input layer for the voltage and current, a hidden layer to accommodate the failure mechanism mapping, and an output layer for the residual stress. The trained network is then applied to the prediction of residual stress in the four specimens. It is concluded that the accuracy of the neural network predicting method is fully comparable with the accuracy achieved by the traditional predicting method.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.5 s.182
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• pp.149-154
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• 2006

The cold expansion method (CEM) is one of the widely used a method to improve the fatigue behavior of materials in aerospace industry. Such improvement is due to the compressive residual stress developed when a tapered mandrel goes through the fastener holes a little smaller than the mandrel. CEM is retarded of crack initiation due to the compressive residual stress developed on the hole surface. Many researchers are studied a finite element analysis of residual stress around fastener hole. But in case of real model, fastener hole has a clamping force after CE. Therefore, it is respected that residual stress distributions should be changed due to clamping forces. In this paper, it was performed finite element analysis of residual stress by clamping force after CE in the plate having adjacent holes. From this study, it has been found that compressive residual stress near the hole increases according to clamping force. Also, the more increase clamping force, the more increases compressive residual stress. However, tensile residual stress increase beyond clamping force area.

• Journal of Welding and Joining
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• v.21 no.7
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• pp.71-77
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• 2003

In this study, an investigation based on the superposition principle to predict residual stress redistribution caused by crack propagation itself initially through residual tensile stress field was performed by finite element method. The tendency in residual stress redistribution caused by crack propagation recognized both from the analytical results and experimental result was the residual stress concentration consecutively occurred in the vicinity of crack tip even the situation that the crack propagated to the region initially residual compressive stress existed. The software for the analysis is ABAQUS, which is a general purpose finite element package. The analytical method that attempt to take the plastic deformation at the crack tip due to tensile residual stress into the consideration of residual stress redistribution caused by crack propagation was proposed. The plastic zone size at the tip of fatigue crack and redistributed residual stresses were calculated by finite element method on the bases of the concept of Dugdale model. Comparing these analytical results with experimental results, it is verified that the residual stress redistribution caused by crack propagation can be predicted by finite element method with the proposed analytical method.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.04a
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• pp.245-251
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• 1999

As the crack grows in the residual stress fields, the distribution of the residual stress is changed. In this study, a finite element modeling technique is developed to simulate the redistribution of residual stress due to crack propagation. To certify the accuracy, the crack propagation tests were carried out and tile effective stress intensity factor range was evaluated considering the redistribution of residual stress from the FE analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.820-823
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• 2002

MEMS structures Generally have been fabricated using surface-machining, but the interface failure between silicon substrate and evaporated thin film frequently takes place due to difference of linear coefficient of thermal expansion. Therefore this paper studied the effect of the residual stress caused by variable external loads. This study did not analyzed accurate quantity of the residual stress but trend for the effect of residual stress. Several specimens were fabricated using other material(Al, Au and Cu) and thermal load was applied. The residual stress was measured by nano-indentation using AFM. The results showed the existence of the residual stress due to thermal load. The indentation area of the thermal loaded thin film reduced about 3.5% comparing with the virgin thin film caused by residual stress. The finite element analysis results are similar to indentation test.