• 대한기계학회논문집A
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• 제25권2호
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• pp.220-227
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• 2001

The fatigue crack initiation life is studied on automotive tensile-shear spot weldment made from cold rolled carbon steel(SPC) sheet by using DCPDM and local strain approach. It can be found that the fatigue crack initiation behavior in spot weldment can be definitely detected by DCPDM system. To predict the fatigue life of spot weldment, the local stresses and strains at the potential critical region are estimated by approximate method based on Neubers rule and elastic-plastic FEM analysis. A satisfactory correlation between the predicted life obtained from Local strain approach based on Neubers rule and experimental life can be found in spot weldment within a factor of 2.

• 대한기계학회논문집A
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• 제24권12호
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• pp.2995-3002
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• 2000

The remaining life estimation for the aged components in power plants as well as chemical plants are very important beacuse mechanical properties of the components are degraded with time of service exposure in high temperature. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components nondestructive techniques are needed to estimate the degradation. In this study, test materials with 4 different degradation levels were prepared by isothermal aging heat treatment at 630$\^{C}$. And the DC potential drop method and destructive methods such as tensile, K(sub)IC and hardness tests were used in order to evaluate the degradation of 1-Cr-1Mo-0.25V steels. The objective of this study is to investigate the possibility of the application of DCPD method to estimated the material degradation, and to analyse the relationship between the electrical relationship between the electrical resistivity and the degree material degradation.

• 대한기계학회논문집A
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• 제24권3호
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• pp.794-802
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• 2000

Since the examination of CTOD problem revealed that the discrepancy among CTOD's was a matte., of definition, the relationships among parameters based on different definitions have been studied Particularly, the relationship between $\sigma$BS R-curve based on BS 7448 and R-curve based on the recently introduced $\sigma$5 parameter was investigated in this research. For the comparison, compact tension specimens of used 1Cr-0.5Mo steel, heat treated 1Cr-0.5Mo steel to mimic the new one, A12024-T6, and A12024-T351 were prepared and tested. Consequently, the relationship between $\sigma$5 and $\sigma$BS R-curves for tested materials were established by shifting the rotational center which could determined by rotation factor and ligament size.