• 대한기계학회논문집
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• 제18권7호
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• pp.1664-1673
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• 1994

As a fundamental study on effects of thermal-cycles on residual stress of ceramics/metal joints, residual stresses in $Si_3N_4$/SUS304 joint specimens were measured before and single thermal-cycle by X-ray diffraction method and finite element method(FEM). The residual stress was found to increase after single thermal-cycle, which was agreeable with the results of residual stress measurement by X-ray diffraction method and residual stress analysis by finite element method. After the residual stress measurement, 4-point bending tests were performed. The relationship between the bending strength, the thermal-cycle temperature and hold time was examined. The bending strength was found to decrease with the increase of residual stress in linear relation.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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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.

• 한국정밀공학회지
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• 제20권9호
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• pp.135-141
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• 2003

MEMS structures generally have been fabricated using surface-machining method, but the interface failure between silicon substrate and evaporated thin film frequently takes place due to the residual stress inducing by the applied the various loads. And the very important physical property in the heated environment is the linear coefficient of thermal expansion. Therefore this paper studied the residual stress caused the thermal loads in the thin film and introduced the simple method to measure the trend of the residual stress by the indentation. Specimens were made of materials such as Al, Au and Cu and thermal load was applied repeatedly. The residual stress was measured by nano-indentation using AFM and FEA. The existence of the residual stress due to thermal load was verified by the experimental results. The indentation length of the thermal loaded specimens increased minimum 11.8％ comparing with the virgin thin film caused by tensile residual stress. The finite element analysis results are similar to indentation test.

• Journal of Welding and Joining
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• 제16권5호
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• pp.67-75
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• 1998

This study aimed at he experimental and finite element analytic investigation of the effect of preheating on he residual stress of weldment. In this study, an autogenous arc welding was used on type 304 stainless steel and MARC as F.E.M. common code was utilized in analysis The analyses include transient and moving heat source and thermal properties as function of temperature. During welding, the thermal cycles of four locations in the weldment were recorded to investigate of the behavior of thermal stress and residual stress. The experimental and analytic results had good coincidence and show that there are two factors influencing the formation of welding residual stress in preheat process. One is the elevation of welding equilibrium temperature and the other is the increase of amount of heat input. The former decrease welding residual stress and the latter increase welding residual stress. Therefore, the cumulative effects result in the welding residual stress not being improved significantly with preheating in 304 stainless steel.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.103-108
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• 2000

Since the ceramic/metal joint material is made at a high temperature, the residual stress development when it is cooled from bonding temperature to room temperature due to remarkable difference of thermal expansion coefficient between ceramic and metal. As residual stress at ceramic/metal joints influences the strength of joints, it is important to estimate residual stress quantitatively. In this study, it is attempted to estimate joint residual stress of $Si_3N_4/STS304$ joints quantitatively and to compare the strength of Joints. The difference of residual stress is measured when repeated thermal cycle is loaded under the conditions of the practical use of the ceramic/metal joint. And 4-point bending test is performed to examine the influence of residual stress on fracture strength. As a residual it is known that the stress of joint decreases as the number of thermal cycle increases.

• Steel and Composite Structures
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• 제17권2호
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• pp.173-184
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• 2014

This study aimed to theoretical calculate the thermal residual stress in continuous SiC fiber reinforced titanium matrix composites. The analytical solution of residual stress field distribution was obtained by using coaxial cylinder model, and the numerical solution was obtained by using finite element model (FEM). Both of the above models were compared and the thermal residual stress was analyzed in the axial, hoop, radial direction. The results indicated that both the two models were feasible to theoretical calculate the thermal residual stress in continuous SiC fiber reinforced titanium matrix composites, because the deviations between the theoretical calculation results and the test results were less than 8%. In the titanium matrix composites, along with the increment of the SiC fiber volume fraction, the longitudinal property was improved, while the equivalent residual stress was not significantly changed, keeping the intensity around 600 MPa. There was a pronounced reduction of the radial residual stress in the titanium matrix composites when there was carbon coating on the surface of the SiC fiber, because carbon coating could effectively reduce the coefficient of thermal expansion mismatch between the fiber and the titanium matrix, meanwhile, the consumption of carbon coating could protect SiC fibers effectively, so as to ensure the high-performance of the composites. The support of design and optimization of composites was provided though theoretical calculation and analysis of residual stress.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.61-64
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• 2002

Fiber reinforced metal laminate(FRML) consists of alternations layers of metal and fiber reinforced composite. The difference in the coefficients of thermal expansion between metal and composite layer produces remarkable amount of thermal residual stresses between layers. Generally, FRML shows a tensile stress in metal layers, a compressive stress in composite layers after curing. In this study, the thermal residual stresses of several types of FRML are investigated to get the best combination of metal and composite which can reduce the thermal residual stresses. The residual stress level is compared with the strength of each layers to explain the fracture mechanism of FRML.

• 한국기계가공학회지
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• 제21권6호
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• pp.50-59
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• 2022

The design of the substrate significantly affects the thermal history and the residual stress formation in the vicinity of a repaired region by a directed energy deposition (DED) process. The occurrence of defects in the repaired region depends on the thermal history and residual stress formation. The objective of this study was to investigate the influence of the inclined angle and depth of the substrate on the thermal and residual stress characteristics in the vicinity of a repaired region by a DED process through two-dimensional finite element analyses (FEAs). The temperature and residual stress distributions in the vicinity of the repaired region were predicted according to the combination of the inclined angle and depth of the substrate. The effects of the inclined angle and depth on the depth of the heat affected zone and the maximum value of the residual stress were examined. A proper combination of the inclined angle and depth of the substrate was estimated to decrease the residual stress in the vicinity of the repaired region.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1541-1550
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• 1997

Since the ceramic/metal joint material is made at a high temperature, the residual stress develops when it is cooled from bonding temperature to room temperature due to remarkable difference of thermal expansion coefficient between ceramic and metal. As residual stress at ceramic/metal joints influences the strength of joints, it is important to estimate residual stress quantitatively. In this study, it is attempted to estimate joint residual stress of Si$_3$N$_4$STS304 joints quantitatively and to compare the strength of joints. The difference of residual stress is measured when repeated thermal cycl is loaded, under the conditions of the practical use of the ceramic/metal joint. The residual stress increases at 1 cycle of thermal load but decreases in 3 cycles to 10 cycles of thermal load. And 4-point bending test is performed to examine the influence of residual stress on fracture strength. As a result, it is known that the stress of joint decreases as the number of thermal cycle increases.

• 한국분말재료학회지
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• 제1권1호
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• pp.52-59
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• 1994

Since the coefficient of thermal expansion (CTE) of matrix phase is larger about 4 times than that of W particle in tungsten heavy alloy, the thermal stresses due to the CTE difference between the two phases are induced in the alloy during heating and cooling processes. In the present study, a series of W heavy alloy containing various W particle volumes of 0 to 90% is made to investigate the residual stress taking place during cooling process. The CTE and residual stress of the series of alloy are measured by dilatometer and X-ray diffractometer. The residual stress of W particle is in compressive stress irrespective of W particle vol% and tends to increase with decreasing W particle vol% while that of the matrix phase is in tensile stress. The measured residual stress of W particle is about a third of calculated thermal stress. The influence of W particle vol% on the residual stress of W heavy alloy is discussed in terms of the deformation behaviors of W particle and matrix phase.