• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2342-2354
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• 2002

The present study has numerically predicted both the flow -induced and thermally-induced residual stresses and birefringence in injection o. injection/compression molded center -gated disks. Analysis system for entire molding process was developed based on an ap propriate physical modeling including a nonlinear viscoelastic fluid model, stress-optical law, a linear viscoelastic solid model, free volume theory for density relaxation phenomena and a photoviscoelasticity and so on. Part I presents physical modeling a nd typical numerical analysis results of residual stresses and birefringence in the injection molded center-gated disk. Thermal residual stress was found to be extensional near the center, compressive near the surface and tend to become toward tensional at the surface. A double-hump profile was obtained across the thickness in birefringence distribution: nonzero birefringence is found to be thermally induced, the outer peak is due to the shear flow and subsequent stress relaxation during the filling stage a nd the inner peak is due to the additional shear flow and stress relaxation during the packing stage. Predicted birefringence including both the flow -induced and thermally-induced one becomes quite similar to the experimental one.

• Journal of Korea Foundry Society
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• v.10 no.5
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• pp.399-407
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• 1990

The effect of thermal cycling and isothermal exposure on the high temperature microstructural stability of unidirectionally solidified $Al-CuAl_2$ eutectic composite has been studied. A coarsening procedures of lamellar eutectic structures were initiated at growth fault region because of diffusion through low angle boundary at this region. It was considered that thermally induced residual stresses produced by thermal cycling were high enough to increase the dislocation density in Al-rich matrix phase. However, it was also considered that dislocations generated by these high thermal stresses were annihilated at high temperature by stress relaxation. Consequently, the thermal cycling up to 1440 cycles between 20 and $520^{\circ}C$ did not affect the microstructural stability.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.539-542
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• 2008

Recently, GMP(Glass Molding Press) process is mainly used to produce aspheric glass lenses. Because glass lens is heated at high temperature above Ty (yielding point) for forming glass, the quality of aspheric glass lens is deteriorated by residual stresses which are generated in a aspheric glass lens after forming. Before this study, as a fundamental study to develop forming conditions for progressive GMP process, compression, strain relaxation and thermal conductivity tests were carried out to obtain the visco-rigid plastic, the visco-elastic and thermal properties of K-PBK40 which is newly developed and applied for precision molding glass material, In this study, using the experimental results we obtained, a glass lens forming simulation in progressive GMP process was carried out and we could forecast the shape of deformed glass lenses and residual stresses contribution in the structure of deformed glass lenses after forming.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.106-111
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• 2000

The residual stresses in molded plastic parts can be divided into the flow induced residual stresses produced in flowing stages and the thermally induced residual stresses produced in cooling state. Reducing residual stresses in the final parts is one of the goals in recent study. The present study focused on comparing the predicted values for thermal residual stresses in freely and constrained quenched plastic plates with and without free volume theory. As a result the final residual stresses showed the opposite pattern in thickness direction. furthermore by applying free volume theory the predicted residual stress at the center showed about 50% of the values without free volume theory for constrained quenched case.

• Corrosion Science and Technology
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• v.14 no.4
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• pp.161-165
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• 2015

This paper presents an analysis of thermal stress induced along the interface between a polymeric coating layer and a steel substrate as a result of uniform temperature change. The epoxy layer is assumed to be a linear viscoelastic material and to be theromorheologically simple. The viscoelastic boundary element method is employed to investigate the behavior of interface stresses. The numerical results exhibit relaxation of interface stresses and large stress gradients, which are observed in the vicinity of the free surface. Since the exceedingly large stresses cannot be borne by the polymeric coating layer, local cracking or delamination can occur at the interface corner.

• Journal of Mechanical Science and Technology
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• v.14 no.1
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• pp.19-29
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• 2000

A viscoelastic finite element analysis is presented to investigate residual stresses occurred in a laminated cylindrical shell during cure. An incremental viscoelastic constitutive equation that can describe stress relaxation during the cure is derived as a recursive formula which can be used conveniently for a numerical analysis. The finite element analysis program is developed on the basis of a 3-D degenerated shell element and the first order shear deformation theory, and is verified by comparing with an one dimensional exact solution. Viscoelastic effect on the residual stresses in the laminated shell during the cure is investigated by performing both the viscoelastic and linear elastic analyses considering thermal deformation and chemical shrinkage simultaneously. The results show that there is big difference between viscoelastic stresses and linear elastic stresses. The effect of cooling rates and cooling paths on the residual stresses is also examined.

• Journal of Ocean Engineering and Technology
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• v.11 no.1
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• pp.113-123
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• 1997

The welding residual stresses produced by welding frequently cause a crack and promote stress corrosion etc. in heat affected zone contained with external load and weakness of material. For the purpose pof relaxation of welding residual stress, post welding heat teratment(PWHT) is widely used. In this paper, the computer program which is based on Thermal-Elasto-plastic-creep theory for plane deformation on developed by finite element method (F.E.M) and verified its propriety by experimental measurement and also by using the developed computer program. The mechanical behavior of butt welding joint is clairfied during PWHT.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.479-485
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• 2006

The residual stress changes on thermo-mechanical loading in the interface region of the Thermal Barrier Coating (TBC)/Thermally Grown Oxide (TGO)/Bond Coat (BC) were calculated on the TBC-coated superalloys using a Finite Element Method (FEM). It was found that the residual stress of the interface boundary was dependent upon mainly the oxide formation and the swelling rate of the oxide by creep relaxation. During an oxide swelling, the relaxation of residual stress which is due to creep deformation increased the TBC's life. In the case of the fine grain size of TGO scale, the TBC stresses piled up by oxide swelling could be relaxed by diffusional creep effect of TGO.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.95-100
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• 2004

An analysis using FEM simulation was conducted to predict residual stresses and birefringence in simple compressed cylindrical glass as a preliminary part of the optimum design determination of optical lenses. The FEM simulation with the Maxwell viscoelastic constitutive model was used to predict thermal induced residual stresses and birefringence during the compression test considering stress relaxation. Also the linear photoelastic theory was introduced to calculate birefringence from the residual stress state. The simulation results were in good agreement with deformation and birefringence distribution in the existing experimental result.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.509-514
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• 2004

An analysis using FEM simulation was conducted to predict residual stresses and birefringence in simple compressed cylindrical glass as a preliminary part of the optimum design determination of optical lenses. The FEM simulation with the Maxwell viscoelastic constitutive model was used to predict thermal induced residual stresses and birefringence during the compression test considering stress relaxation. Also the linear photoelastic theory was introduced to calculate birefringence from the residual stress state. The error of simulation results between experimental results in the birefringence value at the center of glass specimen is $4.2\%$, and the error in the maximum radius of deformed glass specimen is $1.2\%$. The simulation results were in good agreement with deformation and birefringence distribution in the existing experimental result.