• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1995년도 가을 학술발표회 논문집
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• pp.178-184
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• 1995

A new combined isotropic/kinematic and orthotropic hardening viscoplastic model is proposed which can account for not only differential orientations but also preferred orientations of grains in n metal at finite plastic deformations with an introduction of multiple spin (rate of rotation) concept within the general framework of the model, the effects of anisotropy and constitutive spins will be discussed in conjunction with a closed-form solution for simple shear in n rigid-plastic material, which will be used to simulate experimental data of Montheillet, et al. (1984) for fixed-end tortion tests at finite plastic deformations.

• Journal of Mechanical Science and Technology
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• 제17권3호
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• pp.400-408
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• 2003

A study on the progressive inelastic deformation behavior of the 316 L stainless steel cylindrical structure with plate-to-shell junction under moving temperature front was carried out by structural test and analysis. The structural test intends to simulate the thermal ratcheting behavior occurring at the reactor baffle of the liquid metal reactor as free surface of hot sodium pool moves up and down under plant transients. The thermal ratchet load that heats the specimen up to 550$^{\circ}C$ was applied repeatedly and residual deformation was measured. The thermal ratcheting test was carried out with two types of cylindrical structures, one with plate to-shell junction and the other without the junction to investigate the effects of the geometric discontinuities on the global ratcheting deformation. The temperature distributions of the test specimens were measured and were used for the ratcheting analysis. The ratchet deformations were analyzed with the constitutive equation of the non-linear combined hardening model. The analysis results were in good agreement with those of the structural tests.

• 대한조선학회논문집
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• 제49권3호
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• pp.232-238
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• 2012

The effects of temperature on the structural behavior of polar class vessels have been experimentally and numerically investigated. Experiments were carried out on single frame structures made of steel material, DH36, which is used for outer shell of the vessels making transit through the polar region. A knife edge type striker was dropped down onto single frame structures. The temperatures of the single frames were set to $-30^{\circ}C$, $-50^{\circ}C$ and room temperature. The deflection around the mid-point of the single frame was measured and numerically simulated using finite element model. Strain rate effect on the structural behavior has been investigated and turned out that the strain rate effect can be neglected. From the results of the experiment and numerical analyses, it has been noticed that the permanent deflection at lower temperature was reduced due to a temperature hardening of material as expected.

• 대한기계학회논문집A
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• 제21권1호
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• pp.104-111
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• 1997

Accounting for the additional damages come out from non-proportional loading path effect, material damage according to crystal structure dependence was studied. Microscopic observations of damaged material by SEM(Scanning Electron Microscope) showed crystal structure dependence. Biaxial in-phase loaded specimens showed the slips of same direction, which pararell each other, but biaxial 90.deg. out-of-phase loaded specimens showed multiply crossed slips. S. H. Doong and D. F. Socie reported that wavy/planar or planar slip material showed the increase in the cyclic hardening level during non-proportional cycling. From these results, the additional hardening and non-proportional loading effects were related with slip mechanism, and the slip mechanism was related with crystal structure. In the present study, a damage mechanism which accounts for the non-proportional loading effect from crystal structure dependence was considered and applied to A17075-T651.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.427-733
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• 2003

Adiabatic shear bands have been observed in the serrated chip during high strain rate metal cutting process of medium carbon steel and titanium alloy. The recent microscopic observations have shown that dynamic recrystallization occurs in the narrow adiabatic shear bands. However the conventional flow stress models such as the Zerilli-Armstrong model and the Johnson-Cook model, in general, do not predict the occurrence of dynamic recrystallization (DRX) in the shear bands and the thermal softening effects accompanied by DRX. In the present study, a strain hardening and thermal softening model is proposed to predict the adiabatic shear localized chip formation. The finite element analysis (FEA) with this proposed flow stress model shows that the temperature of the shear band during cutting process rises above 0.5T$\sub$m/. The simulation shows that temperature rises to initiate dynamic recrystallization, dynamic recrystallization lowers the flow stress, and that adiabatic shear localized band and the serrated chip are formed. FEA is also used to predict and compare chip formations of two flow stress models in orthogonal metal cutting with AISI 1045. The predictions of the FEA agreed well with the experimental measurements.

• International Journal of Precision Engineering and Manufacturing
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• 제8권4호
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• pp.56-62
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• 2007

An analytical method to predict the post-weld deformation at the heat-affected zone (HAZ) is presented in this paper. The method was based on the assumption that the post-weld deformation is caused by external forces resulting from the inherent strain, which is defined as the irrecoverable strain after removing structural restraints and loadings. In general, the equivalent loading method can be used to analyze distortions in welding areas because it is efficient and effective. However, if additional loads are applied after welding, it is difficult to determine the final strain on a welded structure. To determine the final strain of a welded structure at the HAZ more accurately, we developed a modified equivalent loading method based on the inherent strain that incorporated hardening effects. The proposed method was applied to calculate the residual stress at the HAZ. Experiments were also conducted on welded plates to evaluate the validity of the proposed method.

• 한국정밀공학회지
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• 제29권4호
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• pp.395-408
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• 2012

An experimental investigation with 2.8kW Nd:YAG laser system was carried out to study the effects of different laser process parameters on the microstructure and hardness of STD11. The optical lens with the elliptical profile are designed to obtain a wide surface hardening area with uniform hardness. The Laser beam is allowed to scan on the surface of the work piece varying the power (1600, 1800 and 1900kW) and traverse speed (200, 400, 600, 800 and 1000mm/min) at three different F-numbers of lens. After laser surface treatment three zones, In the microstructure have been observed : melted zone(decarburization), heat affected zone(martensite), and the substrate.

• 열처리공학회지
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• 제9권4호
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• pp.271-280
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• 1996

This study has been performed to investigate into some effects of power density and traverse speed of laser beam on optical microstructure, hardness and wear characteristics of gray cast iron treated by laser surface hardening technique. Optical micrograph has shown that large martensite and a small amount of retained austenite appear in outermost surface layer with fine martensite in inside hardened zone. Hardness measurements have revealed that the range of maximun hardness value is $Hv=650{\pm}15$ and as the power density increases and the traverse speed decreses, the depth of hardened zone increases due to as increase in input power density. Wear test has exhibited that wear rasistance of laser surface hardened specimen is superier compared to that of untreated specimen under the condition of same load at a given sliding distance, showing that absorption results of an wxidized substance due to a heavy abrasion appear in untreated specimen. The amount of weight loss of laser surface hardened specimen with respect to sliding distance at a given load decreses with increasing traverse speed at a given power density and with increasing power density at a given traverse speed.

• 한국방재학회 논문집
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• 제7권5호
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• pp.27-35
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• 2007

본 연구는 지진운동의 영향 하에서 강제 모멘트 골조로 이루어진 post-Northridge 연결부를 갖는 보의 탄성 및 비탄성 거동을 모델하기 위한 부등단면 보 요소를 제시한다. 단면감소 연결부를 갖는 부등단면 보의 탄성강성 행렬은 수치적분이 필요치 많은 수식으로 표현된다. 소성모델은 분포형이며 강체링크로 연결된 일련의 비선형 힌지로 구성 되어있고 경화법칙은 단조 및 임의 주기 하중에 대한 비탄성 거동과 국부좌굴의 효과를 고려할 수 있다. 모델의 대조와 검증은 동반논문에 제시되어있다.

• 한국세라믹학회지
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• 제40권8호
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• pp.730-734
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• 2003

This research examined the effect, which it follows in particle size distribution change of CaHPO$_4$ㆍ2$H_{2}O$ (DCPD). We used two kinds of compositions; tetracalcium phosphate (TTCP)/dicalcium phosphate dihydrate (DCPD) composition and $\alpha$-tricalcium phosphate ($\alpha$-TCP)TTCP/DCPD composition. As the result, the mean particle size of the DCPD decreased, the setting tine shortened at all compositions. The reference powder (DR), which did not milling, showed about 2 times strength value compared with other milling sample. Especially, the compressive strength of 60 : 20 : 20 sample (DR(do$_{0.5}$)=12.08 $\mu\textrm{m}$) after curing 7 days in simulated body fluid solution was 40$\pm$0.5 MPa, which was the highest. This resulted from the packing density at $\alpha$-TCP/TTCP/DCPD combination.