• 한국전산구조공학회논문집
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• 제23권4호
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• pp.353-360
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• 2010

본 논문에서는 단 한번 만의 간단한 구형 인덴테이션 임프레션 실험을 통하여 재료 소성 물성치를 측정함에 있어서 효율적인 알고리즘이 개발되었다. 본 논문에서는 레프리젠터티브 스트레인의 새로운 정의를 기반으로 연구가 수행되어 예전의 연구와 비교할 때 상당한 량의 피팅 매개변수의 개수를 줄이게 됨으로서 계산 량이 대폭 줄어들면서 연구가 쉽게 진행될 수 있었다. 또한 레프리젠터티브 스트레인에 대한 새로운 정의는 보다 명확한 물리적 임의를 부여하였다. 역 해석의 신뢰성을 증명하기 위하여 본 논문에서는 거의 모든 공학적 금속과 합금이 포함되는 재료 세트들을 사용하여 해석을 진행하였다. 수치 해석 모델링을 통하여 얻은 P-${\delta}$ 그래프를 바탕으로 하여 인덴테이션 반응 특성과 재료의 탄소성 물성치가 양 함수에 의하여 연계되었고, 역 해석방법을 적용시켜 재료의 항복응력과 power-law 경화 지수가 얻어진다. 마지막으로, 역 해석을 통하여 얻어진 재료 물성 치와 실제 실험을 통하여 얻어진 재료 물성치가 좋은 일치성을 가진다는 것을 보여준다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.703-708
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• 1997

Continuous indentation test is a very powerful method to monitor the materials reliability since it is very simple, easy and almost non-destructive. It can provide material properties such as elastic modulus, yield strength, work-hardening exponent, etc., than the conventional hardness test. In our study, the true stress-strain curve is derived from the indentation load-depth curve. For this, average indentation strain is defined and the flow stress is obtained from the analysis of the indentation stress field. The residual stress is analyzed from the variation of the indentation behavior with the applied residual stress. And the estimation of fracture characteristic is tried by considering the conventional fracture toughness modeling and the stress/strain state under the spherical indenter.

• Journal of Mechanical Science and Technology
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• 제20권6호
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• pp.819-827
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• 2006

The stress-strain relation of aluminum (Al) alloy foam cell wall was evaluated by the instrumented sharp indentation method. The indentation in a few micron ranges was performed on the cell wall of Al-alloy foam having a composition or Al-3wt.%Si-2wt.%Cu-2wt.%Mg as well as its precursor (material prior to foaming). To extract the stress-stram relation in terms of yield stress ${\sigma}_y$, strain hardening exponent n and elastic modulus E, the closed-form dimensionless relationships between load-indentation depth curve and elasto-plastic property were used. The tensile properties of precursor material of Al-alloy foam were also measured independently by uni-axial tensile test. In order to verify the validity of the extracted stress-strain relation, it was compared with the results of tensile test and finite element (FE) analysis. A modified cubic-spherical lattice model was proposed to analyze the compressive behavior of the Al-alloy foam. The material parameters extracted by the instrumented nanoindentation method allowed the model to predict the compressive behavior of the Al-alloy foam accurately.

• 한국해양공학회지
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• 제11권2호
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• pp.57-69
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• 1997

The objetive of this study is to compare the mechanical proprties of 6000 series Al-Mg-Si aluminum alloy (AC120) with 5000 series Al-Mg aluminum alloy (TG25), and to investigate the influence of corrosion solution for fatigue life. Comparing of TG25 and AC120 alloy sheets, TG25 alloy sheets showing higher plastic ratio and total elongation have better formability than AC120 alloy sheets. The hardness of nugget area was a little higher than that of base metal area. Also, grain coarsening was observed in HAZ(Heat Affected Zone). In a corrosion fatigue experiment, the fatigue life decreased as concentration increased, when a dipping time was constant. The life decreased as dippling time increased, when a concentration was constant.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.25-28
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• 2004

A fracture was generated by change of clearance and deterioration of material properties on the sheet metal through temperature. This paper describes the results of a prediction about the temperature of the sheet metal during continuous stamping process, because the temperature increase of the sheet metal has a detrimental effect on formability. To analyze the temperature increase of the sheet metal during continuous stamping process, tensile and friction tests were performed from room temperature to 300$^{\circ}C$ at warm condition in this study. As temperature increase, tensile strength, elongation, strain hardening exponent and anisotropy coefficient for each specimens were decreased. On the other hand, friction coefficients were increased. From the FE-simulation results, temperature upward tendency was identified on dies and sheet metal. These observations are rationalized on the basis of the material properties, friction coefficient vs. temperature relationship for the sheet.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.210-213
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• 2004

Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined internal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity fur anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy parameter, strain hardening exponent on bursting pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

• 한국레이저가공학회:학술대회논문집
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• 한국레이저가공학회 1999년도 춘계학술발표대회 논문개요집
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• pp.29-32
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• 1999

The material properties of laser welding zone such as strength coefficient, work-hardening exponent, and plastic anisotropic ratio are analytically obtained from those of base metals based on the tensile tests. . The finite element formulation is developed for predicting strain distributions and weld line movements in the forming processes of laser welded blank. The welding zone(WZ) is modelled with the several, narrow finite elements whose material characteristics are based on the experimental results and the analytical equations. In order to show an application of the developed weld element the stamping process of auto-body door inner panel is simulated. FEM predictions are compared and showed good agreements with experimental observations.

• Nuclear Engineering and Technology
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• 제36권3호
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• pp.237-247
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• 2004

To investigate the applicability of automated ball indentation (ABI) tests in the evaluation of the tensile properties of cast stainless steel (CSS), ABI tests were performed on four types of unaged CSS and on 316 stainless steel, all of which had a different microstructure and strength. The reliability of ABI test data was analyzed by evaluating the data scattering of the ABI test and by comparing tensile properties obtained from the ABI test and the tensile test. The results show that the degree of scattering of the ABI test data is reasonably acceptable in comparison with that of standard tensile data, when two points data that exhibit out-of-trend are excluded from five to seven points data tested on a specimen. In addition, the scattering decreases slightly as the content of ${\delta}-ferrite$ in CSS increases. Moreover, the ABI test can directly measure the flow parameters of CSS with error bounds of about ${\pm}10\%$ for the ultimate tensile stress and the strength coefficient, and about ${\pm}15\%$ for the yield stress and the strain hardening exponent. The accuracy of the ABI test data is independent of the amount of ${\delta}-ferrite$ in the CSS.

• 한국안전학회지
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• 제7권2호
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• pp.47-56
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• 1992

The retardation effect of fatigue crack propagation after cyclic overloading seems to be affected by strain hardening exponent. Namely, for the material with high values of n, the delay effect is found to be severe. We proposed a modified crack retardation equation which may apply the retardation of fatigue crack growth after a cyclic overloading, as (da/dN)'$_{cyc}$=($\mu$n＋λ)B $\Delta$ $K^{q}$ /[(1－ $R_{eff}$) $K_{cf}$ －$\Delta$K]. where, $R_{eff}$ is effective stress ratio [＝( $K_{min}$－K, os)/( $K_{max}$－ $K_{res}$)] The constants $\mu$＝－0.5 and λ＝0.6, and the values are found to be identical for materials such as aluminum (A 1060), steel (SS 34), brass ( $B_{s}$ SIB) and stainless steel (SUS 304) used in this investigation. (SUS 304) used in this investigation.ation.n.n.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.66-76
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• 2017

This paper is concerned with investigating the plastic material properties of steel plate formed by line heating method, and is aimed at implementing more rational design considering the accidental limit states such as collision or grounding. For the present study, line heating test for marine grade steel plate has been carried out with varying plate thickness and heating speed, and then microscopic examination and tensile test have been carried out. From the microscopic, it is found that the grain refined zones like ferrite and pearlite are formed all around the heat affected zone. From the tensile test results, it is seen that yield strength, tensile strength, fracture strain, hardening exponent and strength coefficient vary with plate thickness and heat input quantity. The formulae relating the material properties and heat input parameter should be, therefore, derived for the design purpose considering the accidental impact loading. This paper ends with describing the extension of the present study.