• 소음진동
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• 제5권3호
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• pp.395-402
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• 1995

In general low frequency vibration characteristics like an idleshake is mainly influeced by pillar section properties and joints. So the design technique development of vehicle pillar structures is required to initial design and vehicle development stage. In this paper to develop pillar structure design technique considering low frequency vibration characteristics, strain energy method, design sensitivity analysis method, and design optimization method using commercial finite element analysis program and optimization program are presented.

• 소성∙가공
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• 제29권2호
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• pp.69-75
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• 2020

The plastic strain ratio is one of the factors that affect the deep drawability of metal sheets. The plastic strain ratio of fully annealed Cu sheet is low, due to its texture being {001}<100>. In this study, in order to increase the plastic strain ratio of Cu sheets we investigated the effect of two treatments: 1^st the sheet was asymmetrically rolled and annealed, and 2^nd the sheet was symmetrically and asymmetrically rolled and subsequently annealed. The average plastic strain ratio (R_m) of the initial Cu sheet was 0.95 and |Δr| was 1.27. After the 2^nd treatment of 5.3% symmetric rolling and annealing of Cu sheet at 1000℃ for 60 min in Ar gas condition, the R_m was 2.29 times higher and the |Δr| was 1.44 times higher than that of initial Cu sheet specimen. After the 2^nd treatment of 8.2% asymmetric rolling and annealing of Cu sheet at 1000℃ for 60 min in Ar gas conditions, the R_m was 2.51 times higher and |Δr| was 0.53 times lower than that of the initial Cu sheet specimen. These results can be attributed to the change in texture of the Cu sheets due to the differences in the two methods of rolling.

• Smart Structures and Systems
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• 제21권4호
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• pp.407-420
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• 2018

In structural health monitoring, it is meaningful to comprehensively utilize accelerometers and strain gauges to obtain the modal information of a structure. In this paper, a modal estimation theory is proposed, in which the displacement modes of the locations without accelerometers can be estimated by the strain modes of selected strain gauge measurements. A two-stage sensor placement method, in which strain gauges are placed together with triaxial accelerometers to obtain more structural displacement mode information, is proposed. In stage one, the initial accelerometer locations are determined through the combined use of the modal assurance criterion and the redundancy information. Due to various practical factors, however, accelerometers cannot be placed at some of the initial accelerometer locations; the displacement mode information of these locations are still in need and the locations without accelerometers are defined as estimated locations. In stage two, the displacement modes of the estimated locations are estimated based on the strain modes of the strain gauge locations, and the quality of the estimation is seen as a criterion to guide the selection of the strain gauge locations. Instead of simply placing a strain gauge at the midpoint of each beam element, the influence of different candidate strain gauge positions on the estimation of displacement modes is also studied. Finally, the modal assurance criterion is utilized to evaluate the performance of the obtained multitype sensor placement. A bridge benchmark structure is used for a numerical investigation to demonstrate the effectiveness of the proposed multitype sensor placement method.

• 대한기계학회논문집
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• 제18권10호
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• pp.2653-2663
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• 1994

The design of sheet metal working processes is based on the knowledge about the deformation mechanism and the influence of the process parameters. The typical geometric process parameters are the die geometry, the initial sheet thickness, the initial blank shape, and so on. The initial blank shape is of vital importance in the most sheet metal forming operations, especially in the deep drawing process, since the forming load and the strain distribution are significantly affected by the shape of an initial blank. The influence of the initial blank shape on a square cup deep drawing process is investigated by the numerical simulation and the experiment. The numerical simulation is carried out by a modified membrane finite element method which takes bending deformation into account. The numerical and experi-mental results show that the initial blank shape have strong influence on the forming load and the strain distribution. The numerical results are compared with the experimental results and other numerical results which are calculated with the membrane theory.

• 대한기계학회논문집
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• 제17권6호
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• pp.1321-1329
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• 1993

본 연구에서는 이들보다 매우 간단한 IS법, 즉 초기 변형률법(ISM: initial strain method)에 의한 크리프 수명예측식을 고안하여, 현재 화력발전용 고압 로터강 에 사용되고 있는 1%Cr-Mo-V강과 발전소 효율향상을 위해 최근 국내최초로 개발된 12% Cr강에 대하여 도출하였고, 이 도출식이 앞에서 언급한 여러 파라메트에 의한 결과와 비교 평가하여 장시간 강도 및 수명예측식으로 사용될 수 있음을 입증하였다.

• 한국지반공학회논문집
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• 제18권5호
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• pp.169-178
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• 2002

토목섬유 보강점성토의 응력~변형특성을 삼축압축시험을 통하여 조사하였다. 모든 시험은0.05kgf/$cm^2$의 낮은 응력 증분으로 필요한 유효응력 수준까지 등방압밀 혹은 이방압밀한 후 배수조건으로 수행되었다. 보강토벽, 보강토교대, 보강성토와 같은 토류 구조물의 경우 일반적으로 이방응력 상태에 있으며, 이방압밀 배수전단시험의 경우 이러한 현장조건을 재현하기 위한 것이다. 일련의 시험결과로부터 이방압밀 보강점성토의 거동은 등방압밀 보강점성토의 응력~변형특성과 매우 상이한 것으로 나타났다. 특히, 이방압밀 보강점성토의 초기변형계수의 경우 등방압밀의 경우에 비하여 현저히 높은 것으로 나타났다. 또한, 등방압밀의 경우(약 1.0~5.0%)에 비하여 이방압밀의 경우 매우 낮은 축변형률(0.01%)에서 보강효과가 발생하였다.

• 대한기계학회논문집B
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• 제28권6호
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• pp.688-696
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• 2004

Nonlinear dynamic behavior of diffusive-thermal instability in diluted CH$_4$/O$_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution, which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is net observed in this study, which is attributed to both convective flow and preferential diffusion effects.

• 대한기계학회논문집A
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• 제25권12호
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• pp.1933-1943
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• 2001

A micromechanical model is presented for superplasticity in which heterogeneous microstructures are coupled with deformation behavior. The effects of initial distributions of grain size, and their evolutions on the mechanical properties can be predicted by the model. Alternative stress rate models such as Jaumann rate and rotation incremental rate have been employed to analyze uniaxial loading and simple shear problems and the appropriate modeling was studied on the basis of hypoelasticity and elasto-viscoplasticity. The model has been implemented into finite element software so that full process simulation can be carried out. Tests have been conducted on Ti-6Al-4V alloy and the microstructural features such as grain size, distributions of grain size, and volume fraction of each phase were examined for the materials that were tested at different strain rates. The experimentally observed stress-strain behavior on a range of initial grain size distributions has been shown to be correctly predicted. In addition, the effect of volume fraction of the phases and concurrent grain growth were analyzed. The dependence of failure strain on strain rate has been explained in terms of the change in mechanism of grain growth that occurs with changing strain rate.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1512-1519
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• 2002

Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization fer two types of specimens, which are very typical ones in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. Also shape optimization for a cantilever beam in mixed mode was carried out by the same techniques. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was found that shapes of two types of specimens and a cantilever beam optimized by the growth-strain method prolong their fatigue lives significantly. Therefore, it was verified that the growth-strain method is an appropriate technique for shape optimization of a structure having a crack.

• 소성∙가공
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• 제19권8호
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• pp.502-507
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• 2010

The physical and mechanical properties and formability of sheet metals depend on preferred crystallographic orientations (texture). In this research work, the texture development and formability (plastic strain ratios) of AA1050 Al alloy sheets after 3 and 10 passes of asymmetric rolling and subsequent heat treatment were investigated. The plastic strain ratios of 10 passes asymmetrically rolled and subsequent heat treated samples are 1.3 times higher than those of the initial AA1050 Al alloy sheets. The ${\Delta}r$ of 10 passes of asymmetrically rolled and subsequent heat treated samples is 1/30 times lower than those of the initial AA1050 Al alloy sheets. The plastic strain ratios of 10 passes of asymmetrically rolled and subsequent heat treated Al sheets are higher than those of 3 passes ones. These results could be attributed to the formation of $\gamma$-fiber, ND//<111>, and the other texture components by means of asymmetric rolling in Al sheets.