Stress profiles at contact surface in ring compression test

노정훈,김민태,황병복 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.8

A perfectly plastic material has been employed as a model material in simulation to analyze numerically the ring compression process,especially to examine the deformation patterns along the die/workpiece interface, which is strongly related to the frictional condition at the contact boundary. The main objective is to provide the deformation characteristics in detail in ring compression, especially at the tool/workpiece interface. The surface flow patterns at the contact boundary in ring compression are summarized and analyzed in terms of surface expansion, surface expansion velocity, pressure distributions exerted on the die surface, relative sliding velocity between die and workpiece, and sliding distance along the die surface. Movement of neutral positions and folding phenomenon are also investigated to see the effect on the deformation patterns at the interface, that is, geometrical change, which is important to measure the frictional condition at the interface using calibration curves. Finite element (FE) simulation using rigid-plastic finite element code has been performed for analysis. The results of this study reveal that surface expansion as well as other surface flow patterns, such as sliding velocity and so on, shows different and distinctive characteristics between low and high frictional conditions at the interface. This is directly related to the movement of neutral positions and folding, which affects the sensitivity of dimensional changes to tribological conditions at the interface.

반응표면법을 사용한 고 중량물 낙하시험기의 충격에너지 흡수량 예측 연구

강훈(Hoon Kang),장진석(Jin-Seok Jang),김다혜(Da-Hye Kim),강지헌(Ji-Heon Kang),유완석(Wan-Seok Yoo),이재욱(Jae-Wook Lee) 한국기계가공학회 2016 한국기계가공학회지 Vol.15 No.3

This paper presents the characteristics of the energy absorption in an expansion tube type impact absorber that is applied to a high weight drop tester and the use of a response surface methodology to predict the impact energy absorption. In order to identify the characteristics of the energy absorption, a set of finite element analysis was conducted with Abaqus Explicit. Moreover, the ISCD-II sampling method and a first order polynomial were used to build a response surface. As a result, we demonstrated that the impact energy could be controlled by four main design variables, namely an expansion pipe’s thickness, inner radius, pressing die’s expansion angle and expansion ratio. Additionally, we observed the relationship between the four main design variables and the impact energy absorbing time, displacement, and maximum impact force.

원기둥 압축 공정에서 접촉 경계면의 변형 특성

민경호,고병두,이하성,Min, Kyung-Ho,Ko, Byung-Du,Lee, Ha-Seong 한국금형공학회 2014 한국금형공학회지 Vol.8 No.2

In this study, surface deformation patterns have been investigated by the rigid-plastic finite element method for friction factor test in solid cylinder compression process. AA1100 and AA6063 aluminum alloys, which show different work hardening characteristics respectively, have been adopted as model materials used for analysis. The main objective of this study is to provide the deformation mechanics in detail in solid cylinder compression process, especially at the die/workpiece interface that is closely related with the frictional conditions. For this reason, solid cylinder compression process has been numerically analyzed. The surface flow patterns at the contact boundary have been analyzed in terms of surface expansion, surface expansion velocity, pressure distributions exerted on the die surface along the die surface. By defining bulge factor, barreling phenomenon also have been examined with calibration curves to verify their effects on the surface flow pattern that is important for evaluating the frictional condition at the interface.

Effect of thermocycling process on compomers

Kwon, Yong Hoon,Park, Chan-A,Kim, Hyung-Il 大韓齒科器材學會 2003 대한치과재료학회지 Vol.30 No.1

The purpose of this study was to test the effect of thermocycling process of commercial compomers by evaluating the microhardness, coefficient of thermal expansion, and surface modifications. Three compomers (Compoglass F (vivadent), Dyract AP (De Trey), F2000 (3M)) were prepared and light-polymerized for 40 seconds exposure at 700 ㎷/㎠ light intensity conditions. The prepared specimens were thermocycled between 4 and 60℃ water baths for 2000, 5000, and 10000 cycles. As results, the initial value of each compomer's microhardness was significantly reduced after the initiation of the thermocycling process. However, during the process, the changes of hardness of each compomer were statistically insignificant. The coefficient of thermal expansion of each compomer was increased as the number of thermocycle increased, then decreased at the end of the process. From the SEM observations, the reason may be attributed to the detechment of fillers from the surface of Compoglass F and Dyract AP. Unlike these compomers, F2000 showed the formation and propagation of cracks on the surface. These cracks may relax or absorb the generated stress due to the linear thermal expansion of the specimen.

발사체의 고도보정용 3D 프린팅 확장-굴절 노즐에 관한 실험적 연구

이기환,박상현,구자예,허환일 대한기계학회 2019 大韓機械學會論文集B Vol.43 No.12

An experimental study of an expansion-deflection (E-D) nozzle for a launch vehicle is conducted. The E-D nozzle is designed by selecting the pintle inflection angle as the main variable and is manufactured from a metal 3D printer using SLM process techniques. Visualization experiments and surface roughness measurements are performed to compare the characteristics of the E-D nozzle before and after the post-process. As a result, several oblique shockwaves are confirmed to have occurred due to the high surface roughness before the post-processing, which decreased after the post-processing. In addition, a thrust measurement experiment is performed to analyze the performance of the E-D nozzle, showing that the thrust of the E-D nozzle tends to increase as the pintle inflection angle increases. 발사체 고도보정용 확장-굴절 노즐의 실험 연구를 수행하였다. 확장-굴절 노즐은 핀틀 변곡 각도를 주요 변수로 선정하여 설계하였고, SLM 공정 기법을 사용하는 금속 3D 프린터로 제작하였다. 3D 프린터로 제작한 확장-굴절 노즐의 후처리 전/후에 나타나는 특성을 비교하기 위해 표면 조도 측정과 가시화 실험을 수행하였다. 측정 및 실험 결과, 후처리 전의 높은 표면 조도로 인해 다수의 경사충격파가 나타났고, 후처리 후에는 경사충격파가 감소한 것을 확인하였다. 또한 확장-굴절 노즐의 성능을 분석하기 위해 추력 측정 실험을 수행하였으며, 핀틀 변곡 각도가 높을수록 확장-굴절 노즐의 추력이 크게 나타나는 경향을 보였다.

A Stochastic Dual Response Surface Method for Reliability Analysis Considering the Spatial Variability

봉태호,손영환 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.9

To solve spectral stochastic finite element problems, the collocation-based spectral stochastic finite element method (SSFEM) was developed, and the Stochastic Response Surface Method (SRSM) was used to represent uncertainty propagation. Therefore, the accuracy of SRSM is important for obtaining more accurate probabilistic results. The weighted SRSM was developed to improve the global accuracy of SRSM, but it is not suitable for random field problems because weights might distort the response surface. In this study, a new Stochastic Dual-response Surface Method (SDRSM) was developed to improve the accuracy of SRSM. The SDRSM combines the conventional SRSM and target-weighted SRSM (TWSRSM), which is assigned a weight for the numerical result corresponding to the collocation point. Then, the proposed method was extended to deal with problems involving random fields. For comparison with the conventional methods (SRSM and WSRSM), two numerical examples involving random fields were carried out. Compared with Monte Carlo simulation results, SDRSM shows the smallest error without the addition of the collocation points. In addition, the mean absolute errors for equally spaced probability intervals were compared, and their mean and standard deviation of SDRSM were relatively smaller than that of other methods.

성형툴의 상태에 따른 탄소섬유강화 복합재 구조물의 변형 예측

성수환,김위대 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.11

오토클레이브 성형은 성형제품의 품질은 우수하나 생산비용이 비싸다는 단점이 있다. 생산비용 중에서도 큰 비중을 차지하는 것이 성형툴의 제작공정이다. 따라서 본 연구에서는 생산비용 절감을 위한 선행 연구로서 성형툴의 재질 및 표면상태에 따라 L-Shape 제품의 성형후 Spring-in 을 Abaqus Subroutine 을 이용하여 계산하였고, 열팽창계수와 마찰계수에 따른 결과를 나타내었다. 또한 성형툴 제작시 재질 및 표면상태의 기준점을 제시하여 생산비용을 줄이는데 기여하고자 한다. Autoclave processing have good quality of product, but manufacturing cost is expansive. It is very important disadvantage. Manufacturing cost consist of various factor, one of the most biggest factor is tool cost. Therefore, this paper is basic research for reducing manufacturing cost. When manufacture L-shape composite structure occur distortion, such as spring-in. It is calculated using ABAQUS. And then show results about coefficient of thermal expansion and tool surface condition. And this paper suggest reference point of tool material and surface condition selection.

성형툴의 상태에 따른 탄소섬유강화 복합재 구조물의 변형 예측

성수환 ( Su Hwan Sung ),김위대 ( Wie Dae Kim ) 한국복합재료학회 2014 Composites research Vol.27 No.6

오토클레이브 성형은 성형제품의 품질은 우수하나 생산비용이 비싸다는 단점이 있다. 생산비용 중에서도큰 비중을 차지하는 것이 성형툴의 제작공정이다. 따라서 본 연구에서는 생산비용 절감을 위한 선행 연구로서 성형툴의 재질 및 표면상태에 따라 L-shape 제품의 성형후 Spring-in을 Abaqus user subroutine을 이용하여 계산하였고, 열팽창계수와 마찰계수에 따른 결과를 나타내었다. 또한 성형툴 제작시 재질 및 표면상태의 기준점을 제시하여 생산비용을 줄이는데 기여하고자 한다. Autoclave processing has a good quality of product, but manufacturing cost is expansive. After curing ofcomposite, the unwanted deformation and distortion increase the manufacturing cost by redesign of tool parts. Therefore, manufacturing cost down is a big issue in processing level. For the reduction of tool costs, it is importantto investigate the effects of tool materials and tool surface conditions. In this paper, we organized user subroutine inABAQUS to consider the thermal effects of part and tool, and the results are compared with commercial code,COMPRO. And this paper suggests reference point for the selection of tool materials to reduce manufacturing costs.

Tolerance Optimization of a Lower Arm by using Genetic Algorithm and Process Capability Index

이광기,한승호,노윤철 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.

Tolerance optimization that considers variances of design variables should be performed before beginning the manufacturing processfrom a cost-effective perspective in the design process. The authors used a genetic algorithm and the process capability index (Cpk)to solve the robust objectives and probability constraints and to formulate a constrained optimization problem into an unconstrainedone. The design space provided by the Cpk-values of weight and stress on the lower arm of a vehicle’s suspension was explored byusing the central composite design method and the 2nd order Taylor series expansion. The optimal solutions were found via the geneticalgorithm, in which the Cpk-values took into account the variances occurring in a design variable's tolerances. The mean andstandard deviation of Mass and Smax were predicted by using the 2nd order Taylor series expansion and the 2nd order polynomialresponse surface models generated from the central composite design method. The Cpk of Mass and Smax were calculated, wherethe Pareto set was generated by maximizing the Cpk-values via the MOGA (Multi-Objective Genetic Algorithm). From the Paretoset, optimal alternatives were selected and verified by simulated results from FE (Finite Element) analysis and Monte-Carlosimulation.

후방 캔 압출 공정에서 표면 변형 형태에 대한 펀치 형상의 영향

노정훈(J. H. Noh),김동현(D. H. Kim),황병복(B. B. Hwang) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.10

This paper is concerned with the analysis on the surface stress profiles of AISI 1015 steel in backward extrusion process. Heavy surface stress such as surface expansion appeared in backward can extrusion process usually leads to very severe tribological conditions along the interface between workpiece and punch land. In the present study, influence on the punch face angle and reduction has been investigated in terms of the surface stress profiles such as surface expansion, pressure exerted on the tool surface between tool and workpiece, respectively. The main goal of this study is to examine the influence of process conditions such as degree of reduction in area and geometries of punch face on the deformation pattern of the model material in backward extrusion, especially for surface stresses. It is well known that among various surface stresses, surface expansion and contact pressure distribution along the die-workpiece interface are closely related to the condition of lubrication at the interface for both solid and liquid lubricants, and contact pressure and sliding distance between workpiece and tool are essential parameters to evaluate the tool wear. The geometrical parameters employed in analysis include the punch face angle of the punch nose as well as reduction ratio. Extensive simulation has been conducted by applying rigid-plastic finite element method to backward can extrusion process under various geometrical conditions. The simulation results are summarized in terms of surface stresses such as surface expansion, pressure and comparison of surface loads for different process conditions, which constitute of surface stress profiles. It was found from the present study that the surface expansion is more influenced by reductions than the punch nose angle.