• 한국정밀공학회지
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• 제33권1호
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• pp.69-75
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• 2016

Polydimethylsiloxane (PDMS) is used as a scaffold for cell culture. Because both the stress and strain acting on the substrate and the hemodynamic environment are important for studying mechano-transduction of cellular function, the traction force of the surface of a substrate has been measured using fluorescence images of particle distribution. In this study, deformation of the cross-sectional plane of a PDMS block was measured by correlating particle image distributions to validate the particle image strain measurement technique. Deformation was induced by a cone indentor and a shearing parallel plate. Measured deformations from particle image distributions were in agreement with the results of a computational structure analysis using the finite-element method. This study demonstrates that the particle image correlation method facilitates measurement of deformation of a polymer scaffold in the cross-sectional plane.

• 한국도로학회논문집
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• 제14권5호
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• pp.1-9
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• 2012

PURPOSES: A viscoelastic axisymmetric finite element analysis code has been developed for stress analysis of asphalt pavement structures. METHODS: Generalized Maxwell Model (GMM) and 4-node isoparametric element were employed for finite element formulation. The code was developed using $C^{+}^{+}$ computer program language and named as KICTPAVE. For the verification of the developed code, a structural model of a pavement system was constructed. The structural model was composed of three layers: asphalt layer, crushed stone layer, and soil subgrade. Two types of analysis were considered for the verification: (1)elastic static analysis, (2)viscoelastic time-dependent analysis. For the elastic static analysis, linear elastic material model was assigned to all the layers, and a static load was applied to the structural model. For the viscoelastic time-dependent analysis, GMM and linear elastic material model were assigned to the asphalt layer and all the other layers respectively, and a cyclic loading condition was applied to the structural model. RESULTS: The stresses and deformations from KICTPAVE were compared with those from ABAQUS. The analysis results obtained from the two codes showed good agreement in time-dependent response of the element under the loading area as well as the surface deformation of asphalt layer, and horizontal and vertical stresses along the axisymmetric axis. CONCLUSIONS: The validity of KICTPAVE was confirmed by showing the agreement of the analysis results from the two codes.

• 한국전산유체공학회지
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• 제17권3호
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• pp.93-98
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• 2012

The injection molding process is suitable for manufacturing complicated plastic products. As the customer request higher quality products increase, realization of the precise dimensional and shape controls is getting more important. For this purpose it is important to obtain uniform cooling procedure over the whole surface of the high temperature molded plastic. Failure to this may lead to different shrinkage speed, internal stresses and unwanted shape deformations. It is necessary to distribute coolant flow rates to the main channel and to the sub-channels properly to insure uniform cooling process when there are parallel cooling channels. In this study, three-dimensional turbulent flow simulations for representative parallel cooling channels were performed. To insure the intended flow rate to each sub-channels, various shape designs for the channel system were investigated. The results show that as the Reynolds number increases the effect of shape design is more profound. Through the proper flow distribution, uniform cooling effects would be expected.

• 한국의류산업학회지
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• 제18권6호
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• pp.733-745
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• 2016

This paper provides a review of wearable textile strain sensors that can measure the deformation of the body surface according to the movements of the wearer. In previous studies, the requirements of textile strain sensors, materials and fabrication methods, as well as the principle of the strain sensing according to sensor structures were understood; furthermore, the factors that affect the sensing performance were critically reviewed and application studies were examined. Textile strain sensors should be able to show piezoresistive effects with consistent resistance-extension in response to the extensional deformations that are repeated when they are worn. Textile strain sensors with piezoresistivity are typically made using conductive yarn knit structures or carbon-based fillers or conducting polymer filler composite materials. For the accuracy and reliability of textile strain sensors, fabrication technologies that would minimize deformation hysteresis should be developed and processes to complement and analyze sensing results based on accurate understanding of the sensors' resistance-strain behavior are necessary. Since light-weighted, flexible, and highly elastic textile strain sensors can be worn by users without any inconvenience so that to enable the users to continuously collect data related to body movements, textile strain sensors are expected to become the core of human interface technologies with a wide range of applications in diverse areas.

• International Journal of Contents
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• 제6권1호
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• pp.6-11
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• 2010

Recently, there has been research to use portable digital camera to recognize objects in natural scene images, including labels or marks on a cylindrical surface. In many cases, text or logo in a label can be distorted by a structural movement of the object on which the label resides. Since the distortion in the label can degrade the performance of object recognition, the label should be rectified or restored from deformations. In this paper, a new method for label detection and restoration in digital images is presented. In the detection phase, the Hough transform is employed to detect two vertical boundaries of the label, and a horizontal edge profile is analyzed to detect upper-side and lower-side boundaries of the label. Then, the biquadratic transformation is used to restore the rectangular shape of the label. The proposed algorithm performs restoration of 3D objects in a 2D space, and it requires neither an auxiliary hardware such as 3D camera to construct 3D models nor a multi-camera to capture objects in different views. Experimental results demonstrate the effectiveness of the proposed method.

• 한국정밀공학회지
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• 제18권11호
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• pp.93-100
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• 2001

Brittle materials are very weak for impact because of typical characteristics which happen to be easily fractured with low fracture toughness and crack sensitivity. When brittle materials are subjected to impact due to small spheres, high contact pressure is occurred to impact surface and then local damage on specimen is developed, since there are little plastic deformations due to contact pressure compared to metals. This local damage is a dangerous factor which gives rise to final fracture of structures. In this research, the crack propagation process of soda lime glass by impact of small sphere is explained and the effects of the constraint conditions of impact spheres and materials for the material damage were studied by using soda-lime glass. that is the effects for the materials and sizes of impact ball, thickness of specimen and residual strength. Especially, this research has focused on the damage behavior of ring crack, cone crack and several kinds of cracks.

• 한국정밀공학회지
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• 제15권10호
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• pp.156-164
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• 1998

Electronic Speckle Pattern Interferometry(ESPI) has been used to measure surface deformations of engineering components and materials in industrial areas. ESPI, a non-contact and non-destructive technique, is capable of providing full-field results with high spatial resolution and high speed. One of the important application using electronic speckle pattern interferometry is electronic speckle contouring of a diffused object for 3-D shape analysis and topography measurement. Generally the electronic speckle contouring is suitable for providing measurement range from millimeters to several centimeters. In this study, we introduce the contouring method by modified dual-beam speckle pattern interferometer and the shift of the two illumination beams through optical fiber in order to obtain the contour fringe patterns. We also describe formation process of depth contour fringes and grid contour fringes by shifting direction of the two illumination beams. Before the experiments, we performed the geometric analysis for dual-beam-shifted ESPI contouring, and then, the electronic speckle contouring experiment with various specimens. For quantitative analysis of the contour fringes, we used 4-frame phase shifting method with PZT Finally, good agreement between the geometric analysis and experimetal results is obtained.

• International Journal of Automotive Technology
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• 제2권1호
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• pp.9-16
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• 2001

The lifetime of power train components can be improved dramatically by finding crack initiation points with suitable software tools and optimization of the critical areas. With increasing capacities of computers the prediction of the lifetime for components by numerical methods gets more and more important. This paper discusses some applications of the outstanding fatigue simulation program FEMFAT supporting the assessment of uniaxially and multiaxially loaded components (as well as welding seams and spot joints). The theory applied in FEMFAT differs in some aspects from classical approaches like the nominal stress concept or the local one and can be characterized by the term "influence parameter method". The specimen S/N-curve is locally modified by different influence parameters as stress-gradient to take into account notch effects, mean-stress influence which is quantified by means of a Haigh-diagram, surface roughness and treatments, temperature, technological size, etc. It is possible to consider plastic deformations resulting in mean-stress rearrangements. The dynamic loading of power train components is very often multiaxial, e.g. the stress state at each time is not proportional to one single stress state. Hence, the directions of the principal axes vary with time. We will present the way how such complex load situations can be handled with FEMFAT by the examples of a crank case and a gear box.

• 한국지반공학회지:지반
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• 제10권3호
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• pp.17-32
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• 1994

역재하시에 나타나는 흙의 비등방거동을 모델하기 위하여, 본 연구에서는 일반 등방경화규칙에 근거한 비등방 경화이론을 개발하였다. 일반 등방규칙은 등방경화의 기준이 되는 중심응력텐서가 임의의 응력상태에서 존재할 수 있도록 허용하므로, 역재하과정에서 발생하는 소성변형을 예측할 수가 있다. 제안된 구성모델은 단순한 경화함수만을 이용하여 수식화되었고, 일반등방경 화규칙에 적용된 개념을 기존의 비등방경화규칙과 비교하여 서술하였다. 검증을 위하여, 배수 및 비배수조건, 과압밀상태, Ko 압밀등의 초기조건이 상이한 점토에 대하여 관측된 삼축압축시료의 거동을 예측하였다.

• Elastomers and Composites
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• 제54권4호
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• pp.299-307
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• 2019

Rubber friction properties include adhesion friction characteristics of the interface, hysteresis friction characteristics originating from repeated rubber deformations, and cohesion friction characteristics due to wear and tear. Cohesion friction is generally sufficiently small (< 3%) that it can be ignored, whereas adhesion friction has a relatively large contribution of 15%, but has not been investigated thoroughly. Therefore, through an adhesion friction study, the adhesion mechanism was examined and the relationship between friction characteristics and adhesion friction on dry surfaces was derived. The wet grip characteristics of tread rubber are fully described by the hysteresis characteristics of tires, but friction characteristics on dry roads are difficult to determine without adhesion factors. The results presented herein demonstrate that the combination of hysteresis and adhesion properties in the tread rubber sufficiently explained the characteristics of the dry grip. Based on the results of this study, technologies will be developed to determine the key factors governing adhesion friction characteristics and improve dry tire braking performance.