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디지털 이미지 상관관계를 이용한 Al 6061-T6 인장시험편의 변형률 측정에 관한 연구
권오헌 ( Oh Heon Kwon ),김상태 ( Sang Tae Kim ),강지웅 ( Ji Woong Kang ) 한국안전학회(구 한국산업안전학회) 2013 한국안전학회지 Vol.28 No.4
A digital image correlation(DIC) method is a whole-field measurement technique that acquires surface displacements and strains from images information which characterized a random speckle as intensity grey levels. Recently years, this DIC method is being developed and used increasingly in various research. In this study, we tried to apply to aluminum alloy(Al 6061-T6) using DIC method and strain gauge. DIC results demonstrated the usefulness and ability to determine a strain. The test specimen used in this study was an aluminum alloy(Al 6061-T6, thickness 1 mm). For a strain measurement, a strain gauge was attached at the center of a specimen. A specimen was lightly sprayed with a white paint and a black dot pattern was sprayed on its fully dried white surface to obtain a random speckle. The experimental apparatus used to perform the tensile test consisted of universal dynamic tester(5 kN; T.O. Co.) under displacement speed of 0.5, 1.0 and 3.0 mm/min. A Model 5100 B Scanner(V. Co.) used to obtain a strain. A CCD camera connected to a PC uses to record the images of the specimen surface. After acquisition, the images were transferred to PC where the DIC software was implemented. An acquired image was evaluated by the DIC program. DIC method for displacement and strain was suggests and it results show a good consistent remarkably. DIC results demonstrated the usefulness and ability to determine surface strain was better than by using classical measurements. The strain field measurement using a DIC is so useful that it can be applied to map strain distributions at a full area. DIC method can evaluate a strain change so it can predict a location of fracture. The findings of the investigation suggest that the DIC method is an efficient and reliable tool for full-field monitoring and detailed damage characterization of materials.
권오헌 ( Oh Heon Kwon ) 한국안전학회(구 한국산업안전학회) 2011 한국안전학회지 Vol.26 No.5
Recently new technological development needs the advances in the fields of new materials. The most advanced design is not useful if new material`s performance is not realized adequately for bearing the service loads and conditions. FGMs suggests the reasonable solution for the those requirements because of its wide range microstructure and the continuous constitutions. It`s especially good for the heat-resisting components, piezoelectricity and aerocraft fields. However the fabrication and its experimental estimation methods have not been established because of its various freedom of material`s properties. Therefore it is necessary to develope the fabrication method and estimation of strength and deformation. The experiments are conducted under a four point flexural test. According to results, this study shows that FGMs is well fabricated and the deformation and strain fields are expressed very well by digital image correlation method.
변형률-수명 평가기법을 이용한 Al/CFRP 하이브리드 적층 복합재의 피로수명 측정
양성진,권오헌,전상구,Yang, Seong Jin,Kwon, Oh Heon,Jeon, Sang Koo 한국안전학회 2021 한국안전학회지 Vol.36 No.3
Hybrid laminated Al/carbon-fiber-reinforced plastic (CFRP) composites are attracting considerable attention from industries such as aerospace and automobiles owing to their excellent specific strength and specific rigidity. However, when this material is used to fabricate high-pressure fuel storage containers subjected to repeated fatigue loads, fatigue life evaluation for the working load is regulated as an important criterion for operational safety and ease of maintenance. Among the existing evaluation methods for these vessels, the burst test and the hydraulic repeat test require expensive facilities. Thus, the present study aims to develop an improved fatigue life test for Al/CFRP laminated hybrid composites. The test specimen was manufactured using a curved mold considering the shape of a type III high-pressure storage container. The strain-life method was used for fatigue life evaluation, and the life was predicted based on the transition life. The results indicate that the more complex the CFRP stacking sequence, the longer is the transition life. This test method is expected to be useful for ensuring the fatigue safety and economy of hybrid laminate composites.
수소고압저장용기용 팔라듐 첨가 탄소섬유복합재에 대한 멀티스케일 응력해석
박우림,권오헌,Park, Woo Rim,Kwon, Oh Heon 한국안전학회 2018 한국안전학회지 Vol.33 No.2
The multi-scale analysis is more proper and precise for composite materials because of considering the individual microscopic structure and properties of each material for composite materials. The purpose of this study is to verify the validity of using palladium particles in carbon/fiber composites by multi-scale analysis. The palladium is a material for itself to detect leaking hydrogen by using the property of adsorbing hydrogen. The macroscopic model material properties used in this study are homogeneous material properties from microstructure. Homogenized material properties that are calculated from periodic boundary conditions in the microscopic representative volume element model of each macroscopic analysis model. In this study, three macroscopic models were used : carbon fiber/epoxy, carbon fiber/palladium, palladium/epoxy. As a result, adding palladium to carbon/epoxy composite is not a problem in terms of strength.
Multiscale Simulation for a Crack Behavior in Heterogeneous Materials
누룰 파토니,권오헌,Fatoni, Nurul Fajriyah,Kwon, Oh Heon The Korean Society of Safety 2017 한국안전학회지 Vol.32 No.4
Functionally Graded Materials (FGM) as advanced heterogeneous composite materials have a higher performance than a conventional composite or bimaterial composite under some severe environments. As a heterogeneous material, FGM is commonly used in spacecraft, defense, nuclear and automotive industries due to its excellent properties. The purposes of this study are to evaluate the stress distribution and crack behaviors by the multiscale simulation. FGM contains two or more than two materials that the composition is structured continuously. Two types of FGM model are suggested, which are created by arbitrary prediction of the volume fraction and the exponential function. Aluminum as the metal matrix constituent and silicon carbide as the ceramic particle constituent are structured gradually by two types and the three point bending test also estimated. Moreover, two kinds of crack location were introduced in order to get the influences of material property distribution on the stress intensity factor. From the results we found that the stress intensity factors are increased in the case from softer to stiffer material, while vice versa.
복합모드 층간분리특성에 대한 PVC폼 코아 탄소섬유샌드위치 복합재의 실험적 해석
곽정훈,윤유성,권오헌,Kwak, Jung Hoon,Yun, Yu Seong,Kwon, Oh Heon 한국안전학회 2018 한국안전학회지 Vol.33 No.2
The light weight composite materials have been replacing in high performance structures. The object of this study is to examine the effects of the initial crack location about a delamination in a PVC foam cored sandwich composite that is used for the strength improvement of structures. The initial crack location and fiber laminates thickness were changed with several types. The MMB specimen was used for evaluating the fracture toughness and crack behaviors. The material used in the experiment is a commercial twill carbon prepreg in CFRP material and Airex in PVC foam core. Sandwich laminate composites are composed by PVC foam core layer between CFRP face sheets. The face sheets were fabricated as 2 types of 5 and 8 plies. The initial cracks were located in a PVC form core and the interface of upper CFRP sheet. From the results, the crack initiation was affected with the location of the initial crack inserted in the PVC foam core. Among them, the initial crack at 1/3 of the upper part of the PVC foam core was the most rapid progression. And the critical energy release rate was $0.40kJ/m^2$, which is the lowest value when the initial crack was inserted into the interface between a PVC foam core and CFRP laminated with 5 plies. Meanwhile, the highest value of $1.27kJ/m^2$ was obtained when the initial crack was located at the center line in case of the 8 plies.