• Composites Research
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• 제31권5호
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• pp.221-226
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• 2018

변형률 속도 $100s^{-1}{\sim}10000s^{-1}$ 범위에서 사용되는 홉킨스바(SHPB)는 재료의 동석 거동 특성을 확인하기 위해 가장 널리 사용되는 장치이다. SHPB 시험은 입력봉 및 전달봉에서 측정된 변형률을 사용하여 시험편의 응력, 변형률 및 변형률 속도를 얻을 수 있는 응력파 전달 이론을 기반으로 한다. 본 연구에서는 고 변형률 속도에서 폴리프로필렌 자기보강 복합재료(SRPP)의 동적 특성을 얻기 위해 직접 SHPB를 설계 및 제작하였다. 또한 본 연구를 통해 제작된 SHPB에서 얻은 변형률 데이터의 신뢰성 확보를 위하여 Digital Image Correlation (DIC)를 통해 얻은 변형률 데이터와의 비교를 진행하였다. 이는 SRPP 시편의 고속 압축 시험을 통해 이루어 졌으며 SHPB를 통하여 얻은 데이터와 DIC를 통해 얻은 변형률 데이터의 유사함을 확인하였고 이를 통하여 장비의 신뢰성을 검증하였다.

• 소성∙가공
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• 제22권3호
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• pp.150-157
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• 2013

Fiber metal laminates (FMLs) are layered materials comprised of thin metal sheets and fiber reinforced plastic (FRP). This paper presents the numerical study of the formability enhancement of FMLs composed of an aluminum alloy and self-reinforced polypropylene (SRPP) composite. In this study, a numerical simulation based on finite element (FE) modeling is proposed to evaluate the formability of FMLs using ABAQUS/Explicit. The FE model, which included a single layer of solid and shell elements to model the blank, used discrete layers of the solid element with a contact model and shell elements with a friction based model for the aluminum alloy-composite interface conditions. This method allowed the description of each layer of FMLs and was able to simulate the interaction between the layers. It is noted through this research that the proposed numerical simulation described properly the formability enhancement of the FMLs and the simulation results showed good agreement with experimental results.

• Advances in aircraft and spacecraft science
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• 제3권1호
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• pp.61-75
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• 2016

Climate changes brought on by human interventions have proved to be more devastating than predicted during the recent decades. Recognition of seriousness of the situation has led regulatory organisations to impose strict targets on allowable carbon dioxide emissions from automotive vehicles. As a possible solution, it has been proposed that Fibre Metal Laminate (FML) system is used to reduce the weight of future vehicles. To facilitate this investigation, FML based on steel and self-reinforced polypropylene was stamp formed into dome shapes under different blank holder forces (BHFs) at room temperature and its forming behaviour analysed. An open-die configuration was used in a hydraulic press so that a 3D photogrammetric measurement system (ARAMIS) could capture real-time surface strains. This paper presents findings on strain evolutions at different points along and at $45^{\circ}$ to fibre directions of circular FML blank, through various stages of forming. It was found initiation and rate of deformation varied with distance from the pole, that the mode of deformations range from biaxial stretching at the pole to drawing towards flange region, at decreasing magnitudes away from the pole in general. More uniform strain distribution was observed for the FML compared to that of plain steel and the most significant effects of BHF were its influence on forming depth and level of strain reached before failure.

• 소성∙가공
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• 제23권5호
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• pp.289-296
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• 2014

Uniaxial tensile tests were conducted to accurately evaluate the in-plane mechanical properties of fiber metal laminates (FMLs). The FMLs in the current study are comprised of a layer of self-reinforced polypropylene (SRPP) sandwiched between two layers of aluminum alloy 5052-H34. The nonlinear tensile behavior of the FMLs under in-plane loading conditions was investigated using both numerical simulations and a theoretical analysis. The numerical simulation was based on finite element modeling using the ABAQUS/Explicit code and the theoretical constitutive model was based on the volume fraction approach using the rule of mixture and a modification of the classical lamination theory, which incorporates the elastic-plastic behavior of the aluminum alloy and the SRPP. The simulations and the model are used to predict the inplane mechanical properties such as stress-strain response and deformation behavior of the FMLs. In addition, a post-stretching process is used to reduce the thermal residual stresses before uniaxial tensile testing of the FMLs. Through comparison of both the numerical simulations and the theoretical analysis with the experimental results, it is concluded that the numerical simulation model and the theoretical approach can describe with sufficient accuracy the actual tensile stress-strain behavior of the FMLs.

• 소성∙가공
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• 제29권4호
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• pp.179-187
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• 2020

Existing composite forming processes such as the autoclave, prepreg compression forming (PCF), RTM, etc. require high production costs because of their long processing time. On the other hand, microwave heating process (MHP) can reduce the production costs since both mold and composite material can be heated directly. The aim of this study is to manufacture a mold consisting of polytetrafluoroethylene (PTFE), quartz glass, stainless steel clamps, and polyether ether ketone (PEEK) bolts for fabricating FML based on self-reinforced polypropylene (SRPP) using the MHP. First, the flame test was carried out prior to the MHP to check the temperature on the mold and whether the spark occurred at the mold and the edge of the FML. Second, the uniaxial tensile test was then conducted to obtain the mechanical properties of the FML manufactured by the MHP. The mechanical properties were compared with those of the FML fabricated by the PCF. As a result, the MHP using the PTFE mold can manufacture the FML more rapidly than the PCF, and obtain acceptable mechanical properties.

• 소성∙가공
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• 제24권1호
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• pp.52-61
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• 2015

Evaluation of the elevated temperature flow stress for thermoplastic fiber metal laminates(TFMLs) sheet, comprised of two aluminum sheets in the exterior layers and a self-reinforced polypropylene(SRPP) in the interior layer, was conducted. The flow stress as a function of temperature should be evaluated prior to the actual forming of these materials. The flow stress can be obtained experimentally by uniaxial tensile tests or analytically by deriving a flow stress model. However, the flow stress curve of TFMLs cannot be predicted properly by existing flow stress models because the deformation with temperature of these types of materials is different from that of a generic pure metallic material. Therefore, the flow stress model, which includes the effect of the temperature, should be carefully identified. In the current study, the flow stress of TFMLs were first predicted by using existing flow stress models such as Hollomon, Ludwik, and Johnson-Cook models. It is noted that these existing models could not effectively predict the flow stress. Flow stress models such as the modified Hollomon and modified Ludwik model were proposed with respect to temperatures of $23^{\circ}C$, $60^{\circ}C$, $90^{\circ}C$, $120^{\circ}C$. Then the stress-strain curves, which were predicted using the proposed flow stress models, were compared to the stress-strain curves obtained from experiments. It is confirmed that the proposed flow stress models can predict properly the temperature dependent flow stress of TFMLs.