• 한국정밀공학회지
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• 제17권2호
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• pp.169-175
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• 2000

The object of this study was to investigate the feasibility of solid-phase forming of the composites and to characterize the material behavior in the biaxial stretch forming. The materials tested contained 20%, 30%, and 40% glass fibers by weight in a polypropylene matrix. Biaxial stretch forming tests were performed at three forming speeds of 10mm/sec, 1mm/sec, and 0.1mm/sec and at four forming temperatures of $75^{\circ}C, 100^{\circ}C, 125^{\circ}C, and 150^{\circ}C$ to investigate effects of forming speed and forming temperature. The microscopic observation of a formed part was conducted at various strain levels to characterize the material behavior. The strain distribution on a formed part was measured and displayed on the farmed geometry with a contour display The material behavior of the composite in the biaxial stretch forming was strongly influenced by the forming conditions.

• Advances in aircraft and spacecraft science
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• 제3권1호
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• pp.29-43
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• 2016

Composite materials are rapidly gaining popularity as an alternative to metals for structural and load bearing applications in the aerospace, automotive, alternate energy and consumer industries. With the advent of thermoplastic composites and advances in recycling technologies, fully recyclable composites are gaining ground over traditional thermoset composites. Stamp forming as an alternative processing technique for sheet products has proven to be effective in allowing the fast manufacturing rates required for mass production of components. This study investigates the feasibility of using the stamp forming technique for the processing of thermoplastic, recyclable composite materials. The material system used in this study is a self-reinforced polypropylene composite material (Curv$^{(R)}$). The investigation includes a detailed experimental study based on strain measurements using a non-contact optical measurement system in conjunction with stamping equipment to record and measure the formability of the thermoplastic composites in real time. A Design of Experiments (DOE) methodology was adopted to elucidate the effect of process parameters that included blank holder force, pre heat temperature and feed rate on stamp forming. DOE analyses indicate that feed rate had negligible influence on the strain evolution during stamp forming and blank holder force and preheat temperature had significant effect on strain evolution during forming.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.513-517
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• 1997

Glass fiber reinforced thermoplastic composite materials have considerable promise for increased use in low cost high volum applications because of the potential for processing by solid phase forming. However, the forming characteristics of these materials have not been well known. The primary focus of this research is the investigation of the bendability of these composites and spring-back phenomena in pure bending. The materials tested contained 10, 35, and 40 percent by weight of randomly oriented glass fiber in a polypropylene matrix. The bending tests were performed at temperatures ranging form 75 ".deg. c" to 150 ".deg. c" and at punch speeds of 2.54 mm/sec and 0.0254 mm/sec. The measured bendability and spring back angle in pure bending werw compared with the predictions based on the simple analyical models. Goog agreement between experimental and analytical results was observed.esults was observed.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.261-264
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• 2000

The objective of this work was to characterize mechanical properties of thermoplastic composites for various forming condition in compression molding. Randomly oriented long glass fiber reinforced polypropylene(PP) was used in the work. The composite materials contained 20%, 30%, and 40% glass fiber by weight. Compression molding was conducted to make the test specimen. Dimensional stability was measured on each forming condition with the spring-forward angle. Tensile test was conducted to characterize mechanical properties of formed parts in various forming conditions.

• 한국정밀공학회지
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• 제14권10호
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• pp.127-134
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• 1997

열가소성 복합재료는 고상 성형법에 의해 저렴한 가격으로 부피가 튼 제품의 제조에 널리 사용될 수 있어 아주 좋은 전망을 가지고 있다. 그러나, 이러한 재료의 성형성에 대해선 아직 잘 알려지지 않았다. 본 연구의 첫번때 주안점은 2축 인장성형시 성형성에 대한 연구에 두었다. 실험에 사용된 재료는 임의의 방향으로 위치한 유리 섬유를 중량비로 20, 35, 40% 함유한 폴리프로필렌이다. 성형시험은 75 .deg. C 에서 150 .deg. C 사이의 온도에서 행했으며, 펀치 속도는 0.01cm/sec 와 1cm/sec 에서 행했다. 2축 인장성형에서 측정된 한계 변형률(Limiting Strain)은 Marciniak 불완전성 (Imperfection) 이론에 근거한 예견치외 비교되었다. 이론치와 실험치가 잘 일치함을 보였으며, 성형한계선도(Forming Limit Diagram) 로써 결과들을 요약하였다. 성형한계 변형률은 성형온도와 성형속도에 의해 크게 영향을 받는다는 것을 보인다. 이러한 결과들은 적절한 성형조건이 선택된다면 열가소성 복합재료의 인장성형은 실제 상업적으로 이용하기에 충분한 성형성을 갖는다는 것을 보인다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.29-32
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• 2001

The objective of this work was to optimize processing parameters of hybrid thermoplastic composites in compression molding. The mechanical properties of the composites manufactured with various forming conditions were measured to characterize processing parameters. Polypropylene(PP) composites containing randomly oriented long carbon fiber and carbon black were used in this work. The composite materials contained 5%, 10%, 15%, and 20% carbon fiber and 5%, 10%, 15%, 20%, and 25% carbon black by weight. Compression molding was conducted at various mold temperatures. The temperature of the material in the mid-plain was monitored during the forming. Crystallinity was also measured by using XRD. The tensile modulus of the composites increase, with increasing the mold temperature. However, the impact strength of the composites decreases as mold temperature increases.

• 대한기계학회논문집A
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• 제25권8호
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• pp.1220-1226
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• 2001

This study investigates the effects of the pre-strain level on mechanical properties of the solid-phase formed thermoplastic composite. A uniaxial solid-phase forming was performed at the temperature of 125$\^{C}$ and at the constant cross-head speed of 3mm/sec. The composite sheet was formed to various pre-strain levels of 10%, 20%, and 30%. Tension, flexural, and impact tests were carried out to characterize the material properties of a solid-phase formed part. Tensile and flexural strengths decreased with increasing the pre-strain level, while impact strength increased. Various microstructures of the formed part explained the above material behavior.

• Composites Research
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• 제34권5호
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• pp.296-304
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• 2021

본 연구에서는 유한요소법(FEM)에 기반한 CF/PEKK 열가소성 복합재 고속 열 성형 해석을 수행하였고 제작 공정을 예측 및 검증하였다. 대표적인 L 형 구조물 모델에 대해 트리밍 여유에 따른 성형성을 응력, 두께, 주름분포를 분석하였다. 그 결과, 블랭크의 트리밍 여유가 증가할수록 구조물의 성형성이 향상하는 것을 확인하였다. 특히 두께 및 주름 분포 측면에서 해석 모델과 실험 결과를 비교하여서 고속 열 성형 모델의 타당성을 검증하였다. 제작된 구조물은 시차 주사 열량 분석법 및 이미지 분석법을 통해 결정화도와 기공률이 측정되었다. 제작된 열가소성 구조물의 전 영역 기공률은 평균 0.75%, 결정화도는 약 21%로 항공기에 적용 가능한 수치로 평가되었다. 따라서 본 연구를 토대로 열가소성 복합재 고속 열 성형 공정에 대해 효과적인 예측이 가능할 것으로 판단된다.

• Journal of the Korean Wood Science and Technology
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• 제26권2호
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• pp.38-44
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• 1998

A new device that uses turbulent air for mixing wood fibers with thermoplastic fibers was designed and its mixing effectiveness was evaluated in wood fiber and polypropylene fiber composites. Composites made by the turbulent air mixing (TAM) process performed better than composites made by the conventional Rando-Webber forming or nonwoven web process with an additional needling step. Thus, the TAM process proved to be a simple and efficient method in mixing wood fibers with short thermoplastic fibers for the production of wood fiber and thermoplastic fiber composites.

• 한국자동차공학회논문집
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• 제4권5호
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• pp.206-214
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• 1996

Because of the wide variety of the composite materials, inherent variability in properties, and complex temperature and strain rate dependence, large strain behavior of these materials has not been well characterized. Large strain behavior under uniaxial tension is characterized over a range of temperatures and strain rates, and a modified simple linear viscoelastic model is fit to the observed data. Of particular importance is the strain rate and temperature dependence of these composites, and it is the primary focus of this study. The strain rate and temperature dependence is then used to predict limiting tensile strains, based on Marciniak imperfection theory. Excellent correlation was obtained between model and experiment and the results are summarized in maps of forming limit as a function of strain rate and temperature.