THERMAL EFFECTS ON THE STRAIN ENERGY RELEASE RATE FOR EDGE DELAMINATION IN CRACKED LAMINATED COMPOSITES

C Soutis,M Kashtalyan 한국추진공학회 2001 한국추진공학회 학술대회논문집 Vol.2001 No.4

Study on Scaling Effects of Compressive Strenth of Carbon Fibre-Epoxy Laminate

Lee, J.,Soutis C.,Kong, C. 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.2

SPECIMEN SIZE EFFECT ON THE COMPRESSIVE STRENTH OF CARBON FIBRE-EPOXY LAMINATES CONSIDERING THE INFLUENCE OF THE ANTI-BUCKLING DEVICE

Lee, J,Soutis, C.,Kong, C. 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.1

The in-plane size effect of specimen gauge section (length x width) was investigated on the compressive behaviour of a T300/924C (45/-45/0/90]_(3s), carbon fibre-epoxy laminate. A modified ICSTM compression test fixture was used together with an anti-buckling device to test 3mm thick specimens with a 30 x 30, 50 x 50, 70 x 70 and 90mm x 90mm gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post failure examination suggests that 0° fibre microbuckling is the critical damage mechanism that causes final failure. This is a matrix dominated failure mode and its triggering depends very much on initial fibre waviness. It is suggested that manufacturing process and quality may play a significant role in determining the compressive strength. When an anti-buckling device was used to prevent out-of plane deflections, it was observed that the compressive strength of the larger specimens with the device was 6-12% greater than that measured for a 30mm x 30mm specimens with similar anti-buckling device. This is due to surface larger friction between the specimen and the device. From the analytical results on the influence of the anti-buckling device using finite element method, it was found that the compressive stress calculated with the frictional pressure on the gauge section surface introduced by anti-buckling device was about 7% higher than actual compressive stress. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of fibre microbuckling and delamination initiates at the edge of the hole at approximately 80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3 mm (depends on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of compressive unnotched strength and in-plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.

두꺼운 일방향 탄소-에폭시 라미네이트의 정적 압축강도에 관한 연구

이정환,Costas Soutis,공창덕 朝鮮大學校 機械技術硏究所 2006 機械技術硏究 Vol.9 No.1

Existing test methods for thick-section specimens (4mm) have not provided precise compressive properties to date for the analysis and design of thick structure. A survey of the failure behavior of such thick specimens revealed that the failure initiated at the top corner of the specimen and propagated down and across the width of the specimen as premature failure, not typically reported for thin compression specimens. In the current study, the cause of the premature failure for thick specimens (T800/924C and IM7/8552) was identified experimentally and numerically. The premature failure was successfully avoided during compressive testing and the failure mode was quite similar regardless of increasing specimen thickness and specimen volume. Furthermore it was identified that the failure location within gauge section does not have an influence on the compressive strength from the experimental result performed with the unwaisted specimens (failure around junction of end tab and gauge section) and the waisted specimens (failure at the middle of gauge section). Finally, clear 1-D thickness and 3-D scaling effects on the compressive strength of unidirectional composite laminates existed. The main factors influencing the effects were due to manufacturing defects such as void content and fibre waviness.

Modelling of Low Velocity Impact Damage In Laminated Composites

Lee Jounghwan,Kong Changduk,Soutis Costas The Korean Society of Mechanical Engineers 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.4

In this study a simple model is developed that predicts impact damage in a composite laminate avoiding the need of the time-consuming dynamic finite element method (FEM). The analytical model uses a non-linear approximation method (Rayleigh-Ritz) and the large deflection plate theory to predict the number of failed plies and damage area in a quasi-isotropic composite circular plate (axisymmetric problem) due to a point impact load at its centre. It is assumed that the deformation due to a static transverse load is similar to that oc curred in a low velocity impact. It is found that the model, despite its simplicity, is in good agreement with FEM predictions and experimental data for the deflection of the composite plate and gives a good estimate of the number of failed plies due to fibre breakage. The predicted damage zone could be used with a fracture mechanics model developed by the second investigator and co-workers to calculate the compression after impact strength of such laminates. This approach could save significant running time when compared to FEM solutions.

홀을 갖는 복합재 적층판의 압축강도에 대한 크기 효과에 관한 연구

공창덕,방조혁,이정환,C. Soutis 한국항공우주학회 2001 한국항공우주학회 학술발표회 논문집 Vol.- No.-

Scaling Effects on The Compressive Strength of Carbon Fibre-Epoxy Laminate

J. Lee,C. Soutis,공창덕 한국항공우주학회 2005 한국항공우주학회 학술발표회 논문집 Vol.- No.-

홀을 갖는 탄소섬유/에폭시 복합재료 적층판의 압축강도에 관한 크기 효과 연구

공창덕,방조혁,이정환,Soutis, C. 朝鮮大學校 機械技術硏究所 2001 機械技術硏究 Vol.4 No.1

지난 20년 동안 인장하중과 굽힘 하중 상태에서 복합재료 적층판의 크기효과에 관한 많은 연구가 수행되었으며, 시편의 크기를 증가함에 따라 복합재 적층판의 강도가 저하되는 경향은 잘 알려져 있다. 그러나, 복합재 압축시험의 어려움으로 인해 압축하중 상태에서 시편의 파괴강도에 대한 크기효과에 관한 연구는 거의 수행되지 않았다. 본 연구에서는 홀을 갖는 복합재의 압축 강도에 대한 크기효과를 고찰하기 위해 T300/924C, 〔45°/-45°/0°/90°〕_3s를 사용하였으며, 시편의 크기 변화를 위해 2차원 면적 변화(시편의 폭 및 길이 변화)를 고려하는 평면 스케일링 방법을 사용하였다. 실험 결과는 유한 폭을 가지는 평판에 대한 명확한 홀 크기 효과를 보였을 뿐만 아니라, 같은 a/W(홀 직경/시편 폭)를 갖는 시편에서도 크기 효과를 확인할 수 있었다. 반면에 홀이 없는 시편은 명확한 강도 크기 효과를 보이지 않았다. Over two decades, many research have been performed studies on strength size effects in composite laminates under tensile and flexural loads. It is well known that there is a tendency for the strength of fibre-reinforced composites to decrease with increasing specimen size. Under compressive load, however, little work has been done on the effect of specimen size on failure strength. This is due to the fact that compressive testing of composite is very difficult. In this paper, the effect of the test specimen size on the compressive strength of composite containing open hole was considered using T300/924C, 〔45°/-45°/0°/90°〕_3s. For sizing test specimens, the in-plane scaling method is used i.e., the change of two-dimensional specimen area in specimen width and gauge length. The results clearly show that there is a hole size effect in the finite width plates. In addition, the specimens which have the same a/W(hole diameter/specimen width) exhibit a tendency of size effect. In contrast, test results of the unnotched specimens did not show a clear strength size effect.

탄소/에폭시 복합재판의 압축강도 두께효과에 대한 연구

이정환,공창덕,오경원,Soutis, C. 朝鮮大學校 機械技術硏究所 2004 機械技術硏究 Vol.7 No.1

본 연구에서 복합재료의 압축강도에 대한 두께 효과가 〔0₄〕ns,〔45/0/-45/90〕ns and 〔45n/0n/-45n/90n〕s (n = 2 to 8)등의 적층방법을 이용하여 체계적인 실험을 통해 조사되었다. 엇교차 대칭 복합재판의 파괴강도에 대한 적층순서효과도 조사되었다. 이를 위해 2종류의 다른 스케일링을 갖는 (1) 플라이레벨 기법인 〔45n/0n/-45n/90n〕s과 (2)서브라미네이트-레벨기법인 〔45/0/-45/90〕ns가 적용되었다. 일방향 적층시편 〔0₄〕ns과 플라이레벨인 〔45n/0n/-45n/90n〕s에는 분명한 두께효과를 나타내었다. 그러나 서브라미네이트레벨인. 〔45/0/-45/90〕ns의 압축강도는 시편의 두께의 변화에도 불구하고 별 영향을 나타 나지 않았으며,서브라미네이트-레벨 시편에서 구한강도가 플라이-레벨 시편에서 구한 강도보다 약간 높았다. 측정된 파괴강도는 예측 값과 비교되었다. In this study, the effect of laminate thickness on the compressive behaviour of composite materials was investigated through systematic experimental work using the stacking sequences, 〔0₄〕ns, 〔45/0/-45/90〕ns and 〔45n/0n/-45n/90n〕 s (n = 2 to 8). The stacking sequence effects on failure strength of multidirectional laminates were examined. For this purpose, two different scaling techniques were used: (1) ply-level technique 〔45n/0n/-45n/90n〕s and (2) sublaminate level technique [45/0/-45/90]ns. An apparent thickness effect existed in the lay-up with blocked plies, i.e. unidirectional specimens ([0₄]ns) and ply-level scaled multidirectional specimens (〔45n/0n/-45n/90n〕s). From the investigation of the stacking sequence effect, the strength values obtained from the sublaminate level scaled specimens were slightly higher than those obtained from the ply level scaled specimens. The measured failure strengths were compared with the predicted values.

T800/924C 탄소-에폭시 복합재판의 압축강도에 대한 두께 효과

이정환 ( J. Lee ),공창덕 ( C. Kong ),( C. Soutis ) 한국복합재료학회 2004 Composites research Vol.17 No.4