HIGH-STRAIN-RATE FRACTURE OF ADHESIVELY BONDED COMPOSITE JOINTS IN DCB AND TDCB SPECIMENS

조재웅,A. KINLOCH,B. BLACKMAN,F. S. RODRIGUEZ SANCHEZ,한문식 한국자동차공학회 2012 International journal of automotive technology Vol.13 No.7

Double-cantilever beam (DCB) and tapered double-cantilever beam (TDCB) specimens are the test configurations most commonly used to measure the fracture toughness of composites and adhesive joints. Strain rates of 1 to 18.47 m/s were applied to the test specimens via high-speed hydraulic test equipment. Because the fracture occurs through the adhesively bonded joints and the cracks grow rapidly, the crack length and beam displacement were recorded by a high-speed camera. An energy range from 0 to 10 J was often observed in the high-strain-rate fracture experiments for nonlinear plastic behavior of the dynamically loaded adhesively bonded DCB and TDCB specimens. The range of energy release rates (fracture energy) for TDCB specimen was 2 to 3 times higher than that of a DCB specimen for all high strain rates. The fracture energy of automotive adhesive joints can be estimated using the experimental results in this study for the fracture toughness (GIC) under high rates of loading. The crack grows as the applied fracture energy exceeds the value of the critical energy release rate (GIC) at the crack tip. The energy release rate was calculated using the fracture mechanics formula. The key fracture mechanics parameter, the fracture energy GIC, was ascertained as a function of the test rate and can be used to assess and model the overall joint performance.

탄소섬유쉬트로 보강된 철근콘크리트보의 계면박리에 대한 해석적 연구

심종성,배인환,Sim, Jong-Sung,Bae, In-Hwan 한국콘크리트학회 1999 콘크리트학회지 Vol.11 No.2

본 연구의 목적은 탄소섬유쉬트로 보강된 시험체의 주요 파괴모드인 계면모드인 계면박리 모드에 의한 부재의 파괴를 규명하는 것이다. 탄소섬유쉬트로 보강된 손상된 보시험체의 계면박리 모드를 해석하기 위하여 선형탄성 파괴역학(LEFM)의 컴플라이언스법과 유한요소법을 사용하여 계면파괴 역학변수인 에너지해방율(strain energy release rate, G)을 고찰하였다. 손상된 단순 보시험체의 해석결과, 최대 에너지해방율($G_{max}$)은 에폭시 접착두께에 관계없이 바깥 휨균열에서 시작된 계면 전단 균열 길이가 18mm 부근에서 발생하였다. 보강보의 강도 해석결과, 극한강도 설계법에 따른 단면의 공칭 휨 강도에 대한 계면박리에 의해 부재가 파괴되는 것으로 해석되었다. 또한 적용된 접착두께 1mm~3mm는 에너지해방율에 거의 영향을 미치지 않아 계면박리의 주요 인자가 아닌 것으로 나타났다. The purpose of this study is to analyze the interface debonding of RC beams strengthened by carbon fiber sheet(CFS). The behavior of damaged RC beams strengthened with CFS is analytically investigated next using linear elastic fracture mechanics(LEFM) approach and the finite element method. The study includes an investigation of the separation mode by interface fracture of the strengthening materials due to the interfacial shear and normal stresses. The numerical method is presented to obtain the value of interfacial fracture parameter such as the strain energy release rate. Based on the results of this study, it is found that the critical case occurs when the interfacial cracks occur within a short region of the flexural crack. The CFS strengthening has not an adequate factor of safety against interfacial debonding of CFS. Furthermore, for the thicknesses of the adhesive studied[1mm~3mm], it is no noticeable effect on the strain energy release rate.

탄소섬유 / 에폭시 복합재료의 TTSCB 시편을 이용한 Mode Ⅲ 층간분리 특성 연구

유치상(C. S. You),김석산(S. S. Kim),황운봉(W. Hwang),한경섭(K. S. Han) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3

Interlaminar fracture toughness of carbon/epoxy composite materials have been investigated under Mode Ⅲ loading by newly designed test device. Thickness tapered split cantilever beam(TTSCB) specimen modified with width tapered double cantilever beam(WTDCB) was used. The data reduction for evaluating the strain energy release rate is based upon compliance and beam methods. This study have examined the effect of various ply orientation and obtained critical strain energy release rate. The stacking sequence of investigated laminates was 7 cases, which θ is 0°, 30°, 45° and 60° and β is 30°, 60° and 90°. The results difference between two methods was due to difference of compliance slope. As a results, when initial crack between layers has same orientation we can't obtain critical strain energy release rate and critical strain energy release rate decrease while β increase.

Strain energy release rates in the curved spar wingskin joints with pre-embedded delaminations

P.K. Mishra,A.K. Pradhan,M.K. Pandit,S.K. Panda 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.87 No.1

Any pre-existed delamination defect present during manufacturing or induce during service loading conditions in the wingskin adherend invariably shows a greater loss of structural integrity of the spar wingskin joint (SWJ). In the present study, inter-laminar delamination propagation at the critical location of the SWJ has been carried out using contact and multi-point constraint finite elements available with commercial FE software (ANSYS APDL). Strain energy release rates (SERR) based on virtual crack closure technique have been computed for evaluation of the opening (Mode-I), sliding (Mode-II) and cross sliding (Mode-III) modes of delamination by sequential release of multi point constraint elements. The variations of different modes of SERR are observed to be significant by considering varied delamination lengths, material properties of adherends and radius of curvature of the SWJ panel. The SERR rates are seen to be much different at the two pre-embedded delamination ends. This shows dissimilar delamination propagation rates. The maximum is seen to occur in the delamination front in the unstiffened region of the wingskin. The curvature geometry and material anisotropy of SWJ adherends significantly influences the SERR values. Increase in the SERR values are observed with decrease in the radius of curvature of wingskin panel, keeping its width unchanged. SWJs made with flat FRP composite adherends have superior resistance to delamination damage propagation than curved composite laminated SWJ panels. SWJ made with Boron/Epoxy (B/E) material shows greater resistance to the delamination propagation.

변형률 에너지 해방률에 기반한 Carbon/Epoxy 직교적층판의 모드 I 층간 및 층내 파괴 특성 분석

강민송 ( Min-song Kang ),전민혁 ( Min-hyeok Jeon ),김인걸 ( In-gul Kim ),우경식 ( Kyeong-sik Woo ) 한국복합재료학회 2019 Composites research Vol.32 No.1

본 논문에서는 Cross-ply 탄소섬유/에폭시 복합재 적층판의 모드 I 층간분리 특성을 분석하였다. 이를 위하여 Cross-ply 시편에 대한 Double-Cantilever Beam(DCB) 시험을 수행하였다. Cross-ply DCB 시편의 경우 층간 및 층내 파괴를 포함한 복합적인 균열 성장과 기하학적 대변형에 의한 비선형성을 수반하였다. 따라서 변형률 에너지 해방률과 유한요소해석을 기반으로 비선형성을 수반한 DCB 시험에서도 적용되는 모드 I 층간 파괴인성 평가 방법을 제안하고 기존의 선형이론으로 구한 결과와 비교 분석하였다. 본 연구에서 제안한 방법으로 Cross-ply DCB 시편의 모드 I 층간 파괴인성과 모드 I 층내 파괴인성을 분류하였고 모드 I 층내 파괴인성이 더욱 낮음을 확인하였다. This paper describes the characteristics for mode I interlaminar and intralaminar fractures of cross-ply carbon/epoxy composite laminates. We obtained mode I interlaminar fracture toughness and mode I intralaminar fracture toughness based on energy release rate and Finite Element Analysis (FEA). For this purpose, the Double- Cantilever Beam (DCB) test and FEA were performed for cross-ply DCB specimens. Also, the behavior of loaddisplacement curve at the interlaminar and intralaminar crack was analyzed. The results show that mode I intralaminar fracture toughness was lower than mode I interlaminar fracture toughness in the cross-ply DCB specimen.

3D finite element analysis of stress distributions and strain energy release rates for adhesive bonded flat composite lap shear joints having pre-existing delaminations

S. K. Parida,A. K. Pradhan 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.2

The rate of propagation of embedded delamination in the strap adherend of lap shear joint (LSJ) made of carbon/epoxy composites hasbeen evaluated employing three-dimensional non-linear finite elements. The delamination has been presumed to pre-exist in the thin resinlayer between the first and second plies of the strap adherend. The inter-laminar peel and shear stress distributions have been studied indetails and are seen to be predominantly three-dimensional in nature. The components of strain energy release rate (SERR) correspondingto the opening, sliding and cross sliding modes of delamination are significantly different at the two fronts of the embedded delamination. The sequential release of multi-point constraint (MPC) finite elements in the vicinity of the delamination fronts enables to simulatethe growth of the delamination at either ends. This simulation procedure can be utilized effectively for evaluation of the status of thestructural integrity of the bonded joints.

Thermoelastic effect on inter-laminar embedded delamination characteristics in Spar Wingskin Joints made with laminated FRP composites

P.K. Mishra,A.K. Pradhan,M.K. Pandit,S.K. Panda 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.35 No.3

This paper presents two sets of full three-dimensional thermoelastic finite element analyses of superimposed thermo-mechanically loaded Spar Wingskin Joints made with laminated Graphite Fiber Reinforced Plastic composites. The study emphasizes the influence of residual thermal stresses and material anisotropy on the inter-laminar delamination behavior of the joint structure. The delamination has been pre-embedded at the most likely location, i.e., in resin layer between the top and next ply of the fiber reinforced plastic laminated wingskin and near the spar overlap end. Multi-Point Constraint finite elements have been made use of at the vicinity of the delamination fronts. This helps in simulating the growth of the embedded delamination at both ends. The inter-laminar thermoelastic peel and shear stresses responsible for causing delamination damage due to a combined thermal and a static loading have been evaluated. Strain energy release rate components corresponding to the Mode I (opening), Mode II (sliding) and Mode III (tearing) of delamination are determined using the principle of Virtual Crack Closure Technique. These are seen to be different and non-self-similar at the two fronts of the embedded delamination. Residual stresses developed due to the thermoelastic anisotropy of the laminae are found to strongly influence the delamination onset and propagation characteristics, which have been reflected by the asymmetries in the nature of energy release rate plots and their significant variation along the delamination front.

A comparative study for beams on elastic foundation models to analysis of mode-I delamination in DCB specimens

Mahmood Mehrdad Shokrieh,Mohammad Heidari-Rarani 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.2

The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus (E_fx) and out-of-plane extensional stiffness (E_z) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ([0˚]_6) and antisymmetric angle-ply ([±30˚]_5, and [±45˚]_5) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.

A comparative study for beams on elastic foundation models to analysis of mode-I delamination in DCB specimens

Shokrieh, Mahmood Mehrdad,Heidari-Rarani, Mohammad Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.2

The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus ($E_{fx}$) and out-of-plane extensional stiffness ($E_z$) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ($[0^{\circ}]_6$) and antisymmetric angle-ply ($[{\pm}30^{\circ}]_5$, and $[{\pm}45^{\circ}]_5$) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.

Enhancing the ability of strain energy release rate criterion for fracture assessment of orthotropic materials under mixed-mode I/II loading considering the effect of crack tip damage zone

Zahra Khaji and Mahdi Fakoor,Mahdi Fakoor 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.44 No.6

In this study, considering dissipated energy in fracture process zone (FPZ), a novel criterion based on maximum strain energy release rate (SER) for orthotropic materials is presented. General case of in-plane loading for cracks along the fibers is assumed. According to the experimental observations, crack propagation is supposed along the fibers and the reinforcement isotropic solid (RIS) concept is employed as a superior model for orthotropic materials. SER in crack initiation and propagation phases is investigated. Elastic properties of FPZ are extracted as a function of undamaged matrix media and micro-crack density. This criterion meaningfully links between dissipated energy due to toughening mechanisms of FPZ and the macroscopic fracture by defining stress intensity factors of the damaged zone. These coefficients are used in equations of maximum SER criterion. The effect of crack initiation angle and the damaged zone is considered simultaneously in this criterion and mode II stress intensity factor is extracted in terms of stress intensity factors of damage zone and crack initiation angle. This criterion can evaluate the effects of FPZ on the fracture behavior of orthotropic material. Good agreement between extracted fracture limit curves (FLC’s) and available experimental data proves the ability of the new proposed criterion.