Examination and modification of equivalent delamination factor for assessment of high speed drilling

J. Babu,Nevin Paul Alex,Keerthy P. Mohan,Jose Philip,J. P. Davim 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.11

Composite components suffer delamination at the entrance and exit of drilled holes. Many measures have been suggested by different researchers to assess such delamination damage. These include delamination factor, two-dimensional delamination factor, damage ratio, adjusted delamination factor, refined delamination factor, equivalent delamination factor, and minimum delamination factor. Among all these various assessment factors, the equivalent delamination factor looks simple and able to take into account the different features of delamination. However, the method of calculation of the equivalent delamination factor may not provide accurate values for delamination resulting from high speed drilling. The aim of this paper is to evaluate the equivalent delamination factor in high speed drilling of a composite laminate using a twist drill and develop a new approach to determine equivalent delamination factor which can be used for both conventional and high speed drilling conditions. This new method is applied to calculate the equivalent delamination factor in trials of drilling composite specimens at different speeds and feed rates and is found suitable.

Effects of Size and Location of Initial Delamination on Post-buckling and Delamination Propagation Behavior of Laminated Composites

Abebaw Abie Mekonnen,우경식,강민송,김인걸 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.1

In this paper, buckling, post-buckling, and delamination behavior of composite laminates subjected to axial compression was studied. First, compression tests were performed for composite laminate specimens with through-width delamination and the history of buckling and delamination propagation was measured. Next, the tests were simulated using two-dimensional finite-element models. A geometrically non-linear post-buckling analysis was performed for the finite-element mesh seeded with small amount of geometric imperfection based on eigenmodes. The growth of delamination due to sub-laminates buckling was simulated using the cohesive zone modeling. The analysis results were compared with the test results for the verification of the numerical model. Then, the analysis results were examined to study the relation between geometric parameters of initial delamination and buckling loads and post-buckling delamination propagation behavior of the composite laminates. The effects of different sizes and locations of initial delamination on the delamination behavior were systematically investigated. It was found that the buckling loads, mode shapes, and the delamination growth behavior are affected by the geometry variation of pre-included delamination. The long and shallow initial delaminations prompt local buckling the deep delaminations induce global buckling mode.

Post-buckling and delamination propagation behavior of composite laminates with embedded delamination

Abebaw Abie Mekonnen,우경식,강민송,In-Gul Kim 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.3

Delamination occurred due to poor manufacturing process or in-service actions significantly affects the mechanical and failure behavior of laminated composite structures. In this study, the buckling and post-buckling delamination behavior of laminated composite with an embedded initial delamination under in-plane compression was studied experimentally and numerically. First, compression tests for laminated composite specimens with embeded initial delamination were performed and the buckling and delamination responses were obtained. Then the experimental test was numerically simulated using finite element methods with the progressive failure accounted for by using cohesive zone modeling. The load-displacement curve, strain behavior and delamination shapes of experimental specimens obtained from load cells, strain gages installed at different locations, and C scan images, respectively, were compared with the FEM results, and good agreements were attained. The effect of the buckling modes, laminate stacking sequence and shape of initial delamination on the buckling load and propagation behavior was studied by considering different ply stacking and shapes of initial delaminations. It was found that the buckling mode determined the growth direction of the delamination propagation, and the stacking sequence influenced the extent of the propagation area, while the orientation of the delamination affected the buckling loads.

Finite element based dynamic analysis of multilayer fibre composite sandwich plates with interlayer delaminations

Jayatilake, Indunil N.,Karunasena, Warna,Lokuge, Weena Techno-Press 2016 Advances in aircraft and spacecraft science Vol.3 No.1

Although the aircraft industry was the first to use fibre composites, now they are increasingly used in a range of structural applications such as flooring, decking, platforms and roofs. Interlayer delamination is a major failure mode which threatens the reliability of composite structures. Delamination can grow in size under increasing loads with time and hence leads to severe loss of structural integrity and stiffness reduction. Delamination reduces the natural frequency and as a consequence may result in resonance. Hence, the study of the effects of delamination on the free vibration behaviour of multilayer composite structures is imperative. The focus of this paper is to develop a 3D FE model and investigate the free vibration behaviour of fibre composite multilayer sandwich panels with interlayer delaminations. A series of parametric studies are conducted to assess the influence of various parameters of concern, using a commercially available finite element package. Additionally, selected points in the delaminated region are connected appropriately to simulate bolting as a remedial measure to fasten the delamination region in the aim of reducing the effects of delamination. First order shear deformation theory based plate elements have been used to model each sandwich layer. The findings suggest that the delamination size and the end fixity of the plate are the most important factors responsible for stiffness reduction due to delamination damage in composite laminates. It is also revealed that bolting the delaminated region can significantly reduce the natural frequency variation due to delamination thereby improving the dynamic performance.

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.

Experimental evaluation of coating delamination in vinyl-coated metal forming

Young-ki Son,Chan-joo Lee,Jung-min Lee,Sang-doek Byoen,Soen-bong Lee,Byung-MinKim 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.10

In this paper, a new evaluation and prediction method for coating delamination during sheet metal forming is presented. On the basis of the forming limit diagram (FLD), the current study evaluates the delamination of PET coating by using a cross-cut specimen, dome test, and rectangular-cup drawing test. Dome test specimens were subjected to biaxial, plane strain, and uniaxial deformation modes. Rectangular cup- drawing test specimens were subjected to the deep-drawing deformation mode, and compression deformation mode. A vinyl-coated metal (VCM) sheet consists of three layers of polymer on the sheet metals: a protective film, a PET layer and a PVC layer. The areas with coating delamination were identified, and the results of the evaluation were plotted according to major and minor strain values, depicting coating delamination. The constructed delamination limit diagram (DLD) can be used to determine the forming limit of VCM during the complex press-forming process. ARGUS (GOM) was employed to identify the strain value and deformation mode of the delaminated surface after the press forming. After identifying the areas of delamination, the DLD of the PET coating can be constructed in a format similar to that of the FLD. The forming limit of the VCM sheet can be evaluated using the superimposition of the delamination limit strain of the coating onto the FLD of VCM sheet. The experimental results showed that the proposed test method will support the sheet metal forming process design for VCM sheets. The assessment method presented in this study can be used to determine the delamination limit strain under plastic deformation of other polymer coated metals. The experimental results suggested that the proposed testing method is effective in evaluating delamination for specific applications.

테라헤르츠 중첩 신호의 FWHM 분석을 통한 유리섬유 복합재료 내부 미세 박리 검출 기술

김헌수 ( Heon-Su Kim ),박동운 ( Dong-Woon Park ),김상일 ( Sang-il Kim ),김학성 ( Hak-sung Kim ) 한국복합재료학회 2021 Composites research Vol.34 No.3

유리섬유 복합재료(GFRP) 내부 미세 박리에서 나타나는 테라헤르츠(THz) 중첩 신호의 FWHM 분석을 통한 미세 박리 검출 기술을 연구하였다. 테라헤르츠 시간영역 분광(THz-TDS) 시스템의 반사모드를 통해 유리섬유 복합재료 내부의 미세 박리 크기 별 THz 신호를 측정하였고, 미세 박리 위치에서 반사되어 검출되는 THz 중첩 신호의 Full Width Half Maximum (FWHM) 값을 추출하였다. 이후, 유리섬유 복합재료의 복소굴절률을 측정하여 미세 박리 크기에 따른 미세 박리 위치에서의 THz 중첩 신호 및 FWHM 값을 계산하여 비교하였다. 이론적으로 계산된 THz 중첩 신호로부터 미세 박리 크기와 중첩 신호에서의 FWHM 값의 상관관계를 도출하였으며, 미세 박리 위치에서의 THz 신호로부터 추출된 FWHM의 분석을 통해 미세 박리 크기를 예측할 수 있었다. Full width half maximum (FWHM) analysis of superimposed terahertz (THz) signals in the glass fiber reinforced polymer (GFRP) was studied to detect fine delamination inside GFRP. The THz signals were measured for each fine delamination size inside the GFRP using the reflection mode of the terahertz time domain spectroscopy (THz-TDS) system. Then, the FWHM of the superimposed THz signal reflected at the fine delamination was extracted. Thereafter, the complex refractive index of the GFRP was measured using transmission mode of the THz-TDS system. Based on this, the FWHM of the superimposed THz signal at the fine delamination were calculated and compared with respect to the fine delamination size. From the theoretically calculated superimposed signals, the relationship between the fine delamination size and the FWHM in the superimposed THz signal was derived. Consequently, the fine delamination size could be predicted through the analysis of the FWHM extracted from the THz signal at the fine delamination.

Elastic Buckling Analysis of Laminated Composite Plates with Through-the-width Delamination Using EAS Solid Element

Dae Yong Park,Suk Yoon Chang,Sung Soon Yhim 대한토목학회 2007 KSCE journal of civil engineering Vol.11 No.1

Delamination reduces an elastic buckling load of the laminated composite structures and lead to global structural failure at loads below the design level. Therefore, the problem of the delamination buckling of laminated composite structures has generated significant research interest and has been the subject of many theoretical and experimental investigations. However, questions still remain regarding a complete understanding and details of the phenomena involved. In this paper an efficient finite element model is presented for analyzing the elastic buckling behavior of laminated composite plates with through-the-width delamination using a solid element based on a three-dimensional theory. The solid finite element, named by EAS-SOLID8, is based on an enhanced assumed strain method. The study for elastic buckling behavior of laminated composite plates with through-the-width delaminations are focused on various parameters, such as size of delamination, support condition, aspect ratio, width-to-thickness ratio, stacking sequences, and location of delamination and multiple delaminations.

박리된 콘크리트의 진동 모드 형상을 이용한 콘크리트 구조물 박리 손상 영역 가시화 (I) : 모드 시험

오태근 ( Tae Keun Oh ),신성우 ( Sung Woo Shin ) 한국안전학회(구 한국산업안전학회) 2013 한국안전학회지 Vol.28 No.5

Delamination of cover concrete due to re-bar corrosion is a critical damage reducing structural safety of reinforced concrete structures. Therefore, it should be detected and evaluated to provide appropriate maintenance to recover structural integrity. Impact-echo method, which utilizes thickness vibration characteristics of delaminated concrete section, is effective for detection and evaluation of small areal size delamination. However, it may not be applicable for large areal size delamination in which flexural vibration modes are dominated. In this study, applicability of vibration mode shapes of delaminated concrete section is investigated for visualization of delamination region in concrete structures. Numerical and experimental modal tests are performed to estimate mode shapes of delaminated concrete section and linear absolute summation technique is proposed for effective visualization or delamination region based on estimated mode shapes.

Delamination behaviour in differently copper laminated REBCO coated conductor tapes under transverse loading

Gorospe, A.,Nisay, A.,Shin, H.S. North-Holland 2014 Physica. C, Superconductivity Vol.504 No.-

Laminated HTS coated conductor (CC) tapes having a unique multi-layer structure made them vulnerable when exposed to transverse loading. Electromechanical transport properties of these CC tapes can be affected by excessive transverse stresses. Due to the coefficient of thermal expansion (CTE) mismatch and incompatibility among constituent materials used in coil applications, delamination among layers occurs and causes critical current, I<SUB>c</SUB> degradation in the CC tapes. In this study, the delamination behaviors in copper (Cu) solder-laminated CC tapes by soldering and surround Cu-stabilized ones by electroplating under transverse tension loading were investigated. Similarly to the surround Cu-stabilized CC tapes in our previous reports, the Cu solder-laminated CC tapes also showed an abrupt and gradual I<SUB>c</SUB> degradation behavior. However, the Cu solder-laminated CC tapes showed different delamination morphologies as compared to the surround Cu-stabilized CC tapes; the superconducting side and the substrate side of the Cu solder laminated CC tapes were totally separated by delamination. On the other hand, the brass laminate did not show any significant effect on the delamination strength when it is added upon the surround Cu-stabilized CC tapes.