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M.m. Islam - One of the best experts on this subject based on the ideXlab platform.
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A nonlinear cohesive model for mixed-mode Delamination of Composite laminates
Composite Structures, 2013Co-Authors: M.m. IslamAbstract:Abstract An anisotropic nonlinear cohesive model based on continuum damage mechanics is proposed to predict the mixed-mode Delamination initiation and growth of Composite laminates numerically. A damaged exponential traction–displacement jump relationship is proposed for the cohesive model and an exponential damage evolution law on the evolvement of displacement jump is proposed to describe the irreversible Delamination crack propagation. The implementation of cohesive model uses zero-thickness cohesive element and middle-plane isoparametric interpolation technique. The mesh size effect is solved by regulating the Delamination fracture toughness by the cohesive length, and the numerical convergence problem for the snap instability is addressed by viscous regularization. Four representative Delamination cases of Composite laminates are used to validate the proposed cohesive model: (a) double cantilever beam (mode-I), (b) end notch flexure (mode-II), (c) mixed-mode bending fracture, and (d) fixed ratio mixed mode. The effects of the cohesive strengths and mesh sizes on the global load–displacement response for four cases are studied. In addition, the numerical results using proposed cohesive model are also compared with the results obtained by the virtual crack closure technique and other existing cohesive models. The proposed cohesive model is demonstrated to predict the mixed-mode Delamination response of Composite laminates accurately and effectively.
C C Tsao - One of the best experts on this subject based on the ideXlab platform.
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effects of special drill bits on drilling induced Delamination of Composite materials
International Journal of Machine Tools & Manufacture, 2006Co-Authors: H Hocheng, C C TsaoAbstract:Drilling is the most frequently employed operation of secondary machining for fiber-reinforced materials owing to the need for joining structures. Delamination is among the serious concerns during drilling. Practical experience proves the advantage of using such special drills as saw drill, candle stick drill, core drill and step drill. The experimental investigation described in this paper examines the theoretical predictions of critical thrust force at the onset of Delamination, and compares the effects of these different drill bits. The results confirm the analytical findings and are consistent with the industrial experience. Ultrasonic scanning is used to evaluate the extent of drilling-induced Delamination. The advantage of these special drills is illustrated mathematically as well as experimentally, that their thrust force is distributed toward the drill periphery instead of being concentrated at the center. The allowable feed rate without causing Delamination is also increased. The analysis can be extended to examine the effects of other future innovative drill bits.
Y W Han - One of the best experts on this subject based on the ideXlab platform.
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evaluation of fatigue characteristics for adhesively bonded Composite stepped lap joint
Composite Structures, 2004Co-Authors: Jinhee Kim, Byeongju Park, Y W HanAbstract:Abstract The stepped lap joint for Composite structure were manufactured and tested under static and fatigue tensile load. With test results, it was found that crack was initiated at the end of overlap and propagated through the Delamination of Composite adherend. The average tensile load of the joint increased with the increasing of the number of step and edge angle of adherend, while the peak shear stress at the end of overlap decreased. But the average tensile load did not increase and was converged when the ratio value of joint length against the number of step was less than 6. The fatigue endurance limit of stepped joint was found 30% of static tensile load regardless with the geometry of specimen but the fatigue life of each load level increased significantly with the increasing of the number of step to exceed 6, the ratio value of joint length against the number of step, while the fatigue life decreased significantly when the ratio was less than 6. The ratio 6 was the critical value to be able to increase the static tensile load effectively with the increasing of step number for each joint length. The critical crack propagation distance was observed 5–7 mm from the end of overlap.
Francesco Tornabene - One of the best experts on this subject based on the ideXlab platform.
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Numerical Study of the Mixed-Mode Delamination of Composite Specimens
MDPI AG, 2018Co-Authors: Rossana Dimitri, Francesco TornabeneAbstract:The present research deals with the Delamination process in multi-layered Composite specimens, with a reduced computational effort. The adhesive interface between sublaminates is represented as a continuous distribution of elastic-brittle springs in the normal and/or tangential direction depending on the interfacial mixed-mode condition. Each Composite adherend, instead, is modelled according to the Timoshenko’s beam theory. The proposed formulation is here enhanced through the Generalized Differential Quadrature (GDQ) method, where the differential equations of the problem are solved directly in a strong form. Thus, the possibility of tracking the Delamination response of the specimens is provided locally in a numerical sense, in terms of interface stresses, internal forces and displacements but also in terms of critical fracture energies and mode mixity angles. A further check of the proposed formulation is performed with respect to some standard solutions available in literature. The good agreement between numerical and theoretical predictions verifies the efficiency of the proposed GDQ approach for the study of complex mixed-mode Delamination phenomena in Composite materials and joints
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Advanced Modeling for the Mixed-Mode Delamination of Composite Specimens
country:ITA, 2018Co-Authors: Rossana Dimitri, Francesco TornabeneAbstract:In recent years, many engineering components are made of high performance laminated Composites and adhesively bonded interfaces. One of the most important damage modes of laminated structures is related to the non-linear and irreversible Delamination process, including the formation and propagation of inter-laminar cracks, up to the complete detachment of the adherends. In this context, we address the interfacial Delamination problem through an innovative cohesive formulation, named as Enhanced Beam Theory (EBT), where the specimen is considered as an assemblage of two Composite sublaminates, partly bonded together by an elastic interface. This last one is represented by a continuous distribution of elastic springs acting along the normal and/or tangential direction, depending on the interfacial mixed-mode condition. This generalizes the idea suggested recently in [1] for a single mode-I Delamination, and extended in [2] to include mixed loading, geometrical and mechanical conditions. The problem is here handled numerically through the generalized differential quadrature (GDQ) approach, to determine the Delamination onset and propagation along weak interfaces of arbitrary shape, made of Composite materials and subjected to mixed-mode conditions. The accuracy of the proposed formulation is verified against analytical predictions and theoretical formulations available in literature [3], [4]. References [1] Dimitri, R., Cornetti, P., Manti\u10d, V, Trullo, M. and De Lorenzis L. (2017) Mode-I debonding of a double cantilever beam: a comparison between cohesive crack modeling and Finite Fracture Mechanics, International Journal of Solids and Structures 124, 57\u201372. [2] Dimitri, R., Tornabene, F. and Zavarise, G. (2018) Analytical and numerical modeling of the mixed-mode Delamination process for Composite moment-loaded double cantilever beams, Composite Structures 187, 535\u2013553. [3] Suo, Z. and Hutchinson J. W. (1990) Interface crack between two elastic layers. International Journal of Fracture 43(1), 1\u201318. [4] Hutchinson, J. W. and Suo Z. (1992) Mixed mode cracking in layered materials. Advances in Applied Mechanics, 29, 63\u2013191
H Hocheng - One of the best experts on this subject based on the ideXlab platform.
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effects of special drill bits on drilling induced Delamination of Composite materials
International Journal of Machine Tools & Manufacture, 2006Co-Authors: H Hocheng, C C TsaoAbstract:Drilling is the most frequently employed operation of secondary machining for fiber-reinforced materials owing to the need for joining structures. Delamination is among the serious concerns during drilling. Practical experience proves the advantage of using such special drills as saw drill, candle stick drill, core drill and step drill. The experimental investigation described in this paper examines the theoretical predictions of critical thrust force at the onset of Delamination, and compares the effects of these different drill bits. The results confirm the analytical findings and are consistent with the industrial experience. Ultrasonic scanning is used to evaluate the extent of drilling-induced Delamination. The advantage of these special drills is illustrated mathematically as well as experimentally, that their thrust force is distributed toward the drill periphery instead of being concentrated at the center. The allowable feed rate without causing Delamination is also increased. The analysis can be extended to examine the effects of other future innovative drill bits.