Papers by Keyword: Delamination

Abstract: The buckling of the piezoelectric laminated cylindrical shell with throughout circumference delamination is analyzed in this paper. By introducing the Heaviside step function into assumed displacement components and using elastic piezoelectric theory, the constitutive relations of the piezoelectric laminated shell with delamination are established. Then the buckling governing equations of the structure are derived through variational principle. In numerical examples, the effects of delamination length, depth, material property and thickness of piezoelectric layer on the buckling load of piezoelectric laminated shell with delamination are investigated.

Abstract: Wood, a potentially good construction material in terms of sustainability, has less structural use now in India. Due to easy availability, low cost and good working quality there is a scope for the value addition of rubber wood in the Country. Finger jointing technology benefits high economic advantage by upgrading rubber wood. There is a dearth of information for the influence of adhesive on the mechanical properties of jointed rubber wood in India. This study was conducted to evaluate the effects of adhesive type on the end jointing and face gluing of rubber wood. The end jointing adopted for the study was the most common finger joint configuration of the wood industry in Kerala, the largest producer of rubber wood in the Country. The adhesives were polyvinyl acetate (PVAc) and phenol resorcinol formaldehyde (PRF). The face gluing evaluation was done based on the adhesive bond strength and percentage wood failure. The integrity of glue types to delamination was also tested .The results of the study have indicated glue type has no statistically significant effect on modulus of rupture, modulus of elasticity of finger joints and the shear strength of adhesive bond in the dry stage with the same wood failure percentage. The joint efficiency of PRF adhesive was superior to PVAc in tension and compression of finger joints. The PRF adhesive exhibited excellent performance in the exterior exposure condition durability test.

Abstract: Conventional-drilling (CD) methods often initiate discrete damage phenomena such as micro-cracking, matrix burning; delamination and fibre pull-out in difficult-to-machine heterogeneous materials such as carbon fibre-reinforced polymer (CFRP) composites. Ultrasonically assisted drilling (UAD) is a promising machining technique suitable for drilling holes in CFRP composites. UAD has been shown to possess several advantages over CD, including reduction in a thrust force and torque, diminished burr formation at drill exit in ductile materials and an overall improvement in roundness and surface finish of the drilled hole. Recently, our in-house experiments of UAD in CFRP composites demonstrated remarkable reductions in levels of thrust force and torque (average force reductions in excess of 60%) when compared to CD with the same machining parameters. 3D Finite Element (FE) models of CD and UAD techniques for a CFRP laminate were developed using a general-purpose FE software ABAQUS/Explicit and validated using experimental results. The magnitudes of thrust force and torque obtained with FE analysis of UAD are compared with those for CD. The numerical results obtained with the developed FE model were found to be in a good agreement with the experimental data.

Abstract: Glass fiber reinforced plastics (GFRP) are finding increased applications in various engineering fields such as aerospace, automotive, electronics and other industries. Among the various machining processes, drilling is the important process, mainly used in joining of composite structures. As a consequence, the number of authors have discussed on the aspects concerning the machiniability of GFRP composites. In this study, a review has been done on the machinability of drilling of GFRP composites through the various aspects such as tool materials and geometry, machining parameters and their influence on thrust force, torque, surface roughness, delamination factor and hole damage. Additionally, the modeling of the machining parameters on drilling of GFRP composites using response surface methodology (RSM), artificial neural network (ANN), fuzzy logic, NSGA-II etc., have been discussed. The results indicated that the thrust force, torque and surface roughness need to be controlled simultaneously for delamination free drilling. Further, there is a need to create a multi-response optimization in drilling of GFRP composites using different optimization techniques for obtaining optimum results of thrust force, torque, surface roughness and delamination free drilling.

Abstract: Micromechanical cleavage is one of the methods used for isolation of single-and few-layer graphene sheets from bulk graphite. On the surface of peeled graphite flakes, nanosteps of precisely multiple-layer thickness are often observed. The nanosteps are believed to be termination edge of graphene sheets and formed by tearing graphene sheets sandwiched in the mouth of a main cleavage crack during the peeling process. In the present work, we introduce a continuum model to examine the peeling process that involves multiple fractures: the main cleavage fracture at the microscale, delamination of a graphene sheet from bulk graphite at the nanoscale, and tearing fracture of graphene at the atomistic scale. We apply von Karman's plate theory to model the graphene layer, the elastic fracture mechanics for the microscale cleavage crack, and a cohesive zone model for the nanoscale interlayer delamination and for the lattice-scale tearing fracture as well. With a reliable empirical interlayer potential, we could reveal the characteristic length scales involved in the multiscale fracture process. We show that the graphene layer is locally stretched to fracture in mode-I when von Karman's finite deflection effect in a plate is invoked, although the loading by the sandwiching cleavage crack faces is nominally tearing in mode-III.

Abstract: The main purpose of composite materials drilling is the need to put together different parts of a structure, in aeronautics for example. The objective of this study is to experimentally analyze the influence of drilling on a carbon/epoxy composite. Three geometries of drill, a range of cutting speed and feed have been tested. Thrust forces and moments have been recorded during machining and macroscopic analyses have been conducted to examine outside and inside surfaces of the holes. Damages have been also quantified using delamination factor F_d. Experimental results have shown significant influences of feed and drill geometry on delamination and the best results have been obtained using a spur drill.

Abstract: In this study a numerical simulation model was designed for representing the joining process of carbon fiber-reinforced plastics (CFRP) and aluminum alloy with semi-tubular self-piercing rivet. The first step towards this goal is to analyze the piercing process of CFRP numerical and experimental. Thereby the essential process parameters, tool geometries and material characteristics are determined and in finite element model represented. Subsequently the finite element model will be verified and calibrated by experimental studies. The next step is the integration of the calibrated model parameters from the piercing process in the extensive simulation model of self-piercing rivet process. The comparison between the measured and computed values, e.g. process parameters and the geometrical connection characteristics, shows the reached quality of the process model. The presented method provides an experimental reliable characterization of the damage of the composite material and an evaluation of the connection performances, regarding the anisotropic property of CFRP.

Abstract: The drilling of composite materials can produce, around the hole, defects and damages which decrease the mechanical resistance of the drilled workpiece. This study shows the influence of several tools (drill, mill and reamer) on the hole quality obtained, in the context of reference parts where surface integrity is a priority. An experimental study is suggested and the criteria used to assess the hole quality are defined. Results show the behavior of each type of cutting tool and their influence on the defects generated. Finally, this study helps creating a scale of recommended cutting conditions to reduce the tool wear and improve the hole quality.

Abstract: A mathematical model for plates with partially delaminated layers is presented to investigate their behavior. In this formulation account is taken of lateral strains. The principal advantage of the element is that it allows the modeling of delamination anywhere in the structure. The region without delamination is modeled to carry constant peel and shear stresses; while the region with delamination is modeled by assuming that there is no peel and shear stress transfer between the top and bottom layers. Numerical results of the present model are presented and its performance is evaluated for static problems. Laminated beams and plates are often used as primary load-carrying structures. However, the mechanical properties of composite materials may degrade severely in the presence of damage. One of the common types of damage modes in laminated composites is delamination. The presence of delamination is one of the most prevalent life-limiting failure modes in laminated composite structures. Many researchers had been studying the effect of delamination. Wee and Boay [1] developed an analytical model to predict the critical load of a delaminated composite laminated beam. Lee et al. [2] investigated the buckling behavior of the beam plate with multiple delaminations under compression. Kapania and Wolfe [3] examined the buckling behavior of a beam plate with two delaminations of equal length. Wang et al. [4] improved the analytical solution by including the coupling between the flexural and axial vibrations of the delaminated sub-laminates. Lee et al. [5] studied a composite beam with arbitrary lateral and longitudinal multiple delamination. Finite-element methods have been developed using the layerwise theory by Kim et al. [6]. Tan and Tong [7] developed a dynamic analytical model for the identification of delamination embedded in a laminated composite beam. To investigate the effects of delamination of a plate layers, a finite-element model is developed. Both displacement continuity and force equilibrium conditions are imposed between the regions with and without delamination. The accuracy of the approach is verified by comparing results with previously published data.

Abstract: Carbon fiber reinforced plastic (CFRP) composites are often used in combination with other materials, requiring it to be machined during fabrication of a structure. Drilling as the most common machining process of CFRP is complex often results in delamination of the composites. The complexity is contributed by CFRP composites fiber orientation which can be of unidirectional or quasi-isotropic type depending on the applications. This study reviews the machinability of CFRP composites by considering fiber orientation and machining conditions used during drilling. Their relation with machining thrust force which leads to delamination is the central theme. An insight in obtaining delamination-free holes is also discussed.