Ply Laminates Research Articles

The behaviour of compressed plate with a central cut-out, made of composite in an asymmetrical arrangement of layers

The study investigated thin carbon/epoxy composite plate elements with a central cut-out of regular shape, under uniform compression. The aim of the study was to investigate the possibility of using these elements as elastic elements whose stiffness depends on tailoring the cut-out geometry and laminate ply orientation. To ensure stable operation of the structure in the postbuckling range, the plate was assigned the properties of an unsymmetrical lay-up with extension-twisting and extension-bending couplings. The structure was analysed numerically by the finite element method. The scope of numerical simulations included linear analysis of an eigen problem using procedures for geometrically nonlinear analysis and the commercial simulation software ABAQUS®. The aim of the analysis was to determine a laminate ply orientation generating the lowest buckling mode (flexural-torsional) in order to ensure stable operation of the structure in the postbuckling range.

Application of FEM on first ply failure of composite hypar shells with various edge conditions

This study aims to accurately predict the first ply failure loads of laminated composite hypar shell roofs with different boundary conditions. The geometrically nonlinear finite element method (FEM) is used to analyse different symmetric and anti-symmetric, cross and angle ply shells. The first ply failure loads are obtained through different well-established failure criteria including Puck\'s criterion along with the serviceability criterion of deflection. The close agreement of the published and present results for different validation problems proves the correctness of the finite element model used in the present study. The effects of edge conditions on first ply failure behavior are discussed critically from practical engineering point of view. Factor of safety values and failure zones are also reported to suggest design and non-destructive monitoring guidelines to practicing engineers. Apart from these, the present study indicates the rank wise relative performances of different shell options. The study establishes that the angle ply laminates in general perform better than the cross ply ones. Among the stacking sequences considered here, three layered symmetric angle ply laminates offer the highest first ply failure load. The probable failure zones on the different shell surfaces, identified in this paper, are the areas where non-destructive health monitoring may be restricted to. The contributions made through this paper are expected to serve as important design aids to engineers engaged in composite hypar shell design and construction.

Modelling and simulation of natural fibre/epoxy composites - prediction of stress state and deformations

Natural fibres usually include hemp, jute, and flax fibres are gaining importance in composites with an increasing potential to replace synthetic fibres in advanced composites. Current glass and carbon fibre systems require large amount of energy in production, which has led to an upsurge in interest in the reinforcement potential of natural fibres. Especially with natural fibres, higher variability of mechanical properties is a major challenge. Therefore, prediction of laminate performance at early stages of design requires computation. The present work was intended to understand how the flax fibre layups and orientation affect the mechanical behaviour of laminated composites. Unidirectional, cross-ply, angle-ply, and quasi-isotropic laminates made up of flax fibre reinforced epoxy are considered to study tensile, flexural behaviour, and stress distribution in the individual laminae. A classical laminate theory, which considers elastic behaviour of the laminae, and a finite element simulation are used to predict the stress-strain response of a layered composite. Further, results showed that the quasi-isotropic flax/epoxy laminate perform better than angle-ply and cross ply laminates.

Modelling and simulation of natural fibre/epoxy composites - prediction of stress state and deformations

Natural fibres usually include hemp, jute, and flax fibres are gaining importance in composites with an increasing potential to replace synthetic fibres in advanced composites. Current glass and carbon fibre systems require large amount of energy in production, which has led to an upsurge in interest in the reinforcement potential of natural fibres. Especially with natural fibres, higher variability of mechanical properties is a major challenge. Therefore, prediction of laminate performance at early stages of design requires computation. The present work was intended to understand how the flax fibre layups and orientation affect the mechanical behaviour of laminated composites. Unidirectional, cross-ply, angle-ply, and quasi-isotropic laminates made up of flax fibre reinforced epoxy are considered to study tensile, flexural behaviour, and stress distribution in the individual laminae. A classical laminate theory, which considers elastic behaviour of the laminae, and a finite element simulation are used to predict the stress-strain response of a layered composite. Further, results showed that the quasi-isotropic flax/epoxy laminate perform better than angle-ply and cross ply laminates.

Failure mechanisms of cross-ply carbon fiber reinforced polymer laminates under longitudinal compression with experimental and computational analyses

This study investigates the failure mechanisms of cross-ply laminates subjected to longitudinal compressive loading. A sequence of failure initiation and propagation process is observed based on optical microscopy images of failed specimens. Specifically, the failure process in the cross-ply laminates involves a combination of four failure mechanisms: fiber kinking, delamination, matrix cracking, and fiber/matrix splitting. We find that the kink-bands in the middle 0° plies of the cross-ply laminates most often show a wedge shape and the angle of matrix cracks in the 90° plies is slightly larger than that of pure 90° plies. The reason has been attributed to the constraining effects by the adjacent plies. The next focus of this study is to propose hybrid micro-macro models to more systematically study the failure mechanisms of the cross-ply laminates. We show that these models accurately predict the combined failure modes of the cross-ply laminates and enable us to closely investigate the interactions of different failure mechanisms. More importantly, the hybrid models achieve great computational efficiency compared to full-scale microstructural models. The combined experimental and computational analyses presented here provide a new level of understanding of the kink-band morphology and damage mechanisms in the cross-ply laminates.

Stacking Sequence Optimization of Multilayer Composite Materials

AbstractThe application of composite materials in various types of devices has increased steadily in the past decades. Hence, it is worth investigating into the structural behavior of these materials. The optimization of stacking sequences in multilayer composite materials opens a large field of improvements in industrial applications of composite materials. The center of investigation is set on fiber reinforced laminate plies, which are examined in the case of linear anisotropic theory of elasticity and applied to an isoparametric shell element formulation. For these mechanical systems, the modeling approach using lamination parameters is consulted. Under application of these lamination parameters, an optimization problem is formulated which uses an optimization procedure based on the SQP algorithm that optimizes the material properties of laminates to maximize the stiffness of the considered structure. The material properties obtained by the optimization of the lamination parameters are converted into possible stacking sequences for laminates by using simplified approaches.

Stacking sequence selection for defect-free forming of uni-directional ply laminates

In order to meet demands for increased production rates of laminated composite components, aerospace manufacturing is being forced towards highly automated production processes such as forming. However, such automated processes increase the likelihood of inducing defects that lead to manufacturing cost and time inefficiencies which must be avoided. This paper introduces a new compatibility index, based on comparison of minimum energy (resin dominated) modes of adjacent plies that identifies stacking sequences which minimise defect formation. The index is validated using an experimental process where seven laminates with different stacking sequences are formed onto a complex tool geometry using an industrial double diaphragm former. Experimental results confirm that sequences with a high compatibility index produce defect-free parts at elevated temperature. Specifically, sequences with 90° interface angles (high compatibility indices) promote the most formable solutions and continuous 45° interfaces that spiral (e.g. 45/0/-45/90) which have a low compatibility index, produce the most problematic forming conditions owing to a shear locking behaviour. Laminate stacking sequence is thus shown to be a significant contributor, alongside temperature and vacuum rate, to quality of formed parts. The compatibility index method can therefore be used to increase production rate and quality in laminated composite manufacturing, leading to significant cost and efficiency savings.

Buckling and free vibration analysis of piezoelectric laminated composite plates using various plate deformation theories

A finite strip method was developed for buckling and free vibration analysis of piezoelectric laminated composite plates based on various plate theories such as Zigzag, Refined plate and other higher order shear deformation theory by variation of transverse shear strains through plate thickness in the form of parabolic, sine and exponential. The plate edge conditions are considered to be simply supported and the polynomial shape functions are used to evaluate the in–plane and out–of–plane deflection and rotation of the normal cross section of plates in transverse direction. Numerical results were obtained based on various shear deformation plate theories to verify the proposed method. The effects of length to thickness ratio and fiber orientation of cross–ply and angle–ply laminate were presented. Also, the effect of different electrical conditions on the critical buckling load under in–plane forces and strains is investigated and electrical buckling load and natural frequency of piezoelectric laminate composite plates are calculated through numerical examples. In addition, the new results on the effect of piezoelectric layers thickness, placement of piezoelectric layers and also the effect of length to thickness ratio in the interaction of biaxial in–plane loading on critical buckling load were studied.

Prediction of Shape Distortions in Composite Wing Structures

Abstract Shape distortions and warpage are a major source of problems for composite manufacturers. These distortions are usually accompanied by built up residual stresses. They can deform a component so that it becomes useless. It also has the capability to reduce the strength of the structure. In this paper, the three-dimensional version of the constitutive model originally proposed by Svanberg and Holmberg is employed to predict the warpage of a wing planform. The model takes into account important mechanisms such as thermal expansion, resin shrinkage and frozen-in strains developed during curing cycles. The model was implemented into ABAQUS Finite Element code as a user subroutine UMAT. The macromechanical properties of each composite layer were predicted using a micromechanics based approach, implemented into MATLAB. Results show that wings with cross ply laminates with reducing thickness along the span experienced more warpage than quasi-isotropic laminates. Furthermore, for wings with equal thickness along the span, the results show that the quasi-isotropic laminates experienced more warpage than cross ply laminates. Lastly, the results show that wings with progressively reducing thickness experience twist that is varying from the wing root to the wing tip while wings with a constant thickness experience twist mainly at the centre of the wing

Additive manufactured multi-material structure with directional specific mechanical properties based upon classical lamination theory

PurposeThis paper aims to additive manufacture (AM) the multi-material (MM) structure with directional-specific mechanical properties based on the classical lamination theory of composite materials.Design/methodology/approachThe polyjet three-dimensional printing (3DP) process is used to fabricate the MM structure with directional-specific mechanical properties. MMs within a layer are positioned and oriented based on the classical lamination theory to achieve directional-specific properties. Mechanical behavior of the AM structure was examined under various loading conditions to justify the directional-specific properties.FindingsWith MM processing capabilities of the polyjet 3DP machine, AM MM structures with directional-specific mechanical properties were fabricated. From experimentation, it was observed that the AM MM structure with a quasi-isotropic laminate has superior tensile and flexural strength, and the AM MM structure with an angle ply laminate has superior shear strength. Various mechanical properties determined through testing will be useful for the selection of an appropriate layup arrangement within a structure for appropriate loading conditions.Originality/valueThis study presents the innovative methodology for the fabrication of AM MM structures with tailor-made mechanical properties. The developed methodology paves way for using the polyjet 3DP MM structure for applications such as the complaint mechanism, snap fits and thin features, which require directional-specific properties.

Digital image processing and thermo-mechanical response of neat epoxy and different laminate orientations of fiber reinforced polymer composites for vibration isolation applications

In this study, tensile tests are performed under quasi-static loading on neat epoxy and for different laminate configurations [(0/90), (0/90/30/–60), (0/90/45/–45) and (30/–60/60/–30)] of glass/epoxy, carbon/epoxy and cross ply interply hybrid (glass/carbon/epoxy) composites. A camera-based advanced image processing technique called as digital image correlation is employed to obtain the full-field strain fields and identify the direction of failure of the matrix and composites as a function of fiber orientation angle. Further, the viscoelastic properties (storage modulus, loss modulus and loss factor) are measured over the temperature range from 20 °C–140 °C for five different frequencies (1, 10, 20, 33 and 50 Hz) using the dynamic mechanical analyzer. The glass transition temperature (Tg) is found out from temperatures corresponding to the loss modulus and loss factor peak values. The results revealed that as the temperature increases, the storage and loss moduli decrease attributed to the softening of the material because of free molecular movements. The cross ply laminates of GFRP and CFRP exhibit higher storage and loss moduli at all frequencies due to strong fiber network as compared to the other laminate configurations. The hybrid composites possess higher storage and loss moduli than GFRP and neat epoxy. The neat epoxy has higher loss factor values than composites. As the frequency increases, the Tg shifts to higher values. Loss modulus Tg values are found to be lower than that of loss factor Tg values.

Understanding the Thickness Effect on the Tensile Strength Property of Dyneema®HB26 Laminates.

In this study, an experimental and numerical investigation is presented on the effect of thickness and test rate within the pseudo static regime on the tensile properties of Dyneema®HB26 laminates. A detailed experimental presentation on the tensile testing of different thickness is presented and highlights the commonly seen observation that the tensile strength of a laminate reduces as a function of the specimen thickness. To understand these experimental observations, a constitutive material model of the individual macro fibril is developed and applied to modelling the fibre and upscaling to the laminate. The modelling strategy is implemented into ls-dyna and used to perform a parameter study on the specimen geometries used in the experimental study. The model assumes that the fibril strength is a function of the amorphous volume within the fibre and hence fibril. It can be observed that the experimental behaviour can be simulated by modelling the interface between laminate plies and the fibril, and hence fibre failure. The weak interfaces from the fibril to the laminate scale make the testing of fibres and laminates very difficult. Hence, it is proposed that the intrinsic fibril strength should be used as a measure of strength, and the fundamental strength is determined through numerical studies.

On the constitutive modelling and damage behaviour of plain woven textile composite

The present work deals with the constitutive modelling and progressive failure analysis (PFA) of plain woven textile composites (PWTC). Two novel approaches, equivalent cross ply laminate (ECPL) coupled with classical laminate theory and Mori–Tanaka theory, are developed to compute homogenized properties of PWTC lamina. The PFA of PWTC lamina is performed coupling isotropic damage mechanics with ECPL theory, and meso-scale failure modes are identified. The novelty in the proposed PFA is that, the stress-based failure is detected, and the strain-based damage evolution is computed. A user-defined material subroutine of PFA of PWTC lamina is finally developed and test problems are solved in ABAQUS. All the simulation results of the proposed approaches are finally compared with experiments and found to be closely matching.

Numerical analysis of intralaminar damage evolution on various composite laminates

The paper presents the numerical modelling of progressive damage distribution on the layers of various configurations of composite laminates (cross-ply, angle-ply, balanced laminate and quasi-isotropic laminate) under tensile loading. The purpose of the paper is to study the effect of the stacking sequence and fibre orientation angles on the damage propagation on multi-layered composites. These damage initiations do not necessarily imply a complete loss of structural integrity of the composite laminate. Additional load can be supported due to the stress redistribution over the fibres. A post-critical analysis is carried out, in order to analyse the integrity or the degradation state of the layers of composite laminates. The progressive failure analysis is performed in ANSYS Composite Prep/Post, to enable the investigation of damage initiation and damage evolution on each ply with various fibre orientations of the composite laminates. The intralaminar failure is initially detected based on a failure criterion and the post-critical analysis is evaluated based on a damage evolution law. The results are presented in terms of representative tensile displacements, which lead to damage initiation and damage evolution on the layers of the analysed composite laminates. Moreover, the laminas with different fibre orientations are investigated for progressive loading steps, from the first local failure to the total collapse. The obtained results show that the damages distribution on the plies of the composite laminates are strongly influenced by the fibre orientations, but also by the interaction with the other laminas and stacking sequence.

The role of patch-parent configurations on the tensile response of patch repaired carbon/epoxy laminates

This work investigated the individual and associated effects of parent laminate and patch orientations with stacking sequence on the tensile response of adhesively bonded external patch repaired carbon/epoxy laminates. Four kinds of parent laminates ([0]4, [45]4, [0/45]s, [45/0]s) were repaired with double sided external patches of four different configurations ([0]2, [45]2, [45/0], [0/45]), having two laminae on each side. Real time Digital Image Correlation (DIC) was employed to capture the two dimensional strain field, damage onset and damage growth of the repaired specimens during the tests. The results reveal that the angle of orientation of plies of both the patch and the parent laminate is a key design parameter which affects the performance after the repair. The results reveal that the repair of main load bearing plies (0°) of parent laminate with [45]2 patches presented the most favourable residual tensile behaviour by effectively releasing the stress concentration in the damaged area. The maximum residual strength after repair with [45]2 patch for [0]4, [45]4, [0/45]s, [45/0]s laminates was approximately 70%, 115%, 90% and 80% respectively.

Reaching maximum inter-laminar properties in GFRP/nanoscale sculptured aluminium ply laminates

The aim of the present work is to reach maximum inter-laminar properties in fibre metal laminates (FML) consisting of glass fibre reinforced polymer (GFRP) and aluminium (Al) plies. The Al plies are AA5019 and AA5754 alloys and pre-treated by nanoscale sculpturing before the FMLs are manufactured by resin transfer moulding. The nanoscale sculpturing of the Al plies leads to the formation of cubical hook-like structures on the surface giving rise to a three-dimensional mechanically interlocking surface. The inter-laminar properties of the FML are investigated by double-notch shear as well as double cantilever beam (Mode I) and end notched flexure (Mode II) testing methods and compared to untreated Al plies and conventional GRFP laminates as reference. As result the nanoscale sculptured Al plies show drastically increased inter-laminar mechanical properties due to highly improved inter-ply bonding between metal surface and resin. For all FMLs with nanoscale sculptured Al plies the delamination appears in the transition zone between glass fibres and matrix due to the lower adhesion of the glass fibre/matrix interface compared to the nanoscale sculptured Al ply/matrix interface. This proves that the maximum necessary inter-laminar properties are achieved.

Experimental investigation on the enhancement of Mode I fracture toughness of adhesive bonded joints by electrospun nanofibers

ABSTRACTThe use of an electrospun nylon nanofibrous mat at the interface between adjacent plies of a composite laminate is a promising mean to improve the delamination strength, as the nanomat acts a reinforcing web enabling a ply-to-ply bridging. This kind of reinforcement can be potentially used in other applications, such as adhesive bonding, where it may also work as adhesive carrier. The present work is therefore aimed at analysing the potential of an electrospun polymeric nanomat as adhesive carrier and reinforcing web in adhesive bonding. The adhesive is used to pre-impregnate a nylon nanofibrous mat that is then placed at the interface between two metal pieces and cured. The effectiveness of this procedure is evaluated by comparing of the mode-I fracture toughness measured 2024-T3 aluminum alloy DCB (Double Cantilever Beam) specimen bonded using a two-part epoxy resin with and without the nanomat.

Dynamic analysis for anti-symmetric cross-ply and angle-ply laminates for simply supported thick hybrid rectangular plates

In this paper, static and vibration analysis for anti-symmetric cross-ply and angle- ply carbon/glass hybrid laminates rectangular composite plate are presented. In this analysis, the equations of motion for simply supported thick laminated hybrid rectangular plates are derived and obtained through the use of Hamilton\'s principle. The closed-form solutions of anti-symmetric cross-ply and angle- ply laminates are obtained using Navier solution. The effects of side-to-thickness ratio, aspect ratio, and lamination schemes on the fundamental frequencies loads are investigated. The study concludes that shear deformation laminate theories accurately predict the behavior of composite laminates, whereas the classical laminate theory over predicts natural frequencies. The excellent accuracy of the present analytical solution is confirmed by making some comparisons of the present results with those available in the literature. It can be concluded that the proposed theory is accurate and simple in solving the free vibration behaviors of anti-symmetric cross-ply and angle- ply hybrid laminated composite plates.

Realising damage-tolerant nacre-inspired CFRP

In this work, a nacre-inspired Carbon Fibre Reinforced Polymer (CFRP) composite is designed, synthesised and tested. Analytical and numerical models are used to design a tiled micro-structure, mimicking the staggered arrangement of ceramic platelets in nacre and exploiting geometrical interlocks for crack deflection and damage diffusion. The designed pattern of tiles is then laser-engraved in the laminate plies. In order to increase the damage-spreading capability of the material, a thin layer of poly(lactic acid) (PLA) is film-cast on the interlaminar region, both as a continuous film and as a pattern of fractal-shaped patches. Three-point bending tests show how the nacre-like micro-structure succeeds in deflecting cracks, with damage diffusion being significantly improved by the addition of PLA at the interface between tiles. It is observed that a texture of discontinuous fractal-shaped PLA patches can increase damage diffusion, by promoting the unlocking of tiles whilst preserving the interface strength.

Low velocity impact and compression after impact simulation of thin ply laminates

Numerical simulations can help in the understanding of the damage sequence of polymer based composite laminates during an impact event, which is a difficult experimental task when dealing with a large number of plies. Low velocity impact and compression after impact in thin ply fabric laminates are studied through numerical simulations in which special attention has been devoted towards the computational efficiency. The impact results show the importance of delamination during the damage initiation, which takes place at few interfaces. After damage initiation, delamination and fiber breakage propagate until a last stage which is mainly governed by fiber breakage. Compression after impact shows a brittle behaviour with almost no damage propagation prior to failure. The numerical models indicate that matrix cracking effects can be assumed negligible for the studied thin ply laminates while delamination and especially the fiber constitutive law shape are important for accurate predictions.