Asymmetric Laminates Research Articles

Numerical investigation of low-velocity impact in symmetric and asymmetric GFRP laminate with and without pre-crack

Damage induced in symmetrical and asymmetrical glass fiber reinforced polymer (GFRP) laminate overlow-velocity impact (LVI) using a mild steel impactor is investigated. Numerical simulation is done using 3-Dfinite element analysis software LS-DYNA. Orientations for symmetrical and asymmetrical laminate were [(0,90)/(+45,-45)/(+45,-45)/(0,90)//(90,0)/(+45,-45)/(+45,-45)/(90,0)] and [(0,90)/(+45,-45)/(+45,-45)/(0,90)//(+45,-45)/(90,0)/ (90,0)/(+45,-45)] respectively. Two samples each from symmetric and asymmetric laminate with and without pre-crack were numerically simulated. Induced circular pre-crack was modeled in the midplane of the laminate. A circular specimen of radius 75mm with clamped area of 376mm2 is modeled. The velocity of 5 m/sec was assigned to the hemispherical headed cylindrical impactor. The result shows that symmetrical laminates absorb high energy and damage area for it is 24.06 % less than asymmetrical laminate for laminate with pre-crack in mid plate. This study concluded symmetrical laminate design is better for structural purpose as compared to asymmetrical design. Results of proposed investigation are directly applicable in aircraft, automobiles and space equipment. Copyright © 2017 VBRI Press.

Shape prediction of bistable plates based on Timoshenko and Ashwell theories

This work is concerned with the geometrical characterisation of bistable composite plates in order to investigate their curvatures interdependence. The main non linear feature of bistable asymmetric laminates concerns large deflection with small energy input. This is an aspect of particular interest for several applications. Accordingly, there is an increasing importance placed on accuracy/sensitivity of predicting techniques to model bistable deformation shapes. This paper presents a novel forecast model to map the surface profiles of bistable laminates. By Timoshenko and Ashwell approaches, an analytical model is developed to provide an interpretation of the bistable shapes, in terms of principal and anticlastic curvatures. The experimental data (via laser acquisitions), with analytical and Finite Element models, help to understand the relation between material properties, plate dimensions, stacking sequence, curing features of the composite laminates and the bistability phenomenon.

Antiplane shear of an asymmetric sandwich plate

An asymmetric three-layered laminate with prescribed stresses along the faces is considered. The outer layers are assumed to be much stiffer than the inner one. The focus is on long-wave low-frequency anti-plane shear. Asymptotic analysis of the original dispersion relation reveals a low-frequency harmonic supporting a slow quasi-static (or static at the limit) decay along with near cut-off wave propagation. In spite of asymmetry of the problem, the leading order shortened polynomial dispersion relation factorises into two simpler ones corresponding to the fundamental mode and the aforementioned harmonic. The associated 1D equations of motion derived in the paper are also split into two second-order operators in line with the factorisation of the shortened dispersion relation. Asymptotically justified boundary conditions are established using the Saint-Venant’s principle modified by taking into account the high-contrast properties of the laminate.

Analytical Thermal Stress Analysis of Perforated Symmetric Composite Laminates Containing a Quasi-Triangular Hole

In this study, the thermal stress distribution surrounding a quasi-triangular hole within a symmetric composite laminate made of various composite materials was investigated. A composite laminate exposed to uniform heat flux was analyzed using the complex variable method as a thermo-elastic two-dimensional problem under a steady state condition. The analytical solution was achieved with the development of the Lekhnitskii’s solution and using the classical laminated plate theory and a conformal mapping function. The influence of important parameters on thermal stress distribution surrounding a hole such as the hole orientation, bluntness and aspect ratio, the heat flux angle and the laminate stacking sequence and material was studied. The results were achieved for different stacking sequences of [45°/–45°]s and [0°/90°]s. The analytical solution in this study was well validated against the finite element results.

Rapid prediction and inverse design of distortion behaviors of composite materials using artificial neural networks

If the process‐induced distortions (PIDs) of asymmetrical laminates can be predicted accurately and tailored at the early design stage, the production of curved panels from flat molds could be an attractive technique in a cost‐driven production environment. A data‐driven computational methodology which integrates the finite element method (FEM) and artificial neural network (ANN) is presented to rapidly predict the maximum PID and to perform high‐throughput screening of thermosetting‐matrix composites of an asymmetrical laminate for a targeted maximum PID. We performed a grid search on ANN architectures and hyper‐parameters using cross‐validation and obtained a well‐trained ANN model with high generalization performance. For the forward problem, the ANN model was adopted to predict the maximum PIDs of CYCOM X850 and CYCOM 977‐2 prepregs, which were subsequently verified experimentally. For inverse design, a large‐scale screening method based on the ANN model was utilized to determine the candidates for a targeted maximum PID, with an experimental demonstration using one of these candidates. The well‐trained ANN model provides an alternative approach to faster computation with high accuracy for the maximum PID prediction and further guides the discovery of materials with desired distortion behaviors.

Nonlinear modeling of bending-mode magnetoelectric coupling in asymmetric composite structures with magnetization-graded ferromagnetic materials

The bending-mode magnetoelectric (ME) coupling in the asymmetric laminate composite with a magnetization-graded ferromagnetic material has been investigated in this paper. Based on the nonlinear constitutive relationships of the magnetostrictive material, the dynamic piezomagnetic models have been presented for magnetostrictive materials after considering the remanence, demagnetization, and flux concentration effects. In addition, the bending-mode resonant ME coupling model is developed based on the proposed dynamic piezomagnetic model, the motion equation of the ME composite, and the ME equivalent circuit method. The composite structures FeCuNbSiB/Ni/PZT with negative magnetostrictive Ni and FeCuNbSiB/FeNi/PZT with positive magnetostrictive FeNi have been used to confirm the validity and reliability of the theoretical model. The theoretical results show that the bending-resonant ME coefficients reasonably agree with the experimental results. This theoretical model is of importance for understanding the bending-mode ME response of the asymmetric structure with magnetization-graded ferromagnetic materials and designing the ME devices.

Design and analysis of a grid patch multi-stable composite

In this paper, the effect of stacking sequences on the number of stable configurations for multi-patch composite panel is studied. The model is designed by connecting a number of bi-stable composite patches in a grid. The total strain energy equation with a fourth order shape function including variations of the curvatures is applied in conjunction with a Rayleigh-Ritz technique for fast predication of stable shapes. A square panel model consisting of four connected patches of asymmetrical laminate is designed with 0° and 90° ply's angle, and then the model is extended by a mix of symmetric and asymmetric laminates. The stable shapes of model are validated using both FE predictions and experimental tests, and the results show quite good agreements in the stable configurations. Each case of panels exhibits two or more distinct stable configurations, which are mainly dependent on distribution of stacking sequences on surface. These stable configurations are interesting shapes that may be used to create a large multi-stable surface as useful device in a morphing skin application. This work could be used as a guideline for design of a large multi-patch morphing skin for highly degree of stability.

Hygroscopic stresses in asymmetric biocomposite laminates submitted to various relative humidity conditions

Hygroscopicity of natural fibers influences biocomposites lifetime submitted to wet environments. The present study investigates the hygroscopic stresses state in a flax fiber reinforced polypropylene composite when submitted to different environmental conditions from the dried state through various relative humiditiy (RH) to immersion. An experimental and modelling strategy is applied on asymmetric biocomposites to estimate the stresses distribution through their thickness.On dry condition, transverse tensile stresses reached 26.4 MPa. These stresses were nullified at 50%RH and then increased again until 90%RH or immersion conditions are applied. The evolution of the internal stresses influence drastically the tensile strength of biocomposites. Indeed, the internal stresses overcome the transverse strength of Flax/MAPP unidirectional ply, which potentially leads to damage. Environmental loading and gradient effect also drastically influence the internal stresses. A progressive humidification step enables to reduce drastically the stresses intensity with levels lower than 10 MPa thanks to lower hygroscopic gradients.

Developing a thermomechanical and thermochemical model for investigating the cooling rate effects on the distortion of unsymmetrical viscoelastic polymeric composite laminates

An experimental and semi-analytical study of distortion of asymmetric composite laminates with different cooling rates and lay-ups has been presented. In this study, thermomechanical constitutive equations of thin composite laminates are developed using basic viscoelastic constitutive law considering chemical and thermal effects with time-temperature dependent material properties. To solve a fully scouple problem, both the thermochemical and thermomechanical constitutive equations are formulated. The general heat conduction equation known as the Fourier-Biot equation, viscoelastic laws, Boltzmann superposition principle and composite equations are utilized to formulate thin composite laminates. A static model with constant properties in ambient temperature and a transient model by obtaining constitutive equations are simulated. Results are compared with experimental data. Changing lay-up from cross-ply to angle-ply and then quasi isotropic will increase the value of maximum distortion. Results indicated that the increasing cooling rate will increase the value of the maximum distortion. The differences between FEM results with static analysis of different lay-ups and experimental specimens that cooled in the oven, environment and refrigerator is about 3%, 35% and 55% respectively. The differences between FEM simulation with transient analysis of different lay-ups and experimental specimens that cooled in the environment and the refrigerator is less than 9%.

Cure-induced residual stresses for warpage reduction in thermoset laminates

The paper addresses the role played by the cure stage of a vacuum assisted resin transfer molding process in residual stresses generation. The Airstone 780E epoxy resin and Hardener 785H system broadly used in the wind turbine blade industry has been used in this study. The viscous–elastic properties of the resin have been characterized and implemented in a thermo-mechanical FE model. The model has been validated against manufactured [0/90]4 asymmetric laminates. Analysis of residual stresses generation highlighted that compressive stresses generation occurs when the cure is shrinkage dominated and tensile stresses when expansion dominated in the 0° plies. The finding points out that 10% reduction in warpage and 33% reduction in process time can be obtained by selecting cure cycle parameters that allow tensile stresses development during the cure process in the 0° plies.

Investigating the effects of cooling rate on distortion of asymmetric composite laminates

Predicting the final shape of composite laminates after the curing cycles is crucial. An experimental and two numerical (with constant and temperature dependent material properties) studies have been presented. The purpose of this study is to investigate the effects of different cooling rates on the distortion of thin asymmetric composite laminates with different lay-ups after the curing cycle. Properties of a UD layer in different temperature have been obtained using TMA, DMA and micromechanical formulation. The samples were subjected to three different cooling stages. Results indicated that the distortion of the asymmetric composite laminate was significantly depending on the cooling rate and lay-up configurations. Accelerating the cooling rate can significantly enhance the out of plane deformation of the asymmetric laminates. In the slowest cooling rate, the effects of thermal residual stresses due to temperature change are minimum and consequently the results of both numerical analyses are closer to experimental observations. The analysis with temperature dependent material can predict the deformation of specimens with slowest cooling rate better than the analysis with constant material properties. Because of the sudden change in temperature, for prediction of distortion after the higher cooling rates, a transient analysis will be needed.

Effect of Ply Lay Up Sequence on Interlaminar Shear Strength of Symmetric and Asymmetric GFRP Composite

Abstract Fibre reinforcement polymer matrix composite are being used in aerospace, aircraft, and automobile industry etc .These material has high strength, high modulus and low density. Woven Fibres used is in experiment. Reinforcement throughout thickness is better in woven fibres and it show similar properties in warp and weft direction. The composite material properties like load carrying capacity ,stiffness, ILSS etc. is affected by ply orientation and stacking sequence of laminate. Asymmetric laminates have almost similar stiffness characteristics properties to that of symmetric laminates. Symmetric and asymmetric laminate were fabricated by hand layup press moulding process. In the concerned method initially cut plies are wetted by the resin and are placed over each other according to the required stacking sequence. Once the proper layup is achieved, the wet laminate is squeezed under press moulding machine. The magnitude of load defines the final thickness of the laminate. Final thickened laminates’ samples were tested on fully computer controlled universal testing machine using short beam strength method and with the help of ASTM- 2344 ILSS was calculated. This paper show the effect of ply layup sequence on interlaminar shear strength on symmetric and asymmetric laminates of GFRP composite and it was found that interlaminar shear stress is higher for symmetric laminates that of asymmetric laminates. It was also observed that interlaminar shear stress decreases as fibre volume fraction in laminates increases.

Effect of fabric areal density on the mechanical behaviour of symmetric and asymmetric woven GFRP composite

In this work, effects of fabric areal density (AD) on the mechanical behavior of symmetric and asymmetric woven GFRP laminates were investigated. Two different fabric surface densities such as 610 and 210 GSM (gram per square meter) were considered in the preparation of 8 and 16 layered laminates of the same thickness, respectively. Both laminates had two different ply layup sequence, making them asymmetric and symmetric laminates. Laminates were fabricated by hand layup followed by press molding technique. Fiber volume fraction was calculated approximately 55% as per ASTM D3171-15. Tensile, Compressive, and flexural tests were conducted according to their ASTM standard on Hounsfield H50KS, a computer-controlled universal testing machine. Results exhibited that the static mechanical behavior of the laminates was influenced by the ply stacking sequence and fabric areal density. Laminate with higher areal density fiber presented better mechanical properties than the lower one. An increase in areal density from 210 GSM to 610 GSM of fabric irrespective of stacking sequences caused a rise of 45–50% in tensile strength and 35–50% in flexural strength while decrease 10–12% in compressive strength, of a GFRP laminate. While among asymmetric and symmetric ply stacking sequences, symmetric one independent of areal density showed better tensile, compressive, and flexure properties.

Giant Self-biased Magnetoelectric Effect in Pre-biased Magnetostrictive–Piezoelectric Laminate Composites

In this study, it is demonstrated that the giant self-biased magnetoelectric (SME) response can be achieved from a center-clamped magnetostrictive–piezoelectric laminate composite by employing magnetic tip masses. An asymmetric laminate structure consisting of two different magnetostrictive layers (Metglas and nickel) with opposite signs of piezomagnetic coefficient is introduced to promote structural bending resonance, and the effect of layout change of attaching the magnetic tip masses on SME responses is systematically investigated. The highest SME effect is observed when all magnetic tip masses are loaded on the Metglas layer and their magnetization directions are normal to the Metglas surface. It is proposed that not only the parallel magnetic domains to external magnetic field but also the non-parallel magnetic domains effectively contribute to the total magnetostriction. The fabricated SME laminates exhibit giant SME voltage coefficients ranging from 14.11 to 52.35 V cm−1 Oe−1, depending on the direction of the fields of the tip magnets. These high SME voltage output values and their controllability are promising for precision field sensors, magnetic energy harvesters and field-tunable devices.

Notched strengths of asymmetric woven hybrid laminates

In this article, the notched strengths of asymmetric woven hybrid laminates were studied by using both experiment and the finite element-based point stress criterion (FEMPSC). It was experimentally shown that the notched strength decreases with the increase of hole radius for all the laminates machined by water jet cut, drilling, and milling. Particularly, it is noted that the notched strength of specimens of the same hole size made by water jet cut is obviously higher than those made by both drilling and milling, due to stress redistribution. The results also indicate that the notched strengths predicted by FEMPSC agree well with the experimental data, with only a 4% margin of error.

An Experimental Investigation of Combined Symmetric-Asymmetric Composite Laminates

It has been found that certain asymmetric composite laminates exhibit bistability, where the composite laminate exhibits multiple stable static equilibrium states. If the bistable composite is actuated, it will snap to its secondary equilibrium state and then remain there without further actuation. This study investigates how the amount of symmetry in a combined symmetric asymmetric rectangular laminate under an imposed clamped edge boundary condition affects the bistability and the curvature of the laminate. Laminates with varying amounts of asymmetry were fabricated and then measured using a profilometer to capture the curvatures of the equilibrium shapes. The results showed that up to 20% symmetry can be introduced in the laminate without a substantial loss in snap through curvature, and that up to 83% symmetry can be introduced in the laminate before bistability is lost. Finite element simulations were conducted in Abaqus and showed good correlation with the experimental results.

Optimal Design of Shape Memory Alloy Compositeunder Deflection Constraint.

Shape-adaptive or morphing capability in both aerospace structures and wind turbine blade design is regarded as significant to increase aerodynamic performance and simplify mechanisms by reducing the number of moving parts. The underlying bistable behavior of asymmetric cross-ply composites makes them a suitable candidate for morphing applications. To date, various theoretical and experiential studies have been carried out to understand and predict the bistable behavior of asymmetric laminates and especially the curvature obtained in their stable configurations. However, when the bi-stable composite plate is integrated with shape memory alloy wires to control the curvature and to snap from a stable configuration to the other (shape memory alloy composite, SMAC), the identification of the design parameters, namely laminate edge length, ply thickness and ply orientation, is not straightforward. The aim of this article is to present the formulation of an optimization problem for the parameters of an asymmetric composite laminate integrated with pre-stressed shape memory alloys (SMA) wires under bi-stability and a minimum deflection requirement. Wires are modeled as an additional ply placed at the mid-plane of the composite host plate. The optimization problem is solved numerically in MATLAB and optimal design variables are then used to model the SMAC in ABAQUS™. Finite element results are compared against numerical results for validation.

Free-edge stress fields in generic laminated composites via higher-order kinematics

The present work introduces a numerical approach for the study of the free-edge effects that arise in generic laminated composites with arbitrary geometries. The model is based on the use of a higher-order beam theory that employs only displacement unknowns over the cross-section domain, the so-called Lagrange expansion (LE). This allows for the representation of arbitrary sections of laminated structures through a two-dimensional distribution of mathematical domains, accounting for layerwise (LW) kinematics and high refinements towards the free edges. Subsequently, the finite element method (FEM) is employed to solve the problem along the laminate's length, thus enabling the user to introduce arbitrary boundary conditions. Benchmark solutions of the free-edge stresses in symmetric laminates under extension, bending and twisting are included to assess the model. Then, new solutions of a composite C-section beam made of an asymmetric lamination are provided.

Manufacturing and characterization of novel clutch non-conventional fiber-reinforced composite laminates

In this study the manufacture and characterization of novel non-conventional composite laminates coined as clutch laminates are presented. These carbon/epoxy laminates are manufactured using prepreg slit tape in an automated fiber placement (AFP) machine through tow skips. The AFP process allows for the tailoring of material architecture, resulting in woven-like structures without the need for a loom. These laminates are heterogeneous due to variation of fiber orientation and therefore, the material properties at a given section is a function of in-plane spatial coordinates. The thermal and mechanical behavior is studied where the clutch laminate lay-up pattern is represented with a sub cell approach utilizing 3D shell finite elements where the tows are deposited onto the regions mimicking the AFP course. Experimental results show that post-cure thermal warpage for the clutch carbon/epoxy laminates is significantly reduced when compared to conventional asymmetric laminates while also exhibiting tensile properties comparable to traditional laminates of the same ply counts. Based on the model predictions, the reduction in the warpage is attributed to the spatial variations in the local stacking sequences leading to reduced net deformation.

Influence of layer thickness variations on the structural behaviour of optimised fibre reinforced plastic parts

Fibre reinforced plastics (FRP) are considered as a modern high-tech material. The enormous lightweight potential, especially of carbon fibre reinforced plastics, accelerates its spreading in many industrial applications. However, as good as the lightweight potential of FRP is, as difficult is the optimal use in products because of its anisotropic material properties. Recently, methods considering the anisotropic material behavior during the product development process have been developed. These result in optimized nominal laminate layouts with defined laminate parameters like fibre orientation, ply thickness and ply stack-up order. Yet, during the manufacturing process, variations of these parameters, compared to the nominal design, occur. The variations result in asymmetric laminates, which causes couplings in the stiffness matrix and consequently undesired deformations. The effects of varying laminate design parameters have so far mainly been investigated with focus on manufacturing activities. However, to support the design engineer in considering the influence of varying laminate parameters on product behavior, this paper studies the effects on the structural behavior of optimized FRP-parts. The main novelty and contribution of the paper can be found in providing a new approach for the consideration of uncertainties in the ply thickness on FRP parts with optimized fibre layout. For this purpose, sensitivity analyses are performed with the aim of investigating the importance of the parameters on the structural behavior. With this knowledge, the product developer is able to distinguish between critical and non-critical laminate parameters and consider their variations in the product development process as early as possible.