Total Laminate Thickness Research Articles

A new woven composite constitutive model validated by shock wave experiments

In this paper, we present results of plate impact simulations of shock compressed woven glass fiber-reinforced plastic (GRP) performed using the Arbitrary Lagrangian–Eulerian three-dimensional finite element code. A hyperelastic large-strain-based empirical Continuum Damage Mechanics (CDM) formulation is employed to describe damage initiation and growth in the shock-compressed GRP. The model parameters calibration scheme utilizes the Velocity Interferometer System for Any Reflector normal particle velocity measurements at the free surface of the GRP target plates. The impact velocity in the experiments ranged from 8.5 to 418 m/s. The finite element model considered planar 0°/90° bidirectional plies with an individual ply thickness of 0.68 mm, stacked to reach a total laminate thickness of 6.8 mm. The anisotropic elastic strains were estimated from the experimentally determined tetragonal symmetry stiffness matrix for the GRP. The strain-based damage model captures several salient features observed in the measured free surface particle wave profiles, including the shock rise time, onset of Elastic—Elastic Cracking, and the shape of the nonlinear portion of the experimental particle velocity profiles. The CDM model predicts the dominant damage mode to be matrix microcracking due to shear and the associated bulk expansion (bulking) under the global compressive loading in the plate impact configuration.

Experimental analysis of aluminium/carbon epoxy hybrid laminates under flexural load

Industry needs new materials that present very high structural characteristic, such as high strength, low weight and high damage tolerance. To obtain these characteristics a new class of materials has been introduced: Fibre Metal Laminate (FML); they consist in metal sheets alternated to composite material layers: in such manner, the good characteristics of each constituent material confer the utmost properties to the FMLs. However, the mechanical properties depend, among other factors, on the thickness and the numerousness of the layers constituting the FML, as well as the interface between metal and composite. Therefore, in this paper, the influence of the abovementioned factors on the material answer to flexural load was investigated. In particular, different kinds of laminates were produced varying the layers adhesion and the layers thickness, but maintaining unaltered the metal/composite volume ratio and the total laminate thickness. Then their structural behaviour was investigated through three-point bending test, and it was found that the flexural behaviour was affected by both the investigated factors; in fact, the maximum flexural load diminished incrementing the number of layers and inserting an adhesive layer at the metal/composite interface.

Microstructure and twisting ability of an adjusted antisymmetric angle ply laminate

This letter describes an adjusted antisymmetric angle ply laminate that is able to twist as a result of temperature-dependent deformation. A theoretical explanation for this twisting ability is presented and the adjusted architecture of the proposed laminate is described. The effects of fiber and matrix volume fractions, laminate angle, total laminate thickness, and temperature range on the torsion of the laminate are analyzed. A sample of the proposed microlaminate is produced by a microfabrication process and tested as the temperature is increased from room temperature to 80 °C. Microscopy images reveal that the microlaminate twists by more than 180° within a length of 200 μm. The proposed material and its twisting ability show great potential for application in microrobotic actuators.

An optimality criteria-based algorithm for efficient design optimization of laminated composites using concurrent resizing and scaling

Numerical optimization is an indispensable part of the design process of laminated composite structures. Several optimality criteria-based algorithms exist which rely on a sequential resizing and scaling approach. This paper presents a novel design algorithm applicable for stiffness and eigenfrequency optimization of composite structures with concurrent consideration of resizing and scaling operations. A method is introduced that allows for an efficient consideration of nonlinear constraints. This is done by determining stable concurrent scaling parameters from first-order constraint change ratio estimations. Optimization is carried out using optimality criteria in three independent steps, namely with respect to fiber angles, ply thickness ratios, and total laminate thickness. Sensitivity analyses are performed analytically at low computational costs. Numerical examples demonstrate the efficiency and fast convergence of the method. Compared to established algorithms, the number of required function evaluations is reduced significantly.

Study on the dielectric properties of Al2O3/TiO2 sub-nanometric laminates: effect of the bottom electrode and the total thickness

Dielectrics based on amorphous sub-nanometric laminates of TiO2 and Al2O3 are subject to elevated dielectric losses and leakage currents, in large parts due to the extremely thin individual layer thickness chosen for the creation of the Maxwell–Wagner relaxation and therefore the high apparent dielectric constants. The optimization of performances of the laminate itself being strongly limited by this contradiction concerning its internal structure, we will show in this study that modifications of the dielectric stack of capacitors based on these sub-nanometric laminates can positively influence the dielectric losses and the leakage, as for example the nature of the electrodes, the introduction of thick insulating layers at the laminate/electrode interfaces and the modification of the total laminate thickness. The optimization of the dielectric stack leads to the demonstration of a capacitor with an apparent dielectric constant of 90, combined with low dielectric loss (tan δ) of 7 · 10−2 and with leakage currents smaller than 1 × 10−6 A cm−2 at 10 MV m−1.

Optimization of Composite Material System and Lay-up to Achieve Minimum Weight Pressure Vessel

The use of composite pressure vessels particularly in the aerospace industry is escalating rapidly because of their superiority in directional strength and colossal weight advantage. The present work elucidates the procedure to optimize the lay-up for composite pressure vessel using finite element analysis and calculate the relative weight saving compared with the reference metallic pressure vessel. The determination of proper fiber orientation and laminate thickness is very important to decrease manufacturing difficulties and increase structural efficiency. In the present work different lay-up sequences for laminates including, cross-ply [0 m /90 n ] s , angle-ply [±θ] ns , [90/±θ] ns and [0/±θ] ns , are analyzed. The lay-up sequence, orientation and laminate thickness (number of layers) are optimized for three candidate composite materials S-glass/epoxy, Kevlar/epoxy and Carbon/epoxy. Finite element analysis of composite pressure vessel is performed by using commercial finite element code ANSYS and utilizing the capabilities of ANSYS Parametric Design Language and Design Optimization module to automate the process of optimization. For verification, a code is developed in MATLAB based on classical lamination theory; incorporating Tsai–Wu failure criterion for first-ply failure (FPF). The results of the MATLAB code shows its effectiveness in theoretical prediction of first-ply failure strengths of laminated composite pressure vessels and close agreement with the FEA results. The optimization results shows that for all the composite material systems considered, the angle-ply [±θ] ns is the optimum lay-up. For given fixed ply thickness the total thickness of laminate is obtained resulting in factor of safety slightly higher than two. Both Carbon/epoxy and Kevlar/Epoxy resulted in approximately same laminate thickness and considerable percentage of weight saving, but S-glass/epoxy resulted in weight increment.

Heated chamber winding of thermoplastic powder-impregnated composites: Part 2. Influence of degree of impregnation on mechanical properties

A model to study the impregnation process during the heated chamber filament winding of poly(butylene terephthalate) (PBT) powder/sheath glass fibre (GF) bundles is developed. At every time step and through- the-thickness position, once the process variables, material properties and thermochemical characteristics are known, the model is able to evaluate: total laminate thickness, bundle position and displacement, layer thickness and tension, temperature distribution, resin viscosity, crystallization and degree of impregnation, and interlaminar residual stresses. The model algorithm is implemented into a FORTRAN code, the reliability of which is assessed by simulating the winding of a ring of GF/PBT. Scanning electron microscope analyses of the laminate cross-section, estimation of density, evaluation of void content and measurement of the overall elastic deformation of a wound ring cut across its width allow the experimental and numerical results to be compared, as well as verifying their close agreement. Finally, the optimal processing window for the heated chamber filament winding of tubes and rings of GF/PBT bundles is suggested.

High Temperature Mechanical Behavior of Nb5Si3/Nb Laminates

AbstractTwo phase alloys based on the intermetallic system Nb5Si3/Nb system provide potentially superior combination of strength and toughness over their monolithic counterparts at high temperatures. To gain fundamental knowledge of the mechanical behavior of these materials, initial focus has been on the mechanical behavior of Nb5Si3/Nb laminates and composites at elevated temperatures. In this study, laminates have been fabricated at 32 at% Si with Nb, and a total laminate thickness of 2.1mm. Tests are being conducted on notched and unnotched tensile specimens. The unnotched specimens provide the overall strength and ductility of the laminate and a basis for comparison with notched specimens which provide information on crack propagation and ductile phase toughening effects. Results from samples with a variety of laminate spacings are being explored, and preliminary data will be presented.

Optimal Hybridization of Symmetric, Cross‐Ply Laminates against Biaxial Buckling

Optimal ratio of the thickness of the inner layers made of a low‐stiffness fiber‐reinforced material to the total laminate thickness is determined for sandwich hybrid laminates, with the objective of maximizing the buckling load for a given laminate thickness. The sandwich plate is constructed as a symmetric, cross‐ply laminate with outer layers made of a high‐stiffness fiber composite material and inner layers made of a low‐stiffness fiber‐composite material. The fiber orientations of high‐ and low‐stiffness materials (0° or 90°) are determined optimally, noting that the orientations of outer and inner layers affect the maximum buckling load in the case of hybrid laminates. The relative stiffness of outer layers to inner layers is shown to affect the optimal level of hybridization. The optimal laminate configurations are shown to be sensitive to the relative magnitudes of biaxial buckling loads as well as to the changes in the aspect ratio.

Nondestructive Characterizations of Polyethylene/Nylon Laminates by Near-Infrared Spectroscopy

The use of near-infrared (NIR) spectroscopy for the rapid and nondestructive analysis of food packaging laminates containing polyethylene (PE), polyamide-6 (PA-6), and ethylene vinyl alcohol (EVOH) layers is demonstrated. The method of Pathlength Correction with Chemical Modeling (PLC-MC) is used to estimate the total laminate thickness, and Principal Component Regression (PCR), is used to estimate the thickness percentages of PE and EVOH in the laminates, from NIR reflective-transmission spectra in the region 1500–2500 nm. Results indicate that the NIR method can be used to determine the total laminate thickness within 2–4 μm, the PE layer thickness percentage within 0.7–1.8%, and the EVOH layer thickness within 0.7–0.8 μm. In addition, detailed observation of the PCR models indicates that the NIR method is also sensitive to the absorbed water content, the morphology of the polymers, and perhaps the amount of polyurethane adhesive in the laminates. The usefulness of PCR outlier detection, for identification and characterization of strange samples, and principal component rotation, for improvement of PCR model interpretability, is also demonstrated.

Design of antisymmetric hybrid laminates for maximum buckling load: II. Optimal layer thickness

Antisymmetric, angle-ply laminates under biaxial compression are optimized with respect to layer thicknesses. The laminates are constructed with inner layers of a low-stiffness fibre composite material and outer layers of a high-stiffness fibre composite material. The optimal design problem consists of determining the ratio of inner layer thickness to the total laminate thickness so as to maximize the buckling load subject to a mass or thickness constraint. Numerical results are given for laminates of equal total thickness and equal mass made of boron, kevlar and glass fibre reinforced plastics. The optimal laminate configuration is found to be consisting of layers of high-stiffness or low-stiffness material or a combination of both depending on the ply angles and the materials. The optimal layer thickness is observed to have jump discontinuities with respect to fibre orientation.

Buckling of a Sublaminate in a Quasi-Isotropic Composite Laminate

Buckling of a delaminated region can cause high interlaminar stresses which, in turn, lead to delamination growth. Hence, buckling strain is an important parameter in assessing the potential for strength loss due to the delamination. The objective of this study was to predict the buckling of an elliptic delamination embedded near the surface of a thick quasi-isotropic laminate. The thickness of the delaminated ply group (the sublaminate) was assumed to be small compared to the total laminate thickness. Finite- element and Rayleigh-Ritz methods were used for the analyses. The Rayleigh-Ritz method was found to be simple, inexpensive, and accurate, except for highly anisotropic delaminated regions. Effects of delamination shape and orientation, material anisotropy, and layup on buckling strains were examined. Results showed that (1) the stress state around the delaminated region is biaxial, which may lead to buckling when the laminate is loaded in tension, (2) buckling strains for multi-directional fiber sublaminates generally are bounded by those for the 0 deg and 90 deg unidirectional sublaminates, and (3) the direction of elongation of the sublaminate that has the lowest buckling strain correlates with the delamination growth direction.

Graphical Determination of Stiffness and Strength of Composite Laminates

Design of composite laminates requires the determination of changes in stiffness and strength resulting from varying the ply orientation and total laminate thickness. Graphical determination can be made simple by use of laminate stiffnesses in conjunction with failure surface in a special strain space. A set of generalized graphs for all practical laminates of a given composite can now replace the current limitation of one set for each discrete laminate.