Composite Laminate Structures Research Articles

Low Cycle Fatigue Properties Laminate AA2519-TI6AL4V

This paper presents test results of AA2519/TI6AL4V composite laminate structure and mechanical properties. The composite laminate was merged by explosive welding using a transition AA1050 alloy layer. Weld endurance properties were determined through fatigue testing performed in constant total deformation amplitude (ɛac) conditions. The paper also describes the influence of test conditions on hysteresis loop shape, process of cyclic material strengthening and weakening, and fatigue life. Low cycle test results were approximated using a straight line with the following formula: σa = K′(ɛap)n which enables the K′ fatigue strength coefficient, and the n′ cyclic strengthening index to be determined. Test results also include fatigue fracture surface analysis. Distinctive fatigue fissure characteristics were investigated through studying fatigue fracture surface microstructure using a scanning electron microscope.

Characterisation of PAN Carbon Fabric/ Epoxy Resin for Structural Materials

Advanced composites such as fibre reinforced polymer matrix composites are being used for aerospace applications because of their high specific strength, specific modulus and low density. A structural composite laminate are prepared using high strength poly-acrylo-nitrile (PAN) carbon fabric and epoxy resin system by hand layup and match die moulding. Composites do not necessarily give higher performance in all the properties used for material selection such as strength, toughness, formability, joints ability, corrosion resistance, and affordability. New techniques are developed for the blowing of foams from thermoplastics. The laminates are characterised by physical and mechanical properties.

Ultrasonic wave propagation in the corner section of composite laminate structure: Numerical simulations and experiments

Two-dimensional finite element simulations and experiments are presented to examine the ultrasonic wave propagation behavior in the corner section of CFRP (carbon fiber reinforced plastics) laminate structures. The numerical model consists of a right-angle corner section of CFRP laminate immersed in water and subjected to the ultrasonic wave incidence from its inner or outer side. The anisotropic stiffness constants of the unidirectional CFRP are identified experimentally and used to model the curved laminate structure. A commercial finite element analysis code is used to compute the reflection waveforms in the pulse-echo mode, and the effect of the laminate stacking sequence and the wave incidence direction is examined. It is shown that the reflection waveforms for the wave incidence from the outer side of the corner qualitatively resemble those for the plane laminate except that the echo signals of the former are substantially weaker. The numerical simulations are shown to well reproduce the qualitative features of experimental reflection measurements performed for the corner sections of 16-ply CFRP laminate. Experimental results indicate that the porosity content of the corner section can be estimated by the amplitude ratio of the surface and the back-wall echoes when a curvature-dependent calibration relation is properly used.

Piezoresistive in-situ strain sensing of composite laminate structures

Various methods have been developed to monitor the health and strain state of carbon fiber reinforced polymers, each with a unique set of pros and cons. This research assesses the use of piezoresistive sensors for in situ strain measurement of carbon fiber and other composite structures in multidirectional laminates. The piezoresistive sensor material and the embedded circuitry are both evaluated. For the piezoresistive sensor, a conductive nickel nanocomposite sensor is compared with the piezoresistivity of the carbon fiber itself. For the circuit, the use of carbon fibers already present in the structure is compared with the use of nickel coated carbon fiber. Successful localized strain sensing is demonstrated for several sensor and circuitry configurations. Numerous engineering applications are possible in the ever-growing field of carbon-composites.

An experimental investigation on the three-point bending behavior of composite laminate

The response of composite laminate structure to three-point bending load was investigated by subjecting two types of stacking sequences of composite laminate structure by using electronic universal tester (Type: WDW-20) machine. Optical microscope was selected in order to characterize bending damage, delamination, and damage shapes in composite laminate structures. The results showed that the [0/90/-45/45]2s exhibits a brittle behavior, while other laminates exhibit a progressive failure mode consisting of fiber failure, debonding (splitting), and delamination. The [45/45/90/0]2s laminate has a highly nonlinear load- displacement curve due to compressive yielding.

Damage assessment based on general signal correlation. Application for delamination diagnosis in composite structures

Abstract This work presents a Vibration-Based Structural Health Monitoring (VSHM) technique which is developed and applied for delamination assessment in composite laminate structures. It suggests the mutual information as a measure for nonlinear signal cross correlation. The mutual information between two signals measured on a vibrating structure is suggested as a damage metric and its application for the purposes of damage assessment is discussed and compared to the application of the traditional linear signal cross-correlation. The cross correlation is capable to detect linear dependence between two signals and thus can be used for diagnosing damage on linearly vibrating structures. On the other hand the mutual information is a nonlinear metric, and it is shown that it can detect linear as well as nonlinear signal dependence and thus it is particularly appropriate for structures with nonlinear dynamic behavior and for composite structures as such. The application of the mutual information as a damage metric is demonstrated and discussed first for the case of a simple 2 DOF system with a nonlinear stiffness. Eventually the application of the suggested damage metric is developed and demonstrated for the purposes of delamination diagnosis in a composite laminate beam.

Effects of moisture ingression on polymeric laminate composites and its prevention via highly robust barrier films

Three different fiber-reinforced composite test laminates were laid up using carbon-, glass-, and Kevlar-reinforced epoxy prepregs, and then four different hydrophobic barrier films were placed as the out-of-most ply (last ply) on top of the test laminates. The prepared samples were co-cured through an autoclave per recommended cure cycles. These hydrophobic barrier films included polyether ether ketone or PEEK (12.7- and 25.4-μm thicknesses), polytetrafluoroethylene or Teflon (25.4 μm), and polyvinyl fluoride (PVF) or Tedlar (25.4 μm). Tedlar films have been the only source used for moisture prevention in Aerospace composites, so the purpose of the present study was to determine other alternatives and their moisture ingression prevention characteristics. The tape adhesion tests conducted on the barrier films of the composite panels indicated that PEEK and Tedlar films were well bonded on the composite surfaces, while Teflon films failed the tape adhesion tests. The laminate composites that were co-bonded with barrier films were immersed in water up to 29 days, and then 3-point bend tests were conducted on each sample before and after immersion. Test results show that 25.4-μm thick PEEK and Tedlar films on the carbon, glass, and Kevlar laminate composites provided similar mechanical properties. Also, the laminates incorporated with barrier films exhibited significantly higher mechanical properties when compared to the same laminates without any barrier films. This study indicated that these barrier films considerably reduced moisture ingression into the laminate composite structures, which may be useful for applications in composite aircraft and wind turbines.

Quantitative damage detection and sparse sensor array optimization of carbon fiber reinforced resin composite laminates for wind turbine blade structural health monitoring.

The active structural health monitoring (SHM) approach for the complex composite laminate structures of wind turbine blades (WTBs), addresses the important and complicated problem of signal noise. After illustrating the wind energy industry's development perspectives and its crucial requirement for SHM, an improved redundant second generation wavelet transform (IRSGWT) pre-processing algorithm based on neighboring coefficients is introduced for feeble signal denoising. The method can avoid the drawbacks of conventional wavelet methods that lose information in transforms and the shortcomings of redundant second generation wavelet (RSGWT) denoising that can lead to error propagation. For large scale WTB composites, how to minimize the number of sensors while ensuring accuracy is also a key issue. A sparse sensor array optimization of composites for WTB applications is proposed that can reduce the number of transducers that must be used. Compared to a full sixteen transducer array, the optimized eight transducer configuration displays better accuracy in identifying the correct position of simulated damage (mass of load) on composite laminates with anisotropic characteristics than a non-optimized array. It can help to guarantee more flexible and qualified monitoring of the areas that more frequently suffer damage. The proposed methods are verified experimentally on specimens of carbon fiber reinforced resin composite laminates.

Tensile Properties of Angle Cured Laminated Composites Structures under Gravity Effects

As the usage of composites materials are significant in the industries of automobiles, shipping and constructions due to their non-corrosive and high strength to weight ratio. Anyway, the production of composites needed to be increased to meet the demand. At this stage, problem faced by Small and Medium Industries / Entrepreneurs (SMI/E) is the confined and limited space available that restricts the optimum productivity. They commonly cure the composites horizontally that requires ample space and unable to afford for high-end equipment such as mechanical oven and autoclave in the production as a result of high capital cost.This research is carried out to study the feasibility of the gravity effects on curing position of the laminated composite structures to enhance the curing space needed. The aim of the research was to investigate the tensile properties of the thermosetting laminated composite by curing the laminate at different angle using vacuum bagging technique. From the testing, SN 5 which denominated to be 60 ̊ found to have the best tensile properties in term of maximum force exerted and Youngs modulus.

Dynamic characterization of viscoelastic materials used in composite structures

The main focus of this paper is the experimental comparative analysis of the viscoelastic properties of acrylic- and silicon-based viscoelastic materials. These materials are widely used in the aeronautic industry for structural and/or damping applications. It is therefore required to determine their viscoelastic properties such as shear modulus and loss factor following their integration to aircraft composite structures. The influence of material thickness, bonding quality, curing and cocuring with composite material was evaluated using dynamic mechanical analysis machine in plan shear configuration. This comparative analysis in the 0–600 Hz frequency range provides useful information that should be taken into consideration when designing bonded joints for structural and/or damping applications. The small variation of the acrylic-based material loss factor over a wide range of frequencies suggests that this material is a good candidate for damping applications at room temperature in metallic structures where no curing is required. However, cocuring of acrylic-based material with composite laminae increases its shear modulus up to six times with respect to the uncured material whereas its loss factor is reduced by about 20%. On the other hand, the silicon-based material remains stable after thermal treatment (curing and cocuring) suggesting that it is well suited for in situ damping treatment involving laminate composite structure. However, at room temperature its shear modulus after cocuring is lowered by almost 25% due to poor bonding quality, which depends on the nature of the substrate.

Fiber nonlinear predictive model for combined bending-compression loading of an orthogonal plane weave composite laminate structure

To increase understanding of damage evolution in advanced composite material systems, a series of large deflection bending-compression experiments and model predictions have been performed for a woven glass-epoxy composite material system. Theoretical developments employing both small and large deformation models and computational studies are performed. Results (a) show that the Euler–Bernoulli beam theory for small deformations is adequate to describe the shape and deformations when the axial and transverse displacement are quite small, (b) show that a modified Drucker's equation effectively extends the theory prediction to the large deformation region, providing an accurate estimate for the buckling load, the post-buckling axial load-axial displacement response of the specimen and the axial strain along the beam centerline, even in the presence of observed anticlastic (double) specimen curvature near mid-length for all fiber angles (that is not modeled), and (c) for the first time the quantities σeff – ɛeff are shown to be appropriate parameters to correlate the material response on both the compression and tension surfaces of a beam-compression specimen in the range 0 ≤ ɛeff < 0.005 as the specimen undergoes combined bending-compression loading. In addition, computational studies indicate that the experimental σeff – ɛeff results are in reasonable quantitative agreement with unwoven laminate finite element simulation predictions in the range 0 ≤ ɛeff < 0.010, with the effect of the woven structure appearing to provide the key constraint for various fiber angles that leads to the observed consistency in the experimental σeff – ɛeff results on both surfaces.

Nondestructive evaluation of helicopter rotor blades using guided Lamb modes

This paper presents an application for turning and direct modes in a complex composite laminate structure. The propagation and interaction of turning modes and fundamental Lamb modes are investigated in the skin, spar and web sections of a helicopter rotor blade. Finite element models were used to understand the various mode conversions at geometric discontinuities such as web-spar joints. Experimental investigation was carried out with the help of air coupled ultrasonic transducers. The turning and direct modes were confirmed with the help of particle displacements and velocities. Experimental B-Scans were performed on damaged and undamaged samples for qualitative and quantitative assessment of the structure. A strong correlation between the numerical and experimental results was observed and reported.

Guided wave propagation in composite laminates using piezoelectric wafer active sensors

AbstractPiezoelectric wafer active sensors (PWAS) are lightweight and inexpensive transducers that enable a large class of structural health monitoring (SHM) applications such as: (a) embedded guided wave ultrasonics, i.e., pitch-catch, pulse-echo, phased arrays; (b) high-frequency modal sensing, i.e., electro-mechanical impedance method; and (c) passive detection. The focus of this paper is on the challenges posed by using PWAS transducers in the composite laminate structures as different from the metallic structures on which this methodology was initially developed. After a brief introduction, the paper reviews the PWAS-based SHM principles. It follows with a discussion of guided wave propagation in composites and PWAS tuning effects. Then, the mechanical effect is discussed on the integration of piezoelectric wafer inside the laminate using a compression after impact. Experiments were performed on a glass fibre laminate, employing PWAS to measure the attenuation coefficient. Finally, the paper presents some experimental and multi-physics finite element method (MP-FEM) results on guided wave propagation in composite laminate specimens.

Hybrid shuffled frog leaping optimisation algorithm for multi-objective optimal design of laminate composites

In this paper, a hybrid shuffled frog-leaping algorithm (SFLA) is presented for solving multi-objective optimal design of laminate composite structures. A customized neighborhood search algorithm, an adaptive search factor and a crossover operator are suitably incorporated in the proposed algorithm to improve the convergence characteristics apart from features like Pareto dominance, density estimation, and an external archive to store the non-dominated solutions to handle multiple objectives. The performance of the proposed algorithm is demonstrated by solving laminate composite plate, shell and stiffened shell (isogrid) problems. Further, superiority of the proposed algorithm is demonstrated by comparing with four popular meta-heuristic algorithms.

Failure analysis of carbon fiber/epoxy composite cylindrical laminates using explicit finite element method

Based on continuum damage mechanics, the progressive failure analysis using explicit finite element method is performed to predict the failure properties and burst strengths of aluminum–carbon fiber/epoxy composite cylindrical laminate structures in terms of three composite pressure vessels with different geometry sizes. The failure analysis employs the Hashin damage initiation criterion and the fracture energy-based damage evolution law for composite layers. The numerical convergence problem is solved by introducing viscous damping effect into finite element equations for strain softening phenomenon. Effects of the calculation time and mesh sizes on the failure properties of composite laminates are explored. In addition, the predicted failure strengths of composite laminates using explicit finite element analysis are also compared with those by experiments and implicit finite element analysis.

Tensile Test of Composite Laminates and Specimen's Improvement

To obtain the material parameters for the composite laminate structure based on the general strength theory and failure criterion, a series of strength experiments are required to be carried out for some typical laminated fiber reinforced composite laminate plate. Due to complexity of stress state of specimen, some unexpected failure modes will often appear in the tensile test process of composite laminated plate. In this paper, according to the tensile test, the analysis for the failure mechanism of the specimen was executed by using finite element method. The suggestion for suitable geometry of the specimen was put forward, and the experimental results proved that the improvement for the specimen design was effective, thus the success rate of test was improved.

Impact Resistance Research of Composite Laminate Structure

The composite material has been widely used in aircraft structures. But this kind of material has some shortage such as poor impact resistance, low residual compressive strength, which have a negative influence on the performance of aircraft structures. In this paper, simulations of low-velocity impact and compression process of composite laminates with AL ply and different core material has been done. The simulation results show that softer core materials and AL ply with certain thickness can improve the residual compressive strength

Optimal design of laminate composite isogrid with dynamically reconfigurable quantum PSO

Optimal design of stiffened laminated composite cylinder of symmetric and balanced layup with isogrid form stiffeners is investigated and presented. The isogrid stiffened cylinder is subjected to uniform compressive load. In the optimization for the maximum buckling load, the panel skin laminate stacking sequence and stiffener configuration are chosen as design variables. A smeared model is employed in the buckling analysis of the stiffened composite cylinder. A new variant of particle swarm intelligence algorithm, using multiple swarms, built with quantum and dynamically reconfigurable features is developed and employed in the present investigations. The optimization is carried out using the proposed multi swarm based quantum particle swarm optimisation (PSO) algorithm, taking into consideration of the ply contiguous constraint. An optimal layup of the skin and stiffener configuration has also been obtained by using the proposed dynamic quantum PSO algorithm. Comparisons have been made with quantum PSO, cooperative quantum PSO, multi swarm based hybrid PSO, the newly developed multi swarm versions of quantum PSO and cooperative quantum PSO algorithms. Studies clearly indicate that multi swarm version of quantum PSO algorithms are more consistent and also reliable in providing optimal solutions. The methods presented in this paper will be applicable in general to the design of laminate composite structures.

Aeroelastic Behavior of Morphing Wing in Flutter Regions

A morphing of a system is capable of changing the shape from the cruise to dash configurations. During the motion, the aerodynamic and structural characteristics can be varied tremendously, and the new shape will induce the different aeroelastic stability behavior. Thus, the purpose of this study is to investigate the flutter analysis of the folding wing structure including the effect of various parameters such as fold angles et al. of the composite laminates structures. For doing this these works, the aero-elastic analysis of folding wing is performed with respect to the parameters using PK method. Also, Finite Element Method is used in structural analysis, and Doublet Lattice Method is applied in aerodynamic analysis. Generally, the dynamic pressure and frequency during the flutter are sensitive to the structural characteristic, thus the flutter mode alteration is occurred by changed natural frequencies. Also, the alteration causes the flutter dynamic pressure variation. Therefore, results represent the aeroelastic stability variation due to the folding wing system including the effects of ply angles of composite laminates.

Self-biased Dual-phase Energy Harvesting System

ABSTRACTIn this study, we report the design and fabrication of a dual-phase energy harvester which can synchronously harvest both mechanical and magnetic energy in the absence of DC magnetic field. The harvester consists of a magnetostrictive cantilever beam and a magnetostrictive/ piezoelectric (M/P) self-biased laminate composite structure. This structure allows us to utilize piezoelectric and self-biased magnetoelectric effect simultaneously. By combining these mechanisms together, a sum effect for harvesting both magnetic and vibration energy was realized under DC magnetic field free condition. The bilayer structure provides a simplified geometry that can be easily incorporated into MEMS devices. We demonstrate a hybrid synthesis method for fabrication of complex three-dimensional thin films using a cost-effective and mask-less aerosol jet deposition process. The combination of the hybrid aerosol jet process with dual phase harvester design provides the opportunity to fabricate small scale power sources required for structural health monitoring applications.