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In the present study, aluminum alloy (Al/3.25Cu/8.5Si) composites reinforced with fly ash particles was fabricated using stir casting technique. Fly ash particles of three different size ranges 53–75, 75–103 and 103–125$\mu$m of 3, 6 and 9 weight percentages was reinforced in aluminum alloy. The effect of peak current, pulse on time, and pulse off time on surface roughness (SR), material removal rate (MRR) and tool wear rate (TWR) of electric discharge machining (EDM) was investigated. A central composite design using response surface methodology (RSM) was selected for conducting experiments, and mathematical models were developed using Design Expert V7.0.0 software. Analysis of variance (ANOVA) technique was used to check the significance of the models developed. Peak current was the major factor influencing the EDM of aluminum fly ash composites. The MRR, TWR, and SR of aluminum fly ash composites were also influenced by the size of the fly ash particles.

In this paper, a comparative experimental analysis of die-sinking electric discharge machining (EDM) to two most exhaustively used aluminum metal matrix composites (AMMCs) has been performed using Copper and Tungsten as tool electrodes. AMMCs containing silicon carbide (SiC) and alumina (Al₂O${}_3)$ as reinforcement (10wt%) were fabricated by stir casting method. The Box–Behnken Design (BBD) approach of response surface methodology was used to develop experimental models for material removal rate (MRR) and surface roughness (SR). Effect of input parameters such as current ($I=4$–12A), gap voltage ($V_g=40-60$V), pulse-on time ($T_{\mathrm{\text{on}}}=100-200\mu$s), and duty factor ($\tau =4$–6) on the output responses has been investigated with response surface plots. Effectiveness of design of experiment (DoE) and evolutionary algorithm-based multi-objective optimization (MOO) technique have been compared to find the best feasible optimal solution. ANOVA analysis reveals that for alumina reinforced AMMC interaction between $I\times V$ has significant effect on both MRR and SR using Cu electrode. But for tungsten, electrode interaction between $I\times T_{\mathrm{\text{on}}}$, $I\times \tau$, and $V\times \tau$ have major role on MRR whereas SR is mostly influenced by interaction between $I\times V_g$ and $I\times T_{\mathrm{\text{on}}}$. The parametric analysis reveals that an increase of current from 4A to 12A at a higher pulse-ontime increases the MRR more significantly, and higher MRR occurs in cases of alumina-reinforced AMMC. Increase of pulse-ontime at low current (4A) reduces the MRR in AMMC/Al₂O₃. Good surface finish can be obtained by combining high voltage (60V) with either small current (4A) or small duty factor (4) for both AMMCs. Both DoE and metaheuristic-based MOO technique reveals that copper electrode should be preferred for die-sinking EDM of AMMC/SiC. Metaheuristic approach should be preferred for optimization of die-sinking EDM of AMMCs using different electrodes because it requires low current for effective machining of different AMMCs.

As an attempt towards damage detection in composites, in this chapter, an experimental investigation is presented aiming at extending the current understanding of how delamination will affect the vibration characteristics of carbon fiber-reinforced plastics (CFRP). Different percentages of delamination have been applied artificially on CFRPs, and experimental modal analysis has been performed for both natural frequency and modal loss factor parameters. It is a well-established fact that, due to the global nature of lower modes’ natural frequencies, small defects have small effects on these modal parameters and hence, generally speaking, natural frequency is not a good feature for damage indication. On the other hand, modal loss factor can be considered as a good damage index (DI), especially, if the healthy structure is of low damping characteristic. However, the problem with modal loss factor is that it is hard to identify reliable values for this parameter and usually identified values have high scatter. In order to be able to identify reliable modal loss factors, the modal parameter extraction techniques with high order of accuracy in damping identification, i.e. circle fit (CF) and line fit (LF) methods, are used, leading to the rationalization process being optimized, resulting in the extended line fit method, (ELFM). Using ELFM, it has been shown that both natural frequency and modal loss factor have changed due to delamination. While, as expected, natural frequency has experienced insignificant changes, modal loss factor has proved to be a highly sensitive indicator, undergoing major changes even at initial damage stages. Modal damping mechanisms and their relationship with mode shapes have been examined. The results reveal that delamination severity can be detected using modal loss factor variations.

A nonlinear rate dependent constitutive model for fiber-reinforced composites is presented. Through the use of a plastic potential function, effective stress and effective plastic strains are introduced, with which a single equation is established for the orthotropic and nonlinear rate dependent behavior of composites. This viscoplasticity constitutive model is employed together with a microbuckling model to predict compressive strength of composites for different strain rates. Results of qasi-static and high strain rate compression tests using off-axis composite specimens of S2/8552 glass/epoxy are reported and compared with model predictions. Excellent agreement between experimental data and predictions is found. From the experimental results as well as model predictions, it is noted that the longitudinal compressive strength of a composite is significantly influenced by the presence of shear stresses.

This paper presents a new coupled electro-mechanical dynamics model of piezoelectric actuator-sensors. The new model takes the bonding layer between piezoelectric patches and host structures into account in the coupled electro-mechanical analysis by treating the bonding layer as a spring-mass-damper system. Numerical simulations are performed to reveal the effect of bonding layers as well as to demonstrate the application of the new model to debonding detection of composite repair patches.

This paper presents a computational approach for composite materials subjected to ballistic impact. The composite materials are composed of layers of fabric embedded in a matrix material. The fabric is represented by bar elements and the matrix material is represented by solid elements. The geometric characteristics of these composite materials are three dimensional, which in turn requires a three dimensional analysis. The strength and failure characteristics of the fabric are determined directly from the actual fiber characteristics. For the matrix material it is necessary to modify the solid elements, because much of the volume of the solid elements is occupied by the volume of the fabric. The resulting modifications include the determination of effective density, stiffness, strength and failure characteristics for the solid elements. This approach has been shown to provide good agreement with experimental ballistics data. Because this approach treats each of the component materials individually (instead of blending them into a homogeneous anisotropic material), it is possible to examine the effects of individual material properties for both the fabric and the matrix material. This includes the capability to allow for failure of the fabric material and/or the matrix material. Parametric computational results are included to illustrate some of these effects.

Directional short fibre reinforced Li-Al-Si (LAS) glass-ceramic matrix composites (GCMC) were fabricated by hot pressing at 1450°C. Effect of different fibre volume on the properties of composites was studied. R-curves for composites were investigated using a simple compliance method. A remarkable change in the mechanical properties of GCMC was observed by adding short carbon fibre. Fracture toughness, the crack resistance to crack propagation (R-curve behaviour) and the fracture strength showed considerable improvement. Study shows that improvement in crack resistance was attributed to the extensive interaction of cracks with the short fibres. Composites with 30% volume of fibre showed the best crack-growth resistance. Based on microstructural observations, multiple matrix cracks were found to be arrested in matrix around fibre. Fractures observed include multiple matrix cracking (similar to microcracking) crack branching and crack deflection in crack frontal zone.

The purpose of this study is to develop a lightweight design model for an 18ft leisure boat. The existing leisure boat is manufactured using glass fiber-reinforced plastics (GFRP) material and the hand lay-up process. Carbon fiber-reinforced plastics (CFRP) was applied to the new design to reduce the boat’s weight, while an automated tape laying machine was applied to the lightweight boat’s manufacturing process to increase boat manufacturing productivity. The newly designed CFRP model is 25% lighter than the existing GFRP model. It was confirmed that the newly designed lightweight hull has sufficient structural integrity compared to the existing hull through the structural integrity evaluation by the FEA.