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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.

We apply THz imaging technology to evaluate fire damage to a variety of carbon fiber composite samples. The majority of carbon fiber materials have polarization-dependent reflectivities in the THz frequency range, and we show how the polarization dependence changes versus the burn damage level. Additionally, time domain information acquired through a THz time-domain spectroscopy (TDS) system provides further information with which to characterize the damage. The technology is discussed in terms of non-destructive testing applications to the defense and aerospace industries.

Efforts have been made here to develop a proton conducting composite polymeric gel electrolyte, namely, PEG-PVA-(NH₄CH₂CO₂)₂ system and investigate its ion conducting behavior. The gel samples with varying PVA concentration have been prepared in 1 M solution of (NH₄CH₂CO₂)₂ in Dimethyl Sulphoxide used as casting solvent. The XRD of samples exhibit crystalline nature of composite gel electrolytes which increases with increase of PVA concentration in the gel .Shift in endothermic transitions of constituents and corresponding broadness in DSC thermograms of as synthesized samples have been attributed to the formation of composite gel electrolytes. The room temperature ionic conductivity of gel electrolytes (3.5×10⁻⁴S. cm⁻¹)have been found to be comparable to that of liquid electrolytes(5.52×10⁻⁴S. cm⁻¹). Temperature dependence studies of ionic conductivity reflects VTF character of gel electrolytes

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.

Laser cleaning of artworks and antiquities is reaching a mature enough stage both in terms of the procedures employed and the understanding of the interaction processes involved. To this effect, a series of studies have been pursued aiming to process optimization. Appropriate model systems have been studied for elucidating the interaction mechanisms both in polymerized phases as well as inorganic encrustation. An overview of these issues presented and their implications for future directions outlined.

Carbon nanofibers (CNFs) were coated by surfactants of polyoxyetheylene alkyl ether (AEO₉, AEO₇) and polyvinyl alcohol (PVA 1799), respectively, after being mixed with surfactant aqueous solution and then treated with ultrasonication, high shear and magnetic stirring. The CNF/epoxy composites were prepared by mixing the surfactant coated CNFs with epoxy. Tensile strength, elastic modulus and ultimate strain of the composites were studied. The tensile strength and the ultimate strain of the composites were increased by 20% and 70%, respectively, after the CNFs were coated by surfactants. However, the elastic modulus of the composite will be lowered when the CNFs were treated by too high a concentration of surfactant solution.

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.

Composites were prepared with carbon fiber used as the reinforcement. The influence of carbon fiber content and coupling agents on the mechanical properties of the fluorine rubber was studied. Infrared Spectroscopy (IR) showed that C-Si-O bonds were generated in the composites. These improved the compatibility between carbon fiber and fluorine rubber. Scanning Electron Microscopy (SEM) showed that the carbon fiber, treated with KH550, was aligned within the rubber with no obvious sections or pores, indicating a good interphase combination between them. Optimal mechanical properties of the composites were obtained when fluorine rubber had 12 parts per hundred rubber (phr) of chopped carbon fiber.

Composite stiffened-structure consists of the skin and stringer has been widely used in aircraft fuselage and wings. The main purpose of the article is to detect the composite material reinforced structure accurately and explore the relationship between defect formation and structural elements or curing process. Based on ultrasonic phased array inspection technology, the regularity of defects in the manufacture of composite materials are obtained, the correlation model between actual defects and nondestructive testing are established. The article find that the forming quality of deltoid area in T-stiffened structure is obviously improved by pre-curing, the defects of hat-stiffened structure are affected by the mandrel. The results show that the ultrasonic phased array inspection technology can be an effectively way for the detection of composite stiffened-structures, which become an important means to control the defects of composite and improve the quality of the product.

In this paper, the polyaniline (PANI) and PANI-Co_0.5Zn_0.5La_0.1Fe_1.9O₄ (x wt %, x = 10 and 20) composites were synthesized by an in situ polymerization. X-ray diffraction (XRD), scanning electron microscope (SEM) and ultraviolet-visible spectrometer (UV-vis) were used to characterize the morphologies and phase formation of the prepared products. The dielectric loss (tan ε) and the magnetic loss (tan μ) of the samples were measured in Xband (8.2-12.4 GHz) by using vector network analyzer (HB8510B). The results demonstrated that the dielectric loss of PANI-Co_0.5Zn_0.5La_0.1Fe_1.9O₄ were lower than that of the pure PANI and vice versa for magnetic loss. Furthermore, the dielectric loss and magnetic loss of the composites decreased and increased respectively, when the relative content of Co_0.5Zn_0.5La_0.1Fe_1.9O₄ increased. In the measuring frequency range of 8.2∼12.4 GHz, the reflection loss of composites increased with an increase in Co_0.5Zn_0.5La_0.1Fe_1.9O₄ relative content. PANI-Co_0.5Zn_0.5La_0.1Fe_1.9O₄ (20 wt %) composite has the highest reflection loss in the range of -8.73 dB to -12.75 dB, with a maximum reflection loss value at -12.75 dB at the frequency of 11.0 GHz (full frequency width at about half of the peak response).

In the measuring frequency range of 8.2~12.4 GHz, with the increase of Co_0.5Zn_0.5La_0.1Fe_1.9O₄ relative content, the reflection loss of composites increased, and the PANI-Co_0.5Zn_0.5La_0.1Fe_1.9O₄ (20 wt%) composite has the highest reflection loss, which is in the range of -8.73 dB to -12.75 dB, and the maximum values of the reflection loss is -12.75 dB at the frequency of 11.0 GHz. (full frequency width at about a half of the peak response).

Microwave absorption properties (MAP) of manganese soft spinel ferrite (MnFe2O4) nanoparticles (MSF NPs) mixed with multi-walled carbon nanotubes (MWCNTs) and molded as toroid-shaped pellets were experimentally studied using a coaxial line technique in the frequency range of 2-18 GHz. We used the coaxial line technique because of the smaller sample size, a wider frequency range, and a uniform cross section. The MAP were derived from the measured constitutive parameters, according to the transmission line theory. The results indicate that MWCNTs blended with ferrite nanoparticles represent a promising choice for broadband microwave absorbing materials.

This study evaluated the possibility of obtaining bioactive coatings on polyethylene/bioactive glass composites exhibiting a very good mechanical performance. High molecular weight polyethylene (HMWPE) was reinforced with 10 to 40% (wt.) of a bioactive glass (BGE1) and a glass-ceramic (BGE1C), in the SiO₂-3CaOP₂O₅-MgO system. The composites were compounded by twin-screw extrusion (TSE) and then injection moulded into dumb-bell tensile samples. The composites presenting adequate mechanical properties were then coated with a bioactive layer by two methodologies: (i) an adapted biomimetic route using a similar glass as a precursor of calcium-phosphate (Ca-P) film deposition, and (ii) the production of a ‘sandwich’ with bioactive glass particles, previously mixed with UHMWPE powders, made to adhere to both faces of tensile samples by compression moulding. The obtained results indicated that it is possible to produce composites presenting a modulus of 11.2 GPa coupled with a tensile strength of around 117 MPa. The developed composites could be coated with a Ca-P layer by an adapted biomimetic route. Furthemore, the ‘sandwich’ route allowed for the production of load-bearing composites, presenting a highly bioactive surface, which strongly adheres to the HMWPE matrix composites.

Various materials have been used for knee and hip prostheses over the last few decades due to considerations for their mechanical and tribological properties and their biocompatibility. Hydroxyapatite (HA) reinforced high density polyethylene (HDPE) composites have been developed as a new generation biomaterial for skeletal applications. In this investigation, the tribological properties (i.e., wear rate, coefficient of friction, and lubrication in the presence of proteins) of HDPE and HA/HDPE composites were evaluated against duplex stainless steel under dry and lubricated conditions. Lubricants included distilled water and aqueous solutions of proteins (egg albumen or glucose). It was found that HA/HDPE composites had lower coefficients of friction than HDPE under certain conditions. Furthermore, HDPE exhibited more severe fatigue failure marks than the composites. The degradation and fatigue failure due to the presence of proteins were severe for low speed wear testing (100 rpm) as compared to high speed wear testing (200 rpm). Both egg albumen and glucose were found to be corrosive to steel and adversely reactive for HDPE and HA/HDPE composites. This was clearly shown by SEM micrographs of HDPE and HA/HDPE specimen surfaces taken after the tests. The wear modes observed were similar to that of UHMWPE. Specimens tested with egg albumen also displayed higher wear rates, which again were attributed to corrosion accelerated wear of these specimens.

In the research the some problems concerning the disadvantageous effects occurring in cast iron brake discs in operating conditions are presented. The qualitative metallographic investigations of microstructure of materials used in traditional brake discs (cast iron) and modern brake discs (composites reinforced with SiC and fly ash) are presented. The studies of the friction properties of the traditional and composite brake discs are also presented.

It was proved that in the case of not ventilated brake discs only the friction sets consisted of the cast iron brake discs and the investigated friction pads can be used in vehicle brake systems.

The results allow to ascertain that the pressure decreasing in a brake system and in consequence the work temperature decreasing and brake discs wear decreasing will make possible composite brake discs based on Al-alloys to put into use in not high loaded applications, for example in the light passenger cars in a rear axle.

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.