Materials Composites

A composite material or simply a composite is a duplex and multifunctional material composed of at least two elements working together to produce a structural material with mechanical and physical properties that are greatly enhanced compared to the properties of the components taken separately. In practice, most composites consist of a bulk material called the matrix and a reinforcement material or filler, added primarily to increase the mechanical strength and stiffness of the matrix but also sometimes to modify its thermal conductivity and electrical resistivity. This reinforcement is usually made of fibers (e.g., monofilaments, whiskers) but can also be particulates (i.e., dispersion strengthened and particle reinforced) or even material having a more complex shape (e.g., mesh, ribbon, laminates, etc.). Composites are first classified according to their matrix phase into three major classes  

A general classification of the three classes of composites is given in Table 18.1. 

Filler (e.g., metal or ceramic powders, particulate, beads) 

Fibers (e.g., glass fibers, carbon monofilaments/cut wires) 

A composite material is made from two or more substances with different properties that remain separate in the bulk material. Each contributes properties to the overall material, though, such that the composite exhibits the best properties of each of its components. One of the oldest examples of a human-made composite material is the formation of bricks from mud and straw, a process that dates back to biblical times. 

Carbon fibers can be woven into fabrics and threads to be used as the structural components of vehicles and for sporting equipment such as bicycles, tetmis rackets, and skateboards. 

The structural strengthening techniques making use of composite materials, also known as FRP, currently represent a sound reality in national and international scenarios, and have become a constituent part of the restoration works of buildings impacted by earthquakes that have hit many countries. 

Extremely relevant and diverse from other minor technical pubhcations dealing with buildings issues, this volume extensively focuses on the desaiption of the characteristics of the techniques employed for buildings or for the structural restoration of specific monuments or simple common constructions. 

Specific aspects of the implementation of r.c. structures, wood, masonry, and steel are extensively detailed both in terms of the technical design and of the execution stages, as well as the subsequent mechanical performances of the systems obtained. 

This book provides a useful tool that can be applied directly to different kinds of technical documents. 

The examples and descriptions of inspection and monitoring procedures crown the volume, making it an effective support for designers and for final users as well. 

Composites are solids made up of more than one material, designed to have enhanced properties compared with the separate materials themselves. 

There are very many situations in engineering where no single material will be suitable to meet a particular design requirement. However, two materials in combination may possess the desired properties, and provide a feasible solution to the material-selection problem. In this section some of the composites in current use will be mentioned. 

The incorporation of different components (e.g., catalytically active metals [222, 239,403,626,752,773], enzymes [674], photochemically active componnds [585], silicomolybdate [252,703], Keggin-type heteiopolyanions [412], nickel hexacyano-ferrate [417], CoFe204 [498], nncleotides [666], etc.) also results in composite materials with new and advantageous properties. In many cases the enhanced catalytic activity, higher capacity, etc., are due to the increased surface area, while in other cases the interaction between the conducting polymer and the other constituents results in a novel material that can be used for specific applications. Several other composites which are used in sensors, in supercapacitors, or for electrocatalytic purposes will be mentioned in Chap. 7. 

Inzelt G, Chambers JQ, Day RW (1986) Acta Chim Acad Sci Hung 123 137 

OyamaN, Ohsaka T, Yamamoto H, Kaneko M (1986) J Phys Chem 90 3850 

Oyama N, Old N, Ohno H, Ohnuki Y, Matsuda H, Tsuchida E (1983) J Phys Chem 87 3642 

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Reifsnider, K. F., (Editor) Fatigue of Composite Materials (1991), Elsevier, Amsterdam... 

O Brien, T.K., Characterization of Delamination Onset and Growth in a Composite Laminate in Damage in Composite Materials, ASTM STP 775, p. 140-167,1982 Poursartip, A. Ashby, M. F., Beaumont P.W.R., The Fatigue Damage Mechanics of Fibrous Laminates in Proceedings of the European Workshop on Nondestructive Evaluation of Polymers and Polymer Matrix Composites, Polymer NDE (edited by Khg. Ashbee), Technomic Publishing, p. 250-260, 1984... 

Estimation of Quality of Composit Materials by Acoustic Emission Method. 

Lately, polymeric composite materials have found a wide recognition thanks to their unique qualities /1,2/. But use of the materials for construction, is limited, because lack of reliable diagnostic facilities. The non-destructive control method (NC), based on the acoustic emission phenomenon (AE), might offer a prospective solution to the situation. 

K.A. Andrianov, S.A.Kolesnikov and others. Structure and qualities of the composite materials with carbon die. 

A.K Jain M P Debuisson. Segmentation of X-ray and C-scan Images of Fiber Reinforced Composite Materials. Pattern Recognition, vol 25, N°.3, pp 257-270, 1992... 

One more application area is composite materials where one wants to investigate the 3D structure and/or reaction to external influences. Fig.3a shows a shadow image of a block of composite material. It consists of an epoxy matrix with glass fibers. The reconstructed cross-sections, shown in Fig.3b, clearly show the fiber displacement inside the matrix. The sample can be loaded in situ to investigate the reaction of matrix and fibers to external strain. Also absorption and transmission by liquids can be visualized directly in three-dimensions. This method has been applied to the study of oil absorption in plastic granules and water collection inside artificial plant grounds. 

Results of determining a density of a composite material nozzles of the rocket engine before and after impregnation by metal. 

Based upon a piezoelectric 1-3-composite material, air-bome ultrasonic probes for frequencies up to 2 MHz were developped. These probes are characterized by a bandwidth larger than 50 % as well as a signal-to-noise ratio higher than 100 dB. Applications are the thickness measurement of thin powder layers, the inspection of sandwich structures, the detection of surface near cracks in metals or ceramics by generation/reception of Rayleigh waves and the inspection of plates by Lamb waves. 

Multivariable Regression Approach for Porosity Determination in Composite Materials. 

The porosity content in composite material is known to influence the strength of the material. It is therefore of interest to monitor the porosity contents Anting manufacturing. 

In this paper we propose a multivariable regression approach for estimating ultrasound attenuation in composite materials by means of pulse-echo measurements, thus overcoming the problems with limited access that is the main drawback of through-transmission testing. 

The increased use of composite materials in aireraft industry the last years has impliedagrowing need for efficient methods for nondestructive characterization of composite materials. One example is determination of porosity contents in composite specimens during manufacturing. Results have been reported [1], showing that the porosity contents can be estimated with good aceuracy by utilizing a linear relation between the frequeney dependenee of the attenuation, i.e., P = +1, where P is the porosity content, K and I are constants and where is the slope... 

As we have mentioned, the particular characterization task considered in this work is to determine attenuation in composite materials. At our hand we have a data acquisition system that can provide us with data from both PE and TT testing. The approach is to treat the attenuation problem as a multivariable regression problem where our target values, y , are the measured attenuation values (at different locations n) and where our input data are the (preprocessed) PE data vectors, u . The problem is to find a function iy = /(ii ), such that i), za jy, based on measured data, the so called training data. 

A. Ya. Gol dinaii, Prediction of the Deformation Properties of Polymeric and Composit Materials American Chemical Society, Washington (1994). 

Cherepanov G.P. (1983) Fracture mechanics of composite materials. Nauka, Moscow (in Russian). 

BMI intermediate synthesis [COMPOSITE MATERIALS - POLYTffiR-MATRLO - THERMOSETS] (Vol 7) -coumarin reduction [COUMARIN] (Vol 7)... 

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