Damage composite

The increasing use of light ceramic composites for high temperature and space applications has stimulated the development and optimization of the Chemical Vapour Infiltration technique. The use of conventional ceramic techniques for the fabrication of fibre-reinforced composites damages the fibres both mechanically as chemically. Also, the high process temperature causes a thermal degradation of the fibres. 

Fig. 6.16 Definition of damage at the macroscale, mesoscale, and microscale of a composite damage is considered at three different length scales. The microscale is concerned only with the fiber-matrix interaction, The mesoscale concerns the interaction of fibers and matrix with cracks or other defects. The macroscopic properties are independent of any microstructural length dimension. When going from a finer scale to a coarser scale, the description of the finer scale is made through average quantities.

Applications. Nondestructive method of determination of carbon fiber reinforced composites. Damage of woven fiber reinforced composites, distribution of filler due to flow in molding techniques, distribution of fiber in composite, and dispersion of carbon black are examples characterizing potential applications of the method. 

Limited periods of illumination or excitation of the sample represent still another cause of photon starvation. Brief periods of illumination are often necessary in a number of spectroscopic applications to avoid deleterious effects. For example, prolonged irradiation of various fluorescing compounds can often result in bleaching. Similarly, microsample analysis by Raman spectrometry can easily cause structural and compositional damage to the sample upon long exposure to the intense excitation radiation. 

Bathia.s, C., and Cagnasso. A. (1992). Application of X-ray tomography to the nondestructixe testing of high performance polymer composites. Damage Detection in Composite Materials. ASTM. STP 1128. pp. 35 54. 

The primary purpose of the meso-damage modelling is to describe failure as processes occurring at the yam scale. Compared to unidirectional laminated composites, damage accumulation in textile composite has some specific features (1) the early initiation of intra-yam cracking (0.1—0.3% of applied deformation), (2) the concurrent accumulation of crack density and incremental crack length growth. 

All forms of laminated composite damage can take place as shown in Figure 9.1 for a laminate with 0° and 90° layers. 

It should be noted that the composites damage and failure models discussed here are based on an assumption of rate-independent behaviour, and materials properties used for validation studies are based on quasi-static tests. This is currently standard practice in impact simulations of composite structures, which is an important assumption in the work. Reasons for this are the lack of international dynamic test standards for measuring rate-dependent composites properties, so established test procedures are missing. Dynamic failure models for composites are not well understood nor implemented in current commercial FE codes. In justification it should be pointed out that carbon fibres are highly elastic, thus fibre-dominated properties show no... 

This chapter starts with a brief overview of composite damage situations. This is followed by a description of the major NDT methods applied to composite structures during manufacturing and in-service inspection. 

Figure 15.3 Composite damage due to fastener holes, (a) Tjfpical bolted junction between a composite wing skin and metallic connection (b) failure modes in a bolted joint under tension [6] and (c) compressive failure modes in a plate with an open hole.

Campbell FC. Manufacturing processes for advanced composites. Elsevier 2004. Georgeson G, Lea S, Hansen J. Electronic tap hammer for composite damage assessment. In SPIE proc. nondestructive evaluation of aging aircraft, airports, and aerospace hardware 1996. 

For fully supported specimens, frontal contact stresses together with cone cracking played a major role in generating composite damage whereas, for partially supported ones, both frontal contact and backside flexure stresses were combined sources of damage generation. 

In this chapter, the effects of various parameters on the fracture behavior of wood-plastic composites are discussed. Moreover, different methods of composite damage analysis are reviewed and the fracture analysis of WPG is presented. 

Pang, J. W. C. and Bond, I. P. 2005. Bleeding composites - damage detection and selfrepair using a biomimetic approach. Composites Part a - Applied Science and Manufacturing, 36,183-188. 

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