Composite failure modes

Composite failure modes are different from those of isotropic materials such as metals. Because of the fibers, they do not tend to fail in only one area, they do not have the strainbearing capacity of most metals, and they are prone to premature failure if stressed in a direction that was not anticipated in the design. Useful structures nearly always have been constructed from ductile materials such as steel or aluminum, with fairly well defined strengths. This allows designers to accurately comprehend and specify safety factors that provide some assurance that the structures will not fail in service. 

Because of the various characteristics of composite laminates, it is difficult to determine a strength criterion in which all failure modes and their interactions are properly accounted for. Moreover, the verification of a proposed strength criterion is greatly complicated by scatter in measured strengths caused by inconsistent processing techniques (that... 

The possible fatigue failure mechanisms of SWCNT in the composite were also reported (Ren et al., 2004). Possible failure modes mainly include three stages, that is, splitting of SWCNT bundles, kink formation, and subsequent failure in SWCNTs, and the fracture of SWCNT bundles. As shown in Fig. 9.12, for zigzag SWCNT, failure of defect-free tube and tubes with Stone-Wales defect of either A or B mode all resulted in brittle-like, flat fracture surface. A kinetic model for time-dependent fracture of CNTs is also reported (Satapathy et al., 2005). These simulation results are almost consistent with the observed fracture surfaces, which can be reproduced reasonably well, suggesting the possible mechanism should exist in CNT-polymer composites. 

Plastics. Part of the trend to substitute plastic and composite substrates for metals can be attributed to a desire to avoid the process of metallic corrosion and subsequent failure. Relatively little attention has been called to the possible failure modes of plastics under environments considered corrosive to metals. More extensive work should be conducted on the durability and life expectancy of plastic and composite materials under end-use environments. A further consideration is the potential for polymer degradation by the products of metal corrosion in hybrid structures comprising metal and polymer components. Since it is expected that coatings will continue to be used to protect plastic and composite substrates, ancillary programs need to be conducted on the mechanisms by which coatings can protect such substrates. 

Delamination represents the weakest failure mode in laminated eomposites, and is considered to be the most prevalent life-limiting crack growth mode in most composite structures. As such, ever-increasing attention has been directed toward the understanding and characterization of delaminations of various natures, and at... 

Davidovitz, M, Mittelman. A., Roman. I. and Marom. G. (1984). Failure modes and fracture mechanisms in flexure of Kevlar-epoxy composites. J. Mater. Sci. 19, 311-294. 

Shih, G.C. and Ebert, L.J. (1986). Interface strength effects on the compressive-flexure/shear failure mode transition of composites subjected to four-point bending. J. Mater. Sci. 21, 3957-3%5. 

Wimolkiatisak, A.S. and Bell, J.P. (1989). Interfacial shear strength and failure modes of interphase modified graphite-epoxy composites. Polym. Composites 10, 162-172. 

Bader, M.G., Charalambides, B, Ling, J. (1991). The influence of fiber-matrix interface strength on the tensile strength and failure mode in uniaxial CFRP. In Proc. ICCM-VIII, Composites Design. Manufacture and Application (S.W. Tsai and G.S. Springer, eds.), SAMPE Pub. Paper 1II. 

Sohi. M.M., Hahn, H.T. and Williams, J.G. (1987). The effect of resin toughness and modulus on compressive failure modes of quasi-isotropic graphite/epoxy laminates. In Toughened Composites. ASTM STP 937 (N.J. Johnston cd.). ASTM. Philadelphia, PA. pp 37 60. 

In general, the use of FE signals accompanying the deformation and fracture of composites offer elucidation of failure mechanisms and details of the sequence of events leading upto catastrophic failure. The extent of interfacial failure and fiber pull-out are also potential parameters that can be determined. FE can assist in the interpretation of AE and also provide an independent probe of the micro-events occurring prior to failure. FE has been shown to be sensitive to the locus of fracture and efforts are underway to relate emission intensity to fracture mechanics parameters such as fracture toughness (Gjp). Considerable work still remains to fully utilize FE to study the early stages or fracture and failure modes in composites. 

Foam sandwich has seemed for many years to have had much to offer, and yet has rarely been exploited commercially. Details are given of how a foam sandwich bootlid for the Ford Escort CE14 Cabriolet was designed, manufactured and tested. During the project, much was learned about the injection process as well as the properties and failure modes of composite foam sandwich panels. 

Some of the best uses of Kevlar are in aircraft composites and flak jackets for military and police uses, which require high tensile strength and high modulus per unit of weight. It also has the property of damage tolerance, as it has a ductile compressive failure mode, which is very different from the brittle failure of carbon fibers. 

The primary failure modality identified clinically for restorations in posterior teeth is loss of material through abrasion. The complex nature of this failure mode in composite materials makes it difficult to correlate this phenomenon with any one mechanical property. A number of studies have suggested improvements in the system by using various mechanical properties as evidence. These studies have identified major factors such as ceramic filler loading and type of filler [186-191]. Some effects have been identified related to the... 

SEM micrographs of the wear scars of EPDM gum and PTFE-EPDM composites are shown in Fig. 35. EPDM gum shows a characteristic failure mode caused by... 

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