Failure mechanisms of composite

Like mechanically fastened metal structures, composites exhibit failure modes in tension, shear and bearing but, because of the complex failure mechanisms of composites, two further modes are possible, namely cleavage and puUout. Environmental degradation of a bolted joint, after exposure to hot, wet environment is most likely to occur in the shear and bearing strength properties. The evidence shows that for fiber reinforced epoxies, temperature has a more significant effect than moisture, but in the presence of both at 127°C, a strength loss of up to 40 percent is possible. 

Sachse W, Kim KY (1987) (Quantitative acoustic emission and failure mechanics of composite materials. Ultrasonics 25 195-203 Sklarczyk C, Gries H, Waschkies E (1990) Testing during concrete constraction. Reinhardt HW (ed ). Chapman and Hall, London, pp 297-208... 

Greco (1994) conducted a study for determining the strength and failure mechanism of composite rocks. 

Roulin-Moloney A C 1989 Fractography and failure mechanisms of polymers and composites (London Elsevier)... 

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. 

Birger, S., Moshonov, A. and Kenig, S. (1989). Failure mechanisms of graphite fabric epoxy composites subjected to flexural loading. Composites 20, 136-144. 

Friedrich, K. and Karger-Kocsis, J. (1989). Unfilled and short fiber reinforced semi-crystalline thermoplastics. In Fractography and Failure Mechanisms of Polymers and Composites, (A.C. Roulin-Moloney ed.), Elsevier Appl. Science, London, pp. 437-494. 

The results of these experiments indicate that EE may be used to detect microfracture events on the composite surface, and signal the early stages of composite failure. It also clarifies the source of AE as a function of strain by the presence or absence of AE-EE correlations, and allows more details of failure mechanisms and composite characterization to be obtained. 

Fagan, A. F., Bell, J. M., and Briggs, G. A. D. (1989). Acoustic microscopy of polymers and polymer composites. In Fractography and failure mechanisms of polymers and composites (ed. A. C. Roulin-Moloney), pp. 213-30. Elsevier Applied Science, London. [204]... 

Chu, C.Y., Singh, J.P. and Routbort, J.L. High-temperature failure mechanisms of hot-pressed Si3N4 and Si3N4/Si3N4-whisker-reinforced composites , J. Am. Ceram. Soc., 76[5] (1993) 1349-1353. 

Figure 4 shows typical failure surfaces obtained from tensile tests of the co-cured single and double lap Joint specimens. In the case of the co-cured single lap Joint, as the surface preparation on the steel adherend is better, a greater amount of carbon fibers and epoxy resin is attached to the steel adherend. Failure mechanism is a partial cohesive failure mode at the C ply of the composite adherend. In contrast with the co-cured single lap joint, failure mechanism of the co-cured double lap joint is the partial cohesive failure or interlaminar delamination failure at the 1 ply of the composite adherend because interfocial out-of-plane peel stress... 

Based on the measured thermomechanical properties and the microstructure of the graded layer of TiC-NiaAl functionally graded material, using the analysis method, the interface residual thermal stress of TiC-NiyAl sphere in the sintering process was calculated. The relationship between the stress and the content of NiyAl was presented. The results show that the failure mechanics of TiC-NijAl composite may be different in different content of NiyAl. 

The larger the radial compressive stress, the harder to fracture in the radial direction in the material the larger the tangential tensile stress, the easier to fracture in the tangential direction in the material. So, the failure mechanics of TiC-NisAl composite may be different in different content of Ni3Al. 

Dr. Riew has presented more than 50 technical papers and holds more than 25 patents on emulsion polymers, hydrophilic polymers, synthesis and application of telechelic polymers, and toughened plastics for adhesives and composites. His latest research is in the synthesis, characterization, and performance evaluation of impact modifiers for thermosets and engineering thermoplastics. His research interests include correlating polymer chemistry and physics, morphology, engineering, and static and dynamic thermomechanical properties to the failure mechanisms of toughened plastics. 

Soutis, Fleck, and Smith [22], proposed the use of linear elastic fracture mechanics and the principle of superposition to determine the failure strength of composites with holes, in particular, under compression. This approach essentially models the damage developing at the edge of the hole as a crack with loaded surfaces. This is a one-parameter model as the crack surface stress must be determined by tests. 

Nuistner RJ. Continuum modeling of damage accumulation and ultimate failure in fiber reinforced laminated composite materials. In Research workshop, mechanics of composite materials. Durham (NC) Duke University 1978. p. 55—77. 

The properties of composite materials cannot be predicted adequately by considering the fibre and resin constituents one by one. An important mechanism of composite failure under stress is delamination caused by differences between the engineering properties of successive plies or layers. These differences arise from the fact that successive layers may have different fibre orientations [34] or, occasionally, different fibres. It is a feature of laminates made by stacking pre-impregnated layers of reinforcement and is not an issue with, for example, unidirectional pultrusions. The process of delamination has been reviewed by Davies [35]. The fabrication of three-dimensional composites is an important step towards reducing or eliminating unwanted delaminations. Such materials are at an advanced stage of development. 

It is worth pointing out that the failure mechanism of CVl SiC/SiC composites is at variance with that observed in polymer matrix impregnated tows, where a local load sharing occurs when a fiber fails. In these composites, the fibers fail first. Therefore, the uncracked matrix is able to transfer the loads. 

Lee BL, Walsh TF, Won ST, Patt HM, Song JW, Mayer AH. Penetration failure mechanisms of armour-grade fibre composite under impact. J Comp Mater 2001 35 1605-33. 

Three-dimensional (3-D) fiber reinforced polymeric materials have been shown to have a good impact tolerance [108,109], making them attractive candidates in weight sensitive industries such as in aerospace, auto, and maritime. A number of stodies have been conducted to understand the impact response of 3 -D woven composites [ 108,109]. For example, B aucom, Zikry, and Rajendran [110] investigated the effects of fabric architecture on damage progression, perforation resistance, strength, and failure mechanisms in composite systems of... 

Lee, S. W. R., Sun, C. T. Dynamic penetration of graphite/epoxy laminates impacted by a blunt-ended projectile. Composites Science and Technology 1993 49 369-80. Lee, B. L., Walsh, T. F., Won, S. T, Patts, H. M., Song, J. W., Mayer, A. H. Penetration failure mechanism of armour-grade fibre composites under impact. Journal of Composite Materials 2001 35(18) 1605-29. 

The failure mechanisms of carbon fiber reinforced PES have been investigated [154]. Although toughness of the PES composite was lower than comparable results with PEEK, results were independent of the test temperature (—60-100°C), whereas the PEEK composite showed a change to unstable fracture at low temperatures. 

Oya N, Hamada H, Mechanical properties and failure mechanisms of carbon fibre reinforced thermoplastic laminates. Composites Part A-Appl Sci Manuf 28(9-10), 823-832, 1997. 

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