Mechanics of delamination

In the foregoing sections, the energy release rate Q a) for symmetric increase in width a of the strip bulge was determined for film response described 

Derivation of the corresponding result for large deflection response is left is an exercise. 

It was noted above that the phase angle of the interface stress at the edge of the delamination zone is always —45° when it is calculated according to small deflection bending theory with = 0. The incorporation of effects of finite deflection through (5.61) leads to a nonzero membrane stress to even when tni = O The nondimensional ratio of membrane stress ta to bending moment mg, at the edge of the delamination zone is found from the solution of these equations to be 

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Hashemi, S., Kinloch, A.J. and Williams, J.G. (1990a). Mechanics and mechanisms of delamination in a PES-fiber composites. Composites Sci. Technol. 37, 429-462. 

Williams JG. The fracture mechanics of delamination tests. J Strain Analysis 1989 24 207-14. http //dx.doi.org/10.1243/03093247V244207. 

However, a severe and persistent problem in laminated composites made of anisotropic fiber-reinforced plies is delamination. High interlaminar peel and shear stresses near edges start delamination cracks that grow along the non-reinforced interlaminar planes with little resistance. Delamination substantially reduces the load-bearing capacity and durability of advanced composites and has led to disastrous structural failures. Since the discovery and explanation of the mechanisms of delamination in advanced composites in the early 70s, many researchers have tried to... 

Guichenuy M, Watts JF, Abel M-L, Audenaert M (2006) Mechanism of delamination of a polyamide coating modified with an aminosilane. Surf Interface Anal 38 168... 

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... 

Marshall, D.B. and Evans, A.G., Measurement of adherence of residually stressed thin-films by indentation. I. Mechanics of interface delamination. J. Appl. Phys., 56(10), 2632-2638 (1984). 

Local repair of delamination originally caused by non-durable surface treatment is only temporarily successful at best. The surface treatment on the unrepaired portion of the assembly remains susceptible to attack and the area of delamination will likely continue to grow once the assembly is put back into service and exposed to moist conditions. Replacement or complete remanufacture of the component is the only way to permanently address this type of damage. However, time-limited repairs using bonded or mechanical methods can be used to extend the life of the component until a major overhaul is scheduled. In some cases such as widespread disbond of fuselage doublers, mechanical repairs (rivets and fastened doublers) and continued inspection are used to extend the life of the skin indefinitely because of the high cost of replacement. 

Locus of failure studies 75 80) on metal/epoxy joints that had been exposed to water indicate that corrosion of the metal substrate does not occur until after interfacial failure has occurred. This suggests that corrosion itself does not play a primary role in the loss of adhesion strength mechanism of metal/epoxy joints, but rather is a post-failure phenomenon. However, for the case of metal/epoxy protective coating systems, Leidheiser and coworkers 88-91 -92) and Dickie and coworkers 5 87-89-90> have proposed that localized corrosion processes are part of an important delamination mechanism. 

The timing and extent of the Colorado Plateau uplift bears on the possible mechanisms that caused it. Various hypotheses have been suggested including influence of a mantle plume (Parsons et al. 1994), lithospheric thinning and/or delamination (Spencer 1996 Lastowka et al. 2001), and subduction of the Farallon plate margin (East Pacific Rise) (Dickinson and Snyder 1979). With a definitive uplift history, it will be possible to place constraints on the mechanisms of uplift and thereby shed light on mantle processes and lithospheric evolution. 

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... 

Theoretical model of mode I delamination of z-pinned DCB has been developed to study the bridging mechanism of z-pin reinforcement. The numerical results show that the fracture load for delamination in the z-pinned DCB is greatly dependant on the fnctional pull-out force Pf. However, since the deformation of the z-pin is relatively small compared to sliding distance, the effects of debonding force and debonding length on the fracture resistance of the DCB are... 

The presence of Z-pins as the through-the-thickness reinforcement has been shown to result in dramatic increases in the apparent resistance to crack propagation under Mode I and Mode II loading conditions, in laboratory tests on standard unidirectional (UD) beam samples [2]. The Z-pin pull-out has been identified as the dominant energy micro-mechanism responsible for the resistance to delamination under Mode I conditions. The behaviour of individual Z-pins in pull-out from a UD-laminate has been characterised and modelled and the single Z-pin pull-out curves used as input into a 2D Finite Element (FE) model of delamination under Mode I [3, 4]. 

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