Failure modes/mechanisms delamination

Of these failure mechanisms, the major ones associated with delamination include contaminated surfaces, inadequate adhesive coverage, stresses, voids, and moisture absorption. Many of these mechanisms are also responsible for other failure modes besides delamination. 

Lee, S.M., Mode II delamination failure mechanisms ofpolymer matrix composites. Journal of Materials Science, 1997. 32 p. 1287-1295. 

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... 

In composites, Drzal and Madhukar (1993) observed that the failure mode depended on the level of fiber/matrix adhesion at low levels, the mechanism was global delamination buckling at intermediate levels, fiber microbuckling at high levels fiber compressive (shear) failure. This is illustrated in Fig. 27. 

Figure 12.5 shows a schematic of the structure of a V-ribbed belt. The most commonly reported mechanical failure mode for this type of belt is wear, with delamination not generally perceived as a problem. This is of interest as most flexible composite elements will have a delamination failure mode of some description, and so the most obvious question to ask is why the V-ribbed belt does not. The probable answer is that the belt cord in a V-ribbed belt is isolated from the major distortions of the belt through its position above the belt/pulley interface. The large majority of the distortion of the belt takes place in the belt ribs, away from the cord. If the four shear stresses identified previously by Gerbert and Fritzson for a V-belt are considered, it can be seen that of the four i) and ii) do not apply to the cord layer in a V-ribbed belt. The cord layer in a V-ribbed belt therefore does not incur shear stress to the same extent as that in a V-belt. Thus the V-ribbed belt may be considered a better design in composite terms, with the individual elements of the composite more effectively employed and protected. 

When a coating is exposed to an aggressive environment, such as that found in a marine application, the associated failure mechanisms of blistering and delamination are amongst the most important to consider. These two failure modes are often treated separately. However, from a mechanistic point of view, these two modes are quite similar and only differ in their degree of aggressiveness [6]. 

The failure mechanisms which occur due to thermal cycling differ for underfilled parts compared to those with no underfill. In the absence of an underfill, area array solder joints fail due to solder fracture during thermal cycling. With an underfill, solder fracture is suppressed and other parts of the structure fail. These failure modes include chip fracture and delamination of the underfill from a chip, chip carrier, and solder joints. When the underfill adhesion fails, the solder joints locally are subjected to very high strain levels and quickly fracture. 

The possible delamination modes are (i) loss of adhesion at paint/phosphate interface, (ii) within phosphate layer due to mechanical fracture (iii) due to dissolution of phosphate (iv) dissolution of coating (v) mechanical failure at coating/steel interface. 

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