Bonding failure

APAOs has limited their utility in a number of applications. The broad MWD produces poor machining and spraying, and the low cohesive strength causes bond failures at temperatures well below the softening point when minimal stress is applied. To address these deficiencies, metallocene-polymerized materials have been developed [17,18]. These materials have much narrower MWDs than Ziegler-Natta polymerized materials and a more uniform comonomer distribution (see Table 3). Materials available commercially to date are better suited to compete with conventional EVA and EnBA polymers, against which their potential benefits have yet to be realized in practice. 

Moisture Aims are frequently found under unbonded protective coatings of asphalt and plastic tapes. The nature and origin of this water is still unknown but is of great interest because of its relationship to bond failure, microbial utilisation of asphalt and hydrocarbons, and efficiency of cathodic protection. ... 

Fracture energies have been determined for bond failure at either end of the bond line for a sheared rubber block, but the results are inconclusive—it is not clear where bond failure will occur, or at what load, even when the fracture properties of the rubber are known. Thus, the initiation of cracks, especially at interfaces and comers, needs further study. 

A.H. Muhr, A.G. Thomas, and J.K. Varkey, A fracture mechanics study of natural rubber-to-metal bond failure, J. Adhesion Set TechnoL, 10, 593-616, 1996. 

This is a surface analysis technique, used, for example, in examining causes of bonding failure. 

A surface analysis technique used in bonding failure analysis, for example. 

In evident areas of bond failure, fireproofing should be removed and the substrate should be thoroughly cleaned and properly primed before new material is applied. If surface coating is required to prevent moisture from penetrating, it should be renewed at intervals recommended by the manufacturer. The previously listed inspections should be completed prior to renewal of coating so that defects are not hidden by the coating. 

The extent of adhesive bond failure under corrosive environments is greatly accelerated when cyclic mechanical stresses are imposed on the adhesive bond during exposure. Three to four orders of magnitude reduction in fatigue life of adhesive bonds is observed for bonds exposed to environment prior to fatigue testing. 

Table 111. X-Ray Photoelectron Spectroscopy of Composite to Metal Bond Failure in Corrosion...

Bond failure may occur at any of the locations indicated in Fig. 1. Visual determination of the locus of failure is possible only if failure has occurred in the relatively thick polymer layer, leaving continuous layers of material on both sides of the fracture. The appearance of a metallic-appearing fracture surface is not definite proof of interfacial failure since the coupling agent, polymer films, or oxide layers may be so thin that they are not detectable visually. Surface-sensitive techniques such as X-ray photoelectron spectroscopy (XPS) and contact angle measurements are appropriate to determine the nature of the failure surfaces scanning electron microscopy (SEM) may also be helpful if the failed surface can be identified. 

The effect of the HRH system on adhesion is further illustrated by the micrographs (Figures 7-11) of the same rayon-natural rubber composite with and without HRH. Figures 7-9 show a thin section of the composite without HRH stretched to various elongations with the force applied parallel to the direction of orientation. Many voids form as the strain is increased owing to fiber-matrix bond failures. Both the number and size of voids increase with increasing strain. 

With time (under increased temperature and humidity) the crack tip continues to a weaker region which for this surface treatment appears to be near the oxide/alloy interface. Figure 11 summarizes the analysis of the bond failure for this particular surface treatment. The important aspect here is that under identical conditions, different surface preparations show different modes of failure. Weak boundary layers are not developed using some treatment/bonding combinations. Processes have been developed in which the locus of failure remains in the adhesive ("a cohesive failure") and it is necessary to use a mechanical test in which even more stress is placed on the interfacial region (19). 

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