Failure interfacial

Detachment of a particle from a substrate when plastic deformations have occurred is somewhat a more complicated problem than in the case of simple elasticity. Essentially, one has to first determine if the detachment occurs because of a cohesive or interfacial failure and whether the failure is ductile or brittle. For... 

Visually, the failed specimens appeared as shown in Fig. 34. Failure was mostly cohesive within the adhesive. However, there was a small region of apparent interfacial failure at one end of each substrate that was referred to as the metal... 

Visually, failure was mostly eohesive within the adhesive (see Figs. 34 and 46). However, there was a small area of apparent interfacial failure ( initiation zone ) located at one end of each substrate. Line scans were eondueted aeross the initiation zone, from the edge of the substrate to the area of cohesive failure within the adhesive. From the line scans, it was apparent that there were patehes of polymer present in the initiation zone, even when failure appeared to be interfaeial (see Fig. 46). SIMS images of the initiation zone were constructed for various mass numbers (see Figs. 47-49). The images showed well-defined cation-rieh... 

The analysis depends on whether the interfacial failure occurs by yielding or by crack propagation. The simplest analysis is based on interfacial yielding where the shear stress is assumed to be distributed uniformly over the interface from top to bottom. According to this analysis, the interfacial shear stress increases uniformly until every location in the interface gives way simultaneously. 

Identification of Locus of Adhesion Failure. To clarify whether the disruption is cohesive failure of the lacquer or interfacial failure between the substrate and lacquer, the lacquer and metal sides of the fracture surface were both measured by XPS. The results are shown in Fig. 4. For the purpose of comparison, UVC lacquer coated and DOS oiled nickel-plated sheets are shown in the top and bottom of the diagram, respectively. The contribution at ca. 286.5 eV of the lacquer surface is attributed to carbon singly bonded to oxygen... 

CRS which had been phosphated prior to bonding exhibited a significant enhancement of durability and corrosion resistance under the same accelerated conditions (Figure 4). The crystalline barrier layer restricted the exposure of the metal oxide to moisture by reducing the rate of water penetration at the interface. Even samples exposed to the cycle test were able to maintain failure within the adhesive for up to 10 days, after which varying amounts of interfacial failure were noted. Again, room temperature control samples maintained initial joint strength and failure remained cohesive within the adhesive. 

Sastry, A.M., Phoenix S.L. and Schwartz, P. (1993). Analysis of interfacial failure in a composite microbundle pull-out experiment. Composites Sci. Technol. 48, 237-251. 

Schrader, M.E. (1970). Radioisotopic studies of bonding at the interface. J. Adhesion 2, 202-212. Schrader, M.E, and Block, A. (1971). Tracer study of kinetics and mechanism of hydrolytically induced interfacial failure. J. Polym. Sci.. Part C, Polym. Symposia. 34, 281-291. 

Kendall K. (1975). Transition between cohesive and interfacial failure in a laminate. Proc. Roy. Soc. Lond. A 344, 287-302. 

Newaz, G.M, (1985). On interfacial failure in notched unidirectional glass/epoxy composites. J. Composite Mater. 19, 276-286. 

Fracto-emission (FE) is the emission of particles (electrons, positive ions, and neutral species) and photons, when a material is stressed to failure. In this paper, we examine various FE signals accompanying the deformation and fracture of fiber-reinforced and alumina-filled epoxy, and relate them to the locus and mode of fracture. The intensities are orders of magnitude greater than those observed from the fracture of neat fibers and resins. This difference is attributed to the intense charge separation that accompanies the separation of dissimilar materials (interfacial failure) when a composite fractures. 

Acoustic emission (AE) is a technique that has been successfully employed to study fracture events in composites, where potentially, each failure mechanism has a unique acoustic signature (17-191. FE is another technique, which can be used in parallel with AE, and offers better sensitivity to the various microfracture processes. We have shown that interfacial failure between fiber and matrix in a composite produces significantly more intense emission and longer lasting decay... 

The above observations may be interpreted as follows. Prior to rupture in the glass/epoxy system, the stressed specimen suffers minor failures (primarily fiber breakage and epoxy cracking) which produce EE similar to that of the pure components. These failures accumulate, leading to strand rupture and a large amount of interfacial failure between filaments and epoxy. It is this latter form of... 

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. 

Crosby AJ, Karim A, Amis EJ (2003) Combinatorial investigations of interfacial failure. 

The two predominant mechanisms of failure in adhesively bonded joints are adhesive failure or cohesive failure. Adhesive failure is the interfacial failure between the adhesive and one of the adherends. It indicates a weak boundary layer, often caused by improper surface preparation or adhesive choice. Cohesive failure is the internal failure of either the adhesive or, rarely, one of the adherends. 

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. 

When using peel tests on such products as belts to separate the plies, it can be difficult to obtain interfacial failure. Loha et al47 successfully used test pieces including a perforated metal sheet at the interface to measure rubber to rubber adhesion strength. 

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. 

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