Debonding specimens

XPS analysis of the debonded specimens showed that the unprimed and primed FPL control and mercaptosilane-treated specimens failed primarily within the oxide, which represented the weakest layer in the system. On the other hand, the NTMP-treated sample debonded between the oxide and the polyamide primer. 

Secondary Ion Mass Spectrometry used as a solo Instrument or in concert with other methods has proven to be an excellent technique for studying the surface chemistry of adhesive bonding materials. The application of SIMS is shown in re.lation to pretreatments of metals and alloys, chemistry and structure of adhesives, and locus of failure of debonded specimens. 

Sometimes the failure occurs by propagation of a crack that starts at the top and travels downward until the interface is completely debonded. In this case, the fracture mechanics analysis using the energy balance approach has been applied [92] in which P, relates to specimen dimensions, elastic constants of fiber and matrix, initial crack length, and interfacial work of fracture (W,). 

XPS analysis (Fig. 6), in conjunction with SEM examination of the failed debonded sides, identified the true modes of failure. The SAA control (hydrated oxide on both sides under SEM high A1 and 0 levels on both sides) failed within the oxide. Examination of the specimen treated with multilayer-forming 5000 ppm NTMP solution (distinct "metal" and "adhesive" sides under SEM high A1 and 0, low C levels on "metal" side high C, low A1 and 0 levels on "adhesive" side) indicated that the failure occurred between the metal and the adhesive (i.e., adhesive failure). 

Figure 6. XPS surface analysis results for debonded SAA 7075-T6 aluminum specimens.

The single fiber compression test has not been as popular as other microcomposite tests because of the problems associated with specimen preparation and visual detection of the onset of interfacial debonding. To be able to obtain accurate reproducible results, the fibers have to be accurately aligned. With time, this test method became obsolete, but it has provided a sound basis for further development of other testing techniques using similar single fiber microcomposite geometry. 

Whitney, J.M. and Knight, M. (1985). A modified free-edge delamination specimens. In Delamination and Debonding of Materials, ASTM STP 876 (W.S. Johnson, ed.), ASTM, Philadelphia, PA, pp. 298-314. 

Tf is the crack tip debond stress at the boundary between the bonded and debonded regions at z = f, as defined in Section 4.2.3. It should be noted, however, that the actual values of (Tf are different for different specimen geometry even for an identical debond length, t Therefore, the solutions of FAS, and the corresponding MAS, MSS and IFSS are obtained for the bonded region ( [Pg.129]

When these specimens are stressed in tension, the fibers fracture first. If the fiber-matrix bond is weak, the resulting stress is relieved by debonding on either side of the break. These debonded fibers slide back into their holes in the resin, against considerable friction, and the load is built up again in the fibers. 

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