Wedge failure surface with

Figure 9. Wedge failure surface with ISS/SIMS data taken in area C on adherend.

FIGURE 30. Wedge failure surface with SIMS/ISS data taken in area C on the adherend. Reprinted with permission from Reference 35. Copyright 1982 American Chemical Society. 

Eqs. 1-5 hold whether failure is interfacial or cohesive within the adhesive. Furthermore, Eq. 5 shows that the reversible work of adhesion directly controls the fracture energy of an adhesive joint, even if failure occurs far from the interface. This is demonstrated in Table 5, which shows the static toughness of a series of wedge test specimens with a range of adherend surface treatments. All of these samples failed cohesively within the resin, yet show a range of static toughness values of over 600%. 

The failure surfaces of the wedge samples were analyzed using X-ray photoelectron spectroscopy (XPS). Spectra were obtained using a PHI 5300 ESC A system with a magnesium X-ray anode at a power of 400 W. 

XPS analysis of failure surfaces of wedge samples primed at 34% RH and bonded with PES and placed in a 100°C water bath... 

The XPS analysis of the failure surfaces of the wedge samples primed at 51% RH and bonded with PES and immersed in DI water at 100°C are reported in Table 3. The concentration of sulfur in all of the primed samples bonded with PES was about 5% and suggests that failure occurred primarily within the adhesive. The atomic concentrations of aluminum, silicon, and titanium were below 0.5%, precluding assignment of failure within the alkoxide layer. The control sample failed at the interface between the steel and the adhesive. 

The failure surfaces produced following tests of lap shear or wedge samples of titanium alloy bonded with epoxy depended on the surface pretreatment (34). Simple add etching of the adherend produced primarily interfacial failure between the oxide and epoxy whereas chromic acid anodization of the adherend resulted in failure within the oxide layer as in the case discussed above. 

Figure 15. XPS carbon Is and oxygen Is photopeaks for pretreated aluminum alloy after acid etch and before bonding (FPL) two failure surfaces following bonding with polysulfone and testing in the wedge configuration (FPL MFS and FPL AFS) and, neat polysulfone (PSF) (38).

In jointed materials, including hard rock and layered or fissured soils, the shape of the failure surface can partly or fully be governed by discontinuities. In such cases an analysis with three-dimensional wedges should normally be made. 

Optimized grit blast/silane treatments can provide wedge test durability as good as PAA with failure entirely cohesive within the adhesive (Fig. 21) [89]. Maintaining the process parameters within acceptable tolerances is critical with the heat drying of the silane on the treated surface being the most sensitive process parameter. 

Sol-gel film.s deposited on a grit-blasted aluminum surface give performance close to PAA bonds (Fig. 22) with generally cohesive failures observed in wedge tests. Given that one application of this treatment is repair, the performance is... 

A number of ASTM tests and practices involve durability, but one of the most important is the Wedge Test, ASTM D3762-03. In this method, a wedge is forced into the bond line of a flat-bonded aluminum specimen, thereby creating a tensile stress in the region of the resultant crack tip. The stressed specimen is exposed to an aqueous environment at an elevated temperature, or to any other desired environment. The resultant crack growth with time and failure modes is then evaluated. The test is primarily qualitative, but it is discriminatory in determining variations in adherend surface preparation parameters and adhesive environmental durability. 

The above AES results can be correlated to bond performance. Hsu et found that the DQSK adherends, containing the higher concentration of silicon, showed interfacial failure, while only cohesive failure was observed for CRS adherends. The chromium-to-iron ratios, determined from the depth-profile study of pretreated steel surfaces,correlated with the wedge test performance as shown in Figure 24, with minimal crack extension in samples with high Cr/Fe ratios. 

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