Adhesive failure energy

An investigation of the mechanism of adhesive failure of polydimethylsiloxane elastomers was conducted [75]. The study showed that the total adhesive failure energy could be decomposed into energies for breaking chemical bonds, breaking physical bonds and deforming the bulk viscoelastic elastomer. 

Generalized fracturie mechanics (GFM) addresses this problem by expressing the adhesive failure parameters in terms of the interfacial energy and the mechanical hysteresis properties of the bulk phases. This then permits the surface and bulk contributions to adhesive failure energy to be separated, allowing a more profound analysis of the fracture process and the way it is controlled by rate, temperature, and other environmental factors. This will be illustrated by a study of the effects of moisture exposure on adhesive joints. 

FIGURE 2. The sardine tin experiment (a) lid peeled off at 90° (b) lid removed as a coil by turning the key. The recorded adhesive failure energy will be different in the two cases. 

FIGURE 6. Center-crack test specimen for adhesive failure energy. 

None of these conclusions could be drawn without first separating the inteifacial term Oq from the overall adhesive failure energy 0. 

FIGURE 9. Adhesive failure energy vs. rate curves for an epoxy resin from a titanium substrate after aqueous immersion at 80 °C for 120 h at different pH values. 

The adhesive failure energy (peeling energy) is given by... 

The transition between cohesive and adhesive failure in a simple bi-material joint has been studied by Kendall (1975). Based on Griffith s energy approach, a criterion is derived for deflection along the interface for a short crack for an isotropic material... 

The interfacial fracture energy associated with adhesion failure can then be calculated taking into account the elastic properties of the film and the defined critical strains. 

Even if the Al Oj interlayer accelerates the activation of the transverse cracking, it seems to have the opposite effect on adhesion failure. Indeed, we observe for both systems with an Al Oj interlayer (B and E) that the debonding and buckling are delayed. Therefore, the adhesion of the films is improved. The presence of this thermally grown Al Oj interlayer increases the interfacial fracture energy values to about 15 J.m in both systems. Two qualitative explanations can be proposed for the adhesion improvement. First, the Al Oj certainly permits an increase in the number of 0-Si bonds between the interlayer and the film. Second, prior to the... 

The thickness of the TDCB specimens (S = 10 mm) is sufficient to ensure plain strain conditions. It should be noted that during the test the arms remain within their elastic limit. Therefore, from simple beam theory [7], and by the use of linear elastic fracture mechanics, the strain energy release rate of the adhesive can be obtained using Eqn. 2, where P is the load at failure and E, is the substrate modulus. The calculated adhesive fracture energy was employed in the simulation of the TDCB and impact wedge-peel (IWP) tests. 

Figure 16,13. (a) Fracture energy results at different crack speeds for cohesive and adhesive failure 30min interface crosslinking, (b) Crack behavior at the interface for different adhesive fracture energies. 

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