Debond energy measurements

Measurements of the sliding stress, t, and the debond energy, T, have been obtained by a variety of approaches (Table 1.1). The most direct involve displacement measurements. These are conducted in two ways (1) fiber push-through7push-in, by using a small-diameter indentor 33 38,39 and (2) tensile loading in the presence of matrix cracks,5,44,45 Indirect methods for obtaining r... 

For probe tack, the newly measured debonding energies constitute a new dimension for short duration performance. In addition to the peak force, tack energy should be considered in many high speed applications. Since the peak force and tack energy appeared to have originated from different parts of the viscoelastic spectra, it offered an opportunity to adjust the formulation for optimum performance. 

More direct measures of interface debonding energy are provided by the pull-out or push-out tests shown in Fig. 16.26. When a tensile force is applied to a fiber to extract it from its composite matrix, an interface crack eventually starts to run along the fiber. It is obvious from a simple fracture mechanics argument that the stress on the fiber to propagate the crack, assuming a very compliant matrix, must be given by an expression of the form... 

E should be in a window of 0.01-0.1 MPa. Above that level, proper bonding and fibril formation are reduced and below that level, viscoelastic dissipation during the debonding process will be too low. controls the maximum extension of the fibrils and therefore plays a major role in the measured debonding energy. A relatively small e iax is typically desirable for removable PSA, while a larger value is often characteristic of semi-permanent ones. A reasonable idea of the value of iix can, in principle, be obtained by a characterization of the adhesive in elongational deformation. 

Yet, for systems A and C, the measured fracture energies remain low compared with the critical fracture energy of the bulk aluminum 10 J Moreover, we do not observe islands of passivation material on the A1 fracture surface and, inversely, we do not observe A1 on debonded surfaces of the passivation films. This suggests that the loss of interfacial adhesion is close to a brittle fracture process despite the influence of plasticity of the A1 substrate and crack blunting at the interface. This sort of brittle mode of interfacial failure, including plastic flow in a ductile material (the substrate), has been observed or discussed for a sapphire/Au interface. ... 

For the measurement, a loading and unloading mechanism is applied to obtain the local energy dissipation and the actual debonded surface area for the blister propagation, llie procedure is shown schematically in Hg.3. With the introduction of an incompressible uniform hydrostatic pressure at a constant volumetric rate, the thin PI fiim lifts away firom the substrate and forms an initial blister as seen in Hg.3(a). The diameter of the initio blister remains unchanged until a critical pressure (p ) is reached. At this point the thin film blister becomes... 

Fig.5. Measured fracture energy for thin metal films debonded from (un)treated polyimide...

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