A Feasible Experimental Method to Measure the Adhesive Strength of Brittle Adherends

Brittle materials, such as silicon, glass, and ceramics, are widely used in engineering via adhesive bonding. The assessment of adhesive strength of brittle materials to other adherends is essential for their applications. Compared with metals and composites, for which standard testing methods have been established, the experimental method for brittle adherends has been much less explored. During the adhesive strength test, the brittleness of these materials makes them prone to failure, rather than the interface. It remains a challenge to measure the adhesive strength of brittle adherends. Here we develop an experimental method to address this issue by using a strap joint specimen with a backing layer. We use a single crystal silicon wafer and two PCB (printed circuit board) strips as adherends to make a strap joint specimen. A steel backing layer is glued to the silicon wafer to prevent the failure of silicon. This method enables the measurement of adhesive strength up to 35 MPa. In contrast, that without backing layer can only measure the adhesive strength below 10 MPa. It is found that the backing layer can reduce the stress in the silicon remarkably, while it has much less effect on the stress in the adhesive layer. We confirm that the backing layer has a negligible effect on the measured adhesive strength but expands the working space greatly. Combining finite element analysis and experiments, we establish the phase diagram for the failure modes. This work provides guidance for the measurement of adhesive strength of brittle materials.