Exploiting perforations to enhance the adhesion of 3D-printed lap shears

Soft polymeric adhesives capable of experiencing large deformations are used in many applications, including soft robotics, stretchable electronics, and tissue engineering. The growing use of these materials raises many questions regarding their ability to maintain adhesion under loads. This work aims to study the adhesion of soft adhesives to perforated substrates. To this end, we design lap shear-based specimens from the acrylic adhesive VHB 4910 and stiff 3D-printed perforated substrates. Substrates with four different void sizes are investigated and the lap shears are subjected to displacement-controlled and force-controlled loadings. Our experiments show that the shear response can be divided into two main regions. First, the adhesion area between the soft adhesive and the substrate is maintained such that the adhesive experiences shear. Next, a debonding process of the adhesive from the substrate begins and ends with the ultimate rupture of the elastomer. Comparison between displacement and force controlled loadings reveals that the latter is characterized by limited extensibility, since the soft adhesive cannot relax. As opposed to the standard lap shears, the perforations yield a highly heterogeneous stress state that enables one to increase adhesion strength and enhance the performance of lap shears in a variety of applications.