Self-loading loop tack test for measuring the critical energy release rate of weakly adhesive films

• A self-loading loop tack test is proposed to measure critical energy release rates. • Fracture energies are obtained using a loop geometry based on elastica theory. • The method requires no external loading device or specialized testing apparatus. • Experiments confirm critical energy release rates independent of loop length. • Consistent critical energy release rates are obtained for both gravity directions. Quantitatively determining the critical energy release rate for weakly adhesive films, typically on the order of 1 J/m 2 or lower, is challenging as debonding may occur with little substrate deformation and crack growth can be difficult to track. We propose a simple equipment-free method for determining the critical energy release rate of weakly adhesive films. An adhesive-coated polymer film is formed in a closed loop and placed on a flat substrate. The adhered loop deforms into a flattened circular shape, and the equilibrium bonded length is governed by the balance between the self-loading of the film and the adhesive force. By measuring this bonded length, the critical energy release rate of the film–substrate interface can be quantitatively obtained. The film deformation is modeled using the elastica theory, and the strain and potential energies stored in the system are calculated from the obtained deformation curve. The change in these energies with respect to the bonded length provides the critical energy release rate. Experiments were conducted using adhesive films with different total lengths and opposite gravitational orientations, demonstrating a constant energy release rate as long as the film and substrate materials were identical. These results confirm that the proposed self-loading loop tack test provides a material-intrinsic measurement of the critical energy release rate. Because the method requires no external loading device and only simple specimen preparation, it enables reproducible evaluation of weakly adhesive systems for which conventional fracture or peel tests are often impractical.