Quantitative characterization of thin-film cracking behavior enabled by one-step asymmetrical bending

Quantitative characterization of crack behavior in thin-film materials is a fundamental issue in solid mechanics and is of necessity for the development of high-performance flexible electronics. However, such analysis largely relies on the complicated in-situ microscopy technique and the operational skills of experienced researchers, thus leading to difficulties in its widespread applications. To address this challenge, we report herein a facile and efficient characterization method based on the asymmetrical bending strategy to achieve the quantitative analysis of the crack features in thin-film materials without any need for specialized testing instruments. The key to this method is to bend two unparallel edges of the trapezoid-shaped thin film/substrate to form an asymmetrical configuration, in which the local bending radius changes linearly along the bending axis. As such, a large number of bending radii can be achieved on one single sample in one experiment, which significantly simplifies the process of quantitatively relating crack features to mechanical deformation. As a proof-of-concept demonstration, we employ this method for the one-step in-situ investigation of the crack behavior of the Cu film on a polymeric substrate.