Sensing sheet: the sensitivity of thin-film full-bridge strain sensors for crack detection and characterization

Increasing concerns regarding the conditions of civil structures and infrastructure give rise to the need for efficient strategies to identify and repair structural anomalies. 'Sensing sheets' based on large-area electronics consist of a dense array of unit strain sensors. These are an effective and affordable structural health monitoring tool that can identify and continuously monitor the growth of cracks in structures. This paper presents a study on the quantitative relationship between crack width and strain, the latter measured by an individual sensor that would be part of a sensing sheet. We investigate the sensitivity of thin-film full-bridge strain sensors to concrete cracks by conducting laboratory experiments in temperature-controlled settings. The results show a distribution of near-linear relationships with an average sensitivity of 31 µε µm⁻¹. Experiments were also conducted to investigate the effect of crack position and orientation with respect to the sensor, and it appears that both variables affect the sensitivity of strain sensors to cracks. Overall, this study confirms that full-bridge resistive strain sensors can successfully detect and quantify cracks in structural materials and are therefore appropriate as part of a dense array of sensors on a sensing sheet. (paper)