A Mechanical–Electrical Damage Model for Performance Analysis of Crack-based Strain Sensor

The crack-based strain sensor consisted of a metal film and a conductivity substrate, can achieve high-sensitivity and wide-range sensor performance. However, the morphology of micro-cracks in metal film is sensitive to structural and material parameters of the bilayer strain sensor, which makes the quantitative design of the sensors difficult. In this work, a mechanical–electrical damage model was proposed to develop the relationship between the degradation of electrical properties and mechanical damage of metal film, and a reversible electrical damage variable was introduced to characterize the influence of micro-cracks opening and closing behavior on the reversible variation of metal film electrical conductivity. Based on the model, the effect of film-substrate thickness ratio and conductivity ratio on the film-substrate structural strain sensor performance was investigated. The results showed that with the increase of the thickness ratio and conductivity ratio, the sensitivities of the sensors in both the high-sensitivity region and wide-range region are obviously increased. In addition, a grooved structure was introduced in the sensor substrate, and the simulation results indicated that a three-segment linear sensing curve can be obtained. In the grooved sensor, high sensitivity can be achieved in the region close to the strain limit, making the sensor suitable for accurately detecting bending movements of human joints.