Characterization of a soft elastomeric capacitive strain sensor for fatigue crack monitoring

摘要

Monitoring the initiation and propagation of fatigue cracks is one of the primary concerns of bridge engineers in charge of overseeing the condition of structural steel bridges. Given the scarcity of resources available for bridge maintenance, engineers are often forced to prioritize bridge rehabilitation projects, and in many instances have to rely on monitoring fatigue crack growth to make sure that there is no threat to structural integrity while bridges remain in service. Measuring the deformation in the area surrounding fatigue cracks has been shown to be an effective way of monitoring the rate of crack growth. Traditional strain sensors such as metal foil gauges have a limited ability to capture crack initiation and growth due to their small size, limited measurement range, and high failure rate under harsh environmental conditions. Recently, a newly developed soft elastomeric capacitive sensor has shown great promise to overcome these limitations and tests have demonstrated its capability to detect fatigue cracks. In this paper, the crack detection capability of the capacitive sensor is validated through Finite Element (FE) analysis. A nonlinear FE model of a standard ASTM compact tension specimen was created and calibrated using experimental data to simulate its response under fatigue loading, with the objectives of: 1) depicting the strain distribution of the specimen due to cracking under the large area covered by the capacitive sensor; 2) characterize the relationship between capacitance change measured by the SEC sensor and crack width. This relationship facilitates quantitative evaluation of crack development using the newly developed SEC sensor.