Flexoelectric strain gradient sensing

Compared with strain, strain gradient can be a more sensitive measurand to interpret structures' integrity. Defects like fatigue cracks are commonly accompanied by a large strain gradient within a small area near the tip. Flexoelectricity-based strain gradient sensors allow the accurate measurement of the strain gradient in the structures, therefore providing a promising approaching for structural health monitoring. In this chapter the flexoelectric strain gradient sensors are introduced and used to measure the in-plane and out-of-plane strain gradient in the mechanical structures. Their application in measuring the stress intensity factor and monitoring the status of cracks is reported as well.