Abstract

A strain sensor and a method for producing a remanent electrostatic image of the strain gradient existing on the surface of an object are disclosed. The sensor includes a layer of poled, piezoelectric material that is employed as a medium on which the strain gradient image is electrostatically formed. The piezoelectric layer is coated on one side with an electrically conductive layer, and the sensor is adapted to be positioned with the conductive layer in surface-to-surface contact with the object. Thereupon, a stress is applied to the object to place it in a condition of strain whereby the object is dimensionally changed or deformed. Both layers of the sensor are highly compliant to permit the sensor to be bent from its normal configuration to conform to the surface stress of the object without significantly affecting the strain of the object. Next, the surfaces of the piezoelectric layer are neutralized and the stress on the sensor is then relaxed. As the object returns to its normal configuration, an electrostatic image representative of the strain gradient caused by the stress forms on the uncoated surface of the piezoelectric layer.