Resonant sensing devices and methods for determining surface properties of test pieces

摘要

Surface properties, such as, hardness, of a test piece are determined by holding a mechanical resonator, for example, in the form of a sensor rod against a surface of the test piece with a static force sufficient to maintain steady contact with the test piece surface at a contact surface on the sensor rod shaped to provide an increasing area of contact with increasing plastic and/or elastic indentation or deformation of the test piece surface, exciting the test piece into vibration with a frequency which is varied so that the vibrations transmitted from the test piece to the sensor rod will cause the latter to attain a state of resonance, for example, as indicated when a maximum amplitude of the vibration of the sensor rod is sensed, measuring the amplitude of vibration of the excited test piece at a region of the latter which is adjacent to, but outside of the area of contact of the test piece with the contact surface on the sensor rod, for example, by means of an auxiliary sensor, and further varying the frequency of the vibratory excitation of the test piece in a range within which the sensor rod remains in the state of resonance to determine that frequency at which the measured amplitude of vibration of the test piece has a minimum value so that the difference between the frequency thus determined and the resonance frequency of the sensor rod when free of the test piece is an indication of the hardness or some other surface property of the test piece regardless of the mechanical reactance of the latter.