Stress sensor particularly suitable for elastic, plastic and visco- elastic materials

摘要

A cylindrical stress sensor has a case that is long relative to its diameter. The case may be completely imbedded in the body of a host material in which a change of stress is of interest. That portion of the sensor which is imbedded has a rounded end. The rounded end, circular cross section, and relatively large length-to-diameter ratio avoid errors occasioned by stress concentration. A strain transducer of a vibrating wire excited by a magnetic coil is located remote from any imbedded end of the sensor. Changes in strain on the wire alter the frequency of the wire. This change in frequency is picked up by the excitation coil as a signal. A stacked, three-transducer array, with the wire of each transducer at 45° from a neighboring transducer, can detect changes in the magnitudes and directions of the principal stresses, without first establishing the direction of the primary or secondary principal stress. The effective Young's modulus of the sensor is large relative to the host material, being at least equal to, or greater than, four times the latter's modulus. The distance from a transducer to an end of the sensor to be imbedded in the host is sufficient to avoid erroneous signals occasioned by end effects of the case, and is usually at least ten radii.