STRESS SENSOR PARTICULARLY SUITABLE FOR ELASTIC, PLASTIC AND VISCO-ELASTIC MATERIALS

摘要

13106-ERCA STRESS SENSOR PARTICULARLY SUITABLE FORELASTIC, PLASTIC AND VISCO-ELASTIC MATERIALSAbstract of the DisclosureA cylindrical stress sensor has a case that is longrelative to its diameter. The case may be completely imbeddedin the body of a host material in which a change of stress isof interest. That portion of the sensor which is imbeddedhas a rounded end. The rounded end, circular cross section,and relatively large length-to-diameter ratio avoid errorsoccasioned by stress concentration. A strain transducer of avibrating wire excited by a magnetic coil is located remotefrom any imbedded end of the sensor. Changes in strain onthe wire alter the frequency of the wire. This change infrequency is picked up by the excitation coil as a signal. Astacked, three-transducer array, with the wire of each transducerat 45° from a neighboring transducer, can detect changes in themagnitudes and directions of the principal stresses, withoutfirst establishing the direction of the primary or secondaryprincipal stress. The effective Young's modulus of the sensoris large relative to the host material, being at least equal to,or greater than, four times the latter's modulus. The distancefrom a transducer to an end of the sensor to be imbedded inthe host is sufficient to avoid erroneous signals occasionedby end effects of the case, and is usually at least ten radii.