STP101

    The Measurement of Dynamic Modulus in Adhesive Joints at Ultrasonic Frequencies

    Published: Jan 1951


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    Abstract

    A method has been developed to measure, nondestructively, the dynamic modulus of an adhesive in the bond. The dynamic modulus, E, is defined as the stress-to-strain ratio for sinusoidal displacements, and can be expressed as E=E1iE2, where E1 is the ordinary Young's modulus and E2 is the viscous modulus representing dynamic losses in the material. Nolle and Westervelt have derived formulas for E1 and E2 of a thin adhesive layer joining two cylindrical bars end-to-end. The relations require a knowledge of the resonance properties of the cemented bar and a continuous bar of the same length and material. The equipment for obtaining the necessary resonance properties, the resonant frequency and half-power bandwidth, consists of three major parts: a driving system to set up longitudinal ultrasonic vibrations in the specimens, a detecting system to indicate the amplitude of vibrations, and a frequency measuring system. Measurements have been made on stainless steel bar specimens, cemented with a phenol-formaldehyde polyvinyl-butyral adhesive, which have been subjected to various heat treatments. The results of this study indicate that the measured dynamic modulus is useful for selecting from a group of treated specimens those which have deteriorated and have low tensile strength. The method described is applicable to cemented-bar specimens composed of other types of bars and adhesives, provided that certain conditions pertaining to the derivation of the formulas for the moduli are met. There is a possibility that similar principles can be used to measure the dynamic modulus of reed type specimens composed of sections of lap joint or laminate.


    Author Information:

    Dietz, A. G. H.
    Professor of Structural Engineering, Massachusetts Institute of Technology, Cambridge, Mass.

    Closmann, P. J.
    Staff, Division of Industrial Cooperation, Massachusetts Institute of Technology, Cambridge, Mass.

    Kavanagh, G. M.
    Staff, Division of Industrial Cooperation, Massachusetts Institute of Technology, Cambridge, Mass.

    Rossen, J. N.
    Staff, Division of Industrial Cooperation, Massachusetts Institute of Technology, Cambridge, Mass.


    Paper ID: STP46815S

    Committee/Subcommittee: E07.06

    DOI: 10.1520/STP46815S


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