Quasi-residual strain and moduli measurements in materials using embedded acoustic waveguides

Ronald T. Harrold; Zal N. Sanjana; Basavaraju B. Raju

doi:10.1117/12.259199

15 November 1996 Quasi-residual strain and moduli measurements in materials using embedded acoustic waveguides

Ronald T. Harrold, Zal N. Sanjana, Basavaraju B. Raju

Proceedings Volume 2948, Nondestructive Evaluation for Process Control in Manufacturing; (1996) https://doi.org/10.1117/12.259199
Event: Nondestructive Evaluation Techniques for Aging Infrastructure and Manufacturing, 1996, Scottsdale, AZ, United States

Abstract

Following the processing and manufacture of resin and composite parts and during their lifetime, the distribution of internal residual strain and any variations in moduli are generally unknown. Real-time information on these parameters would be valuable for improving material performance and reliability. It is believed that measurements related to material residual stresses or strain and moduli can be obtained by measuring the longitudinal wave velocities within acoustic waveguides (AWG) embedded within a material. The concept is that the wave velocities within embedded AWG are related to the material bulk modulus, density and Poisson's Ratio which are all in some degree related to the material state of cure, and finally the internal residual stresses. Based on this concept it is shown that the AWG of different diameters embedded within the same resin part of uniform internal stress distribution, the AWG wave velocities should vary in relation to the square root of the AWG diameter. Experimental results using AWG of 5, 10, 16, 20, 40 and 62 mil diameter Nichrome embedded within Shell 815 clear resin with optically measured uniform strain, demonstrate a direct relationship between AWG velocities and the square root of the AWG diameter. Consequently, it is reasoned that for a part with several embedded AWG, each of the same diameter, then differences in the AWG velocities would yield information on differences in the residual strain and moduli within the part.

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Ronald T. Harrold, Zal N. Sanjana, and Basavaraju B. Raju "Quasi-residual strain and moduli measurements in materials using embedded acoustic waveguides", Proc. SPIE 2948, Nondestructive Evaluation for Process Control in Manufacturing, (15 November 1996); https://doi.org/10.1117/12.259199

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KEYWORDS

Acoustics

Waveguides

Composites

Interfaces

Velocity measurements

Wave propagation

Signal processing

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