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Proceedings Paper

A Spectral Analyzer for the Thermoelastic and Thermoplastic Response of Solids to Low Frequency Dynamic Loads
Author(s): M. G. Beghi; C. E. Bottani; G. Caglioti; A. Fazzi
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Paper Abstract

In this paper the experimental methodologies based on linear response theory are applied to the thermomechanical behavior of a solid body subjected to external load histories. This is possible due to the linearity of equations of thermoelasticity provided macroplastic flow is avoided. In particular the techniques of spectral analysis of noisy signals passing through linear systems are employed to obtain the Bode diagram of the stress-temperature transfer function of a thermoelastic solid. Both sinusoidal and white noise excitations are used and coherence function tests are included to assess the statistical goodness of the results. From these measurements the Gruneisen parameter of the solid can be estimated whithin the linear thermoelastic region. The experimental apparatus, based on a PDP 11/03 microcomputer system, designed and built to reach the above goals is described in some detail together with the specifically developed software. The problems connected with the calibration of thermal sensors are outlined. Preliminary experimental results are briefly presented. Although the above methodology does imply linearity, the apparatus has also been used to perform local temperature measurements on the surface of compact tension specimens in non linear elastic - plastic conditions, namely during sinusoidal low-frequency fatigue experiments. In the case of fatigue pre-cracked specimens the thermal resolution of the apparatus was high enough to detect non linear phenomena, like e.g. local plastic flow or crack closure, in the vicinity of the crack tip. The non linear part of the thermal response can be nicely pinpointed as harmonics generation in the power spectrum of the local temperature signal.

Paper Details

Date Published: 1 April 1987
PDF: 12 pages
Proc. SPIE 0731, Stress Analysis by Thermoelastic Techniques, (1 April 1987); doi: 10.1117/12.937887
Show Author Affiliations
M. G. Beghi, Istituto di Ingegneria Nucleare (Italy)
C. E. Bottani, Istituto di Ingegneria Nucleare (Italy)
G. Caglioti, Istituto di Ingegneria Nucleare (Italy)
A. Fazzi, Istituto di Ingegneria Nucleare (Italy)

Published in SPIE Proceedings Vol. 0731:
Stress Analysis by Thermoelastic Techniques
B. C. Gasper, Editor(s)

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