High performance very low frequency forced pendulum

doi:10.1016/j.msea.2003.07.023

Materials Science and Engineering: A

Volume 370, Issues 1–2, 15 April 2004, Pages 435-439

https://doi.org/10.1016/j.msea.2003.07.023 Get rights and content

Abstract

A forced torsion pendulum has been constructed for the measurement of mechanical loss angle (tan δ) and elastic shear modulus in three different modes: (a) as a function of temperature (80–1250 K), at imposed frequency, during heating or cooling at imposed heating or cooling rate (0.1–5 K/min); (b) as a function of frequency (10–10⁻⁴ Hz) in isothermal conditions, and (c) as a function of amplitude (5×10⁻⁶ to 5×10⁻⁵) at imposed frequency and under isothermal conditions. The mechanical part of the pendulum has been designed in such a way that torsional plastic deformation of the specimen can be performed in situ, i.e., at low temperatures to generate fresh dislocations in metals, and at high temperatures to enhance grain boundary sliding, for instance. The whole installation is computer controlled and exhibits not only outstanding performances but also a very high capability of working in different conditions, being a useful tool for studying a large variety of mechanisms in different materials.

Introduction

As a powerful tool for the study of materials, Internal Friction techniques have been developed continuously since the first works in the forties [1]. Good overviews of the experimental techniques for the measurements of the internal friction were done in the seventies by De Batist [2] and Nowick and Berry [3] in their books. However while in the first book [2] no reference was done to the sub-resonant techniques, in the second one [3] only a short comment was dedicated to the sub-resonant techniques. At this time the measurement of tan φ was difficult for low internal friction values and consequently these techniques were mainly used for working in materials with high damping ( $tan φ>0.1$ ) as in the case of polymers [3]. Indeed sub-resonant techniques were at this time widely used for the study of polymers because of its large specific damping coefficient (see for example the books [4], [5]), and have been the main techniques used by commercial equipments like dynamic mechanical analysis (DMA). Nevertheless, sub-resonant techniques remained for long time unuseful for the study of metals and ceramics because of its low sensitivity in the internal friction measurement. Recent overviews of the development of the techniques for internal friction measurement can be found in the book of Lakes [6] and in the book of the School on Mechanical Spectroscopy Q⁻¹ [7].

However, owing to the advantages exhibited by the sub-resonant techniques [6], [8], [9] an important effort was done for developing high sensitivity sub-resonant torsion pendulums. Indeed, since the pioneering work of Woirgard [10], [11], who built the first forced pendulum allowing the measurement of tan φ with a resolution of 10⁻⁴, several laboratories developed sub-resonant forced pendulums. In particular, the group of EPFL in Lausanne (Switzerland) has developed a new conception of the suspension system that allows to obtain a high resolution while working as a function of frequency as well as a function of temperature [12], [13]. Since these developments, other prototypes were built at the laboratory of the EPFL in Lausanne in order to overcome the challenge of building a sub-resonant torsion pendulum with high resolution in both working modes and with a high extended working range in both modes. A last-generation prototype developed in the frame of a collaboration between our laboratories is the subject of the present work.

So in this work a sub-resonant torsion pendulum is presented. This type of apparatus works at forced oscillations, that is with an imposed oscillation frequency, in a large frequency range below its resonant frequency (between 10⁻⁴ and 10 Hz) as well as in a broad range of temperatures (between 80 and 1250 K). Consequently this equipment allows to obtain spectra as a function of frequency ω and as a function of temperature T.

Section snippets

Outline of the pendulum

A view of the equipment is shown in Fig. 1. The pendulum is made up of the following different systems: anti-vibratory system, mechanical system, cryogenic and temperature control system, vacuum system, electronic system and automation system. A brief depiction of every system is given focusing on the most significant parts:

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The anti-vibratory system. It isolates the pendulum from vibrations and also provides stability to the equipment. It is made up of a concrete flagstone, specially designed,

Resolution tests and experimental results

In order to test the behavior and resolution of the equipment under different conditions, several samples were used to measure the internal friction as a function of temperature and frequency. The resolution of the internal friction measurements is strongly dependent on experimental conditions (frequency, amplitude, etc.) as well as on the nature of the sample. Consequently, it cannot be considered as a specific performance of the equipment. However, there are some experimental conditions which

Acknowledgements

This work has been carried out with the financial support of the Spanish “Comisión Interministerial de Ciencia y Tecnologı́a” (CICYT) in the framework of the “Plan Nacional de Materiales” (Project number MAT 97-1059-C02-02) and by the Universidad del Pais Vasco (Project number UPV-13646/2001). One of the authors (I. Gutiérrez-Urrutia) wishes to acknowledge the Spanish “Ministerio de Educación y Ciencia” for providing him a postgraduate grant.

References (13)

C. Zener, Elasticity and Anelasticity of Metals, University of Chicago Press, Chicago,...
R. De Batist, Internal Friction of Structural Defects in Crystalline Solids, North-Holland, Amsterdam,...
A.S. Nowick, B.S. Berry, Anelastic Relaxation in Crystalline Solids, Academic Press, New York,...
J.D. Ferry. Viscoelastic Properties of Polymers, Wiley, New York,...
J.D. Aklonis, W.J. MackNight, Introduction to Polymer Viscoelasticity, Wiley, New York,...
R.S. Lakes, Viscoelastic Solids, CRC Press, Boca Raton, USA,...

There are more references available in the full text version of this article.

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¹: Present address: Haute Ecole Valaisanne HEVs, Route du Rawyl 47, CH-1950 Sion, Switzerland.

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