Chapter 22 Measurement of Stress Network in Granular Materials from Infrared Measurement Pawarut Jongchansitto, Xavier Balandraud, Michel Gre´diac, and Ittichai Preechawuttipong Abstract Infrared thermography (IR) was used in this work that aims to experimentally evidence the stress network in granular media composed of two materials featuring different stiffness, without cohesion and under confined compression. Cylinders of polyoxymethylene (POM) and high-density polyethylene (HDPE) were used to build 2D composite granular systems. Cylinders were placed parallely and mixed together in a square metallic frame. The experiments were performed using a uniaxial testing machine. The granular media were first compacted in order to reach static equilibrium configurations. A cyclic compressive load was then applied. IR camera was employed to measure the temperature changes due to thermoelastic coupling on the cylinder network cross-sections. Temperature variations were then processed to obtain the maps of the amplitude of the sum of the principal stresses during the cycles. Three configurations were tested by changing the ratio between the POM and HDPE diameters and the ratio between the numbers of POM and HDPE cylinders. The experimental technique enables us to identify the stress network within the granular media. The experimental results are compared with numerical results obtained with a molecular dynamics software. Keywords Granular material • Infrared thermography • Thermoelastic stress analysis • Stress network • Confined compression 22.1 Introduction Granular materials are composed of particles whose macroscopic mechanical behavior is governed by their interactions. To understand the behavior of such materials at the continuum (macroscopic) scale, an analysis of the force networks must be performed at the grain (microscopic) scale. Photoelasticimetry was first used in 1957 for particles. They had the property to develop birefringence under stress [1]. It was then used in some other studies [2, 3]. Digital image correlation from twodimensional optical measurements was also employed [4, 5], while X-ray technique was used for three-dimensional measurements [6, 7]. Strain components were also measured using particle image velocimetry [8]. To the best knowledge of the authors, it seems that infrared (IR) thermography was used for granular materials only to analyze heat transfer [9]. IR thermography is a full-field measurement technique which can be used for measuring the temperature changes occurring on the surface of specimens subjected to a mechanical load. These temperature changes result from P. Jongchansitto Department of Mechanical Engineering, Faculty of Engineering, Chiang Mai University, 239 Huay Kaew Road, Muang District, Chiang Mai 50200, Thailand Clermont Universite´, Universite´ Blaise Pascal, Institut Franc¸ais de Me´canique Avance´e, Institut Pascal UMR 6602, BP 10448, 63000 Clermont-Ferrand, France X. Balandraud (*) • M. Gre´diac Clermont Universite´, Universite´ Blaise Pascal, Institut Franc¸ais de Me´canique Avance´e, Institut Pascal UMR 6602, BP 10448, 63000 Clermont-Ferrand, France e-mail: xavier.balandraud@ifma.fr I. Preechawuttipong Department of Mechanical Engineering, Faculty of Engineering, Chiang Mai University, 239 Huay Kaew Road, Muang District, Chiang Mai 50200, Thailand N. Sottos et al. (eds.), Experimental and Applied Mechanics, Volume 6: Proceedings of the 2014 Annual Conference on Experimental and Applied Mechanics, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-06989-0_22, #The Society for Experimental Mechanics, Inc. 2015 163
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