Issue 27

M.-P. Luong et alii, Frattura ed Integrità Strutturale, 27 (2014) 38-42 ; DOI: 10.3221/IGF-ESIS.27.05 38 Focussed on: Infrared Thermographic Analysis of Materials Characterization of mechanical damage in granite Minh-Phong Luong, Mehrdad Emami LMS (Solids Mechanics Laboratory), Civil Engineering, Department of Mechanics Ecole Polytechnique – CNRS UMR7649, 91128 Palaiseau Cedex, France luong@lms.polytechnique.fr, luong_mp@yahoo.com A BSTRACT . This paper aims to illustrate the use of infrared thermography as a non-destructive and non-contact technique to observe the phenomenological manifestation of damage in granite under unconfined compression. It allows records and observations in real time of heat patterns produced by the dissipation of energy generated by plasticity. The experimental results show that this technique, which couples mechanical and thermal energy, can be used for illustrating the onset of damage mechanism by stress concentration in weakness zones. K EYWORDS . Differential thermography; Intrinsic dissipation; Mechanical damage in granite; Threshold of acceptable damage. I NTRODUCTION urrent technological developments tend towards increased exploitation of material strengths and towards tackling extreme loads and environmental actions. The tendency to extend the service life of materials and structures by increasing maintenance, rather than replacement, increases the need for monitoring structures and supports the need to perform global or local test loading. Diverse damage analysis methodologies for engineering materials have been developed in recent years which isolate the factors affecting crack initiation and growth, and enable the prediction of their cumulative effects on the fatigue performance of structural components [1]. In cases where continuum mechanics can be applied, the concept of an effective stress  ef =  /(1-  ) has been introduced with a continuous variable  related to the scalar density of defects or faults. This has been the starting point of damage theories developed for fatigue, creep, and creep-fatigue interaction in engineering materials. Brittle geomaterials are mainly characterized by their salient fracturing nature. A different approach has been proposed using the plasticity formalism with the concept of a fracturing stress (considered hereafter as a threshold of acceptable damage TAD) or a fracturing strain to describe the inelastic behavior of progressively fracturing solids [2]. Failure in brittle geomaterial may be viewed as a micro-structural process through the activation and growth of one pre-existing flaw or site of weakness, or through the coalescence of a system of interacting small flaws and growing micro-cracks [3]. The formation of micro-cracks are often associated with points of stress concentration that are located on flaws present in the material, or on existing cracks and notches. Several scientific studies have been carried out in recent years on the infrared radiation in the process of rock deformation leading to fracturing and failure [4-6]. Within the framework of a consistent theoretical approach, this paper emphasizes the application and use of infrared thermography to detect and evaluate quantitatively the extent of damage in brittle geomaterials owing to the non-linear coupled thermomechanical effects. C