Issue 27

M.-P. Luong et alii, Frattura ed Integrità Strutturale, 27 (2014) 38-42; DOI: 10.3221/IGF-ESIS.27.05 41 (4a) Quasi homogeneous diorite D. (4b) Heterogeneous granite G. Figure 4 : Different stages of heat dissipation describing the process of the damage extent in the granite specimen (characterized by its compressive strength Rc). Graphical determination of the threshold of acceptable damage TAD of tested materials subject to unconfined loading up to failure. When the compressive loading (maximal cyclic loading at 50Hz and 0.10Rc of amplitude) is applied on the specimen up to failure, the results suggest a threshold of acceptable damage TAD, separating low and high regimes of dissipation or damage. This threshold TAD is readily determined graphically on Figs. (4a) and (4b) for diorite D and granite G owing to the change of slope of the experimental curve. Its value is consistent with characteristic data obtained from other testing techniques based on strain gages, acoustic emission AE or wave propagation phenomena (Fig. 5) despite of their quite different nature. (5a) Strain based technique (5b) AE based technique (5c) Non-linearity based technique Figure 5 : Experimental results obtained when using other testing techniques on granite specimen. C ONCLUDING REMARKS his work has demonstrated that (1) the evolution of heat change facilitates the detection of damage extent in geomaterials (even for very brittle rocks) subjected to loading up to failure, and (2) the dissipative behavior of geomaterials under solicitations is a highly sensitive and accurate manifestation of damage. Thanks to the thermomechanical coupling, the proposed differential infrared thermography offers a non-destructive, non- contact and real-time testing technique to observe quantitatively the dissipative mechanism of damage in geomaterials. It thus readily provides a measure of the material damage and allows the definition of a threshold of acceptable damage TAD under load beyond which the material is susceptible to failure.