Journal of Sound and < ibration (2001) 241(2), 235}245 doi:10.1006/jsvi.2000.3299, available online at http://www.idealibrary.com on DAMPING FACTOR AS AN INDICATOR OF CRACK SEVERITY S. D. PANTELIOU, T. G. CHONDROS AND V. C. ARGYRAKIS Machine Design ¸aboratory, Department of Mechanical Engineering and Aeronautics, ;niversity of Patras, Patras 265 00, Greece. E-mail: panteliu@mech.upatras.gr AND A. D. DIMAROGONAS =. Palm Professor of Mechanical Design, = ashington ;niversity, St. ¸ouis, MO 63130, ;.S.A. (Received 28 September 1999, and in ,nal form 26 July 2000) When a material is subjected to an alternating stress "eld there are temperature #uctuations throughout its volume due to thermoelastic e!ect. The resulting irreversible heat conduction leads to entropy production, which in turn is the cause for thermodynamic damping. An analytical investigation of the entropy produced during a vibration cycle due to the reciprocity of temperature rise and strain yielded the change of the material damping factor as a function of shape and magnitude of existing crack in the structure. A homogeneous, isotropic, elastic bar of orthogonal shape is considered with a single-edge crack under alternating uniform axial stress. The analytical determination of the dynamic characteristics of the cracked structure yielded the damping factor of the bar, the material damping factor and a good correlation of depth of crack with the damping factor. Experimental results on cracked bars are in good correlation with the analysis.  2001 Academic Press 1. INTRODUCTION It is well known that the existence of a crack in a structure is related to the decrease in its strength. The evaluation of the e!ect of cracks on the strength of the material, especially in relation with fatigue and brittle fracture is a very important consideration in engineering design. Numerous researchers have investigated crack identi"cation extensively. A thorough state of the art review can be found in reference [1]. Barenblatt et al. [2], while dealing with the in#uence of the vibrational heating on the fracture propagation in polymeric materials, considered that the failure process for rigid cracked materials is localized at the crack tips, where stress concentration takes place. Therefore, the intensity of heat generation, which is proportional to the square of the stress amplitude is low, far from the crack tips, but might be considerable and involve a substantial temperature rise near the crack tips. Thus, due to the vibrational stress, a non-uniform temperature distribution in the sample arises, activating the failure process (rupture of bonds) just in the places where it is localized. In the remaining part of the sample the temperature rise is usually negligible. These considerations gave a complete quantitative theory for the local heating e!ect on the rate of the crack propagation. Speci"cally, they gave analytical expressions for the stress and temperature "elds in the cracked structure. 0022-460X/01/120235#11 $35.00/0  2001 Academic Press