Damping factor as an indicator of crack severity

When a material is subjected to an alternating stress field there are temperature fluctuations throughout its volume due to thermoelastic effect. 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. (C) 2001 Academic Press.