International Journal of Damage Mechanics-2011-Amiri-89-112.pdf

An Experimental Approach to Evaluate the Critical Damage M. AMIRI, M. NADERI AND M. M. KHONSARI* Department of Mechanical Engineering Louisiana State University, Baton Rogue, LA 70803, USA ABSTRACT: An experimental study has been carried out to determine the critical damage parameter based on the concept of entropy flow. The fatigue damage is either a cumulative process that progresses toward a maximum tolerable damage, or is an irreversible progression of cyclic plastic strain energy that reaches its critical value at the onset of fracture. In the present study, irreversible heat dissipation in terms of entropy is utilized to experimentally determine the degradation of different specimens subjected to low cyclic bending fatigue. An experimental correlation between entropy and damage is proposed. It is shown that the cyclic energy dissipa- tion in the form of thermodynamic entropy can be effectively utilized to determine the critical damage value. KEY WORDS: fatigue damage, thermography, entropy. INTRODUCTION ALL STRUCTURAL COMPONENTS when subjected to cyclic loading are proneto fatigue and failure will eventually occur if the number of cycles exceeds a certain level. Depending on the intended functions of the compo- nent and its usage in service, the failure impact can be catastrophic (Vasudevan et al., 2001). In materials undergoing cyclic loading, fatigue damage is a cumulative process that progresses toward a critical condition. This critical condition could be used as a warning of imminent fracture and a useful signal for the purpose of structural health monitoring. In the present work, the critical value of damage parameter is not necessarily associated *Author to whom correspondence should be addressed. E-mail: Khonsari@ Figures 2–4, 7 and 913 appear in color online: International Journal of DAMAGE MECHANICS, Vol. 20—January 2011 89 1056-7895/11/01 008924 $10.00/0 DOI: 10.1177/1056789509343082  The Author(s), 2011. Reprints and permissions: http://www.sag