Issue 21

A. Yu Fedorova et alii, Frattura ed Integrità Strutturale, 21 (2012) 46-53; DOI: 10.3221/IGF-ESIS.21.06 46 Infrared thermography study of the fatigue crack propagation A.Yu. Fedorova, M.V. Bannikov, O.A. Plekhov Institute of Continuous Media Mechanics UB RAS,614013, Ac. Koroleva Street, 1, Perm, Russia E.V. Plekhova Perm National Research Polytechnic University,614990, Komsomolsky av, 29, Perm, Russia A BSTRACT . The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone. K EYWORDS . Fatigue crack; Heat dissipation; Infrared thermography. I NTRODUCTION n recent decades, many authors have been actively investigated the processes of heat dissipation due to the material structure evolution under cyclic loading. The main application of infrared thermography for fatigue loading was focused on the development of techniques for rapid determination of fatigue limit of materials. This technique was reported starting from early work by A. Risitano [1], developed further by M.P. Luong [2] and many other authors. The review of this question can be read in [3]. But there are only a few works devoted to direct investigation of temperature evolution at fatigue crack tip. At present, it is well known that in materials under cyclic deformation, fatigue cracks are initiated in the area of plastic deformation localization and lead to an intensive heat dissipation [4]. It makes possible the early detection of crack initiation by infrared thermography [5]. The infrared thermography can be also applied during mechanical tests in order to obtain detailed information about the process of structure evolution, damage accumulation and damage-fracture transition in solids [6-8]. The investigation of the heat dissipation at the fatigue crack tip allows one to develop an effective method for determination of the linear fracture mechanics parameters in a wide range of stress intensity and, as a consequence, gives a way of monitoring of critical state of crack. The solution of this problem requests an analysis of solutions of nonlinear problems of plasticity theory and experimental investigation of plastic deformation localization at crack tip. This work is devoted to the development of experimental technique for measuring the temperature field at the crack tip with a high temperature and spatial resolution. The technique is coupled with mathematical algorithms for experimental data processing. The algorithms allow us to determine the stress intensity factor (SIF) and propose an idea for calculation of J-integral value as a value of energy dissipated at crack tip. The proposed algorithms are universal and can be used for many metals under cyclic loading with different stress amplitudes and frequencies. In this work we applied this technique for study of temperature evolution of the plate titanium specimens with pre-grown fatigue crack. We experimentally investigated the evolution of the temperature distribution and obtained the values of heat dissipation caused by plastic deformation at the fatigue crack. I