Issue 27

P. Hou et alii, Frattura ed Integrità Strutturale, 27 (2014) 21-27; DOI: 10.3221/IGF-ESIS.27.03 21 Focussed on: Infrared Thermographic Analysis of Materials The application of the infrared thermography on titanium alloy for studying fatigue behavior P. Hou, J. Fan, Q. Guo, X. Guo State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China xlguo@dlut.edu.cn , fanjunling@mail.dlut.edu.cn A BSTRACT . The infrared thermography is an attractive tool for studying the fatigue behavior of materials. Based on two theoretical models of fatigue damage indicators, this work studied the fatigue properties of the virgin Ti- 6Al-4V alloy. According to the two damage indicators and the energy theory, the relationship between the macro-phenomenon and the micro-structural evolution during fatigue process was discussed. The fatigue limit of the titanium alloy was rapidly determined based on the measured temperature increment signals. The capability of the infrared thermographic method on the evaluation of fatigue properties was validated. K EYWORDS . Thermography; Fatigue indicator; Ti-6Al-4V alloy; Fatigue limit. I NTRODUCTION n practical applications, fatigue failure occurs everywhere including automobiles, airplanes, and vessels, etc. This often leads to disastrous damage to human beings. As a consequence, fatigue properties of materials should be well known before mechanical designs. However, it is difficult to obtain the fatigue properties of materials due to the time-consuming and expensive costing of the traditional fatigue tests. During the fatigue evolution process, most of the plastic work dissipates into the surroundings as heat energy, and simultaneously generates a heterogeneous temperature field on the surface of materials and components. The measurement of the thermal signals makes it possible to visibly detect the appearance of fatigue damage and to predict the fatigue parameters of materials. There are many measuring methods used to monitor the temperature field evolution [1]. However, the infrared thermography is more promising due to the high accuracy and rapid response of the infrared camera [2, 3]. Over the last 30 years, the infrared thermography, as a non-destructive, full-field and non-contact measuring method, has been widely and successfully used to study the fatigue behavior of materials and components [4-7]. The infrared thermographic method was first proposed by G. Curti et al. [5] by using the surface temperature increment signals as the major fatigue indicator. And also some efficient methods based on the infrared thermographic analysis have been developed to correlate the temperature signal evolution with the corresponding fatigue parameter. Luong et al. [4] proposed to use the dissipated thermal energy under a given number of cycles to get the fatigue limit. La Rosa et al. [8] analyzed the temperature signals of the external surface during the application of cyclic loading to evaluate the dynamic behavior of an element and to determine the fatigue limit. Kim and Jeong [9] found a linear correlation between the temperature increment squared and the logarithm of the fatigue life. Similarly, a modified thermographic method using the iterative algorithm was presented and confirmed by Curà et al. [10], and the method could give more accurate prediction of the fatigue limit. Meneghetti [11] defined a theoretical model in order to derive the specific heat loss per cycle from the temperature measurements during fatigue tests, and the fatigue strength of smooth and notched specimens was analyzed by this model. I

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