13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Fatigue damage indicators based on the infrared thermographic method Pei.J.Hou 1, Xing.L. Guo 2,*, Fang.Han3, Jun.L.Fan 4 1,2,3,4State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116023, China * Corresponding author: xlguo@dlut.edu.cn Abstract It is a new and valuable research that studying the influence of heat treatments on fatigue performance of materials by the infrared thermographgic method. Based on three theoretical models of fatigue indicators, this paper studied mechanical properties of the virgin and heat-treated FV520B steels. With the three indicators and the energy theory, comparison analysis of macro-phenomenon and microstructure evolution during fatigue of the two type specimens was performed. Using the intrinsic dissipation, fatigue limits were fast determined. Influence of heat treatments on mechanical properties and fatigue life was discussed. The research shows that the accuracy of the lock-in thermography could satisfy the needs of engineering design. Keywords Infrared thermographic method, Fatigue indicator, Heat treatment, Energy Approach 1. Introduction Fatigue design requires statistical processing of numerous tests. However, the traditional evaluation methods are often difficult to be performed for their time-consuming and expensive costing[1,2]. The infrared thermographic method was first proposed by Risitano et al. [3] by using the surface temperature increments as the major fatigue indicator. The infrared thermographic method, based on the analysis of the heat during a loading fatigue test, was developed over the last 30 years. Fargione et al. [4] obtained the connection between the quantity of heat dissipated in taking a given element to failure based on the physical hypothesis, which the failure of materials through fatigue occurs when the energy of plastic deformation reaches a constant limiting value, and the fatigue limit by applying fatigue tests. Suitable heat treatments can improve the static tensile strength and fatigue resistance of materials [5,6]. Now it is still a new task to investigate effect of heat treatments on fatigue behavior of materials using the infrared thermographic method. The purpose of this paper is to study the relationship between the internal microstructure and mechanical properties using different fatigue indicators. FV520B steel is a kind of martensite steel developed by Firth-Vickers Materials Lab in British. The steel is widely used in aerospace engineering and medical instruments, etc. due to its high strength, corrosion resistance and weldability [5,7]. However, heat treatments, used in practical engineerings, play an important role in determining the internal microstructure which governs mechanical responses of FV520B. Therefore, it is necessary to investigate the correlation between heat treatments and mechanical behavior useful for directing the mechanical design. In the present paper, the infrared thermographic method was employed to explore influence of different heat treatments on FV520B steel. Fatigue limits of two type steels were determined by the intrinsic dissipation. The internal microstructural changes were studied to understand the fatigue process.
RkJQdWJsaXNoZXIy MjM0NDE=