13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Fatigue Crack Growth Rate Tests of High Performance Steel HPS 485W Lan Duan1, Chun-sheng Wang1,*, Shi-chao Wang1 1 Engineering Research Center for Large Highway Structure Safety of Ministry of Education, College of Highways, Chang’an University, 710064, China * Corresponding author: wcs2000wcs@163.com Abstract Research in this paper is about fatigue and fracture behavior of high performance steel HPS485W produced in Wuyang Steel Factory in China. Fatigue crack growth rate (da/dN) test was conducted for HPS 485W compact specimens with thickness of 7.5mm, 12.5mm and 19.5mm under different fatigue load ratio (R=Fmin/Fmax=0.1, 0.5 and 0.8), respectively. The seven-point incremental polynomial method was adopted for local fitting to obtain fatigue crack growth rate. The test results show that HPS485W has better crack growth resistance compared with traditional steel 14MnNb. What’s more, specimen thickness is an influencing factor for crack growth rate, and fatigue crack growth rate increases with the increase of fatigue load ratio R. For 19.5mm specimen under fatigue load with R=0.1, the engineering threshold was tested and numerical calculation was conducted to obtain theoretical threshold. The calculated theoretical threshold is 7.22MPa.m0.5. Fatigue life of high performance steel bridge can be predicated based on tested fatigue crack growth rate curve. Study in this paper serve as test basic for the fatigue control and fracture control of high performance steel bridge. Keywords high performance steel, fatigue crack growth rate, stress intensity factor, threshold value, fracture 1. Introduction High performance steel (HPS) for highway bridges was developed, which has superior characters in strength, weldability, toughness and corrosion resistance. Compared with steel bridge fabricated by traditional steel, these material characters bring several advantages to HPS bridges such as longer span length, easier fabrication, greater crack tolerance, elimination of painting in operation stage and so forth [1, 2]. Nowadays, about 250 HPS bridges have been constructed in the U.S., and all of these HPS bridges have demonstrated to be structural efficient and economical in whole life cycle [1]. So, the construction of HPS bridge is an attractive choice for modern society. However, with assumption that HPS detail has the same fatigue performance as conventional structural steel, effectively use of HPS may not be possible when fatigue limit state controlling the design [3]. Fatigue and fracture are typical failure mode for steel bridge. With purpose of ensuring high performance steel bridge operation safety, fracture failure control and remaining fatigue life calculation should be studied clearly. Thus, it’s necessary in this paper to carry out study for fracture toughness and fatigue characters study for high performance steel Q&T HPS 485W, which is produced by Chinese Wuyang Iron and Steel Co., Ltd. [4]. In this paper, with purpose of remaining life calculation and safety assessment, fatigue crack growth rate test was conducted under different load ratio to acquire fatigue crack growth parameters by Paris equation under cyclic loading, and threshold value was also tested and calculated. The test study in this paper provide important parameters in high performance steel bridge fracture control design and its remaining fatigue life calculation. 2. Fatigue crack growth rate test Fatigue crack growth rate (da/dN) tests were conducted to determine the fatigue crack growth rate according to ASTM E647-08 and referencing to Chinese GB/T 6398-2000 [5, 6].
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