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Abstract The key problem for fatigue crack growth rates testing of metallic materials at high temperature is how to measure crack length of a compact tensile (CT) specimen accurately. A new compliance method based on the FFCT specimens at high temperature was developed, and the calculation of the real-time crack length for a CT specimen which contains two different materials was also studied using finite element analysis. According to the new compliance method, a series of fatigue crack growth rates tests for nickel-chromium alloy welding materials at room temperature and 350℃ were carried out. The results show that, the new compliance method can be commendably used for fatigue crack growth rates tests at high temperature. For a CT specimen with layered configuration, its equivalent elastic modulus is affected by the elastic modulus ratio b, height ratio m and crack length a, and it has somewhat difficult to get a explicit expression of the crack length. A developed correct method for the calculation of real-time crack length is proposed, and it presents a nicer precision. The parameters of C and m in the Paris formula vary inversely with increasing temperature. For welding rod and wire, the values of C increase and the values of m decrease, but for welding strip the change of the two parameters is reversed. The crack growth resistance of welding strip is obvious lower than the other two welding materials at 350℃. The crack growth curves of the three welding materials have a point of intersection at room temperature and 350℃.
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Received: 03 November 2008
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2010, Vol. 31 
