PSI - Issue 7

R.D. Xu et al. / Procedia Structural Integrity 7 (2017) 84–91 R. D. Xu, et al. / Structural Integrity Procedia 00 (2017) 00–000

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Fig. 1 Schematic of specimen building orientations

(b)

(a)

Fig. 2 Shape and Dimension of the specimens for tensile test (a) and fatigue test (b)

The tensile and fatigue test specimens were manufactured from SLM K536/Hastelloy X cylindrical bars in longitudinal direction. The cylindrical bars were divided into two types, X-orientation specimens parallel with the substrates and Z-orientation specimens vertical to the substrates, see Fig. 1. The shape and dimension of the specimens for tensile test and fatigue test are shown in Fig. 2. The gage length of tensile test specimens is 40 mm, with the gage section diameter 6mm and the overall length 84mm. Tensile tests at room temperature were conducted using an Instron 5587 testing machine, complying with the ASTM E8/E8M standard [8]. Tensile tests at elevated temperatures were conducted using an Instron 5892 testing machine, complying with the ASTM E21 standard [9], with the tested temperatures including 400 º C, 500 º C, 600 º C and 700 º C. All tensile tests were conducted at a 0.005/min nominal strain rate before specimens yield, then at a 0.5mm/min displacement rate. There were three specimens tested in each temperature-orientation condition, taking results average. Fatigue tests were performed with a QBG-50 high-frequency testing machine in accordance with ASTM E466 standard [10] until failure occurred or 10 7 cycles were achieved, in which the test was considered to be a “run-out”. The tests were undertaken at stress ratio R=0.1 and in two different temperatures, 400 º C and 600 º C. To keep the strain rates between tests similar and the frequency low enough to avoid any effects on the cyclic behavior in the ambient laboratory environment, a sinusoidal cyclic loading profile was used, with the frequency adjusted for each strain level.