13th International Conference on Fracture June 16-21, 2013, Beijing, China -2- tensile testing depends much on originally un-tested grain orientation, so different slip systems becomes active depending on grain orientation [6]. Several different research groups have performed tensile in-situ scanning electron microscope (SEM) investigations, studying microstructural changes and deformation and/or fracture mechanisms on different materials [6, 10, 13-15]. From their experiments one can conclude that insitu SEM investigations can give very accurate information about microstructural changes due to external forces. Some of the recent works in this field have also performed EBSD to analyse the microstructural changes, e.g. grain orientation and grain reorientation, due to loading. In this study the crack initiation point(s) and crack propagation in a grey cast iron where studied during axial loading in a SEM. Thanks to a specially designed stage mounted to the SEM, in-situ analysis of the crack initiation and its propagation as well as crystallographic changes were detected with EBSD and analysed. The microstructural features associated with different proportions of the stress-strain curve were investigated and explained. 2. Experimental details The flake cast iron had a fully pearlitic matrix and the composition of the material used is listed in Table 1 below. Table 1. Nominal composition of flake cast iron used Element C Si Mn P S Cu Cr Mo Fe Wt % 3.1 1.8 0.65 <0.08 0.12 0.90 0.14 0.25 Bal. The samples were cut out to a thickness of 1.0 mm from an as-cast cylinder head, using an electronic discharge wire to minimize the effects of surface hardening and residual stresses. On one side of the sample a notch was cut out with a total depth of 1.0 mm and a notch root radius of 0.25 mm. Both sides of the samples were carefully grinded and one side future prepared for EBSD analysis. On the rougher side of the sample a strain gauge were attached to enhance the accuracy of the actual loading when inside the SEM. Due to the brittleness of flake cast iron and the small elongation before rapture, some points on the stress strain curve in vacuum could then be conducted. Strain gauge signals were transmitted through pins on the stage specially designed for signal transmission from the vacuum chamber. The samples were investigated at loadings of approximately 0 MPa, 50 MPa, 90 MPa, 140 MPa, 200 MPa and 250 MPa. EBSD mapping with a step size of 0.3 µm and SE images on each loading were performed in a Hitachi SU-70 FEG-SEM equipped with an OXFORD Electron Backscatter Diffraction system with HKL software. Due to contamination of the surface (carbon diffusion from the material when the electron beam hits the sample) from the EBSD analysis two different locations were used. In all the figures the loading axis is in the horizontal plane, excluding Figure 3 and Figure 7.
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