prepared by using grinding wheels of #80, #200 and #800 grit sizes. In this series, the cutting depths per pass in the conditions using #80, #200 and #800 grinding wheels were respectively 20 µm, 8 µm and 2 µm, while surfaces of specimens ground by using #80 wheel were slightly polished so that the indentation-induced crack could be more easily observed. On the other hand, specimens of SN-PL1 were machined under six different conditions as follows. Three distinct grit sizes of grinding wheel, #170, #270 and #600, were adopted. Two values of the cutting depth were selected for each grit size; i.e. 5 µm and 40 µm for #170 and also for #270, and 1 µm and 25 µm for #600. Testing Procedures In the present study, specimens were indented by using an ordinary Vickers hardness tester, and the indentation force was set to be in the range from 196 to 490 N. The surface length 2a of the crack was measured through an optical microscope, while the crack tip was sometimes identified by using a laser scanning microscope with a higher resolving power. Bending strength has been obtained for AL-PL1 [16], SN-GP [16] and SN-PL1 [5], respectively. Smooth specimens of AL-PL1 and SN-GP were loaded by four-point bending with an outer span of 30 mm and an inner span of 10 mm, while bending tests for smooth specimens of SN-PL1 were conducted under three-point mode with a span length of 20 mm. In each case, tests were carried out under load-controlled condition, and the loading rate was controlled so that the rate of the maximum tensile stress in a specimen might be about 100 MPa/s. −200 −150 −100 −50 0 50 100 −200 −150 −100 −50 0 50 100 AL-PL1, #400 AL-PL1, #800 AL-PL2, #080 AL-PL2, #200 AL-PL2, #800 SN-GP, #400 SN-GP, #800 SN-PL2, #080 SN-PL2, #200 SN-PL2, #800 Residual stress measured by X-ray method (MPa) Residual stress estimated by IF method (MPa) Figure 2: Comparison between residual stresses evaluated by X-ray and IF methods EXPERIMENTS AND DISCUSSIONS Comparison between Residual Stresses Measured by Proposed and X-Ray Procedures Grinding-induced residual stresses in AL-PL1, AL-PL2, SN-GP and SN-PL2 specimens were also measured by using an X-ray diffraction method. For the materials, the residual stress measured by the X-ray diffraction method is compared with that estimated by the present procedure in Fig. 2. Although a little bit large scatter is seen in the figure, a good coincidence is found between the residual stresses by the X-ray and the IF methods. Consequently, it may be concluded that the proposed procedure gives a quantitative correspondence to the
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