Some Experimental Studies on the Fatigue Strength of 7075-T6 Aluminium Alloy having Artificial Defects

Abstract

We have already reported on the effect of intermetallic compound CrAl₇ on the fatigue strength of extruded 7075-T6 aluminium alloy when the compound (about less than 2mm wide) is situated at the central part of the surface of unnotched specimen. This study was performed on the fatigue strength of the alloy specimens having square or hole-type artificial defects at their central surface, and compared with the above mentioned results.
The Schenck's plane-vibrating fatigue tester has been used for fatigue experiments and the measurements of fatigue strengths have been made at 10⁷ cycles. The shape, size and depth of artificial defects are shown in Fig. 2, Tables II and III. The square-type defects are made by electric-discharge method and hole-type defects are made by drilling process. The bottom of each defect is flattened.
The fatigue strengths and fatigue strength reduction factors are shown in Figs. 6, 7, 9 and 10, respectively, and the fatigue strength of the specimen having an intermetallic compound is also indicated in Table IV.
The fatigue strengths of the specimen having intermetallic compounds approximately correspond to the values of square-type 0.1mm depth and the fatigue strengths of hole-type defect specimens are higher than that of square-type defect specimens. Accordingly, the intermetallic compound may be acceptable as a square-type artificial defect, and the depth of the defect affects the fatigue strength more than the width of defect.