impact response of commercial Al-Mg series alloys deformed in the stain rate range of 10-4 to 104s-1 and, further, to investigate the microstructural changes. MATERIALS AND EXPERIMENTS Two kinds of work hardening aluminum alloys used in this investigation are 5052-H112 and 5083-H112 alloys. The chemical compositions are listed in Table1. Geometry and nominal dimensions of the tensile specimens are given in Fig.1 [4,5] and Fig. 2. All specimens used in static tensile, dynamic servo hydraulic tensile and dynamic split-Hopkinson bar tests have the same gage length and diameter. TABLE 1 CHEMICAL COMPOSITIONS OF SAMPLES USED Static tensile experiments were carried out using the Instron testing machine. Intermediate rate tests were made on a servo-controlled hydraulic testing machine over a range of strain rates approximately from 10-1 up to 103s-1. The split-Hopkinson bar test was conducted for strain rate exceeding approximately 103s-1 [6,7]. All of tests were conducted at room temperature. Fracture surfaces of the tested specimens were observed with a scanning electron microscope. RESULTS AND DISCUSSION Stress-Strain Curves over a Wide Range of Strain Rates Figures 3 and 4 show the typical stress-strain curves at four strain rates (4×10-4, 10-1, 1×103 and 3×103s-1) for the 5052-H112 and 5083-H112 alloys, respectively. In comparison with the result of the static loading condition, the 0.2% proof stress, ultimate tensile strength and elongation showed increases with increasing strain rate. Stress-strain curves showed a three-step process in which there were an initial elastic deformation region, uniform plastic deformation region until the maximum stress, then unstable deformation to the failure. In the static loading, the fracture occurred immediately when the stress reached the maximum stress. However, the flow stress decreased gradually at the high strain rate after the maximum stress. In the case of the dynamic tensile test using the split-Hopkinson bar apparatus, the stress-strain curves could be recorded exactly from the initial elastic deformation to the final fracture as compared to the other techniques. (mass%) Si Fe Cu Mn Mg Cr Zn Ti Al 0.09 0.14 0.25 0.20 0.03 0.03 0.04 0.65 2.50 4.64 0.19 0.11 0.01 - 0.01 0.02 bal. bal. 5052-H112 5083-H112 Figure 1: Geometry of a specimen in the static and dynamic tensile tests. Figure 2: Geometry of a specimen in the split-Hopkinson bar test. (mm) 60 20 6 4 M10 P1.5 × R0.5 5 M8 P1 × 36 15 3 6 4 R0.5
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