introduced for characterizing thin, ductile sheet metals in shear. The new specimens were fabricated from the 2024-T351 plate and tested over a shear strain rate range of 0.01–2,000 s 1. Data from these experiments are compared to data from torsion experiments at similar strain rates. 38.2 Experimental The test specimens, shown in Fig. 38.3, were fabricated from a 0.5 in thick 2024-T351 rolled aluminum plate. Figure 38.3a shows the thin-walled tube torsion specimen. The torsion specimen has a wall thickness of 0.015 in., an inside diameter of 0.511 in. and a gage length of 0.1 in.. The flanges at either end of the specimen are used to attach the specimen to the test apparatus. The new simple shear specimen is shown in Fig. 38.3b. The sample is similar to the design used by Isakov et al. [7], however, the gage section is constructed through cuts made 90 to the loading direction opposed to 45 cuts. This significantly reduces the overall length of the specimen reducing the duration required to reach force equilibrium in dynamic tests. The gage section of the specimen is 0.220 in. long, 0.040 in. thick and 0.040 in. wide. 0.020 in. deep slots are milled from either side of an initially 0.080 in. thickness to concentrate the deformation in the gage section. The sample geometries are tested at both low and high strain rates. Low strain rate tests (0.01 s 1) were performed using an axial-torsional servo-hydraulic load frame. The samples were affixed to the load frame using hydraulic wedge grips as illustrated by Fig. 38.4a. High strain rate tests (2,000 s 1) were performed using both a tensile split-Hopkinson bar apparatus [8] and a torsion split-Hopkinson bar apparatus [9]. The samples were glued to the tension and torsion bars as illustrated by Figs. 38.4b, c, respectively. Fig. 38.3 Specimen geometries used in this study: (a) thin walled tube torsion specimen, (b) new simple shear specimen design Fig. 38.4 Specimen attachment methodologies: (a) simple shear sample mounted in hydraulic wedge grips for low rate testing, (b) simple shear sample epoxied to a tensile SHB, (c) spool sample epoxied to a torsion SHB apparatus 38 Characterization of Sheet Metals in Shear over a Wide Range of Strain Rates 315
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