Microstructures and Mechanical Properties of 6061 Al Matrix Smart Composite Containing TiNi Shape Memory Fiber
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Mat. Res. Soc. Symp. Proc. Vol. 459 0 1997 Materials Research Society
composite. The sheet metal was sheared off using a shear cutter into a rectangular shape of 10 mm width and then slits of 0.3 nun width and 1 nmm length were made in both narrow sides with an interval of 1 mm using a low-speed diamond wheel cutter. After removal of oxide layer, TiNi fiber was wound around such 6061 Al alloy sheets through slits, and several prepreg sheets thus made were stacked on a pair of hot press dies. Then, composite specimens were fabricated by a custommade vacuum hot press system at selected holding temperatures and pressures. After holding specimens under a set of holding pressure and temperature for a various period of time, composite specimens were cooled down to room temperature within a furnace. Two volume fractions were chosen in the study and they were 2.7 and 5.3 %. Figure 2 is a schematic illustration showing the hot pressing procedure of wire wound prepreg employed in the present study. Composite specimens were cut to produce tensile specimens, whose dimensions are 10 mm wide and 90 mm long with a gauge length of 26 mm. To obtain mechanical properties and transformation temperatures of TiNi fiber used, tensile tests were performed at temperatures between 297 and 373 K after shape memorizing treatment at 773 K for 30 min. in air followed by quenching into water. The transformation starting and finishing stresses can be obtained from tensile stress-strain curves obtained each test temperature. DSC was also utilized for the measurement of transformation temperatures without stressing. In order to see the effects of T6 aging treatment on mechanical properties of the composite, the heat treatment was performed by following a standard procedure of 6061 Al alloy. That is, the solution treatment was first made at 803 K for 1 hr and then water quenched followed by the second heat treatment at 443 K for 6 hr and quenching. To investigate prestrain effects, various amounts of prestrain were given to some composite specimens by deforming them in tension at 293 K. Tensile tests were performed on an Instron testing machine at a constant strain rate, 1xl0 4/s. The displacement of tensile specimens used in the study was measured by using an extensometer.
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Fig. 1 Concept of smart composite with TiNi fibers.
Fig. 2 Hot pressing procedure of wire wound prepreg
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RESULTS Processing and Microstructures The transformation temperatures of TiNi fiber used in the present study were measured by a differential scanning calorimeter (DSC), which are tabulated in Table 1. This table also contains the elastic moduli of the fiber for both martensite and austenite phases, which were measured from data obtained in tension tests using an extensometer. The table also contains the elastic modulus of 6061 Al alloy. Table 1. Transformation temperatures an
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