| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 100 === The dynamic shear deformation behaviour and fracture characteristics of rolled 6061 aluminum alloy plate under different crystallographic orientations and temperature. Cylindrical torsion specimens will be prepared from rolled plate with three different crystallographic orientations, i.e. longitudinal(L), transverse(T) and through-thickness(TT). After machining, all specimens will be solution heat treated at 565℃ for 1.5 h and aged at 171℃for 16 h. The torsion tests will be carried out using a split-Hopkinson torsional bar system. Shear deformation is conducted at temperatures of -150℃, 25℃ and 300℃ under strain rates ranging from 2×103s-1 to 4×103s-1, respectively.
The experimental results indicate that the shear flow response is found to be sensitive to the strain, strain rate and temperature. The flow stress, fracture strain, work hardening rate, strain rate sensitivity all increase with the increasing strain rate for a fixed temperature, but decrease with the increasing temperature under a constant strain rate. The fracture stress of T, L and TT are not significant but the fracture strain of transverse direction is higher than L and TT.
From the SEM observations, it is found that the fracture surfaces are characterized by a dimple structure, which is indicative of a ductile failure mode. The morphology and the density of these dimples are influenced greatly by strain rate and temperature conditions. Optical microscopy observations reveal that grain of the fracture surfaces are twisted into band like features.
|
|---|
