| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 86 === The purpose of this study is to investigate the plastic
deformation behaviour of 7075 Al alloy subjected to
different manufacturing processes. The"dynamic" ranges (1300s^-1
~4100s^-1 ) and at temperature ranging from 25℃ to 300℃ by
using constant-strain-rate isothermal tester and Split-Hopkinson
bar tester. After mechanical test, the microscopic techniques
were used to examinethe variation of microstructure in terms of
testing conditions. With the macroscopic and microscopic
results, a constitutive equation is used to describethe
plastic deformation behaviour of the material under high strain
rate and high temperature conditions. The experimental results
indicated that temperature and strain rate effect strongly
the mechanical characteristics of 7075 Al alloy,
and that different manufacturing processes also play an
important role to mechanical response of this material.
Microstructural observations find that the strength of tested
material varies markedly with the density of precipitates and
that the features and arrangement of precipitates
depend strongly on strain rate, temperature and different
manufacturing processes. The failure analysis shows that the
fracture is dominated by a shear failure mode and that the shear
bands are theprecursor to crack formation and fracture. The
characteristics of shear bands vary completely with testing
conditions and matrix hardness. Finally, by comparing the
results of mechanical testing with those of Kobayashi & Dodd
equation, the constitutive equation predicts an acceptable flow
stress value with reasonable extent of error.
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