Abstract
We performed series of multi-step loading tests in our Kolsky bar system, and demonstrated that the thermal softening in strong aluminum alloys can be eliminated by multi-step loading. We showed that there is a significant difference in their stress-strain curves, compared with the result of a single shot test, due to adiabatic heating. The tests were carried out using our interferometry-based system, where the bar velocities are measured directly rather than the strains. The optical technique has several advantages over traditional strain gauge measurements; it is non-intervening, highly repeatable, and more accurate at low strains, thus allowing good estimation of the dynamic yield point in these experiments.
Highlights
It is well known that materials tested to large strain at high strain rates, by the Kolsky bar system, can experience a significant flow thermal softening
We performed series of multi-step loading tests in our Kolsky bar system, and demonstrated that the thermal softening in strong aluminum alloys can be eliminated by multi-step loading
We showed that there is a significant difference in their stress-strain curves, compared with the result of a single shot test, due to adiabatic heating
Summary
It is well known that materials tested to large strain at high strain rates, by the Kolsky bar system, can experience a significant flow thermal softening. For materials with relatively low melting point Tm, this temperature increase can bring the specimen to above 0.4–0.5 Tm where the strength of the specimen decreases appreciably This softening effect can mask and moderate strain hardening, which are observed under quasi-static loading conditions, and can even cause a decrease in the stress-strain curve of the solid. The dynamic loading by the Kolsky bar system cannot be interpreted as a high strain rate test, since it contains, inherently, the thermal softening mechanism.
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