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Effects of Impact Velocity and Stress Concentrators in Titanium on Failure by Adaiabatic Shearing

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Final technical rept. 18 Jul 2000-17 Sep 2001

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This Final Technical Report covers the contract period from July 18, 2000 to September 12, 2000. During this period of the Contract all tasks defined by the Statement of Work have been accomplished. Precision machining of the three series of Modified Double Shear MDS specimens the U, V and the sharp notch geometry, total of 62 specimens, has been done in the Laboratory of Physics and Mechanics of Materials LPMM. Machining and heat treatment of the strikers and the support rings have also been done in LPMM. Since titanium alloys are very sensitive to the onset of the adiabatic shear banding ASB it is of great practical interest to study, via experiment and numerical modeling, the effect of stress concentrators on the triggering mechanism of ASBs. The main parameter is the impact velocity or the nominal strain rate in shear. The first series of shear tests was performed on the fast, hydraulic machine. Precise determination of shear characteristics, including failure stress, was performed at the range of the nominal strain rate from 10exp 3 1s to 510exp 2 1s. The second series of experiments was performed with direct impact loading on MDS specimens of the same geometry, using the air gun, series of strikers and the Hopkinson tube. Range of strain rates from 10exp 3 1s to 410exp 4 1s has been covered. Digital records of all tests have been analyzed and the rate spectra of the failure stress have been determined. It appears that response of the Ti-6A1-4V alloy is very non-linear as a function of strain rate for all geometry tested. At high strain rates a high rate sensitivity is found, but at very high strain rates above 10exp 4 1s a substantial drop of the failure shear stress is observed. Further studies of that effect are needed.

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  • Properties of Metals and Alloys
  • Mechanics

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