The dependence of yield stress on strain rate as determined from ball-indentation tests

A ball-indentation experiment was conducted to explore the possibility of using this test for the investigation of strain-rate dependence of yield properties of materials. The initial velocities of indentation used were between 0.0002 and 3 ips. Force and depth of penetration were measured continuously during a test. Using these and the results given in a previous report, the dependence of yield pressure of the indentation test on penetration velocity is shown for a range of velocities from 0.0002 to 300 ips. Results are presented for annealed C1018 steel, annealed 1100 F and annealed 6061-T6 aluminums. For all materials tested, the dependence of yield stress on strain rate seems to be derivable from the ball-indentation results by using Tabor's empirical formulas and an equation relating strain rate and velocity of penetration. The increase of yield pressure over the range of indentation velocities is 100 percent for steel, 30 percent for 1100 aluminum and 20 percent for 6061 aluminum.