No abstract

No abstract

No abstract

A spall fracture criterion based on critical stress versus stress gra&ent is briefly revaewed and discussed, An extension of a technique us~ by Tuler and Butcher is employed to show that the results of the stress-gradient theory can be interpreted in terms of criteria involving critical stress versus either impulse or pulse duration. The latter criteria are represented by smooth curves that depend on two parameters--the static strength limat for long-duration loads and an impulse limit for short-duration loads. Expressions for these parameters are presented in terms of the two parameters of the stress-gradient theory. Examples are ~resented for submicrosecond loads on 1100 aluminum and copper that show the stress-impulse interpretation differs little from the pure-impulse interpretation of Tuler and Butcher.

New spallation threshold data for 6061-T6 aluminum were obtained under stress-wave loading conditions m uniaxial strain, covering the range of tensile pulse durations of 60 to 200 nsec. This range of pulse duration was achieved by using exploding-foil techniques to accelerate thin Mylar plates against thin aluninum specimens. A comparison was made between exploding-foil spallation tests on 6061-T6 aluminum in air and vacuum. The data indicate that the spallation threshold of 6061-T6 aluminum is sensitive to the tensile pulse duration, amplitude, and impulse at the spail location. The exploding-foil impact conditions were reduced to stress-pulse loading parameters by using a onedimensional elastic-plastic hydrodynamic computer code. The time-dependent aspects of the spallation threshold of 6061-T6 aluminum were found to obey failure theories which were rate process onentecl, and which combine the effects of tensile-pulse duration, peak tensile stress, tensile impulse, and tensile-pulse shape. The present data have been used to quantitatively establish failure relationships for 6061 :T6 aluminum. Where apphcable, supplemental information in the literature concerning dynamic fracture of 6061-T6 ahlminum was utilized