Initiation And Propagation Of Adiabatic Shear Localization

Three experiments were designed to investigate the initiation and propagation of adiabaticshear localization which was one of most important failure behavior of materials under high stainrate loading:1) Uniaxial dynamic compression of pure titanium cylinders by Split HopkinsonPressed Bar;2) Forced shear localization of pure titanium flat hat shape samples impacted bySHPB;3) Electric-magnetic force drives Al6061tube making multiply adiabatic shearlocalizations by inner compression. Simultaneously these experiments were simulated by finiteelement method code of ABAQUS/Explicit. The dynamic mechanical property was tested by firstexperiment, and adiabatic shear bands were found in metallic graphics of the result samples, andthe resulting stress-strain curves were used to fit the parameters of Johnson-Cook constitutionrelation. Then the flat hat forced shear experiment showed the process of initiation and propagationof ASB by digital spackle image correlation method, and the real strain of shear band wascalculated by this code. At last, the self-organization characterizations of multiply adiabatic shearlocalization were discussed by electric-magnetic force driving compression test. It was found thatthe initiation of adiabatic shear localization happened when stress started drop sharply and strainincreased rapidly, and this process was generally considered as instability of constitution. Theinitiation critical rule was related to strain, strain rate, temperature and stress state. A critical strainmust be arrived when the shear bands occur, and the larger strain rate, the smaller critical strain, thehigher temperature, the lager critical strain, and the stress state decided the location point and thepropagation direction. The results of FEM show the temperature arrived only about300℃whenthe initiation of localization, but the temperature of inner shear band will arrived at melting point.The maximum propagation speed of shear band can arrived1000m/s, and vividly increases withstrain rate. Self-organizational characteristics were found in multiply adiabatic shear localization,which were influenced by strain rate, temperature and material properties.