A Master of Science thesis in Civil Engineering submitted by Fadi Makarem entitled, "Numerical Study of Localization Failure in Structural Steel under Impact Loading," October 2011. Thesis advisor is Dr. Farid Abed and thesis is available in both soft and hard copies.
High quality steels are used as a skeleton supporting many infrastructure constructions like, for example, skyscrapers, arenas, stadiums, bridges and others. The likelihood that these structures could be severely damaged by postulated accidental extreme loading has been increased recently. Such loading may come about due to impact, blast or fluid jet impingement etc., and is usually of high intensity but short duration. Since most steel structures are capable of absorbing a considerable amount of energy beyond the elastic range, analysis has to extend into the inelastic range in order to avoid excessively pessimistic assessments. This research presents a consistent methodology for the assessment of nonlinear behavior of structural steel under low and high velocity impacts. Three high strength low alloy steels were considered in this study; HSLA-65, DH-36 and HY- 100. Four well-known constitutive models for viscoplastic deformation of metals, i.e., Johnson-Cook (JC), Zerilli-Armstrong (ZA), Rusinek-Klepaczko (RK), and Voyiadjis-Abed (VA), were investigated and compared with reference to existing experimental data. The VA constitutive model was chosen among the others as it exhibited dominant performance in describing the thermoplastic deformation of ferrite steel at a wide range of temperatures and strain rates. The VA model was then integrated and implemented into the commercial finite elements code ABAQUS/Explicit via user material subroutine coded as VUMAT. Finite elements simulation of the formation of shear localizations in a cylindrical hat-shaped specimen was conducted for two ferrite steel alloys, HSLA-65 and DH-36, subjected to certain range of velocity impact. The effect of the VA microstructure based material parameters on the initiation and propagation of shear localization was also investigated. Several conclusions related to the width of the shear bands considering various velocities and temperatures were thoroughly discussed. Finally, a preliminarily study on localization failure in axially preloaded columns made of high strength steel HY-100 (lowest yield stress = 100 ksi) subjected to transverse impact is presented. The effect of impact velocity, impactor mass, impact location and preloading condition on the behavior and failure modes of the steel columns is investigated in an attempt to develop appropriate design calculation methods for steel columns under such loading conditions.