Publications

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We present pulse shaping techniques to obtain compressive stress - strain data for elastic - plastic materials with a split Hopkinson pressure bar. The conventional split Hopkinson pressure bar apparatus is modified by placing a combination of copper and steel pulse shapers on the impact surface of the incident bar. After impact by the striker bar, the copper - steel pulse shaper deforms plastically and spreads the pulse in the incident bar so that the sample is nearly in dynamic stress equilibrium and has a nearly constant strain rate in the plastic response region. We present analytical models and data that show a broad range of incident strain pulses can be obtained by varying the pulse shaper geometry and striking velocity. For an application, we present compressive stress - strain data for 4340 Rc 43 steel. © 2005 Society for Experimental Mechanics.

This research addresses effects of temperature, including adiabatic temperature rise in specimen during dynamic compression and environmental temperature, on the dynamic compressive properties of an epoxy syntactic foam. The adiabatic temperature rise in specimen during dynamic compression is found to be so small that its effects may be neglected. However, environmental temperature has significant effects on dynamic compressive behavior. With decreasing temperature, the foam initially hardens but then softens when below a transitional temperature, which are dominated by mechanisms of thermal-softening and damage-softening, respectively. A phenomenological material model accounting for both temperature and strain-rate effects has been developed, which well describes the compressive and failure behaviors at various strain rates and environmental temperatures. © 2004 Elsevier Ltd. All rights reserved.

We conducted sets of experiments with three diameters of concrete targets that had an average compressive strength of 23 MPa (3.3 ksi) and 76.2-mm-diameter, 3.0 caliber-radius-head, 13-kg projectiles. The three target diameters were D = 1.83, 1.37, and 0.91, so the ratios of the target diameters to the projectile diameter were D/d=24, 18, and 12. The ogive-nose projectiles were machined from 4340 R{sub c} 45 steel and designed to contain a single-channel acceleration data recorder. Thus, we recorded acceleration during launch and deceleration during penetration. An 83-mm-diameter powder gun launched the 13-kg projectiles to striking velocities between 160 and 340 m/s. Measured penetration depths and deceleration-time data were analyzed with a previously published model. We measured negligible changes in penetration depth and only small decreases in deceleration magnitude as the targets diameters were reduced.

Dynamic compressive properties of an epoxy syntactic foam at various strain rates under lateral confinement have been investigated with a pulse-shaped split Hopkinson pressure bar (SHPB). The quasi-static responses were obtained with an MTS 810 materials test system. The quasi-static and dynamic stress-strain behavior of the foam under confinement exhibited an elastic-plastic-like response whereas an elastic-brittle behavior was observed under uniaxial stress loading conditions. The modulus of elasticity and yield strength, which had higher values than those in uniaxial stress case, were both sensitive to strain rates. However, the strain-hardening behavior under confinement was not strain-rate sensitive. A phenomenological elastic-plastic type of material model was employed to describe the strain-rate-dependent compressive properties of the syntactic foam under confinement, which agreed well with experimental results.