Sun Chengwei

Verification of conventional equations of state for tantalum under quasi-isentropic compression

Shock Hugoniot data have been widely used to calibrate analytic equations of state (EOSs) of condensed matter at high pressures. However, the suitability of particular analytic EOSs under off-Hugoniot states has not been sufficiently verified using experimental data. We have conducted quasi-isentropic compression experiments (ICEs) of tantalum using the compact pulsed power generator CQ-4, and explored the relation of longitudinal stress versus volume of tantalum under quasi-isentropic compression using backward integration and characteristic inverse methods. By subtracting the deviatoric stress and additional pressure caused by irreversible plastic dissipation, the isentropic pressure can be extracted from the longitudinal stress. Several theoretical isentropes are deduced from analytic EOSs and compared with ICE results to validate the suitability of these analytic EOSs in isentropic compression states. The comparisons show that the Gruneisen EOS with Gruneisen Gamma proportional to volume is accurate, regardless whether the Hugoniot or isentrope is used as the reference line. The Vinet EOS yields better accuracy in isentropic compression states. Theoretical isentropes derived from Tillotson, PUFF, and Birch-Murnaghan EOSs well agree with the experimental isentrope in the range of 0–100 GPa, but deviate gradually with pressure increasing further.

Overview of Pulsed Power Research at CAEP

Pulsed power research for military and civil applications has been conducted at the China Academy of Engineering Physics (CAEP) for more than 50 years. The pulsed power research activities include development of pulsed power components, such as different kinds of high-voltage switches, series of pulsed power sources and pulsed X-ray machines, high-current accelerators for Z-pinch and flash X-ray radiography, as well as medical application and electromagnetic launch. The most recent progress of pulsed power research at CAEP will be presented.

High velocity flyers accelerated by multi stage explosive slabs

The problem of accelerating metallic flyers to ultra high speed with strong detonating explosive slabs has been analyzed and numerically simulated in this paper, where the next stage slab is impacted by the flyer of previous stage and accelerates the next stage flyer to a higher speed. There is a high plateau in the detonation products pressure profile of the slab, to which the effective acceleration is attributed. A combination of impedance matched flyers of the final stage is impacted by the strong detonating explosive driven flyer at speed 6–7 km/s, and could be sped up over 10 km/s. This kind of high speed impactors have the advantages of simple structure, lower cost, smart design and promising in many applications of high dynamic pressure loading and high velocity impact.

Dynamic Fracture in Metals at High Strain Rate

The response of materials to shock loading has attracted much attention for its applications in high velocity impact, astronautics, explosive working, and defense technology. Scientists are interested in the strain-rate dependence of material performance, especially as it affects dynamic strength, damage, and failure. Since high-strain-rate loading can only be applied for a short time, the available means are: by a plane shock wave produced by plate impact, explosive detonation, gas- or electrically-propelled gun projectiles, and laser-beam irradiation. Other experiments involve freely-expanding rings or exploding cylinders and projectile penetration or plugging of a target. Spall experiments carried out with plane shock waves are most appropriate for fundamental research because two dimensional effects are minimized and loading parameters are easily adjusted over a wide range.

Dynamic fracture of iron under shock loading induced by pulsed laser beam

The ultra high pressure and short duration of stress wave induced by high power laser beam allows us to study the dynamic fracture behaviors of materials at strain rate over 107s−1. In this experiment Nd:glass laser beam with pulse width of 750 ps (FWHM) is focused on iron targets in vacuum chamber. The threshold laser flux for 400 μm thickness targets to spall is about 4× 1012 W/cm2. The detailed microscopic observation of the recovered samples reveal that the main damage mechanism of iron under this loading condition is the microcracks’ nucleation, growth, and coalescence. The microcracks can nucleate both inside the grains or at the plastic deformation area at / or near grain boundaries. The spall thickenss is about 55±10 μm, and the width of the damage zone is in the range 50±8 μm. In addition, corresponding to the laser irradiated area, there is a twinning zone which appears not far from the loading surface and disappears in front of the damage area.

LARGE AREA AND SHORT‐PULSE SHOCK INITIATION OF A TATB/HMX MIXED EXPLOSIVE

The large area and short‐pulse shock initiation experiments on the plastic bonded mixed explosive of TATB(80%) and HMX(15%) have been performed with an electric gun where a Mylar flyer of 10–19 mm in diameter and 0.05∼0.30 mm in thickness was launched by an electrically exploding metallic bridge foil. The cylindrical explosive specimens (Φ16 mm×8 mm in size) were initiated by the Mylar flyers in thickness of 0.07∼0.20 mm, which induced shock pressure in specimen was of duration ranging from 0.029 to 0.109 μs. The experimental data were treated with the DRM(Delayed Robbins‐Monro) procedure and to provide the initiation threshold of flyer velocities at 50% probability are 3.398∼1.713 km/s and that of shock pressure P 13.73∼5.23 GPa, respectively for different pulse durations. The shock initiation criteria of the explosive specimen at 50% and 100% probabilities are yielded. In addition, the 30° wedged sample was tested and the shock to detonation transition (SDT) process emerging on its inclined surface was ...