Measurement of dynamic response of liquid metal subjected to uniaxial strain wave

Abstract
JAERI is carrying out R&D for constructing the facility of high intensity neutron spallation source which may bring us innovative science fields. A high power proton beam will be injected into the liquid mercury target for the neutron spallation. The mercury container will be subjected to the pressure waves generated by rapid thermal expansions because heating phenomena occurs in the mercury. In order to evaluate the pressure wave propagation in the mercury, we have carried out impact experiments on the mercury by a modified conventional split Hopkinson pressure bar apparatus. The chamber consisting of the input and out put bars and a collar was set between the two bars. The mercury was carefully inserted into the chamber without any air bubbles. Such a stiff collar may realize the constraint condition as a uniaxial strain condition in the mercury. The stress propagation on each bar and the liquid mercury was calculated by using an explicit FEM-code LS-DYNA. It is found that except very early time period just after stress wave injection into the mercury, a distinguished discrepancy is present between experimental and analytical results. While, in the early stage of impact, the analyses are appropriately representable to the experimental results. The average axial pressure and volume strain histories in the mercury were obtained as assuming the uniaxial strain condition and Kolsky formulas. It was recognized that the stiffness of mercury under high pressure is almost independent of the impact velocity in the experimental range. Many pits were found on the end surface of input bar being in contact with mercury, which may be associated with the cavitation in mercury.