Quasi-isentropic Compressive Characteristics Of W-Mo-Ti-Mg System Flier-plate With Graded Wave Impedance

Flier-plate with graded wave impedance, which can be regarded as a new type of functionally graded material since its wave impedance changes quasi-continuously along the thickness' direction and thus has quasi-isentropic compressive characteristics, has come to show great potential for the application in dynamic high-pressure technique.In the present dissertation, W-Mo-Ti-Mg system flier-plate with graded wave impedance was chosen as the disquisitive object. According to the correlative theory of hydromechanics and shock wave, theoretical model of creating quasi-isentropic compression via W-Mo-Ti-Mg system flier-plate with graded wave impedance was established, and study on the numerical simulation of the impact process was then carried out. The results showed that quasi-isentropic compression energy waves were produced after the impact with Mg-face of the flier-plate, whose initial velocity jump, peak velocity and front's rise-time were all different from the general shock loading wave profiles.For the sake of acquiring preferable quasi-isentropic compression energy waves, wave impedance distribution of the flier-plate had better be controlled between 2 and 3. Continuity and smoothness of quasi-isentropic compression energy waves after impacting on targets with lithium fluoride windows were markedly better than those after impacting on targets without lithium fluoride windows. The initial velocity jump and velocity peak of the quasi-isentropic waves are greatly concerned with shock wave impedance of the targets. Changing the impact conditions, there are evident differences among the quasi-isentropic energy. Furthermore, the higher the impact velocity, the smaller the extended wave's front while the higher the peak velocity. At the same time, the thickness off target should also be in accord with the impact velocity.Finally, experiments of quasi-isentropic loading to aluminum targets with lithium fluoride windows via W-Mo-Ti-Mg system flier-plate with graded wave impedance, having been fabricated by SPS, were performed on a two-stage light gas gun. The corrected VISAR-measured wave profiles on the interface between targetand window were profiles with an initial velocity jump followed by a stepwise-rising front to the peak velocity amplitude, indicating that quasi-isentropic compression energy waves had been successfully generated. When flier-plate with graded wave impedance impacted targets with different thickness at different velocities, the variation of the impact-induced wave profiles accorded with the numerical simulation results.The physical process of generating quasi-isentropic compression on target via flier-plates with graded wave impedance might be considered as the successive overlap of a series of small shock loading waves generated by the transition layers in the flier-plate. As a result, the P-V curve of the target was a quasi-isentropic compression curve, which consisted of small Hugoniot curves (similar to isentropic curves) from different original states, and was located between the Hungoniot curve and isentropic curve but closer to the latter.