Zhiping Tang

Propagation of macroscopic phase boundaries under impact loading

Abstract The phenomena and rules for one-dimensional propagation of macroscopic phase boundary in shape memory alloys (SMA) under dynamic loading were investigated analytically and numerically with a simple mixture model of phase transformation proposed earlier. The interaction between stress waves and phase boundaries (and/or phase transition waves) yielded the complex wave patterns in x – t diagram. The phase boundary responses both for shape memory effect (SME) and pseudo-elastic effect (PE) of SMA were investigated. For SME, it was found to be very interesting that functionally graded material (FGM) might form during the unloading process. For PE, it was found that there existed three basic types of discontinuous interfaces. The interactions among the steady interfaces, the stress waves and the moving phase boundaries might cause some novel phenomena regarding unloading phase boundaries, such as bifurcation and acceleration of the unloading phase boundaries.

Experimental Investigation on Air‐ Breathing Mode of Laser Propulsion

The recent progress in our experimental investigation on the air‐breathing mode of laser propulsion has been reported. With a high power TEA‐CO2 pulsed Laser, both horizontal and vertical propulsion experiments were conducted. The energy of each pulse is 15–18J. The frequency can be adjusted from 20–180Hz. Several parabolic reflectors of aluminum alloy with different focus f were used in the experiments. A high speed CCD camera was applied to record movement variables of the reflectors. For single pulse experiments, the measured momentum coupling coefficient Cm is 27.7dyne.s/J for f=10mm, and 22.82dyne.s/J for f=15mm. For multi‐pulse experiments (frequency 50Hz, work time 0.5s), the horizontal propulsion distance was greater than 1.5m, and the vertical propulsion height exceeded 1m, but the average Cm is lower than that of single pulse experiments.

Experimental Study of the Momentum Coupling Coefficient with the Pulse Frequency and Ambient Pressure for Air‐Breathing Laser Propulsion

The air‐breathing laser propulsion tests are conducted for parabolic models by using a high power TEA‐CO2 pulsed laser. It is found the momentum coupling coefficient Cm varies with the pulse repeatable frequency and reaches the maximum near 50Hz. With a multi‐use pendulum chamber, the change of Cm at different ambient pressure is measured. The experimental results show that the propulsion efficiency Cm does not decrease below the altitude of 10km, even increases a little bit. The calculated Cm fits the experimental result up to altitude 3km, then, they are separated. One possible reason is the temperature which is constant in the experiments.

An Experimental and Conceptual Investigation of Laser Micro Propulsion

The laser micro‐impulse torsion pendulum has been developed in this lab. A thin glass plate of about 80μm thick is made as the target holder where the propellant film sticks on. Such structure can be used for both the R‐mode and the T‐mode measurements. The minimal resolution of this apparatus is 3×10−9N.s. A package, which combines a 2W single LD with its lenses, is evaluated by the pendulum under R‐mode and T‐mode conditions, respectively, in this lab. the momentum coupling coefficient Cm is about 2dyn/W and the specific impulsion Isp is about 170s. A new conceptual fiber‐distributed structure of laser micropropulsion system for microsatellites has been proposed and discussed in this article.

Study on Thermal-Mechanical Impact Effects on Parabolic Laser Thrusters

Thermal-mechanical impact failure problem of parabolic laser thrusters with air-breathing mode was studied experimentally and numerically. Four thermal loads i.e. the incident laser absorption, the radiation of high temperature gas, the transmitted laser absorption and the hot flow convection were proposed and the computational method of dynamic thermal-mechanical response of laser thruster was established. The calculated temperature rise of thrusters subjected to multiple laser pulses agreed well with the experimental measurement. The results show that for a parabolic thruster the thermal and mechanical damage mainly concentrates in the area near the apex and the mechanical fracturing will occur before melting. For a self-focus parabolic thruster the main temperature increase factors are the incident laser absorption and the high temperature gas radiation, while for an outside focus thruster, the main factor is the transmitted laser absorption near the apex. Thermal protection is needed for future laser ...

3D Discrete meso-element method and its application to spherical collision

Discrete meso-element method was recently introduced to simulate shock processes at meso-scale level with 2D code. In this paper, a 3D Discrete meso-element model, mathematical formulation, and boundary conditions are discussed. For 3D discrete calculation, most CPU time and RAM will spend on checking and storing the neighborhood when the number of elements in the system becomes large. A new “Region Method” was suggested to reduce this problem instead of previous “Window Method.” Examples for normal and inclined collision between two spheres are presented with the updated 3D discrete meso-element code.