Application of Study on Liquid Ablation in Laser Propulsion

It was found that evaporation and thermal elastic stress wave and cavity were dominant phenomenon in laser-induced ablation propulsion with liquid propellant according to our perceptual knowledge established in relative experiment and by analysis of physical mechanism of laser-induced ablation of liquid. The research result of the above phenomenon was introduced in this paper in order to give some elicitations to the researchers who were interested in the mechanism of laser propulsion with liquid ablation.

ON ELASTIC STRESS WAVES IN AN IMPACTED PLATE

Elastic stress wave theory is developed and the stress waves in the impacted plate are examined in the paper. Generalized linear elasticity is adopted where the couple stress and curvature tensor are both deviatoric tensors and they meet a linear constitutive relation. It is found that there exist volumetric, rotational, and deviatoric waves in the generalized elastic solids. However, for macro-scale elastic solids only two wave modes, namely a volumetric wave and a deviatoric wave should be taken into account. Wave motion in plate impact tests is studied that a volumetric wave and a deviatoric wave are proposed. A set of exact solutions is attained for elastic stress waves in an impact plate. Excitation of stress waves at impact surface and reflection at free surface are formulated. Propagation of stress waves in the plate is analyzed in the waveforms. The predicted stress history in a ceramic plate under impact is agreed very well with the experiment measurement.

Extracting Acoustic Emission Signal Feature of Grinding Processing

Acoustic Emission (AE) may be defined as a transient elastic stress wave generated by the rapid release of strain energy in local area of material. To overcome the limitation of some traditional techniques, the AE technique, which provides high sensitivity and responding speed, were developed in the present paper. AE signature is usually difficult to be extracted and characterized in grinding process of 1Cr18Ni9Ti coatings due to their high hardness, great ductility, inhomogeneous structure and irregular surface with lots of hard points and pores. In this paper, AE signal of stationary grinding status before wheel-workpiece contact was characterized first, then AE signal of the grinding process was analyzed using root-mean-square (RMS) and power spectrum method. Results showed that before the contact occurred, the grinding signal is stable, with low amplitude and frequency ranging all frequency channels and no peak signal. However, when contact occurred, the RMS and spectrum of AE signal increased obviously and the bandwidth varied exquisitely between 100 KHz and 300 KHz. The real contact time between wheel and workpiece was about 0.5 to 1 ms.

Study of Stress Wave Propagation in SHPB with NHDMOC

In this paper the NHDMOC method which succeeded in studying stress wave propagation with one dimensional strain was applied to study the one-dimensional stress wave propagation. In this paper, the ZWT nonlinear visco-elastic constitutive relationship with 7 parameters to NHDMOC, and corresponding equations were deduced The equations was verified from the comparison of elastic stress wave propagation in SHPB with elastic bar and visco-elastic bar respectively. Finally the dispersion and attenuation of stress wave in SHPB with visco-elastic bar was studied.

The Optimization of Propagation Characteristic of Elastic Wave in FGM

The reflected coefficient of functionally graded layer to waves is very important as the design of impact-resistant FGMs. In the paper, the Optimization problem of propagation characteristic of elastic wave in FGM has been investigated. The relation between the top layer’s stress and displacement and the bottom layer’s is deduced from elastic propagation equation as the incident wave is a plane and harmonic elastic stress wave, then the reflected coefficient of gradient layer is obtained, and the reflected coefficient is selected as object function of optimization. The thickness of each layer is selected as optimization design parameter. The conjugate gradient method is used to get the optimal results about gradient layers’ thickness.