Qing Ming Zhang

Investigation on the Deformation of TiNi Shape Memory Alloy with a Crack Using Moiré Interferometry

Martensitic phase transformation can greatly affect the mechanical behaviors and the stress-strain response of shape memory alloys (SMAs). In this study, the effect of martensitic phase transformation on the deformation of a single-crystal TiNi SMA specimen with a triangle crack was investigated experimentally by means of moiré interferometry method. A typical displacement field and the corresponding strain field in areas both around and far from the tip of the crack were measured in a certain time during the loading process in which the tensile load is coupled with the stress-induced martensitic phase transformation. Some characteristics of the deformation and the martensitic phase transformation of the specimen are revealed. These results may provide a reliable support for revealing the fracture mechanism of single crystal TiNi SMAs, and may enable further development in putting forward the failure criterion of SMAs.

A New Moiré Grating Fabrication Technique Using Hot Embossing Lithography

Moiré grating is a basic optical component, and can be used in various moiré methods. The conventional grating fabrication technology is based on photolithography and holographic interferometry, however, it requires complex optical components and is very difficult to put into practice. In this study, nanoimprint lithography (NIL), or rather, hot embossing lithography (HEL), is proposed for producing high frequency grating. Compared with silicon mold, holographic moiré grating mold costs less and is not easy to break, thus is chosen to be the mold in HEL. Using this mold and the hot embossing system, the grating structure can be transferred to the polymer after HEL process. Through a number of experiments, the process parameters were optimized and gratings were successfully fabricated. The multi-scale morphology of the fabricated gratings was then characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and moiré interferometry. The microscale images observed by AFM and SEM show the regulate dots with equal spacing and the macroscale moiré patterns illuminate the excellent qualities of fabricated grating in a large area. The successful experimental results demonstrate the feasibility of the grating fabricated by HEL for the moiré measurement.

Digital Image Correlation Study on Micro-Crystal of Poly-Crystal Aluminum Specimen under Tensile Load through SEM

In this study, the digital image correlation method(with Newton-Raphson iteration method) is used to measure the in-plane deformation of poly-crystal aluminum. When the specimen is exerted a tensile load, the strain distribution of the specimen surface will be inhomogeneous. The micro-deformation of the poly-crystal aluminum is studied under a SEM(scanning electron microscope), a series of images of the micro crystal are captured during the loading process. By using digital image correlation to analyze the images, the displacement and strain of a micro-crystal are obtained, which provide important data for further analysis of the inhomogeneous properties of the poly-crystal aluminum.

Nano-Grating Fabrication Technique

In this paper, a novel nano-moiré grating fabrication technique was proposed for nanometer deformation measurement. The grating fabrication process was performed with the aid of Atomic Force Microscope (AFM) on the basis of micro-fabrication technique. On the analysis of some correlative factors of influencing grating line quality, some important experimental parameters were optimized. In this study, some parallel and cross nano-gratings with frequencies of from 10000lines/mm to 20000lines/mm were fabricated. The successful experimental results demonstrate that the nano-grating fabrication technique is feasible and also indicated that these nano-gratings with nano-moiré method can be applied to deformation measurement, which offers a nanometer sensitivity and spatial resolution.

Study on Formative Mechanism of Blasting Crater in Reinforced Concrete under Internal Blast Loading

The variation process of radius and pressure of explosion products in borehole are analyzed in this paper, based on theory of damage and structural mechanics, the formative mechanism of blasting crater in reinforced concrete under internal blast loading is analyzed, the computation method of crater size has been proposed. The calculated results are identical with experimental results on the whole.

Experimental Study on Dynamic Compression of Nylon Reinforced Concrete

Results of tests using two kinds of nylon reinforced concrete samples are described . In order to deal with the heterogeneous effects of samples resulted from large particles which range from7mm to10mm in diameters, a SPH bar which is 74mm in diameter is used. There seems something new and difficult in the method of testing the concrete’s dynamic compressive responses. The results show that there are obvious strain rate effects in both the two kinds of samples , and the failure strength increases with the increasing of the strain rate.

The Experiment Study on Flash Spectrum Produced by Hypervelocity Impact

It is an inevitable phenomenon that flash is generated in the process of hypervelocity impact. The research on impact flash is of important significance for assessing the collision between space debris and spacecraft, identifying the material properties on the surface of planet, evaluating the damage of weapon system. A measurement system was built in order to acquire flash spectrum ranging in wavelength from 200 to 1100nm. The relationship between flash intensity and impact velocity was studied. The spectrum consists of line spectrum and continuous spectrum. Line spectrum mainly concentrates in the range of 200-500nm. The spectral lines of the elements were identified. The strong flash happens within 2.2ms after beginning to impact. In addition, the electron temperature of plasma produced in hypervelocity impact is calculated by spectral method, and compared with the temperature measured by Langmuir three probes.

Projectile Material Model Included Phase Transformation Erosion

High temperature generated by target impact causes projectile austenite phase transformation. At high temperature, the austenite strength decreases rapidly and undergoes phase transformation erosion because of target impact. On this basis, a projectile material model which took phase transformation erosion into consideration was established and then the model was verified. Model simulation showed that after phase transformation erosion the projectile was subjective to tensile and compression instability. Dual-arc head design would significantly reduce projectile penetration resistance and decrease phase transformation influence on projectile stability.

Numerical Simulation of Projectile Material Phase Transformation during Penetration

It was found from the experiment that the high temperature caused by target impact led to projectile austenite phase transformation. Based on this finding, a phase transformation model was established and verified by experiments, which proved the model had a relatively high calculation precision. Then, the model was used for numerical simulation. The result showed that the phase transformation zone was at the projectile head surface and the area increased as the impact velocity increased. The critical impact velocity which would cause phase transformation and affect projectile performance was around 700m/s.

Analysis on EFP Penetrating against Water-Partitioned Armor

Based on the experiments and numerical simulation of EFP penetrating against the water-partitioned armor, the velocity attenuation law of EFP in water is obtained by dimensional analysis. The relationship between the pressure of the water shock wave and the deflection of the latter target is established, which is validated by the experimental results. The influence of the water shock wave on the motion of EFP is also analyzed. The results in this paper provide remarkable benchmark in designing and optimizing the liner, as well as increasing the damage efficiency of the torpedo warhead.