In order to reveal the failure mechanism of the weld structure of the new generation launch vehicle in ultralow temperature environment and to provide scientific basis for improving the welding quality and the carrying capacity of the tank, in this project, this paper studied full-field mechanical parameters inversion and failure mechanism of non uniform joints at ultralow temperature environment. Firstly, the test method of ultralow temperature mechanical properties of aluminum alloy welded specimens based on DIC is described, and an open system for simulating the ultralow temperature environment was established. Secondly, two specimens based on the welding and friction stir welding were studied. In this paper, the relationship between load and stress strain curve, strain distribution along the direction of the load and the strain concentration factor of the welded specimen were analyzed. Results show that the friction stir welding specimen was better than the fusion welding specimen in mechanical properties. Finally, this paper also compared the influence of test area effect on, and it show that the measurement error was not more than 8.8% when heat affected zone size was between 2～8mm. The three tensile specimens were all broken in the gauge length and the fracture location was consistent. There was obvious plastic deformation near the fracture. The microstructure was observed. The tensile specimens were all broken in the gauge length and the fracture location was consistent. There was obvious plastic deformation near the fracture. The microscopic morphology observation showed that the whole section showed shear dimple morphology, and no material defects were observed. The fracture mode of the tensile fracture is plastic fracture.This project would provide a scientific basis for the welding process optimization and improvement of the ultra temperature tank of the new generation launch vehicle in China.
In this paper, a curvelet-based noise suppression bilinear interpolation method for low-dose CT images is proposed. Curvelets provide a multidirectional and multiscale decomposition that has been mathematically shown to represent distributed discontinuities such as edges better than traditional wavelets. Because the traditional linear interpolation results in boundary fuzziness in interpolated images, combined with the advantages of curvelet transform, here we propose a curvelet-based modified bilinear interpolation to improve the accuracy of interpolation. Extensive experiments indicate that the proposed method can effectively improve the quality of the obtained target image based on low-dose CT images and the produced slice image is similar to original slice image.
On the basis of the mechanically scratching using the Atomic Force Microscope, this paper proposes a new method for manufacturing high frequency grating. The grating was fabricated on a polycarbonate compact disc with a silicon AFM tip under the contact mode. The fabrication technique and the optimization of parameters for the technique are discussed in detail. From the experiment, the minimum spacing of the grating can reach 30 nm. The digital nano-moire patterns verify that the grating has good potential to be applied to the nano-deformation measurement.
In this paper, some novel micro/nano- moire grating fabricating techniques are introduced. The gratings are produced by the SPM lithography, FIB lithography, and molecular beam epitaxy (MBE) method. The moire patterns formed with these gratings are also introduced. The gratings are successfully to be used to measure the residual deformation in the surface around a step edge of the Al/Si artificial nanocluster with the moire methods. The successful experimental results verify the feasibility of these methods.