Temperature evolution in the laser aided direct metal deposition (LADMD) process has considerable influence on the micro-structure and properties of the final part. A 3D transient finite element model was developed to study the temperature evolution during the multilayer LADMD process. To make the property analysis from thermal history easier, a critical temperature specific to thermal history was defined and the distribution of it in the part was also discussed. The simulation results indicated that the critical temperature can make the property analysis from thermal history easier. Thermal history of all the deposited materials was similar. It was also concluded that process parameters needed to be time-varying according to the real-time temperature field during the process.
The monodisperse polystyrene spheres are assembled into the colloidal crystal on the glass substrate by vertical deposition method, which is aimed at the so-called photonic crystal applications.The structural information of the bulk colloidal crystal is crucial for understanding the crystal growth mechanism and devel-oping the various applications of colloidal crystal.Small-angle X-ray scattering(SAXS) technique was used to obtain the bulk structure of the colloidal crystal at Beamline 1W2A of BSRF.It is found that the SAXS pattern is sensitive to the relative orientation between the colloidal sample and the incident X-ray direction.The crystal lattice was well distinguished and determined by the SAXS data.
The mechanical properties of laser welded joints under impact loadings such as explosion and car crash etc. are critical for the engineering designs. The hardness, static and dynamic mechanical properties of AISI304 and AISI316 L dissimilar stainless steel welded joints by CO2 laser were experimentally studied. The dynamic strain-stress curves at the strain rate around 10~3s^(-1) were obtained by the split Hopkinson tensile bar (SHTB). The static mechanical properties of the welded joints have little changes with the laser power density and all fracture occurs at 316 L side. However, the strain rate sensitivity has a strong dependence on laser power density. The value of strain rate factor decreases with the increase of laser power density. Thewelded joint which may be applied for the impact loading can be obtained by reducing the laser power density in the case of welding quality assurance.
An air pressure-loading mode incorporated into the friction apparatus is firstly applied to coatings tribology involving large load,automation,stepless and continuous loading processes.A novel measurement principle is proposed and a micro-rotation mechanics model was developed for high precision measurement of friction coefficient.By properly designing and locating two sensors real-time monitoring the normal and friction forces,the troublesome influences in friction measurement is considerably relieved which come from surface characteristics of coatings of the samples in traditional friction test processes.By calculation and analysis,the max rotation angle θ max = 0.001 8 is gained,which indicates that the measurement error of the apparatus is greatly reduced.The whole system error is about 1.15% given by finite element method and indication error of the least square fitting of measurements.
The interpenetrating network structure provides an interesting avenue to novel materials. Locally resonant phononic crystal (LRPC) exhibits excellent sound attenuation performance based on the periodical arrangement of sound wave scatters. Combining the LRPC concept and interpenetrating network glassy structure, this paper has developed a new material which can achieve a wide band underwater strong acoustic absorption. Underwater absorption coefficients of different samples were measured by the pulse tube. Measurement results show that the new material possesses excellent underwater acoustic effects in a wide frequency range. Moreover, in order to investigate impacts of locally resonant units, some defects are introduced into the sample. The experimental result and the theoretical calculation both show that locally resonant units being connected to a network structure play an important role in achieving a wide band strong acoustic absorption.
