Abstract: As a kind of complicated mechanical automation, most of key parts of breech mechanism are cams delivering forces and movements by parts’ outline and figure. The major fault mode of breech mechanism is grain abrasion caused by dry sliding friction. There are no feasible and practical technologies to simulate and predict the abrasion failure lives of key parts for breech mechanism. A new simulation and prediction method is firstly put forward in this paper. Based on Pro/E and ADAMS, the virtual prototype of breech mechanism of semiautomatic vertical sliding-wedge type is established. Key parts’ load spectrum can be obtained based on virtual prototype. Pin-on-disc friction and abrasion testing machine is designed and adopted to obtain typical materials’ abrasion rules. Finial simulation and prediction results are given as abrasion thresholds and operating items, which provide sufficient references for breech mechanism’s design and safeguard.
Abstract: A serious of nitride coatings including chromium, titanium and aluminum are deposited on the glass and stainless steel by Closed-Field unbalanced magnetron sputtering. The friction coefficient is measured by tribolometer and the wear traces of the coatings can be studied by the optical micrographs, those indicate that the friction coefficients of TiN、 CrN、TiAlN、CrAlN and CrTiAlN decrease sequentially as well as the anti-wear of the coatings can be enhanced. According to X-ray photoelectron spectroscopy analysis for the coatings, aluminum nitride can be indentified in the nitride coatings with Al element, which enhances the hardness and anti-wear performance of the coatings. The chrome oxide can be found in the nitride coatings with Cr element, which enhances the self-chip removal ability of the coatings and decreases the friction coefficients of the coatings; titanium oxide existing in the coatings is not good for the friction and anti-wear of the coatings. Chromium titanium aluminum nitride naturally is of higher hardness than the ternary nitride, as well as Chromium and aluminum in the coatings is in favor for the low friction coefficient and good anti-wear property.
Abstract: In order to eliminate the human eyes’ subjective differences in the level recognition of the jet fuel’s silver corrosion, chromatic aberration system is used to calculate chromatic aberration between the image of the standard colorimetric board and the experiment silver corrosion. By contrast, this paper chooses the least chromatic aberration to estimate the level of silver corrosion. The CIEDE2000 of the color difference formula, which can match with person vision theoretically, is applied in the chromatic aberration system at present, and can reflect the minor differences in color correctly. so this paper attempts to use CIEDE2000 color formula to determine the silver strip corrosion, which can reduce the influence of professionals’ subjective factors, and these results are more objective and accurate, which proves the actual feasibility of this method.
Abstract: In this text, the Chlorinated metallic porphyrin (TPPMncl and TPPFecl) thin films were fabricated by Spin-coated technique onto quartz substrates. In order to search for the gas-sensing characterization of Chlorinated metallic porphyrin Spin-coated films, the changes of UV-Visible absorption spectrums of TPPMncl and TPPFecl Spin-coated films respectively exposed in vapor of Chloroform, pyridine, Ammonia, triethylamine and dimethylamine were analyzed. The experimental results show that, the spectral response of TPPMncl and TPPFecl on organic gas molecular is obviously found. And we know that chlorinated metallic porphyrin film formed the J-aggregates. Moreover, through two kinds of chlorinated metallic porphyrin integral area rate of histogram, it is easy to identify and distinguish between the four kinds of volatile organic compounds. It indicates that these Chlorinated metallic porphyrin have gasochromic characteristics while responding with organic gas. Therefore, these materials can be prepared into gas sensor array for detecting VOCS.
Abstract: The surface roughness of carbon fiber reinforced plastics (CFRP) has been studied at different cutting parameters by using PCD tools. The effect of cutting parameters such as cutting velocity, cutting depth, cutting width as well as feed rate on roughness are analyzed. A predictive model for surface roughness in milling was established by regression analysis method. Based on the experimental results, the regression coefficient was calculated and the significance check of the regression equation was carried out. Results show that cutting depth has a significant effect on surface roughness and the next one is cutting velocity, then it is cutting width, feed rate has a little effect under the current experimental conditions. The regression is significant for the prediction model. The parameters used in milling can be selected to improve the quality of the surface based on the model of the paper.
Abstract: Semisolid A356 alloy was prepared by low superheat pouring, and evolution of primary phase morphology in semisolid A356 alloy during isothermal holding was characterized by fractal theory. The results indicated that the primary phase morphology in the alloy had fractal character, and the evolution of the primary phase morphology in the alloy could be characterized by fractal dimension. The primary phase morphology at the different isothermal holding temperature and holding time had the different fractal dimension, which meant the effect of processing conditions on the morphology in the alloy. Solidification of the alloy was a course of change in fractal dimension.
Abstract: The properties of phenolic-epoxy copolymer were studied in this paper. DSC was used to detect the possibility of copolymerization between phenolic resin and epoxy resin. FT-IR monitored the reactive process of mixed resin in various temperature stages. DMA revealed that the copolymer possessed high moduli and glass transition temperatures. The result showed that phenolic-epoxy copolymer can react in appropriate proportion. It is better for the copolymer system to avoid rich epoxy without curing agent. The properties of the copolymer could be increased when sacrificed some excellent properties of phenolic and epoxy. The copolymer 70% phenolic & 30% epoxy and 60% phenolic & 40% epoxy posses higher service temperature, lower volumetric shrinkage and excellent mechanical properties.
Abstract: Zirconium carbide (ZrC) coatings were prepared on C/C composite via molten salt reaction process at relatively low temperatures of 800-1000°C. During the reaction process, potassium fluorozirconate (K2ZrF6) played a role transporting zirconium from the molten salt to the C/C composite surface. Elevating reaction temperature increased the growth rate of coatings, simultaneously leaded to rougher coatings. The coatings growth rate increased with reaction time at first and then decreased gradually. The ZrC coatings prepared at 900°C for 5h was ~2m thickness. At the early stage, the low solubility of zirconium in the molten salt leaded to the low coatings growth rate. Secondly, the growth rate of the ZrC coatings was controlled by the chemical reaction between C/C composites and zirconium once zirconium was saturated in the molten salts. Thirdly, the control step of coatings formation turned into the diffusion of carbon through the formed ZrC coatings and which leaded to a gradual decrease of growth rate.
Abstract: This study explored the electrode excessive burning reason caused by aluminum resistance spot welding and proposed a new electrode failure mechanism. The test shows that the oxide film of aluminum alloy workpieces causes the contact of non-uniform points between electrode and workpieces and instantaneously leads to a local explosion when setting up an electric circuit, bringing about the plastic deformation of the electrode surface in the local area, which will in turn exacerbate the contact of non-uniform points between electrode and workpieces so as to result in the serious burnout of electrodes under the interaction between local explosions and Cu-Al alloying. Cu-Al alloying and brittle material on the electrode surface caused by the contact of non-uniform points will firstly detach from the surface of electrode under the tearing force of mechanical , so that the electrode surface becomes more uneven.
Abstract: The crack behavior of Si-doped GaAs crystals produced by a novel pulling-down method was investigated. Some cracks were observed in the crystal tail part and no twins or polycrystals were observed. The cracking mechanism was discussed considering the growth parameters, such as the pulling-down rate, annealing time and cooling speed of the furnace. The crystal was easily broken if the cooling rate was too fast. To avoid cracking, the temperature profile and the growth parameters had been optimized. The cleavage property of the GaAs crystal was strongly related to its atomic arrangement and corresponding electron density map. Ultrasonic vibration or mechanical machine would make the crystal cleaved along (110) plane. GaAs crystal displayed a strong anisotropic crack property under the force of microindentation test.