查看更多>>摘要：Splines in aero-engine are often excessively worn, seriously affecting flight safety. Manufacturing errors and parallel offset lead to unequal tooth loads, which is one of the main reasons to reduce the spline wear life. However, spline wear life with multiple errors is sometimes hard to predict due to technical or cost reasons. To obtain a more realistic spline wear life, a spline clearance calculation method considering manufacturing errors and parallel offset is proposed. The tooth contact pressure is developed based on the equivalent model of force carried by each tooth. Then, the relative sliding speed between the tooth and the tooth space is deduced by equating the two contact points on the spline as a crank-slider mechanism. Finally, a numerical model of spline wear is established by using the improved Archard's wear model. The case results show that the maximum wear depth at torque of 240 N-m is 1.7 times the wear depth at torque of 80 N-m for the spline with a total of 2×10~5 motion cycles. For a spline with a parallel offset of 30 urn, the maximum wear depth is 66.8 μm, which is 3 times the offset of 5 μm. The wear life results show that the average life of the spline is 0.7 times that of parallel offset when considering multiple errors.
查看更多>>摘要：This work analyzes resistance of polyamide hollow fibers used for heat exchangers against extremely high pressures. Hollow fibers made of five different commercially available polyamides and one type of polyphenylene sulfide were tested at different temperatures ranging from -40 to 160 °C. After getting the fiber to the required temperature, pressure from a nitrogen vessel was gradually applied to the lumen side of a fiber until the fiber rupture. The results obtained for different polymers were then analyzed using various burst pressure models used to predict pressure durability of pipelines. The result showed decreasing burst pressure of polyamide fibers mosdy from 100 bars to about 50 bars with increasing temperature from -40 to 160 °C. This was contrary to polyphenylene sulfide, which increased from 30 to about 60 bars in the same temperature range. The theoretical models were in a strong disagreement with experimental data and the results fluctuated significantly. However, the fibers showed outstanding durability against rupture no matter of the temperature, since the lowest burst pressure was about 40 bars at 160 °C. From the point of view of practical usability of polymeric hollow-fiber heat exchangers in automotive, the results indicate the polymeric fibers are able to operate at a wide range of conditions characterized by extreme temperature and pressure fluctuations typical for a car radiator.
查看更多>>摘要：The damage in the form of the leakage occurred at the end piping transporting industrial water in the press hall of the automotive plant in the specific position of 12 o'clock after twelve years of operation. The piping diameter 80 mm, wall thickness 4 mm, is made of low carbon steel produced according to the Slovak standard STN 41 1353 equivalent to the S235 according to the EU standards or ASTM A519-82 grade 1020. In order to determine the cause and course of corrosion damage to the piping there were performed the analyses of the transported industrial water (composition, properties, pH), ultrasonic measurements of piping wall thickness, piping steel material (microstructure, chemical composition) corrosion products from the entire inner surface of the piping and from the point of the leakage and pinholes (visual, EDS and X-ray). The UT measurements of wall thickness changes revealed the massive corrosion damage manifested as pinholes at the 12 o'clock position with the max. depth of the pinholes 3.6 mm. The analysis of the industrial water confirmed the quality corresponding to drinking water. The X-ray analysis of the corrosion products from the pinholes and leakage confirmed the corrosion process in the humid atmosphere with the dominance of Goethite, Akaganeite and the low CaCO_3 content. The presence of Akaganeite and the direct confirmation of the Cl~- presence in the corrosion products by the pinholes EDS analyses designates Cl~- as the accelerator of pinholes corrosion in the humid atmosphere above the stagnant water level, propagating against the direction of gravity (12 o'clock) in the air bubble created by improper venting of the piping.
NSTL
Elsevier