Papers by Keyword: Threshold Pressure

Abstract: A known phenomenon during the contraction/expansion cycles of pneumatic muscles is the occurrence of hysteresis, caused by the elasticity of their component materials. The inherent hysteresis manifest in pneumatic muscles increases the non-linearity of the systems they are included in and consequently the complexity of the related control systems. The paper discusses a number of experimental results obtained for the hysteresis related behaviour of a small size Festo pneumatic muscle, where the specific hysteresis loops were highlighted via isotonic testing.

Abstract: Threshold pressure is a very important parameter for melt alloy successfully infiltrating into the porous preform. However, the precise measurement for threshold pressure is very difficult for the reason that infiltration process is undertaken very fast under extreme elevated temperature and high pressure without effective measuring devices to monitor it. A totally new measuring device was proposed and fabricated, which can be used to monitor the infiltration process “visually” and measure the threshold pressure directly at the same time. The infiltration speed can be controlled by adjusting the gas flow speed. The infiltration behavior of melt AZ91D alloy in Al2O3sf preform was researched at temperature of 800°C and pressure of 0.6 MPa. The optimized gas velocity was controlled at 25L/min. The degree of vacuum of the infiltration cavity was set 30kPa in experiments. The volume fraction of Al2O3sf was 10%. Under these conditions, the threshold pressure of melt AZ91D alloy into porous Al2O3sf preform was found to be related with vacuum degree in infiltration chamber, and it was about 30 kPa

Abstract: Production prediction model and waterflooding characteristic equation considering threshold pressure were deduced. Based on them, a combined solution model was established, which can predict development indexes in low permeability reservoirs. The development indexes of a typical low permeability block YS2 were forecast using the combined solution model. Forecast results and actual production data fit well, which confirms the practicability and validity of the combined solution model. It has important practical significance to guide low permeability oilfield development.

Abstract: The most promising process for metal matrix syntactic foam (MMSF) production is pressure infiltration. In case if it can be advanced to die casting the cost of the MMSFs will drop significantly. The first step on this road is to characterize the kinetics of the pressure infiltration with respect to infiltration pressure and time. Experimental infiltration equipment was built and many preliminary tests were performed on the AlSi12 + SLG system. The load bearing capacity is also important, therefore the compressive behaviour of MMSFs were investigated. According to the results engineering factors (matrix material, size of the microballoons, applied heat treatment, temperature of the tests) have significant effects on the compressive properties.

Abstract: In this study Nextel 440 type alumina fibre reinforced aluminium matrix composite wires were investigated. Composite wires produced using the continuous process are suitable to simplify the introduction of fibre reinforcements into aluminium castings as well as the production of double composite, sandwich and preferentially reinforced structures. This paper focuses on the porosity of composite wires because minimizing porosity is the primary condition of good mechanical properties. Composite wires were produced with different infiltration pressure (0.83 MPa, 1.03 MPa, 1.24 MPa, 1.52 MPa, and 1.65 MPa) to determine the correlation between infiltration pressure and the porosity of wires. 10 grinded cross-sectional samples were made from each type of composite wires. Based on the micrographs of these samples the volume fraction of aluminium was determined by image analysis, which also yielded information on the porosity of wires. The results show that there is direct (linear) correlation between the infiltration pressure and the decrease in porosity. These findings, however, are valid only for the investigated range of pressure. The measured values were in good agreement with the theoretical model used for comparison.

Abstract: A new “Closely Packed Equal Sphere” (CPES) infiltration model has been developed by us. It differs from the classical capillary infiltration model mainly in the value of the critical contact angle of spontaneous infiltration (50,7o, instead of 90o), and as a consequence, it also differs in the functional relationship between the threshold pressure and the contact angle. Our new equation becomes identical with the Carman equation for perfectly wettability. Our experimental results are in good agreement with these theoretical results.