The fatigue limits and fracture characteristics for three Pd-Ag dental casting alloys (Super Star, Heraeus Kulzer; Rx 91, Pentron; W-1, Ivoclar Vivadent) were studied. Specimens meeting the dimensions for ADA Specifications No. 5 and 38, and having the as-cast surface condition, were subjected to heat treatment simulating dental porcelain firing cycles and fatigued in air at room temperature under uniaxial tension-compression at 10 Hz. A ratio of compressive stress amplitude to tensile stress amplitude (R-ratio) of -1 was used. Alloy microstructures and fracture surfaces were examined with a scanning electron microscope and a transmission electron microscope. Fatigue limits for the three alloys had low values of approximately 15% of the yield strength for 0.2% permanent tensile strain. Complex fracture surfaces with characteristic striations were observed for all three fatigued alloys. Planar slip of dislocations occurred in the Pd solid solution matrix, along with dislocation-precipitate interactions and dislocation networks in the interfaces between the precipitates and surrounding matrix. Twinning occurred in the Pd solid solution matrix of Rx 91, and within discontinuous precipitates in Super Star and Rx 91. The low fatigue limits for these alloys are attributed to their complex microstructures and perhaps to casting defects.
There are many more accidents of gas explosion in heading face than in other working faces. For this reason, the safety measures of the underground heading face have become particularly important. With the trend of the coal mining face becoming longer and longer, the requirements for long-distance excavation ventilation have been increasing. How to conveniently and efficiently solve the energy-saving problem of long-distance ventilation has become a hot topic. In this paper, the ventilation design scheme of the 7323 upper heading face in Panxi Coal Mine is determined based on the 7323 upper heading face in Panxi Coal Mine. In addition, through VB software, the function of accurately calculating the required air volume is realized to ensure that the local fan can provide sufficient air volume, which provides the current conditions for the analysis of safety technology and long-distance ventilation.
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