Previous studies on vented gaseous deflagrations with inertial vent covers and related regulatory aspects are examined. The model of turbulent deflagration dynamics, built on energy and mass conservation principles, is developed further to take into account the influence of vent cover inertia. An engineering formula for conservative estimation of the upper limit of vent cover inertia is presented. Similarity analysis has shown that the scaling relationship between the surface density of the cover, w, and the turbulence factor, , is w 3 ϭ const, indicating a significant interrelationship between vent cover inertia and venting-generated turbulence. Results confirm that turbulence gradually increases after vent opening begins, so that it is possible to increase vent cover inertia significantly. It is demonstrated that instead of widely accepted surface density limits of about 10 kg/m 2 , values of one/two orders higher, depending on the conditions, could be used for explosion protection with 100% efficiency for largescale enclosures.
Hybrid machining processes represent a potential approach to meeting the constantly increasing demands on cutting. In ultrasonic-assisted cutting, as a part of hybrid machining, the machining process is superimposed with a high-frequency vibration of small amplitude. This paper presents investigations on the drilling of stone materials, i.e. different granites and marble, in which this process is applied. It could be observed that the resultant forces and torques were reduced, which had already been discovered in investigations of various other materials. The influence of different parameters on the force reduction is shown, which is basically similar to the theoretical reduction of friction by ultrasound for small speed ratios d, but is considerably increased. This increase must be due to other effects. Besides the force reduction, a reduction of cratering at the drill exit can be observed. Based on the present results, definite conclusions on tool wear cannot be drawn yet.
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