Influence of the “Critical Velocity” Phenomenon on Chromium-Plated Gun Barrels

2003 ◽  
Vol 125 (3) ◽  
pp. 352-354
Author(s):  
Ju¨rg Ho¨lzle
Keyword(s):  
Critical Velocity ◽  
High Frequency ◽  
Pressure Wave ◽  
Design Criterion ◽  
Theoretical Studies ◽  
Chromium Plating ◽  
High Frequency Oscillations ◽  
Gun Barrel ◽  
Experimental And Theoretical Studies

A experimental 120 mm L55 tank gun barrel showed heavy loss of the chromium plating at the muzzle region. Experimental and theoretical studies led to the conclusion that high frequency oscillations, caused by the traveling pressure wave, are responsible for this effect. This so-called “critical velocity” phenomenon must be a design criterion for modern gun barrels.

Evaluation of Interfacial and Permeation Leaks in Gaskets and Compression Packing

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Ali Salah Omar Aweimer ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Experimental Testing ◽  
Design Criterion ◽  
Leak Rate ◽  
Theoretical Studies ◽  
Reasonable Accuracy ◽  
Sealing Material ◽  
Order Of Magnitude ◽  
Global Concern ◽  
Bolted Flange ◽  
Experimental And Theoretical Studies

The quantities of leak rate through sealing systems are subjected to strict regulations because of the global concern on radiative materials. The maximum tolerated leak is becoming a design criterion in pressure vessel design codes, and the leak rate for an application under specific conditions is required to be estimated with reasonable accuracy. In this respect, experimental and theoretical studies are conducted to characterize gasket and packing materials to predict leakage. The amount of the total leak is the summation of the permeation leak through the sealing material and the interfacial leak generated between the sealing element and its mating surfaces. Unfortunately, existing models used to predict leakage do not separate these two types of leaks. This paper deals with a study based on experimental testing that quantifies the amount of these two types of leaks in bolted gasketed joints and packed stuffing boxes. It shows the contribution of interfacial leak for low and high contact surface stresses and the influence of the surface finish of 0.8 and 6.3 μm (32 and 250 μin) resulting from phonographic grooves in the case of a bolted flange joint. The results indicate that most leakage is interfacial, reaching 99% at the low stress while interfacial leak is of the same order of magnitude of permeation leak at high stresses reaching 10−6 and 10−8 mg/s in both packing and gaskets, respectively. Finally, particular focus is put on the technique of precompression to improve material sealing tightness.

The Stabilizing Effect of Pre-Equilibria: A Trifluoromethyl Complex as CF2 Reservoir in Catalytic Olefin Difluorocarbenation

2020 ◽  
Author(s):  
Thomas Louis-Goff ◽  
Huu Vinh Trinh ◽  
Eileen Chen ◽  
Arnold L. Rheingold ◽  
Christian Ehm ◽  
...  
Keyword(s):  
High Selectivity ◽  
Side Reactions ◽  
Theoretical Studies ◽  
Attractive Feature ◽  
Catalyst Recovery ◽  
Wide Range ◽  
Stabilizing Effect ◽  
Experimental And Theoretical Studies

A new, efficient, catalytic difluorocarbenation of olefins to give 1,1-difluorocyclopropanes is presented. The catalyst, an organobismuth complex, uses TMSCF<sub>3</sub> as a stoichiometric difluorocarbene source. We demonstrate both the viability and robustness of this reaction over a wide range of alkenes and alkynes, including electron-poor alkenes, to generate the corresponding 1,1-difluorocyclopropanes and 1,1-difluorocyclopropenes. Ease of catalyst recovery from the reaction mixture is another attractive feature of this method. In depth experimental and theoretical studies showed that the key difluorocarbene-generating step proceeds through a bismuth non-redox synchronous mechanism generating a highly reactive free CF<sub>2</sub> in an endergonic pre-equilibrium. It is the reversibility when generating the difluorocarbene that accounts for the high selectivity, while minimizing CF<sub>2</sub>-recombination side-reactions.

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