Threshold velocity

Erosion-corrosion is a fairly complex failure mode influenced by both environmental factors and metal characteristics. Perhaps the most important environmental factor is velocity. A threshold velocity is often observed below which metal loss is negligible and above which metal loss increases as velocity increases. The threshold velocity varies with metal and environment combinations and other factors. 

Impediments to water flow resulting from inadequate equipment design or lodgement of foreign objects in the tubes can exercise a dramatic effect on the erosion-corrosion process. Much of this influence is linked to the creation of turbulence and the simple increase in fluid velocity past obstructions. The importance of these factors is quickly recognized when the phenomenon of threshold velocity is considered. 

If the fluid dynamic conditions of a droplet are within the spreading regime, i.e., below the threshold curve in the We-Oh map, liquid splashing and ejection from the impact surface can be eliminated. The corresponding threshold velocity can be written as ... 

The splashing criterion derived by Stow and Hadfieldl396 showed that the threshold velocity may be estimated by ... 

Yarin and Weiss[357] also determined the number and size of secondary droplets, as well as the total ejected mass during splashing. Their experimental observations by means of a computer-aided charge-coupled-device camera and video printer showed that the dependence of the critical impact velocity, at which splashing initiates, on the physical properties (density, viscosity, and surface tension) and the frequency of the droplet train is universal, and the threshold velocity may be estimated by ... 

Fig. 13.6 Erosive ratio and threshold velocity of erosive burning for high-energy, reference, and low-energy double-base propellants, showing that the low-energy propellant is most sensitive to the convective heat flux.

Detonation, Threshold Velocities Vc (Theoretical) far Impact Explosions of Massive Targets in. 

Detonation, threshold velocities Vc (theoretical) for impact explns of massive targets in detonation 4 D623... 

Susan, test (Fig 5). The threshold velocity for reaction is probably about 180ft/sec (55m/s), which is rather typical of the TNT-bonded cast... 

Impact to Detonation Threshold Velocity TATB d, Detonation Threshold Flyer Velocity, mm/y sec 42,46... 

Bagnold has determined the Reynolds number which fixes either the critical diameter or the threshold velocity gradient. He has found that when... 

When the wind moves over a bed composed of particles of mixed sizes, those most exposed will be moved first. Much therefore depends on what the bed-surface is like. If the sand is spread out so that particles of all sizes are equally exposed, then those particles will move first for which Vo is a minimum. The threshold velocity gradient as we have employed the term, refers to that value of v0 required to move the particles of predominant diameter. As the grading action continues, larger and larger particles remain on the bed-surface, and hence for these the threshold velocity gradient must increase. 

The curve shown in Figure 113 gives the sand movement in metric tons per hr per m width for various wind velocities. This curve is for sand 0.025 cm in diameter and having a threshold velocity vt = 400 cm per sec. 

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