Pressure-time curve

Impulse A measure that can be used to define the ability of a blast wave to do damage. It is calculated by the integration of the pressure-time curve. 

Figure 3-51. Pressure-time curves for single-acting and double-acting pumps (one piston) [21].

Figure 3-52. Simplex (double-acting), duplex (double-acting), triplex (single-acting), pressure-time curves [21].

Impulse or duration of the blast load (Impulse is the area under the pressure-time curve. Duration is the length of time of the overpressure phase of the blast wave.)... 

Impulse The integration of the pressure-time curve for a given duration. 

Figure 23-10 shows a device used to characterize the combustion of dusts. In this case, the dusts are initially contained in a small carrier external to the vessel, and the dust is blown in just prior to ignition. A typical pressure-time curve for the dust apparatus is shown in Fig. 23-11. The vessel is initially at a pressure less than atmospheric, but the pressure increases to atmospheric after the dust sample is blown in. After the dust is blown in, a delay time occurs in order for the dust to become quiescent but still suspended in the gas. The results are highly dependent on the delay time.

In Figure 3.1, the time over which the blast wave overpressure lasts is referred to as the positive phase duration, or simply duration. The area under the pressure-time curve is the impulse of the blast wave. Consequently, the positive phase impulse, I0, is defined as follows ... 

In order to use the dynamic response charts based on a triangular shaped load, the bilinear pressure-time curve shown in Figure 3.7 can be simplified to an equivalent triangle. This equivalent load is computed by equating the impulse for each load shape and using the same peak pressure, Pt. The impulse, I, under the bilinear pressure-time curve is ... 

Fig. 13.19 Pressure-time curves of stable and unstable combustion in a rocket motor.

Therefore, the pressure-time curve for the combustion of the gunpowder lifting charge will be approximately as illustrated in Figure 4.5. 

Figure 4.5 Approximate pressure-time curve for combustion of lifting charge within a mortar tube.

The break point is defined as the point in the pressure-time curve that is preceded by a pressure drop of exactly 2 psi within 15 minutes and succeeded by a drop of not less than 2 psi in 15 minutes. 

It is further stated by Reitzner in Ref 37b, p 13f, that Arrhenius simplification does not take into account that a large number of expls follow an autocatalytic reaction mechanism, fn the case of the inorganic azides, for example, the metal is considered to be the autocatalyst. The pressure-time curves for such autocatalytic reactions are characterized by an induction period, followed by acceleratory and decay periods. 

Hauver concluded that pressure-time measurements with a sulfur transducer in contact with detonating Baratol gave clear evidence of an initial pressure spike, and lends addnl confirmation to the hydro-dynamic theory of deton proposed by von Neumann and others. The sulfur transducer appeared capable of good resolution over that portion of the pressure-time curve corresponding to the reaction zone, and may offer a method for investigating the reaction process Refs 1) S. Joigneau J. Thouvenin, "Electrical Conductivity of Sulfur Under the Action of a Shock Wave , CR 246, 3422-25 (1958) 2) G.E. Hauver,... 

Haid, Becker and Dittmar Stability Test (Designed for high explosives). 42g of powdered explosive, previously dried over phosphorous pentoxide, is introduced through a side tube into a glass vessel connected with a manometer which is in the form of a U-tube and contains mercury covered with a layer of paraffin oil. The glass vessel is also fitted with a side tap. The ensemble is heated at 75° for several hours and pressures are recorded in mm of Hg as a function of time. The steeper the pressure-time curve the less stable is the explosive... 

Kj and K2 (of Muraour). For a proplnt whose burning rate, V, may be expressed by V=a+bp, where a and b are constants and p is the ambient pressure, Muraour defines a constant, Kj, which is the total area under an ideal pressure-time curve, and not the real pressure-time curve. 

Another adsorption characteristic which can be deduced from the primary experiments described above is the evaporation rate E. This i.s the number of molecules of nitrogen which leave the surface per square centimeter per second and which previously were chemisorbed as atoms. That nitrogen leaves the surface as molecules rather than as atoms follows from the experimental fact that the flash-off experiments yield the same values as the pressure-time curves. If the nitrogen came off as atoms, it would stick to glass walls and would not reach the ion gauge bulb to be recorded as a sudden increase in pressure. Only at very high flash-off temperatures is the evaporation rate of atoms comparable with the evaporation rate of molecules. 

In addition to measuring shock wave and bubble energies, underwater tests also can measure the shock wave impulse, another indicator of explosive strength. The shock wave impulse is derived by measuring the area under the pressure-time curve for a selected integration time interval at a known distance from the explosion... 

The three compounds exhibit the major superficial features of hydrocarbon combustion the pressure-time curves are sigmoidal, and the rate of reaction, as given by (dAp/dt)max, exhibits a region of negative temperature coefficient. 

Cd azide produced pressure-time curves similar to Pb azide. Irradiated Ag azide did not show any acceleration, but this may be due to the... 

Fig 1 Schematic Pressure-Time Curve for High Order Detonation... 

Effect of Sample Holder Geometry on Pressure-Time Curves of Lead Dioxide-Cupric Oxide-Silicon Starter Composition A New Test Fixture Design , NAVAMDEP RDTR142, Crane (1969) 9a) J.R, Gibson J.D. Weber, Hand-... 

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