Quantifying explosions - how to determine force/pressure/etc?

[denver75]

We're doing another demonstration about explosives, discussing the forces created.

Our primary explosive is PETN (detcord) - handled by a licensed technician of course.

I need to prepare some facts about the physical forces at play with the explosions. How can I quantify the energy expended? I've been digging around and the only statistic that is readily available is the rate of detonation. However, as more explosive material is used, the rate of detonation doesn't increase, but the explosion does.

Any info/facts/stats/formulas that might get me on the right path?
Thanks!
-D75

 

[Civilized]

I don't have any expertise in this area, but I do recall that the equation:

$$R = (\frac{E t^2}{\rho}})^{\frac{1}{5}}$$

where R is the radius of the explosion at time t, E is the released in the explosion, and $\rho$ is the ambient density of air in the vicinity, was correctly used by a physicist who wasn't working on the Manhattan project to determine the energy released in the trinity test based on measurements of R vs t, although the value for the total energy was classified for decades, this method yields the answer within 10%. By the way, the formula should also apply for light explosives too.

I will wait for others to say more, since I don't know much about explosives.

 

[astrokreng]

I understand the importance of accurately quantifying the forces and energies involved in explosive reactions. There are several factors that contribute to the force and pressure of an explosion, including the type and amount of explosive material used, the confinement of the explosion, and the surrounding environment.

One way to quantify the energy expended in an explosion is by calculating the explosive energy, also known as the detonation energy. This is the total amount of energy released during the detonation of the explosive material. It can be calculated using the following formula:

Explosive Energy = Mass of Explosive x Heat of Explosion

The heat of explosion is a specific value for each type of explosive material and can be found in reference tables.

Another important factor to consider is the rate of detonation, which is the speed at which the explosive reaction propagates through the material. This can be measured using a detonation velocity meter or calculated using the following formula:

Detonation Velocity = Distance of Travel / Time of Travel

It's also important to note that as more explosive material is used, the rate of detonation may not necessarily increase. This is because the explosive reaction can reach its maximum speed, known as the Chapman-Jouguet velocity, and any additional material will not significantly impact the overall force of the explosion.

In addition to these calculations, it's also important to consider the blast pressure generated by the explosion. This is the force per unit area exerted on the surrounding environment and can be measured using specialized instruments like blast gauges.

Overall, quantifying the forces and energies involved in an explosion requires a combination of measurements and calculations. I recommend consulting with a licensed technician and using reliable reference materials to ensure accurate and safe demonstrations.