Given our last election and some of the rather unusual events I thought I would create a mathematical model to explore this strange space. So the first thing to do is to express the thing in some form and see if it makes sense. An exponential model first comes to mind such as:
One major use for explosives is in the oil and gas industry to complete a well. For a simple well the process is straightforward. The well is drilled, cased and then perforated. This involves inserting a length of tubing with a series of shaped charges along it's length into the cased well and setting off the charges that perforate the casing and the oil and gas bearing strata.
A shaped charge in its simplest form is nothing more than a metal cone surrounded by explosives. The charge is end initiated and the explosive collapses the conical liner into a jet of material that penetrates at very high velocity. The jet penetrates in the same manner as I previously posted about hypervelocity penetration. A model of a simple 65 degree angled shaped charge is shown in the first video. As the detonation proceeds up the charge the cone collapses inward in a symmetrical manner with an upwards momentum. At the collision point the cone coalesces into a jet of material that has a high velocity and has a final form of a long slender rod.
It's getting close to that time of the year when the snow flies. I like to hit the mountains once there is a fair amount of snow. These pictures are from last winter after the first storm. There was 3 feet of snow in that storm. That's me snowshoeing in (uphill, both ways) with a sleigh full of supplies.
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| Mush, Mush I say. |
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| Sweet Seclusion. |
I've been meaning to do this for some time. That is developing a Windows based system for fitting equation of state terms to experimental data, rather then relying on other people's fitting routines. One of the more common equations of state (P-v relationship) people like to use in the explosives world is the Jones-Wilkins-Lee (JWL) equation of state. There are others but I won't go into them for now. One form of the JWL equation of state for the products of detonation is given by:
The data to fit to has to be in an Excel file and can be imported directly into the application. The data file needs to be in the form displayed. The pressure units are in GPa.
I spend most of my time here talking about technology, and acquiring and using one's skills. What I haven't really talked about is the why. Why study this, why learn this, why write about it? The why is just as important as the how. I firmly believe humans are meant to explore and build. We also have a tremendous desire to determine how it all fits together and where we stand within it. Our science, art, religion, and our very cultures are a reflection of this desire. We also have a need to understand the way things work so that we may prosper as an individual and as a species. Anything that furthers this goal of knowing we undertake. Sometimes for better, sometimes for worse.
The Covid-19 pandemic is an excellent example and has brought a few things into better focus for me. I have worked my whole adult life around hazardous materials and under hazardous conditions. It's not my death or injury that concerns me, I'm used to taking that into account. A pandemic, and the response to it, potentially threatens our society and that is an entirely different matter.
Energetic materials in general and explosives in particular are incredibly important to an industrial/technological society. For propellants it's their ability to produce large volumes of gas in a short time frame during combustion. Rocket motors put our satellites in space that provide us with other forms of important technology. The airbags in your car are nothing more than an energetic material undergoing rapid combustion to fill the bag. I don't think you want to know what energetic material is probably in there.
The usefulness of explosives comes from the fast generation of gas, on the microsecond timeframe or less, that provides a large power density and amount of work available. This allows us to do extensive momentum transfers for a relatively low cost (blasting for mining and construction). The metals production industry, and subsequent manufacturing industries heavily depend on the low cost production of raw materials. The power densities in explosives allow for the high velocity acceleration of metals which produces the shaped charge effects needed in oil and gas well completion.
I've posted about some aspects of interior and exterior ballistics but I haven't mentioned the last part of the puzzle, terminal ballistics. Approximately 65 million years ago, it was a very bad day for planet earth. An asteroid impacted at hypervelocity speeds and the ensuing disaster killed off a vast percentage of life on earth (nearly 75% of all species). So this post is about terminal ballistics or impact phenomena.
But first, a video simulating that asteroid impact. The projectile is a nickel/iron mix and the planet is simulated with a layer of water over silica. Consider the scale of the impact. In the model the projectile is scaled such that it would have been about 8 miles long by about 5 miles in diameter. The resulting crater depth would have been nearly 10 miles or roughly twice the height of Mt. Everest.
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