Sciencemadness Discussion Board - Plate-dent testing of explosive charges

Plate-dent testing of explosive charges

Deceitful_Frank - 7-1-2006 at 10:48

Hello again all. I understand that the content of this thread could be perceived as practical application of explosives and damaging of property, (mine) but I am hoping that if I present this in a scientific and articulate manner then it will get a thumbs up from the moderators.

Whilst out cycling a week ago I stumbled across a sheet of 4mm steel plate propped up between a crash barrier and a hedge! Quite sizable and in the region of 150cm square and having a calculated mass of just over 70Kg... I'm not ashamed to admit that I cannot lift it

Anyway, a couple of days ago I decided that I would claim it and put it to good use so I paid another visit with a view to stashing it somewhere secluded before someone got there first. With great effort I manged to wrestle it over the two foot barrier and some 100 yards down a canal footpath where I gracefully threw it in to a very large bush! Yesterday a friend and his father collected it for me and it is now sat in a garage, patiently awaiting a duel with an anglegrinder.

I want to use sections of this steel plate to do some carefully thought out, controlled scientific tests to determin the difference in power/brisance of several explosive charges, all with equal volume ond footprint but obviously differing in mass and density.

They are as follows:

Three charges, each 250ml of my own knipack type formulation at density 1.0, 1.05 and 1.1g/cm3. these charges would oviously range in mass from 250 to 275 grams. I'm aware that ANxx compositions generally fire better at lower densities but I want to find out at which of these three would the brisance/power peak (1.1g/cm3 is as high a density that I can evenly obtain in a handpressed 5cm diameter charge)

With these three charges I would also like to fire a 250ml 60% gelled EGDN, AN sawdust dynamite charge.... identical in volume and footprint though at around 1.4g/cm3 and 350g

Lastly as my fifth plate dent dest I'd like to make one of AXT's ANNMSA charges of said dimensions. Not quite sure of the formulation I'll use as his oxygen balanced for CO2 ratios differ from mine... this will probably need more thought.

I plan to fire each charge identically placed on seperate identical plates and all supported in an identical mannar... maybe three rubber tipped pencils in the ground though I am not sure if this will provide the plates with enough inertia to give good deep and quantifiable denting with these charges? All tests would be carried out within minutes and filmed in one shot from a distance of 30-40 metres to allow the differing sound qualities and intensities to be fairly scrutinised. This should negate differences in atmospherics that could render this data useless.

Now! ... what I;d like from you guys is some idea of how large I should cut these square plates and how to best support then for these tests to maximise their inertia and get usefull and controlled results. I'm thinking that three points of contact with the plates is essential and the larger their size the better?

Obviously I would welcome any other thoughts and ideas!

Thanks in advance

Axt - 7-1-2006 at 13:05

Quote:

Originally posted by Deceitful_Frank
Not quite sure of the formulation I'll use as his oxygen balanced for CO2 ratios differ from mine... this will probably need more thought.

It was formulated with the constraint of having to contain 40% NM, so you cant improve oxygen balance over ~-4%, which shouldn't matter in the whole scheme of things. The ratio is also limited by the solubility of AN in H2SO4, best if it all dissolves.

The plates would be best placed onto soft sand and fired.

Microtek - 8-1-2006 at 10:08

Frank: It seems as if you intend to measure the depression an explosively accelerated plate will make in the ground ? The standard plate dent test is simply to measure the dent in the plate caused by the shock wave itself.

Deceitful_Frank - 10-1-2006 at 13:54

No, I am not hoping to measure the effect on the ground but to measure the depressions on my steel plates.

I have since settled on squares of 42cm length and width though I have also since learned that this is very substantial sheeting... 5mm thick!

I do not have access to soft sand as axt suggested and do not want to venture to the beach as it difficult to find a secluded spot. At this point I am seriously considering two lengths of 2X2X14 to support each steel plate and conducting these tests on the concrete wal at my usual test site.

Nothing is set in stone as yet though.

Microtek - 11-1-2006 at 04:51

I don't think 5 mm will be thick enough; 250 g of a reasonably powerful HE will almost certainly cut the plate completely.

From "Explosives" Kohler, Meyer and Homburg:

Quote:

Method A – The charge is contained in a copper tube, having an internal diameter of 3/4-inch and a 1/16-inch wall. This loaded tube is placed vertically on a square piece of cold-rolled steel plate, 5/8-inch thick; 4-inch and 3-1/4-inch square plate gave the same results. The steel plate is in a horizontal position and rests in turn on a short length
of heavy steel tubing 1-1/2 inches ID and 3 inches OD. The charge rests on the center of the plate, and the centers of the charge, plate, and supporting tube are in the same line. A 20g charge of the explosive under test is boostered by a 5g pellet of tetryl, in turn initiated by a No. 8 detonator.

Method 13 – A 1-5/8-inch diameter, 5-inch long uncased charge is fired on a 1-3/4-inch thick, 5-square inch cold-rolled steel plate, with one or more similar plates as backing. The charge is initiated with a No. 8 detonator and two 1-5/8-inch diameter, 30-g Tetryl boosters.

Boomer - 11-1-2006 at 06:54

Wanted to predict the same. Since you will not likely find (and move) a thicker plate soon, could you use much smaller charges? 5mm steel is rather common and not all of use want to use pound after pound to do comparative tests if we get some plate.

Any way to find out what type of steel you have, like tensile strength? I guess it is construction steel, no NiCr etc. You might saw off a thin piece and compare to steel of known strength (by putting weights on one end and measuring how it bends, or by cutting with a cutting bench (? like giant scissors) and measure the lever force it takes). Yust a rough idea but better than nothing. Or use a 'standard' explosive in a 'standard' (see above) test, then compare with published dent depth!

Deceitful_Frank - 11-1-2006 at 10:05

Microtek, I do see your point about the steel being too thin at 5mm but I must say, this is extremely tough and heavy sheeting and althought my kinepack does an excellent job at shattering concrete, I wouldnt consider it to be THAT powerful/brisant in comparison with for instance, a decent commercial dynamite or a cast charge, quite simply because with a usable and cap sensitive density of just 1.0-1.1g/cm3, its bulk strength would not be high.
I have looked at the book to which you refer and strangely they describe two plate denting tests but dont give any results or even draw conclusions! However, I suppose we can safely assume that they know what they are doing and would choose suitable plate thicknesses and charge sizes

Boomer, I suppose I could use smaller charges but through experience I have found that this kinepack type formulation doesnt really do itself justice untill the charge size gets over 200 grams, this would be my smallest charge at 1.0g/cm3. Obviously I would then follow this with a 210g and a 220g, all packed into identical vessels one and a half times as tall as they are wide and with the same volumes and footprints.
I wasnt aware that there could be that much difference between 5mm steel plate and 5mm steel plate. Its not a high strength nickel chromium alloy as it is very much NOT stainless but a nice even shade of orange-brown

Microtek - 12-1-2006 at 07:18

I don't have much experience with ANNM compositions, but I can tell you that 1.5 g of a homemade 85 % PETN based plastique was powerful enough to blast a hole in 2.5-3 mm steel.

There is also the problem that if the charge is almost powerful enough to actually penetrate the plate, it would likely give a non-linear ( and perhaps not replicateable )denting depth dependent on the exact power of the charge.
So, I think that you can get better measurements by using a greater plate thickness ( or possibly by using several stacked plates ).
However, there is no harm in just performing the experiment to see what happens....

Boomer - 13-1-2006 at 03:44

To give you some figures: A slighly more than chestnut sized lump of HDN/MHN/NG plastique ripped a flat iron of 6x50mm in two pieces. 25g of the same but with RDX/MHN/GPN cleanly cut a 5x100mm plate in two, this time as a ribbon charge. This equals 2.5 grams or only 1.5 ccm per cm of plate at 5mm thickness.
With a cavity (lined AND unlined), 43-45g of gelled dynamite cut a 1cm (!) plate 10x10 cm in two pieces.

Admittedly densities were higher, between 1.6 and 1.7 g/ccm for the first two, and 1.5 g/ccm for the dynamite. Power was not much higher than kinepack, maybe 20-30% (negative OBs). So judge for yourself or take a small piece and test 50g on it.

Deceitful_Frank - 15-1-2006 at 13:40

Well it seems that you guys were right about 250 grams of kinepack being too powerful to give quantifiable denting WITHOUT bursting through 5mm steel plate!

After reading your posts I decided to perform a dummy run against the first cut 42cm square plate using a roughly put together 250 gram charge at about 1.0g/cm3. This was to figure the kind of penetrating power I was dealing with and to save wasting any more of this difficult to cut sheeting and time consuming to prepare kinepack than was necessary.

The test was performed last night in a field chosen to be some 400 yards from the nearest dwelling. The charge was placed supported by a raised tuft of grass and a length of 2X4. The charge placed atop, a 1 gram HMTD 15 second delay detonater inserted and lit.

We retired to about 30 metres and che charge detonated with the expected loud report.

On returning to the charge and test plate we found it to be completely penetrated and by the look of it, missing some material from the centre. The blast had naturally continued downward and produced a sizable hole in the groud.

So it seems this experiment needs more thought! I could reduce the size of the charges but I am not prepared to go below 200 grams as I have not had good results with small charges of kinepack below this mass. 200 grams will be the mass of my smallest charge.
This does simplify things but means I need to either find a stronger target, I dont want to have to do this! Or... figure out a way to tame the blast in a totally reproducable way.

Platey.jpg - 211kB

12AX7 - 15-1-2006 at 16:23

Thinking out loud:
Stack of plates?
Elevate the charge?
Different medium?

Etc.

Tim

Boomer - 16-1-2006 at 04:20

Nice hole, you really showed it to the bitch!

Why does it need 200g minimum? Is self-acceleration needed - then use a (small) booster. Or was that only your *impression* that it was low-order? I would definitely go smaller to save cutting time, you don't want to use (+ carry) a stack of those!

BTW I just tested 40g of 1:3 EtONO2/AN on a 6mm plate. Made a small dent (6-8mm), since it had only 1" dia, but was too long. A thicker but shorter column would have been slightly better, also because of the diameter-effect on VoD. Unfortunately this was a single piece of plate. But I *did* find my stash of steel plates that were lost for a year. There should be some that are 5mm - happy testing!

Axt - 16-1-2006 at 08:27

Example 10 of the original kinepak patent used 5/8" (~16mm) to test 205g charge of ANNM/xylene (I'm assuming thats what you used). It mentions the plate "severly bent and dented". Meaning that your gunna need at least three of those plates if you dont want to reduce the charge size.

Alternatively, buy some sections of heavy steel pipe, inherently stronger then plate and wouldn't have to cart nearly as much weight, lets you measure how much its squashed.

Quote:

Originally posted by Boomer
BTW I just tested 40g of 1:3 EtONO2/AN on a 6mm plate. Made a small dent (6-8mm)

At that ratio I assume its completely saturated? It may have the same shortcomings as NM in that once saturated sensitivity is lost, resulting in LVD's and partials (such as example 9 of patent). COPAE mentions that ethyl nitrate isn't sensitive to a #8 under light confinement.

Quote:

Originally posted by Deceitful_Frank
Lastly as my fifth plate dent dest I'd like to make one of AXT's ANNMSA charges of said dimensions. Not quite sure of the formulation I'll use as his oxygen balanced for CO2 ratios differ from mine... this will probably need more thought.

You may want to try upping the NM content? I never did try more with the presumpition that It probably wouldnt hold together, but I did just now solidify a couple hundred ml of EtOH/NaOH by precipitating a few grams of CH2NO2Na with NM. Idea, perhaps ANNMSA actually can be made to hold more NM, see for example if 60:40:20 will hold together as a solid when mixed & precipitated.

[Edited on 16-1-2006 by Axt]

Attachment: kinepak patent.pdf (669kB)
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Boomer - 17-1-2006 at 04:33

It was a moist powder if slightly tamped, but when compacted by body weight it made "quatsh quatsh" sounds, i.e. all voids were filled.
Finely powderd AN takes more NG, but at the lower density
it was about what I expected for EtN. 1:3 is CO2 balanced btw, and has a density
of 1.45 if compacted. The question is whether it goes low order in that state. EtN *is* more sensitive than NM,
and is said to det well
if absorbed in a solid. I doubt the value of 50cm/2kg, could that be for a 500g weight? Other sources say it is similar to NG, which I doubt again.
My *guess* would be close to PETN or RDX, 50cm is between picric and TNT! At least I could not det it with a hammer (before it evaporated).

Why the f*ck do I have to hit return to keep lines from stretching over five screen? The board would format well until recently.

[Edited on 17-1-2006 by Boomer]

Deceitful_Frank - 19-1-2006 at 11:10

Quote:

Originally posted by Boomer
Nice hole, you really showed it to the bitch!

Why does it need 200g minimum? Is self-acceleration needed - then use a (small) booster. Or was that only your *impression* that it was low-order? I would definitely go smaller to save cutting time, you don't want to use (+ carry) a stack of those!

BTW I just tested 40g of 1:3 EtONO2/AN on a 6mm plate. Made a small dent (6-8mm), since it had only 1" dia, but was too long. A thicker but shorter column would have been slightly better, also because of the diameter-effect on VoD. Unfortunately this was a single piece of plate. But I *did* find my stash of steel plates that were lost for a year. There should be some that are 5mm - happy testing!

Well the reason I dont want to go below 200 grams is basically because I have not been "impressed" by the power of this explosive in charges that small. I know this doesnt exactly sound that scientific or rational but I assumed that this explosive needed a minimum diameter or atleast a strong casing to help it self-confine and reach full velocity without just blowing itself apart?

Maybe I am seriously misguided but another reason is that I feel the larger the charge, the easier it is to replicate it a controlled manner whilst varying the density and the less the effect of unknown variables like imperfections in the steel surface etc!

Lastly there is the matter of finding suitable casings that are cylindrical, reasonably strong and one and a half times as tall as they are wide. I have a source of HDPE pots that fit this criteria and feel this shape is the best trade off between maximum footprint and diameter whilst being tall enough to allow all of the shockwave to arrive across the entire bottom surface of the charge within the minimum amount of time... therefore transfering maximum brisance to the target

Anyway, all this is pretty much acedemic now as I have decided not to persue these plates to test my "kinepak"
I dont think that I have the means to construct a charge that is small enough to dent this plate but without falling foul of not being able to meet the same tolerences that I can with a larger charge. After reading Axt's post I feel that steel tube denting is the way forward and the plate can be saved perhaps for sandwiching and shaped charges and the other little project I have in the pipeline but I may start a new thread for that of include it in the EGDN one

[Edited on 19-1-2006 by Deceitful_Frank]

nitro-genes - 19-1-2006 at 11:46

From my own experimentation 25% NM containing ANNM requires somewhere between 3 and 4 cm in diameter, so 50 grams charges are definitly possible. (750 milligram petn @ 1,6 cm/3 blasting cap).

Nitromethane is very resistant against low-order detonation, so I think the diameter of the charge may have less effect on the DV and brisance than with other explosives, like nitroesters...

[Edited on 19-1-2006 by nitro-genes]

Deceitful_Frank - 19-1-2006 at 11:55

My "kinepak" contains 16% NM by mass and I use 1.1g HMTD in my blasting caps... I suppose we could say that 100 gram charges could have been ok if what you say is plausable

2 inch Steel pipes are ALOT stronger plus with two layers of metal to penetrate... I would NOT be using 100 grams for these! The contact area will also be far less

[Edited on 19-1-2006 by Deceitful_Frank]

Microtek - 20-1-2006 at 11:52

What do you mean when you say "two layers of metal to penetrate" ? If you mean both ( opposite ) sides of the pipe, then you will still have big reproducibility problems if one side is even close to being penetrated.
You need a target that is so strong that your charge is nowhere near powerful enough to penetrate; the stress/strain deformation of the metal will not be linear over the whole range of deformation to penetration.
For this reason you need to limit the power of the charges so they only just "scrape the surface" of the target. That way you can assume with some confidence that brisance/deformation curve will be reasonably smooth.

Deceitful_Frank - 20-1-2006 at 12:17

I think that you misunderstood what I meant about the two layers to penetrate.

I didnt mean as concerning economy and being able to use both sides of the same pipe for two tests!

I meant that with a charge fired on one side, even if it rips through the first layer on all three pipes, chances are I'll be able to defferentiate the difference in power of the blasts on the SECOND layer of pipe OPPOSITE THE FIRST... AFTER they have passed or IF they pass through the first layer

I hope this makes sence.

My 5 cm pipes will probably be a foot long and firmly supported and held at the ends to give the whole deal as much inertia as possible... the charge placed centrally above the pipe to make use of the downwards blast force.

Microtek - 21-1-2006 at 00:20

That's what I thought you meant. I still say that the impact on the far side will be a very unreliable measure of the power. For the reasons I stated above you really do need something that is quite impenetrable to your charges.

Boomer - 23-1-2006 at 01:42

Or, if you have a way to collect fragments (abandoned cellar?), just fill the pipes! There is a brisance test using heavy steel pipes, and brisance is given as a percentage of frags under 10g.
The results, even if the 10g limit is random, are within 5% of the calculated values (d*VoD*Specific Energy/ old "Kast" Brisance values).
I have to look up in which book I found the table, and the exact pipe specification. IIRC they were 32mm ID with 9.5mm walls.

Deceitful_Frank - 25-1-2006 at 01:26

I dont have access to an abandoned cellar though I am a keyholder to a local bar. The beer cellar is genaerally filled with barrels though!

As for filling steel pipes with explosives, I gave this up 15 years ago! These were the days of steel scaffold piping, weed killer and icing sugar. It still makes me cringe when I remember sitting in my garden hammering flat the ends of these FILLED tubes and THEN drilling my fuse hole

Besides, the idea of spendind an afternoon extracting steel fragments from a brickwall doesnt exactly fill me with glee.

I suppose it could be done on a smaller scale with charges burried on the beach and covered with a steel plate... I think I'll stick with the pipe denting for this one. My coffee grinder just gave up the ghost so it may be a while yet.