Lecture 5 - Explosions 5 Flashcards
how does an explosive detonate
in response to a stimuli these can be direct or indirect
name three types of direct stimuli
electrical
mechanical (percussion)
deflagration into detonation
name three types of indirect stimuli
magnetism
acoustic (sound waves)
radar
what is percussion and
what is an example of percussion detonation in guns
striking the explosive leading to a direct explosion of low explosive propellants
pulling the trigger moves a hammer which hits a cartridge case setting off the propellant
the percussion results from a localised heating in a small volume and the hammer compressing gas voids
what issues may arise in percussion detonations in guns
cracks of the cartridge casing due to air compression and heat generation
resulting in a non uniform detonation as not all the energy and gas is going where we want it to
name another example of a percussive force detonation we looked at
‘stabbing’ based systems for example a needle stabbing the explosive to initiate it
what issues can arise with using needles to initiate an explosive
dealing with a smaller area
needle can bend = a misfire (blunt the end of a needle to avoid this)
some material are sensitive to stabs and others are not
in a stabbing detonator what two types of initiation tend to be combined
percussion and friction
which detonation technique is used often in large explosive devices
stabbing
compared to stabbing and percussion what is a more controlled method of detonation
use of electrical detonators
how do electrical detonators works
they heat up the explosive so it detonates
an electrical current is passed through a tungsten filament which gets hot due to resistance
in low power electrical detonations what type of primary explosive is commonly used to start the detonation sequence and why
lead styphnate
it is very sensitive so quick initiation
but it doesn’t have the highest explosive power
explain the concept of an explosive train
there are multiple stages for detonation to occur
pyrotechnic mix leads to a more sensitive primary explosive initiating then a secondary explosive because of this and so on
the main charge is often hard to initiate so we use other more sensitive ones to get it going
what is the difference between a low power and a high power electrical detonator
a low power uses lower currents than a high power
in higher power the wire goes into the actual explosive in lower power it is in the primary explosive used as a propellant
what type of detonator uses electrical current to indirectly detonate an explosive
a slapper detonator
how does a slapper detonator work
wires are connected to a thin metal plate which is propelled the slapper plate into the explosive material at high velocity
the current makes a percussive force driving the plates forward
this initiates an explosive shock
is a slapper or electrical detonator safer and why
slapper
avoids putting electrodes directly in an explosive material
less prone to accidental detonation as harder to accidentally put an electrical current through the explosive
more controlled
when are slapper detonators used over electrical ones
for precise applications e.g nuclear weapons for controlled compressions
as better than relying on a needle for example
can also have multiple slappers in different directions
what is a blasting cap
a small explosive device used to detonate a more powerful explosive
name the 5 types of blasting cap we looked at an how they work (brief)
in the answer BP = blasting cap
1 = pyrotechnic fuse type BP = there is a pyrotechnic ignition mix in front of the primary explosive which comes into contact with the fuse crimped before it
2 = solid pack electric type BP = a wire is embedded in the insulation header and just into the primary explosive, wire heats up at detonates primary explosive then secondary
3 = match or fusehead electric type BP = there is an electric match that contains pyrotechnic material also a wire in the insulation header - wires heats up and pyrotechnic burns then sets of primary explosive then secondary
4 = exploding bridgewire type BP = bridgewire or foil after insulation header, wires heats rapidly and vapurises
5 = slapper type BP = slapper foil after insulation header, wire heats and vapourises causing slapper to push forward with high velocity
what are blasting caps made of chemically
the pyrotechnic ignition mix = metals mixed with salts
followed by the primary explosive = can be a mixture often see addition of Al (oxidiser)
then the secondary or output explosive = main charge
what does the crimping of a fuse allow
the fuse to not fall out and allows good contact between fuse and pyrotechnic mix
when are match or fusehead electric type blasting caps good
when you want to control the explosion and have a slight time delay - allow people to move away
what component of the blasting caps allow these explosive to be traceable
the metals within the pyrotechnic mix e.g Ti, B, Zr
