inertial initiator , acceleration problem
inertial initiator , acceleration problem
(OP)
I have been asked to work on a inertial initiator for an artillery shell that would work at the following coditions. Its been a while since i've had to do any serious mechanical design calculations so i am unsure of how to approach calculations. Although I have no problems drafting the design idea in Acad or Pro/E.
It must initiate an all fire condition when a 950g +/- 150g acceleration of 15 milliseconds or more is applied and must no fire when a 2000g load of 5 milliseconds or less is applied.
The design i'm working on calls for a brass pistion of a known weight (60 grams or so) mounted in a SS sleave/housing. The piston would be pinned using a wire that would fail in double shear when the all fire condition exists.
In order to determine the correct sizing of a wire made from a brass alloy with known properies. Should i determine the kenetic energy of the piston generated during the firing, convert that to a force and then apply that force to the wire and work backwards to obtain a wire size that will shear at the 950g shock and not the 2000g shock.
Any suggestions would help me greatly.
Sunthorn
It must initiate an all fire condition when a 950g +/- 150g acceleration of 15 milliseconds or more is applied and must no fire when a 2000g load of 5 milliseconds or less is applied.
The design i'm working on calls for a brass pistion of a known weight (60 grams or so) mounted in a SS sleave/housing. The piston would be pinned using a wire that would fail in double shear when the all fire condition exists.
In order to determine the correct sizing of a wire made from a brass alloy with known properies. Should i determine the kenetic energy of the piston generated during the firing, convert that to a force and then apply that force to the wire and work backwards to obtain a wire size that will shear at the 950g shock and not the 2000g shock.
Any suggestions would help me greatly.
Sunthorn





RE: inertial initiator , acceleration problem
Barry1961
RE: inertial initiator , acceleration problem
The initiator will activate a chemical process via pyrotechnics in the a joining volume. This chemical process (600 C to 700 C) is very sensitive to organic materials decomposing.
RE: inertial initiator , acceleration problem
If you just use the brass wire it will become weaker with each hit as the repeated small hits cut thru it a bit at a time. Like bouncing down a rough road.
I would be wary of urethane or rubber washers after thinking about it. The spring back time may be to long.
You can get a Belleville washer that is .75" OD by .070" high that has a 432lb load rating at .007" deflection. You are going to have to use up about 207 ft-lb of energy so you may want to decrease the length of the piston and stack some washers to get the stroke you need. The washer above is one of the stiffer ones.
I would go for a much lighter piston with a long stroke and a shear hole oversized enough that the wire would not be touched by it during a false hit.
Barry1961
RE: inertial initiator , acceleration problem
The people at the testing grounds will work with you if you let them know up front what you need. Don't wait until after they build a special machine to test this and it fails before telling them.
Also remember if the test you want done takes 6 months your accounting dept. will lynch you.
Barry1961
RE: inertial initiator , acceleration problem
i didn't even think of heating of a spring if used as a damper when enviromental test are done.
RE: inertial initiator , acceleration problem
Military application, love it. Hope the Noble Prize in engineering is on the horizon.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: inertial initiator , acceleration problem
If you can use the spin it would solve a lot of the problems you would have in testing with heat. It should also be easy to make it immune to any linear forces.
Barry1961
RE: inertial initiator , acceleration problem