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23rd July 2019, 08:14 #1
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Is 17g/30ms shock force greater than 5g/100ms?
Hi, Gurus,
In EIRENE test, a standard of EU train on handheld, "The Operational radio shall be capable of withstanding the following shocks:  semisinusoidal shocks of up to 5g for up to 100ms under normal conditions."
Now since the test lab can NOT reach 100ms, only can reach to 30ms, so if can say, "17g/30ms shock force is greater than 5g/100ms?"
I just want to get the same force as 5g/100ms, not very much gretaer.
I think the force is relate to momentum, i.e. MV. Since M doesn't change, the force is relate to velocity(V). Then the shock force is proportinal to V, which is a*t, so for 5g*100ms, we need 17g*30ms. I don't know if it is right for such calculation.
Pls comment.
Best,
Tony Liu

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23rd July 2019, 13:46 #2
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Re: Is 17g/30ms shock force greater than 5g/100ms?
force is relate to momentum, i.e. MV. Since M doesn't change, the force is relate to velocity(V)....
Force is related to the change in momentum (rate) and is not dependent on the absolute velocity.
I guess the "g" refers to the acceleration due to gravity the acceleration is directly related to the force. The time refers to the duration of the force.
Actually 5g/100ms should be represented as 5g.100ms  force into time is impulse of a force.
Hence 17g.30ms =510 (g.ms) is approximately the same 5g.100ms =500 (g.ms).
Basically this is equal to delta(v); change in velocity (before and after). We use impulse when the actual force acting on the system cannot be accurately measured.
Your results are correct but the logic is not accurate.
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24th July 2019, 03:59 #3
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Re: Is 17g/30ms shock force greater than 5g/100ms?
Hi, c_mitra,
thanks for the reply.
Normaly the DUT starts from still, means V0=0m/s.
Then the equipments starts acceleration, the acceleration is an impulse. So the final velocity is the integration from 0 to Pi, semisinusoidal, for sin(2*pi*f*t), with peak acceleration.
For 5g.100ms, it should be 5*[2/(2*pi*5Hz)], for Xg.30ms, then be X*[2/(2*pi*16.6Hz)], these two functions should be equal, so X=16.6g.
Right?
Best,
Tony Liu

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24th July 2019, 04:46 #4
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Re: Is 17g/30ms shock force greater than 5g/100ms?
Right?
The assumption is that the force is acting on a rigid body. If the same impulse is applied for a shorter time (say 1ms), the force will be much greater but the duration will be much less and the overall result will be same.
But if the body is not rigid, it will produce shock waves that can affect other properties (glass items can *****).
I do not know how to calculate the effects on elastic bodies (or plastic matters).
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