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Car hitting a mass 1
- Thread starter Perrot
- Start date
It depends on how stiff and springy the car is. It will apply very little if that mass is aligned with the side mirror or even the windshield. It will apply more force if it hits the engine block. It also matters if the item is dense or not and what those properties are. You may hit 200 pounds of air while driving a car in a few minutes.
it depends on the time the impact takes. If it is "instantaneous" the force is "infinite". If it takes some time (1 second, 1 millisecond ?) then the force is finite, but depends on assumptions ... uniform deceleration ? "spikey" non-uniform deceleration ??
to get sensible numbers you need to test, or if you trust FEA, run something like Ls-Dyna.
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
to get sensible numbers you need to test, or if you trust FEA, run something like Ls-Dyna.
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
GregLocock
Automotive
In the simple case of side impact a 1 dimensional model of a series of springs masses and dampers gives a good estimate of the force pulse into the structure
Development of a new lumped-parameter model for vehicle side-impact safety simulation
A Deb* and K C Srinivas
Centre for Product Design and Manufacturing, Indian Institute of Science, Bangalore
Here's one I did earlier
rov is rest of vehicle (ie the main body), mdb is the mobile deformable barrier. The difference between the two forces is due to the energy used to deform the structure
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
Development of a new lumped-parameter model for vehicle side-impact safety simulation
A Deb* and K C Srinivas
Centre for Product Design and Manufacturing, Indian Institute of Science, Bangalore
Here's one I did earlier
rov is rest of vehicle (ie the main body), mdb is the mobile deformable barrier. The difference between the two forces is due to the energy used to deform the structure
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
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1
- #6
clearly you don't know that Greg is not a Brit (or at least not living in Britain) ...
and to "accuse" him of such is "fight'n' words" ...
as a fellow "non-Brit".
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
and to "accuse" him of such is "fight'n' words" ...
as a fellow "non-Brit".
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
LittleInch
Petroleum
Given the large discrepancy in mass, the 200lb mass will accelerate to about 23mph.
The question for F=mxa, is how fast does it do it. My guess would be about 1/2 second to maybe 1 second.
Then it's just maths.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
The question for F=mxa, is how fast does it do it. My guess would be about 1/2 second to maybe 1 second.
Then it's just maths.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
LittleInch
Petroleum
"Here's one I did earlier" is an iconic phrase in the UK for those of us of a certain age....
Came from a long running kids TV programme (Blue Peter if anyone is interested). It might have been exported to Australia?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Came from a long running kids TV programme (Blue Peter if anyone is interested). It might have been exported to Australia?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
I'd imagine the post impact speed would be less then 3200/3400*25mph assuming some energy lost in the impact.
This is an unusual impact question, in that the target is not immovable (like a barrier), but instead just some mass that the car has to bring up to speed. If you assume 1 second for the impact, then the car would travel something like 25*1.5 = 38 ft ... unreasonable. a 1/100th of a second would be 5 inches more reasonable but still large.
How much friction between the mass and the ground ? If it is on wheels, the answer is very different.
If the post impact speed is 20 mph, then the car gave the mass an acceleration of 30 ft/sec per second of impact ... if the impact lasted 1/100th of a second then 3000 ft/sec/sec or about 100g or a force of 20000 lbf (with a tonne of caveats).
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
This is an unusual impact question, in that the target is not immovable (like a barrier), but instead just some mass that the car has to bring up to speed. If you assume 1 second for the impact, then the car would travel something like 25*1.5 = 38 ft ... unreasonable. a 1/100th of a second would be 5 inches more reasonable but still large.
How much friction between the mass and the ground ? If it is on wheels, the answer is very different.
If the post impact speed is 20 mph, then the car gave the mass an acceleration of 30 ft/sec per second of impact ... if the impact lasted 1/100th of a second then 3000 ft/sec/sec or about 100g or a force of 20000 lbf (with a tonne of caveats).
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
GregLocock
Automotive
You could make a decent stab at the likely forces by reverse engineering the pedestrian impact test.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
- Thread starter
- #12
Thanks all!
I'm watching a court TV case where the prosecutor's expert says the body would launch 30' and the the defense expert says no way. The only injuries to the body are on the arm with no bruising elsewhere. The only damage to the car is a broken taillight w no blood.
So I looked up some old kinematics and determined I didn't know what the assumptions were for either expert. 1 second impact? Deceleration of the vehicle? Body flying thru air - relatively frictionless?
The right arm of the body has lacerations on the back of the arm - no bruising on the arm nor any other part of the body. So I'm inclined to believe the body only spun at impact with no launch, but was wondering what distance the body might launch if it was a direct mass on mass impact.
Thanks again.
I'm watching a court TV case where the prosecutor's expert says the body would launch 30' and the the defense expert says no way. The only injuries to the body are on the arm with no bruising elsewhere. The only damage to the car is a broken taillight w no blood.
So I looked up some old kinematics and determined I didn't know what the assumptions were for either expert. 1 second impact? Deceleration of the vehicle? Body flying thru air - relatively frictionless?
The right arm of the body has lacerations on the back of the arm - no bruising on the arm nor any other part of the body. So I'm inclined to believe the body only spun at impact with no launch, but was wondering what distance the body might launch if it was a direct mass on mass impact.
Thanks again.
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