kenzo604 Posted November 5, 2012 Report Share Posted November 5, 2012 I am currently running an FE analysis of a rollcage but have hit a slight problem, i know where i want my load case to be but having some trouble defining the force required. the car weighs 200kg and the max speed is 50mph, but how do i know how long the crash will take during a crash into a solid wall ie rigid? it is a linear-static situation before you ask. i could assume it takes a 1/10 of a second, or half a second, but the difference in load case will be dramatic, so anykind of accurate ideas will be much appreciated cheers, ash Quote Link to comment Share on other sites More sharing options...
Ash-Kennard Posted November 5, 2012 Report Share Posted November 5, 2012 my bad, uni computers and fb signed me into an account i havent touched in years haha. my question, replies appreciated. cheers Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted November 5, 2012 Report Share Posted November 5, 2012 That's one seriously light car! I haven't done much FEA but I would say you can't really model it as a step input lasting 0.X seconds but instead would need to consider using a normal distribution type curve where the maximum deceleration and therefore duration of the crash roughly match what the theory says. I'm sure G levels must be available online somewhere for a crash from 50mph... Quote Link to comment Share on other sites More sharing options...
Jon Alty Posted November 5, 2012 Report Share Posted November 5, 2012 If your crashing into a solid wall, then the crash will be instantaneous. The only way the crash time would increase is if your car was to bend in places, which the analysis will take into account? Quote Link to comment Share on other sites More sharing options...
Pete.M Posted November 5, 2012 Report Share Posted November 5, 2012 As above, It's difficult to understand the reasoning or accuracy of such an analysis. At that speed I think it would take 0.0447s to travel a metre? (don't trust me, I cannot math) Not considering any slowing down of the vehicle during crashing. Not sure if that helps at all. Quote Link to comment Share on other sites More sharing options...
Ash-Kennard Posted November 5, 2012 Report Share Posted November 5, 2012 (edited) cheers for the replies guys, turns out weve been given the loadings but the lecturer neglected to tell us! they point of finding the time was to model the EV race car's rollcage at uni to redesign it, the retards that made it put no thought into it and in a small collision the whole lot bent and buggered all the welds at the front. finding the time is essentially back working the loadings required 50mph in m/s times the weight to give the momentum then a factor of time to work out from the bending what force would be needed to then remove the time. pretty special way to do it, but we didnt have a choice at that stage. now we have the loadings weve split the loadings accross 3 areas for a front on collision, then one on each corner to decentralise the collision. same for the rear, sides and 4point roof next! someone in our group managed to calculate it would take about 0.15 seconds for the impact to happen based on a test video we saw on a similar car at 30mph cheers, ash Edited November 5, 2012 by Ash-Kennard Quote Link to comment Share on other sites More sharing options...
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