Impact Load on spindle

[Polaco]

Hi, I am trying to simulate an impact load on a truck spindle. My model contains the spindle, the knuckle,two bearings (modelled as solid) and the brake disc. BCs are: an acceleration pulse in the center of the wheel and fixed boundary condition applied to the knuckle. The maximum measured acceleration in the knuckle is 20g (peak) and lasts 0.05 seconds. I am modelling the material as a Johnson Cook rate dependent material (isotropic law hardening and strain rate effects), although, plasticity will be small (physical test confirms that). I want to see what's the maximum stress caused by this impact, does anyone knows if I should consider dissipation effects caused by viscoelasticity? I am sorry for my english, I hope I was clear.

 

[GregLocock]

Your English is fine. Considering the accuracy that I would expect with that event I would not worry about visco-elasticity in the metal. In fact I think you've already made the model more complex than can really be justified, unless you have some very good data.

Interpreting the results is likely to cause bigger problems than some weird energy absorption model.

Here's a justification. Your event has a bandwidth of 20 Hz. The modal behaviour of the spindle etc is likely to start at around 100 Hz (at least, 300 would be a reasonable target on a car).

However if you are worried about the nylon liner in the ball joints then you may be on to something. I'd still ignore it.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Polaco]

Thanks very much Greg,I understand your explanation. Note that I am not solving the dynamic response of the structure to a periodic excitation. I am using an explicit simulation with a length of 0.05 seg (the duration of the event).

What would occur if the excitation bandwith was in the range of the natural frequencies? Would this add a stronger viscoelastic effect?

Since the objective of this simulation is to determine the maximum stresses generated by this event. What kind of simulation would you recommend for that kind of problems?

Thanks very much for your help...

Polaco
(Mechanical Engineer, 27 years old, Buenos Aires, Argentina)

 

[GregLocock]

Viscoelastic effect where exactly? In the metal? The internal damping of even cast iron is going to be much less than 5% (at a guess).

Having said that, why not try a shorter event and see if these peculiar refinements make any difference to the stresses, my guess is that they will have a small effect only.

Most of the damping in practice will come from the interfaces nad other components, not the internal damping of the knuckle.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Polaco]

Thanks very much Greg. I was supposing the contact will be the responsible of almost every energy loss. Since I dont have a lot of experience with that simulation I wanted to find someone who actually knows about that.

I will let you know about the results.

Thanks a lot for this help.

Polaco