Help with automotive static load cases

[wz07bw]

I have recently hired a new stress analyst. His first task was to evaluate an UCA. We have ADAMS static loads (typical DELPHI static loads like 3g 3g, 6g one side, braking, lateral ...).

I did it myself as an inertial relief problem and created 11 load cases, one for each static load. The ADAMS loads are applied at the bushings and ball joint.

When the new guy did it he created 33 load cases. He separated each of the three loads for each ADAMS load case into its own load case.

He claims this is a worst case analysis but I don't see how this can be done as each load case requires all three loads for equilibrium.

Have any of you heard of doing it this way?

Thanks.

 

[EdR]

So long as it is linear it does not matter as superposition of the various individual loads will give same results as using the equivalent combination of loads.....

Ed.R.

 

[wz07bw]

As I see it, that would be fine if the bushings were constrained and we could add the ball joint loads and stresses.

The problem arises with the inertial relief. The constraint of the control arm is not really its own inertia but the resolved forces at the bushings. The inrel is only there to take care of the small imbalance in forces.

I will need himi to further explain the concept.

 

[BobM3]

It certainly isn't worst case loading to apply one at a time. Longitudinal loads create lateral reactions at the bushings that will add/subtract to the applied lateral loads.

 

[GregLocock]

For worst case loads you need to superimpose all of them, each scaled by +1 -1 or 0.

With regards tot he number of load cases your analyst is right, and so are you, depending on exactly how those loads were created.

I would rather not use inertia relief to provide equilibrium, I would use load sets that are correctly constrained at each joint, albeit with an inertial term if necessary. I have back calculated all this in ADAMS and it works correctly (not surprisingly).







Cheers

Greg Locock

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