Local stress around bolted surfaces vs. fatigue life

[andrewkeisler]

Hello folks,

I'm running into an issue using fasteners in Solidworks FEA- specifically bolting a hub assembly to the upright. When I noticed excessive stress around and under the bolt head surface, I decided to run a simple study with tried and true components- A C5 corvette hub and upright vs. my more complicated design using bolts and spherical bearings at all fixtured locations. Both designs displace excessive stress under and around the hub mounting bolts. Below I have information regarding the basic corvette suspension study-


I'm using a remote load from the tire contact patch on the road surface to the hub face. Simultaneous 1G lateral, 1G longitudinal, and 2g bump force.
The lower ball joint taper is fixed in all 3 axis
The upper ball joint mating surface is fixed on X and Y axis- allowing for bump movement
The steering tie rod mating surface is fixed on only the Y axis
The mating surfaces between the two components are set to no penetration.
I'm using the counter bore screw fastener option for mounting the hub to the upright. I've selected the threaded portion of the hub assembly for bolt contact and the bolt hole circle on the upright for the bolt head mating surface. The 3 M12 fasteners are set to 96 ft lbs (GM spec)
I've selected the hub to be rigid so that I may focus directly on the issue I'm finding on the upright.

With a von mises static loading scenario, you may see the area around the head of the bolts have reached yield while the rest of the upright has minimal stress throughout. It's obvious to me that the results are not accurate to real-world life expectancy of the component. The upright is a well engineered OEM automotive component which displaces stress much more evenly then shown in the simulation results. I assume if I can find a correct method for analyzing this component, then I can take the same method to my custom upright.

Another reason the results are not accurate- As the amount of nodes increase in mesh, the strength of these localized areas decrease at an exponential rate when compared to the rest of the part.


How would you run the study differently for more accurate results, specifically for fatigue?
Ignore the local stress around the bolts assuming the clamping load counter acts these localized stresses is FEA?
Non-linear study?

Any help would be appreciated.

https://files.engineering.com/getfi...c=212727627.5.1593008527026&__hsfp=3526110323

https://files.engineering.com/getfi...c=212727627.5.1593008527026&__hsfp=3526110323

https://files.engineering.com/getfi...c=212727627.5.1593008527026&__hsfp=3526110323

 

[FEA way]

Can you attach a picture showing the whole assembly with fixtures and loads ?

Mesh convergence check is a first thing to do but, as you say, you may have to try nonlinear analysis eventually.

 

[andrewkeisler]

Below I've attached a photo showing the whole scope of things.

The 3 blue areas are the fixtures based on the axis allowance of movement based on the suspension design.

My fixture and load method are identical to how FSAE teams apply loads and fixtures to their uprights. The difference is- most, if not all, FSAE cars use a press in wheel bearing vs. a bolt on hub assembly. This is where I'm running into confusion with the fasteners mating the components.

I prefer to use bolted connections and apply fixtures on the balljoints, but for solving this issue, I'm constraining the surfaces on the upright to simplify the study.

I'm sure I could attach the solidworks part files and my FEA study through google if anyone would like to view or alter it.

Again, this is simple testing on proven components so that I may apply them same parameters to my own design.

https://files.engineering.com/getfile.aspx?folder=949f3169-afc0-4c6d-b0f9-74ba2a92e0a4&file=FEA4.png