Bolt analysis, applying preload 3

[rhmeng]

I am trying to figure out if there is a way to apply a preload to a part in solidworks that is a bolt. We already modeled all of our fasteners to replicate minor diameter to see what the max stress is, but now I want to apply a preload to the bolts. I see that there are bolted connections you can use, and also you can use toolbox items, but what about a part model that is a bolt. I am not seeing an option for that anywhere, maybe we are doing the analysis incorrect? Any input would be appreciated.

 

[academix]

Hello:

Pre-loading of bolts can be achieved using connectors. But, that would be for simulating the joint, its effects, per se.

In your case, you are looking at the bolt itself. Then the approach is to model using gap/contact with pressure loading on the bolt / plate/washer interface appropriately to establish force equilibrium and run the analysis.

Normally, you can ascertain whether the loading was achieved by comparing the results of FEA to axial stress calculations to check convergence and efficacy of the contact boundary conditions, you have provided.

In such situations, when bolt stresses are involved, it is typically the fluctuating stress components, arising out of bending that tends to create havoc.

Hope this help,

Best regards
Nat


Natarajan Ramamoorthy
Design Engineering Consultant

http://www.egsindia.com

 

[rhmeng]

academix, I saw that you are able to apply pre-load using connectors, but you are right I am looking for the bolt. Your approach of applying a pressure load on the bolt to simulate the pre-load is genius. If I run across the need for this again I will definitely keep that in mind. Thanks for the response.

 

[mmar2087]

Here you have some ideas on how to model bolts and their preload.

[URL unfurl="true"]http://blog.gxsc.com/graphics_systems_solidnot/2013/09/bolted-joints-in-fea.html[/url]

 

[jean15paul]

In my experience we always use spring elements, rigid elements, bar elements, or some other type of connector (depending on the specifics of the application and what the software supports). Then we recover forces from the elements representing the bolts and use those forces in a non-FEA bolt calculation (possibly by hand, but usually some type of bolt calculator or spreadsheet). Bolted joints have a number of failure modes that an FEA model could miss.

Shigley's Mechanical Engineering Design Chapter 8 "Screws, Fasteners, and the Design of Nonpermanent Joints" and Bruhn's Analysis and Design of Flight Vehicle Structures Chapter D1 "Fittings and Connections. Bolted and Riveted." are my go-to references for bolted joint analysis.

 

[Culmechanical]

One trick I've used in simulation is to model the bolt, cut the center out so there is a small gap between the two ends of the bolt (now it looks like two screws put into opposing holes with a gap between them... then I grab those cut edges and apply a bolt connector with a preload... this allows the action of a preload and simplicity of that bolt connector interface while allowing evaluation of the bolt head interface. I have found that things "drift" off of theoretical values if the load on the bolts (say a tie rod) exceeds the preload applied to the bolt.

The other approach is to use a temperature delta applied to the part to create a preload... (taking advantage of the shrinking what occurs when something is lowered in temperature). I haven't used this yet because my first trick has provided what I needed, but it is a good option I'm keeping in my pocket if I end up needing it...

 

[TomekZeWschodu]

Try in that way. Do an iterative proces on another model of your conenction.
Build a model i na new file and apply a temperature load that will shrink your bolt. In interative way you will know how temperature you have to apply to get desired pretennsion and then apply it to your work-model.
It's quite easy and works for sure in NX Nastran.

Naval Architect/ Structural Engineer