Discussion Groups

Simulation Mechanical and Multiphysics

Reply
Contributor
PSteven
Posts: 14
Registered: ‎10-16-2011

Fatigue Analysis with Multiple Load Cases

533 Views, 6 Replies
12-10-2011 09:12 PM

 

Hello,

 

I can't seem to use multiple load cases in a fatigue analysis.  I want to apply two forces (loads) to one model and apply different load curves to these forces (loads) while running a fatigue analysis.  I tried several approaches using Static Stress with Linear Materials type analysis. 

 

1. Apply two forces in one Design Scenario and perform analysis.   Run Fatigue Wizard only one load case shows.

2. In two Design Scenarios, run one force in each and perform analysis.

a. Combine the load cases.  Run Fatigue Wizard only one load case shows.

b. Comibne the load cases and select "Use SRSS Combination Mode" option.  Run Fatigue Wizard only one load case shows.

 

 

How can I get the two forces (loads) to show up in Fatigue Wizard?

 

Regards,

PSteven

Please use plain text.
Employee
S.LI
Posts: 398
Registered: ‎05-06-2010

Re: Fatigue Analysis with Multiple Load Cases

12-12-2011 04:55 AM in reply to: PSteven

I guess you should do it in one DS:

1.) simulate two load cases in LSS;

2.) As shown in the attachment, you can input the combination relations in the highlighted cells.

 

 

----------------------------------------------------------------------------------------------
If this response answers your concern, please mark it as "solved".
Please use plain text.
Contributor
PSteven
Posts: 14
Registered: ‎10-16-2011

Re: Fatigue Analysis with Multiple Load Cases

12-14-2011 04:34 AM in reply to: S.LI

 

Thanks S.Li for your reply. 

 

I was applying surface forces instead of nodal forces, and there is no load case assignment option for surface forces.  I switched to nodal forces instead and was able to assign load case numbers to my forces.

 

Why can`t you assign a load case # to surface forces?

 

Regards,

PSteven

Please use plain text.
Employee
S.LI
Posts: 398
Registered: ‎05-06-2010

Re: Fatigue Analysis with Multiple Load Cases

12-14-2011 04:59 AM in reply to: PSteven

I'm not sure if we are talking about the same thing on loadcases.

As shown in the attachment, there are two loadcases for pressure loads, namely surface loads.

----------------------------------------------------------------------------------------------
If this response answers your concern, please mark it as "solved".
Please use plain text.
Contributor
PSteven
Posts: 14
Registered: ‎10-16-2011

Re: Fatigue Analysis with Multiple Load Cases

12-14-2011 08:41 PM in reply to: S.LI

 

I mean Surface Force vs Nodal Force when defining Loads and Constraints for LSS.  There is no load case assignment for a Surface Force but there is for Nodal Force, as illustrated in the attachments.   Multiple surface forces show up as one load case in the fatigue wizard.

 

 

Please use plain text.
Employee
S.LI
Posts: 398
Registered: ‎05-06-2010

Re: Fatigue Analysis with Multiple Load Cases

12-15-2011 05:01 AM in reply to: PSteven

I'm not sure why the loadcase definitions for nodal and surface forces are not consistent.

My guess is no loadcase number input for surface force means surface forces always appear in all loadcases, and they could be controlled by the multiplier in parameter dialog, as shown in my previous attachment. For example, "0" means no surface load in the specific loadcase.

Hope this is helpful in your problem.

 

I'll check this with other people later.

----------------------------------------------------------------------------------------------
If this response answers your concern, please mark it as "solved".
Please use plain text.
Employee
PipePakPat
Posts: 159
Registered: ‎11-12-2009

Re: Fatigue Analysis with Multiple Load Cases

03-26-2012 08:01 PM in reply to: PSteven

A nodal force is its own object, which also has a field that indicates for which load case it will apply.  A nodal force can only be create to act within its specified load case.

 

A surface force is actually a surface pressure.  It is converted to a surface pressure during the decoding process prior to the analysis.  Surface pressures can be scaled from one load case to the next, but cannot change proportions from one surface to another between different load cases of the same analysis.  For this reason, the rules associated with the surface pressure also apply to surface forces.

Pat Tessaro, P.E.
Customer Support Engineer

Autodesk, Inc.
285 Kappa Drive
Suite 250
Pittsburgh, PA 15238
Please use plain text.