An object's weight

  • Last Post 09 April 2018
  • Topic Is Solved
nds88 posted this 02 April 2018

Hello, I am new to ANSYS and I am currently taking a class that focuses on using AIM and Workbench. 

I am running a fatigue analysis of a component and I was wondering if I need to apply the weight of the object in some way? The reason I am asking is because ANSYS should technically have all the information it needs to KNOW the weight already. It has material properties (density) and all the geometric information needed from the uploaded model (volume). Acceleration due to gravity is assigned by the units that are selected. So, do I need to assign a weight for an object to have it become part of the fatigue analysis or is it already part of my solution without my input?

Im using AIM for the fatigue analysis but I am curious about if this is true for Workbench as well. How do I add an objects weight if needed? 

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peteroznewman posted this 02 April 2018


The solid model defines the volume of the body, and if the material has a density property, then the mass of the body is known.

What gives a body weight is gravity. Gravity is not automatically included in AIM or Workbench models. It is a load category called Inertia and can be added to the model. The screen snapshots below show how to add gravity to an AIM model where Y axis is "up".




In Workbench Mechanical, gravity is added like this:


In many models, the forces supported by the body are orders of magnitude larger than the force of gravity, so whether gravity is included in the model or not makes no significant difference to the result. But if the forces are of a similar magnitude to the force of gravity, then gravity should be included. It doesn't hurt to add gravity even if it is not going to significantly change the results.

Fatigue is all about stress cycles.  Applied forces can have a cycle, but gravity is a constant, so it's contribution can only be to the mean stress and not the stress amplitude.


nds88 posted this 09 April 2018

Ok Thanks for the clarification. I ran some simple tests and it seems that the only thing you really need to define for ANSYS to account for an objects weight is the direction that gravity will act in relation to the model, everything else is taken care of.