Evil SolidWorks Factory Default Material Properties Post

Evil SolidWorks Factory Default Material Properties

File: PVE-4261, Last Updated: May 18, 2010, By: LB

Problem

When a new object is created, SolidWorks specifies that the material is <not specified>. However, if the item is evaluated, it has a factory default material density of 0.04 lb/cuin (1000 kb/m^3) or the density of water. The appropriate material density would be “!Error – material density is not set!”.

Example

SolidWorks Model 1x1x1 inch cubes

The model – 1″ x 1″ x 1″ cubes

Example of missing Material Property

A missing material property

An array of cubes is modelled in SolidWorks – each 1″ x 1″ x 1″. The material has been set to 304 stainless steel for all but one which was missed. The bottom faces of the cubes are fixed. Gravity = 386.22 in/sec^2 (1g) is applied.

One material property was missed in SolidWorks. Simulation will wisely not run until it is set. It can be set in two places – in Simulation, or in SolidWorks. Here it is set in Simulation to match the other items.

Material correctly set in simulation

Material set in Simulation

Resultant force displayed.

Resultant Force = 4.6259 lbs.

Time for a quick check – the model is run with gravity only to verify that the correct weight is recorded on the fixed cube faces as a reaction force. A Default gravity for 1g acceleration = 386.22 in/s^2 is applied to all bodies. They are meshed at 1/4″ size and run.

The resultant force in Simulation – the vertical (z) direction = 4.6259 lbf. A quick check back with the SolidWorks Mass Properties tool indicates a problem – the mass is 4.37 lbs vs 4.63 lbs calculated with Simulation. Where does this unacceptable 5.6% error come from?

Displaying mass of 4.37 lbs

SolidWorks Mass = 4.37 lbs

Showing simulation properties not transferred to SolidWorks

Simulation Material properties did not make it back to SolidWorks

The material for the one cube that was specified in Simulation did not make it back into SolidWorks. Further, SolidWorks did not declare an Error “Hey bud – you’re trying to weigh an object with the material properties not set – cut it out”. Instead, SolidWorks tried to make the user happy by assuming that all <not specified> materials should have the density of water and produced the wrong answer.

Suggestions

If I could change the Material <not specified> density to 4 * 10 ^ 17 kg/m^3 – the density of a Neutron star – then it would be impossible to be fooled by the default material properties. “Oh yeah my vessel has the same mass as the Earth, I set the material properties in Simulation again!” SolidWorks has lots of factory default values – each one is a hidden error waiting to happen!

Changes made in Simulation do not (usually) show up back in SolidWorks. This is just like a part that is modified in an assembly does not show the changes back in the part file.

It is a good idea to set material properties in SolidWorks instead of Simulation.