Learning Forum

[h.gunaweera]

I am trying to define Contacts between Weld and the Model surface. 
i have used Bonded + Augmented Lagrage formulation for the contact. When i check the Gaps under Contact tool it is showing me Gaps of -3,65mm. how do i prevent this? the CAD model does not have Gaps between the weld and the model surface. 

i am trying to do a steady state thermal simulation and check the stresses with static structural simulation. the contact patches between the welds and the model surfaces are generating huge amount of stresses because of this.

in the screenshot i have given the model 200 degrees  and checking the stresses. Stresses should be 0 around the model but it is not. 

[张 文]

Maybe you can try extracting weld elements from line bodies.

 

[peteroznewman]

Is the temperature load in the Steady State Thermal analysis a uniform temperature on all bodies of 200 degrees? Is so, you don't need to perform a Steady State Thermal analysis, you can apply that Thermal Condition in a Static Structural analysis directly.  The reason you would need a Steady State Thermal analysis is if the result was a non-uniform temperature.

What boundary conditions are applied in the Static Structural analysis to connect it to ground?  Boundary conditions can generate stress when they constrain the free thermal expansion of the structure.  Special boundary conditions are often used in a thermo-elastic analysis to deliver a stress-free thermal expansion of the part connected to ground so that assessment of stress in connections between parts of the structure can be evaluated independent of the connection to ground. The stress-free constraint to ground during a thermal load is called a kinematic mount and one example is 3 nodes with 3, 2 and 1 displacements set to zero in particular directions.

When all parts in a structure have the identical value of CTE, have a uniform temperature load and a kinematic mount is used to connect to ground, it is possible to get a stress-free expansion of the structure if the connection between weld bodies and parent metal parts uses shared topology so there is no bonded contact.

Bonded contact will cause stress at the weld contact face if there is any gap in the contact because rigid elements cannot be assigned the identical CTE value that is used in the structural parts. The distance between nodes in the contact element will not expand when the underlying material elements expand and this causes stress. The only condition where bonded contact will not cause stress at the connection is when the nodes on each face being bonded align exactly so the rigid elements are all zero-length.  There can only be two nodes for each contact element.