Notch relief with variable reference value

Increasing the stress in one notch can decrease the stress in another near by notch (Neuber’s law of load stress decay). This is typically called a relief notch. This is a very useful tool if you experience too large stresses in an area that you are not allowed to change, but you are allowed to change nearby geometry (the "nearby" is important - the stress decay does not work over great distances but only locally).

This task shows you how to:

Context:

To understand this type of optimization a simple example is the best explanation:

The above figure shows a simple notch with a relief notch. The primary notch is not allowed to be changed only the relief notch. The result is shown in the following figure where the stresses at the reference nodes are drastically minimized through the optimized relief notch.

Notch relief in Tosca Structure.gui

  1. Choose Command > VARIABLE to define the reference stress of the reference nodes.

  2. As Category select Stress/Strain and as Type select SIG_MISES.

  3. As Node/NodeGroup select the reference nodes.

  4. Set Group Operator to Max.

  5. Use this VARIABLE as reference value in the objective function: Select Command > OBJ_FUNC:

SIMULIA Tosca Structure Parameter File

  • The resulting command in the parameter file look like follows: 

    VARIABLE
 ID_NAME        = REF_NODE_STRESS
 DEF_TYPE       = SYSTEM
 TYPE           = SIG_MISES
 ND_GROUP       = refence_nodes
 LC_SET         = ALL,1,All
 LC_SET         = ALL,2,All
 GROUP_OPER     = Max
END_
DRESP
 ID_NAME        = DRESP_VON_MISES
 DEF_TYPE       = SYSTEM
 TYPE           = SIG_MISES
 ND_GROUP       = design_nodes
 LC_SET         = ALL,1,All
 LC_SET         = ALL,2,All
 GROUP_OPER     = Max
END_
OBJ_FUNC
 ID_NAME        = MY_OBJ_FUNC
 TARGET         = MINMAX
 DRESP          = DRESP_VON_MISES, , REF_NODE_STRESS
END_