Discussion Forum

Hello,

ultimately I would like to solve a problem with two linear elastic materials (each with different Lame parameters) and at the interface between the two materials I would like to impose continuity of displacement and a jump in the stress.

I am using the `Solid Mechanics' physics, my study is stationary and I'm running version 5.1.

I started with a toy problem: two cubes placed next to each other with one face in common. At one end (on a square face) I prescribe a zero normal displacement and at the opposing end I apply a small displacement. On two of the long rectangular faces I apply symmetry conditions, on the other two I leave the default free conditions. This should be modelling stacking two cubes and then loading between two plates in the direction of the long axis of the stack. I'm modelling a quarter of a column in unconfined axial compression.

On the common face between the two cubes I would like to impose continuity of displacement and continuity of stress. (I need to see how this works so that later I can modify it to a jump in stress condition). When I built the geometry I formed a union and I have added a Solid Mechanics node for each cube. In the first cube I use a `Prescribed displacement' condition and set the displacement to equal the displacement in the second cube. In the second cube I use a `Boundary Load' condition. The description says `stress dot normal = force per unit area'. However, from a few experiments I have found that typing zeros into the applied force box imposes continuity of stress and a non zero entry actually imposes that jump between the stresses acting on the facing surfaces.

It seems that at an interface the 'boundary load' condition that is actually implemented is on the jump in stress, but obviously I'm a bit nervous about just deciding what Comsol is doing in contradiction to the documentation and wondered if anyone had any ideas about this? If someone can point me to some documentation specifically about using the boundary load condition between two interfaces that would be really helpful. Or perhaps the `boundary load' condition should not be used between two objects and you can suggest the right way to approach this problem?

Thanks