## General Mechanical

Topics relate to Mechanical Enterprise, Motion, Additive Print and more

#### Simple friction problem yet I keep running into errors, any proper resources for Ansys practice?

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• peteroznewman
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nProper guidance is available here for free!nRubbing two parts together requires some careful setup, it's not as simple as you would hope. nI'm not sure what you wanted to do, so I will assume you wanted to hold the green part fixed, and slide the brown part in the Y direction while pushing in the -X direction with some force on the green part to generate a normal force. I assume you defined frictional contact between the two faces. The green face should be the Target and the brown face should be the Contact side of the frictional contact and you can type in a coefficient of friction of 0.3 for example. It looks like you've done that. I also see a Fixed Joint, and that is one way to hold the green part fixed. It would be best if you picked the back face for that. You could also have used Fixed Support.nI see you have a Force and I assume that is on the brown part with a force at a small angle from normal, such as 10 degrees off normal. You could try to have this model solve because the angle of the force from normal is less than an angle of arctan(0.3) which is the angle at which slipping would occur.nBut you can't simulate sliding with this setup. If you had a force at an angle of 20 degrees off normal, then the tangential force is larger than the friction force and the block will slide, but this is a Static Structural analysis and there is no static equilibrium with the force at an angle of 20 degrees off normal with a COF of 0.3. You would need a Transient Dynamics analysis to watch the brown block accelerate away from its starting point.nYou can slide the brown block along the green block in Static Structural, but you have to add to the model.nCreate a Translational Joint to ground on the brown block. It would be best to pick the top face. Edit the Coordinate system for that joint to point along the Y axis. Add a Joint Load of type = Displacement and enter 0.01m as the distance. Now the brown block will move along the Y axis.nDelete the Force, which will be replaced by a Joint Load.nSelect the Fixed Joint on the green body. Change it to be a Translational Joint to ground. Edit the Coordinate system to point along the X axis. Add a Joint Load of type = Force and enter the normal force you want for this problem. Now the green block will push against the brown block.nUnder Analysis Settings, turn on Large Deflection since 0.01 m is large. Change Auto Time Stepping to On and set the Initial and Maximum Substeps to 100.nUnder the Connections folder, insert a Contact Tool. Generate Initial Contact Status. Check to see that the contact is Closed. If it is not, edit the Contact, Interface Treatment to Adjust to Touch.nIt should solve without error. Insert a Joint Probe on the translation joint on the brown block to find the friction force.n
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Thanks for all your help I really appreciate this. I have my final cam design and will employ these tactics once I get it sorted in spaceclaim. I'll come back to this thread should I have any further concerns regarding reading the friction forces.n
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nI've tried adjusting the force so that it's far smaller than 10 degrees of normal (-70 x, -1 y) and I still can't get the system to converge. Does this mean I should switch to a Transient Dynamic problem? I've attached the corresponding files for reference;nThanks for any assistance with this! It should help once I get my log problem sorted in my main project.n
• peteroznewman
Subscriber
nUnfortunately, you applied the Force to the -Y side of the block. That means there is no static equilibrium. The block wants to tip over because the force goes outside the footprint of the block. I increased the side component to -10, so it is easier to visually see the problem, but it is the same problem at -1 for the Y component of force.nIf the force was applied to the top of the block or to the +Y side of the block (shown below), it will solve. It is best to change Auto Time Stepping to On and set the Initial Substeps to 100.nThese are static solutions, where the block is sticking, not sliding.n