General Mechanical

How I evaluate only the deformation in the chassis? (for stiffness calculus)

• paganelli9
Subscriber

Hi everybody!

I want to evaluate the deformation only in the chassis frame, but with the force "passing" throught the suspension arms and making no deformation on then, just on the chassis. I basically want to set all the suspension system like "Rigid elements", but I don't know how to do that in Ansys Mechanical. Can someone help me? Thanks guys!

I will upload my project and some images for illustration.

Here is a image of the deformation in all chassis (with the suspension arms)

• 1shan
Ansys Employee
HelloArray,nTry setting the A-arm material stiffness behavior to rigid. You can find that under Geometry. Also I would suggest you to define a cylindrical joints between A arm and chassis rather then a direct mesh connection and try doing a transient structural analysis. You could have a look at the third tutorial in -https://courses.ansys.com/index.php/courses/time-domain-dynamic-problems/lessons/homework-quizzes-simulation-examples-time-domain-dynamic-problems-lesson-6/nnRegards,Ishan.n
• paganelli9
Subscriber
Hi ArraynThanks for repplying!nSo I changed the material to Rigid in Spaceclaim, because in the Model wasn't making any difference in the deformation, beside I can only change the behavior to Stiff Beam in the Geometry tab inside the Model. But when I make the suspesion A-arms rigid in Spaceclaim I get a very small deformation, a maximum value of 0,00047mm and that can't be correct. I will uppload a image of the situation.nnWhat can I do sir? Again, thanks for your help!n
• 1shan
Ansys Employee
nSince I do not know the kind of boundary conditions and forces you applied to your model I cant really justify the deformation. However you could try a methodology similar to https://www.longdom.org/open-access/analysis-of-torsional-stiffness-of-the-frame-of-a-formula-student-vehicle.pdf or someone else. Also, while calculating torsional stiffness the springs are modelled as solid rods (and not actual spring elements which I see in your first model). If you don't want to model the suspension flexure, delete those components from the geometry and just add remote displacements/forces to the pickup points.nnAll the best.nIshan.n
• paganelli9
Subscriber
Hi Array nThanks again for repplying!nI will uppload a image with all my boundary conditions for more details. The image below is from a simulation without the rigid elements set in Spaceclaim.n
• paganelli9
Subscriber
nHi sir! Sorry to bother you again, but since you helped me with my project a few weeks ago I thought you would know how to solve this situation too.nThanks a lot for your collaboration sir!n
• peteroznewman
Subscriber
nYou got a small displacement, but you didn't say what forces you were putting in to the model. If you want higher displacement, use higher force. In the end, it doesn't matter because stiffness = Force/Displacement.nDeleting all the A-arms and using a Remote Force (type = Deformable) scoped to all the points on the frame the A-arms attached, is the simplest solution.n
• paganelli9
Subscriber
ArraynHi sir! So I put 2 Remote Forces with 1500N each in the A-arms. I understand what you said to do, but how I will calculate in the formula? Because if I set Remote Force in all the points of the chassis that connects with the A-arms the L in the formula will change.nWhere:nKt = Torsional Stiffness of the chassisnF = Force applied in the chassisnL = Distance from the center of the chassis to the point where the force was appliednBeside that, I will have to decompound the forces in the points? Ex: 375N in each point of a A-arm side.nThanks a lot for your help sir!n
• peteroznewman
Subscriber
One Remote Force with a +Y component of F is on the left, at the coordinates of the center of the left wheel. The Remote Force is scoped to all the mount points on the left side of the frame that supports the left wheel, making a spider of rigid elements.nAnother Remote Force is on the right, at the coordinates of the center of the right wheel, with a -Y component of F, scoped to all the points on the right side of the frame that support the right wheel.nPromote each Remote Force to a Remote Point. That will make obtaining the directional deformation of each remote points in the Y direction easy to get deltaY1 and deltaY2.nn
• paganelli9
Subscriber
ArraynHi sir! Thanks for your repllying!nSo I see that you explain my simulation and I understood about the Remote Points for measure the deformation in each side, but if I do that, I'm counting the deformation in the A-arms too, don't it? And if I'm doing that, I'm not calculating only the chassis stiffness, that's my point. Or you are saying that the way that the simulation is set the suspension system is acting like rigid elements? Because in the simulation they are having deformation too. I know how to get the deltasY, but I have to be sure that I'm calculating only the deformations in the chassis. nThanks again for your collaboration, Peter!n
• peteroznewman
Subscriber
ArraynThe chassis is fixed at one end. You have a rigid handle to torque on the chassis at the other end. You have a force F that is applied to the ends of the rigid handle. You measure the displacements at the ends of the rigid handle. You have a formula that includes the length of the handle, L, which is used to compute torsional stiffness.nDo the calculation once, then make the remote points at twice the distance from the center line. The deltaYs will increase, but so will L and those will cancel each other out and give you the same torsional stiffness.n
• paganelli9
Subscriber
nThanks for your answer sir!nI understood it your explanation and how I will do it. I just have one more question: I have to eliminate the spring system? Because the simulation is set with them. I have to eliminate them or I can make the calculus of the chassis stiffness with them in the simulation?nThanks again and have a nice day!n
• peteroznewman
Subscriber
nI expect the springs will have an insignificant effect on the result. I expect you would leave them out to measure just the frame.n
• paganelli9
Subscriber
nHi sir! Thanks for your answer!nSo I leave the spring system out of the calculation, runned the simulation and evaluate this results.nBut then, when I put half of the force that I put before (750N), the results that I obtained aren't linear. Do you know why? And if there are an error?nI will upload my project if you wanna take a look.nThanks again for your help!n
• paganelli9
Subscriber
nHi sir! Thanks for your answer!nSo I leave the spring system out of the calculation, runned the simulation and evaluate this results.nBut then, when I put half of the force that I put before (750N), the results that I obtained aren't linear. Do you know why? And if there are an error?nI will upload my project if you wanna take a look.nThanks again for your help!nnn
• paganelli9
Subscriber
nHi sir! Thanks for your answer!nSo I leave the spring system out of the calculation, runned the simulation and evaluate this results.nBut then, when I put half of the force that I put before (750N), the results that I obtained aren't linear. Do you know why? And if there are an error?nI will upload my project if you wanna take a look.nThanks again for your help!nnn
• paganelli9
Subscriber
nHi sir! Thanks for your answer!nSo I leave the spring system out of the calculation, runned the simulation and evaluate this results.nBut then, when I put half of the force that I put before (750N), the results that I obtained aren't linear. Do you know why? And if there are an error?nI will upload my project if you wanna take a look.nThanks again for your help!nnn