Why is the measured tyre stiffness behaving contrary to what we expect from theory?
My thesis is based on the modelling a light agricultural tyre in ANSYS Mechanical. In my simulations I am subjecting the inside of the tyre to either a 2Bar or 0.8Bar as well as am applying a remote displacement to a road surface which is moved towards the tyre to cause tyre deformation.
I am trying to understand what the smulation is doing but cannot understand where I am going wrong. Below I have attached my results, the solid lines represent the exisitng data that I am trying to match, and the dotted lines represent some of the simulations I have run. At this point in time I have only simulated a 2Bar, 0 camber as well as a 0.8Bar, 0camber case.
I have two issues:
- As the stiffness of the tyre is determined by the slope of the line’s in the figure below, I tried adjusting the Young's Modulus to relax the stiffness of the tyre however found that with a decrease in the Young's Modulus the stiffness increases which is the opposite effect that is expected
- The model fairly estimates the tyres behavour for 20mm for the 2Bar case and around 30mm for the 0.8Bar case, however there after for both simulations the data points exponentially increase.
As you can see in the figure, when removing the belt of the tyre and making it the same material as the tyre tread, the stiffness of the tyre increases which indects that something is happening in the physics that is causing the opposite expected behaviour.
Can anyone make sence of these behaviours?
The following are the connections. The frictional contact has a friction coefficient of 0.64 which is the frictional coefficient between rubber (tyre tread) and stainless steel (road).
The origin of the model sits at [x, y, z] = [0, 0, 0]mm and is at the center of the tyre:
To ensure that the tyre rim is treated as static the displacement [x, y, z] = [0, 0, 0]mm as follows is applied to the faces of the sidewalls which come in contact with the rim:
The internal pressure as said before is applied to the internal surface of the tyre. The image below is a section of the tyre, just so you can see on which surfaces the pressure is applied to.
And a remote displacement is applied to the road surface along the tyre-road interface:
As I have the vertial force-displacement curve of the experimentally tested tyre I can input the vertical displacement value and thoguh using a force reaction probe and a deformation probe I can collect the vertical force and displacement that my model experiences.
The force reaction probe:
where the "Coordinate System" is as follows:
The defomration probe then sits at the same point as the force reaction probe:
Please let me know if there is any other information that you might need.
Thank you in advance