How can I define material other than acrylic,steel, etc... in motion analysis contact? For example I want to have contact between 2 hdpe material, how can I define this contact?
To define contact material other that standard materials, you have to uncheck "Materials" check box and type all properties manually.
see below image:
I know the coefficients of friction between the material I'm using, but not the stiffness,exponent, damping etc... how can I run this? I do not know how to obtain all these parameters
1. Search on Google.
2. Check with the manufacturer of the material. They should be able to provide this number for you
3. You can also try Matereality.com(Need subscription) If you have SW Simulation Premium/Professional, Add Simulation Add-in, Open any part file > RMB on material > Edit Material
In Material dialog, left bottom corner, Click "here". This will launch Matereality.com
Can I also ask you a question regarding using prescribed displacement to find a force?
I am not the right person for this question. But you can post it, someone will Answer.
Stiffness It is the parameter used to define the compression that occurs when parts contact each other. This is the equivalent of spring stiffness where the force generated is equal to the stiffness times the penetration between the parts. The other aspect of this value is that the stiffness is a function of geometry. For example, theoretically, for a steel rod, the stiffness k = A*E / L
A is the cross-sectional area E is the Young's Modulus L is the effective length which is free to deform
It is used for the proportionality of Force with penetration. F=k*x^e, where
e is the exponent. You can therefore have non-linear relationships which is
especially important for incompressible materials. For something like Rubber,
use an exponent of 2, maybe even 3. For metals, a value between 1.3 and 1.5 is
This term (c) indicates the
loss of energy that occurs between parts when they collide. This is the maximum
damping applied. Normally, damping is between 0.1 and 1% of the stiffness value.
This is actually the depth at which maximum damping occurs. When the parts first touch, there is no
damping force, but then at they deform or penetrate, the damping force increases
until at a certain depth it will be applying the maximum damping force
Make sure you don't have d so small that is causing discontinuities or so large
that the damping is never turning on
You can try with stiffness = 82595 N/mm
The stiffness value above is based on the blocks of my design? and what E is taken? for what material?
For plastic, e =2 is logical?
This stiffness value is for contact between a flat plate and a sphere made of HDPE. I don't have value for your model.
Yes, e = 2 is logical for Plastic, SOLIDWORKS use 2 for Acrylic.
Is it possible if I apply a force with several values on a block, and find the maximum displacement with each force, and then curve fit the force vs displacement to find the stiffness and the exponent?
Yes, you can setup a No Penetration contact problem of 2 blocks with the appropriate materials. Measure the contact force
and the displacement at the interacting faces. Then, take an average stiffness = force/displacement and use that in the Impact model.
I tried finding stiffness myself, as well as other properties, but the first 2.25 seconds gave the force attached in this message, which doesn't seem very logical. It is the same problem of dropping the wall. I didnt understand the drop in the force. I stopped the simulation before finishing, and before breaking the wall.
You can try increasing Frame Per second.
Also you can share files with your setup. I will see.
Hello, attached is the file I am testing now. I applied a force when blocks are in contact and found the contact force then divided it the displacement at the contact, for several forces and displacements i got a linear result with the stiffness given and the exponent to be 1. I tried to do the same thing with the steel rail and the plastic block, but applying a force gave a very small contact displacement, which gives a high stiffness. I took the stiffness for steel. I tried to run the study, it took 3 days to reach 2 seconds then after i stopped it it reached about 20000N. These are plastic blocks mounted on top of each other and on a steel rail bolted to the ground, how can 20000 newtons not even tilt the wall? I find something not logical and I cannot figure out why.
Regards and hope you can help.
I am still facing the same problem, maybe the stiffness between steel and plastic is so high it is not like that in real life. I do not think the force is this high to separate this wall but I am not sure what the contact stiffness between steel and plastic is.
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