2D axisymmetric force load

[s.mahvash]

I am trying to match a 2D axisymmetric force load simulation to the CBR results obtained from laboratory tests. I want to match the Force/Displacement graph of the simulation to the actual CBR results. There are only a few of the parameters known from lab tests, the rests should be estimated in order to match the CBR graph. I have been trying for over a week now and can not get the load force to come even close to the obtained CBR force loads. I ve tried increasing and decreasing the E modulus, the Poisson's ratio, cohesion and the friction angle. Yet, still not even close to the required force. 

Can anyone possible give any ideas how to approach this issue. 

Many thanks in advance. 

[John_Holtz]

Hi @s.mahvash. Welcome to the Sim Mech forum.

I think I would have a different lab measure the material properties. (Or stated in a different way, you need to know how a material lab converts the test results into material properties.)

All we know at the moment is that you have measured results. What we do not know are things like the following:

• What was the physical test? (loads? type of material? constraints? results?)
• What is your Sim Mech model? (loads? material model? analysis type? constraints? mesh size?)
• what does "CBR" stands for?

With further information, perhaps someone can provide some ideas on how to solve your problem.

[s.mahvash]

CBR is California Bearing Ratio, I used the CBR machine to test samples in Cylindrical moulds in order to obtain a Force/Displacement graph.

The material is fine Sand.

I only have the maximum dry density, and the optimum water content of the sand, as well as its grading. These are the only data I have obtained in the lab. 

I am trying to do a 2d axisymmetry simulation, with a mesh generated, and with a specified displacement. I need to obtain similar load so that I may use it to predict other parameters of the Sand without further lab tests. 

Many Thanks

[John_Holtz]

Maybe this paper will get you started: http://article.sapub.org/pdf/10.5923.j.jce.20120201.05.pdf (Evaluation of Modulus of Elasticity and Modulus of Subgrade Reaction of Soils Using CBR Test)

Then the questions that come to mind are as follows. I have no experience with geological materials (sand, rock), so I do not know the answers.

1. What material model represents sand over the range of loads needed for the analysis. (In other words, if the analysis is only using the "linear" portion of the load-displacement curve, then nonlinear material properties would not be required.)
2. What test data is needed to determine the material properties.
3. How to calculate (or guess) the material properties from the lab test.

Are your results off by a factor of 6 (or 6.28 = 2*pi to be more precise)? Since the axisymmetric analysis is a 1 radian slice, I am sure that the reaction forces need to be multiplied by 2pi to get the full load measured in the lab test.