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    • Rahul Ponginan

      Please click here for a short but important announcement   03/26/17

      Dear Users Our Commercial and Academic users around the world can use these same forums here as before i.e. the Altair Support Forum , Commercial users from India with solver queries can go to the Solver Forum for India Commercial Users , Academic Users from India and AOC India Participants are requested to go to the Forum for India Academic Users and AOC India Participants , We will be tending to all queries in all the forums promptly as before, thank you for your understanding. 

Roy Duan

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  1. Hi George, How does the material consider the viscous effect if strain rates are included? Which parameter or equation shows the viscous effect? In LS-DYNA, it includes decay constant parameter in the input of *mat_low_density_foam, please see the attach file. Roy MAT_LOW_DENSITY_FOAM (MAT_057).pdf
  2. Hi George, Loading and Unloading curves (two different curves) show a hysteresis effect of this material. However, I don't think this gives the Visco property. From Wikipedia, it shows follows. In /mat/law70, which parameter gives the viscosity of the material? If the strain rate effect is not considered, that is to say only two curves are defined for loading and unloading, is there any visco property in this model?
  3. Hi all, From the Reference Guide of /MAT/LAW70, it says this material model is a visco-elastic foam material. However, I cannot find the right parameter which time dependent. So how to understand the visco property of this material model? Roy
  4. Hi all, How to control the element size for a volume 3D mesh? For example, how can we set the element size for a local area to control the local element mesh? Roy
  5. Hi George, How about the tutorial about foam in Radioss? I'm waiting for it all the time. Roy
  6. MAT LAW

    Hi George, I'm sorry for the late reply. I know the formula of Johnson-Cook model you showed. I just cannot understand the expressions in the Excel. So how to understand this formula? From this excel, n=0.45*elongation,b=(Ultimate-yield)/(n-(Ultimate/205000))^n Roy
  7. Hi George, I use the least squares fitting to get the b,n value based on the tensile testing data. And the result shows the n value is larger than 1. From the theory formula, we also can get the stress-strain curve with different n value as show below. When n is greater than 1, the slope of the curve may larger.
  8. Hi all, In the comments of the /mat/law2 Johnson-Cook, it shows The plastic hardening exponent, n must be less than or equal to 1. Why this limit? From my test data, I do the fitting, and found that the n was large than 1.
  9. MAT LAW

    Hi George, Could you explain the background theory of this Excel sheet for /Mat/law2? From this excel, n=0.45*elongation,b=(Ultimate-yield)/(n-(Ultimate/205000))^n How this formula come from? And what's the scope of the formula? Roy
  10. Hi all, I think the time step should be larger than the value setting in the /DT/NODA/CST. However, in my test, I found the time step sometimes smaller than this value. Why this happen? What's more, my case terminate with an error when using mass scaling. The case terminates normally without using keyword /DT/NODA/CST. What's the problem? I have uploaded my engine file and out file. /DT/NODA/CST 0.67 0.8E-4 Roy NewFoam5_1115_Old_FaceDrop_0001.rad NewFoam5_1115_Old_FaceDrop_0001.out
  11. quasi static test

    Hi George, As we know, the time step of the explicit method is very small, however the total test time is about several minutes. So I think the solution time to calculate this case with explicit method is not acceptable. I want to try with implicit method in Radioss. My problem is I don't know how to set the model with implicit method in Radioss. I don't think the material model have very serious problem. Roy
  12. Hi George, How about the tutorial about foam in Radioss? Roy
  13. quasi static test

    Hi George, With explicit method in Radioss, the solution time is unacceptable. So I want to try implicit method in Radioss. Unfortunately, I cannot do the right set up for implicit method in Radioss. If I use OptiStruct, the same material model cannot be used. The purpose of doing this simulation is to calibrate material parameters for further drop simulation, so the same material model should be used. Could you help me to set up the model for implicit method in Radioss? Thank you in advance. Roy CompressionTest.zip
  14. Thank you George. From my test, I got the same acceleration results by using /TH/ACCEL and /TH/NODE. I'm looking forward for your good news about this topic.
  15. Hi George, 1. I have tried with /th/accel to get node acceleration. From the results comparison, the same results were gotten by using /th/accel and /th/node. Check the model and figure below. Test_T02.zip 2. From the radioss theory reference manual, it seems that the displacement is the first solution variable, and then velocity and acceleration are to be derived. This is a little bit different from what you said (you mentioned we calculate the acceleration using acceleration= nodal force / nodal mass and then integrate to get the velocity and the displacement). Which procedure is used in radioss? could you show some validation documents? 3. I don't think I have understood your opinion about the not matching results. how to understand the meaning of "aliasing"? Roy