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George P Johnson

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Everything posted by George P Johnson

  1. George P Johnson

    Quasistatic analysis of metal honeycomb

    Hi, Try modelling one with post yield values for the stress-strain curve and without any strain rate and please update the nature of the graph.
  2. George P Johnson

    Quasistatic analysis of metal honeycomb

    Hi, How many curves you are defining?. Seems like 2 with strain rate from the excel sheet, but in the above image only one curve is updated. Can you please clarify on this.
  3. George P Johnson

    HM file

    Hi, I presume that you have taken the above screenshot from the Learning and Certification program (Learn HyperWorks Desktop (14.0) for Aerospace course). In Chapter 7: 1D Meshing And 8: Connectors you have the option to download all the model files required for this session. Please try as shown in the image below.
  4. George P Johnson

    Contact between parts with 0.1 mm clearance

    Hi, Type 24 is recommended for all models where there is no physical gap (solids to solids) and also with negligible gap. I don't think this approach is required. Try with any one of this approach (directly Type 19 or Type 7 and 11). Which type of contact is used for this model?. You can try introducing a Stmin value and also introducing a symmetric contact.
  5. George P Johnson

    Quasistatic analysis of metal honeycomb

    Hi, For the true stress-strain curve update the curve as shown in the image below. If you have multiple curves with strain rate dependency also update as below.
  6. George P Johnson

    error id: 760

    Hi, Update the element types (2D page>>elem types>>select 2D & 3D option and select all the elements, click update) in the model. Also for the output block there is nothing specified for the data variable. Input DEF for data variable so that all default variables will be extracted. Update these in the model and run the analysis. The same updated model is attached along. 9.hm
  7. George P Johnson

    Quasistatic analysis of metal honeycomb

    Hi, Please share the snapshot of the material card and the stress-strain curves also.
  8. George P Johnson

    WARNING ZERO OR NEGATIVE SUB-VOLUME

    Hi, With Type 7 interface the model doesn't consider the edge to edge interface and that's why the normal force seems to less for model with only Type 7 interface. Whereas with Type 11 it also considers the edge to edge interface along with the Type 7 general interface.
  9. George P Johnson

    ERROR: Zero or negative volume for 3D-Element

    Hi, Reviewed your model and please make these changes: 1). Remove the tied interface between the rigid surface and foam material, create an Type 7 interface between them. 2). Create a self interface (Type 7) for the foam material. 3). While creating the initial velocity select all the rigid surface nodes including the rigid master node. 4). Finally review the foam material loading curve, The material loading behavior will be based on this curve. I just changed the material parameters and made these changes and was able to run it.
  10. George P Johnson

    how to give rotational velocity to component

    Hi, You can try creating an imposed displacement load for this case and choose the relevant rotation axis (XX,YY or ZZ). Create a rigid for the inner ring and impose this load on to the master node.
  11. George P Johnson

    RUN KILLED : TOTAL MASS ERROR LIMIT REACHED

    Hi, If you review the out file we can see that the time step is very less in this model (e-19) and mass was added to maintain the imposed time step which resulted in run termination. Better I suggest you to remove /DT/NODA/CST from the engine file, run the analysis for a few cycles and find what is causing for this time step drop. From the engine out files check what is causing this issue. It could be an element, or node or interface. For an element, check the related material.There must not be an error in the units system that this data is given in. check the element size also. For a node, check the characteristics of connected elements. If the node is on the master side or the slave side of an interface, this interface must be verified. For an interface, the gap of the interface must be verified if some failure happens on the master or the slave side of the interface. Also check the interface for any penetrations and if any are found depenetrate them all.
  12. George P Johnson

    Error in FAIL_JOHNSON

    Hi, That excel sheet was used long back before this Iflag option was introduced. And much developments also happened with RADIOSS as they optimized many parameters for better simulation and results. We don't recommend to use the excel sheet now as we have the simplified input available.
  13. George P Johnson

    Contact between parts with 0.1 mm clearance

    Hi, Yes, you can model Type 24 interface with contact surface to contact surface. No other specific parameters to be taken care.
  14. Hi, The energy plots of a run gives the energy conservation of the system during the run. For every run you should always monitor the energy plots. Any unprecedented behavior of the model can be traced from the energy plot, like a sudden jump in energy plots or high contact energy, hourglass energy...etc. These helps the users to know whether the simulation they are running is valid or not. For a case like crash test you can cross check the kinetic energy plot value with hand calculation and can confirm whether the plots are fine. KE can be found with 1/2 mv2 and the same value should be the starting point for KE plot. These cross checks helps to validate the simulation. The internal energy shows the energy absorbed by the object upon impact, nothing but the strain energy. For a crash test, the KE will reducing and proportionally the IE will be rising showing that the shock upon impact is absorbed by the material/part. This is how we interpret the energy plots. Similarly for drop test and other cases. Total Energy=IE + KE + RKE + CE + HE (RKE-Rotational kinematic energy, CE-Contact ENery, HE-Hourglass Energy) and the total energy must remain constant or can decrease very slightly. And so checking simulation's energy balance plays an important role in every simulation. The plot below shows a typical global energy plots for an impact case. Hourglass is weird modes of deformation that occur in under integrated elements and no stresses will be produced. This can affect solution accuracy by varying the structure’s true response. This leads to inaccurate stress, strain and deflection results. From the time history file (T01) we finally plots hourglass energy of the system and typically it should be less than 10% of the total energy. If high hourglass energy (HE) is found, we will create HE plot separately for each component and will find which component is contributing for this high HE and will take the control measures. The kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity and in explicit cases we does the same thing as we consider inertia. If you consider a case like drop test, at the instance of where the object meet the ground the total potential energy gained at the height of h is transformed/transferred to kinetic energy,since there is zero potential energy at ground level and PE=KE. For further reading on the theoretical aspects of explicit dynamic analysis with RADIOSS, I recommend you to go download and go through on our free ebook: Introduction to Explicit Analysis using RADIOSS
  15. George P Johnson

    Quasistatic analysis of metal honeycomb

    Hi, For /MAT/LAW36 the material plasticity is calculated based on the post yield curve user provides. And from my understanding, based on your above inputs the issue seems to be with the material parameters provided. You can cross check and ensure values are correct.
  16. George P Johnson

    Contact between parts with 0.1 mm clearance

    Hi, If for some reason a node is highly penetrated, either the nodal time step or the kinematic time step may be very low. Then, it is possible to release this node from the interface using the option /DT/INTER/DEL in the engine file. All nodes reaching dtmin will be removed from the interface. But please note that this option may be useful in order to keep a decent time step during contact, but if the number of released nodes is too large, poor results can be expected.
  17. Hi, incompatible kinematic conditions (IKC) are an undesired warning in a model and need to find out where the nodes are over constrained or where the constraints are violating the loads applied. As nodal constraints are based on kinematic conditions applied on nodal DOF, therefore it is not allowed to apply two nodal constraints to the same set of nodes. True incompatible kinematic conditions can generate local instability. You can check the model for any true incompatible kinematic conditions. If you don't find any true IKC you can ignore this warning.
  18. George P Johnson

    Contact between parts with 0.1 mm clearance

    Hi, Can you try with a minimum stiffness (Stmin=1000N/mm)?. If you still have issues use /DT/INTER/DEL option in engine file so that those slave nodes below the Tmin specified will be suppressed from the interface. This node will no longer impact any master segment for this interface. Normally for zero gap contacts we model with Type 24 interface. This option also you can try.
  19. George P Johnson

    polymer tear test

    Hi, The solid formulation seems fine. Can you please share the model file so that we can review and can suggest the possible workarounds.
  20. George P Johnson

    Error in FAIL_JOHNSON

    Hi, Sig_max is not mandatory for failure modelling. If you input a value for this option then during the analysis the maximum stress developed for that material will be your input.
  21. George P Johnson

    Error in FAIL_JOHNSON

    Hi, For /MAT/LAW2 , KEEP Iflag=1 which is the simplified input flag. With this flag active enter Yield Stress, Ultimate Tensile Stress and Engineering strain at UTS. Internally RADIOSS will calculate the a, b and n values based on these. You can input the failure plastic strain (Eps_max) so that once the material reaches this plastic strain value the same will be deleted. As a trial you can try with small Eps_max (as an example 0.1) and can check the rupture happening.
  22. George P Johnson

    polymer tear test

    Hi, /MAT/LAW36 is the equivalent material law in RADIOSS for Law24 in Dyna. Which element formulation you are using and also for material law is it only a single curve or multiple curves with strain rate dependency?. If possible please share the model file and h3d file through my secure dropbox link.
  23. George P Johnson

    Error id 760

    Hi, This fie runs fine in 2017 version. I strongly recommend you to upgrade to the latest HyperWorks version. Meanwhile for the time being you can try with the attached file which runs fine in 13 version. model1_0000.rad model1_0000.out
  24. George P Johnson

    Error in FAIL_JOHNSON

    Hi, The crack will be initiated and finally the element will be deleted once the damage values reach the one integration point of the element. That is the failed elements are removed. The realistic crack propagation actually depends on the damage parameters we provide and users has to find these parameters manually. Many open web resources are available on Johnson-Cook damage parameters and please go through the same which will give you some idea on these parameters. In the video tutorial a different approach is taken where the property used is sandwich shell (where multi-layer XFEM will be applied) and /FAIL/FLD is used, where the user has to get the forming limit diagram after experimental tests and based on the same damage is initialized in the material model.
  25. George P Johnson

    RADIOSS Johnson cook material

    Hi, This issue with the example values is already known and we will be correcting it soon in the example file. But, thank you notifying the issues as we can improve our documentation much better.
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