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Simon Križnik

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Everything posted by Simon Križnik

  1. Welcome, here is a Hopkinson Bar Radioss example: SHPB_H_0001.rad.zip SHPB_L_0000.rad.zip SHPB_L_0001.rad.zip SHPB_H_0000.rad.zip RD-E_ 0800 Hopkinson Bar.pdf
  2. Hi, A nonlinear analysis can be restarted or continued from the last point at which the previous analysis was interrupted.When running an analysis, you can write the model information and analysis state information which can be used for restart. http://insider.altairhyperworks.com/wp-content/uploads/2017/01/T-amp-T-1219-OptiStruct-Restart-of-Nonlinear-Analysis.pdf
  3. @awe901 Given the large disparity in diameter, try modeling the fibers and matrix with 3D solid elements and nanofibers with 1D beam or truss elements. The challenge is to extract the midline of nanofibers and seed beam/truss element nodes to be coincident with the solid mesh nodes. This approach would greatly reduce element count at the expense of neglecting through thickness thermal gradient in nanofibers, due to 1D element simplification.
  4. Search the forum (in the upper right corner) for similar problems already solved:
  5. @xrek when assigning material orientation, make sure the direction is not perpendicular to shell elements, whose IDs are reported with the error.
  6. The golden rule of finite element analysis: An FE model should be as simple as possible, but as complex as necessary. Start with a coarse mesh and decide on the quantity of interest (usually displacements or stress, with the former converging faster than the latter), then solve it using progressively smaller mesh size (mesh convergence study), reducing mesh discretization error. https://enterfea.com/correct-mesh-size-quick-guide/ If you plan to do a convergence check, consider performing at least one refinement of the model after the first run. If neighboring elements display large differences in quantity of interest, the gradient was probably not captured in these areas, therefore some mesh refinement is recommended. In general, increasing the number of nodes improves the accuracy of the results. But at the same time, it increases the solution time and cost. Usual practice is to increase the number of elements and nodes in the areas of high stress (rather than reducing the global element size and remeshing the entire model) and continue until the difference between the two consecutive results is less than 5 to 10%.   I recommend you to go through free ebook Practical Aspects of Finite Element Simulation (A Study Guide) which covers 9.12 Mesh Density And Solution Convergence.
  7. Hi, node-to-node connectivity is preferred (tool>edges panel (or F3)>equivalence). Make sure to use proper tolerance. Tie or freeze contact can be used to connect nonmatching mesh. Use auto-contact in the tools>contact browser to automatically create contacts.
  8. Welcome, use the query results panel:
  9. @Nadzrin Most FEA solvers are unitless, therefore it is the user's responsibility to follow a consistent set of units: The DOFs 1-3 are displacements and the DOFs 3-6 are rotations (units are radians).
  10. @LFSS Yes, there is. If I remember correctly (I am away from my Hyperworkstation), it should be under Analyze (on the menu bar), towards the right end (probably Run), it is a suboption. Alternatively, search for any keyword with ctrl+f
  11. @Abbas You may find the Lattice Structure Optimization demonstration I made helpful (some lattice parameters are explained):
  12. Hi, Area is the measurement of the surface of the object (square units) Perimeter refers to the outline that surrounds a closed shape (linear units).
  13. To select elements within a circle, Shift + Single click and release of the mouse displays the entity selection pop-up menu: Inside of circle selects the entities that are inside of a circle window. In Hyperworks X, Right Click anywhere in the window:
  14. Hi, simulating maching process can be done in Radioss, but there are some issues: -due to timestep considerations, these simulations are computationally intensive -proper definition of failure (damage)models is essential There are no milling examples in Radioss yet, but the screwing process is analogus: https://altairuniversity.com/learning-library/radioss-sample-of-a-screwing-process/ Try to implement this approach in Radioss:
  15. Hi @KBE, in Radioss user profile rotations can be applied with imposed displacement or velocity boundary condition (XX, YY or ZZ direction of global or local coordinate system- skew) with prescribed displacement/rotation versus time curve. Create rigid bodies on each of the upper and lower tool and apply the boundary conditions only on the master nodes of rigid bodies. Make sure to constrain all unwanted degrees of freedom.
  16. Hi, First you need to extract the midsurface Then you can use any of the following option 1)Create Different properties You can organize the elements of different thickness in different components. then respectively create properties for them with the correct thickness and then assign them. 2)Utility menu>Geometry mesh>midsurface thickness This option will consider the existing elements for assigning the thickness. Here you are allowed to do the surface editing. But the surface which you are meshing should be extracted mid surface of the required Geometry. 3) Menu>>Assign>>Midmesh Thickness This is the best option as you can select the elements and apply the thickness.
  17. Hi, The crushing behavior of the foam cells is represented by a stress plateau with irreversible strains. An elasto plastic behavior is introduced in the deviatoric part of the stress tensor in order to represent this phenomenon. σ dev plas = A + B (1 + C * γvol) with γvol = (V / V0) − 1 where σ dev plas is the plastic stress applied to the principal stress of the deviatoric tensor, γvol is the volume strain and A, B and C are modeling parameters. The densification phenomenon is modeled by a pressure term in the spherical stress tensor. σ spher ij = −P * δij with P = (− P0 * γvol) / (1 + γvol − Φ) where δij is the Kronecker symbol, Φ is the foam porosity and P0 the initial air pressure.
  18. Hi, There has been some changes in the way boundary conditions are applied and organized in Hyperworks X. The BC manager isn't available; instead BCs are applied under Analyze (on the menu bar). Also boundary conditions are now organized under load collectors (similar to Optistruct). I too was not happy at first with the change, but it just takes some time to get used to it.
  19. This material law initially follows the Maxwell-Kelvin-Voight viscoelastic model until it intersects the defined yield curve, which limits the visco-elastic stress in tension and compression. For more details refer to the attached documentation (from Radioss help): Visco-elasto Materials for Foams (LAW33).pdf _MAT_LAW33 (FOAM_PLAS).pdf
  20. Hi, this modelchecker error indicates badly shaped 3D element (meshing issue). The solid is decomposed into sub-volumes associated to each integration point. If the element is badly warped, one sub-volume could be negative. Check your element quality. Tool > check elems > 3D > aspect, jacobian, warpage, tet collapse
  21. Hi, the issue is because the interface "impacteur vs foam" had dtmin=0.6 If the time step of a slave node in this contact becomes less than dtmin, the slave node is deleted from the contact and a warning message is printed in the output file. This dtmin value takes precedence over any model interface minimum time step entered in /DT/INTER/DEL. Because dtmin is quite high, a lot of nodes are deativated from the interface, therefore penetrating the plate. The recommended solid property parameters for material law 70: If there is hourglassing, use Isolid=17, however your model runs fine with the above. model16_edit_0000.rad
  22. Hi, There are initial penetrations; check and resolve using: -in Hypercrash: Quality>Check all Solver Contact Interfaces -in Hypermesh: Tool>penetration check The issue is due to the yield stress vs. volumetric strain curve. Because the curve has a negative last slope Radioss extrapolates negative stress, which is not valid (The input stress should be positive for both tension and compression). As a workaround, define an additional curve segment with a zero or positive slope. IA_Setup_edit2.hm Yield stress vs. volumetric strain curve should look like:
  23. Hi, the minimum timestep warning in the interface is due to the kinematic time step of the interface. It is because the node is penetrating too far into the gap. You can try increasing the Gapmin in your TYPE7 interface which will allow the contact to work sooner and prevent node from penetrating so far. Or you could try making the interface stiffer, Istf=3 which uses the maximum stiffness of the slave and master. First check for initial penetrations and intersections: -in Hypercrash: Quality>Check all Solver Contact Interfaces -in Hypermesh: Tool>penetration check Check the gap that is used for this interface.The value must be physically realistic and based on shell thicknesses in case of contact between shells. In case of constant gap (Igap =0) with no input gap (Gapmin=0), RADIOSS determines a default value for Gapmin and you can check this value in the starter out file. Gapmin=1mm usually works in most simulations. If some elements fail on the master side or on the slave side of the interface, it is important to set Idel =2 (or Idel =1) for this interface. This will prevent nodes connected to deleted elements whose stresses are released to impact with a possible high velocity.
  24. Hi, Ishell/Isolid=QEPH/HEPH=24 is not recommended for orthotropic materials because the physical hourglass stabilization forces are computed based on isotropic assumptions. Instead, use fully integrated elements Isolid=14 or 17. one_element_0000.rad
  25. Make sure to set TYPE=PLASTIC and TYPSTRN=1 on the MATS1 card.
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