/PROP/TYPE14 (SOLID)

Format

Definition

Comments

1. I_solid - Solid elements formulation
   • For most situations, I_solid = 24 (HEPH) hexahedral element is the best compromise between computational cost and quality.
   • Elements formulation I_solid = 1, 2, and 24 are reduced integration elements with 1 Gauss integration point where as I_solid = 14, 17, and 18 are fully-integrated elements.
   • I_solid = 24 (HEPH) solid elements use a physical hourglass formulation that is similar to the hourglass formulation used by I_shell = 24 (QEPH) shell elements. This hourglass formulation returns better results than the viscous hourglass formulation used by I_solid = 1 or 2.
   • I_solid = 18, the I_cpre and I_smstr default values depend on the material and use these recommended values:

     Default	Material Laws
     Icpre = 2	2, 21, 22, 23, 24, 27, 36, 52, 79, 81, 84
     Icpre = 3	12, 14, 15, 25, 28, 50, 53, 68, and If $\nu \le 0.49$ , then 1, 13, 16, 33, 34, 35, 38, 40, 41, 70 and 77 70, 77
     Icpre = 1	All other laws and If $\nu \ge 0.49$ , then 1, 13, 16, 33, 34, 35, 38, 40, 41, 70, and 77
     Ismstr = 10	38, 42, 62, 69, 82, 88, 92, 94, 95, 100 and 101
     Ismstr = 11	70
     Ismstr = 1	28
     Ismstr = 2	All other laws

   • For very soft visco-elastic or hyper-elastic materials I_solid = 5 can improve the material stability with bigger hourglass stiffness.
2. 2D Quad elements.
   The following element formulations are supported for 2D analysis when using /QUAD elements

   • I_solid = 2, 17
   • I_smstr= 4
   • I_frame= 1, 2
   • I_cpre= 1, 2.
3. When using the automatic setting option I_smstr = I_cpre = I_frame=-1, the values for these options are defined using the best options based on the element formulation, element type, and material. Alternatively, defining I_smstr = I_cpre = I_frame=-2 will overwrite the values for these options defined in this property with the best value (refer to /DEF_SOLID) based on element type and material law. To see the values defined by Radioss, review the “PART ELEMENT/MATERIAL PARAMETER REVIEW” section of the Starter output file.
4. I_smstr - Small strain formulation flag
   • For small strain formulations (I_smstr =1, 3, 11) or elements that switch to small strain formulation (I_smstr =2, 12), the strains and stresses calculated in the material laws are engineering strains and stresses. Otherwise, they are true strains (or total strains) and Cauchy stresses.
   • I_smstr = 10, 12 are only compatible with these material laws 1, 38, 42, 62, 69, 82, 88, 92, 94, 100 and 101 that use total strain formulation. Generally, the Left Cauchy-Green strain is used. For User laws, the deformation gradient tensor and the right stretch tensor could be used.
   • I_smstr = 11 has been developed for Law 70 (foam), it is only compatible with material laws using engineering total strain (for example, Laws 1, 38 and 70). Generally, more stable results can be obtained when I_smstr =1.
   • I_smstr=12 can be used with /DT/BRICK/CST to automatically switch elements with a low time step from Lagrange type total strain to total small total strain (I_smstr = 11). However, there can be a slight discontinuity of stresses during the change in strain formulation.
   • The Radioss Engine option /DT/BRICK/CST only works with solid properties that use I_smstr = 2 or 12.
   • Starting with version 2017, Lagrangian elements whose volume becomes negative during a simulation will automatically switch strain formulations to allow the simulation to continue. When this occurs, a WARNING message will be printed in the Engine output file. The following options are supported.

     Element Type and Formulation	Strain Formulation	Negative Volume Handling Method
     /BRICK Isolid = 1, 2, 14, 17, 18, 24 /TETRA4, Itetra4 = 1000 /TETRA10, Itetra10 = 1000	Full geometric nonlinearities. Ismstr = 2, 4	Switch to small strain using element shape from cycle before negative volume.
     	Lagrange type total strain. Ismstr = 10, 12	Lagrange type total strain with element shape at time=0.0.

5. I_cpre - Constant pressure formulation flag
   • I_cpre=1 is used to prevent volumetric locking in incompressible or quasi-incompressible material. For this case, the stress tensor is decomposed into a spherical and deviatoric part. Reduced integration is then used for the spherical part so that the pressure remains constant.
   • I_cpre=2 is only available for elasto-plastic laws. To prevent volume locking, additional terms with Poisson’s coefficient are added to the strain. When the material is still elastic and thus compressible, the Poisson’s coefficient terms are small. As the material becomes plastic and thus incompressible, the Poisson’s coefficient terms increase to prevent volume locking. Refer to the Radioss Theory Manual for additional explanation.
6. I_npts - Number of integration points
   • For I_solid = 14 and 16, the recommended value is I_npts = 222.
7. Tetra elements
   • The I_solid flag is not used with 4-node (/TETRA4) or 10-node (/TETRA10) tetrahedron elements.
   • 4-nodes tetrahedron with the ALE framework is compatible with I_tetra4 = 1000 or I_tetra4 = 3 only.
   • The quadratic tetrahedron element (/TETRA10) with I_tetra10 = 2 uses the same the original integration scheme and shape functions with the time step of the linear tetrahedron (using /DT1/BRICK), using the dynamic condensation. The method implementation is proprietary.
   • The incompatibility list of I_tetra10=2 as:
     • AMS
     • Implicit
     • If the middle node of Tetra10 was defined as dependent node of /RBE3, /MPC or /RLINK.
     • If the middle node of Tetra10 was defined alone as secondary node of /RBODY, /RBE2.
     • If the middle node of Tetra10 was defined alone in /BCS, /IMPACC, /IMPVEL or /IMPDIS.
     • For /INTER/TYPE2 with kinematic types: Spot_flag < 25 and =30, if one of the corner nodes was defined as secondary node.

       (It is recommended to use Spot_flag=27 or 28 of interface TYPE2 with I_tetra10=2.)

8. I_frame - Element coordinate system formulation flag
   • When co-rotational formulation is used (I_frame = 2), the stress tensor is computed in a co-rotational coordinate system. If large rotations are involved, this formulation is more accurate but does have a higher computational cost. It is recommended in cases of elastic or visco-elastic problems where shear deformation is important.
9. d_n - Numerical damping and h - hourglass viscosity coefficient
   • Numerical damping d_n is used in the hourglass stress calculation for I_solid = 24 (HEPH) solid elements. The energy from numerical damping is included in the time history internal energy output.
   • When comparing results between I_solid = 24 and I_solid = 1 or 2 where, d_n=h, the numerical damping is $\left(2/3\right)\times {10}^{-3}$ times smaller for I_solid = 24 than I_solid =1 or 2.
   • The numerical Navier Stokes viscosity model is available for all material laws. Note that the output viscosity stress is available just for users law and I_solid =1 (In time history output the viscosity stress is added in the stress).
10. Output for post-processing
    • For post-processing solid element stress, refer to /ANIM/BRICK/TENS for animation and /TH/BRICK for plot files.
    • In plot and animation files, stress tensor is attached to the co-rotational frame.
11. Solid to SPH properties (Sol2SPH)
    • When using Sol2SPH, solid elements are converted to SPH particles when a solid is deleted due to contact, material failure criteria, or time step criteria.
    • The number activated of SPH particles depends on parameter Ndir. The particles properties are computed using the sphpart_ID part number.
    • The option Sol2SPH is only compatible with I_solid = 1, 2 or 24, I_frame = 1 or 2.
    • The option I_del= -1 or -2 in interface /INTER/TYPE7 needs to be set.
    • Both material laws for solid and SPH parts must be of the same type.
12. Flag I_ale is replacing the old method to enable ALE framework with /ALE/MAT or EULER framework with /EULER/MAT.
13. Quality criteria are calculated as follows:
    • Maximum Volume Ratio: If $Vr=\frac{V}{V_0}<Vdef\_min$ , then element is deleted;
    • Maximum Volume Ratio: If $Vr=\frac{V}{V_0}>Vdef\_max$ , then element is deleted;
    • Maximum Aspect Ratio: If $ASP=\frac{l_{max}}{l_{min}}>AS{P}_{max}$ , then element is deleted with:
      • Hexa: l_max calculated as max length of the 3 medians of the element
      • Tetra: l_max calculated as the square root of the max area
      • Solid: l_min calculated as l_c
      • Tshell: l_max calculated as max length of the 2 medians of the element
      • Tshell: l_min calculated as the area of the middle surface divided by l_max
    • Minimum Tetra Collapse: If $COL=\frac{l_{\min }}{l_{\max }}<CO{L}_{\min }$ , then element is deleted.