{"id":459028,"date":"2026-05-29T19:08:08","date_gmt":"2026-05-29T19:08:08","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/hyperelastic-material-spurious-stress-after-rigid-to-deformable-switch\/"},"modified":"2026-05-29T19:08:08","modified_gmt":"2026-05-29T19:08:08","slug":"hyperelastic-material-spurious-stress-after-rigid-to-deformable-switch","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/hyperelastic-material-spurious-stress-after-rigid-to-deformable-switch\/","title":{"rendered":"Hyperelastic material – spurious stress after rigid-to-deformable switch"},"content":{"rendered":"

<p class=”ds-markdown-paragraph”><span class=””>Solver Version:<\/span><\/strong><\/p><p class=”ds-markdown-paragraph”><span class=””>Version : smp s R14                           <br>Revision: R14.1.1-8-g2ef819c24f <br>AnLicVer: 2025 R1 (20241030+dl-67-g73b144a) <\/span><\/p><p class=”ds-markdown-paragraph”><span class=””>Description:<\/span><\/strong><\/p><p class=”ds-markdown-paragraph”><span class=””>I’ve encountered an issue where hyperelastic materials develop strange initial stresses (solver: SMP single precision, double precison solver will crash the simulation immediately<\/strong>) when a part is switched from rigid to deformable using <\/span>*DEFORMABLE_TO_RIGID_AUTOMATIC<\/code><span class=””>. The same setup works perfectly with elastic materials.<\/span><\/p><p class=”ds-markdown-paragraph”><span class=””>Summary of behavior:<\/span><\/strong><\/p><\/p>\n

    \n
  1. <p class=”ds-markdown-paragraph”><span class=””>A part with hyperelastic material is initially rigid, then automatically switched to deformable at t=10.0<\/span><\/p><\/li>\n
  2. <p class=”ds-markdown-paragraph”><span class=””>Immediately after the switch, the part shows spurious stresses<\/span><\/p><\/li>\n
  3. <p class=”ds-markdown-paragraph”><span class=””>If I replace the hyperelastic material with an elastic material, the problem disappears<\/span><\/p><\/li>\n
  4. <p class=”ds-markdown-paragraph”><span class=””>The same issue occurs whether using full restart with <\/span>*STRESS_INITIALIZATION<\/code><span class=””> to add a new hyperelastic part, or within a single continuous simulation using <\/span>*DEFORMABLE_TO_RIGID_AUTOMATIC<\/code><\/p><\/li>\n<\/ol>\n

    <p class=”ds-markdown-paragraph”><span class=””>Attached test case:<\/span><\/strong><br><span class=””>A minimal working example demonstrating the issue. One single element uses <\/span>*DEFORMABLE_TO_RIGID_AUTOMATIC<\/code><span class=””> to switch from rigid to deformable at t=10.0 with hyperelastic rubber material. Simply swap the material to elastic (<\/span>*MAT_ELASTIC<\/code><span class=””>) to see the problem disappear.<\/span><\/p><p class=”ds-markdown-paragraph”><span class=””>Questions:<\/span><\/strong><\/p><\/p>\n

      \n
    1. <p class=”ds-markdown-paragraph”><span class=””>Is this a known limitation\/bug in R14?<\/span><\/p><\/li>\n<\/ol>\n

      <p class=”ds-markdown-paragraph”><span class=””>Any insights would be greatly appreciated.<\/span><\/p><p class=”ds-markdown-paragraph”><span class=””><\/span><\/p><p class=”ds-markdown-paragraph”><span class=””>Key file to reproduce:<\/span><\/strong><\/p><div><div><span style=”font-size: 12pt;”>*KEYWORD<\/span><\/div><div><span style=”font-size: 12pt;”>*TITLE<\/span><\/div><div><span style=”font-size: 12pt;”>Hyperelastic part – deformable\/rigid automatic switch<\/span><\/div><div><span style=”font-size: 12pt;”>$<\/span><\/div><div><span style=”font-size: 12pt;”>$<\/span><\/div><div><span style=”font-size: 12pt;”>$  Units: mm, kg, ms, kN, GPa, kN-mm<\/span><\/div><div><span style=”font-size: 12pt;”>$<\/span><\/div><div><span style=”font-size: 12pt;”>$<\/span><\/div><div><span style=”font-size: 12pt;”>*CONTROL_TERMINATION<\/span><\/div><div><span style=”font-size: 12pt;”>$   endtim    endcyc     dtmin    endeng    endmas<\/span><\/div><div><span style=”font-size: 12pt;”>      13.0         0       0.0       0.0       0.0<\/span><\/div><div><span style=”font-size: 12pt;”>$<\/span><\/div><div><span style=”font-size: 12pt;”>*DEFINE_CURVE<\/span><\/div><div><span style=”font-size: 12pt;”>$ LCID    SIDR    SFA     SFO     OFFA    OFFO    DATTYP  LCINT<\/span><\/div><div><span style=”font-size: 12pt;”>      1005         0       1.0       1.0       0.0       0.0         0         0<\/span><\/div><div><span style=”font-size: 12pt;”>$ time    timestep<\/span><\/div><div><span style=”font-size: 12pt;”>                 0.0                1e-2<\/span><\/div><div><span style=”font-size: 12pt;”>                 10.0               1e-2<\/span><\/div><div><span style=”font-size: 12pt;”>*CONTROL_TIMESTEP<\/span><\/div><div><span style=”font-size: 12pt;”>$#  dtinit    tssfac      isdo    tslimt     dt2ms      lctm     erode     ms1st<\/span><\/div><div><span style=”font-size: 12pt;”>      1e-2       1.0         0       0.0         0      1005         0         0<\/span><\/div><div><span style=”font-size: 12pt;”>*CONTROL_ENERGY<\/span><\/div><div><span style=”font-size: 12pt;”>$     hgen      rwen    slnten     rylen<\/span><\/div><div><span style=”font-size: 12pt;”>         2         2<\/span><\/div><div><span style=”font-size: 12pt;”>*CONTROL_OUTPUT<\/span><\/div><div><span style=”font-size: 12pt;”>$    npopt    neecho    nrefup    iaccop     opifs    ipnint    ikedit<\/span><\/div><div><span style=”font-size: 12pt;”>         1         3<\/span><\/div><div><span style=”font-size: 12pt;”>*CONTROL_SHELL<\/span><\/div><div><span style=”font-size: 12pt;”>$   wrpang    itrist     irnxx    istupd    theory       bwc     miter<\/span><\/div><div><span style=”font-size: 12pt;”>                                       1         2<\/span><\/div><div><span style=”font-size: 12pt;”>*DATABASE_BINARY_D3PLOT<\/span><\/div><div><span style=”font-size: 12pt;”>$       dt      lcdt<\/span><\/div><div><span style=”font-size: 12pt;”>      1.00<\/span><\/div><div><span style=”font-size: 12pt;”>*DATABASE_EXTENT_BINARY<\/span><\/div><div><span style=”font-size: 12pt;”>$    neiph     neips    maxint    strflg    sigflg    epsflg    rltflg    engflg<\/span><\/div><br><div><span style=”font-size: 12pt;”>$   cmpflg    ieverp    beamip<\/span><\/div><div><span style=”font-size: 12pt;”>                   1<\/span><\/div><div><span style=”font-size: 12pt;”>*DATABASE_BINARY_D3THDT<\/span><\/div><div><span style=”font-size: 12pt;”>$       dt      lcdt<\/span><\/div><div><span style=”font-size: 12pt;”>    999999<\/span><\/div><div><span style=”font-size: 12pt;”>*DATABASE_GLSTAT<\/span><\/div><div><span style=”font-size: 12pt;”>$       dt<\/span><\/div><div><span style=”font-size: 12pt;”>      0.10<\/span><\/div><div><span style=”font-size: 12pt;”>*DATABASE_MATSUM<\/span><\/div><div><span style=”font-size: 12pt;”>$       dt<\/span><\/div><div><span style=”font-size: 12pt;”>      0.10<\/span><\/div><div><span style=”font-size: 12pt;”>*DATABASE_NODOUT<\/span><\/div><div><span style=”font-size: 12pt;”>$       dt<\/span><\/div><div><span style=”font-size: 12pt;”>      0.10<\/span><\/div><div><span style=”font-size: 12pt;”>*DATABASE_RBDOUT<\/span><\/div><div><span style=”font-size: 12pt;”>$       dt<\/span><\/div><div><span style=”font-size: 12pt;”>      0.10<\/span><\/div><div><span style=”font-size: 12pt;”>*PART<\/span><\/div><div><span style=”font-size: 12pt;”>$      pid       sid       mid     eosid      hgid    adpopt<\/span><\/div><div><span style=”font-size: 12pt;”>part1<\/span><\/div><div><span style=”font-size: 12pt;”>         1         2         2<\/span><\/div><div><span style=”font-size: 12pt;”>$<\/span><\/div><div><span style=”font-size: 12pt;”>$  Aluminum<\/span><\/div><div><span style=”font-size: 12pt;”>$<\/span><\/div><div><span style=”font-size: 12pt;”>*MAT_PLASTIC_KINEMATIC<\/span><\/div><div><span style=”font-size: 12pt;”>$      mid        ro         e        pr      sigy      etan      beta<\/span><\/div><div><span style=”font-size: 12pt;”>         1   2.70e-6      68.9     0.330     0.286   0.00689<\/span><\/div><div><span style=”font-size: 12pt;”>$      src       srp        fs<\/span><\/div><br><div><span style=”font-size: 12pt;”>*SECTION_SHELL<\/span><\/div><div><span style=”font-size: 12pt;”>$<\/span><\/div><div><span style=”font-size: 12pt;”>$      sid    elform      shrf       nip     propt   qr\/irid     icomp<\/span><\/div><div><span style=”font-size: 12pt;”>         1         2<\/span><\/div><div><span style=”font-size: 12pt;”>$       t1        t2        t3        t4      nloc<\/span><\/div><div><span style=”font-size: 12pt;”>       1.0       1.0       1.0       1.0<\/span><\/div><div><span style=”font-size: 12pt;”>*SECTION_SHELL<\/span><\/div><div><span style=”font-size: 12pt;”>$       ID    elform      shrf       nip     propt        qr     icomp     setyp<\/span><\/div><div><span style=”font-size: 12pt;”>         2         2  0.833333         3         0         0         0         0<\/span><\/div><div><span style=”font-size: 12pt;”>$       t1        t2        t3        t4      nloc     marea              unused<\/span><\/div><div><span style=”font-size: 12pt;”>       0.1       0.1       0.1       0.1         0         0                    <\/span><\/div><div><span style=”font-size: 12pt;”>*MAT_HYPERELASTIC_RUBBER<\/span><\/div><div><span style=”font-size: 12pt;”>$       ID        ro        pr         N        Nv         G      sigf       Ref<\/span><\/div><div><span style=”font-size: 12pt;”>         2 8.699E-07 0.4999172         0         0         0         0         0<\/span><\/div><div><span style=”font-size: 12pt;”>$      C10       C01       C11       C20       C02       C30             unused1<\/span><\/div><div><span style=”font-size: 12pt;”>   0.11e-3  0.028e-3         0         0         0         0                    <\/span><\/div><div><span style=”font-size: 12pt;”>*NODE<\/span><\/div><div><span style=”font-size: 12pt;”>$   node               x               y               z      tc      rc<\/span><\/div><div><span style=”font-size: 12pt;”>       1             0.0             0.0             0.0<\/span><\/div><div><span style=”font-size: 12pt;”>       2             1.0             0.0             0.0<\/span><\/div><div><span style=”font-size: 12pt;”>       3             1.0             1.0             0.0<\/span><\/div><div><span style=”font-size: 12pt;”>       4             0.0             1.0             0.0<\/span><\/div><div><span style=”font-size: 12pt;”>$$$$  Define Elements<\/span><\/div><div><span style=”font-size: 12pt;”>*ELEMENT_SHELL<\/span><\/div><div><span style=”font-size: 12pt;”>$    eid     pid      n1      n2      n3      n4<\/span><\/div><div><span style=”font-size: 12pt;”>       1       1       1       2       3       4<\/span><\/div><div><span style=”font-size: 12pt;”>*DEFORMABLE_TO_RIGID<\/span><\/div><div><span style=”font-size: 12pt;”>         1<\/span><\/div><div><span style=”font-size: 12pt;”>*DEFORMABLE_TO_RIGID_AUTOMATIC<\/span><\/div><div><span style=”font-size: 12pt;”>$#   SWSET      CODE     TIME1     TIME2     TIME3     ENTNO     RELSW    PAIRED<\/span><\/div><div><span style=”font-size: 12pt;”>         1         0      10.0      1.0e20     0.0         0         0         0<\/span><\/div><div><span style=”font-size: 12pt;”>$#    NRBF      NCSF       RWF     DTMAX       D2R       R2D    OFFSET<\/span><\/div><div><span style=”font-size: 12pt;”>         0         0         0       0.0         0         1       0.0<\/span><\/div><div><span style=”font-size: 12pt;”>$# Rigid to deformable card: one card because R2D = 1<\/span><\/div><div><span style=”font-size: 12pt;”>$#     PID     PTYPE<\/span><\/div><div><span style=”font-size: 12pt;”>         1      PART<\/span><\/div><div><span style=”font-size: 12pt;”>*END<\/span><\/div><\/div><\/p>\n","protected":false},"template":"","class_list":["post-459028","topic","type-topic","status-publish","hentry","topic-tag-bug","topic-tag-ls-dyna","topic-tag-LS-DynaSolverExplicitDynamics-1"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27814"],"_bbp_topic_id":["459028"],"_bbp_subscription":["693444"],"_bbp_author_ip":["161.130.189.244"],"_bbp_last_reply_id":["459029"],"_bbp_last_active_id":["459029"],"_bbp_last_active_time":["2026-05-29 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