Mortar Contact for Implicit Analysis

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1 Mortar Contact for Implicit Analysis Thomas Borrvall Anders Jonsson Marcus Lilja DYNAmore Nordic AB Linköping Sweden

2 Mortar Contact - Name Justification The mortar finite element method describes the coupling of non matching discretization of two subdomains M.A.Puso and T.A.Laursen, A mortar segment-tosegment contact method for large deformation solid mechanics, Comput. Methods Appl. Mech. Engrg. 193 (2004) M.A.Puso and T.A.Laursen, A mortar segment-tosegment frictional contact method for large deformations, Comput. Methods Appl. Mech. Engrg. 193 (2004) Developers' day,

3 Mortar Contact No Friction 3 Developers' day, 2014 Slave segment Master segment O x 3 x 1 x 2 M S M S j m j i s i c c m s T s s j m j m i s i s ds d ds d d d d N N x f x f x x n x x x x x forces Nodal ) ( Constitutive law ) ( Kinematics Isoparametric element

4 Mortar Contact - Summary Penalty based segment to segment contact Finite element consistent force σ Continuous force displacement relation Parabolic constitutive law Continuous stiffness displacement relation Several forms d CONTACT_FORMING_SURFACE_TO_SURFACE_MORTAR CONTACT_AUTOMATIC_SURFACE_TO_SURFACE_MORTAR CONTACT_AUTOMATIC_SINGLE_SURFACE_MORTAR CONTACT_AUTOMATIC_SURFACE_TO_SURFACE_MORTAR_TIED CONTACT_AUTOMATIC_SURFACE_TO_SURFACE_TIEBREAK_MORTAR Relatively expensive Intended for implicit analysis, NOT explicit analysis To the best of our knowledge best total implicit contact algorithm Developers' day,

5 Mortar Contact Example 1 Developers' day,

6 Mortar Contact Example 1 Developers' day,

7 Mortar Contact Example 2 Developers' day,

8 Mortar Contact Example 2 Developers' day,

9 Mortar Contact General Usage In principle append suffix MORTAR to standard FORMING and AUTOMATIC contact keywords Forming contacts require master side orientation and separate interfaces on top and bottom of blank Look-ahead h-adaptivity supported Work in the direction of supporting deformable tools and look-ahead r-adaptivity for forging problems Rigid shells have zero contact thickness in forming contacts but coincides with shell thickness for automatic contacts MPP and SOFT options do not apply Contact stiffness is based on slave side material stiffness and characteristic length Use preferrably part (set) based contact with weak side as slave Characteristic length is thickness for shell elements and minimum element size for solid elements, for solids it may and should be set Extensive warnings about this as of R8.0 Developers' day,

10 Beams and shell edges in automatic contact Flat edge contact always apply in automatic contact Beam lateral surfaces are discretized into segments with mortar contact applied to each segment Work in enhancing beam contact Support rolling Developers' day,

11 Mortar Contact Example 3 Developers' day,

12 Mortar Contact Stiffness and Release c K s f d d c f x cubic x function that depends on IGAP x x K d d c s stiffness scaling stiffness modulus penetration distance 0.03 of characteristic length factor (SFS*SLSFAC) slave segment Contact is released if penetration is larger than half characteristic length after equilibrium Information of penetration may be requested Developers' day,

13 Mortar Contact Pentration Info Number of contact pairs Maximum penetration, absolute and relative, and elements where this penetration occurs Warning if contact is about to release Developers' day,

14 Mortar Contact Example 4 Rubber bushings Two stages Compression Shear Courtesy of Dellner Couplers AB and Alvelid Engineering Developers' day,

15 Mortar Contact Example 4 Mortar contact with use of IGAP a necessity (?) Makes use of robust line search (LSMTD=5 on *CONTROL_IMPLICIT_SOLUTION), nonlinear implicit and contact diagnostics / total/rubber elements solved in 20h 20min on 16 processors No cut-backs in implicit steps and no negative volumes during simulation Dynamics and Poisson s ratio of.495 (solved with.499 as well) Severe element deformation, taken to the limit(?) Developers' day,

16 Penetrations Initial penetrations reported in message file(s) List of all penetrations including elements Report of maximum penetration Treatment reported, governed by IGNORE flag Four IGNORE options IGNORE=0, no action taken IGNORE=1, track initial penetrations IGNORE=2, move contact surface to incident contact and apply optional contact stress IGNORE=3, restore initial penetrations in specified time (small penetrations) IGNORE=4, restore initial penetrations in specified time (large penetrations) IGNORE=3,4 is the Mortar counterpart to INTERFERENCE Developers' day,

17 Mortar Contact Example 5 Courtesy of Volvo GTT Fitting of rubber cylinder between two steel compoonents Penetrations beyond element size, contact not detected unless IGNORE=4 is used solid elements solved in 4h18min on 12 processors Developers' day,

18 Mortar Contact Example 5 Courtesy of Volvo GTT Developers' day,

19 Mortar Contact Example 5 Developers' day,

20 Mortar Contact Example 5 Developers' day,

21 IGNORE.LT.0 in R8.0 In single surface contact, spurious contact states are detected within parts IGNORE.LT.0 works as ABS(IGNORE) but ignore contact within parts Spurious selfcontact Developers' day,

22 Tied and Tiebreak a few words Mortar tied/tiebreak contact is offset and penalty based Only ties segments facing eachother Insensitive to mesh dissimilarity Mortar glue the two sides together with smooth force transmission Non-mortar spotweld slave nodes to master surface For tiebreak, OPTION=9 is supported Corresponds to material 138 (MAT_COHESIVE_MIXED_MODE) Damage output to contact gap in d3intfor database Interesting alternatives to conventional tied contacts if running implicit analysis Not used extensively up to today Efficiency improvements to be expected in the future Developers' day,

23 Mortar contact Example 6 3 cavities and 3 leaflets modelled using shells Pressure boundary conditions for flow, valve moves due to presence of fluid vortices Strong incompressible fluid to elastic structure coupling Mortar contact reported necessary for solving the problem Developers' day,

24 Mortar Contact Example 6 Developers' day,

25 Mortar Contact - Conclusions Mortar contact for implicit analysis Covers many attractive features Robust and accurate Expensive, but makes up for this in implicit Does not cover all features common to explicit contacts Orthotropic friction Beyond R7.0 features IGAP>1 for progressive penalty stiffness Penetration diagnostics Efficiency improvements, especially for single surface Beyond R8.0 features IGNORE.LT.0 FS.LT.0 friction coefficients can be applied on *PART_CONTACT or in a friction table Should be complemented with new developments in implicit nonlinear solver Great advancements in solution of rubber problems New strategies always under investigation Developers' day,

26 A Guide to Solving Implicit Mortar Contact Problems in LS-DYNA, Thomas Borrvall Some Guidelines for Implicit Analyses using LS- DYNA, Anders Jonsson Mortar Contact is in Theory Manual Developers' day,

27 Thank you! Developers' day,

28 Mortar Contact Example 5 Developers' day,

29 Mortar Contact Example 5 Developers' day,

30 Mortar Contact Example 5 Soft foam and steel contact Variants Mortar contact Conventional surface to surface contact, IGAP=1 Conventional surface to surface contact, IGAP=2 SOFT=2 contact, IGAP=2 Mortar contact and IGAP=1 converges Mortar contact takes 15% longer Mortar contact gives smooth force All other variants fail Developers' day,