Oasys LS-DYNA Environment 8.1 VOLUME 3 ... - Oasys Software

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Oasys LS-DYNA Environment: User Guide (Version 8.1) These effects can cause big differences in model behaviour, so it is strongly recommended that for general use SHLTHK is set to zero. NULL SHELLS Shell elements made of *MAT_NULL can be used to coat solid element meshes to help stabilise the contacts. These are often recommended if the solids are soft e.g. foams. RECOMMENDED INPUT PARAMETERS There are many input parameters for contact surfaces in LS-DYNA. OASYS recommend the following: *CONTROL_CONTACT Leave all parameters to take the default settings, except: - If compatibility with OASYS DYNA3D 5.1 is required, set PENOPT = 2 - ORIEN can be set to 2 if all surface-to-surface contacts have initial gaps. *CONTACT Leave all parameters to take the default settings, except: - SPR, MPR should both be set to 1 to allow viewing of contact surfaces in OASYS D3PLOT (also requires user to request a Contact Force file when submitting the job). - FS, FD: generally set both of these to the same value (OASYS suggest 0.2 if no other information is available). - SST, MST (applies only to contact types 4, 13-16, a3, a5, a10 on shell elements). Can be adjusted if required but generally leave as default. - NFLF, SFLF, NFLS, SFLS (contact types 8 & 9 only). Must be non-zero or the contact will break apart immediately. If the contact is required not to break apart, input high values (e.g. 1E8). - NEN, NES (contact type 8 only). Suggested value 2.0. - MAXPEN (contact types 3, 5, 10). OASYS recommend that a non-zero value be set for all type 3, 5 and 10 contact surfaces. Typical values would be 1 to 2mm for metal-on-metal contact; 5 to 10mm for contacts involving foams or other soft materials. Page 9.12
Oasys LS-DYNA Environment: User Guide (Version 8.1) SUMMARY TABLE The contact types can be grouped as follows: Group A B C D Can be defined by list of parts yes yes yes yes Search method Mesh Connectivity Bucket Sort Bucket Sort Mesh Connectivity Contact from both sides no no yes no Orientation of segments important yes yes no yes Default contact depth 10000000000 4 x thickness 0.4 x thickness Type 26: 400 x thickness Variable which limits contact depth infinite MAXPEN XPENE SST, MST (ON LOADCURVE) Contact plane offset from nodes no yes yes no Initial gaps essential no yes yes no A: Types 3, 5, 10 (SHLTHK = 0) B: Types 3, 5, 10 (SHLTHK = 1) C: Types 4, 13, 14, 15, 16, a3, a5, a10, 26 D: Types 19, 20, 21 ERRORS AND WARNINGS Kinematic Constraint Surfaces Surface types 1, 2, 6, 7, 17 and 18 work by imposing motion on nodes to maintain contact between the surfaces. This will clash with any other motion imposed by features such as rigid bodies, restraints, constraints, stonewalls, other tied surfaces, etc. No more than one such feature should be present at any given node. Escape from Concave Surfaces Where neighbouring contact segments form a concave surface, there would appear to be a wedgeshaped region of no-man's land behind the edge which belongs to neither one segment nor the other, and in which nodes may therefore lose contact with the surface. LS-DYNA prevents this by adding a 2.5% margin to the width of each segment (shown shaded in Figure 9.4). Thus node A can pass from one segment to the other without losing contact. If the penetration is very great (node B in Figure 9.4) the 2.5% margin may be insufficient - there Page 9.13
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Oasys LS-DYNA Environment 8.1 VOLUME 3 ... - Oasys Software

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