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

Oasys LS-DYNA Environment: User Guide (Version 8.1)
Applications include:
- elasto-plastic characteristic to reduce rebound and oscillation.
- "soft target" impact calculations in which the deformation of the target is approximated
by a pressure-vs-depth characteristic; the target itself would then be modelled by a flat
rigid element.
Friction and damping can be included as with standard stiffness-based contact surfaces.
The loadcurve points are (penetration distance, force (or pressure for variant 3)). The optional
unload stiffness has units force/distance, except for variant 3 which has units pressure/distance.
The first point on the load curves should be (zero, zero) and all values should be positive.
PART_CONTACT
Contact parameters such as stiffness and thickness can be adjusted for individual parts using
PART_CONTACT. This is useful where soft parts and stiff parts are included in one contact.
SHELL ELEMENTS OVERLAID ON SOLID ELEMENTS
If shell elements are overlaid on solid elements, it is the shell elements that count in determining
contact stiffness and orientation. Note that this is still the case even if the contact is defined by
a list of parts and the shell part is excluded.
CONTACT TIMESTEPS
LS-DYNA computes the timestep at which each contact surface will be stable and prints it to the
OFT file. However, it does not change the analysis timestep. If the printed contact surface
timestep is less than the analysis timestep, unstable behaviour may ensue recommend that the
stiffness of the surface be reduced, either using SFS, SFM on *CONTACT or on
*PART_CONTACT.
EFFECT OF SHLTHK
The flag SHLTHK on *CONTROL_CONTACT (if non-zero) has several important effects on
contact types 3, 5 and 10:
- The contact plane is offset from the nodal plane, so initial gaps of at least a material thickness
must be present.
- The contact depth is related to element thickness and cannot be controlled directly by the user
(i.e. MAXPEN, SST, MST, SFST, MFST on *CONTACT have no effect), except by changing
XPENE on *CONTROL_CONTACT (applies to whole model, not individual surface).
- The contact search method becomes Bucket Sort, so mesh connectivity is not necessary for
the contact to work correctly.
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