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LS-DYNA Analysis for Structural Mechanics
5.2.4
2015
WORKSHOP II: HOURGLASS CONTROL/HOURGLASS
Isoparametric Shell/Solid Elements and Hourglassing*
• All under-integrated isoparametric elements (one Guass
point) have hourglassing present. It is a non-physical “zeroenergy” mode of deformation.
• Fully Integrated formulations do not hourglass. Additionally,
tetrahedron and triangular elements do not hourglass but are
overly stiff in many applications.
• *Control_Hourglass or *Hourglass to set hourglass control.
• Use default unless additional documentation is consulted
(e.g., see Review of Solid Element Formulations Erhart.pdf
(Class Reference Notes / Solid Elements).
• Hourglass energy should be less than 10% of the internal
energy at any stage of the analysis (use *CONTROL_ENERGY
(HGEN=2) to calculate hourglass energy).
• In LSPP, check glstat for total hourglass energy and then
matsum for individual part energy.
How to Limit Hourglassing
• Apply pressures instead of point loads.
• Refine mesh
• Selectively use ELFORM=16 (3x computational cost)
Workshop II: Hourglass Control
• Evaluate current model for hourglassing.
Plot internal energy and hourglass energy.
• Read Hourglass Material.
• Attempt fix with different hourglass type.
• Switch ELFORM to 16.
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