Non linear loading curve failing during unloading
Rue
James Kennedy
Dear Rue,
Perhaps some of the introductory implicit examples given here may be of some interest:
https://lsdyna.ansys.com/wp-content/uploads/2026/08/Intro_Examples_Manual_DRAFT.pdf
Sincerely,
James M. Kennedy
KBS2 Inc.
August 30. 2026
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Rue
James Kennedy
Dear Rue,
Have you validated the foam stress-strain curve for the desired full range of loading and unloading?
Sincerely,
James M. Kennedy
Kbs2 Inc.
August 31, 2026
To view this discussion visit https://groups.google.com/d/msgid/ls-dyna2/d23fbfb0-4ab4-4060-ad6d-6c2491b06b76n%40googlegroups.com.
James Kennedy
Dear Rue,
Some addition MAT_063 NOTES:
In LS-DYNA, *MAT_063 (*MAT_CRUSHABLE_FOAM) dictates that the material
behavior during unloading is fully elastic Because it is a highly simplified model intended
primarily to track energy-absorbing isotropic compression (such as aluminum foams or
crushable wood), it does not capture complex visco-plastic or hysteretic loops during the
unloading cycle.
Key Unloading Characteristics of *MAT_063
Fully Elastic Slope: When the loading is reversed, the stress drops back toward zero
following a path defined by the initial Young's Modulus (E).
Zero Hysteretic Energy Loss: Unlike more complex foam models (like *MAT_057 or
*MAT_083), there are no hysteresis factors (HU or SHAPE) to dictate a custom or non-
linear unloading path.
Immediate Load Drop: If the impactor unloads, the force drops abruptly because no
significant elastic recovery or rebound occurs in the crushed material matrix.
Tensile Threshold: If unloading continues into tension, the response remains linear elastic
until it hits the user-defined Tensile Stress Cutoff (TSC), where it behaves as elastic-perfectly
plastic
Sincerely,
James M. Kennedy
KBS2 Inc.
August 31, 2026
From: James Kennedy
Sent: Sunday, August 30, 2026 4:17 PM
To: 'Rue' <ruva.ny...@gmail.com>; LS-DYNA2 <ls-d...@googlegroups.com>
Subject: RE: [LS-DYNA2] Non linear loading curve failing during unloading
Dear Rue,
Perhaps some of the introductory implicit examples given here may be of some interest:
https://lsdyna.ansys.com/wp-content/uploads/2026/08/Intro_Examples_Manual_DRAFT.pdf
Sincerely,
James M. Kennedy
KBS2 Inc.
August 30. 2026
From:
ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com]
On Behalf Of Rue
Sent: Tuesday, August 25, 2026 9:17 AM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] Non linear loading curve failing during unloading
I am running an implicit analysis on a foam-filled structure. I am using a single curve for both the loading and unloading. The solver crashes during the unloading phase. Usually between 59% and 70% of the run time. The foam on its own loads and unloads following the prescribed paths. Could you please take a look at the keyword file and advise which inputs are incorrect, missing, or causing conflict? Any form of feedback on where I might be getting the physics wrong will be greatly appreciated.
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James Kennedy
Dear Rue,
A paper perhaps of some interest:
Debela N. Gurmu, Krzysztof Wacławiak, and Hirpa G. Lemu “Experimental and numerical
analysis of a 3D-foam model subjected to uniaxial compression and low-velocity impact loading”,
Results in Engineering, Volume 29, March ,2026.
https://www.sciencedirect.com/science/article/pii/S2590123026003567
Sincerely,
James M. Kennedy
KBS2 Inc.
September 1, 2026
I am running an implicit analysis on a foam-filled structure. I am using a single curve for both the loading and unloading. The solver crashes during the unloading phase. Usually between 59% and 70% of the run time. The foam on its own loads and unloads following the prescribed paths. Could you please take a look at the keyword file and advise which inputs are incorrect, missing, or causing conflict? Any form of feedback on where I might be getting the physics wrong will be greatly appreciated.
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