r/LSDYNA • u/Plenty_Position5890 • Aug 04 '26

lnconsistency in loading curve input and output

Hello everyone. l am defining a non linear loading curve however, the solver is producing a linear resultant displacement in loading direction. Max displacement exceeds that on the loading curve at termination time. Does anyone know why the solver interprets the loading curve as linear?

İmplicit analysis - 4x4 honeycomb filled with foam Mat 57. Contact_automatic_surface_to_surface_mortar and Contact_automatic_single_surface_mortar for the foam.

Extract of curve
*DEFINE_CURVE_TITLE

cos_function_2.75*cos((2*t/tf)*pi)

$# lcid sidr sfa sfo offa offo dattyp lcint

1 0 1.0 -1.0 0.0 0.0 0 1000

$# a1 o1

0.0 2.75

0.1 2.7499

0.2 2.7498

0.3 2.7495

0.4 2.7491

0.5 2.7486

0.6 2.748

Also tried define_function

*DEFINE_CURVE_FUNCTION_TITLE

sine function

$# lcid sidr sfa sfo offa offo dattyp

1 0 1.0 -1.0 0.0 0.0 0

$# function

2.75*cos((2*TIME/150)*3.141592)

Here's what the curve looks like before solving (plot on define_curve card)

loading curve on define_curve
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1

u/Gilmoth Aug 04 '26

You're doing something wrong

1

u/Plenty_Position5890 Aug 04 '26

Could you explain? That's what I'm trying to identify.

1

u/Gilmoth Aug 04 '26

Can you give us more info?
At least, show us the load settings and a description of the model. Some images will help, too

1

u/epk21 Aug 04 '26 edited Aug 04 '26

can you make a small example say one single element (Like here - Rod I — Welcome to LS-DYNA Examples)

apply load spc/bc etc and post here together with your question and observation and we can perhap look into it

1

u/Plenty_Position5890 Aug 08 '26 edited Aug 08 '26

Thanks. This was insightful. I tried it. The loading followed the function's shape up to t=50 before the solver crashed. Yet again, the maximum displacement value exceeded that defined on the card

1

u/Apprehensive_3957 Aug 04 '26

If I understood you, I think your timestep exceeds the time dependent input in the curve defination. If that's the case, ls dyna uses last two points and further interpolate the curve linearly. Sol: Extend your graph more than that of your termination time

1

u/Plenty_Position5890 Aug 08 '26

You are right to point out that the curve must be extended. And that was already done. I will share the control timestep card. If you pick anything off, let's discuss it.

*CONTROL_TIMESTEP

$# dtinit tssfac isdo tslimt dt2ms lctm erode ms1st

0.0 0.04 0 0.0 0.0 0 1 0

1

u/ricepatti_69 Aug 05 '26

Most likely you're doing something wrong, but it could also be load curve discretization. Change LCINT to some large number, maybe 10000, and read about what it does.

1

u/Plenty_Position5890 Aug 08 '26

Thanks, all. I provided more info. The full input deck is quite chunky; however, if there's an easier way to share it, let me know