a specimen under tension in LS-DYNA using the implicit solver
Ivan Mosa
Hello everyone,
I have a question regarding the simulation of a cyclic, displacement-controlled loading of a specimen under tension in LS-DYNA using the implicit solver.
The prescribed displacement has the following time history:
Time [s]: 0, 1, 2, 3, 4, 5, 6
Displacement [mm]: 0, 2, 0, 2, 0, 2, 0
The simulation is performed using the implicit solution method.
From a real tensile test, I have the following material data available:
Stress–strain curve
Young’s modulus
Density
Poisson’s ratio
Yield strength
Ultimate tensile strength
Fracture strain
For the material model, I am using MAT_24 (MAT_PIECEWISE_LINEAR_PLASTICITY).
To define the boundary condition, I created a load curve for the prescribed displacement and entered the values listed above. The end time of the simulation is set to 6 seconds.
The goal of the simulation is to generate a force–displacement curve showing the cyclic hysteresis behavior.
However, I am encountering the following issue:
LS-DYNA only processes the first two loading steps and then terminates the job, so the remaining cycles are not computed.
Does anyone have an idea what might be causing this issue or which settings I should check?
Thank you very much in advance!
James Kennedy
Dear Ivan,
Some suggested comments from the internet
Cyclic loading using the LS-DYNA implicit solver is a standard approach for quasi-static analysis where the high computational cost of explicit analysis is prohibitive due to the long duration of the physical event. The implicit solver is well-suited for such problems as it is unconditionally stable and allows for larger time steps, provided convergence can be achieved at each step.
4
Key Steps and Keywords for Implicit Cyclic Loading
To set up a cyclic loading simulation using LS-DYNA implicit, the following keywords and considerations are crucial:
· Activate Implicit Solver: You must include the *CONTROL_IMPLICIT_GENERAL keyword in your input deck. This card flags the solution as implicit and is used to set the initial time step size (DT0).
· Define Load Curve: The cyclic nature of the loading is defined using one or more *DEFINE_CURVE keywords. These curves specify the load (force or displacement) as a function of time, including the necessary loading and unloading cycles.
· Apply Load: The defined load curve is then applied to the relevant nodes or degrees of freedom using keywords such as *LOAD_NODE_SET (for forces) or *BOUNDARY_PRESCRIBED_MOTION (for displacements). The load should be ramped up linearly within the implicit steps to aid convergence.
· Specify Implicit Dynamics: To ensure the analysis is transient dynamic (which is often necessary for true cyclic behavior) rather than a pure static solution at each step, include the *CONTROL_IMPLICIT_DYNAMICS keyword.
· Material Model: Ensure your chosen material model (e.g., those suitable for plasticity and cyclic hardening) is available for implicit analysis. The material should accurately capture the hysteretic behavior under cyclic conditions.
· Element Types: Fully integrated element formulations may be beneficial for implicit analysis as they often provide better performance compared to the default single-point integration elements common in explicit analysis.
· Troubleshooting Convergence: Implicit analysis can be sensitive to boundary conditions, contact, and material nonlinearities. Important control cards for troubleshooting include:
o *CONTROL_IMPLICIT_SOLUTION (used for parameters like the number of iterations and the D3ITER output file).
o *CONTROL_CONTACT with specific flags like IGAP and SHLTHK can help manage contact behavior and improve stability.
o Setting NLP PRINT in *CONTROL_IMPLICIT_GENERAL can provide detailed information in the message files to diagnose convergence issues.
Best Practices
· Use the latest double-precision LS-DYNA executable.
· Avoid initial penetrations in your model, as they can cause convergence problems.
· Consult the official Ansys LS-DYNA documentation and examples for detailed setup guidelines.
--------------------------------------------------------
Some additional notes
https://www.youtube.com/watch?v=uQLPkWmHM90
Sincerely,
James M. Kennedy
KBS2 Inc.
March 14, 2026
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James Kennedy
AI Overview
LS-DYNA implicit cyclic analysis simulates quasi-static, repeating loads (e.g., seismic testing of structures) using *CONTROL_IMPLICIT_GENERAL (IMFLAG=1), *CONTROL_IMPLICIT_SOLUTION, and *CONTROL_IMPLICIT_AUTO for time-stepping. A cyclic load is typically defined using a sinusoidal *DEFINE_CURVE linked to a *BOUNDARY_PRESCRIBED_MOTION node set, demanding high-quality mesh and stable contact settings.
Key Keyword Structure for Implicit Cyclic Example
1. Activate Implicit Solver:
lsdyna
*CONTROL_IMPLICIT_GENERAL
$ impl dt0 imie igs cnstnc form - -
1 0.1 0 0 0 0
1. IMFLAG=1 sets the solver to Implicit.
2. DT0 is the initial time step.
2. Define Cyclic Loading Curve:
lsdyna
*DEFINE_CURVE
$ lcid
1
$ time val
0.0 0.0
1.0 1.0 $ Peak 1
3.0 -1.0 $ Peak 2 (reverse)
5.0 1.0 $ Peak 3
3. Apply Motion:
lsdyna
*BOUNDARY_PRESCRIBED_MOTION_SET
$ nsid dof vad lcid sf
1 1 2 1 1.0
0. DOF=1 (X-direction), VAD=2 (Velocity), LCID=1 (Curve above).
4. Automatic Time Stepping:
lsdyna
*CONTROL_IMPLICIT_AUTO
$ dtf minif maxif
0.5 5 10
0. Ensures convergence by reducing time step if iterations increase.
YouTube
Best Practices for Cyclic Problems
· Solver Selection: Use Nsolver=2 (Default Nonlinear) in *CONTROL_IMPLICIT_SOLUTION for complex contact.
· Contact: Use *CONTACT_MORTAR for smoother, more stable convergence in implicit, as it handles severe nonlinearities better than conventional penalty methods.
· Convergence Issues: If the model fails to converge, reduce the initial time step in *CONTROL_IMPLICIT_GENERAL and tighten tolerances.
· Damping: Use *DAMPING_PART_MASS or stiffness damping to stabilize the structure if necessary, though it should be minimal for quasi-static problems.
YouTube +3
3m
LS-DYNA Tutorial Implicit
YouTube·LSDYNATV
55:52
LS-DYNA: Simulating Cyclic Test for A Reinforced Concrete ..
l...@schwer.net
What is the error message wen the run stops? --len
From: ls-d...@googlegroups.com <ls-d...@googlegroups.com> On Behalf Of Ivan Mosa
Sent: Saturday, March 14, 2026 8:24 AM
To: LS-DYNA2 <ls-d...@googlegroups.com>
--
Ivan Mosa
Hi Len,
hi James,
in the first simulation, there was no error message; the solver simply stopped after about 2 seconds. I have now preprocessed the model in Workbench and applied James’s suggestions: enabled the relevant implicit control cards and meshed the model with ELFORM 23.
The displacement curve looks as follows.
I also generated a force–displacement curve, but it does not look correct.
Do you have an idea what might be causing this?
