Extracting interface data
satish Paudel
Hi,
I’m currently working on extracting interface data between two concrete layers in my simulation. I’ve used a tiebreak surface-to-surface contact definition, where I provided the normal and shear strength parameters as inputs.
I have a few questions and would appreciate any insights:
a) How does the stress evolve in the model during the analysis to reach the defined strength values in the tiebreak contact? Is it treated as a step function, linear progression, or something else? Since I only input the strength values in the contact card, I’d like to better understand the underlying behavior.
b) I attempted to extract interface data using the *intfor option, but the results did not align with my expectations. Has anyone successfully conducted a similar analysis—specifically related to debonding between two layers? If so, could you please share insights on the required input parameters for the tiebreak contact and any best practices for extracting meaningful interface data?
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Best Regards,
Dr. Satish Paudel
Postdoctoral scholar, Department of Civil and Environment Engineering, University of Nevada, Reno
Email: paudel...@gmail.com, sat...@unr.edu
Mobile: (775) 460-6498
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https://www.researchgate.net/profile/Satish-Paudel-5?ev=hdr_xprf
James Kennedy
Dear Satish,
Some general comments.
In LS-DYNA, contact forces between two concrete layers are calculated using contact algorithms that define how the interaction between the layers is modeled. The specific contact algorithm used will determine how the interface force is calculated, with options ranging from automatic to more specialized methods. The chosen algorithm, along with parameters like friction and contact thickness, will influence the predicted contact forces.
Elaboration:
1. Contact Algorithms:
LS-DYNA offers various contact algorithms for modeling the interaction between surfaces. Common types include:
Automatic Surface-to-Surface: This is a general-purpose contact type that can handle many situations, especially with shell elements. It automatically determines master and slave surfaces and checks for penetration on either side of the shell.
Single Surface Contact: This is used for interaction between rigid and deformable surfaces, where the rigid surface acts as the master.
Cohesive Zone Model: This model, used in some user-defined interfaces, defines a material law for separations and traction stresses, allowing for more complex contact behavior.
Mortar Contact: Originally intended for stamping analysis, this contact type is now used as a general-purpose algorithm for implicit analysis.
2. Parameters Affecting Contact Forces:
Several parameters within the contact definition significantly influence the calculated forces:
Friction: The coefficient of friction between the concrete layers determines the tangential force component. LS-DYNA uses a Coulomb formulation for friction.
Contact Thickness: This parameter, along with shell thickness offsets, influences the behavior of automatic contact types. It's important to scale up the default contact thickness if thin shell elements are used to prevent contact failure.
SOFT Option: The SOFT option in LS-DYNA controls how the contact is handled, especially in situations with initial penetrations or complex geometries. SOFT=1 is often used for rigid-deformable contact, while SOFT=2 is recommended for folded airbags with multiple initial penetrations.
3. Force Retrieval:
LS-DYNA offers various ways to retrieve contact forces:
Force Transducers: These provide a convenient means of retrieving contact forces at specific locations.
Output Files: LS-DYNA outputs files with contact force information.
4. Concrete Material Models:
The specific concrete material model used in LS-DYNA (e.g., Concrete Model 159) also plays a role in determining the overall behavior of the structure, including how it interacts with contact forces.
In summary, modeling contact forces between concrete layers in LS-DYNA involves carefully selecting the appropriate contact algorithm, defining relevant parameters like friction and contact thickness, and utilizing force retrieval mechanisms to analyze the results.
Sincerely,
James M. Kennedy
KBS2 Inc.
May 29, 2025
satish Paudel
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James Kennedy
Dear Satish,
See if these presentations are of some help:
Du Bois, P. Feucht, M., Haufe, A., and Kolling, S., “Damage and Failure Models in LS-DYNA”,
LS-DYNA User’s Conference Tokyo, Japan, September, 2006.
https://www.researchgate.net/publication/277311662_Damage_and_Failure_Models_in_LS-DYNA
Effelsberg, J,, Haufe, A., Feucht, M., Neukamm, F, and Du Bois, P., “On Parameter Identification
for the GISSMO Damage Model”, 12th International LS-DYNA Users Conference, Dearborn,
Michigan, June, 2012
https://lsdyna.ansys.com/wp-content/uploads/attachments/metalforming25-a.pdf
Andrade, F., Feucht, M., and Haufe, A., “On the Prediction of Material Failure in LS-DYNA: A
Comparison Between GISSMO and DIEM” 13th International LS-DYNA Users Conference,
Dearborn, Michigan, June, 2014.
Andrade, F., and Feucht, M., “A Comparison of Damage and Failure Models for the Failure
Prediction of Dual-Phase Steels”, 11th European LS-DYNA Conference, Salzburg, Germany,
June, 2017.
Andrade, F., “Short Overview of Failure and Damage Models, in LS-DYNA”, DYNAmore Express,
Stuttgart-Vaihingen, Germany, July, 2022.
Sincerely,
James M. Kennedy
KBS2 Inc.
June 4, 2025