Modelling of Screens in Automobile
PRATHAMESH DEHADRAY
Can anyone help me to model the screens in instrument panel ? Unfortunately, I dont have material details.
Thank you.
James Kennedy
Dear Prathamesh,
See if the following notes are of some help.
Modeling screens in an instrument panel with LS-DYNA
To model screens within an instrument panel using LS-DYNA for simulations (e.g., impact or crashworthiness), a combination of element types, material models, and contact definitions will be crucial:
1. Element types
· Glass panels (layers): Employ shell elements to represent the glass layers. Use two layers of shell elements, one for the outer glass and one for the inner glass.
· Adhesive interlayer: Utilize solid elements (e.g., 8-noded quadratic elements) for the adhesive interlayer (like PVB), placed between the glass layers. You might need to experiment with the thickness, but 0.01mm is a possible starting point.
· Null shells: Consider adding two layers of null shell elements (*MAT_NULL) with coinciding nodes on the upper and lower surfaces of the solid elements used for the interlayer. This helps with proper contact between the shell and solid elements.
2. Meshing
· Element size: A commonly used mesh size for shell elements is approximately 10mm. For more accurate simulations of fracture behavior, particularly for glass, consider using finer meshes, with element lengths potentially below 10 mm. A mesh size related to the BGA pitch of major CSPs (e.g., 0.5mm) can be used for modeling PCBs and components.
· Meshing strategy:
o Start with a chess-board pattern of regular mesh on the PCB geometry.
o Trim the board edges to match the geometry.
o Create components and BGAs by dragging shell elements to form 3D solid elements, referencing the component locations from CAD data.
o Adjust the mesh locally under BGAs for precision.
· Advanced meshing: LS-DYNA offers tools for generating high-quality structured and unstructured meshes. Utilize these tools to create the desired mesh density and refinement, especially in areas of interest or potential stress concentration.
3. Material models
· Glass: An elastic material model with an erosion criterion can represent the glass layers. Consider using a major strain criterion for failure with a critical major strain value (e.g., εmaj = 0.004).
· PVB interlayer: A hyperelastic material model (e.g., *MAT_HYPERELASTIC_RUBBER) is suitable for the PVB interlayer, as it can undergo large deformations. However, if experimental data for hyperelastic parameters are unavailable, a linear elastic model with a Young's modulus of 3 MPa might be used as an approximation.
· Material properties: Gather data on the specific material properties of the screen's components, such as Young's modulus, Poisson's ratio, density, yield strength, tensile strength, and fracture properties.
4. Contact definition
· Contact surfaces: Define contact interfaces between the various parts (e.g., glass layers and PVB interlayer, screen and surrounding instrument panel).
· Coincident coupling: Use coincident coupling of shell and solid elements at the interfaces to accurately model the shear stress transmission between the layers.
· Shell thickness offsets: Model the physical composition of the laminate by offsetting the physical and contact thickness of the shell elements by half their depth. This can be achieved using the CNTCO and NLOC flags in LS-DYNA.
· Initial penetrations: Take care to avoid initial penetrations in the contact surfaces, as this can lead to non-physical contact behavior and inaccurate results. LS-DYNA will attempt to eliminate initial penetrations, but it's best to ensure an accurate initial geometry.
5. Failure criteria
· Element deletion: Implement a failure criterion (e.g., major strain criterion or a hybrid criterion) to govern element deletion (erosion) and model the fracture behavior of the screen.
· Post-failure behavior: Consider modeling the post-critical behavior and energy dissipation after damage initiation, especially if the screen is designed to absorb energy and eventually fail.
6. Simulation and post-processing
· Pre-analysis checks: Thoroughly check the model before running the simulation to ensure proper contact definitions, material properties, and mesh quality.
· During analysis checks: Monitor the simulation's progress by examining output files (d3hsp, .log, messXXX) for timestep information, contact penetration, added mass, and convergence issues.
· Post-processing: Use LS-PrePost to visualize the simulation results, including the eroded elements, and analyze the screen's behavior under the applied loading conditions.
By carefully considering these elements, material properties, meshing strategies, and contact definitions, you can create a robust and accurate LS-DYNA model to simulate the behavior of screens within an instrument panel for various loading conditions. Remember that careful consideration of the specific application and material characteristics will guide the selection of appropriate parameters and models for a successful simulation.
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Another presentation:
Modeling of the Failure Behaviour of windscreens and Component Tests
https://lsdyna.ansys.com/wp-content/uploads/attachments/Sun.pdf
Sincerely,
James M. Kennedy
KBS2 Inc.
August 2, 2025
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