Composite modelling and contact issue

[RAGHAV AGARWAL]

Hello everyone,

I am doing composite modelling for high velocity impacts using solid elements of 8 mm thick plate divided into sub laminates of 0.5 mm. I am using MAT_59 with erosion criteria of MXEPS = 0.4.

I am using eroding surface to surface between projectile and composite plate  while, automatic surface to surface tiebreak between layers. But some elements of sub laminate are penetrating into each other, giving inaccurate results and computational instability.

Please help me to tackle this problem? 

[James Kennedy]

Dear Raghav,

 

For an LS-DYNA simulation of a projectile impacting a composite plate with eroding contact, the following steps and keywords are generally involved:

 

1. Contact definition

Use the *CONTACT_ERODING_SURFACE_TO_SURFACE keyword to define the eroding contact between the projectile and the composite plate.

This contact type is recommended when solid elements are subject to erosion (element deletion) due to material failure criteria, as it allows the contact surface to be updated as elements are deleted.

The slave and master surfaces can be defined by part IDs. 

 

2. Material modeling

Projectile: Model the projectile material using an appropriate material model, potentially including plasticity and failure strain, such as *MAT_PLASTIC_KINEMATIC.

Composite plate: Model the composite material with a suitable composite damage model, such as *MAT_COMPOSITE_TABULATED_PLASTICITY_DAMAGE (MAT_213) or MAT_COMPOSITE_DMG_MSC (MAT162) which can account for rate-dependent damage and multiple failure modes.

Erosion: To model rupture and element deletion, *MAT_ADD_EROSION can be used to define various erosion criteria. 

 

3. Initial conditions

Apply an initial velocity to the projectile using the *INITIAL_VELOCITY_GENERATION keyword. 

 

4. Control settings

Specify the termination time for the simulation using *CONTROL_TERMINATION.

Control contact parameters like the scale factor and penalty method using *CONTROL_CONTACT.

In *CONTROL_CONTACT, the ECDT parameter can be used to bypass the effect of eroding contact on the timestep. 

 

5. Output

Define the frequency of binary database output (d3plot) for post-processing using *DATABASE_BINARY_D3PLOT.

Define the frequency of contact force output using *DATABASE_RCFORC. 

 

6. Meshing

Use appropriate meshing techniques for the projectile and composite plate, potentially employing solid elements for the projectile and a combination of shell and solid elements for the composite plate layers. 

 

7. Boundary conditions

Apply appropriate boundary conditions to the composite plate, such as fully supporting its outer edges. 

 

8. Erosion considerations

Eroding contact will update the contact surfaces as elements are deleted due to material failure, but the contact itself does not cause rupture.

Erosion criteria, particularly failure strain, will be crucial for determining when elements are deleted.

Careful mesh refinement and validation against experimental data are essential when using erosion, as the results can be mesh-dependent. 

 

Example

An example can be found in the LS-DYNA Examples manual, detailing a projectile penetrating a plate using *CONTACT_ERODING_SURFACE_TO_SURFACE. 

Note: This is a general outline. Specific details may vary based on the desired level of fidelity and the specific characteristics of the materials and impact scenario. Consulting the LS-DYNA user manual and relevant literature is recommended for specific implementations.

 

Sincerely,

James M. Kennedy

KBS2 Inc.

August 10, 2025

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[James Kennedy]

Dear Raghav,

 

LS-DYNA eroding surface to surface contact between a projectile and a composite plate using MAT_059 requires a specific setup to accurately simulate the impact and penetration behavior.

 

Here's a breakdown of the key elements involved:

 

1. Contact definition

Use *CONTACT_ERODING_SURFACE_TO_SURFACE to define the contact interface. This type of contact is recommended for situations where elements are deleted due to material failure (erosion).

Specify the surfaces involved: The projectile surface and the composite plate surface.

Eroding contact ensures the contact surface updates as elements are deleted from the projectile and/or the plate during penetration. 

 

2. Material model for composite plate

*MAT_059 (UBC Composite Damage Model - CODAM2) is a suitable material model for fiber-reinforced composite laminates with transversely isotropic layers.

This model captures the overall response, including element erosion and damage mechanics, based on sub-laminate behavior.

It's important to note that MAT_059, when used with solid elements, can incorporate a delamination failure criterion. 

 

3. Erosion criteria

The eroding contact itself does not directly model rupture or erosion; it merely updates the contact surface as elements are deleted.

To trigger element deletion (erosion), you need to define failure criteria within the material model itself or using *MAT_ADD_EROSION.

For MAT_059, failure criteria for transverse tensile failure and reversal of transverse shear strengths have been incorporated and are crucial for capturing the damage progression in the composite plate.

For detailed modeling of rupture and failure mechanisms in the composite, consider the options within MAT_ADD_EROSION, such as defining specific erosion criteria based on strain or stress limits. 

 

4. Initial conditions

Define the initial velocity (magnitude and direction) of the projectile using *INITIAL_VELOCITY_GENERATION. 

 

5. Other considerations

Contact Stability: Consider using SOFT=1 and adjusting SOFSCL or PENMAX if encountering issues with contact stability or premature release of slave nodes, especially with thin elements.

 

Time Step: LS-DYNA automatically adjusts the time step for eroding contact, but you can potentially bypass this effect using the ECDT parameter in *CONTROL_CONTACT.

 

Mass Conservation: Be aware that even with element deletion, slave nodes may still be considered in contact, and mass is generally conserved.

 

Data Output: Ensure you're requesting appropriate output variables for visualizing the damage progression and contact forces, such as by using *CONTACT_FORCE_TRANSDUCER_PENALTY to retrieve contact forces at specific locations. 

 

By combining these elements, you can set up a robust LS-DYNA simulation to analyze the impact and penetration of a projectile into a composite plate with MAT_059, capturing both the contact interactions and the material's failure and erosion behavior. 

 

Sincerely,

James M. Kennedy

KBS2 Inc.

August 10, 2025

 

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