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Hello everyone,

I am developing an LS-DYNA model for shearing a rectangular Cu-ETP copper wire with two rigid cutting blades. The purpose of the model is to simulate separation of the copper wire by shear deformation, similar to a shearing or blanking process. It is not a machining or chip-formation simulation.

The copper wire is modeled with solid elements and a Johnson–Cook material model. Material failure is currently defined using Johnson–Cook damage and/or *MAT_ADD_EROSION. The blades are modeled as rigid bodies, and *CONTACT_ERODING_SURFACE_TO_SURFACE is used between the blades and the copper wire.

The calculation runs successfully, but I do not know whether the predicted separation is physically reasonable or whether it is mainly caused by numerical settings. I would therefore like to understand how the keyword parameters should be selected and improved based on post-processing results.

My main problem is that I cannot find clear recommendations for the reasonable ranges of parameters such as:

• failure strain or EFFEPS in *MAT_ADD_EROSION;
• Johnson–Cook damage parameters D1D_1D1​–D5D_5D5​;
• contact penalty stiffness scaling, especially SFSA;
• static and dynamic friction coefficients FS and FD;
• hourglass control parameters;
• element size in the expected shear zone;
• cutting-edge radius;
• clearance between the two blades;
• blade velocity;
• workpiece constraints and clamping conditions.

When I change these parameters, I obtain very different results. In some cases, the copper wire does not separate. In other cases, elements are deleted too early, the blades penetrate the copper wire, or the fracture surface appears to be controlled mainly by the mesh.

I am therefore unsure which results represent real shearing and which results are numerical artifacts.

At present, I am evaluating the following post-processing results:

• blade force versus time and displacement;
• internal energy, kinetic energy, hourglass energy and total energy;
• contact penetration;
• effective plastic strain;
• effective stress;
• damage variable and element deletion;
• development of the shear zone;
• final fracture and separation geometry.

I would be grateful for advice on the following questions:

1. Which post-processing results are essential for validating a metal shearing simulation?
2. What should physically reasonable force–displacement and energy curves look like during shearing and separation?
3. How can excessive contact penetration be identified quantitatively?
4. How can I distinguish physical shear failure from artificial separation caused by premature element erosion?
5. How should I determine a reasonable EFFEPS value?
   Should it be obtained from tensile-test data, shear-test data, fracture tests or calibration against an experimental shearing process?
6. If Johnson–Cook damage is used, should EFFEPS in *MAT_ADD_EROSION still be active, or should it only be used as a numerical backup criterion?
7. Which parameters are physical process parameters and which are numerical parameters?
   For example, blade clearance, edge radius and friction are physical parameters, whereas contact penalty scaling and hourglass control are mainly numerical parameters.
8. How should a mesh-convergence study be performed when element erosion is used?
   The fracture path and separation time change when the element size is modified.
9. How can I determine whether SFSA is too small or too large?
   In my model, changing SFSA significantly affects penetration, local plastic strain and whether the copper wire separates.
10. What is a reasonable relationship between hourglass energy and internal energy for this type of shearing simulation?
11. Should the blade velocity be low enough to obtain a quasi-static shearing response?
    If so, which energy ratio or other criterion should be used to confirm that inertial effects are sufficiently small?
12. Are there any LS-DYNA example models for wire shearing, sheet-metal shearing, blanking, punching or guillotine cutting?

I am especially looking for an example that explains the complete modelling and validation procedure:

mesh generation → material model → damage and failure definition → blade motion → contact definition → workpiece constraints → post-processing → parameter sensitivity study → validation

My goal is not to find one universal value for every parameter. I would like to establish a systematic method to determine whether the baseline model is reliable and then decide which keywords or parameters should be modified.

Any example keyword files, papers, tutorials or recommendations for copper-wire shearing, sheet-metal shearing would be very helpful.

Thank you very much for your help

[Armin]

Hello,

I suggest finding a published study in the literature and attempting to reproduce its results. Here is an example, but you should be able to find more by searching online.

https://www.researchgate.net/publication/271858732_Shear_cutting_of_press_hardened_steel_influence_of_punch_chamfer_on_process_forces_tool_stresses_and_sheared_edge_qualities

Some of the unknowns you are looking for, such as failure strain and damage model parameters, are associated with material properties that can be found in published literature. Other parameters like element size, cutting-edge radius, etc. should also be discussed in the respective studies.