4. Material and property data verification
In a PAM-CRASH production model, material and property data are the single largest source of silent errors. A mesh can be perfect and a contact definition can be textbook-correct, yet the model will still produce non-physical results if a *MAT_ card is mapped to the wrong PAM-CRASH material law, if a strain-rate curve is attached to the wrong hardening table, or if a failure criterion is activated with a threshold that was never validated. This section covers the verification workflow that catches these defects before release: keyword mapping, strain-rate curve integrity, failure criteria, and data provenance.
4.1 LS-DYNA Keyword Mapping to PAM-CRASH Material Laws
PAM-CRASH and LS-DYNA use different material model numbering and different card structures. A conversion tool (such as the PAM-CRASH LS-DYNA translator or an in-house converter) maps *MAT_024 to MAT_PLASTIC_KINEMATIC (PAM-CRASH material 103), *MAT_003 to MAT_PLASTICITY_COMPRESSION_TENSION (material 114), and *MAT_123 to MAT_MODIFIED_PIECEWISE_LINEAR_PLASTICITY (material 112). The mapping is not one-to-one in every case, and the verification task is to confirm that each mapped law preserves the intended constitutive behavior.
A practical verification procedure is to extract the material card from the converted PAM-CRASH input deck and compare it field-by-field against the source LS-DYNA keyword. The following example shows a typical mismatch discovered during a production model check:
LS-DYNA source:
*MAT_PLASTIC_KINEMATIC
$ MID RO E PR SIGY ETAN BETA
1001 7.85e-9 210000 0.30 355.0 1200.0 0.0
PAM-CRASH converted (material 103):
$ MID RO E NU SIGY ETAN BETA
1001 7.85e-9 210000 0.30 355.0 1200.0 0.0
In this case the mapping is clean. A common defect is ETAN being dropped when the source uses *MAT_024 with a load curve (LCSS) instead of a constant tangent modulus. The converter may map LCSS to a hardening table, but if the table ID is not remapped, the material silently becomes elastic–perfectly plastic. Verification must therefore check not only the material law ID but also every referenced curve ID.
4.2 Strain-Rate Curve Verification
Strain-rate-dependent materials in crash models use either *DEFINE_CURVE tables (LS-DYNA) or function tables (PAM-CRASH). The verification task has three parts: confirm the curve exists, confirm the abscissa is strain rate (not time or strain), and confirm the ordinate is the intended quantity (yield stress, scale factor, or plastic stress).
Consider a DP600 steel with three rate-dependent curves at 0.001, 1.0, and 100 s⁻¹. The source LS-DYNA deck references LCSS = 2001, 2002, 2003. After conversion, the PAM-CRASH deck should reference function IDs 2001–2003 in the material card. A verification script can parse both decks and produce a mapping table:
| LS-DYNA curve ID | PAM-CRASH function ID | Abscissa range | Ordinate type | Status |
|---|---|---|---|---|
| 2001 | 2001 | 0.001–0.001 | Yield stress (MPa) | OK |
| 2002 | 2002 | 1.0–1.0 | Yield stress (MPa) | OK |
| 2003 | — | 100.0–100.0 | Yield stress (MPa) | Missing |
The missing curve 2003 is a release blocker. Without it, the material will use the last available curve (2002) for all rates above 1.0 s⁻¹, underestimating the flow stress in high-rate regions such as the B-pillar intrusion zone. The fix is to re-export the curve from the source deck and re-run the conversion, then re-verify.
Another frequent defect is unit inconsistency. LS-DYNA models often use mm–ms–kg–GPa, while PAM-CRASH production decks may use mm–ms–kg–MPa. A curve with ordinate values in GPa (e.g., 0.355) will be interpreted as 0.355 MPa in a MPa deck, producing a material that yields at 0.1% of the intended stress. Verification must check the unit system declared in the deck header and confirm that all curve ordinates are consistent with it.
4.3 Failure Criteria Verification
Failure criteria in crash models are typically defined through *MAT_ADD_EROSION (LS-DYNA) or the failure card of the PAM-CRASH material law. The verification task is to confirm that the failure mode, threshold, and element deletion behavior are preserved.
For a spot-weld model using *MAT_100 (spot weld) with a force-based failure criterion, the converted PAM-CRASH deck should use the corresponding spot-weld material with the same normal and shear force limits. A common defect is the failure flag being set to 0 (no failure) during conversion, which means the weld will never break. This is particularly dangerous because the model will run to completion and produce plausible-looking results, but the crash energy will be absorbed by the welds instead of by the structure.
Verification should include a targeted check: for each material with a failure criterion, confirm that the failure flag is active, that the threshold value is non-zero, and that the element deletion flag is set consistently with the source. A simple grep-based check on the converted deck can flag all materials where the failure flag is 0 but the source had a non-zero failure criterion.
4.4 Data Provenance and Traceability
Data provenance answers the question: where did this material card come from, and who approved it? In a production model, every material and property card should be traceable to a source document — a test report, a supplier data sheet, a material database entry, or a validated simulation. Without provenance, a reviewer cannot distinguish a validated card from a placeholder.
A practical provenance record for each material includes: material ID, material name, source type (test / supplier / database / assumed), source reference (report number, database name, or "assumed"), date of last update, and approver. This record should be stored alongside the model, not inside the input deck, so that it can be updated without re-running the conversion.
During verification, cross-check the provenance record against the actual card values. A material marked "test-validated" should have a curve that matches the test report within a stated tolerance. A material marked "assumed" should be flagged for sensitivity study before release. The following SVG summarizes the verification flow and the decision points that determine whether a material card is release-ready.
4.5 Practical Verification Checklist
The following checklist is designed to be run as a scripted pass over the converted deck. Each item corresponds to a defect class observed in production models.
- Material law mapping: For every
*MAT_card in the source, confirm the converted PAM-CRASH material law ID matches the intended mapping table. Flag any law that was mapped to a default or fallback. - Curve reference integrity: For every material that references a load curve or function table, confirm the referenced ID exists in the converted deck and that the curve data is non-empty.
- Strain-rate abscissa: Confirm the first column of each rate-dependent curve is strain rate in the deck's unit system, not time or plastic strain.
- Unit consistency: Confirm the ordinate units of all curves match the deck's declared unit system. A curve in GPa in an MPa deck is a release blocker.
- Failure flag: For every material with a failure criterion in the source, confirm the converted deck has the failure flag active and the threshold non-zero.
- Provenance record: Confirm every material ID has a provenance entry with source type, reference, date, and approver. Flag any "assumed" material for sensitivity study.
Running this checklist on a typical full-vehicle model with 80–120 materials takes 10–15 minutes with a scripted parser and catches the majority of material-data defects before they reach the solver. The cost of this pass is negligible compared to the cost of debugging a non-physical crash result after a 12-hour run.