--- name: pfc-burger-viscoelastic description: Select, probe, calibrate, and audit the Burger viscoelastic contact model for PFC 5.0 asphalt-mixture cases, including Maxwell-Kelvin parameter roles, units, temperature/rate dependence, PFC5 cmat assignment, timestep checks, creep/recovery validation, and PFC5-only syntax boundary checks. ---

# PFC Burger Viscoelastic Contact Model

Use this skill for the viscoelastic contact-law stage of `pfc5-asphalt-workflow`. Burger may represent homogenized asphalt mastic behavior at selected contacts, but it does not by itself create an explicit binder phase or guarantee mixture-scale behavior.

## When to use

- assign or audit Burger contacts in a PFC5 asphalt specimen; - interpret Maxwell and Kelvin spring/dashpot roles; - fit temperature- and rate-dependent mixture/mastic response; - build a two-contact or small-RVE verification probe; - review a Burger command block for non-PFC5 contamination.

Do not use this skill to invent production constants from a generic table.

## Required inputs

- PFC2D or PFC3D 5.0 and the unit system; - object/contact pairs that Burger is intended to represent; - all Burger properties with units, or raw calibration curves with units; - test temperature, loading rate/frequency and conditioning history; - specimen/contact geometry and resolution used during inverse fitting; - target creep/recovery, dynamic modulus/phase or other macro curves; - material level and test provenance: binder, mastic or mixture; for JTG 3410-2025 inputs, record the exact DSR/BBR/MSCR/LAS or mixture-performance method rather than writing only “rheology data”; - contact replacement policy for existing versus future contacts; - timestep/damping/stop criteria and acceptance tolerances.

## Constitutive interpretation

Burger combines a Maxwell branch (spring plus dashpot in series) and a Kelvin branch (spring plus dashpot in parallel). Normal and shear directions have separate parameters. Stiffness-like terms control instantaneous/delayed compliance; dashpot terms control time scale and permanent or delayed deformation. Friction and interface choices remain separate physical assumptions.

Property names and dimensions are syntax-family-specific. Read `references/burger-theory.md` for theory and `references/pfc-command.md` for version-labelled syntax notes.

## Workflow

1. Freeze units, temperature, rate/frequency, geometry and contact-pair meaning. 2. Verify the PFC5.0 Burger property names with a minimal runtime probe. 3. Run a minimal PFC5 two-body contact probe: contact creation, load/hold/unload, recovery, save/restore and property listing. 4. Install the model using PFC5 `cmat` semantics, distinguishing future defaults from current-contact changes. 5. Re-equilibrate the specimen and preserve a pre-load save. 6. Classify every curve as binder, mastic or mixture before fitting. JTG T 0627/T 0628, T 0647 and T 0648 binder data are priors or trend constraints, not direct mastic-contact targets. Only a declared test on the same mastic may target a mastic RVE; contact constants still require inverse fitting through the fixed PFC discretization. 7. Validate creep and recovery at the calibration condition, then confirm at another duration/rate/temperature or independent specimen. 8. Check timestep sensitivity and rerun the target Marshall/rutting pilot.

## Working rules

- PFC5 is the only supported target in this package. Unsupported-major-version command blocks are rejected, not retained as migration references. - Do not use numerical “60 °C reference values” as production defaults; their units, geometry scaling and provenance are not established for the user's case. - Never reuse one parameter set at another temperature without an explicit, experimentally supported shift/fitting method. - Do not mix binder-level JTG 3410-2025 outputs with mixture-level T 0738/T 0745/T 0719 curves as if they had the same geometry or stress measure. Record the scale transition and validate it through the RVE/specimen. - Do not label a binder DSR/BBR curve as mastic evidence merely because the Burger contact represents homogenized mastic. If no same-material mastic test exists, record the mastic calibration layer as assumption-bound and test its sensitivity. - Do not delete/recreate all contacts merely as a generic recipe. Choose and verify a version-correct current/future contact transition that preserves the intended state. - Treat a linear fallback as a diagnostic branch, never as evidence that Burger is calibrated. - Mark commands `runtime_verified` only after a PFC5.0 runtime accepts them and the probe response passes.

## Output contract

- PFC2D/PFC3D 5.0, units, temperature/rate and contact-pair meaning; - exact version-labelled assignment command and current/future contact policy; - parameter table with units, bounds, provenance and fitted values; - two-body/RVE probe histories and timestep sensitivity; - calibration/confirmation curves and error metrics; - pre/post contact-installation save map; - unresolved runtime or identifiability risks.

## Local contents

- `references/burger-theory.md` — Maxwell-Kelvin mechanics. - `references/pfc-command.md` — version-labelled command notes and legacy examples. - `references/calibration.md` — guarded macro-response fitting route. - `../pfc5-asphalt-workflow/references/standards-method-map.md` — reviewed test-method roles and scale boundaries. - `scripts/burger_contact_probe.p3dat` — executable PFC3D 5.0 two-ball relaxation probe; parameters are not calibrated material values. - `agents/openai.yaml` — Agent metadata. - `dependencies.json` — package-level link to the standards method map.