# Pfc Gbm Brittle Rock > PFC GBM Brittle Rock - Skill: `jiangnan030-del/pfc-gbm-brittle-rock` (Agent Skill, multi-file: 20 files) - Install (CLI): `npx skillmds@latest add jiangnan030-del/pfc-gbm-brittle-rock` - Raw SKILL.md: https://api.skillmd.com/api/skills/jiangnan030-del/pfc-gbm-brittle-rock/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: jiangnan030-del (https://skillmd.com/u/jiangnan030-del) - Updated: 2026-09-21 - Page: https://skillmd.com/skills/jiangnan030-del/pfc-gbm-brittle-rock --- # PFC GBM Brittle Rock Use this skill to design, explain, or implement PFC2D grain-based brittle-rock models (GBM / equivalent crystal model) from the bundled GBM + prefabricated-crack biaxial-compression case. The core route is: mineral-seeded particle pack -> Voronoi/rblock grain geometry -> mineral geometry export -> fine particle refill by mineral regions -> biaxial consolidation -> prefabricated crack cut -> per-mineral LPBM + smooth-joint grain-boundary assignment -> biaxial loading with fracture, AE-like, and energy histories. ## Parent Skill Relationship `pfc-gbm-brittle-rock` is a child skill of `pfc-workflow`. It owns the GBM specimen-construction and brittle-rock mechanism portion, not the full project lifecycle. Use these handoffs: - Parent `pfc-workflow`: owns full planning, calibration campaign control, solve management, V&V, and delivery. - Sibling `pfc-basics`: basic domain, ball, wall, geometry, group, and range setup. - Sibling `pfc-cad-import`: geometry import/export, geometry ranges, wall import, and rblock/geometry conversion details. - Sibling `pfc-mineral-heterogeneity`: image/mineral fraction intake, mineral phase logic, and per-mineral parameter assignment. - Sibling `pfc-contact-models`: `linearpbond`, `smoothjoint`, CMAT ordering, bond methods, and contact-property audits. - Sibling `pfc-servo-calibration`: biaxial confining pressure, wall-servo gains, and stress convergence. - Sibling `pfc-fish`: fracture tracking, callbacks, histories, and reusable FISH refactoring. - Sibling `pfc-ae-energy`: AE/energy/source-mechanism post-processing if fracture or energy histories are used as AE proxies. - Sibling `pfc-postprocessing`: stress-strain, crack-count, energy, and field plots. Relationship with existing brittle-rock family skills: - `pfc-brittle-rock-bpm`: use for standard BPM limits and baseline brittle-rock theory. - `pfc-equivalent-crystal-model`: use for chapter-level equivalent-crystal explanation and Hoek-Brown validation narrative. - `pfc-flat-joint-brittle-rock`: use when the task is FJM/FJM3D rather than GBM/smooth-joint grain boundaries. ## When To Use Use through `pfc-workflow` when the task asks to: - build or explain a GBM / equivalent crystal model in PFC2D - model brittle rock with mineral grains and grain-boundary interfaces - convert mineral-seeded particles into Voronoi/rblock grain regions - assign quartz, feldspar, and mica-style groups to a fine particle specimen - use `smoothjoint` contacts to represent grain boundaries - add a prefabricated slit/fracture before biaxial compression - monitor tension/shear cracks by `linearpbond` and `smoothjoint` source - compare GBM against standard BPM for brittle-rock compression/tension behavior ## Required Inputs Ask for these if missing: - PFC version and whether the target is PFC2D. - Specimen width/height and particle radius range. - Mineral groups and target proportions or the source case proportions. - Prefabricated crack angle, length, and aperture. - Biaxial confining stress and loading rate. - Mineral contact parameters and smooth-joint grain-boundary parameters. - Required outputs: stress-strain, crack counts, energy terms, AE-like event increments, fractures, or fields. ## Migrated Source Case The bundled canonical case is `scripts/canonical/gbm-prefabricated-crack-biaxial/`. Stages: 1. `stage_01_initial_particle_pack.dat`: coarse mineral-seeded particle pack. 2. `stage_02_voronoi_rblock_geometry.dat`: convert particle centers to Voronoi/rblock geometry. 3. `stage_03_export_mineral_geometry.dat`: assign rblocks back to mineral groups and export geometry sets. 4. `stage_04_refill_particles_by_mineral_geometry.dat`: fine particle refill and mineral group assignment by geometry. 5. `stage_05_biaxial_confining_servo.dat`: biaxial confining stress servo. 6. `stage_06_prefabricated_crack_cut.dat`: create slit geometry and delete balls inside it. 7. `stage_07_gbm_contact_assignment.dat`: assign per-mineral LPBM contacts and smooth-joint grain-boundary contacts. 8. `stage_08_trim_specimen.dat`: trim outer particles and save ready state. 9. `stage_09_biaxial_loading_monitoring.dat`: load in biaxial compression and record mechanics/fracture/energy histories. 10. `fracture_tracking.p2fis`: bond-break callback, fracture creation, and fragment updates. Large/generated source files such as save states and project metadata are intentionally not bundled. ## Documentation-Backed Rules PFC command families checked through `pfc-mcp` are summarized in `references/pfc-doc-notes.md`: - `ball distribute`, `ball group`, `wall generate`, `wall import` - `geometry set`, `geometry polygon create`, geometry range selection - `rblock construct`, `rblock export`, `rblock delete` - `contact cmat`, `contact model`, `contact method`, `contact property` - `smoothjoint` as a version-sensitive contact model term - `fracture create`, `fragment compute`, `fish callback event bond_break` - `history`, `fish history`, `model energy mechanical on` ## Working Rules - Do not use GBM as a 3D solution; this migrated case is PFC2D. - Keep the coarse mineral-seed construction separate from fine particle refill. - Keep mineral-body contacts (`linearpbond`) separate from grain-boundary contacts (`smoothjoint`). - Treat the provided contact parameters as source-case seeds, not universal granite constants. - Route detailed smooth-joint syntax and CMAT inheritance audits to `pfc-contact-models`. - Route biaxial servo stability to `pfc-servo-calibration`. - Route fracture callback refactoring to `pfc-fish`. ## Output Contract A complete handoff back to `pfc-workflow` should include: - GBM stage list and copied command files - mineral group names and proportions - grain-boundary model and smooth-joint parameters - prefabricated crack angle, length, aperture, and geometry selection rule - confining stress, loading velocity, and stop criterion - fracture/energy/history output list - validation plan against stress-strain, crack mode, crack path, and brittle-rock expectations ## Local Contents - `references/overview.md`: scope, model boundary, and stage route. - `references/formulas.md`: brittle-rock BPM, GBM, smooth-joint, biaxial, crack and energy formulas. - `references/source-code-complete-pfc6.md`: full staged code migration notes. - `references/pfc-doc-notes.md`: PFC documentation notes for GBM-related commands. - `references/gbm-prefabricated-crack-case.md`: source case parameters and outputs. - `examples/README.md`: materialization and validation guidance. - `scripts/canonical/gbm-prefabricated-crack-biaxial/`: migrated public-safe `.dat` and `.p2fis` templates. - `scripts/canonical/manifest.json`: script inventory.