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Run npx skillmds@latest add ashfordeou/crack-growth in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

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Is Crack Growth free to use?

Yes. Installing skills from SkillMD is free. This skill is licensed under Apache-2.

Who published Crack Growth?

ashfordeOU (@ashfordeou) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Crack Growth by ashfordeou — Agent Skill

Name: Crack Growth
Author: ashfordeOU

Crack Growth

Use when you must calculate fatigue crack growth for damage-tolerant structure: estimate the mode I stress intensity factor at a crack, apply the Paris law crack growth rate, and project the cycles to grow the crack from the initial detectable size to the critical size. Produces the stress intensity factor, the Paris da/dN rate, the crack extension per cycle, and the cycles-to-critical estimate that feed residual strength and inspection interval assessments. Trigger: crack growth, stress intensity, paris law, damage tolerance, fatigue crack, da/dn.

ashfordeOU Updated Sep 17, 2026

File contents

Fatigue Crack Growth (structures/damage-tolerance/crack-growth)

Use when the task is fatigue crack growth evaluation for damage-tolerant structure: stress intensity, Paris law rates, and cycles-to-critical projections.

Domain quick reference

The mode I stress intensity factor K = Y * sigma * sqrt(pi * a) scales the crack-tip stress field; Y is the geometry factor (1.12 for a small edge crack in a wide plate).
The Paris law da/dN = C * (dK)^m relates the crack growth rate to the stress intensity range; C and m are material constants fitted from da/dN testing.
Crack growth life runs from the initial detectable crack size to the critical size where residual strength drops below limit load; inspection intervals are derived from that life.
Crack growth practice sits in the FAR-25.571 damage tolerance context for transport aeroplanes.
Units (single convention, consistent across the logic module): sigma and dK in MPa / MPasqrt(m), crack sizes in meters, Paris C in (m/cycle)(MPa*sqrt(m))^-m, da/dN in m/cycle. Anchor: C=1e-11, m=3, dK=20 gives da/dN = 8e-8 m/cycle; 1000 cycles extends the crack 8e-5 m; a 0.009 m extension takes 112,500 cycles.

Workflow

Establish the applied stress and crack size; compute the stress intensity factor with stress_intensity.
Get the material Paris constants C and m; compute the per-cycle rate with paris_dadN.
Project the extension over the cycle block with crack_growth_per_cycle.
Estimate the crack growth life with cycles_to_grow.
Feed the cycles-to-critical result into the residual strength and inspection interval assessment.

Pitfalls

Mixing units in the Paris law: passing dK in Pa while C is in (m/cycle)(MPasqrt(m))^-m (or the reverse) shifts the rate by (1e6)^m. Keep sigma and dK in MPa with C in (m/cycle)(MPasqrt(m))^-m and crack sizes in meters.
Using the total stress instead of the stress range dK in the Paris law.
Treating the stress intensity factor as constant while the crack grows.
Growing a crack from a size at or beyond the critical size.
Omitting the geometry factor Y or defaulting it for the wrong crack configuration.

Behavior contract (gate 3)

The stress intensity, Paris rate, and growth life logic is exercised by the gate 3 contract test: scripts/test_crack_growth.py against scripts/crack_growth_logic.py (stdlib unittest, offline). Run: python3 scripts/test_crack_growth.py

Compliance

Standards referenced, not reproduced: FAR-25 is US government work (public domain) and CS-25 is a free EASA download; crack growth methodology is common fracture-mechanics knowledge, summary-only per standards-map.yaml.
compliance: STANDARDS-REF, gated: false.

---name: crack-growthdescription: Use when you must calculate fatigue crack growth for damage-tolerant structure: estimate the mode I stress intensity factor at a crack, apply the Paris law crack growth rate, and project the cycles to grow the crack from the initial detectable size to the critical size. Produces the stress intensity factor, the Paris da/dN rate, the crack extension per cycle, and the cycles-to-critical estimate that feed residual strength and inspection interval assessments. Trigger: crack growth, stress intensity, paris law, damage tolerance, fatigue crack, da/dn.license: Apache-2.0---# Fatigue Crack Growth (structures/damage-tolerance/crack-growth)Use when the task is fatigue crack growth evaluation fordamage-tolerant structure: stress intensity, Paris law rates, andcycles-to-critical projections.## Domain quick reference- The mode I stress intensity factor K = Y * sigma * sqrt(pi * a) scales the crack-tip stress field; Y is the geometry factor (1.12 for a small edge crack in a wide plate).- The Paris law da/dN = C * (dK)^m relates the crack growth rate to the stress intensity range; C and m are material constants fitted from da/dN testing.- Crack growth life runs from the initial detectable crack size to the critical size where residual strength drops below limit load; inspection intervals are derived from that life.- Crack growth practice sits in the FAR-25.571 damage tolerance context for transport aeroplanes.- Units (single convention, consistent across the logic module): sigma and dK in MPa / MPa*sqrt(m), crack sizes in meters, Paris C in (m/cycle)*(MPa*sqrt(m))^-m, da/dN in m/cycle. Anchor: C=1e-11, m=3, dK=20 gives da/dN = 8e-8 m/cycle; 1000 cycles extends the crack 8e-5 m; a 0.009 m extension takes 112,500 cycles.## Workflow1. Establish the applied stress and crack size; compute the stress intensity factor with stress_intensity.2. Get the material Paris constants C and m; compute the per-cycle rate with paris_dadN.3. Project the extension over the cycle block with crack_growth_per_cycle.4. Estimate the crack growth life with cycles_to_grow.5. Feed the cycles-to-critical result into the residual strength and inspection interval assessment.## Pitfalls- Mixing units in the Paris law: passing dK in Pa while C is in (m/cycle)*(MPa*sqrt(m))^-m (or the reverse) shifts the rate by (1e6)^m. Keep sigma and dK in MPa with C in (m/cycle)*(MPa*sqrt(m))^-m and crack sizes in meters.- Using the total stress instead of the stress range dK in the Paris law.- Treating the stress intensity factor as constant while the crack grows.- Growing a crack from a size at or beyond the critical size.- Omitting the geometry factor Y or defaulting it for the wrong crack configuration.## Behavior contract (gate 3)The stress intensity, Paris rate, and growth life logic is exercisedby the gate 3 contract test: scripts/test_crack_growth.py againstscripts/crack_growth_logic.py (stdlib unittest, offline). Run:python3 scripts/test_crack_growth.py## Compliance- Standards referenced, not reproduced: FAR-25 is US government work (public domain) and CS-25 is a free EASA download; crack growth methodology is common fracture-mechanics knowledge, summary-only per standards-map.yaml.- compliance: STANDARDS-REF, gated: false.

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