Fatigue Crack Growth Prediction Worksheet for Articulated Joints (Excel)

This Excel-based worksheet implements linear elastic fracture mechanics (LEFM) to model how pre-existing or post-repair flaws grow under variable-amplitude cyclic loading typical of off-road agricultural machinery. It begins by defining joint geometry (e.g., pin-bore clearance, fillet radius, weld toe profile) and loading conditions—including load history from field-acquired strain data or SAE J2348-compliant duty cycles—to compute stress intensity factor ranges (ΔK) at critical locations such as weld toes or heat-affected zones. Using Paris’ Law and material-specific da/dN–ΔK coefficients (often calibrated for ASTM A572 Gr. 50 or similar structural steels), the worksheet iteratively calculates crack depth increments over successive load cycles, tracking growth until reaching a critical size defined by failure criteria (e.g., net-section yielding or instability per ASTM E647). The tool also incorporates correction factors for residual stresses (from welding/repair), surface roughness, and environmental effects (e.g., corrosion acceleration in humid, chemical-exposed farm environments), enhancing realism beyond textbook models. Crucially, it links predictions directly to weld repair procedure qualification requirements—e.g., verifying that a qualified repair restores ≥95% of original fatigue life per AWS D1.1 Structural Welding Code and ASME BPVC Section VIII, Division 2, Annex 5B—thereby bridging fracture mechanics analysis with regulatory compliance documentation.