Corrosion Fatigue Design Guide for Off-Road Agricultural Structures

Corrosion fatigue represents a critical failure mode in off-road agricultural structures where repeated mechanical stresses—such as those induced by terrain-induced vibrations, hitch loads, and powertrain torque fluctuations—interact synergistically with corrosive agents (e.g., ammonium nitrate-based fertilizers, organic acids in manure slurry, chloride-laden soil moisture) to accelerate crack initiation and propagation beyond what either fatigue or corrosion alone would cause. Unlike standard fatigue design, which assumes inert environments, this guide incorporates time-dependent environmental factors—including pH, conductivity, temperature cycling, and wet-dry intermittency—to modify S–N (stress-life) curves and threshold stress intensity factors (ΔK_th). It prescribes environment-specific fatigue strength reduction factors (FSRFs), surface condition modifiers (e.g., for rust-pitted or galvanized surfaces), and corrosion allowance multipliers based on service life targets (e.g., 10,000–20,000 operational hours). The guide further addresses manufacturing and maintenance influences—such as weld residual stresses, coating integrity, drainage geometry, and crevice-prone joint details—that significantly affect localized corrosion fatigue resistance. Validation relies on accelerated combined-environment testing (e.g., cyclic loading in simulated agro-chemical spray chambers) and probabilistic life prediction using Paris-law extensions coupled with corrosion rate models (e.g., Faraday-based metal loss integration).