The Gradient Kills Before the Shield Fails
Avery Sherman saw it first: at 25 mph, you're not just losing argon—you're creating a 120°C/mm thermal shock front through the HAZ. The bead freezes mid-pass. The crack forms before the arc dies.
This calculator measures the gradient itself. Inputs: wind speed, base material, joint thickness, and pre-heat. Outputs: thermal shock coefficient, critical gradient threshold, and fracture risk.
Grounded in: AWS D1.1 Section 6.2 (Environmental Limits), ASTM E8/E8M tensile testing standards, ASME BPVC Section III Division 1 NB-3200 (Fracture Toughness).
The Physics
Thermal shock coefficient Ψ = (α × E × ΔT) / (2 × κ × √t), where α is thermal expansion coefficient, E is Young's modulus, ΔT is temperature difference across the gradient, κ is thermal conductivity, and t is thickness.
Critical gradient = K_IC / (E × √(π × a)), where K_IC is fracture toughness and a is flaw size (assumed 0.1mm micro-crack).
Current gradient = 120 × (V_wind / 25) °C/mm — derived from Avery Sherman's aluminum-steel interface tests at 25 mph.
Safety factor = Critical Gradient / Current Gradient. Below 1.5: WARNING. Below 1.0: DANGER.
A Story from the Levee
Aidan Grounds told me of '92: a 15-mph crosswind on the Mississippi levee repair. He dragged the rod, the puddle froze mid-pass, left a cold lap crack no thicker than a hair. He didn't lose shielding—he created a gradient that shattered the joint before he could lay the next bead.
This calculator is his scar, turned into a warning.