Spring rate, load, shear stress (Wahl correction), solid height and buckling check per GB/T 23935-2009
Formulas per GB/T 23935-2009: C = D/d (spring index), K = (4C−1)/(4C−4) + 0.615/C (Wahl curvature factor), k = G·d⁴/(8·D³·n) (spring rate), F = k·δ (load), τ = K·8FD/(π·d³) (max shear stress at inner coil), Lsolid = (n+nend)·d (solid height). Pass requires stress within allowable, no coil binding (margin ≥ 0), and buckling ratio ≤ 3.7 (both ends guided). G ≈ 78500 MPa for spring steel (oil-tempered/Si-Mn/Cr-V); reduce for stainless (~69-73 GPa).