Springs — validation & limitations

What it calculates

• Spring rate k = G·d⁴/(8·D³·n) with material shear-modulus library (steel, stainless, chrome-vanadium)
• Wahl-corrected shear stress at two load positions (F1 and F2) — accounts for both wire curvature and direct shear
• Allowable shear stress τ_zul = 0.5·Rm(d) (extension springs: 0.45·Rm after EN 13906-2) from the EN 10270 tabulated tensile-strength tables (wire-size dependent; the banded -2 and -3 tables are read as steps, not interpolated)
• Lateral buckling from the critical DEFLECTION (Shigley Eq. 10-12), driven by how the spring is seated — flat plates, pivoted ends, clamped-free, or running on a guide
• Zimmerli–Goodman fatigue factor with the first-cycle Langer yield check alongside it, on one Goodman diagram
• Fundamental surge (natural) frequency and resonance margin for dynamic applications
• Series and parallel spring-system equivalent stiffness with per-spring load sharing — rate arithmetic only, badged as such

Standards this tool applies

• DIN 2089 — EN 13906-1/-2 (formerly DIN 2089) rate, Wahl stress and screening τ_zul for compression and tension springs and a bending-stress check for torsion springs, plus a Shigley buckling check, surge frequency, a Shigley Zimmerli–Goodman fatigue estimate for compression and tension springs, and series/parallel systems.

Validation evidence — independent reference cases (0)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

No independent reference case is registered for this tool yet. Its engine is covered by the regression suite, but no published worked example has been reproduced end to end.

Limitations

Not checked by this tool

• Relaxation and creep (load loss over time and temperature) — Not assessed; check the EN 13906-1 relaxation data or the wire maker's charts
• Coil diameter growth under load against a guide bore or rod — Check the outside-diameter increase against the bore and the inside diameter against the rod (EN 13906-1)
• Hook fatigue of extension springs — The fatigue panel covers the body; check the hook stresses with a fatigue diagram
• Torsion springs: EN 13906-3 permissible stress, arm bending and friction — A Shigley-based allowable is used; verify against EN 13906-3
• Temperature and corrosion effects on wire strength and modulus — Room-temperature values; derate for hot or corrosive service
• Manufacturing tolerances on rate, length and load — Specify the tolerance grade per EN 15800