Spring Fatigue Life Estimator (Wahl + Goodman) implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t7-052

Effect

Computation or source lookup only

Input and validation requirements

The estimator breaks or must reject inputs at the Wahl singularity C=1 and when the Goodman denominator is zero. Its result also changes materially under plausible signed-force versus load-magnitude conventions, and the specification does not define how negative mean stress is branched or handled.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "material": "music wire ASTM A228",
    "F_min_N": 100,
    "F_max_N": 200,
    "wire_diameter_mm": 2,
    "mean_coil_diameter_mm": 16,
    "Se_MPa": 550,
    "Sut_MPa": 2300
  },
  "expected_outputs": {
    "spring_index_C": 8,
    "Wahl_factor_Kw": 1.1840178571,
    "tau_min_MPa": 603.015343,
    "tau_max_MPa": 1206.030686,
    "tau_a_MPa": 301.507671,
    "tau_m_MPa": 904.523014,
    "fatigue_safety_factor": 1.062172
  },
  "reference_data": {
    "music_wire_Se_MPa": 550,
    "music_wire_Sut_MPa": 2300,
    "source_convention": "widely tabulated standard spring-wire design values for ASTM A228 music wire; interpreted as torsional shear strengths for this vector"
  },
  "working": "C=D/d=16/2=8. Kw=(4C-1)/(4C-4)+0.615/C=(32-1)/(32-4)+0.615/8=31/28+0.076875=1.1840178571. Base stress at F=1 N is 8D/(pi*d^3)=8(16)/(pi*2^3)=128/(8pi)=16/pi=5.092958179 MPa/N. Stress coefficient=Kw*5.092958179=1.1840178571*5.092958179=6.030153430 MPa/N. tau_min=6.030153430*100=603.015343 MPa. tau_max=6.030153430*200=1206.030686 MPa. tau_a=(1206.030686-603.015343)/2=301.507671 MPa. tau_m=(1206.030686+603.015343)/2=904.523014 MPa. Goodman denominator=301.507671/550+904.523014/2300=0.548195766+0.393270876=0.941466642. SF=1/0.941466642=1.062172."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche7/tranche7-results.json