Source: https://guthlabs.ai/docs/instruments/fatigue-s-n-curve-life-estimator/implementation/

instrument implementation / implementation-contract

# Fatigue S-N Curve / Life Estimator implementation

A source-bound implementation contract for Fatigue S-N Curve / Life Estimator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## 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**: t7-012

**Effect**: Computation or source lookup only

## Input and validation requirements

The estimator encounters non-finite or undefined behavior at zero stress amplitude and at Basquin exponent b=0; it also has a major life error if stress range is confused with stress amplitude.

## 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": {
    "method": "log_log_table_lookup",
    "material_class": "steel, idealized fully reversed S-N curve",
    "stress_amplitude_MPa": 900,
    "Su_MPa": 1000,
    "surface_factor": 1,
    "size_factor": 1,
    "load_factor": 1
  },
  "expected_outputs": {
    "N_cycles": 1000,
    "Se_MPa": 500
  },
  "reference_data": {
    "sn_table_rows": [
      {
        "N_cycles": 1000,
        "stress_amplitude_MPa": 900,
        "source_convention": "widely tabulated standard textbook value; canonical idealized steel S-N construction, Sf(10^3)=0.9Su"
      },
      {
        "N_cycles": 1000000,
        "stress_amplitude_MPa": 500,
        "source_convention": "widely tabulated standard textbook value; canonical idealized steel S-N construction, Se=0.5Su"
      }
    ],
    "endurance_factor": 0.5,
    "endurance_factor_source_convention": "widely tabulated standard textbook value for the stated approximation",
    "Su_MPa": 1000,
    "Su_source_convention": "widely tabulated standard textbook value used as the example material strength"
  },
  "working": "The input stress is exactly the first table row: σa=900 MPa at N=10^3 cycles. Therefore N=10^3=1000 cycles. Endurance estimate: Se=0.5Su=0.5×1000 MPa=500 MPa. No interpolation is performed."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/fatigue-s-n-curve-life-estimator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/fatigue-s-n-curve-life-estimator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/fatigue-s-n-curve-life-estimator/qualification/>)

## 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`