Source: https://guthlabs.ai/docs/instruments/goodman-soderberg-fatigue-diagram/implementation/

instrument implementation / implementation-contract

# Goodman / Soderberg Fatigue Diagram implementation

A source-bound implementation contract for Goodman / Soderberg Fatigue Diagram; 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**: t6-064

**Effect**: Computation or source lookup only

## Input and validation requirements

The zero-stress input makes the direct safety-factor calculation divide by zero, and the convention probe shows that interpreting compressive mean stress as signed versus as a magnitude changes the result from 4 to 4/3.

## 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": "Goodman",
    "sigma_a": 120,
    "sigma_m": 80,
    "Se": 240,
    "Su": 600,
    "units": "MPa"
  },
  "expected_outputs": {
    "safety_factor": 1.578947368,
    "operating_point": {
      "sigma_m": 80,
      "sigma_a": 120,
      "units": "MPa"
    },
    "sampled_failure_line_points": [
      {
        "sigma_m": 0,
        "sigma_a": 240
      },
      {
        "sigma_m": 80,
        "sigma_a": 208
      },
      {
        "sigma_m": 600,
        "sigma_a": 0
      }
    ],
    "key_curve_features": {
      "sigma_a_intercept": 240,
      "sigma_m_intercept": 600,
      "roots": [
        {
          "sigma_m": 600,
          "sigma_a": 0
        }
      ],
      "extrema": [],
      "asymptotes": []
    }
  },
  "working": "Goodman denominator = sigma_a/Se + sigma_m/Su = 120/240 + 80/600 = 0.5 + 0.133333333333 = 0.633333333333. Therefore SF = 1/0.633333333333 = 1.578947368. Failure-line samples: at sigma_m = 0, sigma_a = 240*(1 - 0/600) = 240 MPa; at sigma_m = 80, sigma_a = 240*(1 - 80/600) = 240*(0.866666666667) = 208 MPa; at sigma_m = 600, sigma_a = 240*(1 - 1) = 0 MPa."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/goodman-soderberg-fatigue-diagram/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/goodman-soderberg-fatigue-diagram/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/goodman-soderberg-fatigue-diagram/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-tranche6/tranche6-results.json`