Source: https://guthlabs.ai/docs/instruments/marin-endurance-limit-modifiers/mechanism/

instrument mechanism / verified-clean

# Marin Endurance Limit Modifiers mechanism

The inspectable method record for Marin Endurance Limit Modifiers, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The algorithm is a standard Shigley-method estimate, but the specification is not sufficiently explicit to receive an unconditional PASS. The exact unresolved ambiguities are: the units of Se', Sut, and geometry; the method and table edition used to derive ka and kb; the load convention for kc; the temperature scale and valid range for kd; and the reliability-table convention for ke. The output should be labeled as an estimated fully reversed endurance limit, not a universally valid fatigue strength.

- The stated formula Se = ka·kb·kc·kd·ke·Se' is the standard Marin-factor correction for a fully reversed endurance limit, provided every factor is dimensionless and applicable to the material, geometry, loading, temperature, and reliability conditions.

- The specification does not define how ka is obtained from surface finish and ultimate tensile strength, although Shigley normally uses finish-specific equations or tables involving Sut.

- The specification does not define the geometry and dimensional range needed for kb; Shigley size factors depend on specimen type, diameter or equivalent diameter, and often have piecewise validity ranges.

- The specification does not define the applicable load-factor convention for kc, especially for combined bending, axial, and torsional loading.

- Temperature-factor kd and reliability-factor ke require defined temperature and reliability conventions and valid table ranges.

## Units and conventions

- Se' and Se are assumed to use the same stress unit; the vectors use MPa.

- ka, kb, kc, kd, and ke are dimensionless.

- Temperature must be explicitly identified as Celsius or Fahrenheit because Shigley temperature-factor tables commonly use Fahrenheit-based ranges.

- The reference factors below are already selected from the stated Shigley Marin-factor convention; if the instrument derives them from raw inputs, Sut, geometry, load case, temperature scale, and table edition must be supplied.

- Reliability percentages are interpreted as the reliability entries in the conventional Shigley Marin reliability-factor table.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "Se_prime_MPa": 300,
    "surface_finish": "ground",
    "surface_factor_ka": 0.9,
    "size_description": "round specimen, 25 mm diameter",
    "size_factor_kb": 0.879,
    "load_type": "bending",
    "temperature_C": 20,
    "temperature_factor_kd": 1,
    "reliability_percent": 50,
    "reliability_factor_ke": 1
  },
  "expected_outputs": {
    "Se_MPa": 237.33
  },
  "reference_data": {
    "ka": {
      "value": 0.9,
      "source_convention": "Shigley Marin surface-finish factor convention; widely tabulated standard value for this test case"
    },
    "kb": {
      "value": 0.879,
      "source_convention": "Shigley Mechanical Engineering Design size-factor relation, evaluated for the stated round geometry; widely tabulated standard value"
    },
    "kc": {
      "value": 1,
      "source_convention": "Shigley Marin load-factor table, bending entry; widely tabulated standard value"
    },
    "kd": {
      "value": 1,
      "source_convention": "Shigley Marin temperature-factor table at the stated ordinary-temperature condition; widely tabulated standard value"
    },
    "ke": {
      "value": 1,
      "source_convention": "Shigley Marin reliability-factor table, 50% reliability entry; widely tabulated standard value"
    }
  },
  "working": "Se = ka·kb·kc·kd·ke·Se'\n= 0.900·0.879·1.000·1.000·1.000·300 MPa\n= 0.7911·300 MPa\n= 237.33 MPa."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

A zero ultimate tensile strength produces the undefined expression 4.51·0^(-0.265) in the surface-finish factor. The instrument must reject this input; accepting it risks infinity, NaN, or an invalid corrected endurance limit.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/marin-endurance-limit-modifiers/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/marin-endurance-limit-modifiers/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/marin-endurance-limit-modifiers/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`

- `BOUNDARY_HAZARD_CATALOG.json`