[IMPL] Implement stress-life prediction function based on the ASME mean-stress correction

[MartinNesladek]

ℹ️ General Information

Component Name: ASME

Component Location: core/stress_life/damage_params/uniaxial_stress_eq_amp/

Suggested Python Name: calc_stress_eq_amp_asme

FABER WG Relation: 4.1

Brief Description: Uniaxial equivalent stress amplitude based on ASME

Priority: 1

Technical Complexity: 2

Estimated Effort: 2

Dependencies: -

---

Implementation Details

📋 Specification

Using the ASME mean stress correction, compute the value of equivalent stress amplitude, $\sigma_{aeq}$, in MPa for given stress values $\sigma_a$ and $\sigma_m$ representing a single load cycle.

Mathematical Formulation

$$ \displaystyle\sigma_{aeq}=\frac{\sigma_a}{\left[1-\left(\frac{\sigma_m}{R_e}\right)^2\right]^{1/2} } $$

$$  \displaystyle\sigma_{aeq}=\frac{\sigma_a}{\left[1-\left(\frac{\sigma_m}{R_e}\right)^2\right]^{1/2} } $$

Inputs

1. Static tensile parameters

Parameter	Symbol	Type	Description	Units	Constraints
yield_strength	$R_{e}$	array of floats	Tensile yield strength	MPa	$>0$

2. Stress / Strain values

Parameter	Symbol	Type	Description	Units	Range
stress_amp	$\sigma_a$	array of floats	stress amplitude	MPa	$(0; \infty)$
mean_stress	$\sigma_m$	array of floats	mean stress	MPa	$(-\infty;\infty)$

Outputs

Parameter	Type	Description	Units	Range
$\sigma_{aeq}$	array of floats	Equivalent stress amplitude by ASME	-	$(0;\infty)$

Expected Behavior

🔧 Implementation Guidelines

Function Signature

# Suggested function signature
def calc_stress_eq_amp_asme(
    stress_amp: ArrayLike,
    mean_stress: ArrayLike,
    yield_strength: ArrayLike,
) -> NDArray[np.float64]:

Code Structure

Error Handling

✅ Validation & Testing

Test Cases

Test Case	Inputs	Expected Outputs	Notes
Example 1	$R_{e} = 500 MPa; \sigma_a = 180 MPa, \sigma_m = 100 MPa$	$\sigma_{aeq} = 183.7 MPa$

Validation Criteria

• Mathematical accuracy verified against literature
• Edge cases handled appropriately
• Output format matches specification

📚 References & Resources

J. Papuga, I. Vízková, M. Lutovinov, M. Nesládek: Mean stress effect in stress-life fatigue prediction re-evaluated, MATEC Web of Conferences 165, 10018, 2018.
https://www.matec-conferences.org/articles/matecconf/pdf/2018/24/matecconf_fatigue2018_10018.pdf

📝 Technical Notes

Performance Considerations

Edge Cases to Handle

An error handling should be implemented for $\left| \sigma_m \right|\geq R_e$.

Special Requirements

[Vybornak2]

@MartinNesladek
Is it valid to always calculate amount of cycles using Basquin Equation?
Shouldn't be $\sigma_{a,eq}$ be returned instead and Basquin Equation be defined separately ?

I do not know, what are the options, here, but from the point of separation of concerns, it makes sense to me.

[Vybornak2]

@MartinNesladek
Additionally if this is the case, please could you check other mean stress corrections Issues where the same problem reoccurs?