[IMPL] HCF uniaxial SWT criterion

[MartinNesladek]

ℹ️ General Information

Component Name: Stress-based uniaxial SWT

Component Location: core/stress_life/damage_params/uniaxial_stress_eq_amp/

Suggested Python Name: calc_stress_eq_amp_swt_uniax

FABER WG Relation: 4.1

Brief Description: Uniaxial equivalent stress amplitude based on Smith-Watson-Topper parameter.

Priority: 5

Technical Complexity: 2

Estimated Effort: 3

Dependencies: -

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Implementation Details

📋 Specification

For given stress values $\sigma_a$ and $\sigma_m$ representing a single load cycle compute the value of SWT parameter, $P_{SWT}$, in MPa.

Mathematical Formulation

$$ \sigma_{aeq} = \sqrt{\sigma_{a}\cdot(\sigma_{m}+\sigma_{a})} $$

Inputs

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 HCF uniaxial SWT	-	$(0;\infty)$

Expected Behavior

🔧 Implementation Guidelines

Function Signature

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

Code Structure

Error Handling

✅ Validation & Testing

Test Cases

Test Case	Inputs	Expected Outputs	Notes
Example 1	$\sigma_a = 290 MPa; \sigma_m = 10 MPa$	$P_{swt} = 295 MPa$

Validation Criteria

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

📚 References & Resources

• S. Suresh: Fatigue of Materials, Cambridge University Press, 1998

📝 Technical Notes

Performance Considerations

Edge Cases to Handle

Condition $\sigma_a > |\sigma_m|$ should be checked.

Special Requirements

[Vybornak2]

@MartinNesladek please what is the meaning of this edge case?

Question was raised by @KarasTomas and I am not 100% sure.

Edge Cases to Handle

Condition $\sigma_a > |\sigma_m|$ should be checked.

[MartinNesladek]

That is just to ensure positive terms under the square root sign

@MartinNesladek please what is the meaning of this edge case?

Question was raised by @KarasTomas and I am not 100% sure.

Edge Cases to Handle

Condition σ a > | σ m | should be checked.