Stress-life prediction function based on the ASME implementation

src/fatpy/core/stress_life/demage_parameters.py

@@ -1 +1,38 @@
 """Damage parameters calculation methods for the stress-life."""
+
+import numpy as np
+from numpy.typing import NDArray
+
+
+def calc_stress_eq_amp_asme(
+    yield_stress: NDArray[np.float64],
+    stress_amp: NDArray[np.float64],
+    mean_stress: NDArray[np.float64],
+) -> NDArray[np.float64]:
+    r"""Stress-life prediction function based on the ASME mean-stress correction.
+
+    Commputes the value of equivalent stress amplitude, :math:`\sigma_{aeq}` in MPa
+    for given stress values :math:`\sigma_a` and :math:`\sigma_m` representing a
+    single load cycle, using the ASME mean stress correction.
+
+    ### Mathematical formulation:
+
+    $$  \displaystyle\sigma_{aeq}=\frac{\sigma_a}{\left[1-\left(\frac{\sigma_m}{R_e}
+    \right)^2\right]^{1/2} } $$
+
+    Args:
+        yield_stress: :math:`R_e` - Tensile yield strength in [MPa].
+        stress_amp: :math:`\\sigma_a` - Stress amplitude in [MPa].
+        mean_stress: :math:`\\sigma_m` - Mean stress in [MPa].
+
+    Returns:
+        Equivalent stress amplitude by ASME
+
+    References:
+        [1] 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.
+    """
+    stress_aeq = stress_amp / np.sqrt(1 - (mean_stress / yield_stress) ** 2)
+
+    return stress_aeq

tests/stress_life/test_dam_params.py

@@ -0,0 +1,13 @@
+"""Damage parameters calculation methods for the stress-life."""
+
+import numpy as np
+from fatpy.core.stress_life.demage_parameters import calc_stress_eq_amp_asme
+
+
+def test_calc_stress_eq_amp_asme() -> None:
+    yield_stress = 500.0
+    stress_amp = 180.0
+    mean_stress = 100.0
+
+    sigma_aeq = calc_stress_eq_amp_asme(yield_stress, stress_amp, mean_stress)
+    assert np.around(sigma_aeq, 1) == 183.7