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Use copy of x0 in scipy.optimize.newton to prevent side effect #134

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Use copy of x0 in scipy.optimize.newton to prevent side effect #134

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11 changes: 5 additions & 6 deletions src/pylife/materiallaws/notch_approximation_law.py
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
import numpy as np
from scipy import optimize
import pandas as pd
import copy

import pylife.materiallaws.rambgood

Expand Down Expand Up @@ -135,7 +136,7 @@ def stress(self, load, *, rtol=1e-4, tol=1e-4):
'''
stress = optimize.newton(
func=self._stress_implicit,
x0=load,
x0=copy.copy(load),
fprime=self._d_stress_implicit,
args=([load]),
rtol=rtol, tol=tol, maxiter=20
Expand Down Expand Up @@ -192,10 +193,9 @@ def load(self, stress, *, rtol=1e-4, tol=1e-4):
# => sigma/E + (sigma/K')^(1/n') = (L/sigma * K_p * e_star)
# => (sigma/E + (sigma/K')^(1/n')) / K_p * sigma = L * e_star(L)
# <=> self._ramberg_osgood_relation.strain(stress) / self._K_p * stress = L * e_star(L)

load = optimize.newton(
func=self._load_implicit,
x0=stress,
x0=copy.copy(stress),
fprime=self._d_load_implicit,
args=([stress]),
rtol=rtol, tol=tol, maxiter=20
Expand Down Expand Up @@ -225,7 +225,7 @@ def stress_secondary_branch(self, delta_load, *, rtol=1e-4, tol=1e-4):
'''
delta_stress = optimize.newton(
func=self._stress_secondary_implicit,
x0=delta_load,
x0=copy.copy(delta_load),
fprime=self._d_stress_secondary_implicit,
args=([delta_load]),
rtol=rtol, tol=tol, maxiter=20
Expand Down Expand Up @@ -281,10 +281,9 @@ def load_secondary_branch(self, delta_stress, *, rtol=1e-4, tol=1e-4):
# => sigma/E + (sigma/K')^(1/n') = (L/sigma * K_p * e_star)
# => (sigma/E + (sigma/K')^(1/n')) / K_p * sigma = L * e_star(L)
# <=> self._ramberg_osgood_relation.strain(stress) / self._K_p * stress = L * e_star(L)

delta_load = optimize.newton(
func=self._load_secondary_implicit,
x0=delta_stress,
x0=copy.copy(delta_stress),
fprime=self._d_load_secondary_implicit,
args=([delta_stress]),
rtol=rtol, tol=tol, maxiter=20
Expand Down
22 changes: 20 additions & 2 deletions tests/materiallaws/test_notch_approximation_law.py
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Expand Up @@ -32,7 +32,7 @@ def test_extended_neuber_example_1():
K = 1184 # [MPa]
n = 0.187 # [-]
K_p = 3.5 # [-] (de: Traglastformzahl) K_p = F_plastic / F_yield (3.1.1)

L = pd.Series([100, -200, 100, -250, 200, 0, 200, -200])
c = 1.4
gamma_L = (250+6.6)/250
Expand All @@ -52,7 +52,7 @@ def test_extended_neuber_example_1():
assert np.isclose(maximum_absolute_load, 359.3, rtol=1e-3)

binned_notch_approximation_law = pylife.materiallaws.notch_approximation_law.Binned(
notch_approximation_law, maximum_absolute_load)
notch_approximation_law, maximum_absolute_load, 100)

# some rows of PFAD are given in the FKM nonlinear example on p.76
pd.testing.assert_series_equal(binned_notch_approximation_law._lut_primary_branch.iloc[0], \
Expand All @@ -72,6 +72,8 @@ def test_extended_neuber_example_1():
pd.testing.assert_frame_equal(
binned_notch_approximation_law._lut_secondary_branch, expected_matrix_AST_162, rtol=1e-3, atol=1e-5)

assert np.isclose(binned_notch_approximation_law._lut_primary_branch.load.max(), maximum_absolute_load)


def test_extended_neuber_example_2():
""" example under 2.7.2, p.78 of FKM nonlinear, "Welle mit V-Kerbe" """
Expand Down Expand Up @@ -118,6 +120,22 @@ def test_extended_neuber_example_2():
binned_notch_approximation_law._lut_secondary_branch, expected_matrix_AST_171, rtol=1e-3, atol=1e-5)


def test_extended_neuber_example_no_binning_vectorized():
E = 206e3 # [MPa] Young's modulus
K = 1184 # [MPa]
n = 0.187 # [-]
K_p = 3.5 # [-] (de: Traglastformzahl) K_p = F_plastic / F_yield (3.1.1)

notch_approximation_law = ExtendedNeuber(E, K, n, K_p)

load = np.array([150.0, 175.0, 200.0])
stress = notch_approximation_law.stress(load)
stress_secondary_branch = notch_approximation_law.stress_secondary_branch(load)

np.testing.assert_allclose(stress, np.array([148.463622, 171.674936, 193.702502]), rtol=1e-3)
np.testing.assert_allclose(stress_secondary_branch, np.array([149.92007905, 174.81829204, 199.63066067]), rtol=1e-3)


@pytest.mark.parametrize('stress, load', [
(22, 42),
(40, 40),
Expand Down
2 changes: 2 additions & 0 deletions tests/materiallaws/test_notch_approximation_law_seegerbeste.py
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Original file line number Diff line number Diff line change
Expand Up @@ -72,6 +72,8 @@ def test_seeger_beste_example_1():
pd.testing.assert_frame_equal(
binned_notch_approximation_law._lut_secondary_branch, expected_matrix_AST_162_seeger_beste, rtol=1e-3, atol=1e-5)

assert np.isclose(binned_notch_approximation_law._lut_primary_branch.load.max(), maximum_absolute_load)


def test_seeger_beste_example_2():
""" example under 2.7.2, p.78 of FKM nonlinear, "Welle mit V-Kerbe" """
Expand Down
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