The classes for damage calculation#

The following classes perform lifetime assessment according to the guideline FKM nonlinear. The objects are given a load collective and a damage parameter woehler curve. They calculate the damage parameters values for the collective and use the woehler curve to calculate a lifetime or infinite strength.

DamageCalculatorPRAM: uses the P_RAM damage parameter
DamageCalculatorPRAJ: uses the P_RAJ damage parameter
DamageCalculatorPRAJMinerElementary uses the P_RAJ damage parameter but omits the horizontal finite strength line in the Woehler curve, corresponding to the Miner Elementary method.

class pylife.strength.fkm_nonlinear.damage_calculator.DamageCalculatorPRAM(collective, component_woehler_curve_P_RAM)[source]#

Calculate lifetime from a P_RAM damage-parameter collective.

Use this calculator for the FKM nonlinear assessment path based on the P_RAM damage parameter. It expects the first and second HCM runs in one collective and evaluates them against a WoehlerCurvePRAM component Wöhler curve.

Parameters:

collective (pandas.DataFrame) – Damage-parameter collective. Each row represents one hysteresis and must contain P_RAM as damage parameter value, is_closed_hysteresis as full-cycle flag, run_index as HCM run number, and S_min for the hysteresis count. A missing index is replaced by a two-level MultiIndex with hysteresis_index and assessment_point_index.
component_woehler_curve_P_RAM (WoehlerCurvePRAM) – Component Wöhler curve for the P_RAM damage parameter.

Notes

Implement the FKM nonlinear guideline assessment for P_RAM, especially the load-sequence repetition rule of clause 2.6, equation (2.6-90). The damage of hysteresis i is accumulated as

\[\begin{split}D_i = \begin{cases} 1 / N_i, & \text{closed hysteresis}, \\ 0.5 / N_i, & \text{memory-3 hysteresis}. \end{cases}\end{split}\]

The resulting damage sum is dimensionless; a value of 1.0 means failure.

property P_RAM_max#

Return the maximum P_RAM value of the second HCM run.

Returns:: Maximum P_RAM damage parameter per assessment point. Values below or equal to the fatigue strength limit indicate infinite life for this criterion.
Return type:: float or pandas.Series

property collective#

Return the evaluated P_RAM collective.

Returns:: Copy of the input collective enriched with bearable cycle numbers, damage per hysteresis, and cumulative damage per assessment point.
Return type:: pandas.DataFrame

get_lifetime_functions(assessment_parameters)[source]#

Return probabilistic lifetime functions for the P_RAM assessment.

The returned callables scale the deterministic lifetime with the material scatter and safety factor of the FKM nonlinear guideline.

Parameters:

assessment_parameters (pandas.Series) – Assessment parameters. Only the material group is required here to select the f_2.5% scatter constant for P_RAM.

Returns:

N_max_bearable (callable) – Function N_max_bearable(P_A, clip_gamma=False) returning the maximum bearable number of cycles for failure probability P_A.
failure_probability (callable) – Function failure_probability(N) returning the failure probability for N load cycles.

Notes

Use FKM nonlinear guideline clause 2.5, equation (2.5-38), for the material safety factor. If clip_gamma is True, gamma_M is clipped to at least 1.1 for the P_RAM assessment.

property is_life_infinite#

Return whether the P_RAM assessment predicts infinite life.

Returns:: True where P_RAM_max does not exceed the fatigue strength limit of the component Wöhler curve; otherwise False.
Return type:: bool or pandas.Series

property lifetime_n_cycles#

Return load cycles until P_RAM failure.

Returns:: Number of cycles in the collective until the accumulated damage sum reaches 1.0. The value is expressed in counted load cycles, not in seconds or load-sequence repetitions.
Return type:: float or numpy.ndarray

property lifetime_n_times_load_sequence#

Return load-sequence repetitions until P_RAM failure.

Returns:: Number of complete load sequence repetitions until the damage sum reaches 1.0. A value of 0 means that failure occurs before the end of the second HCM run.
Return type:: float or numpy.ndarray

class pylife.strength.fkm_nonlinear.damage_calculator.DamageCalculatorPRAJ(collective, assessment_parameters, component_woehler_curve_P_RAJ)[source]#

Calculate lifetime from a P_RAJ collective by guideline accumulation.

Use this calculator for the official FKM nonlinear P_RAJ assessment. It uses the damage values computed during damage-parameter evaluation, classes the second HCM run logarithmically, and accounts for the guideline’s crack-growth based degradation of the endurance limit.

Parameters:

collective (pandas.DataFrame) – Damage-parameter collective with one row per hysteresis. Required columns are P_RAJ, P_RAJ_D, D, run_index, and S_min. A missing index is replaced by a two-level MultiIndex with hysteresis_index and assessment_point_index.
assessment_parameters (pandas.Series) – Parameters of the nonlinear P_RAJ assessment, including P_RAJ_klass_max, P_RAJ_D_e, d_RAJ, a_0, a_end, l_star, and optionally n_bins. Default for n_bins is 200.
component_woehler_curve_P_RAJ (WoehlerCurvePRAJ) – Component Wöhler curve for the P_RAJ damage parameter.