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]

This class performs the lifetime assessment according to the FKM nonlinear assessment. It holds damage values from two previous runs of the HCM algorithm and a component woehler curve of type WoehlerCurvePRAM. The outputs are lifetime numbers and detection of infinite life.

This class implements the assessment procedure using the damage parameter P_RAM.

property P_RAM_max: The maximum P_RAM damage parameter value of the second run of the HCM algorithm. If this value is lower than the fatigue strength limit, the component has infinite life. The method compute_damage needs to be called beforehand.

property collective

get_lifetime_functions(assessment_parameters)[source]

Return two python functions that can be used for detailed probabilistic assessment.

The first function, N_max_bearable(P_A, clip_gamma=False), calculates the maximum number of cycles that the component can withstand with the given failure probability. The parameter clip_gamma specifies whether the scaling factor gamma_M will be at least 1.1 (P_RAM) or 1.2 (P_RAJ), as defined in eq. (2.5-38) (PRAM) / eq. (2.8-38) (PRAJ)

The second function, failure_probability(N), calculates the failure probability for a given number of cycles.

Parameters:

assessment_parameters (pd.Series) – The assessment parameters, only the material group is required to determine the respective f_2,5% constant.

Returns:

N_max_bearable – python function, N_max_bearable(P_A)
failure_probability – python function, failure_probability(N)

property is_life_infinite: Whether the component has infinite life. The method compute_damage needs to be called beforehand.

property lifetime_n_cycles: The number of load cycles (as defined in the load collective) until failure. The method compute_damage needs to be called beforehand.

property lifetime_n_times_load_sequence: The number of times the whole load sequence can be traversed until failure. The method compute_damage needs to be called beforehand.

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

This class performs the lifetime assessment according to the FKM nonlinear assessment. It holds damage values from two previous runs of the HCM algorithm and a component woehler curve of type WoehlerCurvePRAJ. The outputs are lifetime numbers and detection of infinite life.

This class implements the assessment procedure using the damage parameter P_RAJ.

property P_RAJ_max: The maximum P_RAJ damage parameter value of the second run of the HCM algorithm. If this value is lower than the fatigue strength limit, the component has infinite life. The method compute_damage needs to be called beforehand.

property collective

get_lifetime_functions()[source]

Return two python functions that can be used for detailed probabilistic assessment.

The first function, N_max_bearable(P_A, clip_gamma=False), calculates the maximum number of cycles that the component can withstand with the given failure probability. The parameter clip_gamma specifies whether the scaling factor gamma_M will be at least 1.1 (P_RAM) or 1.2 (P_RAJ), as defined in eq. (2.5-38) (PRAM) / eq. (2.8-38) (PRAJ) The second function, failure_probability(N), calculates the failure probability for a given number of cycles.

Parameters:

assessment_parameters (pd.Series) – The assessment parameters, only the material group is required to determine the respective f_2,5% constant.

Returns:

N_max_bearable – python function, N_max_bearable(P_A)
failure_probability – python function, failure_probability(N)

property is_life_infinite: Whether the component has infinite life. The method compute_damage needs to be called beforehand.

property lifetime_n_cycles: The number of load cycles (as defined in the load collective) until failure. The method compute_damage needs to be called beforehand.

property lifetime_n_times_load_sequence: The number of times the whole load sequence can be traversed until failure. The method compute_damage needs to be called beforehand.

class pylife.strength.fkm_nonlinear.damage_calculator_praj_miner.DamageCalculatorPRAJMinerElementary(collective, component_woehler_curve_P_RAJ)[source]

This class performs the lifetime assessment as a modification to the FKM nonlinear guideline. For the P_RAJ damage parameter, the lifetime is computed directly using the woehler curve, analogous to the procedure with P_RAM. The whole approach with binning and infinite strength decrease is omitted.

The class reuses the DamageCalculatorPRAM class.

class ComponentWoehlerCurvePRAMStub(component_woehler_curve_P_RAJ)[source]

property P_RAM_D: The damage parameter value of the endurance limit

property P_RAM_Z: The damage parameter value that separates the first and second section, corresponding to N = 1e3

calc_N(P_RAM)[source]

Evaluate the woehler curve at the given damage paramater value, P_RAM.

Parameters:: P_RAM (float) – The damage parameter value where to evaluate the woehler curve.
Returns:: N – The number of cycles for the given P_RAM value.
Return type:: float

calc_P_RAM(N)[source]

Evaluate the woehler curve at the specified number of cycles.

Parameters:: N (array-like) – Number of cycles where to evaluate the woehler curve.
Returns:: The P_RAM values that correspond to the given N values.
Return type:: array-like

property d_1: The slope of the Wöhler Curve in the first section, for N < 1e3

property d_2: The slope of the Wöhler Curve in the second section, for N >= 1e3

property fatigue_life_limit: The fatigue life limit N_D of the component, i.e., the number of cycles at the fatigue strength limit P_RAM_D.

property fatigue_strength_limit: The fatigue strength limit of the component, i.e., the P_RAM value below which we have infinite life.

property P_RAJ_max: The maximum P_RAM damage parameter value of the second run of the HCM algorithm. If this value is lower than the fatigue strength limit, the component has infinite life.

property collective

property is_life_infinite: Whether the component has infinite life.

property lifetime_n_cycles: The number of load cycles (as defined in the load collective) until failure.

property lifetime_n_times_load_sequence: The number of times the whole load sequence can be traversed until failure.