Changing the SN curve properties explicitly

Instance attributes "SD", "ND", "k", "S1", "N1", "k1", "miner", "R", "M", "meanCorrType" can be used for accessing the parameters. It can be used also for changing the SN properties.

For changing several parameters in once set_SN_parameters() is probably more useful. It takes the dictionary of all parameters to change.

Using the specialized methods

shift_ND()

Sometimes it is useful to shift number of cycles on the endurance limit with keeping all the other parameters. Use the method shift_ND() in this case. See the figure below for the visualisation.

shift_ND(self, newND)

Parameters
----------
newND : int
    new endurance number of cycles

Returns
-------
None
    Modifies current SN_Curve instance.

alt text

shift_SD_with_slope()

Sometimes there is a need to take into account an influence that has a great effect on the small amplitudes (on endurance limit), but that doesn't influence much the low cycle fatigue. There is a method shift_SD_with_slope() for that. Again, the picure can say more than words -> see the figure below.

shift_SD_with_slope(self, SD_shifted, N0=1)

Parameters
----------
SD_shifted : float
    New shifted amplitude at endurance limit

N0 : int (optional, default = 1)
    Number of cycles where no change in amplitude happens

Returns
-------
None
    Modifies current SN_Curve instance inplace.

alt text

shift_SN_curve()

Method shift_SN_curve() can be used to shift the SN curve up/down. It has the same effect as using shift factor in the load input to the damage computing methods.

shift_SN_curve(self, shift_factor)

Parameters
----------
shift_factor : float
    Shift factor to apply

Returns
-------
None
    Modifies current SN_Curve instance inplace.

alt text

transform_to_R()

If there is several SN-curves available, each obtained from different R-ratio testing. It can be usefull to compare such SN curves. To be able to do so, they must be transformed to the same R-ratio. Usually R=-1 (alternating loading). Method transform_to_R() is used to convert SN curve to required SN ratio. Note that meanstress influence M and the type of meanstress correction is important for such transformation. It is important to realize, that the damage results before and after such transformation are the same.

transform_to_R(self, R=-1)

Parameters
----------
R : float
    R-ratio for SN-curve update,
    default: -1.0

Returns
-------
None
    Modifies current SN_Curve instance inplace.

See the plot of the transformation from R=0 to R=-1, with the meanstress influence factor M=0.5.

alt text