## 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.
```

### 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.
```

### 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.
```

### 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.