Almen Saturation Curve Calculator 5.0  

Features                                                     For details e-mail: peenforming@hotmail.com

Retaining all the functions of Version 4.0, the following powerful features extend the versatility of version 5.0:

1. Error Correction model: Almen Saturation Curves are traditionally drawn with the origin at exposure time zero

         and an arc height of zero. This may not necessarily be the case. There are a number of factors that influence

         arc height of peened Almen strips. These include:

        Almen Strips:         Hardness, Thickness, Flatness, Residual Stress

        Almen Test Block:  Flatness, Restraining screw torque

        Almen Gauge:        Accuracy, Almen Strip location

        Setup:                    Test block location, Shot flow rate, Shot velocity, Exposure time accuracy

        These factors may interact in such a manner as to "pre-load" an Almen Strip to a condition where it can no longer

        be considered flat. When multiple strips are run, the "pre-load" errors may even-out or may accumulate. 

        In Almen Saturation Curves, the average of these errors would shift the origin to:

                    Exposure time = zero

                    Arc height       = not zero (or zero if errors even-out)

        The figure below is a plot of the True Shape and the error corrected shape.

Fig1. Run1 (orange) is the True Shape plot of the Spar 316 data. Run2 (green) is the curve with error correction.

Error correction is a 2-step process. The first step determines the best fit of the True Shape with the origin at exposure

time zero and at arc height zero. The Error Correction model then shifts the origin up and down the vertical axis, 

(arc height), until it finds the best fit. For Spar 316, the best fit is at an origin error of exposure time zero and arc

height of -4.192 (-.004192in). This is a much better fit (Standard deviation of .01 or .00001in) than the one with the 

origin at 0, 0.

2. FindXY function  At times, certain points on the saturation curve are required. For example, the arch height at

        a certain exposure time is required, or the compliment; exposure time for a given arc height. Find Y yields the

        arc height and Find X yields the exposure time.

Fig2. The function "Find Y" when the exposure time is 5 minutes yields an arc height of 11.164...6 (.011164...6in). The

         compliment, "Find X", when the arc height is that from "Find Y" yields an exposure time of 5.000..7 minutes,

         or 5 minutes for all practical purposes. (It takes longer to calculate the value of "X" than it does for "Y". The

         function therefore calculates a number that is within +/- .0001 of the exact value. In this case 5.0001 = 5. Note 

         that the calculated "Y" value is exact.)

Of interest is investigating the shape of the curve at extended exposure times. The function "Find Y" can be called

for this purpose.

Fig3.  With "X" set at 1000 minutes, "Find Y" yields a value of 11.625...6. While not significantly larger than that when "X"

          is 5 minutes (11.164...6), this shows that the slope of the curve approaches, but never becomes, zero. This is

          the true shape of the Almen Saturation Curve.

3. User Defined Equation The dialog box is upgraded to display the values of coefficients.

 Fig4. Values of calculated coefficients are displayed at the bottom of the user dialog box. These can be re-entered

          as fixed values in "what if" situations or manipulated in any other manner. Refer back to Version 4.0 for details

          on entering data in the dialog box.