In some engineering problems, some fluctuating stresses or alternating stresses can occur in time. These alternating stresses are generally below the yield strength of material. But application of these alternating stresses can be problematic for part or material. Generally failure occurs in a certain time of application of these alternating stresses. This failure is called as fatigue failure. Gerber method is generally used for ductile materials to predict the fatigue failure in certain force or stress application.
This is the formula of Gerber method to predict fatigue failure of a certain application. In here, SigmaA is the absolute maximum value of fluctuating or alternating stress. Su is the ultime tensile strength of material that you are using in your application. SigmaM is the mean stress of maximum and minimum peak points of sinusoidal alternating stress. Sn(prime) is the estimated endurance strength of your material.
If the calculated value from Gerber method is bigger than 1, fatigue failure from this application is possible. If the calculated value with this formula is smaller than 1, there is no place for fatigue failure with this application.
Another alternative of Gerber method is also Goodman method to calculate fatigue situation for ductile materials.
The use of Gerber method calculator is very easy like above. You just need to enter required parameters, the biggest absolute value of alternating stress, the estimated endurance stress value of your material, mean stress value of sinusoidal alternating stress and ultimate tensile strength of your material respectively. Click on ‘Calculate!’ to see the result. You will be informed about fatigue failure situation of your application. To calculate or re-calculate an another Gerber method, just click on ‘Reset’ button to calculate.
You need to take care about your UNITS! All the units that you use in this formula must be consistent. Otherwise, you will get incorrect results. Because of that, Mechanical Base does not accept any responsibility from these calculations. A good engineer must check all the calculations by hand.
In here, all the units are pressure units. If you want to obtain consistent values of your stress values, you can use MB-Unit Converter tool.
Also you can take a look at the other engineering calculators like this one in Mechanical Base.