What is Fatigue, and Why is it so Stressful?

Merriam-Webster defines Fatigue as:

1. the state of being very tired: Extreme weariness.
2. the tendency of a material (such as metal) to break after being bent or moved many times

The first definition makes sense for an animal or person.  After a long day of hard work or play you might feel fatigued, tired, or weary.

The second definition pertains to structural material such as steel and their ability to accommodate multiple loading cycles.  This is the fatigue Engineers are concerned with.  Engineers place high importance on fatigue and expend a great deal of energy defining, understanding, and testing a given design for fatigue.

Let us step back a moment and look at the first definition again.  ‘the state of being very tired’ How does a person become very tired?  Usually by repetitious labor.  This sounds a good deal like structural fatigue that engineers are concerned with.  This leads to how I view fatigue.  Fatigue is what happens when your design becomes tired, and worn down.  The design increasingly cannot support as much load (weight, temperature, etc.).

Yes, just like people your design eventually will become tired and weak.  The question is how soon will the design weaken?  Engineers do not want a design that fails prematurely, but will last through its expected life. SOLIDWORKS Simulation Standard and the Fatigue Study help engineers predict and understand fatigue in their designs. Fatigue is an important phenomenon that cannot be overlooked.

SOLIDWORKS Simulation Standard offers an intuitive interface to apply multiple loading conditions and predict life expectancy and percent damage due to fatigue.  The setup is straight forward and requires three main components.

1.    Existing study to repeatedly load.  This could be a static study, thermal, vibration, etc.

2.   Assign the loading cycle including Zero based, Fully Reversed, or Loading Ratio.  Specify the number of cycles you want the design to withstand.

3.    Assign a Stress to Number of Cycles (SN) curve to the material properties.

That’s all.  The setup is that easy.  Let SOLIDWORKS Simulation do the heavy lifting and predict life expectancy and the percent damage of your design.  Don’t let your design grow tired and weary before you want it to.  It is important to know how your design performs once as well as multiple times.  Fatigue analysis gives the engineer just that.