In Part Un we discussed the difference between shanking (mis-hit) and friction failure.  It was obvious that the string was broken.  But what happens when it is not so obvious?

Part Deux, this part, will examine the frictional notching failure of monofilament string and how we can be prepared for it!  To further refine this discussion we will be comparing PET polyester has PEEK monofilament string.  The reason is that each material while both will notch one requires more time to reach the critical dimensional decrease that is a failure!

In almost every Racquet Quest Podcast we talk about tension v string diameter and agree that once 50% of the string diameter is notched away the string is vulnerable!  So a .050 (1.27mm) diameter string that has a tensile strength of 120 pounds at 50% notching will have 60 pounds of tensile strength remaining.

Notched v un notched string

This graph is a string that was broken during use.  The string was removed from the racquet.  The top line is the tensile strength in the area of no notching so you can see that it is pretty strong still and has stabilized due to use.  That stabilization is indicated by the very tight stress/strain grouping.

However, things go sideways when the notched area of the string is put under stress.  The string failed at a force of 63.8 pounds, or about 59% of the used tensile strength.  Not bad!

So, notching is failure-inducing but how long it takes to create the fatal notch differs with string material.  This particular set of strings had about six (6) hours of play.

In Part Trois, we will look at PEEK material under the same conditions!