I'm an engineer, so I decided to check the numbers. According to
this site, music wire meeting ASTM 228 specifications has an ultimate tensile strength of between 230 KSI and 399 KSI. It's incredibly strong, considering that normal mild steel that you see every day for structural steel members like I-beams are typically in the 58-80 KSI range (again, we're talking ultimate tensile strength, not yield strength).
Keep in mind that there are only a couple of wire manufacturers that supply wire to the string companies. When you say "reputable manufacturer", it's important to note that companies like D'Addario and GHS and the others aren't actually manufacturing the wire. They buy spools of it and just cut it to length, then form the loops, do the winding, coating, etc., to make it their own special style. It's the wire manufacturers who are responsible for the quality and strength of the wire.
So, with that said, let's look at an 0.011" E string from your example. At that diameter, it has a cross-sectional area of 0.000095 in^2. So at the low end of the tensile strength range (230 KSI), it will break at 21.86 lbs. At the high end (399 KSI), it will break at 37.91 lbs. One would typically expect wire that meets this specification to fall right in the middle of the range, or around 315 KSI, giving it a break strength of 29.93 lbs.
Now that we know that, we can go back and look at tuning pitches from the D'Addario link you provided. You can see that wire which falls in the low end of the acceptable ASTM 228 range would break somewhere between Eb (20.71 lbs.) and E (23.25 lbs.)! On the strong side of the curve, an E string should be able to go all the way up to G# (36.90 lbs.), almost to a high A (41.42 lbs.) before it breaks. But the "average" music wire that's in the middle of the acceptable range will break somewhere around F# (29.29 lbs.).
Another way to look at it is this: A typical 0.011" E string that is of average quality (i.e. having strength in the middle of the acceptable range) is tuned up to 23.25 lbs., with a break strength of 29.93 lbs., so it's expected to perform at around 78% of its ultimate strength. Or, we could say that it has a safety factor of about 1.29. That's not a huge safety factor, especially considering that this average-quality string will break when tuned up a whole step.
Bookmarks