[NavyChief]

While certainly atypical, I found this little blurb in Jeff Cooper's Commentaries (http://www.molonlabe.net/Commentaries/) sort of interesting. (Underlining mine)Our distinguished family member J.P. Denis of Belgium reports that he discovered an abandoned MP40, together with several magazines, in a building that was being torn down. This piece had been left unattended for 50 years with all magazines in full compression, and they all worked perfectly. I think this is marvelous. When you think of the degree to which our culture depends upon springs, it is good to know that spring construction is so well understood.

[Sir Knight]

That's pretty interesting but doesn't agree with my personal experience ... had a Para-Ordnance P14-45 with a ten round factory magazine loaded for less than half a year and the spring failed on me.

[7.62mmFMJ]

Alan,

I think Para P14 mags are an anomoly. Mine are failing too. In fact, the whole Para thing is beginning to bother me because the magazine is integral.

But I hear over and over about ancient 1911s being found loaded with fully operational springs in the mag.

[Marinesg1012]

I dont think the loading and l;eving loaded kills springs it is the constant loading unloading that wears them out, but I dont know how long a shelf life a spring that is used constantly has, I know we used our mags a lot, especialy the M9 mags and while we had some go we had had them for a long time.

[dipodomys]

It may be more a matter of previous history than it is the one incident of leaving it loaded.

[Zircon]

Marines and Dypodomus are on to it. Springs don't typically fail by being statically loaded if they are properly heat treated. There can be some creep where they take a set, but in general they will not break just sitting there. Breakage comes from fatigue (a metallurgical term, but akin to being tired) that comes from constant flexing. Take a coat hanger and flex it into a constant arc. How long do you think you'll have to sit there before it breaks? It will corrode away before it will break under a single flexure. Now, bend it back and forth a dozen times in a sharp radius. You know the answer.

[Gremper]

I had the same problem with my original Para springs. I replaced them with Wolff springs and have had no further problems.

[Sockrotter]

Marines and Dypodomus are on to it. Springs don't typically fail by being statically loaded if they are properly heat treated. There can be some creep where they take a set, but in general they will not break just sitting there. Breakage comes from fatigue (a metallurgical term, but akin to being tired) that comes from constant flexing. Take a coat hanger and flex it into a constant arc. How long do you think you'll have to sit there before it breaks? It will corrode away before it will break under a single flexure. Now, bend it back and forth a dozen times in a sharp radius. You know the answer.
I think it has more to do with the quality of the spring wire than anything else. Yes, springs will take a set, but then are stable. If flexing springs ruined them, I'd expect auto engine valve springs to fail in an hour or two.
Rob

[Redrum]

I'll wait for Rabbis 02 on this...He's into the spring technology....but I would tend to agree with the heat treatment solution.....I don't have a problem with my Para...I don't use their mags...I have Wilson 43B mags (or is it 42...:dunno:) loaded 24/7...Haven't failed in 4 years!!

[Vibe]

Springs are made from steel. Steel has an elastic deformation limit. So long as that limit is not exceeded the steel will "spring" back to it's original shape. One the elastic limit is exceeded then it goes into the plastic deformation stage at which point it will not return completely. Continual excursions into this plastic deformation stage WILL cause rapid failure - which is what happens to the coat hanger in the previous example. Magazine springs that fail in static loadings are either designed or heat treated in such a way that the full loading puts the stress in the sprin wire just past the elastic limit and into the plastic deformation area. This is whay some magazines have the problem and others (of na otherwise identical design) will not have the problem. If yours has the problem it should show up fairly quickly. If it doesn't it may never have it.

[Zircon]

What Vibe is talking about is known as Hook's Law in an area known as mechanic's of materials. From a metallurgical perspective, there are primarily four things that effect the quality of spring wire. 1) Alloy composition; 2) internal inclusions - e.g., the cleanliness of the steel; 3) the heat treatment; 4) the freedom from surface dings, nicks, etc. that would create stress risers on the most highly stressed portion of the spring.

A compression (or tension) spring is nothing more than a torsion bar. It works because you are torquing the spring about the wire's long axis.

Springs can and do fail by taking a set. As Vibe suggests, the set can be induced very rapidly by exceeding the elastic limit, the point at which the material no longer behaves in a linear response to stress (force/area) and strain (percentage of rotation or torquing); and it can be induced slowly by a process known as creep where a permanent deformation takes place because the atoms in the crystal structure re-arrange or diffuse over time under the continuous application of load (stress.) The higher the stress, the more creep occurs, the more the permanent set takes place. Also, creep is highly temperature sensitive - more of a problem in the auto valve spring example than in a pistol magazine operating at mostly room temperature.

Springs can and do fail catastrophically by fatigue. Fatigue can occur slowly if the spring is working in it's properly designed elastic region, or rapidly as I pointed out in the coat hanger example if the elastic limit (i.e., permanent deformation is immediate) is exceeded - especially cyclically back and forth. Fatigue is effected by the amount of force applied - how close is the spring being loaded to the elastic limit (let's assume that the spring is properly designed and being operated in the elastic limit), and how many cycles have been applied. There are fatigue curves that are set up for most common steels, known as S/n curves where the S = stress, and the n = number of cycles of flexure at that stress. Steels have a fatigue limit. If the stress is below the fatigue limit the number of cycles can be almost infinite - typically defined as a million cycles or ten million cycles. The closer the stress is to the elastic limit (which is well above the fatigue limit) the fewer cycles for fatigue to do it's dirty little deed.

OK, let's take this one step farther. Fatigue can be induced at early onset by stress risers. These can be internal inclusions like stringers of sulphides or phosphides, or they can be external nicks and dings on the surface of the wire. These features concentrate the stress, and magnify it in a local area. Higher stress means working higher up the linear part of the stress/strain curve (the elastic part), and therefore typically above the fatigue limit where repeated cycles will cause failure.

The effect of heat treatment is to increase the yield strength of the wire. This means that more strain (deformation) can be induced in the wire before the elastic limit is reached, e.g., before permanent deformation takes place. No H.T. or poor H.T. reduces this yield strength and means that the spring would take a permanent set at a lower deformation than a properly heat treated spring. Alloy composition has a similar effect as H.T. The more highly alloyed, the higher the elastic limit (the higher the effective yield strength.) Alloy composition can also effect fatigue - certain alloying elements can help resist fatigue.

OK, guyz, I didn't want to get this wordy, which is why I put forth the simple first answer with the coat hangar. Clearly some complex phenomena take place with metallic components loaded with repeated cyclic stress, or even loaded with a static stress. If I had to rank them, fatigue would be #1 failure mechanism and creep would be a distant second. There are several other failure mechanisms including corrosion, combinations of corrosion and fatigue, etc. but these are not something usually seen in a pistol springs.

Designing a spring with adequate life involves the mechanical part of the design (Hook's Law) making sure that the spring is loaded well below the elastic limit, but it also is dependent on the quality of the wire, both metallurgically (heat treat, alloy composition, internal inclusions) as well as surface finish. Rob, the reason your valve springs don't fail is that these design and metallurgical factors have been taken into account. If they hadn't been, you could bet that they would fail, just like the magazine springs.

[Vibe]

Good post Zirc. Well worded and fairly concise, not to mention accurate.