If an object is designed to cope with large forces such as tension, would removing these forces risk damaging the object?

For example: The neck of a guitar is built to handle the tension of steel strings (~800 Newtons), if you removed/reduced the tension (removed the strings) for a long period of time would this risk damaging the guitar neck?

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    $\begingroup$ Check the hysterisis curve. Loading and unloading of stress does not take place in the same line. It is a hint. :-) $\endgroup$ – Sagnik Jan 18 '14 at 13:04

This answer is specifically about guitars because I have guitar building and repair experience. The strings and the truss rod are under tension so the neck itself is mainly under compression. There is some tension on the back side of the neck due to neck relief (forward bow of neck) but not much. Necks are made from wood from the trunk, a material 'built' to handle the compressive stress from the weight of the tree.

The safety factor (failure load/service load)of guitar necks are very large.

A very basic calc. to demonstrate this:

Compressive yield strength parallel to grain for the most common guitar neck wood (maple) = 21.5 M Pa Approximate Cross sectional area = 0.0007 m ^2

F = PA = (21.5 M Pa) * (0.0007 m^2) = 15 Kilo Newtons.

SF = (failure load/service load) = (15 kN)/(800 N) = 18.75

Basically, guitar necks are super strong and only fail due to impact (see Gibsons broken headstock syndrome) or warp due to poorly seasoned wood or extreme humidity or temp. changes.

  • $\begingroup$ So leaving the guitar for an extended period of time with no strings or strings with much less tension would not warp the truss rod? $\endgroup$ – Edd Jan 20 '14 at 11:22
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    $\begingroup$ I've never heard of a truss rod warping. An over tightened truss rod can literately destroy the neck. Most people recommend slackening the strings before any long term storage or large temperature/humidity changes such as being in the cargo hold on an air craft. $\endgroup$ – Fergus Jan 20 '14 at 23:40

A piston-cylinder pressure vessel is an example of an object that commonly fails in this way. Carbide has a high compressive strength but lower strength in tension. Pressure vessels may be pre-loaded externally, with a confinement ring and interference fit, so that they can withstand higher internal pressure. If the carbide creeps during a pressurization experiment (say at elevated temperature) - residual strains may cause the vessel to fail in tension upon unloading. When I used such pressure vessels we stored them in a metal box to protect persons in the lab from the possibility of injury from an unexpected failure of an empty pressure vessel. Failure has occurred like this on occasion.


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