Stress over time does cause relaxation/load loss/creep.
If designed properly, it will not impact the function.
Ex:
http://www.spring-makers-resource.ne...les/fig_37.pdf
Read post 41 in Walts post/reference thread
Also:
http://www.spring-makers-resource.ne...ng-design.html
http://www.spring-makers-resource.ne...g-designs.html
http://www.spring-makers-resource.ne...ce_summary.pdf
And
http://en.wikipedia.org/wiki/Elasticity_(physics))
http://en.wikipedia.org/wiki/Plasticity_(physics))
http://en.wikipedia.org/wiki/Viscoelasticity
http://en.wikipedia.org/wiki/Creep_(deformation))
Just a snippet:
Taken from
http://en.wikipedia.org/wiki/Viscoelasticity
"
All materials exhibit some viscoelastic response. In
common metals such as steel or aluminum, as well as in quartz,
at room temperature and at small strain, the behavior does not deviate much from linear elasticity. Synthetic polymers, wood, and human tissue as well as metals at high temperature display significant viscoelastic effects.
In some applications, even a small viscoelastic response can be significant. To be complete, an analysis or design involving such materials must incorporate their viscoelastic behavior. Knowledge of the viscoelastic response of a material is based on measurement"
Its really not a question if.... its a question of will it impact the function.
Properly designed, not really a concern.