I can easily get what a residual strain means.I can easily visualize it
1) But how do I get a basic understanding of residual stress ? ?
Other follow up questions :
2) What are are the possible ways in which the residual stress could be generated ?
3) Does residual stress change the geometrical shape ?
4) Does the spatial distribution of residual stress automatically satisfies the equilibrium equation ?
5) Is the residual stress, in anyway, related to the anisotropy of a material ?
Omar,
Loading would just lead to stresses and may not be the residual stresses. If you unload the material, after loading it beyond elastic domain, residual plastic strain would be present without any stresses in it.
I best believe that residual stress exist without any external loads.
When you remove the load (thermal load) from a body it wants to springback (due to stored elastic potential). If for some reason the material is not allowed to deform (springback) the way it wants to then the stresses remains in the body (elastic potential). These are residual stresses. For instance during welding a sheet, temperature gradient cause uneven thermal expansion. Consequently the sheet bends. After welding when temperatures get uniform, the sheet wants to become flat again but its not possible because of the weld. So residual stresses will remain in the sheet unless you perform a stress relieving heat treatment..
2. Possible ways: too many ways. Examples: welding, bending, shrink fits, sheet drawing,
3. Residual stress are due to stored elastic potential in equilibrium. The (desired) deformation is constrained so shape must not change unless the residual streses are released or an external load is applied.
4. Yes. Including the constraints which are restricting the (desired) deformation.
5. Yes. When you have elastic anisotropy then obviously the streses are anisotropy dependent. When you have only plastic anisotropy and hardening occurs after yielding, then indirectly because the elastic strain is influenced by plastic anisotropy.
I would give the example of residual stresses generated during wire sawing of silicon wafers using abrasive. The process can be modeled as indentation, one can imagine when the indenter moves into the material, first the material elastically deforms, after a certain limit, there is some plasticity or flow of material in the localized area below the indenter. This material which has undergone plastic deformation is bounded on all sides by material which did not experience loading. If the stressed material wants to flow, it cannot -due to the surrounding material, which causes residual stresses. Some papers by B.R Lawn and others can be referred to.
This is also exemplified by shot peening procees which introduces compressidve residual stresses on the surface- preventing growth of any cracks.
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