|
Whenever you produce a contour plot of stresses or peek at node stresses, you have the option of local stresses (denoted by lower case subscripts) or global or UCS stressees (denoted by upper case subscripts). The lower case values refer to stresses in the local element system. This depends on the numbering order on the element and is usually different from element to element. The upper case values refer to the stresses in the global X-Y-Z system or a UCS and this direction is invariant from element to element.
|
|
|
In a flat plate structure, where the elements lie on one of the global coordinate planes (eg. XY or YZ or ZX planes), it is usually more informative to look at the globally directed stresses. This is appropriate for a concrete slab (say). There are cases where the local stresses are very useful, such as in the following figure, provided care had been taken to properly orientate the elements.
|
|
|
|
|
As shown in the figure, the elements have been numbered in such a way that the local y axis follows the contour of the mesh. Here a plot of local y stresses will give the stresses in a direction indicated by the mid line in the mesh above.
|
|
|
For a general 3D shell structure you may also use either local or Global/UCS stresses. If the elements lie on a coordinate system such as Cartesian, cylindrical, spherical or toroidal, then a UCS could be defined and meaningful stresses on the UCS obtained. Otherwise the local element axes could be aligned as required (by using the align tools or plate axis angle attribute) thereby allowing the extraction of meaningful local stresses.
|