FEA User Beware !

(Source : MECHANICA  Tutorial, By Roger Toogood, Ph.D., P.Eng)

Users of this (or any other FEA) software should be cautioned that, as in other areas of  computer applications, the GIGO (“Garbage In = Garbage Out”) principle applies. Users can easily be misled into blind acceptance of the answers produced by the programs.  Do not confuse pretty graphs and pictures with correct modeling practice and accurate results.

A skilled practitioner of FEA must have a considerable amount of knowledge and experience.   The current state of sophistication of CAD and FEA software may lead non- wary users to dangerous and/or disastrous conclusions. Users might take note of the fine print that accompanies all FEA software licenses, which usually contains some text  along these lines: “The supplier of the software will take no responsibility for the results obtained . . .” and so on. Clearly, the onus is on the user to bear the burden of responsibility for any conclusions that might be reached from the FEA.

We might plot the situation something like Figure 1. In order to intelligently (and safely) use FEA, it is necessary to acquire some knowledge of the theory behind the method, some facility with the available software, and a great deal of modeling experience.

   Figure. 1

Behavior of Contact (In ANSYS)

In   ANSYS,   the   contact   is  generated   by   pair.  For   the   point-surface   contact,   the   “point”   is  contact and the “surface” is target. For surface-surface contact, both contact and target are surfaces   and   they   have   to   be   specified   which   surface   is   contact   and   which   is   target.   No matter it’s point-surface contact or surface-surface contact, as soon as they are identified, they are then one pair.One can not exist without the other.

For the surface-surface contact, it is the first step to specify which is contact surface and which is target surface. Normally,    convex    surface   is  chosen    as  contact   and concave as target. Also when the size of one body in contact compared to another one is very small and then the large surface is chosen as target.  There are several kinds of contact used in ANSYS: frictional, frictionless, rough, bonded, no separation and so on. Contact surface has different types of behavior according to different characteristics of contact.

Figure. 1

Figure. 2