Finite Element Thought For The Day

Finite Element Analysis results tend to converge to correct solutions with mesh refinement. This is achievable, provided the elements pass the "Patch Test." An element patch is commonly referred to all elements attached to a patch node. A good element should provide exact solution to simple problems, when taken individually or as a part of an arbitrary patch. Two types, namely, Displacement Patch Test and Force Patch Test are commonplace. While the former applies boundary displacements to a patch and verifies the patch response in terms of rigid body modes and constant strain states, the latter applies boundary forces and checks the patch response in terms of constant stress states. Mixed patch tests involving displacement and force boundary conditions are also in use. Passing the patch test is a necessary but not sufficient condition for convergence. Popular FE codes such as Cosmos FEA have incorporated numerous tests and criteria to assure accurate computation of displacement, strain and stress fields for varied problems.

Geometric Dimensioning & Tolerancing - Simplifying Complex Requirements

GD & T symbols are used to convey design specifications for manufacture and inspection. Sometimes complex requirements can be easily addressed using symbols in an elegant and unambiguous manner. Unquestionably, GD & T addresses design challenges in a manner that cannot be matched by explanatory notes.

Often an engineer comes across a fixture or a machine element drawing, wherein the surfaces are to be controlled as shown in the figure below.

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Surfaces are controlled for parallelism, collinearity and flatness using a composite Feature Control Frame in an elegant manner resulting in clarity of design specification. It is important that we denote the height dimension using Basic Dimension to ensure completeness in definition of the Feature of Size.