Geometric shape

Design analysis is required to convert applied loads and other external constraints into stress and strain distributions within the product, and to calculate associated deformations (Chapters 1 and 2). The nature and complexity of these calculations is influenced strongly by the shape of the component. It is most convenient if the component approximates to some simple idealized form, such as a plate or shell (for example a body panel), a beam or tube (for example a chassis member or bumper), or a combination of idealized forms (for example a box structure). In these cases, standard design formulae can be provided into which appropriate parameters can be substituted for a particular application.

However, there are many more cases where the component shape does not approximate to a simple standard form (for example a wheel, pump housing, or manifold) or where a more detailed analysis is required for part of a product (for example the area of a hole, boss, or attachment point). In these cases, the geometry complicates die design analysis and it may be necessary to carry out a direct analysis, possibly using finite element analysis.

One of plastics' design advantages is its formability into almost any conceivable shape. It is important for designers to appreciate this important characteristic. Both the plastic materials and different ways to fabricate products provide this rather endless capability. Shape, which can be almost infinitely varied in the early design stage, is capable for a given volume of materials to provide a whole spectrum of strength properties, especially in the most desirable areas of stiffness and bending resistance. With shell structures, plastics can be either singly or doubly curved via the different fabricating processes.

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