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Use of Finite Element Analysis in the Design of Plastics Parts
Design optimization has become an important issue for most of the companies in the plastics industry.
Due to the cost of high quality molds and challenges in accurate prototyping , FEA prove itself as a powerful
tool in the design of safe but economical products.
A number of new FEA software got on the market in the last couple of years. Many of these packages
derive from what used to be dedicated aerospace or military software. This led to a drop in the price
of FEA software, which became more accessible to engineers.
Solid models ease considerably the task of designers, but they also can be automatically translated into
FEA models, consisting of meshes and nodes.
New features added to nonlinear analysis software, has made FEA more powerful for the design of plastics parts.
While linear analysis can help a preliminary design of the part, nonlinear methods allow the designer to take
full advantage of material capacity.
It is known the response of plastics components is not proportional to loads, and also hollow parts with
thin walls show little resistance at small deformations, but more resistance when subjected to larger deformations.
We must note that while latest FEA software packages provide a variety of approaches for nonlinear
analysis, like: Newton-Raphson, modified Newton-Raphson, Quasi-Newton, Crisfield, Riks, Modified Riks, etc.,
the difficulty resides in assigning correct mechanical properties (Poisson ratio, Young's modulus, hyperelastic
constants, etc.), which can be sometimes difficult to obtain from resin manufacturers.
The example provided by Eastpoint Design shows the design of a PE pallet, which has to resist compression loads
due to stacking, but also impact loads, from accidental dropping.
The preliminary analysis shows the stresses concentrated in the corner of the pallet, where an
impact load is applied. The maximum stress is over 7,000 psi (green), which is not acceptable.
The designer wanted the stresses to disperse more into the pallet, and consequently to reduce
the magnitude of the stress. He added more ribs to the part, and larger radii on edges.
The results are shown in Fig.3, where the maximum stress is only 1,700 psi. (yellow).
You can visit Eastpoint Design's web site at www.plasticsusa.com/epoint
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