Choosing the right polymer

The CES Optimal Polymer Selector is a new software package from Granta Design that provides designers and engineers with a new way to select polymers.

For years, computer-based packages have been helping plastics users through the minefield of trying to choose the correct grade for an application. They have become valuable tools in the engineer’s armoury.

But according to Granta Design Product Manager, Andrew Fenn, today’s packages have serious limitations. ‘How many times have you carefully entered your property constraints into a package only to be told no materials meet your requirements? That’s not because there aren’t any, but because of holes in the measured data.’

Another problem is that design requirements don’t easily translate into material properties, says Fenn. ‘The best material for a stiff panel is not the same as for a stiff beam, but typical materials databases are not set up to tell you which is best. Nor do they look at the trade-offs between price and performance.’

Granta Design, whose roots are in the work of Professor Mike Ashby of Cambridge University, teamed up with established experts in the polymer materials selection field; the CAMPUS group, M-Base GmbH, and Rapra Technology Limited, to create the new product.

The Optimal Polymer Selector package is comprised of three linked modules, CES PolymerUniverse, CES CAMPUS, and CES ChemRes.

Users carry out an initial selection, that can also be refined according to the chemical environment the part will encounter, on a carefully designed generic database where each datasheet represents all similar materials from many manufacturers. They then move seamlessly on to compare specific commercial grades in the second stage of the optimal selection process.

Fenn says that the power of the package comes from the combination of generic and grade databases and from the Ashby selection methods.

‘Ashby methods are new to most engineers, but you soon get to appreciate their power. Starting with design requirements, you express these criteria with the aid of performance indices, for example for a ‘light stiff panel’ or ‘light stiff beam’. Then you use a series of graphical charts to optimise material choice and analyse the different selection trade-offs.’

Granta claims the CES PolymerUniverse database is the broadest generic database of its kind, covering virtually all filled and unfilled plastics available. Compiled from leading polymer reference sources, it contains a range of properties with every datasheet being complete.

CAMPUS is a worldwide database for plastics materials, developed through close co-operation of the leading plastics producing companies. One of the key philosophies is that of directly comparable data and the data is generated according to specifically developed ISO standards. The CES CAMPUS module, developed with M-Base of Aachen, Germany, contains the full set of CAMPUS data for all participating suppliers, which can be easily accessed and used for grade selection using the Ashby methodology.

The CES ChemRes module incorporates chemical resistance criteria into the CES selection process. It ranks the polymers in CES PolymerUniverse by their resistance to an impressive array of over 190 different chemicals, from olive oil to concentrated sulphuric acid. Derived from data collected at Rapra Technology over many years, the CES ChemRes module is a comprehensive source of experimentally derived information.

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