Predicting Performance

Avoiding nonstructural or structural failure can depend in part on the ability to predict performance of materials. When required, designers have developed sophisticated computer methods for calculating stresses in complex structures using different materials. These computational methods have replaced the oversimplified models of materials behavior relied upon previously. The result is early comprehensive analysis of the effects of temperature, loading rate, environment, and material defects on structural reliability. This information is supported by stress-strain behavior data collected in actual materials evaluations.

With computers the finite element analysis (Chapter 5) method has gready enhanced the capability of the structural analyst to calculate displacement, strain, and stress values in complicated plastic structures subjected to arbitrary loading conditions.

Nondestructive testing (NDT) is used to assess a component or structure during its operational lifetime. Radiography, ultrasonics, eddy currents, acoustic emissions, and other methods are used to dctcct and monitor flaws that develop during operation (Chapter 7).

The selection of the evaluation method(s) depends on the specific type of plastic, the environment of the evaluation, the effectiveness of the evaluation method, the size of the structure, the fabricating process to be used, and the economic consequences of structural failure. Conventional evaluation methods are often adequate for baseline and acceptance inspections. However, there are increasing demands for more accurate characterization of the size and shape of defects that may require advanced techniques and procedures and involve the use of several methods.

Designing a good product requires a knowledge of plasdcs that includes their advantages and disadvantages (limitadons) with some familiarity of the processing methods (Chapter 1). Undl the designer becomes familiar with processing, a fabricator must be taken into the designer's confidence early in the development stage and consulted frequendy during those early days. The fabricator and the mold or die designer should advise the product designer on plastic materials behavior and how to simplify the design to permit easier processability.

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