Plastic product design corners

Stress Concentration The magnification of applied stress in the vicinity of a notch, hole, inclusion, or inside corner. Minimizing stress concentrations is an important aspect of plastics product design. 

One common design issue is the lack of filleted comers as demonstrated in Fig. 27.11. While filleting the comers is a recurring mle in plastic product design, it is often avoided for aesthetic or cost reasons or simply overlooked. The importance of avoiding sharp comers stems from the avoidance of stress concentrations, K, which are a function of the corner radius, R ... 

In all plastics products it is preferable to avoid sharp corners and intersections, and design well-radiused ones. This is to minimize stress concentrations at sharp corners, which can allow the initiation of cracks. Figure 4.10 shows some of these features diagramatically. 

Some understanding of the various mechanisms of failure is necessary before suitable tests can be chosen. Tests need not be complex but must be relevant. For example, a simple measurement of product thickness may establish that there has been a departure from the specified design thickness. The radii of corners, moisture content of plastic, bubbles produced during molding, and a host of other factors may have contributed to the failure, and it is important to keep an open mind when carrying out tests of this type. The absolute accuracy of the test may not be important, but it is essential that it be capable of di.s-criminating between the good and the bad product. 

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