DEVELOPMENT OF A PRACTICAL LABORATORY PROCEDURE TO BE USED IN EVALUATING THE FORMING QUALITIES OF PLASTIC SHEET MATERIALS
Final rept. Jan 1952-Jan 1953 on Transparent Materials
IIT RESEARCH INST CHICAGO IL
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Special tests duplicating manufacturing operations were adequate for evaluating the modulus of workability of plastic sheet. The unconfined bubble test was the only satisfactory measure of the deformative maximum. The test consisted of forming, by positive air pressure, an unconfined bubble of plastic heated to optimum forming temperature. The rating was based on the pressure required to form the bubble and the extent of formation before fracture. Standard engineering tests, such as those measuring maximum elongation, creep, and ball penetration, failed to evaluate formability satisfactorily.