Mechanical Strength of Plastics

Many modifications of the elastomers above have been developed chiefly by copolymerization with various synthetic resins. These modified elastomers furnish the engineer with a wide selection of materials suitable for special uses. An example of a relatively new hydrocarbon rubber is a copolymer of ethylene and propylene, EPR. This rubber has outstanding resistance to ozone weathering. It has lower tear resistence and higher air permeability than Buna S (SBR), but can be lined with butyl to correct the latter property. 

The mechanical properties of materials are usually studied by means of tensile testing machines or dynamometers. The stress-strain curve obtained characterizes the plastic and determines its usefulness for specific applications. 

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