Scott flexer

ASTM D4304 specifies three machines for flex-cracking. The Scott Flexer is included specifically to test for ply separation of composites such as belting or tyres and is not used for rubber alone. It is a somewhat bulky apparatus in which the test pieces are reciprocated over a rotatable hub whilst held in tension. The arc of contact is about 165° but was at one time was erroneously given as 135°, resulting in at least one out of spec machine... 

A dynamic ply separation test is really a fatigue test on the rubber fabric composite to weaken the bond or to determine the number of cycles until the bond fails. In principle any flexing test (see Chapter 15) could be used, but there has been little standardization for this particular product type. A notable exception is the Scott flexer detailed in ASTM D430 [33], which is specifically intended for testing ply separation of belts and tires, etc. The relative bond strengths of different rubber/textile systems may be different in dynamic and static tests, and hence it would seem important to assess any composite that will be subjected to fatigue in service by a dynamic method. 

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