The ability of rubber products to withstand repeated flexing without developing cracks is of prime importance where such products are used in conditions undergoing repeated flexing.
Flexing endurance of rubber products is determined by simulating in the laboratory the action of flexing repeatedly under standard conditions of speed, mode, and degree of flexing.
One of the accepted procedures for determination of flexing resistance makes use of a De Mattia flexing tester. This tester provides useful information about the resistance of compounds of vulcanized rubber to flex cracking when subjected to flexing. Cracks develop in that part of the surface where stresses are set up during flexing, or if that part of the surface initially contains a crack, cause this crack to extend in a direction perpendicular to the stress.