in order to determine the fatigue limit of elastic materials , especially rubber , under completely reversed stress by applying a load which alternates between zero and a maximum value and in order to determine the number of load alternations which leads to the breaking of the material , a plurality of strip - shaped rubber samples are clamped between two stationary clamping beams and a rocker . the rocker is approximately parallel to the beams and is moved at one end thereof by means of a crank mechanism . the rubber samples are each positioned parallel to one another in at least one row and are alternately stretched and relaxed to a different extent , depending on their spacing from the fulcrum of the rocker .