A pair of opposing grips is separated to the maximum distance. One end of the test piece is mounted in the upper stationary clamp, and the other end of the test piece is secured in the lower movable clamp, ensuring that the groove on the outside of the test piece sits in the middle of two clamps. The specimen is placed at 90° to the clamps. Visual examinations at frequent intervals are needed after machine actuation until the first small sign of cracking is detected on the specimen. Measurements of the length of cut on the test piece before and during the test are necessary for the determination of crack growth.
The DeMattia flex machine features static clamps for fixing one end of each of the specimens in a fixed position, and the similar but moving clamps for holding the other end of each of the specimens. The stroke of each of movable clampss is 57 ± 0.5 mm. The maximum distance between each set of opposing grips is 75 ± 1 mm. The planes of the gripping surfaces of each opposing pair of grips remain parallel during the motion. The eccentric which actuates the to-and-fro movement is driven by a constant-speed motor to give as high as 5 Hz, to flex 6 test pieces at one determination.