Firestone flexometer

The Firestone flexometer method in D623 is not very specific. The standard test pieces are in the shape of a frustum of a rectangular pyramid but the use of any suitable shape is permitted when cut from products. The apparatus operates at 800 cycles/min and a range of compression loads and amplitudes of oscillation are possible, but no particular conditions are specified. The test piece is fatigued until a definite, but unspecified, decrease in the height of the test piece is reached, which is supposed to represent the onset of internal porosity. Parameters such as temperature rise and changes in compression are reported. 

The principles of flexometer testing are described in ISO 4661/1 (BS903, Part A49). The best known test machine is the Goodrich compression flexometer described in ISO 4661-2. (BS903 A40 and ASTM D623). An alternative is the rotary flexometer of ISO 4661 2 a specific example, the Firestone flexometer, is specified in ASTM D623. 

The ISO rotary flexometer and the Firestone both operate by superimposing a cyclic shear deformation onto a static compressive deformation but the cyclic action of the two machines is not the same. The ISO apparatus is derived from the St Joe flexometer, which at one time was included in the ASTM standard (up to 1962). 

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