Compression fatigue testing

Fig. 8. Stress-strain hysteresis as a function of the number of number, measured in a tensile/compression fatigue test at 150 Hz and 0.13 % strain (SiC/SiC)...

COMPRESSIVE FATIGUE TESTS ON A UNIDIRECTIONAL GLASS/POLYESTER COMPOSITE AT CRYOGENIC TEMPERATURES... 

Compressive Fatigue Tests on a Unidirectional Glass/Polyester Composite at Cryogenic Temperatures... 

Coupons through compression and tension/compression fatigue testing. Spars by fatigue testing in flapwise mode. 

The Goodrich Flexometer is used for heat buildup testing (ASTM D-623). A cylindrical test specimen is alternately compressed and then released in rapid cycles for a specified period of time. The temperature rise within the test specimen is recorded. Additional data obtained are permanent set and static compression. The Goodrich Flexometer Test is sometimes called the Compression Fatigue Test, because the test specimen is fatigued, or weakened, by the rapidly cycling compression stress. 

Machine components ate commonly subjected to loads, and hence stresses, which vary over time. The response of materials to such loading is usually examined by a fatigue test. The cylinder, loaded elastically to a level below that for plastic deformation, is rotated. Thus the axial stress at all locations on the surface alternates between a maximum tensile value and a maximum compressive value. The cylinder is rotated until fracture occurs, or until a large number of cycles is attained, eg, lO. The test is then repeated at a different maximum stress level. The results ate presented as a plot of maximum stress, C, versus number of cycles to fracture. For many steels, there is a maximum stress level below which fracture does not occur called the... 

Several criticisms of these parameters have recently been pointed out. First, they have no specific association with a material plane (i.e., they are scalar parameters), despite the fact that cracks are known to nucleate on specific material planes. With traditional parameters it is difficult to account for the effects of crack closure under compressive loading. Traditional parameters have not been successful at unifying experimental results for simple tension and equibiaxial tension fatigue tests. Finally, a nonproportional loading history can always be constmcted for a given scalar equivalence parameter that holds constant the value of the scalar parameter, but which results in cyclic loading of material planes. For such histories, scalar parameters incorrectly predict infinite fatigue life. 

Potanova, M.A., Poc, C.C., Whitecomb, J.D. (1992). Open hole and post-impact compressive fatigue of stitched and unstitched carbon fiber-epoxy matrix composites. In Composite Materials Testing and Design (lOlh Volume), ASTM STP-1120 (G.C. Grimes ed.), ASTM, Philadelphia, PA, pp. 37-53. 

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