ON SPECIMEN GEOMETRY-EFFECTS IN STRAIN-CONTROLLED LOW-CYCLE FATIGUE

Strain-controlled low-cycle fatigue tests have been conducted in air a t room temperature on three different specimen geometries: (1) an hour glass specimen with a minimum diameter of 10 mm; (2) a cylindrical spe cimen with a gauge length of 50 mm and a gauge diameter of 10 mm; and (3) a cylindrical specimen with a gauge length of 25 mm and a gauge di ameter of 10 mm. The effect of specimen geometry on the cyclic stress response and fatigue life is discussed. At all the strain ranges teste d the hourglass specimens showed the highest life. The 50 mm gauge-len gth specimen showed the least life, while the 25 mm gauge-length speci mens exhibited an intermediate life. The constants and coefficients in the Coffin-Manson, Basquin and cyclic stress-strain relationships are evaluated for the three geometries. The existing models for the predi ction of the fatigue ductility exponent are also applied.