This work,evaluated the applicability of Goodman, Gerber and Sonderberg proposal for equivalente stresses in non-reversible and fully reversible loads were evaluated. Specimens of DIN 34CrNiMo6 structural steel were machined with geometries in accordance with the passage of ultrasonic waves through the samples. Subsequently, these specimens were subjected to two distinct loading series; one with non-zero mean stress (non-reversed stress) and another with equivalent stresses for mean stress equal to zero (completely reversed stress). The results indicated that Goodman s model has a higher applicability for Mega and Giga load cycles (10 raised to 6 - 10 raised to 9 cycles), followed by Soderberg s model and, finally, Gerber s.