The influence of surface roughness parameter on the fatigue life is studied using rotory bending loading under room temperature and zero mean stress (R=-1).
Three levels of average surface roughness (Ra), namely smooth, medium and rough, are considered. For the above three levels, three equations which describe the S-N curve are established. The application of these equations to specimens tested under cumulative fatigue damage shows that the roughness parameter must not be ignored. Hence a new model considering this parameter is formulated which may take the form
From the applications of the proposed model, it is concluded that fatigue life predictions are in good agreement with the experimental results.