Fatigue Life Prediction for Specimens with an Open Hole with a Pre-Compressed Boundary Via the Nominal Stresses Under Regular Cyclic Loading

Abstract

The method of predicting the fatigue life of structural elements containing open holes with a preliminary compressed material in the hole vicinity under cyclic loading is proposed. The method is based on the commonly accepted approach of the life prediction via nominal stresses. The presence of residual stresses caused by plastic deformation of the material in the hole zone is taken into account by adjusting the cyclic load ratio in calculations. The concept of “fictitious compression stresses” is introduced for this purpose; its value is determined by solving the contact problem in an elastoplastic formulation in a finite element package. A functional relation between the value of residual stresses and the fatigue life of specimens with pre-compressed hole surface is established. The calculation results via the proposed method are compared with fatigue test results for specimens with pre-compressed hole surface. Satisfactory correlation between calculated and experimental data is obtained. The advantage of the proposed method is the reduction of required input data to construction of the fatigue curve for standard specimens with a stress-free hole. Considering that for the same alloy with identical heat treatment such curves may differ for different material batches, testing of standard specimens under regular loading is mandatory. Despite a usual scatter in fatigue life experimental values, the proposed method allows one to obtain a reliable and conservative assessment of the effect of hole boundary zone pre-compression on the fatigue life at the design stage.