Evaluation of Tensile and Fatigue Properties of Metals Using Small Specimens

Small specimens are increasingly being used in getting mechanical properties directly when there are limited materials to facilitate standard specimens, which play a great role in the rapid measurement of mechanical properties and residual life assessment of in-service reactor components. Although tensile and fatigue properties of the small specimens are investigated extensively, theoretical models for describing the mechanical properties of small specimens need to be established. Here, we conduct a systematic investigation of tensile and fatigue properties of pure Cu specimens with thicknesses ranging from 3 to 0.2 mm. The results show that the decrease in uniform elongation of the 0.2 mm-thick specimens is mainly due to the effects of grain boundary and free surface on the strain hardening rate. A modified theoretical model correlated with the ratio of the surface grain layer thickness to the grain size is proposed to predict variation in yield strength of the small specimens more accurately. Furthermore, the mechanism for the difference in fatigue life between the 0.2 mm-thick specimen and other thicker specimens is elucidated. The Basquin equation-based model is presented as a potential way to evaluate the fatigue life of metals using small specimens.