Residual stresses in wires: Influence of wire length

Residual stresses are one of the causes of failures in structural components. These stresses may arise in the fabrication process from many causes. They cannot be easily accounted for because they are both difficult to predict and to measure. X-ray diffraction (XRD) is nowadays a widespread technique for measuring surface residual stresses in crystalline materials. Very small specimens are often used for this purpose due to geometrical restrictions of either the diffractometer sample holder or the component to be inspected. However, the cutting process itself may affect the residual stress state in these specimens, so measured stresses could be misleading. In this work, the influence of specimen length on residual stresses was investigated in cold-drawn ferritic and pearlitic steel wires by XRD measurements and finite element simulations. In the ferritic wires, numerical simulations coincide with experimentally measured stresses. However, in the pearlitic wires the effect of the stresses in cementite (which could not be measured by XRD) has to be taken into account to explain the observed behavior. T he results obtained have shown that in both materials the cutting process affects residual stresses, so it is recommended that specimens larger than five times the wire diameter be used.