Fretting fatigue analysis of aluminium conductor wires near the suspension clamp: Metallurgical and fracture mechanics analysis

Abstract

Fretting fatigue is the main phenomenon inducing reduction of fatigue strength in overhead transmission conductor lines which are subjected to aeolian vibrations. Using the Bersfort ACSR 48/7 conductor, fatigue tests were conducted under several traction forces and relative vibration amplitudes. By metallographic examinations it has been observed that fretting induces microcracks which are mainly located between the keeper edge (KE) and the last point of the contact (LPC) of the conductor at the mouth of the suspension clamp. Under the fatigue tests conditions, several cross-sections of wires in the external layer of the conductor were instrumented using strain gauges. Wire strains recorded near to the suspension clamp show that the alternating strains were predominantly traction strains near the KE and that bending alternating strains become significant near the LPC. On the basis of fatigue tests results and assuming some simplified hypothesis, stress intensity factors were computed at the tip of cracks. The computed stress intensity factors take into account the combined effect of fretting behaviour at the contact points and both traction and bending stresses. The computed stress intensity factor ranges for low fatigue bending vibration amplitudes show good agreement with the endurance limit of the conductor.