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This paper concerns about a failure analysis of an electric all aluminum alloy conductor (AAAC) damaged and broken for fretting fatigue phenomena induced by aeolian vibrations. Life of electric conductors is often reduced by various degradation mechanisms such as repeated bending, fluctuating tension, distortion, fatigue, wear and corrosion phenomena. However the main limiting factor of the electrical conductors is related to aeolian vibrations in the high frequency range (between 5 to 50 Hz). Conductor oscillations may lead to fretting fatigue problems (otherwise called fretting wear) caused by wind excitation, mainly in the suspension clamp regions, spacers or other fittings. The induced aluminium wire fracture imply a drastic reduction in the transmission line service. Vibration dampers are considered the most effective method to extend service life of electric conductors, as they are the means to reduce fretting damage of aluminium wires. The aim of the present work is to investigate the failure of an AAAC conductor of a 400kV overhead transmission line (twin conductors) located in Touggourt Biskra (Algeria); the damaged and broken conductors were operated in-service only for six months without spacers or dampers. Three different types of conductors have been taken as experimental samples: the in-service broken conductor, another in-service damaged conductor and a new conductor from warehouse as terms of comparison. Samples have been analysed to identify the root cause of the failure and to verify the conformity of the conductor elements to the international standards. The investigation has outlined the morphology of the fretting damage: in all cases the fractured wires have shown typical static deformation marks and dynamic fretting wear tangential marks associated with intense presence of Al2O3 debris.

A mathematical model was developed to describe the mechanical and thermal behaviour of stainless steels during hot extrusion. The reference point for the study was the experimental data of the extrusion process performed on two stainless steels in order to take into account the most significant features of the process: temperature, velocities, extrusion ratio and the shape of the extrusion die. The developed simulation approach is based on the Navier-Stokes equations which were used to compute the speed field in the steel during its passage in the die; this formalism allows to reach the resolution of the structural problem from the data easily measured during the industrial practice, i.e. press velocity and velocity of the extruded material at the exit from the die. The behaviour of the steel can be calculated through its constitutive law at high temperature from the fields of velocity, strain rate, strain and stress. The structural model is coupled with a thermal one based on the Fourier equation which provides the thermal field that plays a fundamental role in the microstructural features of the final product. The validation of the computational approach has been realized by an analysis of the obtained velocity distribution in the material and by a comparison between the calculated temperature field, the metallographic structure and the measured micro-hardness values.