Banca de DEFESA: Ian de Medeiros Matos

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Ian de Medeiros Matos
DATE: 29/02/2024
TIME: 08:30
LOCAL: Microsoft TEAMS
TITLE:

Fatigue life prediction of overhead conductors and their wires: Experimental and numerical investigations

KEY WORDS:

overhead conductor; aluminum alloy wire; fretting fatigue; life prediction

PAGES: 120
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

Overhead conductors are the mechanical components used in transmission lines to transport electricity over long distances. In-service conductors are susceptible to several types of oscillatory motions, including wind-induced vibrations. One of the most common types of wind-induced cyclic motion is the aeolian vibration, which is caused by the vortex shedding that occurs when wind flows by the conductor. It has been widely known that the aeolian vibrations can be critical to the safe operation of transmission lines, as they can lead to fretting fatigue. Fretting occurs at the contact surfaces of the conductor’s wires and is usually critical near or within clamp devices. Cracks usually initiate and propagate from the fretting marks and can eventually lead to wire rupture. The fatigue behavior of conductors is a complex problem, involving several contact regions, localized plasticity, wear, and friction. These complexities have led utilities to traditionally rely on fatigue test data obtained from resonant test benches for the safe design and operation of transmission lines. However, the recent advances in finite element (FE) 3D modeling of conductor-clamp systems have motivated researchers to pursue FE-based approaches for the fatigue damage analysis of the conductor. These approaches are based on a combination of a global-scale analysis of the conductor-clamp system with a local-scale analysis of the wires under fretting fatigue. Compared to the traditional approach based on stress-life curves, these global-local approaches require simpler and less expensive laboratory infrastructure, and can be used to optimize the design of the conductor-clamp system. Since the last decade, significant progress has been made regarding the fatigue damage analyses of conductors and their wires, aimed at the development of the aforementioned global-local approaches for fatigue life prediction. However, additional research is still required to better evaluate the applicability of these approaches to different conductor geometries, wire materials, and loading conditions. In this regard, this thesis aims to investigate methodologies for life prediction of overhead conductors and their wires by means of experimental and numerical analyses. This thesis is organized as a collection of three research papers by the author and collaborators, which have already been published or are under the process of submission/review. In the first paper, fretting fatigue tests under constant amplitude loading (CAL) were performed using 1120 aluminum alloy (AA) wires of an AAAC (All Aluminum Alloy Conductor) 823 MCM conductor. A tension test and axial fatigue tests on smooth and V-notched wire specimens were also carried out. The fatigue test data were used to compare the AA1120 with the AA1350 and AA6201, two alloys typically used to manufacture the wires of conductors. Under tension, the AA1120 displayed an intermediate ultimate tensile strength between the ones from the AA1350 and the AA6201. For the same stress amplitudes, the AA1120 wires used in the axial fatigue tests had longer lives than the AA1350 wires but considerably shorter lives than the AA6201 wires. However, under fretting fatigue, both AA1120 and AA6201 wires had similar fatigue strength. The test data were also used to evaluate a life prediction criterion for wires under fretting fatigue based on the Theory of Critical Distances (TCD). Most of the predicted lives were within a factor of 3 of the measured lives. The accuracy of the predictions was similar to that observed in previous studies, in which the same methodology was applied to data from fretting fatigue tests on AA1350 and AA6201 wires. These results show that the methodology can be a reliable tool for the fatigue damage analysis of wires made of different materials subjected to fretting fatigue and CAL. In the second paper, fretting fatigue tests under variable amplitude loading (VAL) were carried out on AA6201-T81 wires of an AAAC 900 MCM conductor. The amplitude variation was represented by a three-block loading history. The loading conditions were defined using vibration measurements from an operating transmission line located in the center-west region of Brazil. Two methodologies for life prediction of wires were extended to VAL conditions and were evaluated using the fretting fatigue test data. One of the methodologies is the same TCD-based criterion considered in the first paper, while the other is based on a master fatigue curve. Both methodologies provided life predictions within factors of 4 of the measured lives. The accuracy achieved in this study supports the use of the proposed methodologies for predicting the lives of wires under VAL conditions. The third paper is concerned with the life prediction of an ACSR (Aluminum Conductor Steel Reinforced) Ibis 397.5 MCM conductor under high-low and low-high loading sequences. To this end, a life prediction methodology based on finite element 3D modeling of conductor–clamp systems was extended to include VAL conditions. Firstly, the methodology was applied to CAL fatigue test data to assess whether it can accurately describe the fatigue failure of the ACSR Ibis conductor. Subsequently, the methodology was evaluated using the data from fatigue tests conducted under a two-block loading history. Most life predictions were within factors of 3 of the measured lives. For the VAL tests, the methodology accurately took into account the effect of loading sequence on fatigue failure, providing longer life estimates for the tests under high-low sequence than for those under low-high sequence. Additionally, the methodology was capable of predicting the positions of the wire breaks for the VAL tests in accordance with the experimental observations. These results suggest that the methodology can be extended to VAL conditions and be used to accurately predict the lives, the loading sequence effects, and the fatigue critical regions of conductors.

COMMITTEE MEMBERS:
Presidente - 1646090 - FABIO COMES DE CASTRO
Interno - 1249764 - JORGE LUIZ DE ALMEIDA FERREIRA
Interno - 1345908 - JOSE ALEXANDER ARAUJO
Externo à Instituição - ANDRÉ LUIS PINTO - IFB
Externo à Instituição - RAIMUNDO CARLOS SILVÉRIO FREIRE JÚNIOR - UFRN