Ref.: MmeCa03-006
Apresentador: Marcelino Pereira Nascimento
Autores (Instituição): Nascimento, M.P.(Universidade Estadual Paulista-Faculdade de Engenharia de Guaratinguetá);
Resumo:
Failures in aircraft are usually attributed to fatigue of materials, project errors or aerodynamic overload. Since 1950's, fatigue is the most important project and operational considerations for both civil and military aircrafts. For some aircraft models (e.g. agricultural, military training and acrobatic) one the most solicited component is one that supports the motor, called “Engine Mounts”. This component has a complex geometry made of AISI 4130 tubular steel from different dimensions and TIG welded in several angles. In the Brazilian aircrafts T-25 Universal and T-27 Tucano, besides supporting the motor in balance, they also maintain fixed the nose landing gear in another extremity. Considered critical to the flight safety the aeronautic standards are extremely rigid in their production, by imposing a "zero index of defects" on the final weld metal quality (Safe Life), 100% inspected by Non-Destructive Testing/NDT. As a consequence aeronautic welded structures are frequently submitted to successive repairs in attendance to the current standards. After that, welded components approved by NDT may be containing an historical of welding repairs whose effects on their structural integrity are not computed. In addition, these structures are also submitted to weld repairs along their useful life, turning this question more complex. As a first approach, this study had as objective to evaluate the effects of successive welding repairs (4x), on the axial fatigue strength of AISI 4130 steel plate, 0,89mm thick. After TIG welding and re-welding processes, samples were prepared in accordance with ASTM E 466 standard and fatigue tested in the room temperature, on constant amplitude and sinusoidal loading, 20Hz frequency and load ratio R=0,1. The results obtained were associated to the weld bead geometry (notch sensitivity) resultant of successive repairs, as well as to the microstructural and microhardness variations along of the weld metal and heat-affected zone (HAZ). Key-conclusion is that all the welding repairs were detrimental to fatigue strength and that the first and third weld repairs were more detrimental to the fatigue behavior of AISI 4130 steel than the second and fourth repairs.