Análise do estado plano de tensões em chapas de aço ASTM A131 por métodos ultrassônicos

Abstract

Residual stresses affect the mechanical component in the same way that external stresses do. These stresses usually arise in the manufacturing process. By knowing the residual stresses, mainly the tensile stresses, present in a component or those that may be generated by some manufacturing process, it is possible to take actions to avoid or minimize their effects, thus extending the component's useful life. Thus, residual stress will always be a demand to be studied, both by academia and by the metal-mechanic industry. Therefore, the objective of this work was to determine the plane state of residual stresses in ASTM A131 steel plates by combined shear and compressive ultrasonic wave methods. A TIG welding torch was used to induce residual stresses in the plates by the high thermal gradient. The specimens were xed by supports to avoid deformation, thus preserving the residual stresses. Three different methods were applied, named, in this paper, as: Hirao I; Clark; and Hirao II. The major difference between them is related to the preferred direction of wave propagation. Stresses in different directions from the anisotropy axis can change this direction. Consequently, the angle between the anisotropy and the preferential direction of propagation of the ultrasonic wave (φ) is changed. To measure the propagation time of the ultrasonic waves, a software was developed for the acquisition of the ultrasonic response signals and another one for the data processing.To end the preferential angle of wave propagation, a support was made by 3D printing, which allowed the transducer to be moved using a stepper motor. In all three methods, very high tensile stresses were observed near the melt zone, which decreased rapidly as the distance from this region increased. In addition, the values of φ were lower in the center line than in the lateral lines, indicating variation in residual stress levels as function of distance from the constraints.