Beneficial Effects of Thermal Autofrettage-Induced Residual Stresses in Functionally Graded Plate with a Central Aperture

Functionally Graded (FG) plates with circular holes are extensively used in engineering applications due to their superior mechanical and thermal properties. The gradual variation of material composition across the length of plate provides enhanced resistance to thermal and mechanical loads, making them suitable for aerospace, biomedical, and nuclear applications. This study investigates the generation of beneficial compressive residual stresses around the hole in an FG plate due to thermal autofrettage, where material properties vary continuously in the axial direction from ceramic (left side of the plate) to metal (right side of the plate) based on a suitable power law model. The compressive residual thermal stress through thermal autofrettage is introduced around the hole in the FG plate by partially plasticizing the material around the hole creating a temperature gradient between the hole-edge and edges of the plate and later vanishing the gradient. A cold fluid may be flown through the hole while uniformly heating the plate edges to create the desired temperature gradient. The procedure is exemplified for a typical FG plate made with Al/SiC composite containing a central aperture. The results highlight the asymmetric stress distribution around the hole in the FG plate. It is found that by applying a temperature difference of 65 °C between the plate edges and the hole, and subsequently upon cooling to room temperature, the maximum residual stresses induced at the hole surface is -42 MPa on the left side and -63 MPa on the right side. These high magnitude of compressive residual stresses offset the peak tensile stress around the hole in the next phase of loadings such as in axial tension or pin loading. This amounts to reduction in net tensile stresses around the hole indicating the load carrying capacity of the structure.