Analysis of residual stress in threaded regions of SiC fiber-reinforced Ti₃Al composite

Continuous SiC fiber-reinforced Ti3Al（SiCf/Ti3Al） composite combines the advantages of high damage tolerance and ease of forming for Ti3Al matrix and high-strength for SiC fibers. It is an ideal candidate material for lightweight， high-strength， and high-temperature resistant fasteners in the aerospace field. However，complex residual stresses are inevitably introduced during the thread machining process of SiCf/Ti3Al composites. Therefore，analyzing the residual stresses in the threaded regions of SiCf/Ti3Al composites is of great significance for enhancing the service safety and reliability of fasteners. Given the complex geometric structures of the threaded regions in turned SiCf/Ti3Al composites and the close relationship between their stress distribution and core diameter， the characterization and analysis of stress are challenged by the intricate thread profile and limited dimensions. Residual stress measurements and analyses are conducted on the thread crest and radial cross-sections of the threads using side-inclined X-ray diffraction and nanoindentation method，respectively. The results show that the thread crest is in a state of compressive stress after turning. When the core diameter increases from 3.0 mm to 4.0 mm，the compressive stress increases from 387.6 MPa to 540.6 MPa. The radial cross-sections of the thread are also under compressive stress. As the core diameter increases from 3.0 mm to 4.0 mm，the compressive stress at the same location 100 μm from the thread crest increases from 326.9 MPa to 430.8 MPa. Furthermore， the compressive stress decreases with increasing distance from the thread crest.