A 3D-XIGA rotating cracked model for vibration analysis of blades

Abstract

Cracking of blades is one of the common failures in rotating machinery. Traditionally, the finite element method (FEM) is a typical tool to simulate the crack effects, which needs refined mesh processing and then limits computational efficiency. A three-dimensional (3D) rotating cracked model relying on the extended isogeometric analysis (XIGA) is developed for the vibration analysis of blades with inclined single and multiple cracks in this study. In the XIGA method, the representation of cracks can be well expressed by using enriched elements which allow modeling stress singularity ahead of the crack tip and discontinuity of the crack face precisely. The level set method (LSM) is used to identify the element type, so the number of elements is independent of the crack parameters. Considering penetrating cracks in the thickness direction, the 3D level set problem can be reduced to a 2D one. The stress and vibration displacement fields are exactly described by 3D elasticity theory combined with a two-stage solving progress. Numerical data of the established rotating cracked model with single or multiple cracks are obtained and compared with the existing results. The frequency steering and crossover phenomena due to the dimensional and locational parameters of the cracks are discussed in detail, which is crucial to accurately identify cracks. The influence of rotating speed and parameters of single and multiple cracks on the vibrational characteristics are also considered, which shows that cracks make the centrifugal stress field and frequency parameters more complex.