Supported by British Aerospace Systems

crackgrowth3.1.gifAerospace structures are subject to stringent damage tolerance requirements, which require engineers to assess how cracks will develop and impact on the structural integrity of the aircraft. Current methodologies require engineers to make gross simplifications or extremely time consuming and complex models to assess the potential risks associated with the crack growth.

Main Objectives

The main objective of this project was to develop new technology, which radically simplified the modelling process while providing highly accurate results.

Results

  • This project used a combination of the boundary element method (BEM) and the J integral technique, which provides an efficient and versatile mechanism for the solution of complex three-dimensional crack problems, as well as the development of a multi-region boundary element formulation for setting up and solving the system matrix.
  • An out-of-core solver was developed that specifically optimises the structure of the BEM system matrix, which substantially reduced both disk space and computation cost compared with one region models.
  • The development of the mixed mode J integral technique was tackled by two methods: the decomposition and the displacement ratio methods. Both these methods start by splitting the J integral into two components: one comprised of symmetric elastic fields and the other comprised of anti-symmetric elastic fields.    
  • The J integral method has been tested on an inclined penny shaped crack in a large body under tensile loading. The decomposition and displacement ratio methods produced almost identical results of good accuracy, to within 2.5% for a coarse mesh.
  • This methodology has been applied to a straight shanked lug with various types of loading. The accuracy of the method was demonstrated for a straight crack in the lug and for a single elliptical crack in the lug. A full parametric study has been undertaken of the lug with two elliptical flaws and a comprehensive set of graphs was produced.

This project demonstrated the power and versatility of the 3D BEM formulation plus J integral technique to tackle complex 3D crack problems.

Project Partners 

  • Wessex Institute of Technology, UK
  • British Aerospace, UK