Coupled approach to modelling damage in bonded composite structures

Abstract

A fully coupled global-local approach for structural analysis has been developed. It is motivated by the need to use a range of scales and modelling techniques when designing a structure in composite materials. These range from the microscale at which the interfaces between fibres and matrix, or buckling of fibres themselves may play a role in the material behaviour, through intermediate scales where delamination and debonding may have an influence up to the macroscale where entire structures may be modelled with service loads directly applied. The method is based on passing boundary conditions from larger to smaller length scale models while passing information about damage and stiffness degradation up through the scales. By using nested levels of submodel, a greater range of length scales may be included in a single set of coupled analyses.

Here an explanation of the methods of coupling two scales of solid models as well as coarse shell models to relatively refined solid models is presented. Each of these methods is validated against equivalent models using established modelling techniques, and are shown to produce results comparable to a complete model at the refined scale and preferable to other global-local approaches. Experimental tests have also been carried out on a stiffened panel with two stiffener runouts undergoing debonding. Not only did the coupling method model these tests accurately, but it was also shown to be more appropriate than simple submodelling in this case.

A further demonstration of the techniques is included. The largest scale consisting of a shell element mesh is coupled with an intermediate scale with a continuum shell mesh, which in turn is coupled to a refined scale solid model. This demonstration shows how the methods developed here could be used to unify various analyses in the composites design process which until now have remained separate.