Events

Dr. Stergios Goutianos 'Designing against failure in wind turbine blades made of composite materials'

Date:	Wednesday 26 October 2011 11:00 - 12:00
Location:	SEMS Seminar Room (3rd Floor Engineering)

Dr. Stergios Goutianos from the Materials Research Division, Risø DTU, Denmark & High Performance Materials, Saint-Gobain, USA

Abstract:
Large off-shore wind turbines are projected to be used for a long time and due to their size, are costly to manufacture. Thus, it is important that the wind turbines are well designed and their behaviour is well understood so that they can be properly repaired if damage should develop.

The largest rotating components of a wind turbine are the blades. They are large structures, manufactured from strong, fatigue resistant composite materials and low-weight core materials, bonded together by polymer adhesives. The blades can develop different types of damage (usually at different length scales) such as delamination and adhesive joint failure. Such damage can result from processing-induced flaws. In order to avoid development of significant damage, the damage evolution in each material and in the interfaces between them, must be properly characterised in terms of mechanical properties, which then are used in reliable (numerical) models. Such models/tools can be used to determine the maximum allowable defect and damage sizes and thus provide criteria for quality control for new-manufactured blades. Furthermore, they can be used to evaluate the effect of damage found in a blade in service, on the residual life of the blade.

The tools presented here are based on fracture mechanics (the mechanics discipline of predicting the strength behaviour of components accounting for cracks). The fracture mechanics approach differentiates between various failure modes and requires the measurements of the fracture parameters of materials and interfaces. Potentially, the approach should also consider the interaction between different damage/fracture modes. Such a complete tool does not exist today for composite materials. The use of fracture mechanics induces a paradigm shift in the approach to strength prediction contrary to the commonly used probabilistic design approaches.

The long term aim is to develop reliable simulation tools that allow quantitative predictions of the strength and fatigue lifetime of wind turbine blade with damages, based on knowledge of the damage/crack types, size and location in the wind turbine blade as well as the appropriate fracture mechanics properties. The presentation will concentrate on:

1) The development of new fracture mechanics characterisation methods to measure fracture mechanics parameters.
2) The development of new modelling tools for predicting the load-carrying capabilities of structures.
3) The experimental verification of the characterisation methods and modelling tools.

The developed experimental and numerical methods are general methods that can be applied in a great variety of problems, ranging from micromechanics models of materials to structural parts i.e. aerospace components.