Influence of Gradual Damage on the Structural Dynamic Behaviour of Composite Rotors: Experimental Investigations.

Angelos Filippatos,Maik Gude

doi:10.3390/ma11122421

Abstract

Fibre-reinforced composite structures subjected to complex loads exhibit gradual damage behaviour with the degradation of the effective mechanical properties and changes in their structural dynamic behaviour. Damage manifests itself as a spatial increase in inter-fibre failure and delamination growth, resulting in local changes in stiffness. These changes affect not only the residual strength but, more importantly, the structural dynamic behaviour. In the case of composite rotors, this can lead to catastrophic failure if an eigenfrequency coincides with the rotational speed. The description and analysis of the gradual damage behaviour of composite rotors, therefore, provide the fundamentals for a better understanding of unpredicted structural phenomena. The gradual damage behaviour of the example composite rotors and the resulting damage-dependent dynamic behaviour were experimentally investigated under propagating damage caused by a combination of out-of-plane and in-plane loads. A novel observation is the finding that a monotonic increase in damage results in a non-monotonic frequency shift of a significant number of eigenfrequencies.

Highlights

Composite materials provide high strength and stiffness-to-weight ratios and adjustable directional material properties
The gradual damage strongly affects the structural vibration behaviour, which means that an altered dynamic behaviour of the composite structure can be treated as a symptom of a new damage state, which can be of major relevance to advanced damage identification methods, especially for vibration-based diagnostic approaches
The aim of this paper is to investigate the structural dynamic behaviour of composite rotors subjected to propagating damage from a combination of out-of-plane and in-plane loads

Summary

Introduction

Composite materials provide high strength and stiffness-to-weight ratios and adjustable directional material properties. Besides outstanding specific strength and stiffness properties, fibre-reinforced composites offer the significant advantage of cost-efficient manufacturing due to the feasibility of producing very complex, near-net-shaped fibre reinforcements for rotor components. Their adjustable gradual damage behaviour is advantageous—in contrast to the classical metallic materials—as it allows for the development of rotors which are characterised by a gradual damage behaviour. Due to this gradual damage behaviour, the remaining structural strength of composite rotors is generally not reduced critically, and a structural failure will often be prevented as long as the loads do not further increase. The gradual damage strongly affects the structural vibration behaviour, which means that an altered dynamic behaviour of the composite structure can be treated as a symptom of a new damage state, which can be of major relevance to advanced damage identification methods, especially for vibration-based diagnostic approaches

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