In-situ impact analysis during fatigue tests of open-hole carbon fibre reinforced polymer specimens

Dimitrios Zarouchas,Casper Van Dien,Nick Eleftheroglou

doi:10.1016/j.jcomc.2021.100199

Dimitrios Zarouchas, Casper Van Dien + Show 1 more

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https://doi.org/10.1016/j.jcomc.2021.100199

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Abstract

This paper presents the results for an experimental campaign of in-situ impact during tension-tension fatigue loading for open-hole carbon fibre reinforced polymer specimens. High-speed low energy impact was introduced to the specimen with the use of a canon, which was attached to testing bench enabling the impact without the need to remove the specimens from the test bench. Digital Image Correlation, C-scan and Acoustic Emission were utilized to record health monitoring data for damage diagnostics. A strain-based criterion was used to identify a common threshold for the timing of impact ensuring a fair comparison between the different tests. The results indicate that while an impact causes the total amount of damage to increase as one would expect, it does not necessarily increase the damage level in the critical area where final fracture occurs. A dependence on the moment of impact with the fatigue failure was found for specimens subjected to impact before the initiation of the fatigue loading. In contrast, impacting specimens in the presence of fatigue damage had no detrimental effect on the fatigue life, although it was observed that the damaged area was enlarged. Overall, the paper showcases the need to study systemically the effect of in-situ impact on the fatigue life in order to understand better the implications that may be introduced to the integrity of a composite structure.

Highlights

Composite structures are increasingly used in commercial aviation replacing the traditional aerospace aluminium alloys, with some of the newest generations of passenger aircraft having over half of their structural weight made from composites
This paper presents the results for an experimental campaign of in-situ impact during tension-tension fatigue loading for open-hole carbon fibre reinforced polymer specimens
The purpose of this paper was to investigate experimentally the ef fects of the timing of impact on the fatigue life and damage accumula tion process for open-hole carbon fibre reinforced specimens subjected to tension-tension fatigue loading

Summary

Introduction

Composite structures are increasingly used in commercial aviation replacing the traditional aerospace aluminium alloys, with some of the newest generations of passenger aircraft having over half of their structural weight made from composites Due to their distinct nature, a different design and damage tolerance philosophy has to be taken into account as their anisotropic behaviour and variety of failure mecha nisms foster complex damage patterns and stochastic damage degrada tion processes [1,2]. The idea of the multi-state process goes back to the ‘80 s, where Reifsneider et al described the damage accumulation as a three-stage process [4] It was the first time proposed in literature that the prediction of strength and life of a composite structure should be based on the damage accumu lation process. A common understanding has been established regarding the three states of damage development during fatigue of unidirectional, cross-ply and angle-ply composites [11,12,13];

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