Quantifying fibre reorientation during axial compression of a composite through time-lapse X-ray imaging and individual fibre tracking

Abstract

The sudden compressive failure of unidirectional (UD) fibre reinforced composites at loads well below their tensile strengths is a cause of practical concern. In this respect and more generally, analytical and numerical models that describe composite behaviour have been hard to verify due to a lack of experimental observation, particularly in 3D. The aim of this paper is to combine fast in-situ X-ray computed tomography (CT) with advanced image analysis to capture the changes in fibre orientation in 3D during uninterrupted progressive loading in compression of a UD glass fibre reinforced polymer (GFRP). By analysing and establishing correspondence between a sequence of time-lapse X-ray CT images of the composite, we are able for the first time to follow each fibre and quantify the progressive deflection that takes place during axial compression in the steps leading up to fibre micro-buckling and kinking. Even at just 25% of the failure load, fibres have started to tilt in approximately the direction of the ultimate kink band. The rate of tilting increases as the composite approaches the collapse load. More generally, our approach can be applied to investigate the behaviour of a wide range of fibrous materials under changing loading conditions.

Influence of in-plane shear on kink-plane orientation in a unidirectional fibre composite

“…The kink-plane angle has been characterised post-mortem and not in-situ. However, recent results from notched circular specimens show that the kink-plane orientation is very similar from initiation to final failure [4], supporting the validity of the post-mortem analysis performed here.…”

“…Geometric information of the kink-bands was obtained and information about the failure mechanisms within the kink-band was provided from tomographic reconstructions with high spatial resolution. CT monitored compressive tests have also been performed to study damage growth in-situ [3,4]. The progression of a kink-band can occur with very high speed and an attempt to capture this using ultra-fast time-laps CT with a synchrotron X-ray source was made by Ueda et al.…”

“…[3]. In a recent study by Emerson et al [4], kink-band formation and growth in notched CFRP specimens was studied in-situ using ultra-fast time-laps CT. Tracking of individual fibres enabled characterisation of fibre orientations with a very high level of accuracy.…”

In situ statistical measurement of local morphology in carbon-epoxy composites using synchrotron X-ray computed tomography

“…However, no results are presented on in situ following the damage accumulation. Emerson et al ([31]), have reached a fibre-by-fibre detection level, characterising orientation in glass and carbon fibre composites from relatively low contrast images, and presented quantitative results on the axial compression of composites in [32]. Where Emerson's algorithm comprises a training process to generate a dictionary that reduces the degree of false centre detection, in this study a simple Otsu's threshold ( [33]) has been shown to track fibres accurately.…”

Review of microwave techniques used in the manufacture and fault detection of aircraft composites

“…piezoelectric transducer-based (19,20) and angle beam transducer-based (21,22) ), air-coupled ultrasonics (23)(24)(25)(26)(27)(28)(29)(30) , thermography (31)(32)(33)(34)(35)(36) , optical fibre sensing (37)(38)(39)(40)(41)(42) , digital image correlation (DIC) (43)(44)(45)(46)(47)(48) , electromagnetic testing (49)(50)(51) (e.g. eddy current (52)(53)(54)(55)(56)(57)(58) ) and X-ray imaging (59,60) . In particular, acoustic emission sensors are used to detect bursts of acoustic waves from the fracture events (e.g.…”