Investigation of Kink Bands Formation under Compression in Carbon Fibre Reinforced Composites

Tez Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: The University of Manchester, Faculty of Science and Engineering, School of Materials, İngiltere

Tez Danışmanı: Philip Withers

Tezin Onay Tarihi: 2018

Tezin Dili: İngilizce

Açık Arşiv Koleksiyonu: AVESİS Açık Erişim Koleksiyonu

Özet:

Carbon fibre reinforced polymers (CFRPs) have been prevalently used in aerospace and automotive applications owing to their improved mechanical properties in which lightness is considered more than expenditure. CFRPs have poor resistance to compressive stress which is usually 40% lower than their tensile stress, and various failure mechanisms such as fibre failure, delamination, and matrix splitting are developed in order to predict compressive strength of composite components. One of the most important failure mechanisms under longitudinal compression in unidirectional (UD) CFRPs is kinking failure which suddenly and catastrophically occurs in the composite structure between misaligned fibres. In this thesis, a novel visualisation technique has been utilised to investigate precursors to kink bands formation in CFRP coupons under compression incurred by four point bending (FPB) test by using in situ X-ray micro computed tomography (µ-CT) scanning technique. The analyses were performed by using the high resolution images captured during the PhD study entitled as “Damage Mechanisms Associated with Kink-Band Formation in Unidirectional Fibre Composites” written by Dr Ying Wang in 2015. It is observed that kink bands initiated on the compressive stress side near free notch surface and developed into the specimen with increasing fibre waviness and shear stress. This study confirmed that fibre microbuckling, fibre kinking, longitudinal splitting, and buckle delamination were the onset of kink band formation with the cooperative manner.

Kink band formation occurs when maximum bending curvature of fibre kinking reaches a critical radius value at the highest curvature owing to compression damage mechanism accompanied by shear.

Keywords: CFRP, kink band formation, fibre micro-buckling, splitting, image processing, in situ X-ray µ-CT