Effect of Interface Layers on Delamination Growth in Hybrid Plain Woven Composite Laminates Under Quasi Static and Fatigue Mode-I Loading and their Modal Characteristics

Abstract

Effect of similar and dissimilar interface layers on delamination in hybrid plain woven glass/carbon epoxy composite laminates double cantilever beam for quasi- static and fatigue under Mode-I loading has been investigated experimentally and analytically. Further, the modal characteristics of the hybrid laminates has been investigated for the tensile specimens. Glass-glass, glass-carbon interface layers in three different configurations of hybrid plain woven glass/carbon epoxy laminated composites were fabricated. Mode partition method is utilised to compute individual modal contributions and total fracture toughness of the hybrid composite laminates. Mode-I fracture toughness contribution is compared with standard data reduction schemes of ASTM D5528-13. The comparison reveals that mode partition method considers mode-mixity and provides conservative results. The mode partition method does not require any correction factors including curve fitting, it provides a straightforward method for evaluating fracture toughness as they are based on the mechanics of composite materials. The comparison of R- curves of hybrid configurations reveal that the insertion of carbon with glass at the interface of symmetric hybrid configuration enhances initial fracture toughness and stabilises whereas, with the change in layer configuration of anyone arm of the double-cantilever beam, the crack growth trend is also affected irrespective of same interface layers. The fractography analysis of delamination surfaces reveals that crack propagation through a resin-rich layer creates a rougher fracture surface resulting in higher energy dissipation as compared to crack propagation through resin-rich pockets. Fracture toughness evaluation of glass/carbon hybrid composites with different symmetry and asymmetry beam configurations with the same and different material interfaces subjected to pure Mode-I loading is investigated experimentally. Data reduction schemes suggested in ASTM D5528-13are utilised to estimate strain energy release rate, 𝐺𝐺𝐼𝐼 of all the hybrid configurations. Further, mode partition method is developed for estimating the effect of symmetry and asymmetry on hybrid configurations. Fractography of fractured surfaces of all configurations is carried out to correlate the mechanism of crack propagation and factors affecting the fracture toughness of hybrid configurations. Further, the analytical method developed for fracture toughness evaluation under monotonic loading is extended for evaluating the delamination growth rate for any given stress ratio (load or displacement ratio) using data from a relatively small number of tests. First, quasi-static tests were carried out to obtain the fracture resistance. Then, constant amplitude fatigue tests were performed to determine the delamination growth rate considering normalisation of 𝐺𝐺𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 and Δ𝐺𝐺𝑒𝑒𝑒𝑒𝑒𝑒 with 𝐺𝐺𝐼𝐼𝐼𝐼(𝑎𝑎). The results obtained are compared with modified beam theory and mode partition (MPV) method. It is observed that the results plotted gives a conservative result in MPV method as compared to modified beam theory. Lastly, frequency response analysis carried out on tensile specimens of plane woven glass/carbon hybrid composites revealed that hybridisation affects modal frequency characteristics. First two natural frequencies of beam are increased by use of high stiffness fibre in the upper layer. The damping effect in beam with carbon fibre as middle layer is found to be higher as compared to dedicated plain woven glass composites.