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Mohan, Joseph
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Mohan, Joseph
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Mohan, Joseph
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- PublicationInfluence of an Atmospheric Pressure Plasma Surface Treatment on the Interfacial Fracture Toughness on Bonded Composite JointsThe aim of this work is to investigate the influence of a variety of plasma treatments on the surface properties of an epoxy-based composite material and to establish a relationship between these properties and the subsequent mechanical behaviour of adhesively bonded joints. To this end, specimens were subjected to three different types of plasma treatment: two short treatments (2min) of Helium and Helium plus Oxygen, and one long treatment (15min) of Helium plus Oxygen. The variation in surface energy of the composite specimens was examined in each case over a period of up to 3 days using contact angle measurements. Initial results show that the surface energy was increased from an untreated value of approximately 40 mJ/m2 to a value of 65 mJ/m2 immediately after treatment. The surface energy then fell by approximately 10 mJ/m2 over the course of three days for each treatment. The composite substrates were then bonded together using an epoxy film adhesive and the Mode I fracture toughness of the joint was determined from a series of symmetric and asymmetric double cantilever beam (DCB) tests. It was found that for both test geometries the adhesive failed cohesively. As a result, the values calculated for the mean propagation strain energy release rate, GIC, were those of the cohesive fracture toughness of the adhesive as opposed to the interfacial fracture toughness between the composite surface and adhesive.
243 - PublicationThe Influence of Plasma Surface Treatment on the Fracture Toughness Peel Ply Prepared Bonded Composite JointsThe increasing use of composite materials in various industries, such as aerospace, automotive and renewable energy generation, has driven a need for a greater understanding of the fracture behaviour of bonded composite joints. An important prerequisite for the adhesive bonding of composites is the existence of a uniform surface free from contaminants and mould release agents. While there are several ways in which this may be achieved, the use of peel plies has emerged as the preferred choice for many industries due to the repeatable nature of the resulting surface, particularly in the highly regulated aerospace industry. The use of peel plies can present some problems. It is possible that contamination from the peel ply can be transferred to the composite substrate and adversely affect the adhesive joint [1]. Plasma treatments have been shown to improve the fracture toughness of adhesively bonded composite joints [2] and can be used to remove contaminants, such as mould release agents, from the surface [3]. The aim of this work is to evaluate the influence of various peel ply treatments on the mode I fracture toughness of different aerospace grade bonded composite joints and to assess the subsequent benefits of employing an atmospheric pressure plasma (APP) surface treatment prior to adhesive bonding in each case.
248 - PublicationAn Experimental and Numerical Investigation of the Mixed-mode Fracture Toughness and Lap Shear Strength of Aerospace Grade Composite JointsThe increasing use of composite materials in various industries, such as aerospace, automotive and renewable energy generation, has driven a need for a greater understanding of the fracture behaviour of bonded composite joints. An important prerequisite for the adhesive bonding of composites is the existence of a uniform surface free from contaminants and mould release agents. While there are several ways in which this may be achieved, the use of peel plies has emerged as the preferred choice for many industries due to the repeatable nature of the resulting surface, particularly in the highly regulated aerospace industry. However, the use of peel plies can present some problems. It is possible that contamination from the peel ply can be transferred to the composite substrate and adversely affects the adhesive joint [1]. Composite joints are typically evaluated using lap shear type tests. While these tests are relatively simple to perform and post-process compared to their fracture mechanics based counterparts, the results can often be misleading and are greatly dependent on the overlap length, the thickness of the substrate and the type of fillet employed [2, 3]. The aim of this work is to show that composite joint systems can be modelled using material properties determined from fracture mechanics based tests. The fracture parameters will be used to develop numerical models of the fracture tests that accurately predict the wide-area lapshear test.
661 - PublicationEnhanced Carbon/Epoxy Composite Fracture Toughness Achieved Using Atmospheric Pressure Plasma TreatmentsComposite materials are used in a wide range of industry sectors including automobiles, aeronautics and sports equipment. Two types of composite joints, co-cured and secondary bonded joints are used in the industries. Co-curing of composite joints is an efficient and cost-effective method of joining composites. The objective of this research is to enhance the bond strength between the composite material and adhesive, specifically in this study the bond between carbon-epoxy prepregs and an epoxy adhesive. The research investigated how the use of atmospheric plasma treatments of the uncured composite prepreg influenced the fracture toughness of the co-cured composite joints. The use of atmospheric pressure plasma treatment in the surface activation of prepregs was examined using contact angle measurements and X-ray photoelectron microscopy (XPS). Failure mechanism of the co-cured composite joints was studied by double cantilever beam (DCB) tests. Composite interface morphology was examined by scanning electron microscopy (SEM/FIB).
201 - PublicationEffect of an Atmospheric Pressure Plasma Treatment on the Mode I Fracture Toughness of a Co-cured Composite Joint(Informa UK (Taylor & Francis), 2014-04-21)
; ; ; In this study, the surface of a composite prepreg was treated using an atmospheric pressure plasma in an attempt to improve the fracture toughness of a co-cured joint system. Three gas mixtures were investigated; Helium, Helium/Nitrogen and Helium/Oxygen. The processing parameters of the system were varied to obtain the maximum increase in surface energy of the prepreg. A He/O2 plasma was found to be the most efficient treatment, giving the largest increase in surface energy in the shortest time. Co-cured joints were then fabricated using prepreg that had been treated with various plasmas. A modest 15–18% increase in the mode I fracture toughness was achieved. However, the locus of failure remained interfacial. It was also observed that a He/O2 plasma treatment could be detrimental to joint toughness for long treatment times.861Scopus© Citations 19