Now showing 1 - 4 of 4
  • Publication
    Effect 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.
    Scopus© Citations 19  855
  • Publication
    Mode I fracture toughness of co-cured and secondary bonded composite joints
    The mode I fracture toughness of a single co-cured and two secondary bonded joint systems were determined using the double cantilever beam test. The initiation values of fracture toughness from the PTFE film insert and a mode I crack-tip were considered as well as propagation values. It was found that the starting defect had a large influence on the initiation values for fracture toughness. It was also found that the two secondary bonded systems predominantly resulted in cohesive failure while the co-cured joiailed interfacially. Thermogravimetric analysis coupled with mass-spectrometry was used to show how moisture in the composite prepreg and adhesive affected the toughness of the joints. Microscopy methods were used to gain further insight into the damage mechanisms of the three joint systems.
      586Scopus© Citations 30
  • Publication
    Effect of prepreg storage humidity on the mixed-mode fracture toughness of a co-cured composite joint
    The present work investigated the effect of the level of prepreg moisture content on the mixed-mode fracture toughness of a co-cured composite joint. It was found that moisture was stored in the prepreg as either free or bound water. It was also shown that the prepreg stores moisture from high humidity environments as free water, while the level of bound water remains unaffected. The excessive moisture was shown to plasticise the adhesive, lowering the glass transition temperature. The fracture toughness decreased under mode I and mode II loading as the humidity level was increased. The mixed-mode toughness also reduced with increasing storage humidity. However, the measured mixed-mode fracture toughness never reduced below that of the joints fabricated using the as-received material. This indicates that the moisture has a more pronounced effect on the bulk properties of the adhesive rather than on the interfacial adhesion between the composite and adhesive.
    Scopus© Citations 39  750
  • Publication
    Influence of an Atmospheric Pressure Plasma Surface Treatment on the Interfacial Fracture Toughness on Bonded Composite Joints
    The 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.
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