6 results found
Yu B, Katafiasz TJ, Nguyen S, et al., 2021, Hygrothermal effects on the translaminar fracture toughness of a highly toughened aerospace CFRP: Experimental characterisation and model prediction, Composites Part A: Applied Science and Manufacturing, Vol: 150, Pages: 1-12, ISSN: 1359-835X
The translaminar fracture toughness and its dependence on the environmental condition are key considerations in designing aerospace-grade composites with a high damage tolerance to severe service conditions in terms of temperature and moisture. The present work characterises and models the hygrothermal effects on the translaminar fracture toughness of an interlaminar toughened aerospace carbon/epoxy composite under six environmental conditions: −55 °C, 23 °C, and 90 °C, for both ‘dry’ (i.e. moisture free) and ‘wet’ (fully moisture-saturated) specimens. Cross-ply compact-tension experiments show that the translaminar fracture toughness increases with the rise of temperature for both dry and wet conditions with the latter exhibiting a much greater increase. A model to predict the effect of moisture and temperature on the translaminar fracture toughness is here proposed and developed. This approach yields good agreement with experimental results, and it allows an improved understanding of the complex synergistic effects of interfacial properties on the overall translaminar toughening mechanisms.
Greenhalgh ES, Canturri C, Katafiasz TJ, 2021, Fractographic study into the effect of drilling damage on bearing mechanisms and performance in carbon-fibre epoxy composites, Engineering Failure Analysis, Vol: 129, Pages: 1-29, ISSN: 1350-6307
With the widespread adoption of polymer composites in primary structures, understanding and prediction of the performance of composite to metal hybrid joints is now critical to engineering design of transport structures. This work investigated the damage processes associated with bearing failure of such composite joints, for both pristine holes and holes damaged during drilling. An aerospace grade composite was drilled under three different conditions, tested to failure under quasi-static double bearing loading, and then characterised using fractographic techniques. In the pristine condition, the initial damage process was 0° longitudinal splitting tangential to the lateral extents of the hole which then dictated the extent of the subsequent bearing damage development. Beneath the bearing face of the hole inclined lines of in-plane microbuckled fibres had developed whilst beyond the constraint of the washer there was considerable delamination and massive out-of-plane fibre microbuckling. As the degree of drilling damage increased, 0° longitudinal split development was inhibited, and the local pre-existing damage at the periphery of the hole had extended into the bearing damage zone, directly initiating out-of-plane fibre microbuckling. Consequently the bearing damage zone exhibited irregular distributions of fibre microbuckles, both across the thickness and depth beneath the bearing face of the hole. The observations in this work provide a means to validate predictive models and offer potential routes to improve bearing performance and the tolerance of laminates with drilling damage when under bearing loads.
Katafiasz T, Greenhalgh ES, Allegri G, et al., 2021, The influence of temperature and moisture on the mode I fracture toughness and associated fracture morphology of a highly toughened aerospace CFRP, Composites Part A: Applied Science and Manufacturing, Vol: 142, ISSN: 1359-835X
This paper addresses the characterisation of the mode I interlaminar fracture toughness of a carbon fibre/epoxy composite material, toughened with thermoplastic particles in the ply interlayers. The characterisation is undertaken at −55 °C, 19 °C, and 90 °C, on both dry and fully moisture saturated coupons. Fractographic observations of the delamination surfaces allows identification of the failure mechanisms. The mode I propagation fracture toughness tested at wet/90 °C exhibits a 176% increase compared to the dry/19 °C specimens, due to enhanced plastic deformation of the interlayers and more prominent fibre bridging. Moisture-saturated coupons tested at −55 °C suffered a 57% reduction of mode I fracture toughness compared to those under dry/19 °C conditions. This is due to the dis-bond and consequent plucking of the thermoplastic particles from the surrounding matrix. This observation points to the fact that wet/cold conditions may represent the worst-case scenario for the interlaminar fracture performance of composite systems toughened with thermoplastic interleaves.
Katafiasz TJ, Iannucci L, Greenhalgh E, 2019, Development of a novel compact tension specimen to mitigate premature compression and buckling failure modes within fibre hybrid epoxy composites, Composite Structures, Vol: 207, Pages: 93-107, ISSN: 1879-1085
A Notched Curved Compact Tension (NCCT) and Extended Notched Curved Compact Tension (ENCCT) specimen geometry are presented for the measurement of translaminar critical strain energy release rates in composite laminates with low compressive to tensile strengths. Premature compressive and buckling failure occurred when a conventional Compact Tension (CT) specimen geometry (similar to ASTM E399 ) was utilised for monolithic Non-Crimp Fabric (NCF) S2-Glass / MTM57 epoxy and an interlayer fibre hybrid T700 carbon spread tow / NCF S2-glass epoxy composite. The NCCT and ENCCT specimen design methodology and manufacturing routes are presented where premature compressive failure was mitigated through a curvature at the rear of the profile and the introduction of a through-thickness groove that had been pre-cured along the crack growth region. The latter ensured that buckling was eliminated, whilst stable crack growth was achieved. The development involved FE model material validation and optimisation for the novel specimen design. Experimental tests presented both interlayer and intralayer fibre hybrid composites with good repeatability and low scatter within the results.
Katafiasz TJ, Iannucci L, Greenhalgh ES, 2016, Interlaminar and intralaminar properties of carbon spread tow and glass fibre hybrid composites for cost saving in the mass production of automotive components
As the efficiency of the automotive engine shows signs of slow-down and the consumer is becoming more aware of the consequential ecological impact, the industry's need for lighter component materials grows more prominent. Carbon fibre composite materials have been subject to neglect within the consumer automotive industry due to their expense (whereas glass fibre materials have been used favourably over the last few decades ). Cost effective composite materials have therefore become an area of interest for the consumer automotive market, where year-on-year engine efficiency performance improvements and monetary savings are integral to company profits. The purpose of this research is to verify that the use of fibre hybrid composites, where two-stage pseudoductile responses can be found , , are a viable alternative to monolithic structures (which exhibit a more traditional one-stage brittle failure) in interlaminar and intralaminar failure modes. In recent years, there has been much work to understand the tensile response of fibre hybrid composites - but a lack of research in types of failure modes which are more likely within automotive components; these being delamination (interlaminar) and through-thickness tearing (intralaminar); the latter of which most likely occurs at stress concentrations at bolt holes and through-thickness discontinuities.
Katafiasz TJ, Iannucci L, Greenhalgh E, 2015, Hybrid Fibre Composites for De-lamination Resistance and Cost Saving, Cyclitech
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