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Hertfordshire, United Kingdom

Giannis S.,Materials Engineering Research Laboratory Ltd. | Hansen K.,Materials Engineering Research Laboratory Ltd.
25th Technical Conference of the American Society for Composites and 14th US-Japan Conference on Composite Materials 2010

Adhesive bonding is a mature and very effective technique when it comes to joining similar or dissimilar structural parts. With the continuously increasing use of fibre reinforced composites in structural, load bearing parts of aircrafts, adhesive bonding is explored since it offers significant advantages over riveting when it comes to performance under fatigue loading. In this work, the performance of composite-to-composite and composite-to-aluminium bonded joints is investigated experimentally and their failure mode is analysed. The results were used to feed into the design process of a prototype composite roof for a 4-seater aircraft. Source

Winzer J.,TU Darmstadt | Winzer J.,Materials Engineering Research Laboratory Ltd. | Winzer J.,Slovak Academy of Sciences | Weiler L.,TU Darmstadt | And 2 more authors.

The wear behaviour of a variety of alumina-copper interpenetrating composites was tested as a function of copper ligament diameter and volume fraction of copper. The wear mechanisms of pure copper and pure alumina were adhesive and abrasive wear, respectively. In the composites with 1μm, 5μm and 15μm copper ligament diameters, the wear mechanism was a mixture of adhesive and oxidative; in composites with a 30μm copper ligament diameter a mixture of abrasive and oxidative. Increasing the amount of copper decreased hardness and thus increased wear, except where cyclic tribolayer behaviour occurred or where the alumina grains were weakly bonded. Increasing the copper ligament diameter decreased wear, although this trend was only clear under a load of 20. N. The composites with the highest wear resistance had the highest copper ligament diameter of 30μm. This was probably due to the higher heat conductivity and fracture toughness caused by the coarse, fibrous copper network replicating the wool felt used to produce it. This was possibly also because these composites had the smallest alumina grain size. © 2011 Elsevier B.V. Source

Giannis S.,Materials Engineering Research Laboratory Ltd. | Jeenjitkaew C.,Materials Engineering Research Laboratory Ltd.
2nd Joint US-Canada Conference on Composites - American Society for Composites, 26th Annual Technical Conference: Canadian Association for Composite Structures and Materials

In this paper, the experimental procedures and results of four different tapered laminates are presented and discussed. Symmetric and asymmetric multi-directional laminates were tested with and without artificial delamination defects. The aim of the experimental work was to investigate the potential effect of manufacturing induced delamination type defects on the performance of the laminates. For the asymmetric laminates, failure occurred at the same through the thickness location independent of the presence of the defect and there was a significant reduction in fatigue life for the laminates containing the artificial delamination defects. The effect was less pronounced for the symmetric laminates. Further to the experimental work, finite element procedures were employed to analyse and understand the performance of the laminates. By employing fracture mechanics principles the strain energy release rate was evaluated at the tip of the artificial delaminations as well as at the most critical locations of the pristine laminates using the Virtual Crack Closure Technique and a global energy balance method. The interlaminar fracture analysis of the laminates was combined with a mixed mode delamination criterion developed for the IM7/8552 composite to derive predictions of the fatigue life. The predicted fatigue life agreed well with the experimental data. Source

Giannis S.,Materials Engineering Research Laboratory Ltd. | Martin R.H.,Materials Engineering Research Laboratory Ltd.
Plastics, Rubber and Composites

The debonding of Glare skin-stringer configurations for aerospace applications has been studied. Fatigue life curves were produced experimentally for two types of skin-stringer configurations. Using the double cantilever beam specimen configuration and applying different loading conditions, material models for pure mode I and mixed mode I and mode II fatigue loading were generated for the adhesive used to bond the skin to the stringer. These material models describe the crack growth rate, da/dN, as a function of the maximum cyclic strain energy release rate, G max, and were used together with finite element analysis of the cracked skin-stringer configuration to derive predictions of the fatigue life. The predicted fatigue life was compared to the experimental results. © 2010 Maney Publishing. Source

Mohammed M.H.,University of Strathclyde | Banks W.M.,University of Strathclyde | Hayward D.,University of Strathclyde | Liggat J.J.,University of Strathclyde | And 2 more authors.
Polymer Degradation and Stability

The property changes occurring when poly(ether ether ketone) (PEEK) is subject to methane and carbon dioxide at high pressures (108 Pa) and high temperatures (175-200 °C) are reported. Differential scanning calorimetry, density gradient techniques, positron annihilation lifetime spectroscopy, dynamic mechanical thermal analysis and tensile tests measurements were used to monitor the changes which occur during the ageing process. Over the period of the study an overall increase in the tensile strength was noted, with little or no change in 0.2% and 2% proof stresses, whilst there was a decrease in bending modulus and glass transition temperature due to the effects of plasticization. The Young's modulus generally increases for samples exposed to a temperature of 175 °C in the presence of a mixture of 90% methane and 10% carbon dioxide, or carbon dioxide alone, but it decreases at 200 °C in the presence of carbon dioxide alone. The observed effects are consistent with the polymer undergoing initially a densification of the matrix associated with annealing-induced crystallisation, followed by plasticization as the gases permeate into the disordered regions of the matrix. When de-pressurised, the gas dissolved in the matrix attempts to leave the matrix and morphological changes are observed. The complexity of the changes in crystallinity and plasticization in the disordered phase are reflected in changes in the positron annihilation data. © 2013 Published by Elsevier Ltd. Source

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