Research trends: February 2013

Mechanical behaviour of pultruded glass fibre reinforced polymer composites at elevated temperature: Experiments and model assessment

João R. Correia, Marco M. Gomes, José M. Pires and Fernando A. Branco, Composite Structures, Volume 98, April 2013, pages 303-313


While FRP is being increasingly used in civil engineering applications, concerns include the performance of FRP when exposed to fire, especially in building applications. This is because the strength, stiffness and bond properties of FRPs severely deteriorate when the glass transition temperature (Tg) of the resin is approached (typically in the range of 60-140°C). Furthermore, when exposed to temperatures of about 300-500°C, the organic matrix of FRPs decompose, releasing heat, smoke, soot and toxic volatiles. However, fire resistance tests on glass fibre reinforced polymer (GRP) pultruded tubular beams carried out at Instituto Superior Técnico (IST) showed that it is possible to fulfill stringent building code fire requirements. Different passive and active fire protection systems were successfully used and provided fire resistances longer than 60 min and 120 min, respectively. It was observed that GFRP profiles are much more vulnerable under compression and shear than under tension.


This paper presents further research on the mechanical response at elevated temperature of GRP pultruded profiles. It describes an extensive study of the tensile, shear and compressive responses of the GRP at temperatures of 20-250°C. Results confirm that the mechanical performance of GFRP severely deteriorates at moderately high temperatures, particularly when loaded in shear and compression, owing to the glass transition of the resin. The accuracy of different models to estimate the tensile, shear and compressive strengths of GRP pultruded material as a function of temperature are assessed.

Improving fail-safety of road bridges built with ­non-ductile fibre composites

Markus Gabler, Jan Knippers, Construction and Building Materials 


In countries with fully developed infrastructure, e.g. within the EU, bridge construction focuses on substitution of deteriorated structures or on complementing infrastructure already in use. Therefore, prefabrication and rapid mounting on-site are becoming ever more important. Moreover, the problems occurring with corrosion of steel or RC bridges demand a more durable construction material. Due to their low weight, FRP bridges can be prefabricated and shipped fully equipped to the construction site, and their high corrosion resistance makes composites more durable. In past years, several systems of FRP bridge decks have been investigated. Pultruded units show the most reliable mechanical and geometrical properties.


The bridge deck investigated in this paper is composed of prismatic bars made of glass fibre reinforced polymer (GFRP). The hollow sections are produced by pultrusion and adhesively bonded together. The brittle failure modes of fibre composite materials leads to low material utilisation when designing structural members. For other applications, the low elastic modulus of glass fibre composites compared to steel is also limiting the material utilisation. However this is no decisive design aspect for FRP bridge decks. Several structural details of fibre composite road bridges are scrutinised regarding their failure mode and optimised solutions are developed. As an additional means of improving fail-safety, a structurally integrated sensor network is being developed which is capable of allowing in part for the safety deficits of the brittle material. The fibre optic sensors allow for online monitoring and early detection of damage. The complex sensor-lamina-interaction is being analysed in order to predict measurement results and optimise the sensor layout.

Effect of thermal treatment temperatures on the reinforcing and interfacial properties of recycled carbon fibre-phenolic composites

Joung-Man Park, Dong-Jun Kwon, Zuo-Jia Wang, Ga-Young Gu, K. Lawrence DeVries, Composites Part A: Applied Science and Manufacturing


It has been estimated that 3 million kg (6.6 million lbs) of carbon fibre composite (CFRP) scrap is generated annually in the USA and Europe. Furthermore, some 6000 to 8000 commercial planes are expected to reach end-of-life and ready for dismantlement by 2030, while the annual production of virgin carbon fibre is expected to increase to 110 million kg by 2018. Adding to the challenges of recycling of composites are the facts that they are composed of multiple phases, the thermosetting matrix cannot be remoulded and the resin frequently contains other materials that might produce noxious combustion by-products. Several countries are intensifying efforts to solve the waste disposal issue by trying to recycle waste materials. This study explores the potential of recycling carbon fibre (CF) at a competitive price and with minimally impaired mechanical properties. The method explored in this study, in essence, burned away the epoxy in a reduced oxygen combustion process.


Carbon fibre reinforced plastic (CFRP) chips were thermally treated to clean their surfaces and their use as reinforcing materials in composites explored. Electrical resistance measurements were used to evaluate the state of dispersion of the recycled carbon fibres (RCF) in the RCF-phenolic composites. The surfaces of the RCFs and the fracture surfaces of the RCF-phenolic composites were studied for the different treatment temperatures (200-600°C). There were differences in the nature and amount of residual epoxy resin on the surface of recycle CF subsequent to different thermal treatments. Properties of RCF-phenolic composites were affected by the presence of residual epoxy. The optimal treatment temperature was approximately 400°C, where the surface was clean of the residual epoxy material and still relatively free of thermal damage. The decrease in diameter as well as damage to the fibres at the higher temperatures was accompanied by reduced mechanical properties for composites manufactured with the recycled chips. The interfacial properties of the CFRP chips were generally improved by the appropriate thermal treatment, resulting in better interfacial adhesion between the recycled fibres and the phenolic resin.

Damage assessment of composite materials by means of thermographic analyses

F. Libonati, L. Vergani, Composites Part B: Engineering


Composites are largely used for structural applications, thanks to their high strength-to-weight ratios. However, it is difficult to make accurate estimations on their mechanical behaviour, as it is affected by several factors, involved both in the manufacturing process and in the experimental testing. In this study, GFRP laminates, with different stacking sequences, are tested under static loading conditions. During testing, thermal analyses are performed by means of a thermal camera. The thermographic method allows both qualitative and quantitative analyses to be performed in a relatively short time. Besides thermal analyses, damage is also assessed by means of static tests, interrupted at different load levels, and followed by stiffness reduction measurements and microscopic analyses, allowing for a comparison of the obtained results.

Optimisation of hybrid high-modulus/high-strength carbon fibre reinforced plastic composite drive shafts

O. Montagnier, Ch. Hochard, Materials & Design, Volume 46, April 2013, pages 88-100


This study deals with the optimisation of hybrid composite drive shafts operating at subcritical or supercritical speeds, using a genetic algorithm. A formulation for the flexural vibrations of a composite drive shaft mounted on viscoelastic supports including shear effects is developed. In particular, an analytic stability criterion is developed to ensure the integrity of the system in the supercritical regime. Then it is shown that the torsional strength can be computed with the maximum stress criterion. A shell method is developed for computing drive shaft torsional buckling. The optimisation of a helicopter tail rotor driveline is then performed. In particular, original hybrid shafts consisting of high-modulus and high-strength carbon fibre reinforced epoxy plies were studied. The solutions obtained using the method presented here made it possible to greatly decrease the number of shafts and the weight of the driveline under subcritical conditions, and even more under supercritical conditions. This study yielded some general rules for designing an optimum composite shaft without any need for optimisation algorithms.

Structural optimization study of composite wind turbine blade

Jin Chen, Quan Wang, Wen Zhong Shen, Xiaoping Pang, Songlin Li, Xiaofeng Guo, Materials & Design, Volume 46, April 2013, pages 247–255


In this paper the initial layout of a 2 MW composite wind turbine blade is designed first. The new airfoils families are selected to design a 2 MW wind turbine blade. The finite element parametric model for the blade is established. Based on the modified Blade Element Momentum theory, a new one-way fluid–structure inter-action method is introduced. A procedure combining finite element analysis and particle swarm algorithm to optimise composite structures of the wind turbine blade is developed. The procedure proposed not only allows thickness variation but also permits the spar cap location variation over the structure. The results show that, compared to the initial blade, the mass of the optimised blades is reduced and especially for the scheme II (the location of blade spar cap is seen as one of the variables) which exhibit more mass saving. This present study has significance for the structural design and optimisation of wind turbine blades.

Materials selection in design of structures and engines of supersonic aircrafts: A review

Zainul Huda, Prasetyo Edi, Materials & Design, Volume 46, April 2013, pages 552–560


This article reviews the advances in the materials selection for applications in structures and engines of current and future supersonic aircraft. A brief overview of configuration design of the supersonic aircraft is first given, which also includes techniques to improve configuration design for future supersonic aircrafts. The operating and ambient environmental conditions during supersonic flight and the resulting material requirements have been discussed, and consequently various aerospace aluminium alloys, titanium alloys, superalloys, and composites have been recommended. Finally, a new materials-selection chart is presented that would enable aerospace designers to select appropriate materials for application in high-performance current and future supersonic/hypersonic aircraft. ♦  

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