Papers by Author: António Torres Marques

Abstract: The aim of this investigation work is threefold: 1) To analyse and quantify freeze-thaw resistance of glass fibre reinforced epoxy polymer mortars, comparatively to both normal cement mortars and plain epoxy polymer mortars; 2) To determine glass fibre reinforcement effect on freeze-thaw behaviour; and 3) To evaluate the reliability of ASTM C666M-03 test methodology for the assessment of freeze-thaw resistance of polymer concrete materials. For this purpose several test specimens, normal cement mortars, plain and glass-fibre reinforced epoxy polymer mortars were submitted to freeze-thaw cycling between 36 up to 300 cycles, according to the above norm. Dynamic elasticity modulus, with basis on fundamental resonance frequency measurements, was calculated every 36 cycles, and the correspondent relative dynamic elasticity modulus was determined for each cycling period. In order to assess the reliability of this non-destructive test methodology, three specimens of each formulation were withdrawn at regular periods and tested in bending and compression. Relative mechanical strengths, as function of conditioning period, were compared with corresponding relative dynamic modulus of elasticity.

Abstract: The aim of this work is to assess the feasibility of using polymer mortars reinforced with untreated natural fibres instead of artificial ones, for applications requiring highly alkali resistant materials, such as tanks and drainage systems for wastewater treatment plants. For this purpose, several formulations of polyester polymer mortars reinforced with different contents of jute and piassava natural fibres were investigated. Flexural and compressive behaviour, before and after exposure to a strong alkaline solution was analysed and quantified. Test results highlighted the high potential of these materials as basis construction material for precast applications requiring specific resistance under alkaline environments.

Abstract: This work establishes process windows for efficient towpreg production on a developed powder coating equipment. Three different thermoplastic towpregs were studied: one for highly demanding markets (carbon fibre/PrimospireTMPR-120) and other two for commercial applications (glass/polypropylene and glass/polyvinyl chloride). Mechanical properties of compression moulded composites obtained from the produced towpregs were also obtained and discussed.

Abstract: This paper summarizes the results obtained in the use of plastisols of vinyl chloride homopolymer (PVC), obtained by the process of emulsion polymerization, as thermoplastic matrix in the production of composite pipes and in pipe repairing. Two processing techniques commonly used with thermosetting matrices were studied: filament winding and hand lay up. The produced composite structures of PVC reinforced with glass fibres were subsequently subjected to tests in order to determine their mechanical properties. This paper concludes that it is possible to use the described technique for piping repairing with good results.

Abstract: The distinguishing characteristics of carbon fibre reinforced laminates, like low weight, high strength or stiffness, had resulted in the increase of their use during the last decades. Although parts are normally produced to “near-net” shape, machining operations like drilling are still needed. In result of composites non-homogeneity, this operation can lead to delamination, considered the most serious kind of damage as it can reduce the load carrying capacity of the joint. A proper choice of tool and cutting parameters can reduce delamination substantially. In this work, the results obtained with five different tool geometries are compared. Conclusions show that the choice of adequate drill geometry can reduce the thrust forces and consequently, the delamination damage.

Abstract: The distinctive characteristics of carbon fibre reinforced plastics, like low weight or high specific strength, had broadened their use to new fields. Due to the need of assembly to structures, machining operations like drilling are frequent. In result of composites inhomogeneity, this operation can lead to different damages that reduce mechanical strength of the parts in the connection area. From these damages, delamination is the most severe. A proper choice of tool and cutting parameters can reduce delamination substantially. In this work the results obtained with five different tool geometries are compared. Conclusions show that the choice of an adequate drill can reduce thrust forces, thus delamination damage.

Abstract: In the present study, fire reaction improvement of an epoxy polymer mortar (PM) formulation, induced by polymer modification with three different flame retardant (FR) systems, was analyzed and quantified. For this purpose, several epoxy PM formulations, modified with different contents and/or types of phosphate, metal hydroxide and brominated based FR systems, were manufactured and tested for both, fire reaction and flexural strength. The results were compared with those of plain epoxy PMs. Fire reaction of PM formulations was assessed by means of the Oxygen Consumption Calorimeter test, also known as Cone Calorimeter test. This test allows the determination of the main parameters that assess fire reaction behaviour of combustible materials: heat release rate, smoke extinction area, carbon dioxide and monoxide release rates, and ignitability. Test results revealed that all FR systems, in particular the phosphate based one, are effective in improving fire reaction performance of epoxy PMs. Moreover, this improvement is attained without significant losses of bearing carrying capacity of PM materials.

Abstract: The use of fibre reinforced plastics – FRP’s – in structures is under a considerable increase. Advantages of their use are related with their low weight, high strength and stiffness. The improvement of the dynamic characteristics has been profitable for aeronautics, automobile, railway, naval and sporting goods industries. Drilling is a widely used machining technique as it is needed to assemble parts in a structure. This is a unique machining process, characterized by the existence of two different mechanisms: extrusion by the drill chisel edge and cutting by the rotating cutting lips. Drilling raises particular problems that can reduce mechanical and fatigue strength of the parts. In this work, quasi-isotropic hybrid laminates with 25% of carbon fibre reinforced plies and 4 mm thickness are produced, tested and drilled. Three different drill geometries are compared. Results considered are the interlaminar fracture toughness in Mode I – GIc –, thrust force during drilling and delamination extent after drilling. A bearing test is performed to evaluate tool influence on the load carrying capacity of the plate. Results consider the influence of drill geometry on delamination. A correlation linking plate damage to bearing test results is presented.

Abstract: In this study the embedding of piezoelectric ceramics in carbon-fibre/epoxy laminates is studied with the purpose to be used for structural health monitoring from vibration measurements. Piezoelectric elements were embedded in two laminate types made of two weaved prepregs and with four additional unidirectional prepregs, respectively. The efficiency of the embedding process was analysed from the capability of the piezoelectric ceramic to transmit vibrations to the composite plate. The sensing element was successfully used to monitor the composite plate when submitted to three-point bending dynamic tests at different frequencies.

Abstract: Thermoplastics are replacing traditional thermosetting resins as matrices in composite materials in many applications due to their enhanced properties. Thermoplastics exhibit better toughness, durability and damping properties and provide the options of continuous processing, reshaping, and reparability, as well as more favourable recycling and processing routes that do not involve chemical reactions [1]. However, their high melt viscosity makes it difficult to impregnate continuous fibres, which restricts commercial applications. Recently developed dry coating techniques allow the production of long fibre thermoplastic matrix towpregs without most of the previous impregnation problems [2, 3]. In this work, a new coating line was developed to produce long fibre dry coated thermoplastic matrix towpregs at rates compatible with industrial production. The polymer deposition rate was considerably increased to allow processing towpregs at greater speeds (approx. 10 m/min) than current equipment. A new coating chamber was used to allow improved control of the fibre and polymer contents and the towpreg impregnation quality. Other general improvements were also made in the equipment to allow better monitoring of the towpreg processing. Glass or carbon fibres with polypropylene towpregs (GF/PP and CF/PP, respectively) were produced on the new coating line which were then submitted to extensive tests to verify their polymer content and impregnation quality. This paper presents the results of the tests and discusses the optimization of the new dry coating line. The results show that the new deposition chamber allows production of economical thermoplastic matrix towpregs with improved efficiency that may be used in the industrial production of composites for commercial markets.