Acrylic adhesives in the polyolefins joining

The mechanical behaviour of single lap adhesive joints was characterized, using two commercial acrylic adhesives. For this purpose the surfaces were cleaned and abraded using fine grit abrasives. The effect of temperature and moisture in the mechanical strength was, also, evaluated. For this characterization, mechanical tests were carried out according procedure and geometry foreseen by ASTM D3163-01 [1] and ASTM D4501-01 [2] standards. The results show that it is possible to get good strengths without great surface preparation. The temperature and moisture effect observed don���t seem to be relevant for the mechanical behaviour.

Drilling of fibre reinforced plastic laminates

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.

Microstructure, mechanical properties and chemical degradation of brazed AISI 316 stainless steel/alumina systems

The main aims of the present study are simultaneously to relate the brazing parameters with: (i) the correspondent interfacial microstructure, (ii) the resultant mechanical properties and (iii) the electrochemical degradation behaviour of AISI 316 stainless steel/alumina brazed joints. Filler metals on such as Ag���26.5Cu���3Ti and Ag���34.5Cu���1.5Ti were used to produce the joints. Three different brazing temperatures (850, 900 and 950 ��C), keeping a constant holding time of 20 min, were tested. The objective was to understand the influence of the brazing temperature on the final microstructure and properties of the joints. The mechanical properties of the metal/ceramic (M/C) joints were assessed from bond strength tests carried out using a shear solicitation loading scheme. The fracture surfaces were studied both morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The degradation behaviour of the M/C joints was assessed by means of electrochemical techniques. It was found that using a Ag���26.5Cu���3Ti brazing alloy and a brazing temperature of 850 ��C, produces the best results in terms of bond strength, 234 �� 18 MPa. The mechanical properties obtained could be explained on the basis of the different compounds identified on the fracture surfaces by XRD. On the other hand, the use of the Ag���34.5Cu���1.5Ti brazing alloy and a brazing temperature of 850 ��C produces the best results in terms of corrosion rates (lower corrosion current density), 0.76 �� 0.21 ��A cm���2. Nevertheless, the joints produced at 850 ��C using a Ag���26.5Cu���3Ti brazing alloy present the best compromise between mechanical properties and degradation behaviour, 234 �� 18 MPa and 1.26 �� 0.58 ��A cm���2, respectively. The role of Ti diffusion is fundamental in terms of the final value achieved for the M/C bond strength. On the contrary, the Ag and Cu distribution along the brazed interface seem to play the most relevant role in the metal/ceramic joints electrochemical performance.

Strength prediction of adhesively-bonded scarf repairs in composite structures under bending

This work reports on the experimental and numerical study of the bending behaviour of two-dimensional adhesively-bonded scarf repairs of carbon-epoxy laminates, bonded with the ductile adhesive Araldite 2015��. Scarf angles varying from 2 to 45�� were tested. The experimental work performed was used to validate a numerical Finite Element analysis using ABAQUS�� and a methodology developed by the authors to predict the strength of bonded assemblies. This methodology consists on replacing the adhesive layer by cohesive elements, including mixed-mode criteria to deal with the mixed-mode behaviour usually observed in structures. Trapezoidal laws in pure modes I and II were used to account for the ductility of the adhesive used. The cohesive laws in pure modes I and II were determined with Double Cantilever Beam and End-Notched Flexure tests, respectively, using an inverse method. Since in the experiments interlaminar and transverse intralaminar failures of the carbon-epoxy components also occurred in some regions, cohesive laws to simulate these failure modes were also obtained experimentally with a similar procedure. A good correlation with the experiments was found on the elastic stiffness, maximum load and failure mode of the repairs, showing that this methodology simulates accurately the mechanical behaviour of bonded assemblies.

Strength prediction and experimental validation of adhesive joints including polyethylene, carbon-epoxy and aluminium adherends

Polyolefins are especially difficult to bond due to their non-polar, non-porous and chemically inert surfaces. Acrylic adhesives used in industry are particularly suited to bond these materials, including many grades of polypropylene (PP) and polyethylene (PE), without special surface preparation. In this work, the tensile strength of single-lap PE and mixed joints bonded with an acrylic adhesive was investigated. The mixed joints included PE with aluminium (AL) or carbon fibre reinforced plastic (CFRP) substrates. The PE substrates were only cleaned with isopropanol, which assured cohesive failures. For the PE CFRP joints, three different surfaces preparations were employed for the CFRP substrates: cleaning with acetone, abrasion with 100 grit sand paper and peel-ply finishing. In the PE AL joints, the AL bonding surfaces were prepared by the following methods: cleaning with acetone, abrasion with 180 and 320 grit sand papers, grit blasting and chemical etching with chromic acid. After abrasion of the CFRP and AL substrates, the surfaces were always cleaned with acetone. The tensile strengths were compared with numerical results from ABAQUS�� and a mixed mode (I+II) cohesive damage model. A good agreement was found between the experimental and numerical results, except for the PE AL joints, since the AL surface treatments were not found to be effective.

Shear modulus and strength of an acrylic adhesive by the notched plate shear method (Arcan) and the thick adherend shear test (TAST)

In this work, the shear modulus and strength of the acrylic adhesive 3M�� DP 8005 was evaluated by two different methods: the Thick Adherend Shear Test (TAST) and the Notched Plate Shear Method (Arcan). However, TAST standards advise the use of a special extensometer attached to the specimen, which requires a very experienced technician. In the present study, the adhesive shear displacement for the TAST was measured using an optical technique, and also with a conventional inductive extensometer of 25 mm used for tensile tests. This allowed for an assessment of suitability of using a conventional extensometer to measure this parameter. Since the results obtained by the two techniques are identical, it can be concluded that using a conventional extensometer is a valid option to obtain the shear modulus for the particular adhesive used. In the Arcan tests, the adhesive shear displacement was only measured using the optical technique. This work also aimed the comparison of shear modulus and strength obtained by the TAST and Arcan test methods.

Interlaminar fracture characterization of a carbon-epoxy composite in pure mode II

The interlaminar fracture toughness in pure mode II (GIIc) of a Carbon-Fibre Reinforced Plastic (CFRP) composite is characterized experimentally and numerically in this work, using the End-Notched Flexure (ENF) fracture characterization test. The value of GIIc was extracted by a new data reduction scheme avoiding the crack length measurement, named Compliance-Based Beam Method (CBBM). This method eliminates the crack measurement errors, which can be non-negligible, and reflect on the accuracy of the fracture energy calculations. Moreover, it accounts for the Fracture Process Zone (FPZ) effects. A numerical study using the Finite Element Method (FEM) and a triangular cohesive damage model, implemented within interface finite elements and based on the indirect use of Fracture Mechanics, was performed to evaluate the suitability of the CBBM to obtain GIIc. This was performed comparing the input values of GIIc in the numerical models with the ones resulting from the application of the CBBM to the numerical load-displacement (P-���) curve. In this numerical study, the Compliance Calibration Method (CCM) was also used to extract GIIc, for comparison purposes.

Synthesis of titanate nanostructures using amorphous precursor material and their adsorption/photocatalytic properties

This article reports on a new and swift hydrothermal chemical route to prepare titanate nanostructures (TNS) avoiding the use of crystalline TiO2 as starting material. The synthesis approach uses a commercial solution of TiCl3 as titanium source to prepare an amorphous precursor, circumventing the use of hazardous chemical compounds. The influence of the reaction temperature and dwell autoclave time on the structure and morphology of the synthesised materials was studied. Homogeneous titanate nanotubes with a high length/diameter aspect ratio were synthesised at 160 degrees C and 24 h. A band gap of 3.06 +/- 0.03 eV was determined for the TNS samples prepared in these experimental conditions. This value is red shifted by 0.14 eV compared to the band gap value usually reported for the TiO2 anatase. Moreover, such samples show better adsorption capacity and photocatalytic performance on the dye rhodamine 6G (R6G) photodegradation process than TiO2 nanoparticles. A 98% reduction of the R6G concentration was achieved after 45 min of irradiation of a 10 ppm dye aqueous solution and 1 g L-1 of TNS catalyst.

Evaluation of tools and cutting conditions on carbon fibre reinforced laminates

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.

Biofunctional composite coating architectures based on polycaprolactone and nanohydroxyapatite for controlled corrosion activity and enhanced biocompatibility of magnesium AZ31 alloy

In this work a biofunctional composite coating architecture for controlled corrosion activity and enhanced cellular adhesion of AZ31 Mg alloys is proposed. The composite coating consists of a polycaprolactone (PCL) matrix modified with nanohydroxyapatite (HA) applied over a nanometric layer of polyetherimide (PEI). The protective properties of the coating were studied by electrochemical impedance spectroscopy (EIS), a non-disturbing technique, and the coating morphology was investigated by field emission scanning electron microscopy (FE-SEM). The results show that the composite coating protects the AZ31 substrate. The barrier properties of the coating can be optimized by changing the PCL concentration. The presence of nanohydroxyapatite particles influences the coating morphology and decreases the corrosion resistance. The biocompatibility was assessed by studying the response of osteoblastic cells on coated samples through resazurin assay, confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The results show that the polycaprolactone to hydroxyapatite ratio affects the cell behavior and that the presence of hydroxyapatite induces high osteoblastic differentiation. (C) 2014 Elsevier B.V. All rights reserved.

Aquisi����o por Vis��o Artificial e Medi����o Autom��tica de Micro Dureza Vickers

O ensaio de dureza, e mais concretamente o ensaio de micro dureza Vickers, �� no universo dos ensaios mec��nicos um dos mais utilizados quer seja na ind��stria, no ensino ou na investiga����o e desenvolvimento de produto no ��mbito das ci��ncias dos materiais. Na grande maioria dos casos, a utiliza����o deste ensaio tem como principal aplica����o a caracteriza����o ou controlo da qualidade de fabrico de materiais met��licos. Sendo um ensaio de relativa simplicidade de execu����o, rapidez e com resultados compar��veis e relacion��veis a outras grandezas f��sicas das propriedades dos materiais. Contudo, e tratando-se de um m��todo de ensaio cuja interven����o humana �� importante, na medi����o da indenta����o gerada por penetra����o mec��nica atrav��s de um sistema ��tico, n��o deixa de exibir algumas debilidades que da�� adv��m, como sendo o treino dos t��cnicos e respetivas acuidades visuais, fen��menos de fadiga visual que afetam os resultados ao longo de um turno de trabalho; ora estes fen��menos afetam a repetibilidade e reprodutibilidade dos resultados obtidos no ensaio. O CINFU possui um micro dur��metro Vickers, cuja realiza����o dos ensaios depende de um t��cnico treinado para a execu����o do mesmo, apresentando todas as debilidades j�� mencionadas e que o tornou eleg��vel para o estudo e aplica����o de uma solu����o alternativa. Assim, esta disserta����o apresenta o desenvolvimento de uma solu����o alternativa ao m��todo ��tico convencional na medi����o de micro dureza Vickers. Utilizando programa����o em LabVIEW da National Instruments, juntamente com as ferramentas de vis��o computacional (NI Vision), o programa come��a por solicitar ao t��cnico a sele����o da c��mara para aquisi����o da imagem digital acoplada ao micro dur��metro, sele����o do m��todo de ensaio (For��a de ensaio); posteriormente o programa efetua o tratamento da imagem (aplica����o de filtros para elimina����o do ru��do de fundo da imagem original), segue-se, por indica����o do operador, a zona de interesse (ROI) e por sua vez s��o identificadas automaticamente os v��rtices da calote e respetivas dist��ncias das diagonais geradas concluindo, ap��s aceita����o das mesmas, com o respetivo c��lculo de micro dureza resultante. Para valida����o dos resultados foram utilizados blocos-padr��o de dureza certificada (CRM), cujos resultados foram satisfat��rios, tendo-se obtido um elevado n��vel de exatid��o nas medi����es efetuadas. Por fim, desenvolveu-se uma folha de c��lculo em Excel com a determina����o da incerteza associada ��s medi����es de micro dureza Vickers. Foram ent��o comparados os resultados nas duas metodologias poss��veis, pelo m��todo ��tico convencional e pela utiliza����o das ferramentas de vis��o computacional, tendo-se obtido bons resultados com a solu����o proposta.

Performance assessment of waste fibre-reinforced mortar

Materials Science Forum Vols. 730-732 (2013) pp 617-622

Evaluation of Pozzolanic Reactivity of Artificial Pozzolans

Materials Science Forum Vols. 730-732 (2013) pp 433-438

Compact ion-source based on superionic rubidium silver iodide (RbAg4I5) solid electrolyte

Disserta����o para obten����o do Grau de Mestre em Engenharia F��sica

Development of polymer wicks for the fabrication of bio-medical sensors

Polymer based wicking structures were fabricated by sintering powders of polycarbonate (PC), ultra-high molecular weight polyethylene and polyamide 12, aiming at selecting a suitable material for an innovative electroencephalography (EEG) bio-electrode. Preliminary experiments showed that PC based wicks displayed the best mechanical properties, therefore more detailed studies were carried out with PC to evaluate the influence of powder granulometry and processing parameters (pressure, temperature and time) on the mechanical properties, porosity, mean pore radius and permeability of the wicks. It was concluded that the mechanical properties are significantly enhanced by increasing the processing time and pressure, although at the expense of a significant decrease of porosity and mean pore diameter (and thus permeability), particularly for the highest applied pressures (74kPa). However, a good compromise between porosity/permeability and mechanical properties could be obtained by sintering PC powders of particle sizes below 500��m at 165��C for 5min, upon an applied pressure of 56kPa. Moreover, PC proved to be chemically stable in contact with an EEG common used disinfectant. Thus, wicking structures with appropriate properties for the fabrication of reusable bio-electrodes could be fabricated from the sintering of PC powders.