Nanoscale precipitation in advanced high strength steels

Precipitation strenghthening is one of the most important approaches for enhancing the strenght of microalloyed steels. This study has made a significant contribution in understanding the nucleation and growth mechanism of nanoscale interphase precipitates in steel during commercial processes. Atom Probe Tomography revealed the existence of nanoscale clusters with precipitates that then dictate the final strength.

Glass/carbon fibre hybrid composite laminates for structural applications in automotive vehicles

Light-weight structure is one of the keys to improve the fuel efficiency and reduce the environmental buden of transport vehicles (automotive and rail). While fibreglass composites have been increasingly used to replace steel in automotive industry, the adoption rate for carbon fibre composites which are much lighter, stronger and stiffere than glass fibre composites, remains low. The main reason is the high cost of carbon fibres. To further reduce vehicle weight without excessive cost increase, one technique is to incorporate carbon fibre reinforcement into glass fibre composites and innovative design by selectively reinforcing along the main load path. Glass/carbon woven fabrics with epoxy resin matrix were utilised for preparing hybrid composite laminates. The in-plane mechanical properties such as tensile and three-point-bending flexural properties were investigated for laminates with different carbon fibre volume and lay-up scheme. It is shown that hybrid composite laminates with 50% carbon fibre reinforcement provide the best flexural properties when the carbon layers are at the exterior, while the alternating carbon/glass lay-up provides the highest compressive strength.

Utilizing polypropylene fibers to improve physical and mechanical properties of concrete

The influence of polypropylene fibers has been studied in different proportioning and fiber aspect ratios to improve physical and mechanical properties of fiber-reinforced concretes. Fibers are used in two different lengths (12 mm and 19 mm) and proportions (0.1% and 0.3%) in concrete mixture design. Hardened concrete properties, such as 7- and 28-day compressive strength, splitting tensile strength, flexural strength, water and air absorption, and restrained shrinkage cracking were evaluated.

No statistically significant effects were observed for polypropylene fibers on the compressive strength of concrete, while toughness indexes, splitting tensile and flexural strength and durability parameters showed an increase in the presence of polypropylene fibers. Increased fiber availability (fiber aspect ratio) in the concrete matrix, in addition to the ability of longer polypropylene fibers to bridge on the micro cracks, are suggested as the reasons for the enhancement in mechanical properties. Finally, crack width in fiber-reinforced concrete is calculated analytically with fiber property variables (fiber type, length, diameter and proportion). Results are compared with experimental values and concluded that with an increase in fiber length and/or decrease in fiber diameter crack width, decrease significantly.

Structural composites embedded with lithium polymer batteries

Structural battery composites that concurrently carry load and store electric energy will
transform future vehicles. They can replace inert structural components and simultaneously provide supplementary power for light load applications. Rechargeable lithium polymer battery cells are embedded into carbon fibre/epoxy matrix composite laminates, which are then tested under tension and three-point bending to investigate the mechanical and electrical performances of structural batteries. The experimental results show that the integration of battery cells into composite laminates has negligible impact on the mechanical strengths of the composite structures. Furthermore, the battery cells remain 95% effective at loads up to about 60% of the ultimate flexural failure load and 50% of the ultimate tensile failure load.

Mechanical behaviour of functionally graded carbon nanofibre/phenolic nanocomposites: numerical modelling and experimental validation

In this study, a finite element-based model was developed to investigate the mechanical behaviour of functionally graded carbon nanofibre (CNF)/phenolic nanocomposites. Four functionally graded nanocomposites (FGNs), a non-graded nanocomposite (NGN), and a pure phenolic with the same geometry and total carbon nanofibre content were designed and fabricated. Flexural tests were conducted to validate the proposed finite element model. Close agreement was obtained between experimental results and numerical predictions. The results showed that flexural modulus can be improved about 45% by controlling the CNF content across the thickness of the samples.

The effect of a rapid heating rate, mechanical vibration and surfactant chemistry on the structure-property relationships of epoxy/clay nanocomposites

The role of processing conditions and intercalant chemistry in montmorillonite clays on the dispersion, morphology and mechanical properties of two epoxy/clay nanocomposite systems was investigated in this paper. This work highlights the importance of employing complementary techniques (X-ray diffraction, small angle X-ray scattering, optical microscopy and transmission electron microscopy) to correlate nanomorphology to macroscale properties. Materials were prepared using an out of autoclave manufacturing process equipped to generate rapid heating rates and mechanical vibration. The results suggested that the quaternary ammonium surfactant on C30B clay reacted with the epoxy during cure, while the primary ammonium surfactant (I.30E) catalysed the polymerisation reaction. These effects led to important differences in nanocomposite clay morphologies. The use of mechanical vibration at 4 Hz prior to matrix gelation was found to facilitate clay dispersion and to reduce the area fraction of I.30E clay agglomerates in addition to increasing flexural strength by over 40%.

Effects of mechanical deformation on electric performance of rechargeable batteries embedded in load carrying composite structures

Integrating rechargeable battery cells with fibre reinforced polymer matrix composites is a promising technology to enable composite structures to concurrently carry load and store electric energy, thus significantly reducing weight at the system level. To develop a design criterion for structural battery composites, rechargeable lithium polymer battery cells were embedded into carbon fibre/epoxy matrix composite laminates, which were then subjected to tensile, flexural and compressive loading. The electric charging/discharging properties were measured at varying levels of applied loads. The results showed that degradation in battery performance, such as voltagea and energy storage capacity, correlated well with the applied strain under three different loading conditions. Under compressive loading, battery cells, due to their multilayer construction, were unable to prevent buckling of composite face sheets due to the low lateral stiffness, leading to lower compressive strength that sandwich panels with foam core.

Bending behaviour of step-wise graded carbon nanofiber/polymer nanocomposites

In this study, a finite element-based model was developed to investigate the mechanical behavior of step-wise graded carbon nanofibre/phenolic nanocomposites. Four step-wise graded nanocomposites (FGNs), a non-graded nanocomposite (NGN), and a pure phenolic with the same geometry and total carbon nanofiber content were designed, fabricated and analyzed. Flexural tests were conducted to validate the finite element model. Close agreement was obtained between experimental results and numerical predictions. The results showed that flexural modulus was highly influenced by the compositional gradients.

A simple and effective method to ameliorate the interfacial properties of cellulosic fibre based bio-composites using poly (ethylene glycol) based amphiphiles

In order to overcome interfacial incompatibility issues in natural fibre reinforced polymer bio-composites, surface modifications of the natural fibres using complex and environmentally unfriendly chemical methods is necessary. In this paper, we demonstrate that the interfacial properties of cellulose-based bio-composites can be tailored through surface adsorption of polyethylene glycol (PEG) based amphiphilic block copolymers using a greener alternative methodology. Mixtures of water or water/acetone were used to form amphiphilic emulsions or micro-crystal suspensions of PEG based amphiphilic block copolymers, and their deposition from solution onto the cellulosic substrate was carried out by simple dip-coating. The findings of this study evidence that, by tuning the amphiphilicity and the type of building blocks attached to the PEG unit, the flexural and dynamic thermo-mechanical properties of cellulose-based bio-composites comprised of either polylactide (PLA) or high density polyethylene (HDPE) as a matrix, can be remarkably enhanced. The trends, largely driven by interfacial effects, can be ascribed to the combined action of the hydrophilic and hydrophobic components of these amphiphiles. The nature of the interactions formed across the fibre-matrix interface is discussed. The collective outcome from this study provides a technological template to significantly improve the performance of cellulose-based bio-composite materials.

Properties of bio-based polymer nylon 11 reinforced with short carbon fiber composites

In this work, micro-composite materials were produced by incorporating 3-mm long reclaimed short carbon fibers into bio-based nylon 11 via melt compounding. A systematic fiber length distribution analysis was performed after the masterbatching, compounding and an injection moulding processes using optical microscopy images. It was found that the large majority of the fibers were within the 200-300 μm in length range after the injection moulding process. The mechanical (flexural and tensile), thermo-mechanical, and creep properties of the injection moulded materials are reported. We found that an enhancement in flexural and Young's modulus of 25% and 14%, respectively, could be attained with 2 wt% carbon fiber loading whilst no significant drawback on the ductility and toughness of the matrix was observed. The creep resistance and recovery of the nylon 11, tested using dynamic mechanical thermal analysis at room temperature and 65°C, was significantly improved by up to 30% and 14%, respectively, after loading with carbon fiber. This work provides an insight into the property improvement of the bio-based polymer nylon 11 using a small amount of a reclaimed engineered material. © 2014 Society of Plastics Engineers.

Phase morphology, thermomechanical, and crystallization behavior of uncompatibilized and PP-g-MAH compatibilized polypropylene/polystyrene blends

In this article, we discuss the phase morphology, thermal, mechanical, and crystallization properties of uncompatibilized and compatibilized polypropylene/polystyrene (PP/PS) blends. It is observed that the Young's modulus increases, but other mechanical properties such as tensile strength, flexural strength, elongation at break, and impact strength decrease by blending PS to PP. The tensile strength and Young's modulus of PP/PS blends were compared with various theoretical models. The thermal stability, melting, and crystallization temperatures and percentage crystallinity of semicrystalline PP in the blends were marginally decreased by the addition of amorphous PS. The presence of maleic anhydride-grafted polypropylene (compatibilizer) increases the phase stability of 90/10 and 80/20 blends by preventing the coalescence. Hence, finer and more uniform droplets of PS dispersed phases are observed. The compatibilizer induced some improvement in impact strength for the blends with PP matrix phase, however fluctuations in modulus, strength and ductility were observed with respect to the uncompatibilized blend. The thermal stability was not much affected by the addition of the compatibilizer for the PP rich blends but shows some decrease in the thermal stability of the blends, where PS forms the matrix. On the other hand, the % crystallinity was increased by the addition of compatibilizer, irrespective of the blend concentration.

Structure-property relationships in nylon 6 nanocomposites based on octaphenyl-, dodecaphenyl-POSS, montmorillonite, and their combinations

Binary and ternary nanocomposites were produced by incorporating, via melt compounding, two types of octa-and dodecaphenyl substituted polyhedral oligomeric silsesquioxanes (POSS), montmorillonite (MMT), and combinations of POSS with MMT into nylon 6. The tensile, flexural, and dynamic thermo-mechanical properties of these materials were characterized and their structure-property relationships discussed. The results show that the losses in ductility and toughness experienced after inclusion of MMT into nylon 6 can be balanced out by co-mixing MMT with the dodecaphenyl- POSS to produce a ternary nanocomposite. This trend however was less pronounced in the ternary MMT/octaphenyl-POSS system. Analysis of the microstructure organization in these materials using XRD and SEM sheds some light on understanding the differences in behavior. Both types of POSS particles mixed alone in nylon 6 were found to be polydisperse (500 nm to a few microns in size) and locally aggregated, yielding materials with similar mechanical performance. The co-mixing of MMT with the octaphenyl- POSS served to break down the POSS crystal aggregates, enhancing their micro-mechanical reinforcing action. On the other hand, the POSS crystals were not affected in the MMT/dodecaphenyl-POSS system, which led to improving their toughening ability.

Assessment of bond strength in CFRP retrofitted beams under marine environment

Carbon fibre reinforced polymer (CFRP) sheet has gained its popularity to retrofit civil structures which is bonded externally, typically on the soffit of a beam. In this study, the bond between carbon fibre reinforced polymer (CFRP) and concrete is improved by modifying the property of commercial epoxy and compared against normal epoxy. The deterioration in bond strength was produced by placing the beam into salt water under wet dry cycles. Also, a model is proposed to determine the bond strength from flexural test and compared against the available bond strength models which are typically obtained from pull out test. This proposed model shows promising results in terms of predicting the bond strength from flexural test. In addition, a strength reduction factor is introduced to incorporate the effect of wet dry cycles to predict the long term behaviour. It is found that the modified epoxy enhance the ductile property and bond strength.

Estudo de pelotização e briquetagem de finos de carvão mineral

O aumento da produção de carvão previsto para os próximos anos nas minas da CRM localizadas em Leão, Butiá, RS, originará uma considerável quantidade de finos beneficiados por ciclonagem autôgena. Estes finos caracterizam-se pelos seus altos teores de umidade e granulometria <1 mm o que onera e dificulta os processos de manuseio, estocagem e transporte. O presente estudo visa à análise comparativa dos processos de aglomeração, a briquetagem e a pelotização com o objetivo de obter um produto com melhores características de comercialização do que o atual. As principais variáveis estudadas na aglomeração por briquetagem foram: teor de umidade, tipo e concentração de agente ligante, relação massa/volume de carvão, tempo e pressão de moldagem. Os melhores resultados em termos de resistência à compressão, foram obtidos utilizando um resíduo de refinaria de petróleo - REVAC - como ligante numa concentração de 10% em peso, uma temperatura de cura de 120° C, um tempo de moldagem de 0,5 minutos e uma pressão de compactação entre 150 e 250 kgf/cm². A pelotização foi estudada utilizando um tambor e um disco de laboratório e as principais variáveis estudadas foram: umidade da alimentação, tipo e concentração de agente ligante, temperatura de cura e outras. Os melhores resultados foram obtidos utilizando como ligante MOGUL (amido de milho pré-gelatinizado em pó) numa concentração de 5% em peso, uma faixa de umidade ótima entre 30 e 40%, uma inclinação do disco entre 45 e 51° e uma temperatura de cura de 80 e 100°C. Os resultados obtidos para ambos os carvões (CE 5900 e CE 4700) são discutidos em termos dos diversos fenômenos que ocorrem na interface carvão-solução-ligante e algumas considerações econômicas são apresentadas.

Mapeamento e caracterização geomecânica das unidades geotécnicas de solos oriundos dos granitos, gnaisses e migmatitos de Porto Alegre

O trabalho consta do estudo do meio físico geotécnico do município de Porto Alegre visando a identificação e caracterização de unidades geotécnias, formadas por associações de solos com características físico-morfológicas e origem semelhantes. As unidades geotécnicas são definidas por um estudo de escritório baseado em levantamentos geológicos, pedológicos, topográficos e geográficos e também com o auxílio de fotografias aéreas, acompanhado de uma investigação de campo com a amostragem de perfis das diferentes unidades estimadas. Uma carta com a ocorrência das unidades geotécnicas e com a representação das estruturas geológicas de maior importância geotécina é construída. Destaque é dado ás unidades geotécnicas de solos subtropicais oriundos dos granitos, gnaisses e migmatitos. E executada uma avaliação das características físicas (mineralogia, granulometria, plasticidade, e índices físicos) e propriedades geotécnicas (compressibilidade, colapsividade e resistência ao cisalhamento) dos solos dos principais horizontes de perfis típicos destas unidades. São utilizados ensaios de caracterização, análises mineralógicas de rochas por lâminas delgadas, análises mineralógicas de argilas por meio de difratograma de raio X, ensaios de compressão confinada e ensaios de cisalhamento direto. Os resultados são apresentados em função dos principais horizontes de solos das unidades geotécnicas , são eles horizontes saprolíticos, formados por solo residual que ainda apresentam minerais primários e vestígios estruturais da rocha de origem e horizontes superficiais muitas das vezes laterizados. A análise foi feita à luz dos processos de formação e dos decorrentes fatores que determinam o comportamento geotécnico destes solos de intemperismo subtropical.