D. Tzetzis

Shear strength behaviour of polypropylene fibre reinforced cohesive soils

Soil reinforcement through the inclusion of oriented or randomly distributed discrete elements such as fibres has recently attracted increasing attention in geotechnical engineering. Therefore, the purpose of this paper is to investigate the influence of certain parameters (the strength properties of the fibre, the relative size of the fibres and grains, and the rate of shear) on the shear strength of polypropylene fibre reinforced cohesive soils. A series of consolidated drained or undrained direct shear tests were conducted on unreinforced and reinforced sandy silt and silty clay specimens. Two types of polypropylene fibres with different mechanical indices were used. The fibre content was varied between 0.3% and 1.1% by weight of dry soil. The test results revealed that the inclusion of fibres in soil significantly increases the shear strength. The attainment of the high shear strength is attributed to the micromechanisms involved in the fibre/soil interactions as studied through scanning electron micrographs. The results also showed that the reinforcement effect was more pronounced under undrained shearing conditions. An important outcome from the current work is that, from the data obtained, the strength of the reinforced soil composites is not practically affected by the fibre mechanical indices.

Double cantilever beam Mode-I testing for vacuum infused repairs of GFRP

This study presents the feasibility of the vacuum assisted resin infusion (VARI) process for strengthening and repair of glass/vinyl ester composites. The process has attracted considerable interest in the marine sector as a route to the manufacture of new structures such as boat hulls but has not been discussed as a route to repair damaged parts where adhesion is required between a repair preform and the original material. In this work, the adhesion that may be obtained between an infusion resin and a composite substrate is interpreted using a fracture mechanics approach involving double cantilever beam (DCB) Mode-I fracture toughness tests. It is shown that once adequate adhesion is established from a comparison of particular pretreatments, both Mode-I critical strain energy release rate values and crack resistance curves are increased by the introduction of ultra-thin polyester veils to toughen the impregnation resin at the critical bonding area of the repair configuration. Post-failure examination of the fracture surfaces show that the failure locus is transferred from the interface to the reinforced resin bondline. This exploits the high strain-to-failure characteristics of the thermoplastic veil materials. The strong crack resistance observed is attributed to the ply bridging mechanism of the thermoplastic fibres that deform plastically in the wake of the crack. Two different data reduction methods are adopted for the current study, namely the compliance calibration (CC) and the modified beam theory (MBT) and a relationship is derived from the variation of their parameters n and Δ in order to analyse and compare the fracture energy values obtained.

Alternative production strategies based on the comparison of additive and traditional manufacturing technologies

Additive manufacturing technology has been evolving for several years. New material options, better processing speeds and greater autonomy are some of the characteristics of this technology that are still under research. However, in its current state, many commercially available 3D printers are competing with traditional manufacturing techniques in the fabrication of end-use products. In this paper, different additive manufacturing technologies are compared with injection moulding in a real-world case study. The comparison is conducted in terms of lead time and total production cost. From the case under study, it becomes obvious that none of the additive manufacturing technologies examined is yet able to practically replace injection moulding for medium- and high production volumes. However, when considering low-volume production, both rapid tooling and additive manufacturing may offer an alternative that could result into shorter lead times and decreased total production costs. In addition, the introduction of Additive Manufacturing in a producer’s production portfolio can increase flexibility, reduce warehousing costs and assist the company towards the adoption of a mass customisation business strategy.

Infield composites repair techniques for combat aircraft: research and development perspective

Abstract Combat aircraft that are damaged and reside on the ground are completely ineffectual to air component commanders. Aircraft battle damage repair (ABDR) aims to rapidly restore these damaged aircraft to some level of combat capability. To be effective, the repairs must allow the aircraft to return to combat in time to affect the outcome of the battle. The Composite Group at Department of Materials, Queen Mary College, University of London, has worked on various aspects of the rapid repair concept for composite materials. In the present paper in particular, the vacuum infusion method is highlighted as an alternative reliable bonded infield repair approach for composite monolithic skins. The study identifies certain technical challenges that the repair technique must address to be viable. Results are presented from a novel toughening method developed by incorporating polyester and carbon veils at the infused bondline, while single scarf coupons as well as full scale testing data demonstrate the effectiveness of the vacuum infusion repair technology in accordance with the ABDR specifications.

Modal testing of epoxy carbon–aramid fiber hybrid composites reinforced with silica nanoparticles

In the current paper, the modal characterisation of aramid–carbon fiber hybrid composites (ACFRP) and ACFRP reinforced with silica nanoparticles (nACFRP) is investigated through the analytical-experimental transfer function method. The modal properties, such as resonant frequencies and modal loss factors, are measured by vibrating cantilever beam specimens with an impact hammer, while the vibratory response is detected through an acceleration transducer. The procedure for the identification of analytical-experimental transfer functions is carried out using a genetic algorithm by minimising the difference between the measured response from tests and the calculated response, which is a function of the modal parameters. The analytical transfer functions provide a substructuring process to identify modes, as a function of damped natural frequencies and loss factors of a complex structure, and it is insensitive to experimental noise as well as the modal coupling effect. The validation of the proposed method is verified with 10 degrees of freedom mass-spring dashpot model. The effectiveness of the proposed method is demonstrated by investigating the static and dynamic behaviour of the ACFRP and nACFRP specimens. Results indicate that the inclusion of nanosilica particles increase the stiffness of the ACFRP, although the damping response of the reinforced specimens is moderately improved.

A New Music Instrument from Ancient Times: Modern Reconstruction of the Greek Lyre of Hermes using 3D Laser Scanning, Advanced Computer Aided Design and Audio Analysis

The current paper proposes a unique approach by examining the ancient Greek literature and antique black figure amphorae’s representations (also known as melanomorpha) for the reconstruction, after digital design processing, of a modern top-quality replica of an ancient tortoise lyre. Through the review of certain ancient Greek documents, the observation of the amphorae’s relevant representations, 3D scanning and reverse engineering as well as 3D design using advanced Computer Aided Design (CAD) software, this study illustrates the detailed drawings and the fabrication procedures followed for a modern version of the ancient musical instrument. By using only materials available in antiquity such as specific kinds of wood, tortoise carcasses and sheep strings, as well as modern carpentry technology, a high-quality musical instrument was produced suited for use by today’s professional musicians. Two variations were produced and tested utilizing the Phrygian and Lydian ancient Greek music scales in a specialized unechoic chamber, in order to define their sound properties. Typical statistics were computed in the frequency domain such as spectral centroid, spectral standard deviation, spectral skewness, spectral kurtosis along with spectral rolloff and spectral smoothness in order to justify the lyres’ quality as musical instruments. The result was a prototype music product using advanced 3D design procedures that can be produced in a rather repeatable manner.

The role of surface morphology on the strength and failure mode of polymer fibre reinforced single lap joints

The present study shows the relation between the surface properties of composite materials, treated with common surface preparation methods, and the mechanically measured bond strengths as quoted from lap-shear tests. The surface properties are studied by roughness measurements, surface free energy assessment, X-ray photoelectron spectroscopy and scanning electron microscopy. The procedures followed, reveal the measure of significance of the mechanical interlocking, kinetics of wetting, chemical reactivity and intermolecular adhesion of the interfaces. It is shown that the governing adhesion qualities determine significantly the fragmentation process and the strength of the joints alongside the load transfer mechanism that is analysed by a simple finite element model. Based on the results, an emphasis is given on elucidating the difference between the intrinsic interfacial adhesion strength and the measured bond strength.

A 3D printed bilayer oral solid dosage form combining metformin for prolonged and glimepiride for immediate drug delivery

&NA; Fused Deposition Modelling (a.k.a. FDM‐3D printing) has been previously employed in the development of personalized medicines with unique properties and release behavior. In the present work, a bilayer dosage form containing two anti‐diabetic drugs with different daily dosage regimens; i.e. metformin and glimepiride, was manufactured via FDM 3D printing, studied using a variety of techniques and characterized in vitro. Metformin and glimepiride were embedded in Eudragit® RL sustained release layer and polyvinyl alcohol (PVA) layer respectively. Incorporation of more than one APIs into the formulation is desirable, as it increases patient compliance and reduces cost of treatment, especially when distinct dosages of APIs can be adjusted individually in situ, in order to meet each patients specific needs, a capability provided by 3D printing. A number of different preparation methods, which involved different plasticizers and extruders, were tested on manufacturing Eudragit® RL drug‐loaded filaments for printing the sustained release layer. The properties of the produced filaments were assessed by means of mechanical and physicochemical characterization techniques and the filaments with the optimum properties were used for printing. Microfocus computed tomography (&mgr;CT) imaging‐based actual/nominal comparison analysis showed a printing accuracy ranging between −100, +200 &mgr;m, while X‐ray (XRD) diffractograms revealed the incorporation of the (initially crystalline) APIs as amorphous dispersions into polymer matrices. Dissolution tests showed sufficient drug release for both drugs in desired time frames (75 min for glimepiride and 480 min for metformin). The results from the current study emphasize the potentiality of 3D printing technology for tailor‐made solid dosage forms for combined pharmacotherapy, even at the cases when APIs with different desirable release profiles are employed. Graphical abstract Figure. No Caption available.

Nanoindentation, compression and fractural characterization of highly dispersed epoxy silica nanocomposites

Uniaxial compression tests were conducted in this study in order to investigate the compressive properties of the unmodified and nanomodified epoxy with silica nanoparticles. An instrumented nanoindentation technique was also used to investigate its applicability for measuring mechanical properties for such nanocomposite systems. Additionally, the fracture toughness of the unmodified and nanomodified epoxy was measured with single-edge-notch bending tests. The Young’s modulus was found to significantly improve with addition of silica nanoparticles and increase with increasing filler content when measured with both compression and nanoindentation tests. The modulus obtained from the nanoindentation testing was 4–8% higher than the one obtained from the compression tests. As expected, the addition of silica nanoparticles had a significant impact on the fracture toughness and fracture energy and increased with increasing filler content, while observation of the fracture surfaces using SEM suggested that the nanoparticles affected the fracture behavior of such epoxy systems. Implementation of an analytical model in the current nanomodified epoxy network as compared with the experimental fracture energy results showed that the 15% matrix void growth, from debonded nanoparticles, as well as the matrix shear banding are the governing mechanisms of energy absorption.

Dynamic Mechanical Characterization of Polyurethane/Multiwalled Carbon Nanotube Composite Thermoplastic Elastomers

ABSTRACT An effective analytical–experimental test method is used in the current work to characterize the vibration isolation behavior of thermoplastic polyurethane multiwalled carbon nanotube nanocomposites with five different concentrations. To determine the static compression stiffness and hysteresis of the specimens, compression and cyclic tests were conducted. The vibration isolation properties were determined through the analysis of transmissibility of a suitably designed test system. Thermoplastic polyurethane’s mechanical properties and vibration isolation properties were improved with the addition of multiwalled carbon nanotubes. Considering the obtained results, the dynamic stiffness of thermoplastic polyurethane and its capacity to isolate vibration can be adjusted by controlling the proportion of multiwalled carbon nanotubes. GRAPHICAL ABSTRACT