Adrian Lowe

Mode I and mode II delamination properties of glass/vinyl-ester composite toughened by particulate modified interlayers

Abstract Various vinyl-ester (VE)/poly(acrylonitrile-butadiene-styrene) (ABS) blends were used for interlayer-toughening of a glass/VE composite to increase delamination resistance of the base material under mode I and mode II loading. Dry ABS powder was mixed with the liquid resin in four weight ratios: 3.5, 7, 11 and 15 phr (parts per hundred parts of resin) while the layer thickness was varied within the range of 150–500 μm. Firstly, mode I fracture toughness and tensile properties of the VE/ABS blends were assessed. By using the Raman Spectroscopy technique a chemical reaction was discovered which occurred during ABS–VE mixing: i.e. butadiene transition from the ABS particles to the VE. A butadiene saturation was discovered to occur in the VE beyond 7% ABS particle content. Both mode I and mode II fracture toughness were significantly improved with application of the interlayers. Mode I fracture toughness was found to be a function of layer thickness and particle content variations. The latter dominated G Ic after the saturation point. On the other hand mode II fracture toughness was found to be independent of the layer thickness (within the used layer thickness range) and only moderately influenced by the particle content. Important Toughening mechanisms were plastic deformation and micro-cracking of the layer materials. Evidence of both mechanisms has been found using optical and scanning electron microscopy (SEM).

On crack-initiation conditions for mode I and mode II delamination testing of composite materials

Abstract An investigation of the influence of pre-crack conditions on the fracture behavior of a unidirectional vinyl-ester/E-glass composite has been undertaken. For this investigation, recommendations from three different testing standards for preparing double-cantilever beam (DCB) specimens were followed. For this purpose two sets of specimens were tested: a set of specimens with a blunt starter crack and the one with a fatigue pre-crack (i.e. sharp). The two sets of specimens exhibited similar fracture behavior during testing, with the crack propagation being stable and not influenced by the different pre-crack conditions. As expected, propagation values of the strain-energy release rate were unaffected by the pre-crack conditions and, owing to the extensive fiber bridging, propagation G Ic prop values were significantly larger than initiation G Ic ini values. However, the influence of the pre-cracking on the initiation values of the G Ic was noticed. A similar investigation was also conducted for mode II, with ENF specimens. No influence of the pre-crack condition on the fracture toughness of the composite under the mode II loading was noted. Scanning electron micrographs were taken to provide additional explanations for the observations made during the testing.

One-Dimensional Assembly of Conductive and Capacitive Metal Oxide Electrodes for High-Performance Asymmetric Supercapacitors

A one-dimensional morphology comprising nanograins of two metal oxides, one with higher electrical conductivity (CuO) and the other with higher charge storability (Co3O4), is developed by electrospinning technique. The CuO-Co3O4 nanocomposite nanowires thus formed show high specific capacitance, high rate capability, and high cycling stability compared to their single-component nanowire counterparts when used as a supercapacitor electrode. Practical symmetric (SSCs) and asymmetric (ASCs) supercapacitors are fabricated using commercial activated carbon, CuO, Co3O4, and CuO-Co3O4 composite nanowires, and their properties are compared. A high energy density of ∼44 Wh kg-1 at a power density of 14 kW kg-1 is achieved in CuO-Co3O4 ASCs employing aqueous alkaline electrolytes, enabling them to store high energy at a faster rate. The current methodology of hybrid nanowires of various functional materials could be applied to extend the performance limit of diverse electrical and electrochemical devices.

The microdroplet test: experimental and finite element analysis of the dependance of failure mode on droplet shape

The microdroplet technique is usually designed as a fibre embedded in a drop of resin and subsequently pulled out while the drop is being supported by two knife edges, resulting in either debonding of the droplets from the fibres, or breakage of the fibres before debonding can occur. In this study, the microdroplet technique was performed using a platinum ring with a 40 μm hole instead of the usual two knife edges, giving an axisymmetric geometry, load and stress distribution. Glass/phenolic and glass/polyester composite systems were tested experimentally and subsequent finite element modelling studies were performed to assess the variation of droplet size, and contact angle between the droplet and fibre. It was found that contact angle is of major influence in the proposed failure model. This study characterizes the influence of the contact angle between the droplet and the fibre on the subsequent stress distribution in the microdroplet specimen.

Effect of Chemical Treatments on Flax Fibre Reinforced Polypropylene Composites on Tensile and Dome Forming Behaviour

Tensile tests were performed on two different natural fibre composites (same constituent material, similar fibre fraction and thickness but different weave structure) to determine changes in mechanical properties caused by various aqueous chemical treatments and whether any permanent changes remain on drying. Scanning electronic microscopic examinations suggested that flax fibres and the flax/polypropylene interface were affected by the treatments resulting in tensile property variations. The ductility of natural fibre composites was improved significantly under wet condition and mechanical properties (elongation-to-failure, stiffness and strength) can almost retain back to pre-treated levels when dried from wet condition. Preheating is usually required to improve the formability of material in rapid forming, and the chemical treatments performed in this study were far more effective than preheating. The major breakthrough in improving the formability of natural fibre composites can aid in rapid forming of this class of material system.

Sheet Thickness Optimization for Superplastic Forming of Engineering Structures

This paper explores two optimization strategies; the gradient search and proportional control methods, for determining the initial sheet thickness of superplastic forming to ensure final desired part thickness. A hemispherical dome model was involved in the testing of both optimization methods. Also, a three-dimensional rectangular box model was optimized by the proportional control method. The gradient search technique is shown to be acceptable in terms of the optimized thickness obtained, but displays poor convergence rates. The proportional control approach presented is easy to be implemented, and yields not only more accurate sheet thickness, hut much higher convergence speeds that makes such optimization possible on complex geometric models.

Numerical simulation of elastic-plastic interlaminar crack propagation in interlayer-toughened composite materials

A numerical analysis was conducted, using previously obtained experimental results, to establish basic toughening mechanisms and fracture behaviour of an interlayer-toughened composite material, containing particulate modified toughened layers. The aim of the analysis was to examine the influence of the particles on the plastic zone size that develops in front of the crack tip, and the interaction between the particles and the crack tip. Good agreement with the experimental data was found.

Enhanced electrochemical performance of electrospun V2O5 fibres doped with redox-inactive metals

AbstractThe structural and electrochemical effects of electrospun V2O5 with selected redox-inactive dopants (namely Na+, Ba2+ and Al3+) have been studied. The electrospun materials have been characterised via a range of analytical methods including X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area measurements and scanning and transmission electron microscopy. The incorporation of dopants in V2O5 was further studied with computational modelling. Structural analysis suggested that the dopants had been incorporated into the V2O5 structure with changes in crystal orientation and particle size, and variations in the V4+ concentration. Electrochemical investigations using potentiodynamic, galvanostatic and impedance spectroscopy analysis showed that electrochemical performance might be dependent on V4+ concentration, which influenced electronic conductivity. Na+- or Ba2+-doped V2O5 offered improved conductivities and lithium ion diffusion properties, whilst Al3+ doping was shown to be detrimental to these properties. The energetics of dopant incorporation, calculated using atomistic simulations, indicated that Na+ and Ba2+ occupy interstitial positions in the interlayer space, whilst Al3+ is incorporated in V sites and replaces a vanadyl-like (VO)3+ group. Overall, the mode of incorporation of the dopants affects the concentration of oxygen vacancies and V4+ ions in the compounds, and in turn their electrochemical performance. Graphical abstractᅟ

Structural and Electrical Characterization of Doped Zirconia Nanostructured Fibres

Pure and lithium-doped zirconia fibres have been produced using the electrospinning process. These fibres are seen to be mesoporous in nature and possess a dense outer skin that correlates with the existance of tetragonal structure. This tetragonal form exists in materials below a certain average grain size and also correlates well with capacitance retention, CV measurements and impedance response. During electrical performance, an initial irreversible solid electrolyte interface is believed to form and average grain size has a significant effect. This study suggests that in this mesoporous/skin form, electrospun zirconia fibres are promising energy storage materials.

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Publisher Summary This chapter deals with materials that are studied in the context of modern technological materials advancement. A natural material is something that nature uses to build things. Nature uses wood as tree trunks to provide support for large plants, whereas humans have modified these trunks into simplest geometric shapes that are used in the design and construction of boats, buildings, and numerous other products. Biomaterials involve the study of materials that can be used within the human body to initiate improvements in some condition. These materials can be existing bodily materials or materials specially created. Furthermore, the chapter discusses protein-based and plant-based traditional natural materials.