Study on braided textile composites for sports protection

Braided textile reinforced composites become increasingly attractive as protection materials in sports (e.g. hockey sticks, helmets and shin guard) due to their high structural stability and excellent damage tolerance. There are requirements to develop an effective way to enhance product optimisation, test and design; however, the mechanical behaviours and energy dissipation mechanisms of braided composites have not been fully understood. There are no numerical modelling paradigms which are widely accepted due to the sheer complexity of the problem. Therefore, the aim of this thesis is to build a robust multi-scale modelling framework which will account for damage in the composite under static and dynamic loading states. Validated with corresponding experiments, the modelling capability should finally allow us to design braided composite structures for targeted performance before they are manufactured. [Continues.

Braided textile composites for sports protection: Energy absorption and delamination in impact modelling

Composites reinforced with braided textiles exhibit high structural stability and excellent damage tolerance, making them ideal materials for use in sports-protection equipment. In sports impact scenarios, braided composites need to maintain their structure integrity and dissipate impact energy to protect a human body. Thus, it is crucial to study the dynamic response of a composite structure and its energy-dissipation mechanisms. Here, a multi-scale computational approach was explored to capture main damage modes of a braided textile composite; simulations were supported by experimental verification. A drop-weight test was performed with a spike-shape impactor to imitate real-life sports impact collision scenarios, followed by X-ray computed micro-tomography to characterize damage morphology of the specimen. The experimental results were compared with analytical models. The extent of delamination was quantified by applying surface- and element-based cohesive zone models. A ply-level model with three-dimensional continuum and shell elements was employed to explore the effect of through-thickness failure modes on energy absorption of the composite. The propagation mechanism of matrix cracks is also discussed. In addition, with the developed model, impact-attenuation performance of a shin-guard structure was simulated. The presented modelling capability can improve design of braided composite structures for sports and other protective and structural applications

Damage accumulation in braided textiles-reinforced composites under repeated impacts: Experimental and numerical studies

© 2018 Elsevier Ltd Composites reinforced with braided textiles exhibit high structural stability and excellent damage tolerance, making them very attractive for defence, aerospace, automotive and energy industries. Considering the real-life service environment, it is crucial to study a dynamic response of a composite structure and its energy-dissipation ability, especially under repeated low-velocity impacts. So, a series of drop-weight tests were carried out followed by X-ray computed micro-tomography to characterize damage morphology of braided composite specimens. Meanwhile, a multi-scale computational approach was explored and implemented as a user-defined-material subroutine (VUMAT) for ABAQUS/Explicit to capture main damage modes of a braided textile composite, while its delamination was modelled by employing cohesive-zone elements. Load- and energy-time curves were obtained both experimentally and numerically. The predicted levels of peak forces and absorbed energy were found to agree with the experimental data. An extent of delamination and damage accumulation in the braided composite was predicted numerically and analysed; it was found that material responses to repeated impacts had two types depending on the level of normalised impact energy. The presented modelling capability could contribute to design of braided composite structures for various applications

Shear strength and fracture toughness of carbon fibre/epoxy interface: effect of surface treatment

© 2015 Elsevier Ltd. Textile-reinforced composites have become increasingly attractive as protection materials for various applications, including sports. In such applications it is crucial to maintain both strong adhesion at fibre-matrix interface and high interfacial fracture toughness, which influence mechanical performance of composites as well as their energy-absorption capacity. Surface treatment of reinforcing fibres has been widely used to achieve satisfactory fibre-matrix adhesion. However, most studies till date focused on the overall composite performance rather than on the interface properties of a single fibre/epoxy system. In this study, carbon fibres were treated by mixed acids for different durations, and resulting adhesion strength at the interface between them and epoxy resin as well as their tensile strength were measured in a microbond and microtensile tests, respectively. The interfacial fracture toughness was also analysed. The results show that after an optimum 15-30. min surface treatment, both interfacial shear strength and fracture toughness of the interface were improved alongside with an increased tensile strength of single fibre. However, a prolonged surface treatment resulted in a reduction of both fibre tensile strength and fracture toughness of the interface due to induced surface damage

Penciptaan Komunikasi Visual Perancangan Program Edutainment “Seri Aktivitas Alam: Gunung Meletus”

This research is the continuation of previous research. The research is included in the creation of visual communication solutions on how a process of visual communication strategy can contribute a persuasive invitation. Research aims to expose the solution in the realm of visual communication. The research applied qualitative method. It began with the development of communicators becoming a mascot, continued on the delivery of messages through the comics, and invited children as audience target for design experience with game and gimmick. Result of the research is the visual design, as well as including the process of visual communication creation. As a conclusion, creating a visual communication solution could be carried out by the same method, similar matching scope, as well as the contents adjusted with new needs

Strength prediction for bi-axial braided composites by a multi-scale modelling approach

Braided textile-reinforced composites have become increasingly attractive as protection materials thanks to their unique inter-weaving structures and excellent energy-absorption capacity. However, development of adequate models for simulation of failure processes in them remains a challenge. In this study, tensile strength and progressive damage behaviour of braided textile composites are predicted by a multi-scale modelling approach. First, a micro-scale model with hexagonal arrays of fibres was built to compute effective elastic constants and yarn strength under different loading conditions. Instead of using cited values, the input data for this micro-scale model were obtained experimentally. Subsequently, the results generated by this model were used as input for a meso-scale model. At meso-scale, Hashin’s 3D with Stassi’s failure criteria and a modified Murakami-type stiffness-degradation scheme was employed in a user-defined subroutine developed in the general-purpose finite-element software Abaqus/Standard. An overall stress–strain curve of a meso-scale representative unit cell was verified with the experimental data. Numerical studies show that bias yarns suffer continuous damage during an axial tension test. The magnitudes of ultimate strengths and Young’s moduli of the studied braided composites decreased with an increase in the braiding angle

2D/3D Heterostructure Interface Design and Property Modification

2D/3D Heterostructure Solar Cells have attracted numerous attention due to its potential to be an alternative to the silicon (Si) Wafer-based photovoltaic technologies. However, most 2D/3D Heterojunction photovoltaic cells suffer from long-term instability in power conversion efficiency. This is mainly due to the interfacial charge carrier recombination owing to the low 2D/3D built-in electric field. Therefore, it is critical to overcome these challenges via interfacial engineering. Here in my thesis, I have introduced 2D thin film like hexagonal boron nitride (h-BN) and ultrananocrystallinediamond (UNCD) as tunneling inter-layer in Graphene/Si heterojunctions. The 2D/2D/3D architecture of graphene/h-BN/Si or graphene/UNCD/Si forms a metal-insulator-semiconductor (MIS)-type junction, where h-BN and UNCD act as an electron-blocking or hole-transporting medium and they avoid interfacial charge carrier recombination. A 4-fold increase in open-circuit voltage (VOC) is found for graphene/h-BN/Si heterojunction cell (0.52 V) in contrast to the graphene/Si cell (0.13 V), which is due to the increase in the effective Schottky barrier height and hence built-in electric voltage

Anisotropic Phonon Scattering and Thermal Transport Property Induced by the Liquid-like Behavior of AgCrSe₂

Superionic conductors exhibiting a periodic crystalline lattice and liquid-like ionic conductivity have emerged as promising materials in energy-conversion devices. Herein, we have investigated the interplay among anharmonic lattice dynamics, thermal conduction, and ultrafast atomic diffusion across the superionic transition of AgCrSe2. We show that the thermal conductivity (κ) contributions from convection and conduction–convection interactions increase simultaneously due to the gradual fluidization of Ag atoms, leading to a temperature-independent κ in the superionic state. We demonstrate a non-Peierls type thermal transport behavior induced by the strong lattice anharmonicity of Ag atoms, which promotes a nontrivial wave-like phonon tunneling in the normal state of AgCrSe2. Our current fluctuation analysis demonstrates an anisotropic phonon-liquid scattering behavior that the in-plane nondispersive transverse acoustic (TA) phonons near the zone boundary collapse, while the zone center and boundary TA phonons in the direction perpendicular to the liquid-like flow of Ag atoms survive

Genotype dataset of ground tit for Dryad

The dataset includes genotype information of all the ground tit individuals used in this paper

Sub-Nanosecond Resonance Energy Transfer in the Near-Infrared within Self-Assembled Conjugates of PbS Quantum Dots and Cyanine Dye J‑Aggregates

Energy transfer (EnT) of near-infrared (NIR) excitons enables applications in harvesting of solar energy and biological imaging. Fast exciton extraction from NIR-absorbing Pb-chalcogenide quantum dots (QDs) may allow utilization of the photon downconversion (multiple exciton generation) process that occurs in those QDs to amplify signal in QD-based sensors or photocurrent in QD-based photovoltaics. This paper describes subnanosecond extraction of NIR excitons from PbS QDs by adsorbed J-aggregates of cyanine dye in aqueous dispersions. The QD/J-aggregate complexes form through electrostatic self-assembly, and the rate and yield of EnT within the complexes can be optimized by adjusting spectral overlap between QD emission and the J-aggregate absorption, which are controlled by density of charged ligands on the QD surface and the pH. The primary EnT pathways have rate constants ranging from (800 ps)⁻¹ to (2.2 ns)⁻¹, which are 1–2 orders of magnitude faster than previously reported examples with PbS QDs as exciton donors. The fastest EnT process occurs in 90 ps and is potentially competitive with Auger recombination of biexcitonic states in PbS QDs