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- Fractography (2)
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Organisationseinheit der BAM
Blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) were processed into biaxially drawn films, and samples taken from the bi-oriented films were then investigated by dynamic rheology experiments in the melt state. Storage modulus G and loss modulus G were determined in the frequency range of 10-2-102 rad/s at temperatures between 260 and 300°C. Although the time-temperature superposition (TTS) principle was found to hold in the high frequency regime, a breakdown of TTS was observed at low frequencies, and the terminal behavior of the storage modulus G of the blends departs drastically from the terminal behavior observed for the blend components. This is caused by interfacial surface tension effects. The results indicate that despite the effect of transesterification reactions, the PET/PEN blend systems investigated consist of a microseparate phase of PEN platelets in a matrix of PET. This morphology is produced when the blends are processed into biaxially oriented PET/PEN films, and droplets of PEN are deformed into a lamellar structure consisting of parallel and extended, separate layers. The large interfacial surface area of the bi-oriented PET/PEN blends leads to remarkably strong interfacial tension effects in dynamic rheology measurements.
To reveal and improve our understanding of the ignition behavior and mechanism, G-G furnace experiments of three typical organic dusts were performed to investigate the minimum ignition temperature (MIT) in O2/N2, O2/ Ar and O2/CO2 atmospheres with oxygen mole fraction from 8.4% to 50%. The experimental results were presented in oxygen-lean and oxy-fuel atmospheres to evaluate the ignition sensitivity of dusts in different atmospheres. It was found that CO2 is the strongest in terms of lowing the ignition sensitivity of the three dusts, and the dust explosion risk increases significantly with increasing O2 mole fraction for the three dusts through a logarithmically and significantly reducing MIT. However, for different dusts, inert gases show different suppression effects. In addition, a modified steady-state homogeneous ignition model was proposed and successfully applied to oxygen-lean atmospheres, and in oxy-fuel atmospheres, this model has also been improved to estimate the ignition mechanism. This ignition mechanism model could be used to successfully predict the minimum ignition temperature of high volatile dust under different inert atmospheres controlled by homogeneous ignition, which will provide a reference for the ignition hazard assessment of dust on hot surfaces.
Industrial fires and explosions initiating from self-ignition of combustible porous dust deposits represent a serious hazard for human beings, environment and industry. Understanding the fundamental basis of combustible dust ignition behaviours at different geometries is of importance to prevent and mitigate the accidental risks. A correlation of self-ignition temperatures (SITs) measured by hot-oven tests and minimum ignition temperatures of dust layers (MITLs) determined by hot-plate tests has been established previously. However, this analogy approach based on Frank-Kamenetzkii model is limited by ignoring the influence of oxygen diffusion. In this work, an improved method is developed by implementing a correction factor for the pre-exponential factor caused by the boundary geometry. This method is testified by comparing with experimental data, previous analogy method and numerical simulation. Results show that our proposed method performs a better predictability of MITLs and simplicity. The improved analogy method indicates that the different boundary geometries of a dust deposit significantly impact the apparent pre-exponential factor, while have an ignorable influence on the activation energy, which is also verified by numerical investigations. Furthermore, the numerical model with the corrected kinetic parameters provides a satisfactory explanation compared with experimental observations regarding to temperature and concentration evolutions of dust layers.
Mechanical and microstructural characterisation of multifunctional structural power composites
(2013)
Although the inherent anisotropy of polymer composites has presented daunting technical challenges, these materials now offer engineers considerable opportunities for efficient structural design. More recently, the advent of multifunctional composites which can fulfill more than one role within a system has attracted considerable interest, providing designers with exciting opportunities to innovate. Of particular interest here are structural power composites, which simultaneously carry mechanical load whilst storing/delivering electrical energy. Although the development of these composites is highly challenging, often with conflicting constituent requirements, the STORAGE consortium has had considerable success in the development of these materials for automotive applications.
The focus of this paper is structural supercapacitors, the basic architecture of a single cell of which is shown in Fig. 1. This entails two carbon fibre woven lamina (electrodes) which sandwich a glass fibre woven lamina (separator), all of which is embedded within a multifunctional matrix (electrolyte). This architecture has been the focus of the research to date, leading to components such as that shown in Fig.1 having been fabricated. This paper reports on the mechanical properties and microstructures of the different reinforcement and matrix combinations for structural supercapacitors.
Multifunctional composites which can fulfil more than one role within a system have attracted considerable interest. This work focusses on structural supercapacitors which simultaneously carry mechanical load whilst storing/delivering electrical energy. Critical mechanical properties (in-plane shear and in-plane compression performance) of two monofunctional and four multifunctional materials were characterised, which gave an insight into the relationships between these properties, the microstructures and fracture processes. The reinforcements included baseline T300 fabric, which was then either grafted or sized with carbon nanotubes, whilst the baseline matrix was MTM57, which was blended with ionic liquid and lithium salt (two concentrations) to imbue multifunctionality. The resulting composites exhibited a high degree of matrix heterogeneity, with the ionic liquid phase preferentially forming at the fibres, resulting in poor matrix-dominated properties. However, fibre-dominated properties were not depressed. Thus, it was demonstrated that these materials can now offer weight savings over conventional monofunctional systems when under modest loading.