Modelling of the thermal chemical damage caused to carbon fibre composites

Previous investigations relating to lightning strike damage of Carbon Fibre Composites (CFC), have assumed that the energy input from a lightning strike is caused by the resistive (Joule) heating due to the current injection and the thermal heat ux from the plasma channel. Inherent within this statement, is the assumption that CFCs can be regarded as a perfect resistor. The validity of such an assumption has been experimentally investigated within this thesis. This experimental study has concluded that a typical quasi-isotropic CFC panel can be treated as a perfect resistor up to a frequency of at least 10kHz. By considering the frequency components within a lightning strike current impulse, it is evident that the current impulse leads predominately to Joule heating. This thesis has experimentally investigated the damage caused to samples of CFC, due to the different current impulse components, which make up a lightning strike. The results from this experiment have shown that the observed damage on the surface is different for each of the different types of current impulse. Furthermore, the damage caused to each sample indicates that, despite masking only the area of interest, the wandering arc on the surface stills plays an important role in distributing the energy input into the CFC and hence the observed damage. Regardless of the different surface damage caused by the different current impulses, the resultant damage from each component current impulse shows polymer degradation with fracturing and lifting up of the carbon fibres.This thesis has then attempted to numerically investigate the physical processes which lead to this lightning strike damage. Within the current state of the art knowledge there is no proposed method to numerically represent the lightning strike arc attachment and the subsequent arc wandering. Therefore, as arc wandering plays an important role in causing the observed damage, it is not possible to numerically model the lightning strike damage. An analogous damage mechanism is therefore needed so the lighting strike damage processes can be numerically investigated. This thesis has demonstrated that damage caused by laser ablation, represents a similar set of physical processes, to those which cause the lightning strike current impulse damage, albeit without any additional electrical processes.Within the numerical model, the CFC is numerically represented through a homogenisation approach and so the relevance and accuracy of a series of analytical methods for predicting the bulk thermal and electrical conductivity for use with CFCs have been investigated. This study has shown that the electrical conductivity is dominated by the percolation effects due to the fibre to fibre contacts. Due to the more comparable thermal conductivity between the polymer and the fibres, the bulk thermal conductivity is accurately predicted by an extension of the Eshelby Method. This extension allows the bulk conductivity of a composite system with more than two composite components to be calculated. Having developed a bespoke thermo-chemical degradation model, a series of validation studies have been conducted. First, the homogenisation approach is validated by numerically investigating the electrical conduction through a two layer panel of CFC. These numerical predictions showed initially unexpected current flow patterns. These predictions have been validated through an experimental study, which in turn validates the application of the homogenisation approach.The novelty within the proposed model is the inclusion of the transport of produced gasses through the decomposing material. The thermo-chemical degradation model predicts that the internal gas pressure inside the decomposing material can reach 3 orders of magnitude greater than that of atmospheric pressure. This explains the de-laminations and fibre cracking observed within the laser ablated damage samples. The numerical predictions show that the inclusion of thermal gas transport has minimal impact on the predicted thermal chemical damage. The numerical predictions have further been validated against the previously obtained laser ablation results. The predicted polymer degradation shows reasonable agreement with the experimentally observed ablation damage. This along with the previous discussions has validated the physical processes implemented within the thermo-chemical degradation model to investigate the thermal chemical lightning strike damage

Preliminary Investigation into Modeling The Damage to Carbon Fibre Composites Due to the Thermo-electric Effects of a Lightning Strikes

The impact of a lightning strike causes a short high electrical current burst through Carbon Fibre Composites (CFC). Due to the electrical properties of CFC the large current leads to a rapid heating of the surrounding impact area which degrades and damages the CFC. It is therefore necessary to study in detail the thermal response and possible degradation processes caused to CFC. The degradation takes place in two ways, firstly via direct mechanical fracture due to the thermal expansion of the CFC and secondly via thermo-chemical processes (phase change and pyrolysis) at high temperatures. The main objective of this work is to construct a numerical model of the major physical processes involved, and to understand the correlation between the damage mechanisms and the damage witnessed in modern CFC. For this work we are only considering the thermo-chemical degradation of CFC. Bespoke numerical models have been constructed to predict the extent of the damage caused by the two thermo-chemical processes separately (e.g. a model for phase change and a model for pyrolysis). The numerical model predictions have then been verified experimental by decoupling of the damage mechanisms, e.g. the real Joule heating from a lightning strike is replaced by a high power laser beam acting on composite surface. This was done to simplify the physical processes which occur when a sample is damaged. The experimentally damaged samples were then investigated using X-ray tomography to determine the physical extent of the damage. The experimental results are then compared with the numerical predictions by considering the physical extent of the polymer removal. The extent of polymer removal predicted by the numerical model, solving for pyrolysis, gave a reasonable agreement with the damage seen in the experimental sample. Furthermore the numerical model predicts that the damage caused by polymer phase change has a minimal contribution to the overall extent of the damage

Localization and broadband follow-up of the gravitational-wave transient GW 150914

A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams

Offshore wind farm export cable current rating optimisation

The appropriate sizing of subsea export systems for offshore wind farms presents a number of challenges when striking an appropriate balance between design conservatism and cost effectiveness. Several areas of potential conservatism have been investigated through numerical modelling that has been backed by data that has been obtained from experimental 132kV 3-phase submarine cable

Transport properties and current flow patterns in homogeneous strongly anisotropic materials

A finite element model has been used to study potential distribution and current flow paths in highly anisotropic composite materials. Unexpected results are obtained, which are found consistent with minimising of Joule heat release in the material

Brian Chippendale

Born in 1973, Brian Chippendale grew up around the Philadelphia area. His entry into the Providence art and music scene came after graduating from the Rhode Island School of Design in printmaking in the early 1990s. He began to make posters and comics and was one of four founders of Fort Thunder, a warehouse space in an old textile factory in Olneyville, that was a center for underground art and music from 1995 until 2001. Chippendale is well known as the drummer/vocalist for the noise rock band Lightning Bolt that has performed internationally and released five albums. Chippendale has produced the poster art for Lightning Bolt as well as art comic books including Ninja, Maggots and If’n Oof. networksrhodeisland.orghttps://digitalcommons.risd.edu/alumniwork_networksri_risdalumni/1005/thumbnail.jp

Effects of different components of a lightning strike waveform on the heating of different material: Aluminium Alloys vs. Carbon Fibre

The energy input into a piece of Carbon Fibre Composite due to a lightning strike was investigated. The lightning strike has been broken down into its separate components, i.e. current impulses and the plasma heat flux. The energy deposited into the system from each of these components was examined separately. Before the energy input due to the current impulses could be considered, the AC electrical behave of CFC panels was investigated. The experiments showed that there were no capacitance or inductance effects in the 1 Hz - 1 kHz window. This means the CFCs can be treated as a purely DC resistive material (in this freq. range). A quasi-static DC model was then developed to determine the energy input from each of the lightning components. The model predicts that with CFCs the majority of the damage is caused by current component A