Dynamic behaviour of composite sandwich beams and plates with debonds

Fibre Reinforced Polymer (FRP) composites are continuing to gain prominence in structural as well as non-structural applications all over the world due to their outstanding properties such as high strength to weight ratio, corrosion resistance, good thermal performance, anti-fire performance and reduction of carbon dioxide emissions both through its method of production and their effective thermal insulation qualities. The increased popularity and demand for FRP composites have spurred research efforts in both academia and civil construction industry. A composite sandwich structural element can be made-up by attaching two thin and stiff skins to a lightweight and thick core, which serves as a building block for constructing laminated structural sandwich composites for civil engineering applications. A structural composite multilayer beam or plate can be manufactured by gluing two or more composite sandwiches together to form a laminated composite. An Australian manufacturer has fabricated a new generation structural Glass Fibre Reinforced Polymer (GFRP) sandwich panel made from E-glass fibre skin and a high strength modified phenolic core for civil engineering applications, the outstanding features of the sandwich material being high strength to weight ratio, good thermal insulation and termite resistance. These features offer the composite panel a wide range of applications in Australian construction industry as structural elements such as beams, slabs, bridge decks and railway sleepers. While sandwich composite construction has some great benefits, the behaviour of sandwich structures containing damage is much more complex and one of the major factors limiting the optimum usage of the same. Although perfect bond between the skin and the core is a common assumption, an important issue that needs to be considered in using a composite beam or slab is the development of debonding between the skin and the core, which is a predominant damage mode of these sandwiches. Interlayer debonding or delamination is also a predominant form of damage phenomenon in laminated composites, which can often be pre-existing or can take place under service conditions. Debonding and delamination cause significant changes in the vibration parameters, such as natural frequencies and mode shapes of structures leading to serviceability issues related to deflection limits. During the design stages of FRP composite structures, it is vital to identify how the global response of these structures will be affected by skin-core debonding and interlayer delamination. Even though the dynamic behaviour of undamaged sandwich panels is the subject of extensive research, papers reported on the dynamic behaviour of sandwich panels with debonding are less presented in the literature. Specifically, knowledge on seismic behaviour of composites with debonds is severely limited. Further research is therefore needed into investigation of the dynamic behaviour of debonded composite structural elements to gain wider acceptance of composites by the structural composite field around the globe. Finite element method is particularly versatile and effective in the analysis of complex structural behaviour of the composite structures. The use of dynamic analysis methods helps the engineer to better understand the behaviour of a structure subjected to an earthquake. This research deals with the investigation of the influence of debonding on the dynamic characteristics of novel GFRP beams and plates by finite element based numerical simulations and analyses using STRAND7 finite element (FE) software package. The research approach is to develop a three dimensional computer model and conduct numerical simulations to assess the dynamic behaviour. The FE model developed has been validated with published experimental, analytical and numerical results for fully bonded as well as debonded beams and slabs. Dynamic seismic response investigation of structures containing GFRP slab panels with debonds subjected to a probable earthquake loading is also incorporated. The influence of various factors such as debonding size, location of debonding, boundary condition of the structural member and the effect of multiple debonding has been delineated with the aid of an extensive parametric investigation and comparative analyses. Generally it was evident from all the analyses that debonding and interlayer delamination cause reduction in magnitudes of natural frequency. Moreover, some vibration modes and accordingly the mode shapes are also noticeably changed. It is generally observed that higher natural frequencies and mode shapes are more influenced by the presence of debonding. Yet there are exceptions to this trend depending on how severely the local modes are affected by debonding. It is observed that the associated mode shapes explain the causes of these inconsistencies. Furthermore, the results show that the presence of relatively small debonding or delamination has an insignificant effect on the natural frequencies and associated mode shapes. The results also suggest that fastening the delamination region is an effective corrective measure in decreasing the natural frequency variation, hence improving its dynamic performance compared to the delaminated panel. To sum up, the results suggest that debonding and delamination predominantly leads to reduction of the natural frequencies and modifying the modes of vibrations thus altering the mode shapes as well, resulting in dramatic changes in dynamic characteristics when extents of debonding are large. The more the supports are restrained, the greater the influence on free vibration characteristics. Most importantly, the findings demonstrate the feasibility of non-destructive methods to detect debonding and delamination damage in practical composite structures. The results of the seismic study show that the seismic performance of the considered buildings is unresponsive to small percentages of debonding of the GFRP slab panels. An existence of extensive percentage of debonding causes a slight increase in the maximum vertical displacement and reduction of natural frequencies of the buildings due to loss of stiffness occurring due to debonding. The results of this study will offer engineers and designers a better understanding of the influence of debonding and delamination on the dynamic performance of FRP composites in general, in addition to its direct application to Australian composite industry. Finally, the study provides valuable insights into the seismic behaviour of composite slabs with debonding thus facilitating the actual application of these findings in worldwide composite industry

The Synthesis and Characterization of Multifunctional Nanoparticles of Elastin-Like Polypeptides for Theranostic Applications

Theranostics is a promising field that aims to combine therapeutics and diagnostics into single multifunctional formulations. This field is driven by advancements in nanotechnology and specifically in the creation of multifunctional nanoparticles capable of providing the necessary functionalities. Elastin-like polypeptides (ELPs) are a class of environmentally responsive biopolymers that are known to undergo a transition in response to various stimuli. The organic nature of ELPs along with the ability to control their design at the gene level and the aforementioned responsive behavior make them a promising candidate for use in theranostic systems. The system presented here is one of the first examples of using ELPs as the base for multifunctional theranostic nanoparticles. Presented in this study is a fully protein based self-assembling nanoparticle system based on micelles of ELPs for use in theranostic applications. Micelle forming ELP constructs have been modified through the fusion of the protein based MRI contrast agent CA1.CD2 to the C terminal of existing protein constructs. Micelles were then crosslinked into stable nanoparticles that relied only on changes in temperature to drive the transition. In addition to that, a targeting peptide has been added to the system as well to provide active targeting to cancer cells. As a contrast agent the system has been shown to bind and retain gadolinium while effectively providing contrast in T1 weighted imaging and having higher relaxivity values than clinical contrast agents. Modification of the architecture of the construct through changes of the tail length, and through creation of mixtures did not drastically affect the behavior of the system demonstrating its flexibility. Here I detail, the design, synthesis of the expression, purification and characterization of all the required properties of the constructs

The Synthesis and Characterization of Multifunctional Nanoparticles of Elastin-Like Polypeptides for Theranostic Applications

Theranostics is a promising field that aims to combine therapeutics and diagnostics into single multifunctional formulations. This field is driven by advancements in nanotechnology and specifically in the creation of multifunctional nanoparticles capable of providing the necessary functionalities. Elastin-like polypeptides (ELPs) are a class of environmentally responsive biopolymers that are known to undergo a transition in response to various stimuli. The organic nature of ELPs along with the ability to control their design at the gene level and the aforementioned responsive behavior make them a promising candidate for use in theranostic systems. The system presented here is one of the first examples of using ELPs as the base for multifunctional theranostic nanoparticles. Presented in this study is a fully protein based self-assembling nanoparticle system based on micelles of ELPs for use in theranostic applications. Micelle forming ELP constructs have been modified through the fusion of the protein based MRI contrast agent CA1.CD2 to the C terminal of existing protein constructs. Micelles were then crosslinked into stable nanoparticles that relied only on changes in temperature to drive the transition. In addition to that, a targeting peptide has been added to the system as well to provide active targeting to cancer cells. As a contrast agent the system has been shown to bind and retain gadolinium while effectively providing contrast in T1 weighted imaging and having higher relaxivity values than clinical contrast agents. Modification of the architecture of the construct through changes of the tail length, and through creation of mixtures did not drastically affect the behavior of the system demonstrating its flexibility. Here I detail, the design, synthesis of the expression, purification and characterization of all the required properties of the constructs

Characterization on the Structure and Dynamics of Protein-Protein Complexes Between Cytochrome P450 and its Redox Partners.

Cytochrome P450s are a ubiquitous superfamily of monooxygenases responsible for the metabolism of thousands of compounds, including steroids, hormones, vitamins, and over 70% of the pharmaceuticals on the current market. They have been found to be related to human diseases including breast cancer and brain cancer. Therefore, it is of great importance to better understand the mechanism of how these enzymes function. In order for cytochrome P450s to complete the catalytic cycle, two electrons are required to be sequentially delivered to cytochrome P450 from its redox partners – cytochrome P450 reductase and cytochrome b5. Mammalian cytochrome P450s and redox partners are membrane bound proteins mostly found on the cytoplasmic side of the endoplasmic reticulum membrane. In order to provide insights into these essential electron-transfer steps, it is important to better understand complex formation between cytochrome P450 and its redox partners. In this thesis, complex formation between cytochrome P450 and cytochrome b5 is investigated under the effect of substrates and membrane. It is found that substrates and lipid bilayer facilitates stronger and more specific binding between the two proteins. Better membrane mimetics are developed in order to provide more physiologically relevant environment for future study on the cytochrome P450 system. A protein-protein complex structure is simulated using a docking program HADDOCK for the FMN binding domain of cytochrome P450 reductase and cytochrome P450. An electron transfer pathway is predicted based on this complex structure. This study provides better understanding on the interaction, binding interface and electron transfer process between the FMN binding domain of cytochrome P450 reductase and cytochrome P450. Substrates are found not to perturb the interaction between these two proteins, but affect the interplay of the three proteins when all of them are present in the same system, unravelling a competitive binding mechanism between cytochrome P450 reductase and cytochrome b5 for binding to cytochrome P450. This result provides structural explanation on the perplexing roles that cytochrome b5 plays in the cytochrome P450 activity and better understanding of substrate modulation on the tertiary protein complex system.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133298/1/zmzt_1.pd

FTIR and X-ray investigation of triphenylene based discotic liquid crystals.

Novel disc like molecules based on hexa-n-alkoxy benzoates of triphenylene were synthesised at Hull university. The compounds exhibited thermotropic liquid crystalline behaviour. The compounds differed chemically based upon the number and position of methyl additions to the ester benzoate linkage. Unsymmetrical compounds based on hexa-n-alkoxy triphenylenes were also examined. A number of techniques were employed to observe and measure the physical properties of these compounds. Polarising optical microscopy was used to observe and record the phase behaviour. Typical schlieren nematic textures were often observed in the liquid crystalline phase. The transition temperatures of the phase transitions were recorded to within +/-0.1 °C. Methyl additions to the ester benzoate linkage plays a major role in determining transition temperatures and also the ranges of liquid crystal phase. X-ray diffraction investigations allowed the molecular planar spacings to be measured, use of a heating stage enabled measurements to be taken in the liquid crystalline phase. All the samples produced a diffuse broad diffraction ring in the liquid crystalline phase, indicating that the samples are not highly ordered and that they are likely to have adopted a hexagonal packing arrangement. Planar spacings measured were in the range 22 - 30A, only one sample, DB26, showed a diffraction ring corresponding to a planar spacing of 4.1A, indicating that molecular columns or partial columns were able to form from molecules stacking one on top of another. Thus methyl groups on the ester benzoate linkage disrupt the formation of columns, in turn reducing transition temperatures. A number of methods of successfully aligning the discotic materials using surface treatments are presented. Rubbed PVA and HTAB layers aligned the samples hometropically, while SiO deposited layers aligned the samples homogeneously. (The SiO deposition used an evaporation angle of 45°, a deposition angle of 5° is commonly used to obtain homotropic alignment of calamitic materials.) Methods that produced homogeonous alignment of calamitic materials produced hometropically aligned discotic materials and vice-versa. FTIR allows conformational information about a molecule to be determined. The CH[2] wagging region was investigated to determine conformational information relating to the alkyl arms. Combination of FTIR and aligned samples allowed the alignment process to be investigated, it was determined that the alignment of the molecules occurs in a series of stages, the triphenylene cores align first on cooling, followed by the ester benzoate linkages and finally the alkyl arms. Computer modelling simulations allowed various molecular conformations to be observed, combination with X-ray diffraction data allowed molecular structures to be generated. The software allowed various molecular dimensions to be easily measured and the effect and extent of interdigitation of molecular arms to be observed. The molecular dynamics calculations were only able to calculate energy minimisations for crystalline structures, but the crystalline results offered valuable insights into the liquid crystalline structures and behaviour

Aeronautical Engineering: A special bibliography with indexes, supplement 75, October 1976

This bibliography lists 300 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1976

Nucleotide-Dependent Preferential Localization of Ras in Model Membranes with Lipid Raft Nanodomains

Membrane proteins constitute a third of all proteins in the cell and more than 50% of drug targets. However, the analysis of membrane proteins has many challenges owing to their partially hydrophobic surfaces, flexibility and lack of stability. One example of an essential membrane protein is Ras superfamily. Ras is a small monomeric GTPase involved in regulation of cell growth, proliferation and differentiation. Therefore, Ras and its effectors are among the most important targets for cancer therapy. A detailed knowledge of the processes occurring during signal propagation via Ras might help to elucidate the mechanisms of the involved signal cascades. The preparation of lipid-modified Ras proteins and their study in the presence of the lipid membrane mimic is the subject of this work. Here we investigate the Ras interaction with lipids in isolation from a possible modulation by other cellular membrane proteins. In our study we focus on a property of Ras that it does not act as an ordinary membrane protein, which stays anchored at the same lipid domain throughout its lifetime. Instead, Ras is capable of moving between raft and disordered lipid domains during its functional cycle. It is suggested that Ras binds to some membrane proteins, and thus changes its localization. We have demonstrated that Ras molecule directly recognizes lipid domains, and its binding affinity depends on the activation state of Ras. The results of this work contribute to the further elucidation of the mechanisms of tumorogenesis and may provide new starting points for further developments in cancer therapy