Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Micromechanical analysis of the effective elastic properties of carbon nanotube reinforced composites

We seek to obtain continuum level elastic properties for carbon nanotubes and carbon nanotube reinforced composites through a variety of micromechanics techniques. Using the in-plane elastic properties of graphene sheets the effective properties of carbon nanotubes are calculated using a modified composite cylinders micromechanics technique to treat the hollow nanotube as a transversely isotropic solid cylinder. Effective properties found for single-walled carbon nanotubes in this fashion are found to be in good agreement with both experimentally and theoretically obtained results available in the literature. Having a solid fiber then allows for the calculation of an Eshelby tensor and hence, the use of additional more advanced micromechanics techniques to calculate carbon nanotube reinforced composite effective elastic properties. In what are termed two-step approaches, the generalized self-consistent and Mori-Tanaka micromechanics techniques are employed to obtain effective elastic properties of composites consisting of aligned single or multi-walled effective carbon nanotubes embedded in a polymer matrix of EPON 862 at various effective carbon nanotube volume fractions. These results are compared to a single step composite cylinders approach wherein an additional phase consisting of the polymer matrix is placed around the carbon nanotube prior to obtaining the effective carbon nanotube properties, thereby obtaining the effective composite properties in a single calculation. It is found that the two-step Mori-Tanaka results yield nearly identical results as the single step composites cylinders approach. Finally, it has been observed in the literature that electrostatic clumping of nanotubes into nanotube bundles complicates the adequate dispersion of the nanotubes within the polymer matrix. The quantification and modeling of this clustering in aligned nanotube composites is accomplished herein using Dirichlet tessellation in conjunction with an n-phase generalized self-consistent technique. It is observed that the effect of clustering is to reduce in magnitude only the transverse to fiber alignment properties of the transversely isotropic effective composite as compared to the randomly distributed aligned carbon nanotube composite’s effective elastic properties, and that this reduction in transverse elastic properties increases with increasing global volume fraction of effective carbon nanotubes. Results indicate that, while the clustering effect does contribute to some reduction in composite properties, other factors such as cluster misalignment and poor fiber-matrix bonding may play a significantly larger role. Nomenclature 11 E = the one-direction Young’s modulus 12 ν = the one-direction Poisson’s ratio 23 κ = the 2-3-plane bulk modulus 12 μ = the 1-2-plane shear modulus 23 μ = the 2-3 plane shear modulus A E = the axial Young’s modulus of a fiber

Effective Elastic Properties of Carbon Nanotube Reinforced Composites

A composite powder with a fine homogeneous distribution of the reinforcement phase in the whole particle can be obtained by mechanical alloying. Aluminium PM6061 unreinforced, and matrix composite reinforced with Si 3 N 4 and AlN powder, are milled in a high-energy attritor mill and the powder properties are compared with those of the same composite composition mixed in a horizontal low-energy ball mill. The correlation observed between the apparent densities and the milling time, explained by the morphological and microstructural evolution of the powder particles during the high-energy milling process, is used to determine the steady state of the process. At short milling times, the apparent density decreases as the milling time is extended, due to the deformation dominant at this stage; at longer milling times, it starts to increase with increasing milling time due to the piling up of the flattened particles and fracture of the welded particles. When mechanical alloying reaches the steady state, the apparent density is stabilized. A simple model is proposed to illustrate the mechanical alloying of a ductile–brittle component system. The particle size distribution and the microhardness of the mechanically alloyed particles are determined.

Effect of mechanical alloying on the morphology, microstructure and properties of aluminium matrix composite powders

A numerical investigation of the effect of particle clustering on the mechanical properties of composites

Age forming of Al based alloys for damage tolerant applications requires an alloy with good age formability and good post-forming mechanical properties. To investigate optimisation of this balance, several newly designed Al–Cu–Mg–Li (Mn, Zr, Sc) alloys were subjected to artificial ageing representative of age forming. It was seen that combinations of yield strength and fatigue crack growth resistance could be achieved that are at least comparable to the incumbent damage tolerant material for such applications, whilst creep rates at the ageing temperatures applied were better than those achieved in commercially applied age forming processes of heat treatable Al based alloys. Coarse grain structure and high Li content are associated with good fatigue crack growth resistance but reduce age formability. The underlying physical aspects responsible for the balance between creep rates and resulting properties are discussed. The metallurgical and micromechanical mechanisms analysed and discussed provide a framework for optimisation of composition and forming conditions for age forming of damage tolerant parts.

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Relations between microstructure, precipitation, age-formability and damage tolerance of Al-Cu-Mg-Li (Mn,Zr,Sc) alloys for age forming

Various reports in the literature have highlighted the effects of particle distribution on the fatigue behaviour of particulate reinforced metal matrix composites (PMMCs), although few attempts have been made at modelling such effects. A micromechanical understanding of the effects of clustering on short crack growth behaviour in Al–SiCp composites has been achieved via finite element modelling. Comparison of preliminary models with the literature has shown that shielding/anti-shielding effects were significantly affected by the relative sizes of the particle and the overall model such that, when edge effects were removed, a crack was predicted to be accelerated rather than decelerated as it propagated through closely spaced pairs of particles. Consistent differences were identified between models with homogeneous versus clustered particle arrangements in terms of crack path morphologies and local crack–tip stress intensity fluctuations. Furthermore, predicted influences of clustering on growth rates in the numerical models were found to be consistent with previous experimental results (i.e. growth rates rose with increased clustering), demonstrating that load transfer effects associated with changes in particle distribution may play a direct role in controlling the growth of short cracks in these materials.

Numerical modelling of particle distribution effects on fatigue in Al–SiCp composites

The suitability of age forming for the shaping of damage tolerant structures is investigated by formulating and testing new alloy-age forming combinations. The alloy formulation process is driven initially by modelling of strength and semi-quantitative understanding of other microstructure-property relations. Using this a range of Al-Cu-Mg-Li-(Zr-Mn) based alloys predicted to provide yield strengths in aged condition comparable with incumbent 2024-T351 alloy for lower wing skins are selected. It is shown that several of these new alloys after artificial aging representative of age-forming have proof strength (PS), fatigue crack growth resistance (FCGR) and toughness that are comparable or better than 2024-T351. UTS to PS ratios of the new alloys are lower than 2024-T351.

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P.D. Pitcher

Papers

Relations between microstructure, precipitation, age-formability and damage tolerance of Al-Cu-Mg-Li (Mn,Zr,Sc) alloys for age forming

Numerical modelling of particle distribution effects on fatigue in Al–SiCp composites

Development of New Damage Tolerant Alloys for Age-Forming

Quantitative assessment of particle distribution effects on short crack growth in SiCp reinforced Al-alloys

Numerical Modelling of Particle Distribution Effects on Fatigue in Al-SiCp Composites