Browsing by Author "Mills, Andrew R."

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    Accommodating repair actions into gas turbine prognostics
    (PHM Society, 2013-10-08) Skaf, Zakwan; Zaidan, Martha A.; Harrison, Robert F.; Mills, Andrew R.
    Elements of gas turbine degradation, such as compressor fouling, are recoverable through maintenance actions like compressor washing. These actions increase the usable engine life and optimise the performance of the gas turbine. However, these maintenance actions are performed by a separate organization to those undertaking fleet management operations, leading to significant uncertainty in the maintenance state of the asset. The uncertainty surrounding maintenance actions impacts prognostic efficacy. In this paper, we adopt Bayesian on-line change point detection to detect the compressor washing events. Then, the event detection information is used as an input to a prognostic algorithm, advising an update to the estimation of remaining useful life. To illustrate the capability of the approach, we demonstrated our on-line Bayesian change detection algorithms on synthetic and real aircraft engine service data, in order to identify the compressor washing events for a gas turbine and thus provide demonstrably improved prognosis.
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    Comparative study of strain energy storage mechanisms between carbon fibre-reinforced peek and epoxy composites subjected to static and cyclic loading
    (European Society for Composite Materials, 2018-06-30) Hernandez, Thibault. P. A.; Mills, Andrew R.; Yazdani Nezhad, Hamed
    Experimental studies were performed on the strain energy storage behaviour of aerospace grade PEEK and toughened epoxy carbon fibre-reinforced composite prepreg laminates having identical fibre content. The strain energy stored up to failure was recorded at the highest point of deflection for static three point bending (3PtB) samples laminates with different thicknesses. Ductile and brittle behaviors at failure have been the key focuses of this study therefore cyclic loading tests were also performed. Firstly, high strain 3PtB fatigue loading was carried out on the two prepregs with identical quasiisotropic stacking sequences, and secondly in order to characterise the plasticity parameters for the two laminates cyclic shear tests at high strain levels was carried out. The results have shown that the strain energy storage characteristics of the PEEK laminates are much better than those of the epoxy laminates in several ways; such as the independence of the strain energy storage level to thickness. Furthermore, at the same level of applied stress, the PEEK laminates tend not to lose strain energy compared to the toughened epoxy laminates. This study shows that the thermoplastic nature of the PEEK gives it an improved plasticity level which enhances its strain energy storage capability. PEEK carbon laminates are therefore serious candidates for spring applications.
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    Shear driven deformation and damage mechanisms in high-performance carbon fibre-reinforced thermoplastic and toughened thermoset composites subjected to high strain loading
    (Elsevier, 2020-11-11) Hernandez, Thibault. P. A.; Mills, Andrew R.; Yazdani Nezhad, Hamed
    High strain loading response of high-performance aerospace grade polyether-ether-ketone (PEEK) and toughened epoxy carbon fibre-reinforced composites has been investigated in pre-impregnated laminates having identical carbon fibre volume fraction, i.e. nearly 65%. Tensile cyclic loading tests have been carried out on the laminates with [±45°]8S stacking sequence, in order to characterise inelastic (plasticity) parameters for the two laminates progressively up to high strains (up to 11% strains), in correlation with the fibre and matrix micro-scale deformation and damage characteristics. The most suitable processes to achieve ultimate mechanical performance were used for manufacturing of the laminates. It has been observed that the PEEK composite exhibits higher mechanical performance at high strains under cyclic loads compared to epoxy composites (150% ultimate failure strain, 380% strain hardening and 200% ultimate failure stress) due to having superior micro-scale shear deformation in PEEK attributed to. interfacial strength of fibre-matrix prior to the ultimate failure, as opposed to extensive micro-cracking, coalescence and fibre-matrix debonding in the epoxy composite