Wave interaction with defects in pressurised composite structures

There exists a great variety of structural failure modes which must be frequently inspected to ensure continuous structural integrity of composite structures. This work presents a Finite Element (FE) based method for calculating wave interaction with damage within structures of arbitrary layering and geometric complexity. The principal novelty is the investigation of pre-stress effect on wave propagation and scattering in layered structures. A Wave Finite Element (WFE) method, which combines FE analysis with periodic structure theory (PST), is used to predict the wave propagation properties along periodic waveguides of the structural system. This is then coupled to the full FE model of a coupling joint within which structural damage is modelled, in order to quantify wave interaction coeffcients through the joint. Pre-stress impact is quantified by comparison of results under pressurised and non-pressurised scenarios. The results show that including these pressurisation effects in calculations is essential. This is of specific relevance to aircraft structures being intensely pressurised while on air. Numerical case studies are exhibited for different forms of damage type. The exhibited results are validated against available analytical and experimental results

Accurate structural identification for layered composite structures, through a wave and finite element scheme

We present for the first time an approach for identifying the geometric and material characteristics of layered composite structures through an inverse wave and finite element approach. More specifically, this Non-Destructive Evaluation (NDE) approach is able to recover the thickness, density, as well as all independent mechanical characteristics such as the tensile and shear moduli for each layer of the composite structure under investigation. This is achieved through multi-frequency single shot measurements. It is emphasized that the success of the approach is independent of the employed excitation frequency regime, meaning that both structural dynamics and ultrasound frequency spectra can be employed. It is demonstrated that more efficient convergence of the identification process is attained closer to the bending-to-shear transition range of the layered structure. Since a full FE description is employed for the periodic composite, the presented approach is able to account for structures of arbitrary complexity. The procedure is applied to a sandwich panel with composite facesheets and results are compared with two wave-based characterization techniques: the Inhomogeneous Wave Correlation method and the Transition Frequency Characterization method. Numerical simulations and experimental results are presented to verify the robustness of the proposed method

Wave interaction with nonlinear damage and generation of harmonics in composite structures

© 2019 Elsevier Ltd This work presents a generic Finite Element (FE) based computational scheme for quantifying guided wave interaction with Localised Nonlinear Structural Damage (LNSD) within structures of arbitrary layering and geometric complexity. The through-thickness mode-shape of the structure is obtained through a wave and finite element method. This is applied in a time domain FE simulation in order to generate time harmonic excitation for a specific wave mode. Interaction of the wave with LNSD within the system is computed through an element activation and deactivation iteration. The scheme is validated against experimental measurements and a WFE-FE methodology for calculating wave interaction with damage. Case studies for guided wave interaction with crack and delamination are presented to exhibit the robustness of the proposed method in classifying and identifying damage

Lipid Profile and Liver Histochemistry in Animal Models Exposed to Cigarette Smoke

Cigarette smoke is known to be an important predisposing factor to many diseased conditions, such as cardiovascular diseases, liver disease, atherosclerosis and other metabolic disorders. The aim of this study was to examine the effects of exposure to smoke from burnt cotton wool and cigarette on plasma lipids, liver biochemistry and histology, in adult Wistar rats. The animals were divided into three groups of Control A: exposed to fresh atmospheric air; Group B: exposed to cotton wool smoke; and, Group C, exposed to cigarette smoke; and the experiment lasted for 35 days. The animals exposed to cigarette smoke and cotton wool smoke showed higher values of low density lipoprotein (LDL), and lower values of high density lipoprotein (HDL) compared to the control. The observation of the micro architecture and enzymes of the liver tissue revealed reduction in the number and size of liver cells, numerous fibrous tissues, elevated liver transaminases and reduction in endogenous anti-oxidants, with evidence of fatty degeneration, in animals exposed to cigarette smoke compared to those exposed to cotton wool smoke and fresh atmospheric air. Cigarette smoke caused accumulation of lipids in the liver cells, with evidence of on-going necrosis and fibrosis, which indicated the presence of non-alcoholic fatty liver disease

Lipid Profile and Liver Histochemistry in Animal Models Exposed to Cigarette Smoke

Cigarette smoke is known to be an important predisposing factor to many diseased conditions, such as cardiovascular diseases, liver disease, atherosclerosis and other metabolic disorders. The aim of this study was to examine the effects of exposure to smoke from burnt cotton wool and cigarette on plasma lipids, liver biochemistry and histology, in adult Wistar rats. The animals were divided into three groups of Control A: exposed to fresh atmospheric air; Group B: exposed to cotton wool smoke; and, Group C, exposed to cigarette smoke; and the experiment lasted for 35 days. The animals exposed to cigarette smoke and cotton wool smoke showed higher values of low density lipoprotein (LDL), and lower values of high density lipoprotein (HDL) compared to the control. The observation of the micro architecture and enzymes of the liver tissue revealed reduction in the number and size of liver cells, numerous fibrous tissues, elevated liver transaminases and reduction in endogenous anti-oxidants, with evidence of fatty degeneration, in animals exposed to cigarette smoke compared to those exposed to cotton wool smoke and fresh atmospheric air. Cigarette smoke caused accumulation of lipids in the liver cells, with evidence of on-going necrosis and fibrosis, which indicated the presence of non-alcoholic fatty liver disease