Generation of higher harmonics in longitudinal vibration of beams with breathing cracks

This paper was accepted for publication in the journal Journal of Sound and Vibration and the definitive published version is available at http://dx.doi.org/10.1016/j.jsv.2016.06.025.Classical nonlinear vibration methods used for structural damage detection are often based on higher- and sub-harmonic generation. However, nonlinearities arising from sources other than damage – e.g. boundary conditions or a measurement chain – are a primary concern in these methods. This paper focuses on localisation of damage-related nonlinearities based on higher harmonic generation. Numerical and experimental investigations in longitudinal vibration of beams with breathing cracks are presented. Numerical modelling is performed using a two-dimensional finite element approach. Different crack depths, locations and boundary conditions are investigated. The results demonstrate that nonlinearities in cracked beams are particularly strong in the vicinity of damage, allowing not only for damage localisation but also for separation of crack induced nonlinearity from other sources of nonlinearities

Autoimmune diseases and pregnancy: analysis of a series of cases

BACKGROUND: An autoimmune disease is characterized by tissue damage, caused by self-reactivity of different effector mechanisms of the immune system, namely antibodies and T cells. All autoimmune diseases, to some extent, have implications for fertility and obstetrics. Currently, due to available treatments and specialised care for pregnant women with autoimmune disease, the prognosis for both mother and child has improved significantly. However these pregnancies are always high risk. The purpose of this study is to analyse the fertility/pregnancy process of women with systemic and organ-specific autoimmune diseases and assess pathological and treatment implications. METHODS: The authors performed an analysis of the clinical records and relevant obstetric history of five patients representing five distinct autoimmune pathological scenarios, selected from Autoimmune Disease Consultation at the Hospital of Braga, and reviewed the literature. RESULTS: The five clinical cases are the following: Case 1-28 years old with systemic lupus erythematosus, and clinical remission of the disease, under medication with hydroxychloroquine, prednisolone and acetylsalicylic acid, with incomplete miscarriage at 7 weeks of gestation without signs of thrombosis. Case 2-44 years old with history of two late miscarriages, a single preterm delivery (33 weeks) and multiple thrombotic events over the years, was diagnosed with antiphospholipid syndrome after acute myocardial infarction. Case 3-31 years old with polymyositis, treated with azathioprine for 3 years with complete remission of the disease, took the informed decision to get pregnant after medical consultation and full weaning from azathioprine, and gave birth to a healthy term new-born. Case 4-38 years old pregnant woman developed Behcet's syndrome during the final 15 weeks of gestation and with disease exacerbation after delivery. Case 5-36 years old with autoimmune thyroiditis diagnosed during her first pregnancy, with difficult control over the thyroid function over the years and first trimester miscarriage, suffered a second miscarriage despite clinical stability and antibody regression. CONCLUSIONS: As described in literature, the authors found a strong association between autoimmune disease and obstetric complications, especially with systemic lupus erythematosus, antiphospholipid syndrome and autoimmune thyroiditis

Vibro-impact response of the cracked structures to monitor structural health

A method of simulation is developed for studying the dynamics of the structures with discontinuities using Matlab-Simulink. Simulation and experiments were performed to analyse the nonlinear behaviour of the cracked bar. It is found that the crack-induced nonlinearity leads to the generation of higher harmonics along with side band frequencies. Their intensity diminishes with increase in distance of measurement from the crack. The presence of sideband frequencies indicates modulation of exciting frequency due to systematic interaction of crack faces. The nonlinear transformation of modulated vibration by crack leads to generation of a low frequency periodic component. Its amplitude is proportional to the forced response of the cracked bar at the exciting frequency. The phenomenology described here can be effective for Structural Health Monitoring (SHM)

Vibro-impact response of the cracked structures to monitor structural health

A method of simulation is developed for studying the dynamics of the structures with discontinuities using Matlab-Simulink. Simulation and experiments were performed to analyse the nonlinear behaviour of the cracked bar. It is found that the crack-induced nonlinearity leads to the generation of higher harmonics along with side band frequencies. Their intensity diminishes with increase in distance of measurement from the crack. The presence of sideband frequencies indicates modulation of exciting frequency due to systematic interaction of crack faces. The nonlinear transformation of modulated vibration by crack leads to generation of a low frequency periodic component. Its amplitude is proportional to the forced response of the cracked bar at the exciting frequency. The phenomenology described here can be effective for Structural Health Monitoring (SHM)

Vibro-Impact Response of a Cracked Bar

The presence of a crack in a structure affects its dynamic behaviour under working conditions. Cracks introduce nonlinearities into the system; the use of such nonlinearities for damage detection should be investigated. A model of a one-dimensional cracked cantilever bar subjected to longitudinal harmonic excitation is used to analyse a vibro-impact response as a way to monitor structural health. The effect of contact nonlinearity due to crack's faces interaction is considered. This nonlinear information is obtained based on a combination of the analytical technique and the Matlab-Simulink computation. The procedure uses a numerical approximation for dynamic compliance operators and a nonlinear model of contact faces interaction implemented numerically as a nonlinear feedback. Nonlinear resonant phenomena due to vibro-impact interaction in the cracked bar are obtained and analysed. A distribution of the higher harmonics along the bar length, generated due to the nonlinear response of the crack, is revealed as a function of the distance from the crack. Recommendations on structural health monitoring of cracked bars due to contact nonlinearity are presente

Development of Texture and Microstructure During Cold Rolling and Annealing of a Fe-Based Shape Memory Alloy

Texture evolution and microstructural changes during cold rolling and annealing of Fe-14Mn-6Si-9Cr-5Ni shape memory alloy have been investigated. The starting solution-annealed material has a nearly random texture with microstructure composed of equiaxed austenite grains with epsilon martensite plates inside. Cold rolling induces a strong alloy type texture with Brass {011}aOE (c) 211 > and Goss {011}aOE (c) 100 > as major components. Annealing of the cold-deformed material produces a nearly random texture. The microstructural investigation reveals that with increase in cold deformation, the amount of stress-induced epsilon and alpha' martensite volumes increase. The electron back-scattered diffraction (EBSD) phase mapping shows that reversion of the epsilon martensite begins only after recrystallization sets in at a temperature of 1073 K

Exact vacuum solutions of six dimensional Bianchi Type-I space-time in f (R) theory of gravity

In this paper, we have extended the five dimensional work refer it to [2] regarding the accelerating expansion of the universe to higher six dimension and obtained exact vacuum solutions of six dimensional Bianchi type-I space time in f (R) theory of gravity using metric approach. In particular, two different models of the universe have been investigated using the law of variation of Hubble parameter. We observed that, the first model is singular and second one is non singular. The physical properties of these models have been discussed and evaluated function of Ricci scalar, f (R) for both the models. It is interesting to note that, our five dimensional work explained in [2] and the work of M. Sharif and M. Farasat Shamir ( (2009) in 4 V regarding the universe expansion can be reproduced by reducing the dimensions

Acquired pure red cell aplasia in a child

Primary acquired pure red cell aplasia is a rare occurrence in childhood. An eleven-year old boy presented to us with pallor, which required multiple packed red cell transfusions. He did not have hepatosplenomegaly, jaundice or lymphadenopathy. Bone marrow examination revealed the diagnosis of pure red cell aplasia. All possible investigations were done to exclude secondary causes of pure red cell aplasia. No secondary cause was found on investigations. Rheumatoid factor and anti-nuclear antibodies were positive. He was started on oral steroids, to which he did not respond. He was then given cyclosporine A. Response to cyclosporine was dramatic and the child now does not require any transfusions

Role of grain/Phase boundary nature on the formation of hydrides in Zr-2.5% Nb alloy

Hydride formation in a fully recrystallized Zr-2.5%Nb alloy having equiaxed grains of α and β was studied. Primarily the electron back scatter diffraction (EBSD) technique was used for the characterization of the hydrides in conjunction with optical and transmission electron microscopy. Hydrides were found to have preferentially formed along the α/β interfaces. Microtexture measurements showed that the orientation relationship (OR) between α and δ -hydride phase was (0 0 0 1)<SUB>α</SUB> || (1 1 1)<SUB>δ</SUB> and [21<SUP>‾</SUP>10]<SUB>α</SUB> || [1 1 0]<SUB>δ</SUB>. It was shown that the hydrides have higher preference to form along such α/β interfaces which have one of the low index planes of the β phase constituting the interface

Automated reconstruction of pre-transformation microstructures in zirconium

An automated reconstruction of the pre-transformation microstructure from the microtexture data of the post-transformation product phase is proposed. The method involves identifying triplets of neighboring product grains with a common variant and linking such neighboring triplets via a generalized misorientation criterion. The approach is non-iterative and extremely efficient computationally. The method was tested successfully for different post-transformation microstructures in zirconium