707 research outputs found

    Fractal Analysis of Microstructural and Fractograpghic Images for Evaluation of Materials

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    Materials have hierarchically organized complex structures at different length scales. Quantitative description of material behaviour is dependent on four fundamental length scales [1], which are of concern to materials scientists. These are (1) nano scale, 1-103 nm, (2)micro scale, 1-10 3 μm, (3) macro scale, 1-103mm, and (4) global size scale, 1-106 m. While the nano scale corresponds to, often, highly ordered atomic structures, the global size scale relates geophysical phenomena and large man made engineering structures. Micro scale and macro scale correspond to size of material samples used in laboratories, for designing and for fabrication of miniature to small machineries

    Fatigue crack analysis of ferrite material by acoustic emission technique

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    Among various methods of Non-destructive techniques (NDT), analysis using released acoustic emission (AE) waves due to crack propagation is very effective due to its dynamic monitoring features. In fragmentation theory for AE there are some proportional relationships among the AE parameters i.e. AE event, AE energy, area and volume of cracks etc., which are calculated from the released AE waves from the dynamic crack inside any material. The necessity of calculating the fractal dimension has been found in such relationships and the value is emphasized for determining the geometry of the irregularity in crack surface and crack volume. In this paper a novel approach for evaluating that value based on image processing by MATLAB is proposed. The images of the cracks during propagation are preserved and utilized to find out the fractal dimension for analyzing the crack propagation characteristics. The AE energy is also estimated from the received AE waves. The positioning of the sensors plays a great impact on this calculation. Finally, the theoretical proportionality relations of AE parameters are interpreted experimentally during crack propagation behavior in ferrite cast iron under fatigue loading

    Experimental and Novel Analytic Results for Couplings in Ordered Submicroscopic Systems: from Optomechanics to Thermomechanics

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    Theoretical modelling of challenging multiscale problems arising in complex (and sometimes bioinspired) solids are presented. Such activities are supported by analytical, numerical and experimental studies. For instance, this is the case for studying the response of hierarchical and nano-composites, nanostructured solid/semi-fluid membranes, polymeric nanocomposites, to electromagnetic, mechanical, thermal, and sometimes biological, electrical, and chemical agents. Such actions are notoriously important for sensors, polymeric films, artificial muscles, cell membranes, metamaterials, hierarchical composite interfaces and other novel class of materials. The main purpose of this project is to make significant advancements in the study of such composites, with a focus on the electromagnetic and mechanical performances of the mentioned structures, with particular regards to novel concept devices for sensing. These latter ones have been studied with different configuration, from 3D colloidal to 2D quasi-hemispherical micro voids elastomeric grating as strain sensors. Exhibited time-rate dependent behavior and structural phenomena induced by the nano/micro-structure and their adaptation to the applied actions, have been explored. Such, and similar, ordered submicroscopic systems undergoing thermal and mechanical stimuli often exhibit an anomalous response. Indeed, they neither follow Fourier’s law for heat transport nor their mechanical time-dependent behavior exhibiting classical hereditariness. Such features are known both for natural and artificial materials, such as bone, lipid membranes, metallic and polymeric “spongy” composites (like foams) and many others. Strong efforts have been made in the last years to scale-up the thermal, mechanical and micro-fluidic properties of such solids, to the extent of understanding their effective bulk and interface features. The analysis of the physical grounds highlighted above has led to findings that allow the describing of those materials’ effective characteristics through their fractional-order response. Fractional-order frameworks have also been employed in analyzing heat transfer to the extent of generalizing the classical Fourier and Cattaneo transport equations and also for studying consolidation phenomenon. Overall, the research outcomes have fulfilled all the research objectives of this thesis thanks to the strong interconnection between several disciplines, ranging from mechanics to physics, from structural health monitoring to chemistry, both from an analytical and numerical point of view to the experimental one

    Smart FRP Composite Sandwich Bridge Decks in Cold Regions

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    INE/AUTC 12.0

    Mechanical Wear Debris Feature, Detection, and Diagnosis: A Review

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    Mechanical debris is an important product of friction wear, which is also a crucial approach to know the running status of a machine. Many studies have been conducted on mechanical debris in related fields such as tribology, instrument, and diagnosis. This paper presents a comprehensive review of these studies, which summarizes wear mechanisms (e.g., abrasive wear, fatigue wear, and adhesive wear) and debris features (e.g., concentration (number), size, morphology, and composition), analyzes detection methods principles (e.g., offline: spectrograph and ferrograph, and online: optical method, inductive method, resistive-capacitive method, and acoustic method), reviews developments of online inductive methods, and investigates the progress of debris-based diagnosis. Finally, several notable problems are discussed for further studies. (C) 2017 Chinese Society of Aeronautics and Astronautics

    An experimental rock mechanics investigation into shear discontinuities and their influence in the hydrocarbon resevoir environment

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    Abstract unavailable please refer to PD

    An investigation with fractial geometry analysis of time series

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    Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2005Includes bibliographical references (leaves: 83-84)Text in English; Abstract: Turkish and Englishxiii,94 leavesIn this thesis, three kinds of fractal dimensions, correlation dimension, Hausdorff dimension and box-counting dimension were used to examine time series. To demonstrate the universality of the method, ECG (Electrocardiogram) time series were chosen. The ECG signals consisted of ECGs of three persons in four states for two applications. States are normal, walk, rapid walk and run. These three people are selected from the same age, and height group to minimize variations. First application was made for approximately 1000 samples of size of ECG signals and the second for the whole of the measured ECG signals. Fractal dimension measurements under different conditions were carried out to find out whether these dimensions could discriminate the states under question. A total of 24 ECG signals were measured to determine their corresponding fractal dimensions through the above-mentioned methods. It was expected that fractal dimension values would indicate the states related to the different activities of the persons. Results show that no direct link was found connecting a certain dimension to a certain activity in a consistent manner. Furthermore, no congruence was also found among the three dimensions that were employed. According to these results, it can be stated that fractal dimension values on their own may not be sufficient to identify distinct cases hidden in time series. Time series analysis may be facilitated when additional tools and methods are utilized as well as fractal dimensions at detecting telltale signs in signals of different states

    Delamination effect on response of a composite beam by wavelet spectral finite element method

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    Transform methods are very useful to solve the ordinary and partial differential equations. Fourier and Laplace transforms are the most commonly used transforms. Wavelet transforms are most popular with electrical and communication engineers to analyse the signals. From last few years, Wavelet transforms are in use for structural engineering problems, like solution of ordinary and partial differential equations. Dynamical problems in structural engineering fall under two categories, one involving low frequencies (structural dynamics problems) and the other involving high frequencies (wave propagation problems). Spectral Finite Element (SFE) method is a transform method to solve the high frequency excitation problems which are encountered in structural engineering. SFE based on Fourier transforms has high limitations in handling finite structures and boundary conditions. SFE based with wavelet transforms is a very good tool to analyse the dynamical problems and eliminate many limitations. In this project, a model for embedded de-laminated composite beam is developed using the wavelet based spectral finite element (WSFE) method for the de-lamination effect on response using wave propagation analysis. The simulated responses are used as surrogate experimental results for the inverse problem of detection of damage using wavelet filtering. The technique used to model a structure that, through width de-lamination subdivides the beam into base-laminates and sub-laminates along the line of de-lamination. The base-laminates and sub-laminates are treated as structural waveguides and kinematics are enforced along the connecting line. These waveguides are modeled as Timoshenko beams with elastic and inertial coupling and the corresponding spectral elements have three degrees of freedom, namely axial, transverse and shear displacements at each node. The internal spectral elements in the region of de-lamination are assembled assuming constant cross sectional rotation and equilibrium at the interfaces between the base-laminates and sub-laminates. Finally, the redundant internal spectral element nodes are condensed out to form two-noded spectral elements with embedded de-lamination. The response is being obtained by coding programs in MATLAB

    Fractal Geometry and Porosity

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    A fractal is an object or a structure that is self‐similar in all length scales. Fractal geometry is an excellent mathematical tool used in the study of irregular geometric objects. The concept of the fractal dimension, D, as a measure of complexity is defined. The concept of fractal geometry is closely linked to scale invariance, and it provides a framework for the analysis of natural phenomena in various scientific and engineering domains. The relevance of the power law scaling relationships is discussed. Fractal characteristics of porous media and the characteristic method of the porous media are also discussed. Different methods of analysis on the permeability of porous media are discussed in this chapter
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