bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation on Improving Electromechanical Impedance Based Damage Detection by Temperature Compensation
Authors: Siebel Thomas , Lilov Mihail
Published: July 2013

The sensitivity of the electromechanical impedance to structural damage under varying temperature is investigated in this paper. An approach based on maximizing cross-correlation coefficients is used to compensate temperature effects. The experiments are carried out on an air plane conform carbon fiber reinforced plastic (CFRP) panel (500mm x 500mm x 5mm) instrumented with 26 piezoelectric transducers of two different sizes. In a first step, the panel is stepwise subjected to temperatures between-50 °C and 100 °C. The influence of varying temperatures on the measured impedances and the capability of the temperature compensation approach are analyzed. Next, the sensitivity to a 200 J impact damage is analyzed and it is set in relation to the influence of a temperature change. It becomes apparent the impact of the transducer size and location on the quality of the damage detection. The results further indicate a significant influence of temperature on the measured spectra. However, applying the temperature compensation algorithm can reduce the temperature effect at the same time increasing the transducer sensitivity within its measuring area. The paper concludes with a discussion about the trade-off between the sensing area, where damage should be detected, and the temperature range, in which damage within this area can reliably be detected.
RFID Based Sensing for Structural Health Monitoring
Authors: Lisowski Mateusz , Uhl Tadeusz
Published: July 2013

RFID is a rapidly developing technology of wireless communication and identification mostly used in supply chain systems, logistic and access control. Nowadays attempts to transfer this technology to other applications are carried out. This paper presents review of global researches performed last years, on application of RFID technology to tasks connected with wireless passive sensing in Structural Health Monitoring, with additional overview of works conducted in this subject by the authors. Sensors based on this technology require neither battery nor wire. It could be interrogated from distance, its lifetime is almost unlimited. Investigations, focused both on using RFID transponder as a sensing element, as well as, using antenna as a energy harvesting part that could power the sensor circuit, are mentioned. Performed studies show, that despite problems connected with using high frequencies, described wireless sensors should be useful for SHM tasks.
Structural Health Monitoring under Varying Environmental Conditions Using Wavelets
Authors: Tjirkallis Andreas , Kyprianou Andreas , Vessiaris George
Published: July 2013

A novel structural health monitoring system to detect damages in structures under varying operational and environmental conditions is presented in this paper. A noncontact, full-field measurement using a high speed camera offers a convenient and less expensive measurement procedure, enabling the measuring of responses in elevated temperatures and in conditions where contact sensors are unable to be used. In this paper, a combination of Decay lines of the Wavelet Transform Modulus Maxima (WTMM) and Holder Exponent (HE) are used to distinguish changes on the time response of a vibrating structure due to the operational and environmental variations to changes due to the presence of damage, thus minimising the possibility of false alarm. The proposed methodology is demonstrated using a 3-DOF system under conditions of varying and constant temperatures with the presence of damage, as well as using an experimental setup of a cantilever beam under intact and damaged conditions.
Damage Assessment in a Cracked Fiber-Reinforced Cantilever Beam Using Wavelet-Kurtosis Techniques
Authors: Montanari L. , Basu Biswajit , Spagnoli Andrea , Broderick B.
Published: July 2013

In the last decades the use of composite materials has increased especially in light-weight structural applications, such as wind turbine blades. These structural components require reliable methods for damage assessment to avoid progressive or sudden and catastrophic failures. In this paper, a model of a fiber-reinforced composite cantilever beam with a bridged edge crack, representing an existing damage state, is considered. The composite matrix of the beam exhibits a linear-elastic behavior, whereas a fracture mechanics-based theoretical model incorporating the crack bridging forces in the fiber-reinforcement is used to describe the elastic-plastic response of the cracked beam section subjected to bending moment. This model is employed to simulate the nonlinear static deflection of cantilever beams with different crack locations and depths. Wavelet and kurtosis-based identification techniques are employed in the localization and calibration of this damage in presence of noise. The influence of the bridging effect of the fibers on the success of the damage assessment is discussed.
Application of Multiple Objective Particle Swarm Optimisation in the Design of Damaged Offshore Mooring Systems
Authors: Wang Zhuo , McCarthy Timothy  J. , Sheikh M. Neaz
Published: July 2013

The offshore hydrocarbon industry operates in more hostile environments as more of marginal fields become economically viable. This means that more floating production systems and economical mooring systems will be needed. With this increase in the use of marginal fields goes the need to re-use vessels and moorings. Floating production systems, such as FPSOs, need to survive extreme events and extreme damage conditions. When one mooring line is damaged, the remaining ones must be sufficient to avoid a complete failure and still protect critical components such as the riser. This paper looks into applying an evolutionary optimisation technique, namely multiple objective particle swarm optimisation, to the damaged mooring design and analysis. The evaluation of offshore objective functions is computationally expensive since it requires use of complex simulations. When the number of objective function evaluations is large, as is the case with evolutionary methods, even a fast computer takes undesirably long to complete the job. Hence, a robust optimisation algorithm with great efficiency is required to minimise the number of total runs.
Evaluation of Timber-Concrete Floor Performance under Occupant-Induced Vibrations Using Continuous Monitoring
Authors: Omenzetter Piotr , Kohli Varun , Desgeorges Yohann
Published: July 2013

This paper describes the design of a system to monitor floor vibrations in an office building and an analysis of several months worth of collected data. Floors of modern office buildings are prone to occupant-induced vibrations. The contributing factors include long spans, slender and flexible designs, use of lightweight materials and low damping. As a result, resonant frequencies often fall in the range easily excited by normal footfall loading, creating potential serviceability problems due to undesirable levels of vibrations. This study investigates in-situ performance of a non-composite timber-concrete floor located in a recently constructed innovative multi-storey office building. The floor monitoring system consists of several displacement transducers to measure long-term deformations due to timber and concrete creep and three accelerometers to measure responses to walking forces, the latter being the focus of this paper. Floor response is typically complex and multimodal and the optimal accelerometer locations were decided with the help of the effective independence-driving point residue (EfI-DPR) technique. A novel approach to the EfI-DPR method proposed here uses a combinatorial search algorithm that increases the chances of obtaining the globally optimal solution. Several months worth of data collected by the monitoring system were analyzed using available industry guidelines, including ISO2631-1:1997(E), ISO10137:2007(E) and SCI Publication P354. This enabled the evaluation of the floor performance under real operating conditions.
The Concept of Buildings Stability Monitoring and Damage Diagnostics
Authors: Volkovas Vitalijus
Published: July 2013

The concept of the buildings stability, based on experimental methodology consists of objective monitoring of the parameters defined by modelling and control using hardware tools, i.e. systems monitoring and diagnostics, which allows generating appropriate response to emerging defects, their fixing and prognosis of their location. In the framework of the problem of buildings stability the complex research was done in which mathematical models of buildings construction were created, defects identification method developed and also monitoring concept was composed according which automated monitoring system and software prototypes and structures were implemented. The strategic aim of the development of buildings monitoring system was realized by mathematical and physical modelling of the damages (e.g. defects like crack or destroy of linkage); analysis of characteristics sensitive to defects; selection of stability parameters and measurements; creation of automated system prototype; investigation of the methods applied for the monitoring system and diagnostics; development of software and separate elements of the system and approbation of the whole complex. Thorough evaluation of the technical state of the buildings numerical is executed using physical models and natural objects which support reliable state identification of the building and also helps to track changes.
Rapid Assessment of Natural Periods of Large Short-Period Civil Engineering Structures
Authors: Pakrashi Vikram , Basu Biswajit , Ryan Kevin
Published: July 2013

Rapid assessment of large, short-period structures is extremely important for establishing structural integrity. This paper demonstrates experimental non-contact detection of consistent frequency peaks from the ambient vibration of a range of large buildings. Long distance, remote Laser Doppler Vibrometry is employed to estimate the dominant response frequencies of these large building structures from their ambient vibration. These dominant frequencies were reproducible in the frequency domain. The results demonstrate potential field applications of this method in a number of important applications. Such applications include model-free and rapid assessment or monitoring of historical structures, strategically important structures, lifelines, assessment and monitoring of structures such as nuclear facilities and rapid evaluation of large scale structures following disasters. Empirical formulas specified in codes do not cover such special structures and experimental determination of periods employing the method proposed may thus become essential.
The Sensitivity of Vibration Characteristics of Reinforced Concrete Beams under Incremental Static and Cyclic Loading
Authors: Hamad Waleed I. , Owen John S. , Hussein Mohammed F.M.
Published: July 2013

The use of changes in vibration properties for global damage detection and monitoring of existing concrete structures has received great research attention in the last three decades. To track changes in vibration properties experimentally, structures have been artificially damaged by a variety of scenarios. However, this procedure does not represent realistically the whole design-life degradation of concrete structures. This paper presents experimental work on a set of damaged reinforced concrete beams due to different loading regimes to assess the sensitivity of linear and non-linear vibration characteristics. Of the total set, three beams were subject to incremental static loading up to failure to simulate overloading, and two beams subject to 15 million loading cycles with varying amplitudes to produce an accelerated whole-life degradation scenario. To assess the vibration behaviour in both cases, swept sine and harmonic excitations were conducted at every damage level. The results show that resonant frequencies are not sensitive enough to damage due to cyclic loading, whereas cosh spectral and root mean square distances are more sensitive, yet more scattered. In addition, changes in non-linearity follow a softening trend for beams under incremental static loading and are significantly inconsistent for beams under cyclic loading. Amongst all examined characteristics, changes in modal stiffness are found to be most sensitive to damage and least scattered, but modal stiffness is tedious to compute due mainly to the difficulty of constructing restoring force surfaces from field measurements.
Identification of Composite Delamination Using the Krawtchouk Moment Descriptor
Authors: Wang Wei Zhuo , Wang De Zhi , Mottershead John E. , Lampeas George
Published: July 2013

Damage assessment of composite materials is crucial for health monitoring of engineering structures. It is particularly important to detect damage invisible to the human eye caused by low speed impact. Optical non-contact sensing techniques enable full-field measurements from structural responses. However, damage is generally associated with its local effect on deformation and strain patterns while full-field measured data is highly information redundant. It is possible to apply image processing techniques [1, 2] to extract succinct and efficient features, or attributes, from full-field data. Iterative reanalysis of large and detailed numerical models is generally very expensive and may not be feasible. Meta modeling is one of the practical ways to overcome the problem of high computational cost. In this paper, a case study of composite delamination assessment based on simulation is discussed. The damage mode in the composite plate is assumed to be a delamination of elliptical shape. Surface strain of a specimen under tensile loading is considered to be the measured structural output. The Krawtchouk moment descriptor is applied to extract a small number of features from the strain map. A meta model in the form of a Kriging predictor [3] is constructed to map the damage parameters to Krawtchouk shape features of the strain distribution. The delamination region is quantified using an inverse procedure based on the trained Meta model. Furthermore, a biomimicry algorithm, particle swarm optimisation, is applied to detect the location of the delamination.
Dynamic Testing and Long Term Monitoring of a Twelve Span Viaduct
Authors: Chen Xing Hua , Omenzetter Piotr , Beskhyroun Sherif
Published: July 2013

Because of the critical importance of bridges in land transport networks and broader economy, an increasing interest in permanent observation of their dynamic behavior under traffic, seismic and other live loads has been observed during the past decade. In addition, recent technological advances have made the installation and operation of permanent dynamic monitoring systems much more practical and economical. A multi-channel dynamic monitoring system is being installed in the 12 span pre-cast, post-tensioned Newmarket Viaduct, recently built using the balanced cantilever method and situated in Auckland, New Zealand. This paper first describes the preliminary studies including extensive one-off ambient vibration tests using wireless sensors that provided important information for the design of the monitoring system shortly after construction of the bridge. Then the designed monitoring system is characterized and proposed research that will be undertaken using the monitoring data is outlined.
Failure Stress in Notched Paper Sheets
Authors: Mora Santos Carlos A. , Susarrey Huerta Orlando , Flores Lara Vicente , Bedolla Hernández Jorge , Mendoza Nuñez Maribel A.
Published: July 2013

In this work the crack initiation stress of notched specimens of filter paper is studied. The paper in the microstructure has a random array in their fibers while macroscopically it behaves anisotropically. The self-affine crack mechanics is used to study the size effect in the tensile behavior of this kind of paper under the presence of several conditions of geometrical notches. While in the traditional fracture mechanics the crack initiation stress is a material parameter when is reached a critical level at the crack tip, in the self-affine crack mechanics, depends moreover of the resulting tortuosity of the crack. Four geometrical arrangements in two sizes we considered: centered circular notch, centered lineal notch, sided circular notches and without notch at 10 and 300 mm width with a relation 2a/w = 0.25 under the same loading conditions. In this, the without notch specimens present the higher stress, all other notched specimens presented a similar crack initiation stress about 1 % of difference among them, and the crack growth is not affected by the geometry of notch. In spite of this difference, no one of the specimens reach the theoretical stress concentration of 3 such as predicted the classical stress theory.
Detection of Bearing Spalling Faults Using IAS Monitoring System - Experimental Studies on the Influence of Operating and Environmental Parameters
Authors: Bourdon Adeline , André Hugo , Rémond Didier
Published: July 2013

Experimental works carried out in recent years have demonstrated the feasibility of detecting a bearing fault through the spectral analysis of the Instantaneous Angular Speed (IAS) in the angular domain. Since these works have been carried out on complex mechanical systems (automotive gearboxes, vehicle wheels, wind turbines), neither the influence of operating parameters, nor the influence of structural parameters over the observed angular speed variations have been clearly identified. However, the implementation of effective tools for condition monitoring prospects requires a deep understanding of these interactions. In this regard, a test bench has been designed to allow defective bearing monitoring through IAS observation of a simple shaft running under varying loads and speeds, the system being simple enough to be easily described in various kind of mechanical or phenomenological models. The aim of this paper is to present a better understanding of the relationships between the speed variation induced by the monitored fault, the structural response and the observed phenomena. In the first part results obtained for a healthy bearing will be analyzed. These initial results serve as a reference for analysis of the results obtained with bearing defects. Coupled with dynamic modeling, they will also highlight the existence of a low frequency torsion mode. The results of this first part also highlight the wider interest of the IAS analysis for the study of rotating systems. In a second part, the measurements are performed with bearings having spalling type defects on their outer ring. The aim of this section is to estimate the influence of operating conditions on IAS monitored indicators. All these results will provide further phenomenological explanations of coupling between bearing fault and rotating speed.
Utilizing Data from a Sensorless AC Variable Speed Drive for Detecting Mechanical Misalignments
Authors: Abusaad Samieh , Benghozzi Ahmed , Shao Yi Min , Gu Feng Shou , Ball Andrew
Published: July 2013

Conventional condition monitoring techniques such as vibration, acoustic, ultrasonic and thermal techniques require additional equipment such as sensors, data acquisition and data processing systems which are expensive and complicated. In the meantime modern sensorless flux vector controlled drives can provide many different data accessible for machine control which has not been explored fully for the purpose of condition monitoring. In this paper polynomial models are employed to describe nonlinear relationships of variables available from such drives and to generate residuals for real time fault detection and performance comparisons. Both transient and steady state system behaviours have been investigated for optimal detection performance. Amongst 27 variables available from the drive, the torque related variables including motor current, Id, Iq currents and torque signals show changes due to mechanical misalignments. So only these variables are explored for developing and optimising detection schemes. Preliminary results obtained based on a motor gearbox system show that the torque feedback signal, in both the steady and transient operation, has the highest detection capability whereas the field current signal shows the least sensitivity to such faults.
Non-Linear Aeroelastic Stability of Wind Turbines
Authors: Zhang Z.L. , Sichani M.T. , Li Jie , Chen J.B. , Nielsen S.R.K.
Published: July 2013

As wind turbines increase in magnitude without a proportional increase in stiffness, the risk of dynamic instability is believed to increase. Wind turbines are time dependent systems due to the coupling between degrees of freedom defined in the fixed and moving frames of reference, which may trigger off internal resonances. Further, the rotational speed of the rotor is not constant due to the stochastic turbulence, which may also influence the stability. In this paper, a robust measure of the dynamic stability of wind turbines is suggested, which takes the collective blade pitch control and non-linear aero-elasticity into consideration. The stability of the wind turbine is determined by the maximum Lyapunov exponent of the system, which is operated directly on the non-linear state vector differential equations. Numerical examples show that this approach is robust for stability identification of the wind turbine system.
Impact Localisation in Orthotropic Plates Using Flexural Wave Intensity Measurement
Authors: Halkyard C.R. , Masson Patrice
Published: July 2013

In this paper, a method for the localisation and quantification of impacts on orthotropic plates, based on the measurement of the resulting vibrational energy flow, or structural intensity, is presented. The outputs of a compact array of bonded piezo-electric sensors are digitally filtered and combined to yield a local estimate of the instantaneous vibrational energy flow. In the case of transient vibration due to an impact, two or more such estimates can be used to localise the point of impact. The use of energy flow vectors for localisation requires a priori knowledge of the material properties, but may provide more direct access to position information than conventional techniques. Furthermore, the magnitude of the measured energy flow, when combined with knowledge of the impact location, can provide a quantitative measure of impact severity. The approach is based on Kirchhoff orthotropic plate theory, and is thus applicable to low frequencies, and utilises instantaneous estimates of the local wave field to allow the estimation of the various forces, moments and velocities that are required to calculate the vibrational energy flow. The theoretical background and principles of implementation of the approach are outlined, and the effects of sensor array design on systematic errors and sensitivity to measurement noise are discussed. Numerical simulations are used to assess the effectiveness of the technique and to determine its sensitivity to noise and other errors. These simulations suggest that the obtained energy flow estimates can be used for impact localisation.
Sensors and Methods for Blade Damage Operational Assessment in Low-Pressure Steam Turbine Stages
Authors: Procházka Pavel , Vaněk František
Published: July 2013

The study deals with the opportunities for the assessment of damage to blades in low-pressure steam turbine stages under operation. So far existing methods are based on measurements and evaluation of blade vibrations. Calculations of fatigue cycles are used as a basis for an estimate of the residual life of the blades. A new approach using the analysis of impulse blade signals generated by non-contact stator sensors was applied. Basis for the assessment of blade damage are static characteristics and mutual position of blades. Geometrical and mechanical characteristics of blades change due to creation and progress of a crack. The presence of the crack leads to a change in position between adjacent blades. This method has been applied and verified by long-term measurements at the nuclear power plant Temelin. Other static methods based on blade untwisting and elongation are suggested for monitoring the state of turbine blades.
Interpolation Damage Detection Method on a Suspension Bridge Model: Influence of Sensors Disturbances
Authors: Domaneschi Marco , Limongelli Maria Pina , Martinelli Luca
Published: July 2013

In this paper the IDDM (Interpolation Damage Detection Method), recently proposed as a speedy damage detection and localization technique, is applied to the numerical model of a cable suspended bridge derived from the ANSYS model of the Shimotsui-Seto Bridge in Japan (940m length of the main span). The wind excitation is simulated as a spatially correlated process acting in the horizontal direction, transversal to the deck. The bridge is assumed to be monitored by sensors located at the nodes of the model along the longitudinal axis, and recording the absolute acceleration of the bridge deck in the transversal direction Noise in recorded responses can reduce the sensitivity of the method to damage. The influence of noise on the results of the damage detection method is herein investigated by adding a white-noise signal to the structural responses. The mutual relationship between level of noise, intensity of damage and lengths of recorded signals is also investigated with reference to various damage scenarios.
Wireless Sensor Network for Helicopter Rotor Blade Vibration Monitoring: Requirements Definition and Technological Aspects
Authors: Sanchez Ramirez Andrea , Das Kallol , Loendersloot Richard , Tinga Tiedo , Havinga Paul
Published: July 2013

The main rotor accounts for the largest vibration source for helicopter fuselage and components. However, accurate blade monitoring has been limited due to the practical restrictions on instrumenting rotating blades. The use of Wireless Sensor Networks (WSNs) for real time vibration monitoring promises to deliver a significant contribution to rotor performance monitoring and blade damage identification. This paper discusses the main technological challenges for wireless sensor networks for vibration monitoring on helicopter rotor blades. The first part introduces the context of vibration monitoring on helicopters. Secondly, an overview of the main failure modes for rotor and blades is presented. Based on the requirements for failure modes monitoring, a proposition for a multipurpose sensor network is presented. The network aims to monitor rotor performance, blade integrity and damage monitoring at three different scales referred to as macro layer, meso layer and micro layer. The final part presents the requirements for WSNs design in relation with sensing, processing, communication and actuation. Finally power supply aspects are discussed.
Sensor Fusion on Structural Monitoring Data Analysis: Application to a Cable-Stayed Bridge
Authors: Zonta Daniele , Bruschetta Federico , Zandonini Riccardo , Pozzi Matteo , Wang Ming , Glisic Branko , Inaudi Daniele , Posenato Daniele , Zhao Yang
Published: July 2013

This paper illustrates an application of Bayesian logic to monitoring data analysis and structural condition state inference. The case study is a 260 m long cable-stayed bridge spanning the Adige River 10 km north of the town of Trento, Italy. This is a statically indeterminate structure, having a composite steel-concrete deck, supported by 12 stay cables. Structural redundancy, possible relaxation losses and an as-built condition differing from design, suggest that long-term load redistribution between cables can be expected. To monitor load redistribution, the owner decided to install a monitoring system which combines built-on-site elasto-magnetic and fiber-optic sensors. In this note, we discuss a rational way to improve the accuracy of the load estimate from the EM sensors taking advantage of the FOS information. More specifically, we use a multi-sensor Bayesian data fusion approach which combines the information from the two sensing systems with the prior knowledge, including design information and the outcomes of laboratory calibration. Using the data acquired to date, we demonstrate that combining the two measurements allows a more accurate estimate of the cable load, to better than 50 kN.
Estimating Vibration-Fatigue-Life on Experimentally Acquired Data
Authors: Mrsnik Matjaz , Slavič Janko , Boltezar Miha
Published: July 2013

It is a common practice in the automotive industry to expose products to accelerated vibration tests, that simulate the load, predicted to occur during the products service time. To avoid long testing times, higher amplitudes are used. Usually such tests come late in the development process, and can result in unexpected costs. A common tool for predicting time-to-failure or expected fatigue-life of the product is the time-domain method, using the rainflow counting algorithm and the Palmgren-Miner summation method. However, if one chooses to apply this method inside a FEM environment on a large amount of nodes with different time histories dependent on the structure excitation, the time-domain method becomes computationally complex. This has led to more effective methods, that estimate the time-to-failure in frequency-domain but are less accurate, compared to the time-domain approach. In this research, a group of such methods is presented and compared using real signals, namely: Tovo-Benasciutti, Wirsching-Light, Petrucci-Zuccarello, empirical α0.75, Dirlik and Gao-Moan method. Separately, only some of those methods were already compared side by side. Usually the comparison was made on simulated random signals, while this research compares them based on a real signal, collected by measuring different groups of spectra (e.g. typical vibration test profiles, different background noise levels, spectral width, number of modes etc.). In existing studies, Dirlik is usually identified as most accurate but in this research, conclusions show, that the Tovo-Benasciutti and Zhao-Baker methods can be more accurate than the Dirlik method and should therefore also be considered for vibration fatigue analysis.
Damage Detection Using Cointegration Technique and Wavelet Analysis of the Post-Cointegrated Lamb Waves
Authors: Dao Phong B. , Staszewski Wieslaw Jerzy
Published: July 2013

This paper presents an application of Lamb-wave-based damage detection under varying temperature conditions. The method used is based on the cointegration technique and wavelet analysis that are partially built on the analysis of non-stationary behaviour and multi-resolution decomposition of time series, respectively. Instead of directly using Lamb wave data for damage detection, two approaches are used: (1) analysis of cointegrating residuals obtained from the cointegration process of Lamb wave responses and (2) analysis of stationary characteristics of the multi-level wavelet decomposed cointegrating residuals. These two approaches are tested on undamaged and damaged aluminium plates exposed to temperature variations. The experimental results show that the method can isolate damage-sensitive features from the temperature effect and reliably detect damage.
Damage Detection Using Principal Component Analysis Based on Wavelet Ridges
Authors: Gharibnezhad Fahit , Mujica Luis Eduardo , Rodellar José , Fritzen Claus Peter
Published: July 2013

Principal Component Analysis (PCA) and Wavelet Transform (WT) aretwo well-known signal processing tools that are widely used indifferent fields. PCA playsa vital role in statistical analysis as a dimensional reduction tool. Besides, WT has proven its abilityto overcome many of the limitation of the others among various time-frequencyanalyzers. The present work attempts to use the properties and advantagesof both methodologies together in damage detection. To achieve thisaim, PCA is applied on ridges of wavelet transform of measured signalsfrom the structure. The results show that the proposed combination improvesthe accuracy of detection comparing with PCA damage detection basedon original data captured from sensors. According to the result, when PCA uses the ridges of transformed data, theidentifications of damages are more clear and accurate. This work involvesexperiments with an aluminum beam using piezoelectrictransducers as sensors and actuators. Damages are introduced intothe structure as a cut in several steps enlarging the depthof cut.
Non-Linear Vibro-Acoustic Wave Modulations - Analysis of Different Types of Low-Frequency Excitation
Authors: Klepka Andrzej , Staszewski Wieslaw Jerzy , Dziedziech Kajetan , Aymerich Francesco
Published: July 2013

Signal processing method based on wavelet transform used in non-linear acoustic test is presented in the paper. The method is applied for sidebands identification in response signal acquired during vibro-acoustic modulation test of impacted carbon fiber reinforced plate (CFRP). The plate was impacted with known energy using drop-weight testing machine. The modulation effect in investigated specimen results from the interaction of low and high frequency excitation with damage. The paper investigates different than mono-harmonic low-frequency excitation usually used in non-linear acoustics tests. Application of aperiodic low-frequency excitation signal allows to omit the modal test, where natural frequency of the structure are estimated. However, this requires the use of dedicated signal processing methods.
Unscented Kalman Filter for Non-Linear Identification of a New Prototype of Bidirectional Tuned Vibration Absorber: A Numerical Investigation
Authors: Matta Emiliano , Ceravolo Rosario , de Stefano Alessandro , Quattrone Antonino , Zanotti Fragonara Luca
Published: July 2013

Several nonlinear system identification methods have been presented in the past, such as the Extended Kalman Filter, the H filter and the Sequential Monte Carlo methods. One of the most promising ones is the Unscented Kalman Filter (UKF) recently proposed for the on-line identification of structural parameters. In the present study the UKF is proposed to the purpose of the nonlinear identification of a new prototype of rolling-pendulum tuned vibration absorber which, relying on an optimal three-dimensional guiding receptacle, can simultaneously control the response of the supporting structure along two orthogonal horizontal directions. Unlike existing ball vibration absorbers, mounted on spherical recesses and used in axial-symmetrical structures, the new device can be bidirectionally tuned to both fundamental structural modes even when the corresponding natural frequencies are different, by virtue of the optimum shape of the rolling cavity. Based on preliminary numerical simulations, the UKF is shown to be effective in identifying the structural parameters of the new device and particularly the nonlinear rolling friction dissipation mechanism at the interface between the ball bearing and the rolling surface.
Investigation of Nonlinear Vibro-Acoustic Wave Modulation Mechanisms in Composite Laminates
Authors: Pieczonka Łukasz , Staszewski Wieslaw Jerzy , Uhl Tadeusz
Published: July 2013

This paper investigates the effect of low-frequency vibration and the related temperature field on nonlinear vibro-acoustic wave modulations. Experimental modal analysis was used to find natural frequencies and mode shapes of a composite laminate plate with seeded delamination. Temperature distribution was analyzed with a thermographic camera in the vicinity of damage for the identified vibration modes. These frequencies of these vibration modes were then used for low-frequency excitation in nonlinear acoustic tests. The correlation between the thermal field and the observed wave modulations was analyzed.
Real-Time Autonomous Structural Change Detection Onboard Wireless Sensor Platforms
Authors: Carbajo Ricardo Simon , Carbajo Esther Simon , Basu Biswajit , McGoldrick Ciaran
Published: July 2013

Real-time structural health monitoring is becoming increasingly tractable on commodity wireless sensor devices and platforms. Such algorithmic implementations must be realised in as efficient a manner as possible, in terms of memory, computation, radio communications and power efficiency. This work describes an efficient, real-time, structural change detection algorithm implemented on constrained, commodity wireless sensor nodes. The algorithm, based on the Hilbert Huang transform, initially characterises the structure and reliably signals subsequent change using a hierarchical monitoring and alert infrastructure. The system operates entirely autonomously, and algorithmic parameterisations, such as sensitivity and training period duration, can be dynamically and remotely adjusted across the air interface. The system has been evaluated on two different structures which were subject to structural change during the experiments; a Single-Degree-of-Freedom discrete dynamical system, and a 5kW wind turbine blade. The system demonstrated a highly reliable capacity to promptly detect and actuate response to structural change.
Statistical Approach for Modeling Abrasive Tool Wear and Experimental Validation when Turning the Difficult to Cut Titanium Alloys Ti6Al4V
Authors: Halila F. , Czarnota C. , Nouari M.
Published: July 2013

Tool wear and tool failure are critical problems in the industrial manufacturing field since they affect the quality of the machined workpiece and raises the production cost. Improving our knowledge of wear mechanisms and capabilities of wear prediction are therefore of great importance in machining. The three main wear modes usually identified at the tool/chip and the tool/workpiece interfaces are abrasion, adhesion and diffusion. Besides, because of their difficult experimental analysis and measurements of their friction interface features (such as temperature, pressure, particles embedded in the contact …), understanding mechanisms that govern these wear modes is still incomplete. The objective of this research work is to develop a new wear model in which abrasive particles are assumed embedded between the tool and the chip at the interface. These particles are considered with a conical shape and are characterized by two main geometric parameters: the corresponding apex angle and size. The wear particles can be seen as a non-metallic inclusions or wear debris generated during the machining process. A probability density function has been adopted to describe the fluctuation of the size and the apex angle of particles in the tool/chip contact area. The influence of the used statistical distribution has been analyzed depending on which law has been adopted: Gaussian or Weibull. The Volume of the removed material per unit of time was chosen, in this study as the main abrasive wear parameter and detailed on a parametric study. Finally, wear tests were carried out with an uncoated WC-Co carbide tool machining a Ti6Al4V titanium alloy to validate the proposed approach.
Laser Assisted Machining of Titanium Alloys
Authors: Warap N.M. , Mohid Zazuli , Rahim Erween Abdul
Published: July 2013

Laser assisted machining is categorized in preheat machining process. The laser beam used to heat up work materials is very flexible in providing a localized heat area. However the combination between two processes which has totally different fundamental has contributed to complex processing characteristics. In the case of hard to machined metal processing, problems in surface integrity and accuracy are frequently arise. Tool ware and work material properties changes are some of the issue that drove engineers and researchers to seek for optimized processing parameters. This chapter introduces resent finding in research done on laser assisted machining (LAM). Focus is given on laser assisted mechanical machining consist of laser assisted milling (LAM) and laser assisted turning (LAT).
Photocatalytic Activities of CdO-Fe2O3, CdO-CuFe2O4 and CdO-ZnFe2O4 Nanocomposites
Authors: Karunakaran C. , Vijayabalan A.
Published: July 2013

Magnetically separable CdO-Fe2O3, CdO-CuFe2O4 and CdO-ZnFe2O4 nanocomposites have been prepared by precipitation method. The X-ray diffractogram shows face centered cubic CdO, cubic CdO2, rhombohedral α-Fe2O3, orthorhombic β-Fe2O3, cubic γ-Fe2O3 and tetragonal FeOOH as the constituents of CdO-Fe2O3 composite. The components of CdO-CuFe2O4 composite are face centered cubic CdO, body centered tetragonal CuFe2O4 and cubic γ-Fe2O3. Face centered cubic CdO and ZnFe2O4, cubic γ-Fe2O3 and rhombohedral α-Fe2O3 are the constituents of CdO-ZnFe2O4 composite. The energy dispersive X-ray spectra confirm the presence of the corresponding elements and provide the composition. The scanning electron micrographs show that the composite particles are of spherical shape and of nanodimension. The composites absorb visible light. The charge transfer resistances of the composites are larger than their constituents. CdO-Fe2O3 and CdO-CuFe2O4 composites display ferromagnetic behavior. The visible light-photocatalytic activities and bactericidal activities of the composites are larger than their precursors.
Melt Quenched High Pressure Die Casting (MQ-HPDC) of an A356 Alloy
Authors: Ji Shou Xun , Jiang Bo , Yang Wen Chao , Fan Zhong Yun
Published: July 2013

Melt quenched high pressure die casting (MQ-HPDC) is a new die casting process developed recently for improving the casting quality of the conventional HPDC process. In the MQ-HPDC process, an alloy melt with a specified dose and superheat is quenched by directly pouring the alloy melt into a preheated metallic container. The thermal mass and preheating temperature of the container is selected so that the alloy melt is quenched just below the alloy liquidus and heterogeneous nucleation takes place during the melt quenching. The quenched alloy melt is then fed immediately into the shot sleeve for component casting. In this paper we present the MQ-HPDC process and the resultant microstructures and mechanical properties of a MQ-HPDC A356 alloy.
Plasma Treatment Casting of Cast Aluminum 6XXX Wrought Alloys
Authors: Bamberger Menachem , Kiperwasser-Karbian Esther
Published: July 2013

The Plasma Treatment Casting (PTC) process is an advanced stirring process that stirs molten metals and alloys during solidification in conductive and nonconductive dies. The intensive stirring has several major benefits: finer microstructure, better chemical homogeneity and much more efficient feeding in both macro and micro scales. Today the casting industry is continuously pursuing methods to improve casting quality, and to save time, energy and materials, which together result in price reduction and environmental benefits. Direct-chill (DC) casting is currently the most common semi-continuous casting practice in production of 6XXX aluminium alloys. This method results in course and non-homogenous microstructures. This requires homogenization treatment to follow the casting process in order to give 6XXX DC cast billets workability in extrusion and the required mechanical properties. The PTC process can be the solution to improve the microstructure in terms of refining the microstructure, reducing porosity and creating a more homogenous microstructure.
Modelling of the Effects of Entrainment Defects on Mechanical Properties in a Cast Al-Si-Mg Alloy
Authors: Yue Yang , Griffiths William D. , Green Nick R.
Published: July 2013

Entrainment defects such as double oxide films and entrapped bubbles occur frequently in aluminium alloy castings during the mould-filling process, and are very detrimental to both mechanical properties, and reproducibility of casting properties. In this study a modelling algorithm was used to predict the formation and distribution of entrainment defects in Al-Si-Mg alloy castings. The tensile strength of cast test bars was compared with either the number of defects, or the defect concentration within the bars obtained from the simulation. A general relationship between the mechanical strength of the cast test bars and the quantity of estimated defects was apparent.
Manufacture of CNTs-Al Powder Precursors for Casting of CNTs-Al Matrix Composites
Authors: Ko Seh Yun , Kim Bo Young , Kim Yong In , Kim Taeh Yeong , Kim Ki Tae , McKay Brian J. , Shin Je Sik
Published: July 2013

CNTs-Al matrix composites are considered to be promising heat dissipating materials because thermal conductivity can potentially be improved whilst their density is reduced. Although casting has many advantages in the fabrication of large, complex components, this process cannot be easily employed when manufacturing CNTs-Al composites. In order to produce CNTs-Al matrix composites by casting a CNTs-Al powder precursor was manufactured using mechanical milling and electroless plating processes. Aluminium powder with CNTs of 10 wt.% and 20 wt.% were mixed and ball milled using a horizontal mill. After milling for 3 hrs., the milled powder exhibits a flattened morphology with a band-type distribution of CNT clusters observed within the aluminium particles. Prolonged milling of up to 24 hrs. introduces an equiaxed particle shape for the milled powders with a uniform distribution of CNTs within the aluminium particles. However, as milling time increases, the CNTs become fractured by ball-to-ball collisions. There was no reaction evident between the aluminium and the CNTs at milling times up to 24 hrs. In order to improve the wettability between the CNTs-Al powder precursor and Al melt during the casting process, electroless Ni plating was performed. The processing time for the Ni-plating affects the uniformity of the coating layer. For a uniform coating condition, the average thickness of the coating was ~1.87 μm, with no evidence of gaps between the milled powders and coatings observed.
Novel Forming of Ti-6Al-4V by Laser Engineered Net Shaping
Authors: Zhai Yu Wei , Lados Diana A.
Published: July 2013

Titanium alloys offer important weight and performance advantages, but are relatively expensive. Traditional “subtractive” manufacturing causes up to 95% material waste, which makes the manufacturing of titanium components even more expensive. Laser Engineered Net Shaping (LENS) is an effective method of “additively” making components layer-wise, directly from unit materials, based on 3D digital models. Parts fabricated by LENS are net/near-net shape, and therefore, this process minimizes, or even eliminates massive machining costs and material waste. In this study, as-fabricated LENS Ti-6Al-4V test specimens were investigated. The resulting microstructures were extensively characterized and correlated to processing parameters. In addition, room temperature tensile tests were conducted to obtain static mechanical properties and to understand the behaviour at LENS deposition-substrate interface. These results will be presented and discussed.
Microstructural and Mechanical Characterization of ARB AZ31
Authors: Schwarz Friederike , Lange Katja , Krüger Lutz , Kawalla Rudolf , Reichelt Stephan
Published: July 2013

In this work the influence of accumulative roll bonding (ARB) process on the microstructure and the mechanical characteristic is investigated. Therefore, AZ31 magnesium sheets were successfully deformed through ARB for a maximum of three passes. Twin roll cast sheets and twin roll cast sheets with subsequent heat treatment (480 °C, 1 h) were used as initial materials. After one ARB pass, the highest microstructure changes were measured. Electron backscattered diffraction (EBSD) reveals a bimodal microstructure with an average grain size of ~1µm. In comparison to the initial material a strong basal texture was measured. The significant refinement of grain size after severe plastic deformation cause an increase of tensile and compressive strength, e.g. rising yield stress and ultimate tensile strength of 42% and 15%, respectively. However, the maximum formability remains nearly at the same level. Further ARB passes do not improve the mechanical characteristics further.