Showing papers in "Key Engineering Materials in 2005"

Vibration-Based Structural Health Monitoring – Concepts and Applications

Abstract: This paper gives an overview on the current status of vibration-based methods for Structural Health Monitoring. All these methods have in common that a structural change due to a damage results in a more or less pronounced change of the dynamic behavior. The use of modal information is discussed, as well as the direct use of forced and ambient vibrations. From this information, different strategies can be deduced which depend on the type of measurement data (time/frequency domain) but also on the frequency spectrum. The incorporation of actuation and sensing devices into the structure leads to modern concepts of Smart Structural Health Monitoring. Examples from civil and aerospace engineering show the applicability of these methods.

Formation and Evolution of Hydrated Surface Layers of Apatites

Abstract: Nanocrystalline apatites exhibit a very fragile structured hydrated surface layer which is only observed in aqueous media. This surface layer contains mobile ionic species which can be easily exchanged with ions from the surrounding fluids. Although the precise structure of this surface layer is still unknown, it presents very specific spectroscopic characteristics. The structure of the hydrated surface layer depends on the constitutive mineral ions: ion exchanges of HPO42- ions by CO32- ions or of Ca2+ by Mg2+ ions result in a de-structuration of the hydrated layer and modifies its spectroscopic characteristics. However, the original structure can be retrieved by reverse exchange reaction. These alterations do not seem to affect the apatitic lattice. Stoichiometric apatite also shows HPO42- on their surface due to a surface hydrolysis after contact with aqueous solutions. Ion exchange is also observed and the environments of the surface carbonate ions seem analogous to that observed in nanocrystalline apatites. The formation of a hydrated layer in aqueous media appears to be a property common to apatites which has to be taken into account in their reactivity and biological behavior.

Ultrasonic/Guided Waves for Structural Health Monitoring

Abstract: Structural damage detection and monitoring is one of the major maintenance activities in transportation, processing and civil engineering. Current procedures are based on scheduled inspections which are often time/labour consuming and expensive. Guided ultrasonic waves offer the ability of inspecting large structures with a small number of transducers. Recent developments in smart sensor technologies allow for integration of these transducers with monitored structures. This is associated with a new design philosophy leading to more efficient and economically attractive structures. The paper briefly discusses various damage detection methods based on structural, ultrasonic and guided ultrasonic waves. The focus is on recent research advances in damage monitoring techniques, smart sensor technologies and signal processing.

Applications of Spectral Kurtosis in Machine Diagnostics and Prognostics

Abstract: Many machine faults, such as local defects in bearings and gears, manifest themselves in vibration signals as a series of impulsive events. Kurtosis is a measure of the impulsiveness of a signal, and spectral kurtosis (SK) gives an indication of how the kurtosis (of a bandpass filtered signal) varies with frequency. This not only gives an indication of the frequency bands to be processed, but can also be used to generate a filter to extract the most impulsive part of a signal. The first step in calculating SK is to perform a time/frequency decomposition of the signal, and then calculate the kurtosis for each frequency line. The paper compares the original STFT (short time Fourier transform) with wavelet analysis for the time/frequency decomposition, and for determining the optimum combination of centre frequency and bandwidth for maximizing the SK. The paper also describes how the SK can be enhanced by “prewhitening” the signal using an autoregressive (AR) model, this sometimes revealing an incipient fault at a much earlier stage.

Impact Force Spectrum for Damage Assessment of Earthquake-Induced Structural Pounding

Abstract: Past earthquakes indicate that pounding between inadequately separated structures may cause considerable damage or even lead to collapse of colliding structures. Intensive study has been recently carried out on mitigation of pounding hazards. The assessment of damage due to structural pounding, or its prediction under a particular ground motion, requires the knowledge of the maximum impact force value expected during the time of earthquake. The aim of the present paper is to consider the concept of impact force response spectrum for two closely-spaced structures, which shows the plot of the peak value of pounding force as a function of the natural structural vibration period. The spectrum can be used as a practical tool to assess the magnitude of the expected pounding-induced damage and, if necessary, to apply some damage reduction techniques. In the analysis, both interacting structures have been modelled by single-degree-of-freedom systems and pounding has been simulated by the non-linear viscoelastic model, which accounts for the energy dissipation during impact. The examples of response spectra show that the appropriate selection of the separation gap between structures as well as the dynamic structural parameters, such as the natural vibration period, mass and damping, might have a significant influence on the intensity of damage due to earthquake-induced pounding.

Acupuncture Meridian and Intravascular Bonghan Duct

Abstract: Current anatomical theory does not recognize the existence of an extended floating threadlike structure inside the blood vessels. Nonetheless, this study developed a new method for observing such an intravascular threadlike structure. The key technique involves injecting acridineorange into the femoral vein to circulate along the blood vessels and stain the nuclei of the intravascular threads inside the blood vessels. In-situ observations were then made under a fluorescence stereomicroscope after saline-perfusion. Confocal microscope images revealed a distinctive characteristic pattern of nucleus distribution that was clearly distinguishable from fibrin, capillaries, small venules, arterioles, or lymph vessels. Accordingly, it is suggested that the identified intravascular threads are part of the Bonghan's circulatory network that is distributed throughout the body, including inside the blood vessels.

Modal analysis of acoustic emission signals from artificial and fatigue crack sources in aerospace grade steel

Abstract: Current analysis of Acoustic Emission (AE) signals is dominated by waveform parameter assessment, such as amplitude, rise-time, absolute energy, initiation frequency etc. whilst the actual waveform collected is often ignored. This paper explores the dispersive behaviour of Lamb Wave propagation as a means of estimating source to sensor distance and source orientation from collected waveforms.

Wireless structural health monitoring using MEMS

Abstract: So far, the inspection of building structures and especially of bridges is mainly done visually. Therefore, the condition of the structure is examined from the surface and the interpretation and assessment is based on the experience of the expert. However, the main purpose of monitoring civil structures is not to substitute visual inspection. Continuous structural health monitoring should provide data from the inside of a structure to better understand its structural performance and to predict its durability and remaining life time. Monitoring should render objective data and observable alterations in the structure continuously, which cannot be done by visual inspection. More detailed information is needed with respect to different exposure due to dynamic and static loads and also temperature and moisture. Today mainly wired monitoring systems are used to monitor structures, which are relatively expensive and time consuming to install. In this paper the basic principle of a wireless monitoring system equipped with MEMS sensors is presented, which can be easily installed at different structures. Microelectromechanical systems (MEMS) are small integrated devices or systems that combine electrical and mechanical components. A wireless monitoring sensor network equipped with such MEMS could be produced with a very low budget and becomes very efficient. This permits a wide area of applications not only in civil engineering. With respect to different applications relevant properties of a wireless monitoring system are described. In detail network configuration, power consumption, data acquisition and data aggregation, signal analysis and data reduction as well as reliability and robustness are discussed.

A Comprehensive Evaluation Model for Assessments of Grinding Machining Quality

Abstract: Grinding machining quality contains machining precision and grinding surface integrality. The factors influencing grinding machining quality have fuzzy characteristics. For example, the magnitude and measure methods of grinding surface roughness have fuzzy uncertainties. The grades of the machining quality are vague, and there is no definite boundary between “good” and “bad” machining quality. Analytical Hierarchy Process (AHP) combined with the fuzzy comprehensive evaluation technique is used to evaluate the grade condition of the quality in this paper. Considering the fuzziness of the factors, a two-stage fuzzy comprehensive evaluation model is proposed to evaluate the grinding machining quality. In light of different reliable degrees of different kinds of fuzzy operator models, the weighted average method is used. The membership degrees of the evaluation factors are determined by experts’ knowledge and experiences. The factor weights are calculated via the AHP method. Certain synthetic importance of each stage evaluation is presented through weighted sum of the relative important degree. Examples of conventional external grinding machining illustrate the effectiveness of the proposed model.

ATZ – A New Material with a High Potential in Joint Replacement

Abstract: The present study has been aimed to combine the advantages of the two single-phase materials, Al2O3 and ZrO2 while avoiding their disadvantages, by producing a mixed ceramic. Within a study of an ATZ ceramic we tested the influence of aging by a hydrothermal treatment on the strength, phase composition and surface properties. We found that the hydrothermal treatment of the ATZ ceramic did not significantly influence these parameters, unlike those of a single-phase ZrO2 ceramic.

Electroforming of Copper/ZrB2 Composites Coatings and Its Performance as Electro-Discharge Machining Electrodes

Abstract: Copper electroforming, together with rapid prototyping (RP) technology, provides a method for manufacturing EDM electrodes rapidly. However, the use of conventional electroformed copper electrodes is restricted because of the high electrode wear rate in EDM processes. This paper presents a study on the electroforming technique of copper/zirconium diboride (ZrB2) composite coating and its performance as an EDM electrode. Cu-ZrB2 composite coating is electroformed from a copper nitrate bath containing micro-sized ZrB2 particles in such a way that by varying the process parameters, ZrB2 particles approximate to 20 Vol.% are incorporated in the coatings. Analyses by optical microscopy and scanning electron microscopy reveal that ZrB2 particles are uniformly dispersed in the copper matrix and the grains of the coating are refined due to the incorporation of ZrB2 particles. The electroformed coatings deposited on copper substrates with approximately 1mm thickness are used as electrodes. EDM experiment shows that performance such as the spark-resistance of the new electrodes is improved compared with that of conventional electroformed copper electrodes because the incorporation of refractory particles in the copper matrix as well as the refinement of the grains of the coating, and the. Cu-ZrB2 composites show good performance in finish machining condition.

Thermal Shock Behavior of an Al2O3/ZrO2 Multilayered Ceramic with Residual Stresses due to Phase Transformations

Abstract: In this work, the thermal shock behavior of an Al2O3-5%tZrO2/Al2O3-30%mZrO2 multilayer ceramic is studied. On these materials, a tetragonal to monoclinic phase transformation within the Al2O3-30%mZrO2 layers takes place when cooling down from sintering. The latter induces an increase in volume and therefore compressive residual stresses arise in these layers. The residual stress distribution profile in the laminate influences the thermal shock response of the material. A finite element model has been developed to estimate both the thermal strain effects during the sintering process as well as the temperature distribution and stress profile within the laminate during thermal shock testing. Experimental tests on the monoliths and laminates were carried out and compared to the model. It is observed that the presence of the compressive layers within the laminate inhibits the penetration of thermal shock cracks into the body at even more severe conditions than in the monolithic material.

Ultra-Structural Study of the Laminin-Apatite Composite Layer Formed on Ethylene-Vinyl Alcohol Copolymer by a Biomimetic Process

Abstract: Mechanism of formation of a laminin-apatite composite layer on the surface of an ethylene-vinyl alcohol copolymer (EVOH) using a liquid phase coating process was investigated by transmission electron microscopy (TEM). In this coating process, an EVOH substrate is alternately dipped in calcium and phosphate solutions, and then immersed in a laminin-containing calcium phosphate (LCP) solution. From the results obtained by the present study, formation of the laminin-apatite composite layer on EVOH is likely to proceed via the following events. By the alternate dipping process, particulate amorphous calcium phosphate, which is a precursor of apatite, was deposited onto the EVOH surface. When the specimen was subsequently immersed in the LCP solution, the amorphous calcium phosphate on the specimen transformed itself into needle-like apatite crystal, and then grew into a layer. During this process, laminin molecules contained in the LCP solution were incorporated into a matrix of the apatite crystals to produce a laminin-apatite composite layer on the EVOH surface.

Preparation of Porous Biphasic Tricalcium Phosphate and Its In Vivo Behavior

Abstract: Biphasic ceramic consisting of tricalcium phosphate with α- and β -phases (αβ-TCP) is a candidate as biodegradable bone substitutes since its biodegradability may be controlled by the ratio of the phases. In the present study, preparation of porous αβ-TCP body with continuous pores of 10-50 µm in diameter was attempted using additives of Mg, and its in vivo behavior was examined. Powder of β-TCP was mixed with Mg and potato starch to form slurry, followed by loading in polyurethane foam. The sample was fired at 1400°C for 12 hours for sintering process. α-TCP content of the sample decreased with increasing the Mg content, while β-TCP increased. Ceramic body consisting of β-TCP phase was obtained when 1.0 mass% of Mg was added. Porosity of the body decreased with increasing the content of Mg. The αβ-TCP body with 80% porosity was obtained when the content of Mg was 0.1 mass%. The in vivo experiments showed that the rate of degradation of the obtained αβ-TCP was almost same as α-TCP, and much higher than β-TCP.

Effect of Microstructure on Dielectric Properties of Si3N4 at Microwave Frequency

Abstract: Silicon nitride (Si3N4) has been researched intensively because of superior mechanical properties up to high temperature The mechanical properties of Si3N4 are strongly related to microstructure The microstructure control of silicon nitride is well known to be a key issue for tailoring the mechanical properties of structural ceramics This work was performed to reveal the effect of microstructure on dielectric properties at microwave frequency Three starting powders were used fine, course a-Si3N4 and b-Si3N4 Sintering additives, 5 wt% Y2O3, 2 wt% Al2O3 and 1 wt% MgO were mixed with each starting powder Si3N4 ceramic with different b/a phase specimen were obtained by hot pressing The post-resonator method was used for the measurement of dielectric properties, dielectric constant (e′) and dielectric loss (tand), at microwave frequency range Silicon nitride ceramics show dielectric constant of 81 – 86 and dielectric loss 11 x 10-3 – 56 x 10-3 The effect of grain size and the role of phase on microwave dielectric properties are discussed

Effects of Temperature and Light on Microcystin Synthetase Gene Transcription in Microcystis Aeruginosa

Abstract: Microcystis aeruginosa is known to form a water bloom and produces the hepatotoxic heptapeptide microcystin. M. aeruginosa NIER10039 isolated from the Paldang reservoir in Korea produces microcystin-LR and microcystin-RR. The microcystin is synthesized by multifunctional enzyme complexes known as microcystin synthetase encoded by the mcy gene cluster. In this study, M. aeruginosa NIER10039 was grown under various culture conditions, e.g., temperature, light intensity, and UV irradiation. The level of mcyB transcripts was analyzed by competitive RT-PCR. The copy number of mcyB transcripts ranged from 4.69 x 10 to 2.83 x 10 copies/g of cells. The strain cultivated at 25°C had more transcripts than strains at 20°C or 30°C. Increase in mcyB transcripts was observed when the light intensity was raised from 7.53 to 45.15 μmol photons/m/s. UV irradiated strain showed higher level of mcyB transcripts with the time of UV exposure. These results can explain the high content of toxin in the aquatic ecosystem during summer.

Vibration Based Modal Parameters Identification and Wear Fault Diagnosis Using Laplace Wavelet

Abstract: Wavelet transform is a powerful technique well suited to non-stationary signal processing. The properties of wavelet are determined by its basis function. In the fields of modal analysis, mechanical condition monitoring and fault diagnosis, impulse responses or transient responses are very common signals to be analyzed. The Laplace wavelet is a single-sided damped exponential wavelet and is a desirable wavelet basis to analyze signals of impulse response. A correlation filtering approach is introduced using the Laplace wavelet to identify the impulse response from vibration signals. Successful results are obtained in identifying the natural frequency of a hydro-generator shaft, and diagnosing the wear fault of intake valve of an internal combustion engine.

Study on Ultrasonic Vibration Grinding Character of Nano ZrO2 Ceramics

Abstract: Nano ceramics possessed ascendant mechanical property and physical characteristics contrast with engineering ceramics, so it has extensive application prospect in various industries. On the basis of applying the indentation fracture mechanics to analyze the removal mechanics of ceramic material, this paper analyzed the critical ductile grinding depth of the nano ZrO2 ceramics. Adopting ultrasonic composite processing we describe the influence of different processing parameters and grain size of diamond wheel on the grinding forces and surface roughness. Based on the grinding forces and surface roughness the grinding process with and without vibration is analyzed. By means of SEM and AFM the surface character and critical ductile grinding depth of nano ZrO2 ceramics are also discussed. The paper supplied the theoretical and experimental basis for the grinding of the large-sized ultraprecision plate structure of nano ZrO2 ceramics (nm).

Determining Representative Stress and Representative Strain in Deriving Indentation Flow Curves Based on Finite Element Analysis

Abstract: A new method [1] to evaluate indentation flow curves using an instrumented indentation test has been applied to many materials for several years. Though the method produces relatively good results compared to uniaxial tensile tests, a few parameters had not been verified by theoretical or numerical methods. In this study, proportional constants of representative strain and representative stress were verified using finite element analysis and proven to be unaffected by the elastic property and strain level. The constants were generally dependent on the plastic property; however, one combination of the constants is independent of all properties. The values of this combination are consistent with early research and produced overlapping indentation flow curves with uniaxial curves.

Alumina Matrix Composites in Arthroplasty

Abstract: It is well known that the introduction of zirconia into the alumina matrix has a positive effect on bending strength of the material, and especially on toughness which is the main limit of alumina ceramics. While the many attempts made in the past to develop alumina matrix composites suitable for biomedical applications containing zirconia as a toughening phase (Zirconia Toughened Alumina – ZTA) did not leave the developmental stage, recently ball heads and inlays for THR bearings made out a three phase alumina matrix composite were introduced into the market. In the alumina matrix of this material both zirconia and exagonal aluminate platelets are distributed, and then it belongs to the class of Zirconia and Platelets Toughened Alumina – ZPTA. Besides ball heads and inlays, also several other innovative orthopedic devices made out this new ceramic biomaterial are in different development stage. This paper reviews the present status of alumina matrix composites in orthopedic application, with special attention to ZPTA.

Pattern Classification of Acoustic Emission Signals during Wood Drying by Principal Component Analysis and Artificial Neural Network

Abstract: This study was performed to classify the acoustic emission (AE) signal due to surface check and water movement of the flat-sawn boards of oak (Quercus Variablilis) during drying using the principle component analysis (PCA) and artificial neural network (ANN). To reduce the multicollinearity among AE parameters such as peak amplitude, ring-down count, event duration, ring-down count divided by event duration, energy, rise time, and peak amplitude divided by rise time and to extract the significant AE parameters, correlation analysis was performed. Over 96 % of the variance of AE parameters could be accounted for by the first and second principal components. An ANN was successfully used to classify the AE signals into two patterns. The ANN classifier based on PCA appeared to be a promising tool to classify the AE signals from wood drying.

Biological Behaviour of Bonelike® Graft Implanted in the Tibia of Humans

Abstract: This paper reports the ability of Bonelike® to regenerate bone defected areas when implanted in the tibia of 3 patients (average age of 59 years) during a high tibial osteotomy (HTO) to treat medial compartment osteoarthritis of the knee. Bonelike® is a synthetic bone graft designed to mimic the inorganic composition of bone using a patent process that consists of liquid sintering hydroxyapatite in the presence of CaO-P2O5 based glass. The preliminary clinical evaluation performed showed that an intimate contact between new formed bone and Bonelike® was established (67±10 %), with no fibrous interface. Therefore, Bonelike® is a single-handedly viable osteoconductive synthetic grafting material as it has been demonstrated from the profiles of radiological, histological and scanning electron microscopy analyses for the six months implantation period.

Application of Microbial Polyesters-Polyhydroxyalkanoates as Tissue Engineering Materials

Abstract: Poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) has improved mechanical properties over the existing PHA and our results have shown that PHBHHx has better biocompatibility over polyhydroxybutyrate (PHB) and polylactic acid (PLA). Surface treatment with lipases dramatically changed the material surface properties and increased the biocompatibility of the PHBHHx. PHBHHx and its PHB blends had been used to make three dimensional structures and it has been found that cartilage, osteoblast, and fibroblasts all showed strong growth on the PHBHHx scaffolds. The growth was much better compared with PLA. The molecular studies also showed that mRNA encoding cartilages were strongly expressed when cartilage cells were grown on the PHBHHx. As PHBHHx has strong mechanical properties, easily processible and biodegradable, this material can be used to develop a new class of tissue engineering materials.

In Vitro Analysis of Protein Adhesion to Phase Pure Hydroxyapatite and Silicon Substituted Hydroxyapatite

Abstract: The adhesion of bovine collagen type I, bovine serum albumin, bovine IgG, 1 % and 10 % (v/v) human serum to hydroxyapatite (HA), silicon-substituted hydroxyapatite (Si-HA) and tissue culture plastic were studied. The materials were incubated at 37 °C for 30 minutes, after which the protein solution was removed and analyzed. The adsorbed protein was evaluated by electrophoresis and immunoassay after extraction from the materials. The degree of adhesion was higher for collagen, followed by IgG and albumin on all materials. However there was no difference in the amount of collagen adsorbed onto the surface of each material and this was also the finding with albumin and IgG. These results suggest that the increased bioactivity seen with Si-HA is not due to the degree of protein adhesion, but may possibly be due to changes in the conformation of the bound proteins.

Novel Vibration-Based Methods for Detecting Delamination Damage in Composite Plate and Shell Laminates

Abstract: The paper describes an on-going research effort aimed at detecting the presence of delamination damage in composite panels based upon their higher-frequency structural response. Two alternative damage indexes are examined that facilitate the identification of the location and extent of delaminations. The damage indexes do not require vibration measurements to be performed on the undamaged structure. Use is made of the bending and twisting curvatures corresponding to the higher-frequency mode shapes that are post-processed via two different smoothing techniques. The modal data are obtained via finite element models based on Mindlin theory and including delaminations. These are introduced using a sub-laminate strategy that permits multiple damages to be modelled through the thickness. Various delamination sizes and locations are examined with a random noise superposed on the data in order to ascertain the degree of sensitivity of the damage index to the noise in the experimental data.

Scratchability of Soda-Lime Silica (SLS) Glasses: Dynamic Fracture Analysis

Abstract: Grinding and polishing are widely used for glass machining with fine finished surfaces. These processes result from abrasion due to repeated contacts between hard sliding particles and the glass surface. The study of contact mechanics problem is of fundamental interest to understand the process of material removal in glasses. In order to get insight into this problem, an experimental set up was designed which allows a monotonic loading of the indenter combined with a controlled sliding of the specimen to simulate a slow abrasive machining process. In addition, the experiments are conducted with an in-situ video monitoring that allows for the observation of the different fracture phenomena beneath the indenter. Fracture surfaces were also studied using SEM and AFM for multi-scale investigation. Fracture analysis was carried on a standard float glass, four different SLS glasses and a fused silica glass. The observed phenomena were discussed in the light of the influence of the normal load and the chemical composition.

Polyurethane Foam with a Negative Poisson's Ratio for Diabetic Shoes

Abstract: This study fabricated polyurethane foam after transforming the cell structure from a convex polyhedral shape to a concave shape. Polyurethane was synthesized and fabricated after changing the cellular structure of the foam using two methods. Scanning electron microscopy showed that the cellular structure was a more concave structure than in control foam. The Poisson’s ratio of the experimental foam was negative. The average range of the Poisson’s ratio was –3.4~0, versus 0.3~1.3 for the control foam.

Thermal Conductivity of the New Candidate Materials for Thermal Barrier Coatings

Abstract: Rare-earth zirconate ceramics (Gd2Zr2O7, Sm2Zr2O7, Nd2Zr2O7, Dy2Zr2O7, Er2Zr2O7 and Yb2Zr2O7) were successfully prepared by pressureless sintering at 1550oC for 10 hours. The thermal conductivities of these ceramics were measured and the results indicated that the thermal conductivities of rare-earth zirconates were much lower than that of YSZ in the temperature range 20-800oC.

Preparation of Electrospun PLA Nanofiber Scaffold and the Evaluation In Vitro

Abstract: A electrospinning process to prepare soft tissue engineering scaffold was introduced in this study. This kind of scaffold was composed with ultrathin fiber and characterized with high porosity, well-interconnected pores and high surface-to-volume ratio. Biodegradable polylaticacid (PLA) was used to spin the scaffold and the scaffold was evaluated in vitro by analysis the microscopic structure, porosity, mechanical property, especially cytocompatibility. The results indicated that the electrospun PLA scaffold showed good cytocompatibility and the tensile property of electrospun scaffold was similar to human’s soft tissue. It could be expected that the electrospun scaffold would be potential in soft tissue engineering or soft tissue repair.

Effect of Some Physical-Chemical Variables in The Synthesis of Hydroxyapatite by the Precipitation Route

Abstract: The synthetic hydroxyapatite is a very useful material for numerous applications in medicine as a biomaterial. One of the most economic manufacturing process is the precipitation route. In the present work, synthetic hydroxyapatite was prepared using the precipitation route, starting with aqueous solutions of calcium nitrate (Ca(NO 3).4H 2O ) and ammonium phosphate (H 2(PO 4)NH 4). The effects of physical-chemical variables such as pH, temperature, time of agitation, ageing time and heat treatment of the mixture were evaluated. The characterization of the samples obtained in different conditions made possible to conclude about the optimal values of the studied variables for the synthesis of this material in laboratory conditions.