bluuebunny/crossref_metadata_2025 huggingface dataset:
The Structure Effect of Polymeric Dispersant on Rheological Behavior of Highly Concentrated Silicon Nitride Gelcasting Slip
Authors: Ryu Beyong Hwan , Choi Young Min , Lee Jae Do
Published: March 2009

Gelcasting has been expected as a promising approach to prepare near-net-shaped ceramic products. The preparation of highly concentrated gelcasting slip is one of key point in this process. The rheological behavior of concentrated silicon nitride gelcasting slip was investigated with the structure effect of polymeric dispersant and the ratio of dispersant to acrylamide monomer in order to prepare highly concentrated gelcasting slip. The slip was prepared by ball milling of silicon nitride batch composed of acrylamide monomer and polymeric dispersant after premixing them by an attritor. The slip mixed with initiator will be deaired in vacuum and cast into molds, and then polymerized. The consolidated green body will be obtained by drying the gelated slip. The polymeric dispersants with different kinds of polyelectrolyte were poly(methylmetacrylic ammonium salt), poly(acrylic ammonium salt), and poly(acrylic amine salt). Before the polymerization of gelcasting slip, the viscosity vs. shear rate was measured to evaluate the rheological behavior of the slip. In case of using the polyacrylic amine salt (PAAm), the high solid loading of silicon nitride slip was obtained up to 47vol% with a low viscosity.
Spark-Plasma Sintering of Molybdenum Disilicide
Authors: Kim Ji Soon , Kim Young Do , Lee Choong Hyo , Choi Pyuck Pa , Kwon Young Soon
Published: March 2009

The effect of milling on the densification behavior of MoSi2 powder during spark-plasma sintering (SPS) was investigated. MoSi2 starting powder with an average particle size of 10 µm was milled to reduce particle sizes to less than 1 µm. Sintering was performed in a SPS facility, varying the sintering temperature from 1200°C to 1500°C. Changes in relative density and the densification rate were measured as a function of temperature. Additionally, the microstructure of sintered compacts was analyzed by means of SEM and EPMA. The sintered density was lower for ballmilled
powder compacts (having 94-95% relative density) than for as-received ones (having 94- 98% relative density) despite a higher densification rate of the former in the early and middle stages of sintering. These apparently contradictory results can be explained by a pick-up of oxygen (from 0.3 to 1.8 wt. % O) during the milling process, leading to the formation of silicon oxide and its decomposition into a gas phase at temperatures above 1200°C.
Microstructure and Mechanical Properties of Silicon Nitride/h-BN Based Machinable Ceramics
Authors: Cho Won Seung , Lee Jae Hyung , Cho Myeong Woo , Lee Eun Sang , Park Dong Sam , Munir Z.A.
Published: March 2009

The effects of h-BN content on the microstructure, mechanical properties, and
machinability of Si3N4 ceramics were investigated. The relative density of the sintered compact decreased with increasing BN content. The flexural strength also decreased with h-BN content, mainly due to lower Young’s modulus of h-BN compared to Si3N4. With increasing h-BN content, Si3N4/h-BN based ceramic composites revealed enhanced crack resistance (R-curve) behavior. The
Vickers indentation crack paths in specimens are sinusoidal due to bridging and pull out of grains during crack propagation. The grain size of ß-Si3N4 slightly decreased with h-BN content. During milling and micro-drilling process, monolithic Si3N4 ceramic could not be machined, due to brittle fracture. However, thrust forces measured for Si3N4/h-BN composites decreased with increasing h-BN content, showing the excellent macro and micro machinabilty.
The Effects of β-Si3N4 Whisker Content and Orientation on R-Curve Behaviors of Si3N4 Ceramics
Authors: Zou Lin-Hua , Park Dong Soo , Kim Hai Doo , Wang Chang An , Huang Yong
Published: March 2009

The b–Si3N4 whisker randomly and unidirectionally reinforced Si3N4 composites were fabricated respectively. The high whisker alignment was obtained by extrusion processing. The R-curve behaviors were studied for the Si3N4 ceramics with addition of 3wt%, 5wt% and 10wt% b–Si3N4 whisker seeds respectively, and the effects of whisker orientation and content on the R-curve behaviors were analyzed and discussed. The ceramics with different whisker content and orientation showed well-defined R-curve behaviors. However, for the whisker random distribution, as its whisker content increased from 3wt% to 10wt%, the corresponding fracture toughness changed at an irregular trend; for the whisker unidirectional reinforcement, the fracture toughness in the direction perpendicular to whisker alignment was considerably improved, and most of indentation impressions
tend to be very abnormal. The effects of whisker orientation and contents on the R-curve behaviors of the Si3N4 ceramics were further discussed.
Erosion Behavior of Silicon Nitride with Graded Microstructure
Authors: Lim Dae Soon , Park Jong In , Lim Dong Phill , Han Byung Dong , Park Dong Soo
Published: March 2009

Silicon nitride has been considered as candidate tribological material due to their excellent mechanical and thermal properties. This study investigated the effect of graded grain size on the erosion behavior of silicon nitride at room and high temperatures. Erosion tests were carried out with a gas blast-type erosion tester at temperatures up to 800 °C. Weight loss after impact of SiC particles were measured. The erosion rate varied with temperature and microstructure. Different erosion
behavior depending on microstructure were discussed based on SEM observation Auger depth profile of worn surfaces.
Strength Degradation of Silicon Carbide Hot Gas Filter in the Simulated PFBC Condition
Authors: Lee Kee Sung , Han In Sub , Seo Doo Won , Woo Sang Kuk
Published: March 2009

Strength degradations of porous silicon carbide hot gas filters bonded with clay and
calcium carbonate are investigated in the simulated condition of the pressurized fluidized bed combustion (PFBC). Thermal cycling, static fatigue, thermal shock, and hot corrosion tests are conducted to differentiate the independent parameter that affects the strength degradation during the filtration using silicon carbide filter in PFBC condition. The results indicate that hot corrosive gas mainly causes the strength reduction because of the degradation of grain boundary region.
A New Type Gene Delivery System – Gene Nanoparticles
Authors: Yang Jing , Song Cun Xian , Sun Hong Fan , Wu Li , Tang Lina , Zeng Yong , Zhu Wen Ling
Published: March 2009

A reporter gene pEGFP and a therapeutic antisense monocyte hemotactic protein-1
(MCP-1) gene were encapsulated into poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) using an emulsification / solvent evaporation technique. The gene-NPs were around 300 nm in diameter with very narrow size distribution. The encapsulation efficiency of DNA was significantly improved when poly (lysine) was used in cooperation with DNA. The NPs demonstrated a steady in vitro release of DNA with more that 95% of total enclosed DNA released within 14 days. In cell
culture, pEGFP -loaded NPs were able to express in smooth muscle cells at a level same as that of Lipofectin induced plasmid. To observe the effects of antisense MCP-1 NPs on the inhibition of restenosis, balloon catheter-induced injury was used to establish an intimal hyperplasia model of rabbit carotid artery. Antisense MCP-1 expression was confirmed in the artery tissue with local delivery of the therapeutic NP into the injured artery. Intima/media ratio of arteries treated with the antisense NPs was reduced by 43% compared with control group. In conclusion, NP could be an effective gene carrier for intravascular site-specific gene therapy.
Preparation of Porous Multi-Channeled Chitosan Conduits for Nerve Tissue Engineering
Authors: Ao Q. , Wang A.J. , Cao W.L. , Zhao C. , Gong Ya Dong , Zhao N.M. , Zhang X.F.
Published: March 2009

A new method to fabricate porous chitosan nerve conduits with multi-channels was
described. A uniquely designed mold was composed of 7-50 stainless steel needles and a set of plastic pedestals. Porous or imperforate chitosan tubes with 2-5mm inner diameter and 0.2-1.0 mm wall thickness were made firstly. The chitosan tubes were injected with 3% chitosan gel. The stainless steel needles longitudinally perforated through the chitosan tubes filled with chitosan gel, and the plastic pedestals were used to fix the needles. Lyophilization was used to finish fabrication.
The diameter of channels was 0.2-0.4mm. Swelling property and biodegradability of
Multi-channeled chitosan conduits were investigated. Wright’s staining and scanning electron microscope (SEM) were used to observe spread and proliferation of Neuroblastoma cells (N2A, mouse) on the conduits. It is promising that the porous chitosan nerve conduits with multi-channels are used as nerve tissue engineering scaffolds in repair of peripheral nerve and spinal cord injuries.
Nucleation and Growth of Bone-Like Apatite on Surfaces of Metals, Ceramics and Polymers in Simulated Body Fluids
Authors: Weng Jie , Feng Bo , Wang Min , Zhang Xing Dong
Published: March 2009

The biomimetic approach of mineralization in vitro is adopted to investigate
systematically the nucleation and growth of bone-like apatite on the surface of biomaterials such as bioceramics, metals and polymers, and those chemically surface-treated. The simulated environment is kept isothermic at the human body temperature of 36.5C with three kinds of simulated physiological fluids. The experimental results show that (1) inherent properties of biomaterials determine their bioactivity and the different crystalline structure of same materials results in the
difference in bioactivity; (2) the bioactivity can effectively be improved by the surface treatment of biomaterials via chemical methods and by the addition of bioactive particles in a polymer matrix; (3) the bone-like apatite, nucleated and grown in the simulated body fluid with the same ion concentrations to that of the human plasma, possesses the same composition, structure and morphology despite of matrixes; (4) the difference in bioactivity with biomaterials is indicated by the different time for bone-like apatite to nucleate and to grow on their surfaces.
Influence of Characteristics of Titanium Oxide Film on the Biological Behavior of Cultured Human Umbilical Vein Endothelial Cells (Huvec)
Authors: Chen Jun Ying , Leng Yong Xiang , Ge Sh.N. , Yang Ping , Wang Jin , Sun H. , Wan Guo Jiang , Zhao An Sha , Huang Nan
Published: March 2009

In the work reported here, titanium oxide film were synthesized using magnetron
sputtering from a high-purity Ti metal target while sustaining a differential oxygen partial pressure of from 0.02 to 0.30 Pa. The biological behavior of endothelial cells grown on the film surface was studied by in vitro human umbilical vein endothelial cell (HUVEC) culture investigation. Our studies revealed that the adherence, growth, and proliferation of endothelial cells on different Ti-O film surfaces were strongly affected by the oxygen partial pressure. The biocompatibility mechanisms of ECs on Ti-O film surfaces were explored using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), a-step profilometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). We conclude that the
various film characteristics such as structure, composition and surface morphology due to the different oxygen partial pressures significantly influence the biological behavior of EC.
Glucosamine Coating for Inhibiting Bacterial Adhesion to Titanium Surfaces
Authors: An Yuehuei H. , Farino Melissa , Kang Qian K. , Demcheva Marina V. , Vournakis John
Published: March 2009

It is known that glucosamine/chitosan derivatives have the ability of inhibiting bacterial adhesion to tooth and biomaterial surfaces. The hypotheses of this article included 1) the inhibition effects of different (chemically) glucosamine products are different and 2) more water-soluble glucosamine preparation(s) may have a superior inhibition effect. The basic testing systems are in vitro static adhesion models and the amount of the adhesion is evaluated by direct counting using epifluorecense microscopy. The test material is a smooth surfaced commercially pure titanium (cp-Ti). The bacterium tested is Staphylococcus aureus. The results showed that compared to the control samples (without glucosamine or chitosan coating) the sulfated p-GlcNAc and Sigma glucosamine HCl significantly inhibited S. aureus adhesion to titanium surfaces (94% and 78% respectively)
Preparation and Characterization of Collagen by Hydrogel Formation Method
Authors: Lu Jian , Lin Xiao Yan , Jiang Bo , Li Xu Dong , Chen Ji Yong , Zhang Xing Dong
Published: March 2009

A kind of medical collagen was prepared by hydrogel formation method. Chemical and physical properties were investigated by FTIR, amino acid analysis, SDS-PAGE, carbohydrate content analysis, heavy metal content analysis. Degradation experiments in vivo and subsequent histological investigations were carried out to evaluate the biological performance. The results suggested that the collagen achieved is promising in tissue engineering scaffold materials for a long-term (more than 12 weeks) implantation application.
Fabrication and Characterization of Mechanically Reinforced Collagen Sponge
Authors: Hiraoka Yosuke , Hiroki Ueda , Kimura Yu , Tabata Yasuhiko
Published: March 2009

This study describes an investigation of collagen sponge mechanically reinforced
through the incorporation of poly(glycolic acid)(PGA) fiber. A collagen solution with PGA fiber homogeneously dispersed was freeze-dried, followed by dehydrothermal cross-linking to obtain collagen sponges incorporating PGA fiber. A collagen sponge without PGA fiber was prepared similarly by using the collagen solution. By scanning electron observation, the collagen sponges exhibited isotropic and interconnected pore structures with an average pore size of 180 µm, irrespective of PGA fiber incorporation. As expected, PGA fiber incorporation enabled the collagen sponge to significantly enhance the compression strength. In vitro cell culture studies revealed that the number of L929 fibroblasts initially attached was significantly greater for the collagen sponge incorporating PGA fiber than for the collagen sponge. In vitro cell proliferation studies revealed that the proliferation of cell was higher for the collagen sponge incorporating PGA fiber, by day 21, than the collagen sponge without PGA fiber. It is possible that shrinkage suppression results in the superior cell attachment and proliferation of sponge incorporating PGA fiber. After subcutaneous implantation into the backs of mice, the residual volume of collagen sponge incorporating PGA fiber was significantly large compared with that of collagen sponge. We concluded that the incorporation of PGA fiber is a simple way to reinforce collagen sponge without impairing the biocompatibility.
Determination of Residual Acrylamide Monomer in Medical Polyacrylamide Hydrogel by HPLC-SPE
Authors: Wan Zi Yi , Xi Ting Fei , Zhao P. , Sun Y. , Feng Z.G.
Published: March 2009

The polyacrylamide hydrogel (PAMG) has been used in cosmetology in China, Ukraine and Russia since 1990s. Because the monomer acrylamide(AM) used to produce PAMG has been implicated as a potential mutagen and reproductive toxicant[1,2], it is important to accurately determine the amount of residual AM monomer in the PAMG. In this study, a quick, practical and simple method to determine AM is presented with respect to the hydrogel. AM is analysed quantitatively by ODS-3 column with ultraviolet (UV) absorbance detector. AM is separated from interferential component with an aqueous solution of 0.9%NaCl (NS) adjusted at pH~3.7 using hydrochloric acid and then detected at a UV wavelength of 210 nm. The results show that ODS-3 is effective approach for quantifying AM concentrations in PAMG. This method has a lower detection limit of 0.003µg/ml and a linear response range of 0.003 and 0.9 µg/ml (depending on the range required for analysis). Precision studies give coefficients of variation of <3.2%(n=5) for 0.003µg/ml. The recoveries for this method are greater than 90%. When AM content in PAMG is lower than the detection limit of this method, SPE (solid phase extraction) could be used to concentrate AM. In the case, C18 cartridge is used. And the recoveries are about 70% for SPE when AM concentration is lower than ppb.
Biomimetic Mineralization and Bioactivity of Phosphorylated Chitosan
Authors: Chen Zhi Qing , Li Quan Li , Zen Quan , Li Gang , Jiang Hao Bin , Liu Laikui , Darvell Brian W.
Published: March 2009

Phosphorylated chitosans were synthesized as templates to manipulate hydroxyapatite (HA) crystal nucleation, growth and microstructure. Two kinds of insoluble phosphorylated chitosan were soaked in saturated Ca(OH)2 solution for 4 d and in 1.5× SBF (simulated body fluid) solutions for 14 d at 37 °C for biomimetic mineralization. A lower [P]-content of phosphorylated chitosan promoted greater mineralization than higher [P]-content. Phosphorylated chitosan inhibited osteoblast proliferation and differentiation in vitro, while calcium phosphate phosphorylated chitosan composites did not.
Synthesis and Biocompatibility Evaluation of Poly(HEMA-Co-MMA) Orbital Implant
Authors: Shi Yi Ping , Yin Don Fang , Hu Ping , Huang Yi Fei , Liu Lin
Published: March 2009

Orbital implant, used for filling the space after enucleation, played an important role in
the optical orthopedic operations. However, the clinical application of soft orbital implants was in a limited extent. This paper focused on the synthetic method of a new kind of soft poly (2-hydroxyethyl methacrylate) (PHEMA) orbital implant. This method included two steps, making the orbital implant with through-holes by salt leaking method and improving the compress property of PHEMA by copolymerizing it with methyl methacrylate (MMA). Scanning electronic microscope (SEM), thermo gravimetric analysis (TGA), and compress experiment were carried out
to evaluate the physical properties of the implant. And to evaluate the biocompatibility of this poly (HEMA-co-MMA) orbital implant, short term and long term observations were studied after subcutaneous implantation of material blocks and implantation of orbital implants (diameter in 14mm) in rabbits’ orbits.
Biodegradable Polymer Scaffold for Tissue Engineering
Authors: Tateishi Tetsuya , Chen Guo Ping
Published: March 2009

A new method for the preparation of biodegradable porous scaffolds has been developed by using preprepared ice particulates as porogen material. A novel kind of hybrid biodegradable porous scaffold has been developed by forming collagen microsponges in the pores or interstices of a synthetic polymer sponge or mesh. A hybrid sponge of synthetic polymer, collagen and hydroxyapatite has been developed for hard tissue engineering. Bovine articular cartilage-like tissue has been engineered by culturing chondrocytes in the PLGA-collagen scaffolds.
Torsion Property and Cyclic Fatigue Fracture Behavior of Nickel-Titanium Endodontic Instruments
Authors: Zheng Yu Feng , Li Chao , Huang Chen , Zhao Lian Cheng
Published: March 2009

The torsion property and rotary fatigue fracture behavior of SmartÒ K file and R reamer made of nickel titanium alloy have been studied by means of Shimadzu Autograph DDS-10T universal tester and man-made cyclic system with curved copper tubes as simulated root canal. The instrument surface and the cyclic fatigue fracture surface have been investigated by optical microscope and scanning electron microscope. Comparing with ANSI/ADA specification no.28, maximum torsion values of both SmartÒ K and R endodontic instruments are satisfied in practice. Tensile stresses on the outer surface of the endodontic instruments play a dominant role in fracture initiation during cyclic fatigue fracture. The cyclic number corresponding to cyclic fatigue fracture decreases with the increase of the instrument size number/ curvature. SmartÒ K- and R endodontic instruments exhibit good ductility characteristics, therefore superior resistance to fracture.
Use of Polyglycolic Acid Unwoven and Woven Fibers for Tendon Engineering In Vitro
Authors: Wei Xian , Zhang P.H. , Wang W.Z. , Tan Z.Q. , Cao De Jun , Xu F. , Cui Lei , Liu Wei , Cao Yi Lin
Published: March 2009

Objective: To compare biocompatibility, degradation, and mechanical properties of
polyglycolic acid (PGA) unwoven and woven fibers as scaffolding materials for tendon engineering in vitro. Methods: Three kinds of PGA fibers were included in this study. PGA raw material (Purac Co, Holland) was spun into single PGA filaments that were further twisted into woven fibers (PGA- 1). PGA filaments (Nantong Holycon, China) were twisted into woven fibers (PGA-2) as well.
PGA-1 and PGA-2 served as experimental groups 1 and 2, while unwoven PGA fibers (Albany Co, USA) served as control group. Three types of PGA fibers were made into cord-like scaffolds that mimic tendon shape and compared with each other for biocompatibility, degradation and biomechanical properties. Avian tenocytes were isolated from digital flexor tendon and expanded in vitro. Cells of the second passage were seeded onto the PGA scaffolds. In the first 2 weeks, the cell-
PGA constructs were in vitro cultured without tension and observed for cell adhesion and matrix production. The constructs were then cultured under dynamic loading in a bioreactor for another 2 weeks followed by gross and histological examinations. Results: PGA unwoven fibers have the median diameter of 10µm, while PGA-1 and PGA-2 fibers have the median diameters of 200µm and 60µm, respectively. Microscopy showed that tenocytes adhered well to all three types of PGA fibers in the first 10 days and produced abundant matrices. However, cells showed poor viability on PGA-2 fibers after 10 days, yet good viability on the other two PGA fibers over 2 weeks of observation period. H&E staining showed that there were viable cells and abundant matrices in the control and PGA-1 groups, but not in PGA-2 group after 4 weeks of in vitro culture. Additionally, PGA unwoven fibers degraded faster than woven fibers (PGA-1 and -2). Interestingly, the PGAtenocyte constructs formed tendon-like tissue after 4 weeks of in vitro culture grossly and histologically. Furthermore, mechanical test demonstrated that both PGA woven fibers had much higher tensile strength than unwoven fibers. Conclusion: Different PGA fibers have different biocompatibility with seeded tenocytes. PGA woven fibers could bear more intense mechanical loading and degrade slower than unwoven fibers, which is essential for in vitro generation of tendon tissue. Thus PGA woven fibers might serve as a proper form of scaffolding material for in vitro tendon engineering in a bioreactor.
Biomimetic Synthesis of Apatite - Polyelectrolyte Complex (Chitosan - Phosphorylated Chitosan) Hydrogel as an Osteoblast Carrier
Authors: Li Quan Li , Chen Zhi Qing , Ou Guo Min , Liu Laikui , Jiang Hao Bin , Zeng Quan , Li Gang , He G. , Mo An Chun , Darvell Brian W.
Published: March 2009

A novel three-dimensional scaffold of hydroxyapatite(HA)-polyelectrolyte complex (PEC) composite hydrogel was synthesized by a biomimetic method. PEC hydrogel was formed from equal volumes of 1% phosphorylated chitosan in water and 1% chitosan in 1% acetic acid solution. This PEC hydrogel was soaked in saturated Ca(OH)2 solution for 4 d and then in accelerated calcification solution (ACS) for 7 d, both at 37 oC. The PEC hydrogel was a nano-composite material with multiple levels of hierarchical porosity; hydroxyapatite (HA) crystals nucleated and grew on the fiber surfaces of the hydrogel; Rat osteoblasts were then seeded in this three-dimensional scaffold of HA-PEC composite hydrogel, the three-dimensional scaffold of HA-PEC hydrogel revealed excellent biocompatibility.
Edge Flaking - Similarity between Quasistatic Indentation and Impact Mechanisms for Brittle Materials
Authors: Morrell Roger
Published: March 2009

The process of edge flaking of brittle materials is a significant limitation in design, handling and use of components. Simple quasistatic tests to identify resistance to edge flaking can be based on near-edge indentation and scratching towards an edge, and these produce rankings of materials that broadly correlate with GIc or KIc. However, most edge damage occurs in practice by impact. Using a drop-weight impact tester, edge chipping tests have been performed dynamically on a range of brittle materials, using repeated impact with step-wise height increments until fracture. It has been found that when impact energy rather indentation force is used as the correlative parameter against distance of the impact site from the edge of the test-piece, a similar relationship to that of quasistatic indentation is found. The shapes of edge flakes produced may also similar. This suggests that even when a relatively blunt impactor is used, compared with conventional indenters, the mechanics of the failure are similar. However, the occurrence of ring cracks can lead to unusual flake shapes. It follows that simpler-to-perform quasistatic tests can model the less well-defined dynamic impact situation in terms of testing for the effects of geometry or for comparing performance of different material types.
Failure Behaviour of High Toughness Multi-Layer Si3N4 and Si3N4-TiN Based Laminates
Authors: Blugan Gurdial , Dobedoe Richard , Gee I. , Orlovskaya Nina , Kübler Jakob
Published: March 2009

Multi-layer laminates were produced using alternating layers of Si3N4 and Si3N4+TiN. The differences in the coefficient of thermal expansions between the alternating layers lead to residual stresses after cooling. These are compressive in the Si3N4 layers and tensile in the Si3N4+TiN layers. The existence of these stresses in the laminates effect the crack propagation behaviour during failure. Different designs of laminates were produced with external layers under compression and tension exhibiting different failure mechanisms. Facture toughness was measured by SEVNB method. In systems with external layers under compression the measured fracture toughness was up to three times that of Si3N4, i.e. up to 17 MPa m1/2. In systems with external layers under tension during failure the energy absorbing effects of crack deflection and crack bifurcation were obtained. High temperature tests were performed to determine the onset temperature for residual stresses in these laminates. Micro-laminates with compressive layers of only 30 µm thickness with high strength and fracture toughness and were manufactured.
R-Curves in Al2O3 - Al2O3/ZrO2 Laminates
Authors: Pascual Javier , Chalvet Francis , Lube Tanja , de Portu Goffredo
Published: March 2009

In order to better understand the fracture behavior of Al2O3-Al2O3/ZrO2 laminates, controlled crack growth experiments were carried out. The method proposed consists of a threepoint bending test of a sandwich beam in which a notched specimen is located in between two metallic bars. Under certain conditions that will be commented, stable crack growth can be obtained. The fracture pattern is related to the residual stresses present in the laminate. R-curves for the laminate were also calculated using the weight function method, including the influence of the free surface. Toughness values are presented in the R-curve after friction considerations.
Contact Fatigue in Ceramic Laminated Composites
Authors: Ceseracciu Luca , Chalvet Francis , Jiménez-Piqué Emilio , Anglada Marc , de Portu Goffredo
Published: March 2009

In this work, the study of the contact fatigue of an alumina-based laminated composite with compressive residual stress in the surface is presented, together with monolithic alumina as a reference material. Hertzian indentation techniques were employed, which better represent the inservice actual contact loading. Different tests were performed under static and cyclic loading. The evolution of damage and the different types of fracture produced were examined, and an improvement in contact resistance of the composite, due to compressive residual stress, was highlighted. A better resistance of the laminated composite was observed for every test in comparison with the monolithic reference material.
The Preparation and Properties of Functionally Graded Alumina/Zirconia-Toughened Alumina (ZTA) Ceramics for Biomedical Applications
Authors: Beranič Klopčič Sabina , Novak Saša , Kosmač Tomaž , Richter H.G. , Hecht-Mijic S.
Published: March 2009

Functionally graded alumina/zirconia-toughened alumina (ZTA) ceramics for biomedical applications were designed with a hard, wear-resistant alumina surface and a tough, zirconia-rich core. The main goal was to achieve an improved mechanical performance by introducing a residual compressive stress in the outer surfaces. Symmetrical, 7-layered samples were prepared by the sequential slip-casting of specimens from suspensions prepared at the inherent pH values, close to the pH values at which the maximum (negative) zetapotential was measured. No sintering or tunneling cracks were observed in the samples, but large defects, such as big agglomerates, air bubbles and large circular pores at layer interfaces, which resulted from preparing the samples using the slip-casting technique, were readily observed. The strength of the symmetrical composites is influenced by the presence of defects, which most probably originate from the shaping process. Therefore, the defects have to be regarded as the reason why the strength of the 7-layered composites is low.
Delayed Fatigue of Hydroxy- and Fluorhydroxyapatite Ceramics in Simulated Body Fluid
Authors: Barinov Sergej M. , Fadeeva I.V. , Fateeva L.V. , Tumanov S.V.
Published: March 2009

Ultrafine hydroxyapatite (HA) and fluorhydroxyapatite (FHA) powders were
synthesized and dense bioceramic samples were fabricated thereof. The samples were treepoint bend tested in different environments, i.e. in ambient air, distilled water and simulated human saliva, in the wide deformation rate range. Weibull’ statistics test was performed under standard testing conditions but in different media. The stress velocity exponent was evaluated from the dynamic fatigue testing data. The mean strength is shown to decrease when both ceramics are exposed to water or to simulated saliva. HA ceramics is more susceptible to the environment compared to FHA ceramics, due to the later is less subjected to the stress corrosion. Fracture surface observations revealed the crack propagation is of mixed trans- and
intergranular mode. Strength distribution changes from uni-modal in air environment to bimodal in harsh conditions of water and saliva, indicating slow increment of flaw size in ceramics. Crack velocity exponent values correspond to transient region from dissociative chemisorption to ion solvation mechanisms of stress corrosion in both HA and FHA ceramics. Generally, FHA ceramics is considered to be much more reliable for application in bone defects replacement or dental reconstruction.
Nanofractography of Alumina by Scanning Probe Microscopy
Authors: Tatami Junichi , Ohbuchi Tomoko , Komeya Katsutoshi , Meguro Takeshi
Published: March 2009

Observation of fracture surfaces in ceramics is useful for improving their mechanical
properties. In this study, fracture surfaces of polycrystalline alumina were observed using scanning-probe microscopy (SPM) on a nanoscale, also called “nano-fractography.” The average grain size of polycrystalline alumina specimen used in this study was 4.5µm, and the fracture toughness was 3.0MPa･m-1/2. The fracture mode was found to be a mixture of intergranular and transgranular fractures. The fracture surface of intergranular fractures consisted of smooth and rough areas composed of very small steps, whose detection was impossible using scanning electron microscopy. Cleavage and non-cleavage fractures were observed in transgranular fracture grains. The fracture surface of single-crystalline alumina, which is the typical model of the transgranular fracture, was also observed by SPM. The cleavage plane of alumina macroscopically exhibited a very smooth, glass-like surface. However, sub-nano meter steps can be observed on the cleavage fracture surface and appear to be formed by plastic deformation during crack propagation because the size of the step nears that of the Burgers vector.
Effect of Cutting Edge Truncation on Ground Surface Morphology of Hard and Brittle Materials for Optical Devices
Authors: Kang X. , Tamaki Junichi , Kubo Akihiko , Yan Ji Wang , Iyama Toshirou
Published: March 2009

For the purpose of investigating the effect of cutting edge truncation on ground surface morphology, several kinds of hard and brittle materials used for optical devices, borosilicate glass, glass quartz, crystal quartz and sapphire, are plunge ground with a SD600 metal-bonded grinding wheel, the cutting edges of which are truncated so as to be aligned with the height level of the grinding wheel working surface, after electrocontact discharge truing and dressing. It is found that an
improvement of roughness can be obtained for every material investigated, although the degree of roughness improvement depends on the kind of material. Ductile-mode grinding is most likely to be realized in the case of crystal quartz.
Development on Micro Precision Truing Method of ELID-Grinding Wheel (1st Report: Principle & Fundamental Experiments)
Authors: Ohmori Hitoshi , Yin Shao Hui , Lin Wei Min , Uehara Yoshihiro , MORITA Shinya , Asami Muneaki , Ohmori M.
Published: March 2009

Metal bonded diamond grinding wheels are widely used in the grinding process, especial in ELID grinding. However, truing is difficult owing to the high toughness of metal bond materials and high hardness of diamond abrasives. To realize high precision and high-efficiency truing, we propose a new micro-truing method consisting of electro-discharge truing and electrolysis-assisted mechanical truing in this paper. The process principle and fundamental experimental results are introduced, and the truing performance is discussed. Research results show that the proposed new method is effective for truing metal bonded diamond grinding wheels.
Study on Internal Magnetic Field Assisted Finishing Process Using a Magnetic Machining Jig
Authors: Zou Yan Hua , Shinmura Takeo
Published: March 2009

This paper examines a new magnetic field assisted machining process using a magnetic machining jig. By using this process, a high efficiency and high quality internal finishing process can be achieved, and it was clarified that it was very effective to finish the internal surface of a thick tube (5~30mm in thickness). In this study, the experiments performed on the SUS304 stainless steel tubes (10mm in thickness) examine the applicability of improving the internal surface roughness and the roundness of inside tube, and it also examine the effects of a rotational speed of the magnetic machining jig. The results showed that this processing method enables improve the internal surface roughness and the roundness of inside tube. It is clarified that the roundness of inside tube is highly dependent on the rotational speed of magnetic machining jig, and the roundness can be improved rapidly at a higher rotational speed with the magnetic machining jig.
Fundamental Verification of Ultraviolet-Excited Abrasion and Polishing Characteristics of Copper - Study of Luminescence Machining -
Authors: Chiwaya Y. , Tanaka Takeshi
Published: March 2009

When a light-excitation substance such as a high polymer absorbs the light energy of an ultraviolet ray, it will be excited. If this substance reacts with the processing material in an atomic order under the excited conditions, it may be available for use in fine processing. Thus, it appears that the processing in a sub-nanometer order may be realized by a phenomenon called luminescence. The following merits can be considered: 1) little reaction heat, 2) little heat influence on the processed material, 3) easy reaction control in comparison with chemical processing. In this research, the processing principle was verified by dipping the processing material for a fixed time in pure water mixed the fluorescent substance exposed to an ultraviolet ray. The surface of copper that had been precisely lapped was used in the experiment. The abrasion of its surface was observed by AFM. Based on the results of these basic experiments, an ultraviolet-ray irradiation type polisher was manufactured for use in the polishing experiment of copper. This paper describes
the polishing characteristics of copper exposed to an ultraviolet ray.
Prevention from Delamination of Composite Material during Drilling Using Ultrasonic Vibration
Authors: Aoki Shigeru , Hirai Seiji , Nishimura Tadashi
Published: March 2009

Composite materials are used for many structures because of its high strong-to-weight ratio and easy formation. Secondary machining processes such as drilling and sawing are required to assemble and join composite materials to other structures. When composite materials are machined, delamination occurs at adhesive layer between laminated layers. It is well known that it is possible to
cut hard metals and to improve precision of machined surface by using ultrasonic vibration. This method is applied to machining composite materials in this paper. Drilling of composite materials is focused on. First, this method is examined experimentally. Next, experimental results are examined by analytical method. Using condition of experiment, prevention of delamination can be demonstrated from the proposed analytical method.
Electroforming of Copper/ZrB2 Composites Coatings and Its Performance as Electro-Discharge Machining Electrodes
Authors: Jin Zhu Ji , Zhang Min , Guo Dong Ming , Kang Ren Ke
Published: March 2009

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.
The Research of Carbon Steel Surface Finished by Pulse Electrochemical Finishing Technology
Authors: Wang H. , Zhou Jian Jiang , Xu Wen Ji
Published: March 2009

This paper deals with a new finishing technique called pulse electrochemical finishing
technology (PECF) and its application to column surface of carbon steel. PECF makes use of pulse current and neutral electrolyte. There is nearly no wear of the cathode, and nearly no cutting force or cutting heat, which may result in the deformation of wokpiece. The principle of the technique is put forward, and the equipment as well as a typical finished sample is shown in this paper. The key
technological parameters of PECF are studied and the favorable values are presented. With the moving cathode PECF technology, the roughness value of ground surface could be reduced from Ra 0.217～1.13μm to Ra 0.041μm. Combined with NC technology, PECF could be applied to the finishing field widely.
Hilbert-Huang Transform and Its Application in Gear Faults Diagnosis
Authors: Li H. , Zheng H.Q. , Tang L.W.
Published: March 2009

Time-frequency and transient analysis have been widely used in signal processing and faults diagnosis. These methods represent important characteristics of a signal in both time and frequency domain. In this way, essential features of the signal can be viewed and analyzed in order to understand or model the faults characteristics. Historically, Fourier spectral analyses have provided a general approach for monitoring the global energy/frequency distribution. However, an assumption
inherent to this method is the stationary and linear of the signal. As a result, Fourier methods are not generally an appropriate approach in the investigation of faults signals with transient components. This work presents the application of a new signal processing technique, empirical mode decomposition and the Hilbert spectrum, in analysis of vibration signals and gear faults diagnosis for a machine tool. The results show that this method may provide not only an increase in the spectral resolution but also reliability for the gear faults diagnosis.
Theoretical Models and Experimental Techniques in Nondestructive Evaluation of Concrete
Authors: Brigante Michele , Modano Mariano
Published: March 2009

When evaluating concrete strength, common opinion is that adequate precisions can be achieved only by a particular or even total destruction. However, such methods are not always applied, besides they are very laborious. The NDE methods have a number of merits, when compared with destructive ones: a possibility to find cracks and hidden flaws in concrete; besides, they show good results in testing materials of other types, such as metals and composites. At the same time, application of NDE methods to concretes is difficult because of their complex internal structure. No existing theory can predict these properties of the transmitted wave. Therefore, the main goal of the present work is to propose a theoretical model enabling the wave penetration of ultrasonic wave through a medium with multiple internal obstacles to be described adequately. Practical applications of this ultrasonic method is toward the evaluation of mechanical properties of concrete, where the influence of internal dislocations, such as pores and cracks, is of significant importance.
Novel Vibration-Based Methods for Detecting Delamination Damage in Composite Plate and Shell Laminates
Authors: Gherlone Marco , Mattone Massimiliano , Surace Cecilia , Tassotti Alessandra , Tessler Alexander
Published: March 2009

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.
Crack Detection Using Acoustic Emission Methods – Fundamentals and Applications
Authors: Rogers Leonard M.
Published: March 2009

This paper addresses the fundamentals of the acoustic emission effect associated with fatigue and stress corrosion cracking in metals. It considers the microstructure of cracks and the magnitude of the different types of physical event that can occur at the crack tip during plastic deformation and stable crack growth. Expressions are given for the threshold plastic zone size ‘Dl’ at which local fracture instability occurs and the stress-wave displacement amplitude as a function of distance ‘ui(r)’ for the different wave types ‘i’ produced during crack extension. Dispersion of the stress-wave and its convolution into an electrical burst signal at the sensor is considered together with the choice of appropriate sensing frequency. A methodology is described for correcting the measured signal amplitude for attenuation in the structure and for determining the maximum sensor spacing for the detection and location of events of a specified magnitude ‘Mae’ similar to the Richter scale. Case studies are presented to illustrate the extensive database now available on acoustic emission from crack growth in metallic structures and the technical and commercial benefits to be gained from an acoustic emission based inspection strategy. The applications considered are:
• Fatigue crack growth in the node joints of offshore structures,
• Stress corrosion cracking in platform flow lines.
Dynamics of Large Power Rotating Machine with Cracked Shaft
Authors: Banaszek Slawomir
Published: March 2009

The paper presents the course and results of crack propagation simulation research. The object taken into account is a large power turbo-set rotor. The computer code system NLDW is presented. It uses a non-linear model of journal bearings, and well known crack model. Crack depth is marked by a crack coefficient. It is shown the crack generates a coupled forms of lateral, axial and torsional vibrations in multi-support rotor. Their intensity depends on the axial and circumferential crack location on the shaft. The attempt at pointing a proper diagnostic indicator for crack detection in large rotating machine is made according to obtained results.
Effect of Shaft Unbalance on the Operation of Worm Gear Rolling Bearings
Authors: Strzelecki Stanislaw , Towarek Z.
Published: March 2009

The vibration generated by the deformed and unbalanced shaft has caused the
damage and the failure of the rolling bearings of worm gears that are coupled by universal joints shaft. These worm gears operate in heavy duty machine. Based on the analysis of the dynamic loads applied to the rolling bearings of worm gear and the measurements of velocities of displacements the reasons of worm gears vibration were determined. The recommendations for avoiding the damage of worm gears are given too.
Tracking of Cracks in Airplane Components Using Nonlinear Surface Wave Propagation Techniques
Authors: Vanlanduit Steve , Guillaume Patrick , Vermeulen Jimmy , Harri Kristof
Published: March 2009

Ultrasonic surface waves provide a sensitive means to detect cracks in airplane structures. Until now several obstacles remained to use ultrasonic surface waves for on-line damage detection (i.e. in-flight). In this article a method will be proposed to detect a growing fatigue crack while the aircraft is operating. In contrast to classical ultrasonic measurement methods, that use a high voltage pulse, we applied an optimized multi-sine excitation signal with an amplitude of a few volts only (this agrees better with the applicable safety regulations for aircraft). Furthermore, an indicator quantifying the nonlinearity of the ultrasonic surface wave propagation is used. By using a nonlinearity index the influence of changing operation conditions that can be observed with most linear methods is eliminated. The proposed method is validated on a steel beam that is fatigue loaded with a force signal obtained from in-flight data.