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Bending Strength (bending + strength)
Selected AbstractsThree-Dimensional Printing of Complex-Shaped Alumina/Glass Composites,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Wei Zhang Abstract Alumina/glass composites were fabricated by three-dimensional printing (3DPÔ) and pressureless infiltration of lanthanum-alumino-silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600,°C for 2,h prior to glass infiltration at 1100,°C for 2,h. The influence of layer thickness and sample orientation within the building chamber of the 3D-printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150,µm resulted in an increase of the total porosity from ,19 to ,39,vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y -axis of the 3D-printer compared to those orientated along the X - or the Z -axis, respectively. Fabricated Al2O3/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6,MPa m1/2, 175,MPa, 228,GPa, and 12,GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process. [source] Bending strength and depth of cure of light-cured composite resins irradiated using filters that simulate enamelJOURNAL OF ORAL REHABILITATION, Issue 1 2004H. Arikawa summary, This study evaluates the light-attenuating effects of enamel on the properties of light-cured restorative resins using simple experimental filters. Three filters were designed to replicate the light transmittance characteristics of 0·5, 1·0 and 1·5 mm thick human enamel. The bending strength, depth of cure, and levels of residual monomer for 12 shades of three commercial light-cured composite resins were examined. These resins were cured either using direct irradiation from a light source or irradiation through one of the filters. For all materials, the bending strength and depth of cure of specimens irradiated through a filter were lower and the levels of residual monomer were higher than those found in specimens irradiated directly. The results indicate that the light-attenuating effect of enamel reduces the polymerization efficiency, resulting in poorer mechanical properties of light-cured composite resins. [source] Health Monitoring of Rehabilitated Concrete Bridges Using Distributed Optical Fiber SensingCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2006Wei Zhang As newly developed techniques, distributed optical fiber sensing (DOFS) have gradually played a prominent role in structural health monitoring for the last decade. This article focuses on the employment of two types of DOFS, namely fiber Bragg grating (FBG) and Brillouin optical time domain reflectometry (BOTDR), into an integrated HMS for rehabilitated RC girder bridges by means of a series of static and dynamic loading tests to a simply supported RC T-beam strengthened by externally post-tensioned aramid fiber reinforced polymer (AFRP) tendons. Before the loading tests, a calibration test for FBG and another one for BOTDR were implemented to, respectively, obtain good linearity for both of them. Monitoring data were collected in real time during the process of external strengthening, static loading, and dynamic loading, respectively, all of which well identified the relevant structural state. The beam was finally vibrated for 2 million cycles and then loaded monotonously to failure. Based on the bending strength of externally prestressed members, ultimate values for the test specimen were numerically computed via a newly developed simplified model, which satisfactorily predicted the ultimate structural state of the beam. And then the alert values were adopted to compare with the monitoring results for safety alarm. The investigation results show a great deal of applicability for the integrated SHM by using both DOFS in rehabilitated concrete bridges strengthened by external prestressing. [source] Vitrified Silica-Nanofiber Mats as Reinforcements for Epoxy ResinsADVANCED ENGINEERING MATERIALS, Issue 5 2009Oliver Weichold The effects of vitrified, electrospun silica nanofiber mats on the tensile and bending strength (see Figure) of epoxy resins are presented. The mats consist of randomly oriented, amorphous filaments of 600,800,nm diameter. The effects of annealing conditions and surface functionalization on the fiber/matrix adhesion is discussed. The results are compared to those of reference materials. [source] Microstructures and Mechanical Properties of Hot-Pressed ZrB2 -Based Ceramics from Synthesized ZrB2 and ZrB2 -ZrC Powders,ADVANCED ENGINEERING MATERIALS, Issue 3 2009Wei-Ming Guo The influence of ZrC on the microstructure and mechanical properties of ZrB2 -SiC ceramics was investigated. SEM observation showed that the presence of ZrC greatly inhibited the grain growth of ZrB2 and SiC phases. With the introduction of ZrC, the Vickers' hardness, fracture toughness, and bending strength of the sintered ceramics increased significantly. [source] Crack-healing behaviour and resultant high-temperature fatigue strength of machined Si3N4/SiC composite ceramicFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2008Y.-S. JUNG ABSTRACT The crack-healing behaviour of machining cracks in Si3N4/20 wt% SiC composite was investigated. The machining cracks were introduced by a heavy machining process, during the creation of a semicircular groove. The machined specimens were healed at various temperatures and times in air. The optimized crack-healing condition of the machined specimens was found to be a temperature of 1673 K and a time of 10 h. The specimens healed by this condition exhibited almost the same strength as the smooth specimens healed. Moreover, the bending strengths and the fatigue limits of the machined specimens healed were systematically investigated at temperatures from room temperature to 1673 K. The machined specimens healed at the optimized condition exhibited an almost constant bending strength (,700 MPa) up to 1673 K. Also, the specimens exhibited considerably high cyclic and static fatigue limits at temperatures from 1073 to 1573 K. These results demonstrated that the crack-healing could be an effective method for improving the structural integrity and reducing machining costs of the Si3N4/SiC composite ceramic. [source] A new methodology to guarantee the structural integrity of Al2O3/SiC composite using crack healing and a proof testFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2007M. ONO ABSTRACT Structural ceramics are brittle and sensitive to flaws. As a result, the structural integrity of a ceramic component may be seriously affected by inherent flaws. Self-crack-healing is an excellent answer to this problem. At the moment, however, there is no technique to heal embedded flaws. Therefore, a technique to guarantee the reliability of ceramic components is demanded, and thus a technique using crack healing followed by proof test was developed by K. Ando et al. to accomplish this. With this technique, testing the mechanical behaviour of the crack-healed zone is very important for ensuring the structural integrity of a ceramic component. In this study, first Al2O3/SiC composite with an excellent crack-healing ability was sintered. Second, a crack was introduced on the sample (3 mm × 4 mm × 36 mm), which reduced the bending strength by about 80%, and subsequently the crack was healed. Third, a proof test was carried out on the crack-healed sample. Last, using the crack-healed and proof-tested sample, a fracture test was carried out up to 1373 K. The measured minimum fracture stress (,Fmin) was compared with the theoretical minimum strength (,G) from room temperature (R.T.) to 1373 K. It was concluded that ,G showed good agreement with ,Fmin up to 1373 K and that the crack healing followed by proof test was an excellent technique to increase the survival probability by administering a proof test and to guarantee the reliability of Al2O3/SiC composite. [source] Processing of urea-formaldehyde-based particleboard from hazelnut shell and improvement of its fire and water resistanceFIRE AND MATERIALS, Issue 8 2009M. Gürü Abstract The purpose of this study was to manufacture urea-formaldehyde-based particleboard from hazelnut shell and eliminate its disadvantages such as flammability, water absorption, swelling thickness by using fly ash and phenol-formaldehyde. Synthesized urea-formaldehyde and grained hazelnut shells were blended at different ratios ranging from 0.8 to 3.2 hazelnut shell/urea-formaldehyde and dried at 70°C in an oven until constant weight was reached. In addition, other parameters affecting polymer composite particleboard from hazelnut shell and urea-formaldehyde were investigated to be the amount of fly ash, amount of phenol formaldehyde and the effects of these parameters on bending stress, limit oxygen index, water absorption capacity and swelling in the thickness. The optimization results showed that the maximum bending strength was 4.1N/mm2, at urea-formaldehyde ratio of 1.0, reaction temperature of 70°C, reaction time of 25,min, hazelnut shell/urea-formaldehyde resin of 2.4 and mean particle size of 0.1,mm. Although the limited oxygen index and smoke density of composite particleboard without fly ash has 22.3 and 1.62, with fly ash of 16% (w/w) according to the filler has 38.2 and 1.47, respectively. Water absorption and increase in the swelling thickness exponentially decreased with increasing phenol formaldehyde. Copyright © 2009 John Wiley & Sons, Ltd. [source] Sintered Reaction-Bonded Silicon Nitride with High Thermal Conductivity and High StrengthINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2008You Zhou Sintered reaction-bonded silicon nitride (SRBSN) materials were prepared from a high-purity Si powder doped with Y2O3 and MgO as sintering additives by nitriding at 1400°C for 8 h and subsequently postsintering at 1900°C for various times ranging from 3 to 24 h. Microstructures and phase compositions of the nitrided and the sintered compacts were characterized. The SRBSN materials sintered for 3, 6, 12, and 24 h had thermal conductivities of 100, 105, 117, and 133 W/m/K, and four-point bending strengths of 843, 736, 612, and 516 MPa, respectively. Simultaneously attaining thermal conductivity and bending strength at such a high level made the SRBSN materials superior over the high-thermal conductivity silicon nitride ceramics that were prepared by sintering of Si3N4 powder in our previous works. This study indicates that the SRBSN route is a promising way of fabricating silicon nitride materials with both high thermal conductivity and high strength. [source] Development, Analysis, and Application of a Glass,Alumina-Based Self-Constrained Sintering Low-Temperature Cofired CeramicINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2007Takahiro Takada The effects of an inner constraint layer and alumina particles on the microstructure, strength, and shrinkage of the laminated low-temperature cofired ceramic (LTCC) green sheet were investigated. Alumina particles of several sizes were used in the inner-constraint layer in order to strengthen the LTCC substrate. Smaller alumina particles in the inner-constraint layer produced a substrate with a high bending strength. Sintering shrinkage in the x,y direction of the LTCC is related to the bending strength of the debinded alumina particle layer used for an inner-constraint layer. A larger pore size in the inner-constraint layer was found to increase the distance of the glass penetration from the glass,alumina layer into the inner-constraint layer. The total thickness of the constraint layer changes the shrinkage in the x,y direction and the bending strength. [source] Low Skeletal Muscle Mass Is Associated With Poor Structural Parameters of Bone and Impaired Balance in Elderly Men,The MINOS Study,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 5 2005Pawel Szulc MD Abstract In 796 men, 50-85 years of age, decreased relative skeletal muscle mass index was associated with narrower bones, thinner cortices, and a consequent decreased bending strength (lower section modulus), as well as with impaired balance and an increased risk of falls. Introduction: In men, appendicular skeletal muscle mass (ASM) is correlated positively with BMC and areal BMD (aBMD). In elderly men, low muscle mass and strength (sarcopenia) is associated with difficulties in daily living activities. The aim of this study was to evaluate if ASM is correlated with bone size, mechanical properties of bones, balance, and risk of falls in elderly men. Materials and Methods: This study used 796 men, 50-85 years of age, belonging to the MINOS cohort. Lifestyle factors were evaluated by standardized questionnaires. Estimates of mechanical bone properties were derived from aBMD measured by DXA. ASM was estimated by DXA. The relative skeletal muscle mass index (RASM) was calculated as ASM/(body height)2.3. Results: After adjustment for age, body size, tobacco smoking, professional physical activity, and 17,-estradiol concentration, RASM was correlated positively with BMC, aBMD, external diameter, and cortical thickness (r = 0.17-0.34, p < 0.0001) but not with volumetric BMD. Consequently, RASM was correlated with section modulus (r = 0.29-0.39, p < 0.0001). Men in the lowest quartile of RASM had section modulus of femoral neck and distal radius lower by 12-18% in comparison with men in the highest quartile of RASM. In contrast, bone width was not correlated with fat mass, reflecting the load of body weight (except for L3), which suggests that the muscular strain may exert a direct stimulatory effect on periosteal apposition. After adjustment for confounding variables, a decrease in RASM was associated with increased risk of falls and of inability to accomplish clinical tests of muscle strength, static balance, and dynamic balance (odds ratio per 1 SD decrease in RASM, 1.31-2.23; p < 0.05-0.001). Conclusions: In elderly men, decreased RASM is associated with narrower bones and thinner cortices, which results in a lower bending strength. Low RASM is associated with impaired balance and with an increased risk of falls in elderly men. It remains to be studied whether low RASM is associated with decreased periosteal apposition and with increased fracture risk in elderly men, and whether the difference in skeletal muscle mass between men and women contributes to the between-sex difference in fracture incidence. [source] The Influence of an Insulin-Like Growth Factor I Gene Promoter Polymorphism on Hip Bone Geometry and the Risk of Nonvertebral Fracture in the Elderly: The Rotterdam Study,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 8 2004Fernando Rivadeneira Abstract The absence of the wildtype allele of a promoter polymorphism of the IGF-I gene is associated with increased risk (1.5; 95% CI, 1.1-2.0) of fragility fracture in women (n = 4212) but not in men (n = 2799). An approximation of hip bone geometry (from DXA) suggested the polymorphism is associated with bone strength and stability in gender-specific ways. Introduction: Previously, we found a CA-repeat promoter polymorphism in the insulin-like growth factor I (IGF-I) gene associated with IGF-I levels and BMD in postmenopausal women, but the relationship with fractures is unclear. In this large population-based study of elderly men and women, we examined the association between this IGF-I promoter polymorphism with parameters of bone geometry and the occurrence of fractures. Material and Methods: Within the Rotterdam Study, a prospective population-based cohort, the IGF-I polymorphism was analyzed in relation to incident nonvertebral fractures in 2799 men and 4212 women followed on average for 8.6 years. Furthermore, we estimated structural parameters of hip bone geometry indirectly from DXA outputs of the femoral neck in 2372 men and 3114 women. We studied neck width, cortical thickness, and the cortical buckling ratio and the section modulus as indexes of bone stability and bending strength. Results: Women heterozygotes and noncarriers of the allele had, respectively, 1.2 (95% CI, 1.0-1.5) and 1.5 (95% CI, 1.1-2.0) increased risk of having a fragility fracture at older age compared with homozygotes for the 192-bp allele (p trend = 0.0007). In men, fracture risk was not influenced by the polymorphism. Compared with homozygotes for the 192-bp allele, noncarrier males had ,1% narrower femoral necks and 2.2% lower section moduli (p trend < 0.05). Noncarrier females had 1.7% thinner cortices and 1.6% higher buckling ratios (p trend < 0.05) but no significant differences in femoral neck widths and section moduli. In women with low body mass index, genotype differences in bone strength (section modulus) and fracture risk were accentuated (p interaction = 0.05). The genotype-dependent differences in hip bone geometry did not fully explain the genotype-dependent differences in fracture risk. Conclusions: The CA-repeat promoter polymorphism in the IGF-I gene is associated with the risk for fragility fracture at old age in women and with bone structure in both genders. [source] A Randomized School-Based Jumping Intervention Confers Site and Maturity-Specific Benefits on Bone Structural Properties in Girls: A Hip Structural Analysis Study,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 3 2002M. A. Petit Abstract We compared 7-month changes in bone structural properties in pre- and early-pubertal girls randomized to exercise intervention (10-minute, 3 times per week, jumping program) or control groups. Girls were classified as prepubertal (PRE; Tanner breast stage 1; n = 43 for intervention [I] and n = 25 for control [C]) or early-pubertal (EARLY; Tanner stages 2 and 3; n = 43 for I and n = 63 for C). Mean ± SD age was 10.0 ± 0.6 and 10.5 ± 0.6 for the PRE and EARLY groups, respectively. Proximal femur scans were analyzed using a hip structural analysis (HSA) program to assess bone mineral density (BMD), subperiosteal width, and cross-sectional area and to estimate cortical thickness, endosteal diameter, and section modulus at the femoral neck (FN), intertrochanter (IT), and femoral shaft (FS) regions. There were no differences between intervention and control groups for baseline height, weight, calcium intake, or physical activity or for change over 7 months (p > 0.05). We used analysis of covariance (ANCOVA) to examine group differences in changes of bone structure, adjusting for baseline weight, height change, Tanner breast stage, and physical activity. There were no differences in change for bone structure in the PRE girls. The more mature girls (EARLY) in the intervention group showed significantly greater gains in FN (+2.6%, p = 0.03) and IT (+1.7%, p = 0.02) BMD. Underpinning these changes were increased bone cross-sectional area and reduced endosteal expansion. Changes in subperiosteal dimensions did not differ. Structural changes improved section modulus (bending strength) at the FN (+4.0%, p = 0.04), but not at the IT region. There were no differences at the primarily cortical FS. These data provide insight into geometric changes that underpin exercise-associated gain in bone strength in early-pubertal girls. [source] Bending strength and depth of cure of light-cured composite resins irradiated using filters that simulate enamelJOURNAL OF ORAL REHABILITATION, Issue 1 2004H. Arikawa summary, This study evaluates the light-attenuating effects of enamel on the properties of light-cured restorative resins using simple experimental filters. Three filters were designed to replicate the light transmittance characteristics of 0·5, 1·0 and 1·5 mm thick human enamel. The bending strength, depth of cure, and levels of residual monomer for 12 shades of three commercial light-cured composite resins were examined. These resins were cured either using direct irradiation from a light source or irradiation through one of the filters. For all materials, the bending strength and depth of cure of specimens irradiated through a filter were lower and the levels of residual monomer were higher than those found in specimens irradiated directly. The results indicate that the light-attenuating effect of enamel reduces the polymerization efficiency, resulting in poorer mechanical properties of light-cured composite resins. [source] Manufacture of Biomorphic SiC Components with Homogeneous Properties from Sawdust by Reactive Infiltration with Liquid SiliconJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Noelia R. Calderon Biomorphic SiC components with homogeneous properties were manufactured from sawdust using a novel method to produce preforms, without addition of any extra binder, but with enough mechanical strength to be carbonized up to 1400°C without deformation. Reactive infiltration of carbon preforms of an adequate open porosity with liquid silicon has been successfully used to prepare biomorphic components. Moreover, the modification of bioSiC properties induced by the structural rearrangement of carbon preforms when they are further heat treated at 2500°C was additionally studied. BioSiC components showed a maximum in bending strength when the material is processed from carbon preforms exhibiting around 40% of open porosity, which seems to be the optimum value for carbon preforms treated at 1400° and 2500°C. However, the heat treatment of the carbon preforms at 2500°C produced bioSiC components with a finer and more homogeneous microstructure than those obtained from carbon preforms treated at 1400°C, improving their bending strength up to 22%. [source] Mechanical Properties and Dimensional Effects of ZnO- and SnO2 -Based VaristorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Miguel Angel Ramírez A comparison between traditional ZnO-(modified Matsuoka system, [ZnO]) and SnO2 -based varistors (98.9%SnO2+1%CoO+0.05%Nb2O5+0.05%Cr2O3, [SCNCr]) regarding their mechanical properties, finite element (FE) modeling, and macroscopic response with current pulse is presented in this work. The experimental values of the elastic (static and dynamic) modulus and bending strength are given. Both the static and the dynamic modulus were two times higher for SnO2 (,200 GPa) with respect to ZnO (,100 GPa). A similar behavior was found for the bending strength, confirming the superior mechanical properties of SCNCr associated with a homogeneous microstructure. The finite element analyses yielded the most appropriate thickness/diameter aspect ratio (H/D), while thermomechanical stress is minimized. The values of (H/D) were lower for the SCNCr in comparison with the ZnO-based varistors, allowing the production of smaller pieces that can resist the same thermomechanical stress. Finally, preliminary analyses of the macroscopic failures for samples treated with degradation pulses of 8/20-,s type allowed to confirm the absence of failures due to cracking and/or puncture in the SCNCr. The absence of these failures originates from the good thermomechanical properties. [source] Pressureless Sintering of ,-Si3N4 Porous Ceramics Using a H3PO4 Pore-Forming AgentJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2007Fei Chen A new method for preparing high bending strength porous silicon nitride (Si3N4) ceramics with controlled porosity has been developed by using pressureless sintering techniques and phosphoric acid (H3PO4) as the pore-forming agent. The fabrication process is described in detail and the sintering mechanism of porous ceramics is analyzed by the X-ray diffraction method and thermal analysis. The microstructure and mechanical properties of the porous Si3N4 ceramics are investigated, as a function of the content of H3PO4. The resultant high porous Si3N4 ceramics sintered at 1000°,1200°C show a fine porous structure and a relative high bending strength. The porous structure is caused mainly by the volatilization of the H3PO4 and by the continous reaction of SiP2O7 binder, which could bond on to the Si3N4 grains. Porous Si3N4 ceramics with a porosity of 42%,63%, the bending strength of 50,120 MPa are obtained. [source] Synthesis, Microstructure, and Mechanical Properties of a Novel Ti2AlC/TiC/Al2O3In Situ CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006D. L. Zhang This paper describes a novel process for synthesizing a Ti2AlC/TiC/Al2O3in situ composite. This route utilizes TiO2, carbon, and Al powders as raw materials, and involves high-energy mechanical milling and powder sintering. The Ti2AlC/TiC/Al2O3 bulk in situ composite produced has a phase composition of Ti2AlC,20 vol% TiC,35 vol% Al2O3 with fine Al2O3 particles (size: 0.5,15 ,m) embedded in a Ti2AlC/TiC matrix. The Ti2AlC grains exhibit a nanometer scale lamellar structure, and most of the Al2O3 grains contain fine cubic TiOmC1,m precipitates (size: 10,200 nm). The average hardness and bending strength of the composite are in the ranges of 11,12.5 GPa and 380,440 MPa, respectively. Here we have demonstrated that the mechanical performance (mainly hardness and bending strength) of the composite is directly correlated with the size of the Al2O3 particles present in the as-fabricated in situ composite. [source] Novel Fabrication Route to Al2O3,TiN Nanocomposites Via Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006Lianjun Wang A novel method for the preparation of Al2O3,TiN nanocomposites was developed. A mixture of TiO2, AlN, and Ti powder was used as the starting material to synthesize the Al2O3,TiN nanocomposite under 60 MPa at 1400°C for 6 min using spark plasma sintering. X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy were used for detailed microstructural analysis. Dense (up to 99%) nanostructured Al2O3,TiN composites were successfully fabricated, the average grain size being less than 400 nm. The fracture toughness (KIC) and bending strength (,b) of the nanostructured Al2O3,TiN composites reached 4.22±0.20 MPa·m1/2 and 746±28 MPa, respectively. [source] Transparent Sintered Corundum with High Hardness and StrengthJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003Andreas Krell Commercial corundum powder and a liquid-shaping approach are used for manufacturing complex hollow components and large flat windows of sintered and hot isostatically pressed Al2O3 ceramics having grain sizes of 0.4,0.6 ,m at relative densities of >99.9%. High macrohardness (HV10 = 20,21 GPa) and four-point bending strength (600,700 MPa; 750,900 MPa in three-point bending) are associated with a real in-line transmission of 55%,65% through polished plates. The submicrometer microstructure and the optical properties can be retained for use at >1100°C using dopants that shift the sintering temperature to high values without additional grain growth. [source] Control of Composition and Structure in Laminated Silicon Nitride/Boron Nitride CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Chang-an Wang Based on a biomimetic design, Si3N4/BN composites with laminated structures have been prepared and investigated through composition control and structure design. To further improve the mechanical properties of the composites, Si3N4 matrix layers were reinforced by SiC whiskers and BN separating layers were modified by adding Si3N4 or Al2O3. The results showed that the addition of SiC whiskers in the Si3N4 matrix layers could greatly improve the apparent fracture toughness (reaching 28.1 MPa·m1/2), at the same time keeping the higher bending strength (reaching 651.5 MPa) of the composites. Additions of 50 wt% Al2O3 or 10 wt% Si3N4 to BN interfacial layers had a beneficial effect on the strength and toughness of the laminated Si3N4/BN composites. Through observation of microstructure by SEM, multilevel toughening mechanisms contributing to high toughness of the laminated Si3N4/BN composites were present as the first-level toughening mechanisms from BN interfacial layers as crack deflection, bifurcation, and pull-out of matrix sheets, and the secondary toughening mechanism from whiskers in matrix layers. [source] Effects of Heat Treatment on the Surface Microstructure and Mechanical Properties of MoSi2 -TiC0.7N0.3 CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002Yu-Ping Zeng MoSi2 -TiC0.7N0.3 composites were prepared by hot-pressing under vacuum, and MoSi2,TiC0.7N0.3 composites were heat-treated in air at various temperatures. SEM analysis showed that the surface microstructure of the MoSi2 -TiC0.7N0.3 composite changed because of the oxidation of MoSi2 and TiC0.7N0.3 and that many TiO2 whiskers appeared on the surfaces of the composites. Compared with the non-heat-treated MoSi2 -TiC0.7N0.3, the bending strength of the heat-treated MoSi2 -TiC0.7N0.3 was significantly improved. [source] Water-Based Gelcasting of Surface-Coated Silicon Nitride PowderJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2001Yong Huang A layer of Y2O3,Al2O3, used as a sintering aid, was coated onto the surface of Si3N4 particles by the precipitation of inorganic salts from a water-based solution containing Al(NO3)3, Y(NO3)3, and urea. The electrokinetic and colloidal characteristics of the Si3N4 powder were changed significantly by the coating layer. As a result, dispersion of the Y2O3,Al2O3 -coated Si3N4 powder was significantly greater than that of the original powder. Furthermore, the Y2O3,Al2O3 coating layer prevented the hydrogen-gas-discharging problem that occurred during gelcasting of the original Si3N4 powder because of reaction between the uncoated powder and the basic aqueous solution in suspension. Surface coating, as well as the gelcasting process, significantly improved the microstructure, room-temperature bending strength, and Weibull modulus of the resulting ceramic bodies. [source] Crack Healing Behavior of Silicon Carbide CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000Jan Korou This study focuses on the crack healing behavior of three kinds of commercial SiC ceramics. Specimens with and without cracks were subjected to thermal treatment at different temperatures, and their strengths were measured by a three-point bending test in accordance with JIS standards. The tests were performed in air at both room temperature and elevated temperatures between 600° and 1500°C. The healed specimens showed a complete recovery of strength at room temperature for the investigated crack sizes of 2c, 100 ,m and 2c, 200 ,m, and their strength increased in accordance with the healing temperature. The behavior of the healed specimens at elevated temperatures was influenced by the material used and the test temperature. Generally, the strength decreased at a high temperature, but the degree of strength reduction was determined by the kind of ceramic. The most important difference between the healed and smooth specimens was exhibited in material A. It was observed that at 1400°C, the bending strength of the healed specimens made from this ceramic was about 37% of the value for specimens in an as-received state. Static fatigue tests were also performed for ceramic B at 900° and 1000°C. The experiment demonstrated that the static fatigue limit of a healed specimen is about 75% of the monotonic bending strength at the same temperature. [source] Further Improvement in Mechanical Properties of Highly Anisotropic Silicon Nitride CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Hisayuki Imamura Si3N4ceramics were fabricated by tape casting of a raw-powder slurry seeded with three types of rodlike ,-Si3N4particles. The effects of seed size on the microstructure and mechanical properties of the sintered specimens were investigated. All the seeded and tape-cast silicon nitrides presented an anisotropic microstructure, where the elongated grains grown from seeds were preferentially oriented parallel to the casting direction. The orientation degree of these grains, f0, was affected by seed size, and small-seed addition led to the highest f0value. This material exhibited high bending strength (,1.4 GPa) and high fracture toughness (,12 MPa.m1/2) in the direction normal to the grain alignment, which were attributed to the highly anisotropic and fine microstructure. [source] Processing and Mechanical Behavior of CrN/ZrO2(2Y) CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Yoshihiko Takano CrN powder consisting of granular particles of ,3 ,m has been prepared by self-propagating high-temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2(2Y) composites in the CrN-rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness (KIC) of 3.3 MPa ·m1/2 and a bending strength (,b) of 400 MPa. In the latter materials almost all of the ZrO2(2Y) grains (0.36,0.41 ,m) are located in the grain boundaries of CrN (,4.6 ,m). The values of KIC (6.1 MPa · m1/2) and ,b (1070 MPa) are obtained in the composites containing 50 vol% ZrO2(2Y). [source] Bite forces, canine strength and skull allometry in carnivores (Mammalia, Carnivora)JOURNAL OF ZOOLOGY, Issue 2 2005Per Christiansen Abstract Skull variables were analysed for allometry patterns in 56 species of extant carnivores. As previously reported, many skull variables scale near isometrically with either skull length or lower jaw length. The maximal gape angle scales insignificantly (P<0.05) with skull size, but the clearance between the canines shows a significant relationship with skull size and scales near isometrically. Maximal bite forces were estimated from geometrical cross-sectional areas of dried skulls, and the bending strength of the canines was computed by modelling the canines as a cantilevered beam of solid, homogeneous material with an elliptical cross section. Previous hypotheses of large taxon differences in canine bending strengths, so that felids have stronger canines than canids, are corroborated when actual bite forces at the upper canine are ignored. Incorporation of bite force values, however, nullifies the differences in canine bending strength among felids and canids, and ursids seem to have stronger canines than felids. This is probably because of the significantly longer canines of felids compared to canids and ursids, and the generally high bite forces of felids. [source] Reinforcement of Biodegradable Poly(DL -lactic acid) Material by Equal-Channel Angular ExtrusionMACROMOLECULAR SYMPOSIA, Issue 1 2006Hongxiang Cui Abstract The purpose of this study was to reinforce biodegradable poly(DL -lactic acid) (PDLLA) material using a new method, equal-channel angular extrusion (ECAE). Different processing parameters, including the number of extrusion passes and the process temperature, were investigated to analyze their effect on the PDLLA properties. Experimental results indicate that the mechanical strength of PDLLA increased with the number of extrusion passes. The extrusion temperature also affected the mechanical strength of the PDLLA. After two ECAE passes, the bending strength of PDLLA increased from 83.3 to 178.7 MPa. The bending fracture mode for PDLLA changed from brittle failure for initial specimens to ductile fracture after ECAE processing. SEM micrographs showed that the longitudinal split surfaces of PDLLA are of a fibrillar structure. Taken together, the results suggest that ECAE might represent a useful approach for the preparation of reinforced PDLLA. [source] Super-Hard Carbon Layers Produced on the Al2O3/Al2O3+x%SiC (whiskers) Ceramic Cutting EdgesPLASMA PROCESSES AND POLYMERS, Issue S1 2007Andrzej R. Olszyna Abstract The aim of the present study was to examine how the cutting properties of tool blades are affected by super-hard ceramic (carbon) coatings produced by the RF PECVD method. The cutting plates were made of the gradient-type Al2O3/Al2O3,+,x%SiCwhiskers composites. The highest density, the greatest bending strength and the highest stress intensity factor were obtained with the layered Al2O3/Al2O3,+,x%SiCwhiskers composite. The phase composition of the coatings was examined and the deposited carbon layers were identified to be nanocrystalline diamond (NCD) contaminated with super-finegrained graphite. The thickness, roughness, adhesion to the substrate, friction coefficient and hardness of the coatings were examined. The results evidently show that, when tested in cutting hard aluminium alloys, the carbon coatings deposited on the Al2O3/Al2O3,+,x%SiCwhiskers cutting plates by RF PECVD have advantageous cutting properties. The service life of the coated plates compared to that of uncoated plates increased by 65% with the NCD coatings. [source] Compatibilizing effect of ethylene,propylene,diene grafted maleic anhydride terpolymer on the blend of polyamide 66 and thermal liquid crystalline polymerPOLYMER COMPOSITES, Issue 6 2006Qunfeng Yue Polyamide 66,thermal liquid crystalline polymer (PA66/TLCP) composites containing 10 wt% TLCP was compatibilized by ethylene,propylene,diene-grafted maleic anhydride terpolymer (MAH- g -EPDM). The blending was performed on a twin-screw extrusion, followed by an injection molding. The rheological, dynamic mechanical analysis (DMA), thermal, mechanical properties, as well as the morphology and FTIR spectra, of the blends were investigated and discussed. Rheological, DMA, and FTIR spectra results showed that MAH- g -EPDM is an effective compatibilizer for PA66/TLCP blends. The mechanical test indicated that the tensile strength, tensile elongation, and the bending strength of the blends were improved with the increase of the content of MAH- g -EPDM, which implied that the blends probably have a great frictional shear force, resulting from strong adhesion at the interface between the matrix and the dispersion phase; while the bending modulus was weakened with the increase of MAH- g -EPDM content, which is attributed to the development of the crystalline phase of PA66 hampered by adding MAH- g -EPDM. POLYM. COMPOS., 27:608,613, 2006. © 2006 Society of Plastics Engineers [source] | |||||||||||||||||||||||||||||||