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Mechanical Performance (mechanical + performance)
Selected AbstractsMicrostructure and Mechanical Performance of Brand-New Al0.3CrFe1.5MnNi0.5 High-Entropy Alloys,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Wei-Yeh Tang The microstructure, hardening behavior, and adhesive wear behavior of Al0.3CrFe1.5MnNi0.5 high-entropy alloys were investigated. All alloys exhibit superior adhesive wear resistance to cast iron FC-300, bearing steel SUJ-2, and hot-mold steel SKD-61. The superior wear resistance of the alloys is attributable to the formation of , phase during the furnace cooling from the homogenization at 1100 °C or the in situ formation of the ,phase induced by the high interface temperature and severe plastic deformation during wear sliding. [source] Characterization and Mechanical Performance of the Mg-Stabilized ,-Ca3(PO4)2 Prepared from Mg-Substituted Ca-Deficient ApatiteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Sanjeevi Kannan The preparation of Mg-stabilized ,-tricalcium phosphate (,-TCP) was carried out by an aqueous precipitation method and the characterization of the powders was performed by powder X-ray diffraction, FT-IR spectra, Raman spectroscopy, and elemental analysis. The transformation of calcium-deficient apatite into ,-TCP has occurred in the range of 700°,800°C. The calculated values for lattice parameters confirm the stabilization role played by Mg. The thermal stability of the Mg-stabilized ,-TCP powders was evident until 1400°C, thus broadening the sintering temperature range without transformation into the undesirable ,-TCP. Accordingly, the mechanical properties of the Mg-stabilized ,-TCP were improved in comparison with those of pure ,-TCP. [source] Enhanced Mechanical Performance of Self-Bundled Electrospun Fiber Yarns via Post-TreatmentsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2008Xuefen Wang Abstract A new route to high-performance electrospun polymer fibers was developed using a self-bundling electrospinning technique combined with post-treatments such as stretching and annealing under conditions similar to those used for conventional fibers. Self-bundled electrospun PAN fiber yarns were characterized by SEM, mechanical tests, polarized FT-IR spectroscopy and WAXD. The obtained results revealed that the PAN nanofiber yarns possessed enhanced alignment, a higher degree of crystallinity and higher molecular orientation after treatments, resulting in a remarkable improvement in mechanical performance, approaching the strength value of the corresponding conventional fibers. [source] Synthesis and Mechanical Performance of Biological-Like Hydroxyapatites.CHEMINFORM, Issue 27 2006S. Kannan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Ultra-Fast Atomic Transport in Severely Deformed Materials,A Pathway to Applications?,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Sergiy Divinski Abstract Severe plastic deformation of pure Cu and Cu-rich alloys was found to create a hierarchical combination of fast and ultra-fast diffusion paths ranging from non-equilibrium grain boundaries to non-equilibrium triple junctions, vacancy clusters, nano- and micro-pores, and finally to general high-angle grain boundaries. Under certain conditions, a percolating network of porosity can be introduced in the ultra-fine grained materials by a proper mechanical and thermal treatment. This network may offer promising opportunities for creating materials with tailor-made properties, including combinations of improved mechanical performance with a possibility of self repair using "vascular structures" for atom transport. Applications in such areas as drug eluting bioimplants and lead or polymer eluting materials for reduction of friction based on impregnation of porosity networks with these agents are also envisaged. [source] Transition of Failure Mode and Enhanced Plastic Deformation of Metallic Glass by Multiaxial Confinement,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Fu-Fa Wu Multiple shear bands are formed in a confined metallic-glass specimen under small-punch loading. The intersecting of shear bands and the formation of profuse secondary shear bands are promoted under this confinement; accordingly, the failure mode changes from catastrophic fracture to stable multiple shear banding. Multiaxial confinement is an effective method to stabilize shear banding and further enhance the mechanical performance, especially the plastic deformation capability of metallic glass. These results present a simple step for making shear banding more stable and exploiting the shear-deformation capability of metallic glasses, leading to the toughening of brittle metallic glasses and potentially broadening their applications. [source] Influence of Filler Composition on the Microstructure and Mechanical Properties of Steel,Aluminum Joints Produced by Metal Arc Joining,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Leonardo Agudo Jácome Chemical joining of aluminum to steel parts is one of the main challenges in the automotive industry to achieve sound economical solutions for required automobile weight reduction. The cold metal transfer (CMT) is a fusion welding process developed to meet that challenge. It is shown in this paper how the choice of proper filler materials can yield appropriate mechanical performance of specially designed dissimilar CMT butt joints by improving the seam characteristics and weld bead properties. [source] Compressive Behavior of Pyramidal, Tetrahedral, and Strut-Reinforced Tetrahedral ABS and Electroplated Cellular Solids,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009Samuel Markkula Fused deposition modeling combined with electroplating provides a novel manufacturing methodology for building low relative density engineered cellular topologies. Here the mechanical performance of tetrahedral, pyramidal, and strut-reinforced tetrahedral cellular solids manufactured from multiphase nickel-copper-ABS is studied. The novel processing and geometric optimization places these engineered topologies into an unoccupied location in the material universe. [source] 3D Powder Printing of ,-Tricalcium Phosphate Ceramics Using Different Strategies,ADVANCED ENGINEERING MATERIALS, Issue 12 2008E. Vorndran Custom made macroporous ,-tricalcium phosphate (,-TCP) bone substitutes were fabricated using 3D powder printing comparing three different preparation strategies. Samples fabricated using a novel hydraulic cement setting reaction showed the best printing resolution and highest mechanical performance. This method is a significant step forward in producing ,-TCP monoliths by rapid prototyping and would decrease processing time for commercial fabrication due to their rapid hardening and ease of handling. [source] Correlation of ,-skeletal actin expression, ventricular fibrosis and heart function with the degree of pressure overload cardiac hypertrophy in ratsEXPERIMENTAL PHYSIOLOGY, Issue 3 2006Donatella Stilli We have analysed alterations of ,-skeletal actin expression and volume fraction of fibrosis in the ventricular myocardium and their functional counterpart in terms of arrhythmogenesis and haemodynamic variables, in rats with different degrees of compensated cardiac hypertrophy induced by infra-renal abdominal aortic coarctation. The following coarctation calibres were used: 1.3 (AC1.3 group), 0.7 (AC0.7) and 0.4 mm (AC0.4); age-matched rats were used as controls (C group). One month after surgery, spontaneous and sympathetic-induced ventricular arrhythmias were telemetrically recorded from conscious freely moving animals, and invasive haemodynamic measurements were performed in anaesthetized animals. After killing, subgroups of AC and C rats were used to evaluate in the left ventricle the expression and spatial distribution of ,-skeletal actin and the amount of perivascular and interstitial fibrosis. As compared with C, all AC groups exhibited higher values of systolic pressure, ventricular weight and ventricular wall thickness. AC0.7 and AC0.4 rats also showed a larger amount of fibrosis and upregulation of ,-skeletal actin expression associated with a higher vulnerability to ventricular arrhythmias (AC0.7 and AC0.4) and enhanced myocardial contractility (AC0.4). Our results illustrate the progressive changes in the extracellular matrix features accompanying early ventricular remodelling in response to different degrees of pressure overload that may be involved in the development of cardiac electrical instability. We also demonstrate for the first time a linear correlation between an increase in ,-skeletal actin expression and the degree of compensated cardiac hypertrophy, possibly acting as an early compensatory mechanism to maintain normal mechanical performance. [source] Bioinspired Structural Material Exhibiting Post-Yield Lateral Expansion and Volumetric Energy Dissipation During TensionADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Lifeng Wang Abstract Nature has inspired the design of improved synthetic materials that achieve superior and more efficient mechanical performance. Here microstructures inspired by the inner nacreous layer of seashells are designed and their mechanical properties including stiffness, strength, and energy dissipation are computed using micromechanical analysis. The hierarchical mineral/polymer microstructure can be tailored to achieve not only stiffness and strength, but also lateral plastic expansion during tension providing a volumetric energy dissipation mechanism. [source] Plastic Dissipation Mechanisms in Periodic Microframe-Structured PolymersADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Lifeng Wang Abstract Novel lightweight micro- and nanostructured materials are being used as constituents in hierarchically structured composites for providing high stiffness, high strength, and energy absorbing capability at low weight. Three dimensional SU-8 periodic microframe materials with submicrometer elements exhibit unusual large plastic deformations. Here, the plastic dissipation and mechanical response of polymeric microframe structures is investigated using micromechanical modeling of large deformations. Finite element analysis shows that multiple deformation domains initiate, stabilize, and then spread plasticity through the structure; simulated deformation mechanisms and deformation progression are found to be in excellent agreement with experimental observation. Furthermore, the geometry can be used to tailor aspects of 3D behavior such as effective lateral contraction ratios (elastic and plastic) during tensile loading as well as negative normal stress during simple shear deformation. The effects of structural geometry on mechanical response are also studied to tailor and optimize mechanical performance at a given density. These quantitative investigations enable simulation-based design of optimal lightweight material microstructures for dissipating energy. [source] Experimental Study of the Aging and Self-Healing of the Glass/Ceramic Sealant Used in SOFCsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2010Wenning N. Liu High operating temperatures of solid oxide fuel cells (SOFCs) require that the sealant must function at a high temperature between 600°C and 900°C and in the oxidizing and reducing environments of fuel and air. This paper describes tests to investigate the temporal evolution of the volume fraction of ceramic phases, the evolution of micro-damage, and the self-healing behavior of the glass,ceramic sealant used in SOFCs. It was found that after the initial sintering process, further crystallization of the glass,ceramic sealant does not stop, but slows down and reduces the residual glass content while boosting the ceramic crystalline content. Under a long-term operating environment, distinct fibrous and needle-like crystals in the amorphous phase disappeared, and smeared/diffused phase boundaries between the glass phase and ceramic phase were observed. Meanwhile, the micro-damage was induced by the cooling down process from the operating temperature to room temperature, which can potentially degrade the mechanical properties of the glass/ceramic sealant. The glass/ceramic sealant exhibited self-healing upon reheating to the SOFC operating temperature, which can restore the mechanical performance of the glass/ceramic sealant. [source] Influence of resin viscosity and vacuum level on mechanical performance of sandwich structures manufactured by vacuum baggingADVANCES IN POLYMER TECHNOLOGY, Issue 1 2010A. Valenza Abstract The choice of process parameters is critical in optimizing the mechanical properties of sandwich structures produced using the vacuum bagging technique. The aim of this paper is to analyze how the viscosity of the resin/curing agent system and the vacuum level influence the morphology and the mechanical behavior of sandwich beams with composite faces (epoxy resin and glass fiber fabric named COMBI 900) and a PVC foam core. Four different sandwich structures were produced by varying the viscosity of the epoxy resin/curing agent at constant maximum vacuum pressure. Three further structures were manufactured by varying the strength of the vacuum with the resin viscosity maintained constant at the minimum level. Three point bending tests were carried out on all seven sandwiches. The analysis shows that although both parameters affect the mechanical characteristics of the structure, the viscosity of the resin system is clearly the more influential of the two. The morphological structure of the sandwiches was analyzed both by scanning electron microscope (SEM) and by muffle furnace ignition to calculate the percentage of fibers, matrices, and voids present in the different samples © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:20,30, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20172 [source] In situ generated hydroxyl-terminated polybutadiene nanoparticles in polyimide filmsADVANCES IN POLYMER TECHNOLOGY, Issue 1 2009Anand Kumar Gupta Abstract Polyimide (PI) has been extensively investigated as matrices for blends in the search for novel materials for microelectronics and engineering application. The processing of the PI with hydroxyl-terminated polybutadiene (HTPB) offers a considerable advantage to develop a material having good mechanical and thermal stability. Taking this into account, the HTPB was blended with polyamic acid, which is precursor to PI to form PI + HTPB films. A number of properties were evaluated for PI + HTPB films with ultra low concentrations of HTPB. The films prepared with ultra low concentration (10,3,1 wt%) showed unusual synergism, which is attributed to the presence of in situ generated micro/nanostructures derived from HTPB. The microhardness study was used to elucidate the actual mechanical performance due to structure formation of HTPB in a nanometer regime within PI matrix. Atomic force microscopy analysis confirmed the dispersion of HTPB at nano regime within PI matrix. The enhanced thermal stability as determined by thermogravimetric analyzer and Fourier transform infrared spectrometry was attributed to the presence of micro/nanoparticle of HTPB within the PI matrix. The water absorption isotherms were measured and their abnormal behavior was correlated with micro-/nano-sized particles in the PI/HTPB film. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:48,59, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20144 [source] Effect of UV and hygrothermal aging on the mechanical performance of polyurethane elastomersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008H. Aglan Abstract In this study, the effects of environmental aging on the mechanical performance of elastomeric polyurethane (PU) were investigated using two accelerated aging techniques, namely, ultraviolet (UV) and hygrothermal (HT). Samples were prepared and subjected to UV and HT exposure for a period of 5 months and removed and mechanically tested at different time intervals. Differential scanning calorimetry (DSC) was performed. A noticeable change in the chemical structure of the PU after 1 month of UV exposure was found, however, that was not the case after 1 month of HT exposure. The stress and strain to failure, tearing energy, and storage modulus were evaluated at different intervals for both aging techniques. It was found that the UV exposure caused severe degradation of the PU in comparison with the HT. A reduction of more than 98% in the tearing energy was observed for the UV-exposed samples after 5 months when compared with only a 35% reduction in the tearing energy for the HT-exposed samples. A similar trend was observed for tear strength and storage modulus. The degradation mechanisms of the PU elastomers have been identified using SEM and correlated with the tearing energy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Improving mechanical performance of injection molded PLA by controlling crystallinityJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Angela M. Harris Abstract Currently, use of poly(lactic acid) (PLA) for injection molded articles is limited for commercial applications because PLA has a slow crystallization rate when compared with many other thermoplastics as well as standard injection molding cycle times. The overall crystallization rate and final crystallinity of PLA were controlled by the addition of physical nucleating agents as well as optimization of injection molding processing conditions. Talc and ethylene bis-stearamide (EBS) nucleating agents both showed dramatic increases in crystallization rate and final crystalline content as indicated by isothermal and nonisothermal crystallization measurements. Isothermal crystallization half-times were found to decrease nearly 65-fold by the addition of only 2% talc. Process changes also had a significant effect on the final crystallinity of molded neat PLA, which was shown to increase from 5 to 42%. The combination of nucleating agents and process optimization not only resulted in an increase in final injection molded crystallinity level, but also allowed for a decreased processing time. An increase of over 30°C in the heat distortion temperature and improved strength and modulus by upwards of 25% were achieved through these material and process changes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Reactive extrusion to synthesize intumescent flame retardant with a solid acid as catalyst and the flame retardancy of the products in polypropyleneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Yuan Liu Abstract Reactive extrusion and solid acid catalysis technologies were adopted in the pentaerythritol,melamine phosphate (PER-MP) reaction to synthesize intumescent flame retardant, melamine salt of pentaerythritol phosphate (MPP), which was applied in flame retardant polypropylene (PP). This environment-friendly synthesis method provided a solution to the problems of conventional methods. On one hand, reactive extrusion in a twin screw extruder can effectively mix and transfer viscous materials that usually results in a tough stir in a conventional reactor, and achieve a continuous synthesis process. On the other hand, the solid acid, silicotungstic acid (STA) serving as a catalyst, can maintain a satisfactory conversion even with a low extrusion temperature and a short residence time, thus effectively suppressing foaming in the process of the reaction. Furthermore, without removal like other catalysts in general chemical reactions, STA was kept in produced MPP to constitute a synergism flame retardant system, therefore further improved the flame retardancy. LOI and UL94 test showed that the STA-catalyzed MPP (by reactive extrusion) possessed much better flame retardancy in PP when compared with the noncatalyzed MPP (by reactive extrusion), as well as present commercial MPP (by POCl3 method). In our investigation, the catalytic and synergistic effects of STA, as well as the related factors of the reactive extrusion affecting the conversion of the PER-MP reaction, flame retardancy and mechanical performance of the corresponding flame retardant PP, were systematically investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Analysis of the mechanical behavior of a titanium scaffold with a repeating unit-cell substructureJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2009Garrett Ryan Abstract Titanium scaffolds with controlled microarchitecture have been developed for load bearing orthopedic applications. The controlled microarchitecture refers to a repeating array of unit-cells, composed of sintered titanium powder, which make up the scaffold structure. The objective of this current research was to characterize the mechanical performance of three scaffolds with increasing porosity, using finite element analysis (FEA) and to compare the results with experimental data. Scaffolds were scanned using microcomputed tomography and FEA models were generated from the resulting computer models. Macroscale and unit-cell models of the scaffolds were created. The material properties of the sintered titanium powders were first evaluated in mechanical tests and the data used in the FEA. The macroscale and unit-cell FEA models proved to be a good predictor of Young's modulus and yield strength. Although macroscale models showed similar failure patterns and an expected trend in UCS, strain at UCS did not compare well with experimental data. Since a rapid prototyping method was used to create the scaffolds, the original CAD geometries of the scaffold were also evaluated using FEA but they did not reflect the mechanical properties of the physical scaffolds. This indicates that at present, determining the actual geometry of the scaffold through computed tomography imaging is important. Finally, a fatigue analysis was performed on the scaffold to simulate the loading conditions it would experience as a spinal interbody fusion device. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2009 [source] The influence of thermal treatment on the mechanical characteristics of a PLLA coiled stentJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2009Tré R. Welch Abstract We studied the effects of thermal treatment on the expansive characteristics of a coil-within-coil Poly(L -lactic acid) (PLLA) fiber stent developed at our institution to improve its mechanical performance and reproducibility. Following fabrication, furled stents were thermally treated at 62°C for 25 min. The mechanical characteristics were measured compared with those of untreated stents when both were expanded via sequential balloon catheter pressure loading up to 12 atm. Treated stents reached full diameter at 3 atm and maintained that diameter despite further pressure increases. Using measurements of pressure, diameter, and axial length, we calculated the sequential mechanical work required to unfurl the stent. The mechanical work for complete unfurling of treated stents was significantly less than that required for untreated controls. Little axial dimensional change was observed for treated stents. Treated stents exhibited higher stiffness than controls at all pressure levels and also demonstrated higher resistance to external pressure-induced collapse, as measured in a special apparatus developed in our laboratory. Differential scanning calorimetry measurements indicated higher crystallinity values for fibers used in treated stents compared with controls. SEM examination of striations revealed that treated stents underwent less twist than controls following balloon-induced unfurling. The results indicate that, thermal treatment improves the reorientation and realignment of fiber crystalline structure, and favorably influences on the fiber stress-strain behavior and the expansive mechanical characteristics of the PLLA fiber stents. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Enhancing the mechanical integrity of the implant,bone interface with BoneWelding® technology: Determination of quasi-static interfacial strength and fatigue resistanceJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2006Stephen J. Ferguson Abstract The BoneWelding® technology is an innovative bonding method, which offers new alternatives in the treatment of fractures and other degenerative disorders of the musculoskeletal system. The BoneWelding process employs ultrasonic energy to liquefy a polymeric interface between orthopaedic implants and the host bone. Polymer penetrates the pores of the surrounding bone and, following a rapid solidification, forms a strong and uniform bond between implant and bone. Biomechanical testing was performed to determine the quasi-static push-out strength and fatigue performance of 3.5-mm-diameter polymeric dowels bonded to a bone surrogate material (Sawbones solid and cellular polyurethane foam) using the BoneWelding process. Fatigue tests were conducted over 100,000 cycles of 20,100 N loading. Mechanical test results were compared with those obtained with a comparably-sized, commercial metallic fracture fixation screw. Tests in surrogate bone material of varying density demonstrated significantly superior mechanical performance of the bonded dowels in comparison to conventional bone screws (p < 0.01), with holding strengths approaching 700 N. Even in extremely porous host material, the performance of the bonded dowels was equivalent to that of the bone screws. For both cellular and solid bone analog materials, failure always occurred within the bone analog material surrounding and distant to the implant; the infiltrated interface was stronger than the surrounding bone analog material. No significant decrease in interfacial strength was observed following conditioning in a physiological saline solution for a period of 1 month prior to testing. Ultrasonically inserted implants migrated, on average, less than 20 ,m over, and interfacial stiffness remained constant the full duration of fatigue testing. With further refinement, the BoneWelding technology may offer a quicker, simpler, and more effective method for achieving strong fixation and primary stability for fracture fixation or other orthopaedic and dental implant applications. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Recent advancement on polybenzoxazine,A newly developed high performance thermosetJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2009Yusuf Yagci Abstract Polybenzoxazine is a newly developed addition polymerized phenolic system, having a wide range of interesting features and the capability to overcome several shortcomings of conventional novolac and resole type phenolic resins. They exhibit (i) near zero volumetric change upon curing, (ii) low water absorption, (iii) for some polybenzoxazines Tg much higher than cure temperature, (iv) high char yield, (v) no strong acid catalysts required for curing, (vi) release of no byproduct during curing and also possess thermal and flame retarding properties of phenolics along with the mechanical performance. Though benzoxazine based materials possess several advantages, they have not yet became very attractive to the industries. To improve the mechanical properties and processibility several strategies have been reported including (i) synthesis of benzoxazine monomers with additional functionality, (ii) incorporation of benzoxazine in polymer chain, and (iii) benzoxazine based composites or alloys. In this article, we have discussed about the recent development of benzoxazine chemistry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5565,5576, 2009 [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] The influence of endothelial cells on the ECM composition of 3D engineered cardiovascular constructs,JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, Issue 1 2009Rolf A. A. Pullens Abstract Tissue engineering of small diameter (<5 mm) blood vessels is a promising approach to develop viable alternatives for autologous vascular grafts. Development of a functional, adherent, shear resisting endothelial cell (EC) layer is one of the major issues limiting the successful application of these tissue engineered grafts. The goal of the present study was to create a confluent EC layer on a rectangular 3D cardiovascular construct using human venous cells and to determine the influence of this layer on the extracellular matrix composition and mechanical properties of the constructs. Rectangular cardiovascular constructs were created by seeding myofibroblasts (MFs) on poly(glycolic acid) poly-4-hydroxybutyrate scaffolds using fibrin gel. After 3 or 4 weeks, ECs were seeded and co-cultured using EGM-2 medium for 2 or 1 week, respectively. A confluent EC layer could be created and maintained for up to 2 weeks. The EGM-2 medium lowered the collagen production by MFs, resulting in weaker constructs, especially in the 2 week cultured constructs. Co-culturing with ECs slightly reduced the collagen content, but had no additional affect on the mechanical performance. A confluent endothelial layer was created on 3D human cardiovascular constructs. The layer was co-cultured for 1 and 2 weeks. Although, the collagen production of the MFs was slightly lowered, co-culturing ECs for 1 week results in constructs with good mechanical properties and a confluent EC layer. Copyright © 2008 John Wiley & Sons, Ltd. [source] Fabrication and properties of nano-ZnO/glass-fiber-reinforced polypropylene compositesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2010Yi-Hua Cui Polypropylene (PP) is widely used in many fields, such as automobiles, medical devices, office equipment, pipe, and architecture. However, its high brittle transformation temperature, low mechanical strength, dyeing properties, antistatic properties, and poor impact resistance, considerably limit its further applications. Nano-ZnO treated by KH550 coupling agent and glass fibers (GFs) were introduced in order to improve the mechanical performance and flowability of PP in this research. The crystallization behavior and microstructure of nano-ZnO/GFs/PP hybrid composites were analyzed by differential scanning calorimetry, transmission electron microscopy, and scanning electron microscopy. The effect of crystallization behavior on the mechanical properties of the nanocomposites was investigated and analyzed. The results indicated that nano-ZnO surface-coupled by KH550 could be uniformly dispersed in the PP matrix. The incorporation of nano-ZnO and GFs resulted in increases of the crystallization temperature and crystallization rate of PP and a decrease of the crystallization degree. The introduction of nano-ZnO and GFs also enhanced the tensile strength and impact toughness of the hybrid composites and improved their fluidity. Composites containing 2% of nano-ZnO and 40% of GFs possessed the optimum mechanical properties. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers [source] In Vitro Degradation of Trimethylene Carbonate Based (Co)polymersMACROMOLECULAR BIOSCIENCE, Issue 9 2002Ana Paula Pêgo Abstract Trimethylene carbonate (TMC) was copolymerized with D,L -lactide (DLLA) or with , -caprolactone (CL), and the degradation of melt-pressed solid copolymer films in phosphate-buffered saline at pH 7.4 and 37,°C was followed for a period of over two years. The parent homopolymers were used as reference materials. The degradation profile of TMC-DLLA- and TMC-CL based copolymers was similar and was best described by autocatalyzed bulk hydrolysis, preferentially of ester bonds. The hydrolysis rates varied by two orders of magnitude, depending on polymer composition and physical characteristics under the degradation conditions. TMC-DLLA copolymers degraded faster than the parent homopolymers. The copolymers lost their tensile strength in less than five months, after which mass loss occurred. Copolymers with 50 or 80 mol-% of TMC underwent total degradation in eleven months. For TMC-CL copolymers, a slow and gradual decrease in molecular weight and deterioration of the mechanical performance was observed. These copolymers maintained suitable mechanical properties for seventeen months or longer. Chain scission in the semicrystalline copolymers resulted in an increase in crystallinity. In comparison with the CL homopolymer, the introduction of a small amount of TMC (10 mol-%) significantly reduced the increase in crystallinity during degradation. Poly(TMC) specimens were dimensionally stable and showed a negligible decrease in molecular weight. A 60% decrease in the initial tensile strength of the polymer samples was observed after two years. [source] In situ Preparation of Polyimide Composites Based on Functionalized Carbon NanotubesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2009Rohit Srivastava Abstract Three series of composite films based on polyimide and MWNTs were prepared by conversion of pyromellitic dianhydride and 4,4,-oxydianiline in the presence of the nanotubes, followed by thermal imidization. Carboxy- and amino-functionalized as well as unmodified nanotubes were used. It was demonstrated that just 0.5 wt.-% of nanotubes increased the tensile properties of the composite films distinctly. Surprisingly, a significant influence of the functional groups on the mechanical performance of the composite films could not be demonstrated. However, it was shown that functional groups may reduce the conductivity of the films. Furthermore, the influence of ultrasonication is discussed. [source] Role of Star-Like Hydroxylpropyl Lignin in Soy-Protein PlasticsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2006Ming Wei Abstract Summary: Star-like hydroxypropyl lignin (HL) was compounded into soy protein isolated (SPI) to develop a potential biodegradable plastic with better mechanical performance than pure sheet-SPI. The structure and properties of the composite materials were characterized by WAXD, DSC, SEM, TEM and tensile tests. The addition of just 2 wt.-% HL resulted in tensile strength (,b) of 16.8 MPa, 2.3 times that of pure sheet-SPI, with no accompanying decrease in elongation at break as a result of strong interaction and with good miscibility among components. As the HL content increased, the HL molecules could self-aggregate as oblate supramolecular domains, while the stronger interactions between HL and glycerol resulted in the detaching of glycerol from the SPI matrix. It can be concluded that the insertion of HL as single molecules into the SPI matrix would provide materials with optimum mechanical properties. Compared with other lignin/SPI composites, the stretching chains on HL play a key role in the improvement of mechanical properties because of a stronger adhesion of HL onto the SPI matrix as well as the interpenetration of SPI into supramolecular HL domains. Schematic illustration of the supramolecular domain created by the aggregation of hydroxypropyl lignin, which can interpenetrate with soy protein isolate. [source] Compatibilization of Polyamide-6/Polyarylate Blends by Means of an IonomerMACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2005Aritz Retolaza Abstract Summary: Polyamide-6 (PA6)/polyarylate of bisphenol A (PAr) blends rich in PA6 and modified with an additional 15% poly[ethylene- co -(methacrylic acid)] partially neutralized with zinc (PEMA-Zn) as a compatibilizer were obtained by melt mixing. Their phase structure, morphology, and mechanical performance were compared with those of the corresponding binary blends. The ternary blends were composed of a PA6 amorphous matrix and a dispersed PAr-rich phase in which reacted PA6 and PEMA-Zn were present. Additionally, minor amounts of a crystalline PA6 phase, and a PEMA-Zn phase were also present. The chemical reactions observed led to a clear decrease in the dispersed particle size when PEMA-Zn was added, indicating compatibilization. Consequently, the mechanical behavior of the blends with PEMA-Zn improved, leading, mainly in the case of the blend with 10% PAr, to significant increases in both ductility and impact strength with respect to those of the binary blends. These increases were more remarkable than the slight decrease in stiffness as a consequence of the rubbery nature of the compatibilizer. Cryogenically fractured surface of the PA6/PAr-PEMA-Zn 70/30-15 ternary blend. [source] Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular WeightsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2005Claudia Stern Abstract Summary: The processability, morphology, and resulting mechanical properties of novel polypropylene (PP) samples of varying molecular weight () were studied. A series of homopolymer PP in a wide range from 101,000 to 1,600,000 g,·,mol,1 was polymerised in a liquid pool (LP) under defined conditions. The LP-PP with a well-known polymerisation history was manufactured into micro dumbbell specimens by means of a micro injection-moulding process. The morphology and mechanical properties of the samples were studied by light microscopy, transmission and scanning electron microscopy, and a quasi-static tensile test. Simulation of the filling behaviour of the molten polymer inside the mould shows that the shear rate increases as the molecular weight increases, up to a maximum shear rate of 750,000 s,1. In addition, the present crystallisation time of the high-molecular-weight PP samples is clearly lower than their retardation time; the long macromolecules do not have sufficient time to retard while cooling. As a result of the shear-induced crystallisation, a highly oriented crystalline structure is formed as a function of the acting shear rate. SEM and TEM investigations show the existence of an oriented shish kebab structure. The density of the shish kebab increases as the molecular weight increases. Evaluations of the shear rate and the morphological structure indicate a critical shear rate of about 300,000 s,1. Above this shear rate level, shish kebab structures are favourably formed. The shear-induced crystallisation and, therefore, the preferred formation of a highly oriented shish kebab structure lead, obviously, to unusual solid-state properties of the analysed LP-PP samples. With a tensile strength up to 100 N,·,mm,2 and an attainable strain at break of more than 30%, the mechanical performance is much higher than results ever reported in literature. True strain,stress behaviour of moulded the LP-PP samples of different molecular weight. [source] | |||||||||||||||||||||||||||||||||||||