玻璃纤维增强铅网/橡胶阻尼复合材料研究

为了改善橡胶的力学性能和阻尼性能,以橡胶、纤维和铅为原料设计了玻璃纤维增强铅网/橡胶阻尼复合材料,研究了不同玻璃纤维增强铅网铺层数量的横向玻璃纤维增强铅网/橡胶复合材料力学性能和阻尼性能,分析了其阻尼机制.结果表明,复合材料具有比橡胶更高的力学性能和阻尼特性,其刚度随铅网铺层数量的增加而提高,而阻尼损耗因子与铺层数呈非线性关系.复合材料中存在材料变形耗能、界面耗能、摩擦耗能等多种阻尼损耗机制.     

Histomorphological, histomorphometrical and biomechanical analysis of ceramic bone substitutes in a weight-bearing animal model

It was the purpose of this investigation to prove the biomechanical properties, the osteoconductive capacity and the degradation rate of tricalcium phosphate ( TCP), a neutralized glass ceramics (GB9N) and a composite material (GB9N+copolymers). In a weight-bearing animal model six substitutes each were implanted in the medial tibial head of the right lower leg of adult Merino-sheep in a standardized surgical technique. After nine months the implants were harvested and prepared for histomorphological and histomorphometrical investigations (undecalcified Masson Goldner staining). For additional biomechanical testing of the specimens, non-operated bone blocks from the contralateral tibia as well as native implants served as controls. No significant differences for the maximum fracture load as well as for the yield strength were detected between harvested specimens and bone blocks from the contralateral tibia. However there were marked differences to ceramics that were not implanted. All substitutes showed osteoconduction, leading to a continuous ingrowth of new formed bone. However in the composite material soft tissue could be identified within the scaffold and there were signs of ongoing bone remodeling, nine months after implantation. The bone per tissue volume of -TCP in conjunction to new bone (=percentage of trabecular bone volume plus percentage of residual substitute) was higher than for GB9N and the composite material. Nine months after implantation the percentage of residual -TCP was 48%, it was 32% for GB9N and 28% for the composite.The intention of further studies should be to accelerate the degradation rates of substitutes and to improve biomechanical properties of implants by either modifying the chemical composition or combining materials with agents as, e.g. growth factors.     

Dielectric and pyroelectric properties of a composite of ferroelectric ceramic and polyurethane

Flexible piezo- and pyroelectric composite was made in the thin film form by spin coating. Lead Zirconate Titanate (PZT) ceramic powder was dispersed in a castor oil-based polyurethane (PU) matrix, providing a composite with 0–3 connectivity. The dielectric data, measured over a wide range of frequency (10^–5 Hz to 10⁵ Hz), shows a loss peak around 100 Hz related with impurities in the polymer matrix. There is also an evidence of a peak in the range 10^–4 Hz, possibly originating from the glass transition temperature T_g of the polymer. The pyroelectric coefficient at 343 K is 7.0×10^–5 C·m^–2·K^–1 which is higher than that of β-PVDF (1×10^–5 C·m^–2·K^–1). Electronic Publication     

A new analytical model to simulate impact onto ceramic/composite armors

A very simple one-dimensional and fully analytical model of ballistic impact against ceramic/composite armors is presented in this paper. The analytical model has been checked both with ballistic tests and numerical simulations giving predictions in good agreement with them. The model allows the calculation of residual velocity, residual mass, and the projectile velocity and the deflection or the strain histories of the backup material. These variables are important in describing the phenomenological process of penetration. Described are modifications to previous work of impact into ceramics combined with a new composites model. The development of this composite model is based on studies of the impact in yarns, fabrics and finally composites.     

The numerical analysis of dynamically loaded ceramic: a crack softening approach

A physically based crack softening approach to modelling the failure of brittle materials that have been subjected to dynamic loading is presented and applied to a two‐dimensional non‐linear transient dynamic hydrocode. It is assumed that there are a number of evenly distributed and orientated microflaws within the brittle material that are activated by a dynamically applied stress. Modes I and II stress intensity factors are calculated and compared to critical values, at which point the cracks grow at a velocity dependent on mode I stress intensity factor. The strength of the ceramic is degraded according to the length of the cracks. A simulation of a steel sphere impacting and penetrating a ceramic target at 1500 m/s is presented. Comparisons are drawn from experimental data. Copyright © 2000 John Wiley & Sons, Ltd.     

Fibre-reinforced composite implant: in vitro mechanical interlocking with bone model material and residual monomer analysis

The aim of this study was to examine in vitro the mechanical interlocking of an experimental implant made of E-glass fibre-reinforced polymethyl methacrylate (PMMA)-based composite (FRC) to dental stone. FRC implants with a porous surface were embedded into the dental stone, which was chosen to simulate bone ingrowth into the porous surface of the implant, after which push-out tests were performed. PMMA cylinders with smooth and grooved surface were used as controls. In addition, the release of residual methyl methacrylate monomer (MMA) into water from FRC and control implants with different compositions and fabrication methods was determined using high performance liquid chromatography (HPLC). The highest push-out force (2149 ± 263 N) was measured for the implants with grooved surface and the lowest value for the implants with smooth surface (194 ± 68 N). The push-out forces were over five times higher for FRC implants with a porous surface (958 ± 217 N) than for implants with smooth surface. During the first day of testing, the MMA release into water was 1.4–2.8 times higher from the FRC implants than from the control PMMA implants, depending on fabrication method. With time, the difference between the implants diminished.     

Implementation of a constitutive micromechanical model for damage analysis in glass mat reinforced composite structures

A micromechanical model based on a probabilistic approach is implemented in the finite element code CASTEM 2000 to develop numerical simulations that efficiently predict the overall damaged behaviour of random oriented fibre composites. The proposed damage constitutive model is based upon the generalised Mori and Tanaka scheme and Eshelby's equivalence theory. Damage mechanisms occurring at each composite constituent (fibres, matrix and interface) are associated to Weibull probabilistic functions to model their onset and progressive growth at the microscopic scale level. It is obvious that the damaged behaviour of the composite material depends widely on the microscopic material parameters (fibre length, fibre volume fraction, fibre orientation, …). On one hand, the micromechanical model uses homogenisation techniques which enabled us to link these microscopic parameters to the material behaviour and to evaluate explicitly their influences. On the other hand, the implementation of the derived behaviour law into a finite element code enabled us to reflect on the effect of these microscopic parameters on the overall response of a simple composite structure presenting heterogeneous stress fields. In fact, the damage evolution in each constituent (local scale) and the related stiffness reduction are estimated at any material point (integration point) or node of the considered structure subject to a specific loading. Numerical simulations of a composite plate with a hole under in-plane tension were performed to validate the implementation of the behaviour law. Numerical results have been compared to experimental curves and damage evolutions monitored by acoustic emission techniques. Simulations agree well with experimental results in terms of damage onset and growth.     

Failure analysis of a ceramic ball race bearing made of Y-TZP zirconia

Full ceramic ball bearings have some advantages compared to conventional steel bearings. They have for instance higher stiffness and hardness, lower density and reduced friction. Because they need less lubrication than steel bearings and owing to their wear and corrosion resistance they are generally materials of choice for pharmaceutical and food industries.In this work a full ceramic bearing that was used in a small mixer in the pharmaceutical industry is investigated. The bearing, consisting of two ZrO₂ rings and silicon nitride balls in between, was damaged during service because of premature wear. A failure analysis is performed by fractography and Raman spectroscopy, and it is shown that a stress induced phase transition from the tetragonal to the monoclinic phase was the reason behind the failure of the ZrO₂-rings.     

Characterization of porous glass fiber-reinforced composite (FRC) implant structures: porosity and mechanical properties

The aim of this study was to characterize the microstructure and mechanical properties of porous fiber-reinforced composites (FRC). Implants made of the FRC structures are intended for cranial applications. The FRC specimens were prepared by impregnating E-glass fiber sheet with non-resorbable bifunctional bis-phenyl glycidyl dimethacrylate and triethylene glycol dimethacrylate resin matrix. Four groups of porous FRC specimens were prepared with a different amount of resin matrix. Control group contained specimens of fibers, which were bound together with sizing only. Microstructure of the specimens was analyzed using a micro computed tomography (micro-CT) based method. Mechanical properties of the specimens were measured with a tensile test. The amount of resin matrix in the specimens had an effect on the microstructure. Total porosity was 59.5 % (median) in the group with the lowest resin content and 11.2 % (median) in the group with the highest resin content. In control group, total porosity was 94.2 % (median). Correlations with resin content were obtained for all micro-CT based parameters except TbPf. The tensile strength of the composites was 21.3 MPa (median) in the group with the highest resin content and 43.4 MPa (median) in the group with the highest resin content. The tensile strength in control group was 18.9 MPa (median). There were strong correlations between the tensile strength of the specimens and most of the micro-CT based parameters. This experiment suggests that porous FRC structures may have the potential for use in implants for cranial bone reconstructions, provided further relevant in vitro and in vivo tests are performed.     

A new empirical model of glass formation in multicomponent systems

A new empirical model is proposed for the a priori determination of vitrification conditions of multicomponent systems. Based on the concept of antagonistic bonds, the model takes into account the contradictory effects of the glass modifier : i) generally highly ionic it tends to induce a recrystallization, ii) simultaneously it enhances the covalency of the glass former, increasing the polymerization of the species in the liquid phase and favoring the vitrification. The diagrams (enthalpy of formation of the glass modifier vs. polarizing power of the cation contained in the glass modifier) emphasize this double role. The model is applied to some oxychloride and fluoride glasses.     

A new concept of a bus structure made of composite materials by using continuous transversal frames

In the transportation industry vehicles made of steel often have common problems which it can be feasible to solve using other materials or by improving the design, depending on the nature of the problem. Several types of pseudo-solutions can be applied so that nondesirable problems can be avoided at the present, but the trouble remains until new designs or acceptable solutions are discovered. One of the principal problems throughout the life of a vehicle made of metallic materials is the corrosion of some of its parts due to environmental exposure, therefore a maintenance service is necessary. Purely aesthetic damage or even weakening of the structure are also encountered during its life. The phenomenon of corrosion which tends to alter the mechanical characteristics of the materials which make up the vehicles and reduce its resistive capacity make necessary the establishment of periodical revisions which increase the total cost during the life of service. Much work has been done in order to obtain vehicles with optimum durability characteristics (aesthetics, functional, etc.) over a period of time, in most cases an increment of safety and low maintenance cost are recommended. Composite materials offer a wide spectra of possible solutions since corrosion is not considered as a problem, so typical parts of structures in machines (made of metallic materials) subjected to an environmental exposure have been replaced by pieces made of nonmetallic materials as bumpers, hub caps and bodywork components.     

Deformation micromechanics of a model cellulose/glass fibre hybrid composite

Interfacial stress transfer in a model hybrid composite has been investigated. An Sm³⁺ doped glass fibre and a high-modulus regenerated cellulose fibre were embedded in close proximity to each other in an epoxy resin matrix dumbbell-shaped model composite. This model composite was then deformed until the glass fibre fragmented. Shifts of the absolute positions of a Raman band from the cellulose fibre, located at 1095 cm⁻¹, and a luminescence band from a doped glass fibre, located at 648 nm, were recorded simultaneously. A calibration of these shifts, for both fibres deformed in air, was used to determine the point-to-point distribution of strain in the fibres around the breaks in the glass fibre. Each break that occurred in the glass fibre during fragmentation was shown to generate a local stress concentration in the cellulose fibre, which was quantified using Raman spectroscopy. Using theoretical model fits to the data it is shown that the interfacial shear stress between both fibres and the resin can be determined. A stress concentration factor (SCF) was also determined for the regenerated cellulose fibre, showing how the presence of debonding reduces this factor. This study offers a new approach for following the micromechanics of the interfaces within hybrid composite materials, in particular where plant fibres are used to replace glass fibres.     

A new asymptotic model of flexible composite shells of a regular structure

A new model of a flexible composite shell of a regular structure is obtained within the framework of the nonlinear membrane theory. The fundamental relations which describe the geometry and deformation of a thin shell on the basis of the geometrically nonlinear theory are used. It is assumed that the shell is made of an inhomogeneous composite material of a periodic structure, i.e. the midsurface consists of a large number of piecewise-homogeneous unit cells, whose dimensions are small in comparison with the characteristic tangential dimensions of the shell. Using the two-scale asymptotic homogenization technique, a system of nonlinear constitutive equations is obtained and a formulation is given of local problems on a unit cell, from whose solution the effective stiffnesses of the shell are determined. The general theory is applied to the derivation of the constitutive relations of the high-modulus reinforced flexible shells.     

Bone regeneration with glass ceramic implants and calcium phosphate cements in a rabbit cranial defect model

Hydroxyapatite cement (BoneSource®) and brushite calcium phosphate cement (chronOS? Inject) were tested for fixation of glass ceramic implants (Bioverit®) in experimentally created cranial defects in 24 adult New Zealand White rabbits. Aim of the in vivo study was to assess and compare the biocompatibility and osseointegration of the implanted materials. Macroscopic and histological evaluations were performed 1 month, 3 months, and 6 months postoperatively. All implanted materials were well tolerated by the surrounding tissue. Both bone cements exhibited osteoconductive properties. Differences could be detected regarding to the rates of cement resorption and new bone formation. The brushite cement was resorbed faster than the hydroxyapatite cement. The chronOS? Inject samples exhibited a higher rate of connective tissue formation and an insufficient osseointegration. BoneSource® was replaced by bone with minimal invasion of connective tissue. New bone formation occurred faster compared to the chronOS? Inject group. Bioverit® implants fixed with BoneSource® were successfully osseointegrated.     

Feasibility, tailoring and properties of polyurethane/bioactive glass composite scaffolds for tissue engineering

This research work aims to propose highly porous polymer/bioactive glass composites as potential scaffolds for hard-tissue and soft-tissue engineering. The scaffolds were prepared by impregnating an open-cells polyurethane sponge with melt-derived particles of a bioactive glass belonging to the SiO₂–P₂O₅–CaO–MgO–Na₂O–K₂O system (CEL2). Both the starting materials and the composite scaffolds were investigated from a morphological and structural viewpoint by X-ray diffraction analysis and scanning electron microscopy. Tensile mechanical tests, carried out according to international ISO and ASTM standards, were performed by using properly tailored specimens. In vitro tests by soaking the scaffolds in simulated body fluid (SBF) were also carried out to assess the bioactivity of the porous composites. It was found that the composite scaffolds were highly bioactive as after 7 days of soaking in SBF a HA layer grew on their surface. The obtained polyurethane/CEL2 composite scaffolds are promising candidates for tissue engineering applications.     

An empirical model of the strength of a porous glass wool composite

The tensile strengths of porous glass wool composites have been determined by means of normal tensile tests and parting strength tests. The experimental results thus obtained were then used, with the aid of a computer, to develop a mathematical correlation between tensile strength and composite structural parameters. By experimental adaptation and by using different boundary conditions, the equation $\text{T = 1·36GH + √H + 0·15G}{}^3$ was developed where $\text{T = tensile strength}$, $\text{G = glass content}$ and $\text{H = 100 × resin/glass}$ ratio. This equation is valid over the entire density and resin content ranges examined, and the correlation between empirical results and values predicted by the model is excellent.In addition, our model has been developed in relation to variations of both fibre and resin contents, and the analytic solution has proved to be valid in relation to some structural changes, which suggests that the model also has physical significance.     

Analysis and model of the crack bridging mechanisms in a ductile fiber reinforced ceramic matrix composite

The force resisting the opening of a crack in a brittle matrix composite that is bridged by ductile fibers was studied (Acta Mater. 46(18) (1998) 6381; Acta Mater. 45(9) (1997) 3609). to gain a generic understanding of the crack-bridging process by ductile reinforcements. The matrix was alumina, initially containing a parallel array of fine cylindrical holes. Molten Al was cast into the holes to produce the fibers in situ. A crack was gently introduced to traverse the specimen. The matrix halves were pulled apart in a controlled manner to open the crack. The resisting force increased proportionally to the crack opening over a wide range until a force plateau was reached. Thereafter the force diminished very gradually until failure intervened. Analysis of this counter-intuitive behavior indicated that the excellent adhesion between the fiber and the matrix in combination with the large thermal expansion mismatch must have led to extensive but spotty debonding already from the start of the start of the crack opening. In spite of the well-known ductility of the fibers, the bridging showed quasi-elastic behavior over much of the crack opening. Necking appeared to be suppressed until the separation approached failure. Detailed modeling is offered to provide interpretation of this observed behavior.     

Microcharacterization of a new injectable polymer/ceramic composite as bone substitute in spine surgery

The results of microscopic and spectroscopic analysis of a mixture of biphasic calcium phosphate (BCP) powder and cellulose ether aqueous sol are reported in this study. This new composite is injectable and is aimed to be used as bone substitute for spine surgery. The influence of the polymer on the physico-chemical properties of BCP was investigated by complementary techniques such as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), infrared and Raman spectroscopies and X-ray photoelectron spectroscopy (XPS). When brought into contact with the polymer solution, the ceramic is modified in its granulometry, crystallinity, and surface chemistry. A dissolution/precipitation reaction occurs, leading to a phosphorus-rich and amorphous outer layer of the ceramic surface. Moreover, the bonding state of the composite involves new features that could be assigned to calcium complexes (calcium carbonate or calcium hydroxide).     

Low-temperature sintering and microwave dielectric properties of a new Ba/Ti-based diphase composite ceramic

Journal of Materials Science - The phase composition, grain morphology and microwave dielectric performances of a novel BaZn2Ti4O11-based (BZT) composite ceramic were investigated through X-ray...     

A new estimator for sensitivity analysis of model output: An application to the e-business readiness composite indicator

In this paper we propose and test a generalisation of the method originally proposed by Sobol’, and recently extended by Saltelli, to estimate the first-order and total effect sensitivity indices. Exploiting the symmetries and the dualities of the formulas, we obtain additional estimates of first-order and total indices at no extra computational cost. We test the technique on a case study involving the construction of a composite indicator of e-business readiness, which is part of the initiative “e-Readiness of European enterprises” of the European Commission “e-Europe 2005” action plan. The method is used to assess the contribution of uncertainties in (a) the weights of the component indicators and (b) the imputation of missing data on the composite indicator values for several European countries.