Dynamical Elastic Moduli of the Ti-13Nb-13Zr biomaterial alloy by mechanical spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of Biomimetic Remineralization on the Dynamic Nanomechanical Properties of Dentin Hybrid Layers

The mineral and organic phases of mineralized dentin contribute co-operatively to its strength and toughness. This study tested the null hypothesis that there is no difference in nano-dynamic mechanical behavior (complex modulus-E*; loss modulus-E ''; storage modulus-E'; in GPa) of dentin hybrid layers (baseline: E*, 3.86 +/- 0.24; E '', 0.23 +/- 0.05; E', 3.85 +/- 0.24) created by an etch-and-rinse adhesive in the presence or absence of biomimetic remineralization after in vitro aging. Using scanning probe microscopy and nano-dynamic mechanical analysis, we demonstrated that biomimetic remineralization restored the nano-dynamic mechanical behavior of heavily remineralized, resin-sparse regions of dentin hybrid layers (E*, 19.73 +/- 3.85; E '', 8.75 +/- 3.97; E', 16.02 +/- 2.58) to those of the mineralized dentin base (E*, 19.20 +/- 2.42; E '', 6.57 +/- 1.96; E', 17.39 +/- 2.0) [p > 0.05]. Conversely, those resin-sparse, water-rich regions degraded in the absence of biomimetic remineralization, with significant decline [p < 0.05] in their complex and storage moduli (E*, 0.83 +/- 0.35; E '', 0.88 +/- 0.24; E', 0.62 +/- 0.32). Intrafibrillar apatite deposition preserves the integrity of resin-sparse regions of hybrid layers by restoring their nanomechanical properties to those exhibited by mineralized dentin.

Evaluation by Free Vibration Method of Moisture Absorption Effects in Polyamide/Carbon Fiber Laminates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermally activated dynamics of the tilts of the CuO6 octahedra, hopping of interstitial O, and possible instability towards the LTT phase in La2CuO4+δ

The anelastic spectrum (dynamic Young's modulus and elastic energy absorption) of La2CuO4+δ has been measured between 1 and 700 K with 0<δ<0.02. The spectrum of stoichiometric La2CuO4 in the low-temperature orthorhombic (LTO) phase is dominated by two intense relaxation processes which cause softenings of 16% around 150 K and 9% below 30 K at f∼1 kHz. The relaxation at 150 K is attributed to the presence of a fraction of the CuO6 octahedra which are able to change their tilted configuration by thermal activation between orientations which are nearly energetically equivalent, possibly within the twin boundaries. The relaxation below 30 K is governed by tunneling, and involves a considerable fraction of the lattice atoms. It is proposed that the double-well potentials for the low-temperature relaxation are created by the tendency of the LTO phase to form low-temperature tetragonal (LTT) domains, which however are not stabilized like when La is partially substituted with Ba. On doping with excess O, the relaxation rates of these processes are initially enhanced by hole doping, while their intensities are depressed by lattice disorder; an explanation of this behavior is provided. Excess O also causes two additional relaxation processes. The one appearing at lower values of δ is attributed to the hopping of single interstitial O2- ions, with a hopping rate equal to τ-1=2×10-14exp(-5600/T) s. The second process is slower and can be due to O pairs or other complexes containing excess O.

Remarks on orthotropic elastic models applied to wood

Wood is generally considered an anisotropic material. In terms of engineering elastic models, wood is usually treated as an orthotropic material. This paper presents an analysis of two principal anisotropic elastic models that are usually applied to wood. The first one, the linear orthotropic model, where the material axes L (Longitudinal), R(radial) and T(tangential) are coincident with the Cartesian axes (x, y, z), is more accepted as wood elastic model. The other one, the cylindrical orthotropic model is more adequate of the growth caracteristics of wood but more mathematically complex to be adopted in practical terms. Specifically due to its importance in wood elastic parameters, this paper deals with the fiber orientation influence in these models through adequate transformation of coordinates. As a final result, some examples of the linear model, which show the variation of elastic moduli, i.e., Young's modulus and shear modulus, with fiber orientation are presented.

Developing a system for down-hole seismic testing together with the CPTU

This paper presents a system for performing down-hole seismic test together with the piezocone test in order to determine the shear wave velocity (Vs) and for calculating the maximum shear modulus (Go); a basic parameter for analyzing the dynamic soil behavior and a reference value of the soil stiffness. The system components are described and tests results for checking the geophone response are also presented, both before and after installation into the probe. The system was used in down-hole tests carried out at three experimental research sites located in the interior of Sao Paulo State, Brazil, where in situ seismic test results are available. The Vs values measured in down-hole tests carried out with this system were consistent with those determined in cross-hole tests and with a commercial seismic piezocone, which enabled to validate the developed system.

The seismic SPT to determine the maximum shear modulus

This paper presents the first results of a system to carry out seismic SPT, which associates the up-hole seismic technique to the currently used SPT test. This hybrid test allows determining the maximum shear modulus (G 0) together with the SPT test. G 0 is the most important dynamic soil parameter and it is calculated based on the shear wave velocity (V S) measurements. The equipment and the method of analysis will be briefly described. The V s values measured using the S-SPT in one experimental research site located inland of Sao Paulo State-Brazil are presented and compared with down-hole and Seismic CPT test data. These preliminary results indicate that the S-SPT was satisfactory and can be used for dynamic site characterization.

The non-ideal problem behavior using a dynamic vibration absorber with nonlinear essential stiffness and timedependent damping properties

The purpose of this study is to develop a dynamic vibration absorber using viscoelastic material with nonlinear essential stiffness and time-dependent damping properties for a non-ideal vibrating system with Sommerfeld effect, resonance capture, and jump phenomenon. The absorber is a mass-bar subsystem that consists of a viscoelastic bar with memory attached to mass, in which the internal dissipative forces depend on current, deformations, and its operational frequency varies with limited temperature. The non-ideal vibrating system consists of a linear (nonlinear) oscillator (plane frame structure) under excitation, via spring connector, of a DC-motor with limited power supply. A viscoelastic dynamic absorber modeled with elastic stiffness essentially nonlinearities was developed to further reduce the Sommerfeld effect and the response of the structure. The numerical results show the performance of the absorber on the non-ideal system response through the resonance curves, time histories, and Poincarésections. Furthermore, the structure responses using the viscoelastic damper with and without memory were studied. © IMechE 2012.

Simple green approach to reinforce natural rubber with bacterial cellulose nanofibers

Natural rubber (NR) is a renewable polymer with a wide range of applications, which is constantly tailored, further increasing its utilizations. The tensile strength is one of its most important properties susceptible of being enhanced by the simple incorporation of nanofibers. The preparation and characterization of natural-rubber based nanocomposites reinforced with bacterial cellulose (BC) and bacterial cellulose coated with polystyrene (BCPS), yielded high performance materials. The nanocomposites were prepared by a simple and green process, and characterized by tensile tests, dynamical mechanical analysis (DMA), scanning electron microscopy (SEM), and swelling experiments. The effect of the nanofiber content on morphology, static, and dynamic mechanical properties was also investigated. The results showed an increase in the mechanical properties, such as Young's modulus and tensile strength, even with modest nanofiber loadings. © 2013 American Chemical Society.

Efeito do oxigênio nas propriedades anelásticas e biocompatibilidade das ligas de Ti-8%pTa e Ti-16%pTa utilizadas como biomaterial

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da adesividade (TACK) de pré-impregnados de resina epóxi reforçada com fibras de carbono

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo do sistema celulose bacteriana-poliuretano para a produção de novos compósitos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Um estudo da estabilidade mecânica de poços a partir de perfis geofísicos em formações pouco consolidadas

A análise da estabilidade mecânica de um poço pode ser feita a partir do cálculo de parâmetros elásticos da formação utilizando a densidade do meio e as velocidades de propagação das ondas compressional e cisalhante na formação rochosa, os quais podem ser obtidos de perfis geofísicos do poço. Em formações sedimentares pouco consolidadas as ferramentas de perfilagem sônica convencionais (monopolares) não conseguem registrar com acuidade a velocidade da onda cisalhante pois a primeira chegada dessa onda é camuflada pela chegada de outras ondas que podem ser mais rápidas que a onda cisalhante num poço perfurado neste tipo de formação. Medidas das velocidades sônicas são feitas em laboratório em amostras da formação, sob condições semelhantes às condições in situ, servindo como ajuste das velocidades registradas no poço pela ferramenta de perfilagem sônica. Para a análise de estabilidade da formação, perfis auxiliares são necessários como o perfil de porosidade, saturação de fluidos e perfis de composição mineralógica da formação rochosa. Exige-se ainda dados de testes de avaliação da formação e de condições do reservatório, mas que são comuns em poços de petróleo, como o teste de formação e os testes de pressurização do poço, tais como o teste de micro-fraturamento hidráulico ou o teste de absorção. A avaliação das tensões principais efetivas que atuam distante do poço, e que não são afetadas pela sua presença, é feita através da associação de um modelo de deformação elástica apropriado e o resultado do teste de pressurização disponível para o poço em estudo. Utilizando resultados clássicos da teoria da elasticidade geral pode-se calcular o campo de tensões modificado na vizinhança da parede do poço devido ao efeito da própria presença do poço ali perfurado e da diferença de pressão existente entre o interior do poço e a formação rochosa. A determinação das propriedades mecânicas da formação a partir das velocidades sônicas e a avaliação do campo de tensões assumindo um modelo elástico de deformação, supõem o meio rochoso no qual as ondas se propagam como elástico, homogêneo e isotrópico. Esta suposição representa a principal aproximação assumida pela metodologia descrita neste trabalho. De posse das propriedades mecânicas da formação e do campo de tensões que age na vizinhança do poço resta definir o critério segundo o qual a rocha sofre instabilidade mecânica quando submetida aquele campo de tensões. Isto permite determinar se, nas condições avaliadas do poço e da formação, haverá quebra da parede do poço por excesso de tensão e, se houver, qual a sua extensão. Assim o problema é como analisar o comportamento mecânico de um poço em uma formação pouco consolidada a partir de perfis geofísicos os quais podem ter problemas no registro das propriedades físicas do meio em formações deste tipo. A metodologia proposta é aplicada a dois intervalos de profundidade pertencentes a dois poços onde arenitos e folhelhos se intercalam e nos quais todos os dados necessários estão disponíveis. Os resultados obtidos mostram que, exceto quando outros mecanismos de quebra da parede do poço agem na formação, a metodologia proposta consegue com sucesso detectar zonas de ocorrência de instabilidade mecânica do poço provocadas por um campo de tensões que excede a resistência mecânica da formação.

Biomaterials from blends of fluoropolymers and corn starch-implant and structural aspects

The development of polymeric blends to be used as matrices for bone regeneration is a hot topic nowadays. In this article we report on the blends composed by corn starch and poly(vinylidene fluoride), PVDF, or poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), to obtain biocompatible materials. Blends were produced by compressing/annealing and chemically/structurally characterized by micro-Raman scattering and Fourier transform infrared (FTIR) absorption spectroscopies, dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM), besides in vivo study to evaluate the tissue response. Vibrational spectroscopy reveals no chemical interaction between the polymers and starch, absence of material degradation due to compressing/annealing process or organism implantation, and maintenance of a and ferroelectric crystalline phases of PVDF and P(VDF-TrFE), respectively. As a consequence of absence of interaction between polymers and starch, it was possible to identify by SEM each material, with starch acting as filler. Elastic modulus (E') obtained from DMA measurement, independent of the material proportion used in blends, reaches values close to those of cancellous bone. Finally, the in vivo study in animals shows that the blends, regardless of the composition, were tolerated by cancellous bone. (C) 2013 Elsevier B.V. All rights reserved.

Effect of Ceramic Thickness and Shade on Mechanical Properties of a Resin Luting Agent

Purpose: This study aimed to investigate the influence of ceramic thickness and shade on the Knoop hardness and dynamic elastic modulus of a dual-cured resin cement.Materials and Methods: Six ceramic shades (Bleaching, A1, A2, A3, A3.5, B3) and two ceramic thicknesses (1 mm, 3 mm) were evaluated. Disk specimens (diameter: 7 mm; thickness: 2 mm) of the resin cement were light cured under a ceramic block. Light-cured specimens without the ceramic block at distances of 1 and 3mm were also produced. The Knoop hardness number (KHN), density, and dynamic Young's moduli were determined. Statistical analysis was conducted using ANOVA and a Tukey B rank order test (p = 0.05).Results: The bleaching 1-mm-thick group exhibited significantly higher dynamic Young's modulus. Lower dynamic Young's moduli were observed for the 3-mm-thick ceramic groups compared to bleaching 3-mm-thick group, and no difference was found among the other 3-mm groups. For the KHN, when A3.5 3-mm-thick was used, the KHN was significantly lower than bleaching and A1 1-mm-thick ceramic; however, no difference was exhibited between the thicknesses of the same shade.Conclusions: The dual-cured resin cement studied irradiated through the 1-mm-thick ceramic with the lightest shade (bleaching ceramic) exhibited a better elastic modulus, and there was no effect in KHN of the resin cement when light cured under different ceramic shades and thicknesses (1 and 3 mm), except when the A3.5 3-mm-thick ceramic was used.Clinical Significance: Variolink II irradiated through ceramic with the lowest chroma exhibited the highest elastic modulus; therefore, the light activation method might not be the same for all clinical situations.