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排序方式: 共有247条查询结果,搜索用时 62 毫秒
11.
A new expression of the equations describing the locked states of two oscillators coupled through a resistor is presented in this article. This theory has led to the elaboration of a CAD tool which provides, in a short simulation time, the frequency locking region of two coupled differential oscillators. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012. 相似文献
12.
Dental implant has been used and studied for the replacement of missing teeth for many years. It has been well known that the success of dental implant is heavily dependent on initial stability and long-term Osseointegration due to optimal stress distribution in the surrounding bones. For this reason, the search of the rational solutions to reduce these stresses has become an important issue in this field. Alternatives to reduce the forces transmitted to implants have been studied, including variations in implant positioning, implant design, prosthesis shape, occlusal requirements, prosthetic components and prosthetic materials. Thus, a new concept of adding a bio-elastomer to the prosthetic components of implant system was interposed between the abutment and the framework crown in order to damp the occlusive shocks and to attenuate the stress concentrated at the implant/bone interface. The new implant system design was assessed by the three dimensional finite element techniques using ABAQUS program to study the effect of elastomer material under an occlusal load on the induced equivalent von Mises interface stresses. These stresses were compared with those provoked by the standardized implant. The von Mises stress distribution indicated that stress was maximal around the top of the implant with varying intensities in the different loading cases. The stress was highest in the cortical bone at the neck of implant and lowest in the cancellous bone. Overall, the novel implant provoked lower interface stresses only in the cortical bone due to the stress shielding effect of the elastomeric stress barrier. 相似文献
13.
To examine the performance of nonlinear models proposed in the estimation of fatigue damage and fatigue life of components under random loading, a batch of specimens made of 6082 T 6 aluminium alloy has been studied and some of the results are reported in the present paper. The paper describes an algorithm and suggests a fatigue cumulative damage model, especially when random loading is considered. This paper contains the results of mono-axial random load fatigue tests with different mean and amplitude values performed on 6082 T 6 aluminium alloy specimens. Cycles were counted with rainflow algorithm and damage was cumulated with a new model proposed in this paper and with the Palmgren–Miner model. The proposed model has been formulated to take into account the damage evolution at different load levels and it allows the effect of the loading sequence to be included by means of a recurrence formula derived for multilevel loading, considering complex load sequences. It is concluded that a ‘damaged stress interaction damage rule’ proposed here allows a better fatigue damage prediction than the widely used Palmgren–Miner rule, and a formula derived in random fatigue could be used to predict the fatigue damage and fatigue lifetime very easily. The results obtained by the model are compared with the experimental results and those calculated by the most fatigue damage model used in fatigue (Miner’s model). The comparison shows that the proposed model, presents a good estimation of the experimental results. Moreover, the error is minimized in comparison to the Miner’s model. 相似文献
14.
Alireza Sayyidmousavi Habiba Bougherara Ihab Elsawi Zouheir Fawaz 《Mechanics of Time-Dependent Materials》2014,18(2):423-436
In the present study, a novel micromechanical approach is introduced to study the time-dependent failure of unidirectional polymer matrix composites. The main advantage of the present micromechanical model lies in its ability to give closed-form solutions for the effective nonlinear response of unidirectional composites and to predict the material response to any combination of shear and normal loading. The creep failure criterion is expressed in terms of the creep failure functions of the viscoelastic matrix material. The micromechanical model is also used to calculate these creep failure functions from the knowledge of the creep behavior of the composite material in only transverse and shear loadings, thus eliminating the need for any further experimentation. The composite material used in this study is T300/934, which is suitable for service at high temperatures in aerospace applications. The use of micromechanics can give a more accurate insight into the failure mechanisms of the composite materials in particular at high temperatures where the general behavior of the polymer matrix composite is governed by matrix viscoelasticity and the time-dependent failure of the matrix is a localized phenomenon. The obtained creep failure stresses are found to be in reasonable agreement with the experimental data. 相似文献
15.
Ihab El Sawi Zouheir Fawaz Redouane Zitoune Habiba Bougherara 《Journal of Materials Science》2014,49(5):2338-2346
In this paper we investigated the fatigue damage of a unidirectional flax-reinforced epoxy composite using infrared (IR) thermography. Two configurations of flax/epoxy composites layup were studied namely, [0]16 unidirectional ply orientation and [±45]16. The high cycle fatigue strength was determined using a thermographic criterion developed in a previous study. The fatigue limit obtained by the thermographic criterion was confirmed by the results obtained through conventional experimental methods (i.e., Stress level versus Number of cycles to failure). Furthermore, a model for predicting the fatigue life using the IR thermography was evaluated. The model was found to have a good predictive value for the fatigue life. In order to investigate the mechanism of damage initiation in flax/epoxy composites and the damage evolution, during each fatigue test we monitored the crack propagation for a stress level and at different damage stages, a direct correlation between the percentage of cracks and the mean strain was observed. 相似文献
16.
A persisting major challenge for optical network operators is to meet the various availability requirements of the different subscribed services through the deployment of effective protection strategies. Priority-aware shared protection is a promising scheme that has been proposed in the open literature as a potential approach to tackling this challenge. However, the priority-aware protection strategy is rigid in the sense that it privileges the high priority connections regardless of the low priority ones. Hence, this letter proposes to improve priority-aware protection by introducing the mutation probability parameter. This parameter expresses the likelihood that a highpriority connection be relegated temporarily to a lower priority level during recovery. In this way, the mutation-based protection strategy offers optical operators the possibility to increase the availability of their low-priority clients without violating the availability requirements of their high-priority ones. Performance of this novel protection strategy is analyzed in this letter by precisely calculating the connection availabilities resulting from its deployment. 相似文献
17.
In the south of Algeria, to supply sufficient fresh water for the population, desalination is necessary because water resources (underground and geothermal) are brackish.This paper presents the theoretical study and the results of experiments carried out with a capillary film multi-effect distiller installed in the south of Algeria (in a village near Touggourt, where the temperature of the groundwater is about 65°C at the source). The name of this device is DIFICAP (
stiller with a
lm in
illary motion).The aim of our study is to improve the efficiency of this distiller. The research and development of this desalination process is carried out under the following aspects: modelisation of heat and mass transfer, experimentation under direct solar radiation in South Algeria and technical development to aim to optimize the efficiency of this distiller.The theoretical and experimental results show that the efficiency of this distiller increases when the temperature of the brackish water, the intensity of the solar radiation and the number of stages increase. 相似文献
18.
Jacques G. Noudem Sophie Meslin Daniel Horvath Christelle Harnois Daniel Chateigner Bachir Ouladdiaf Sophie Eve Mousta Gomina Xavier Chaud Masato Murakami 《Journal of the American Ceramic Society》2007,90(9):2784-2790
The recently reported hole-patterned YBa2 Cu3 O y (Y123) bulks with improved superconducting properties are highly interesting from material quality and application variety points of view. It is well known that the core of plain bulk superconductors needs to be fully oxygenated and some defects like cracks, pores, and voids must be suppressed in order that the material can trap a high magnetic field or carry a high current density. To minimize the above defects, we have used a combination of standard superconducting ceramic processing and an infiltration technique to prepare regularly perforated YBa2 Cu3 O y (Y123) bulk superconductors. This process leads to negligible shrinkage upon annealing and a uniform distribution of Y211 inclusions. Texture was evidenced by neutron pole figure measurements. Flux mapping was used to verify the superconducting homogeneity of the samples and to investigate the field-trapping ability. In addition, the textured drilled samples were reinforced using resin or metal impregnation and the influence of the different processing steps on the hardness of the materials has been investigated. 相似文献
19.
Studies have been made on the dynamic oscillation and static properties in the molten state of blends from polybutene-1 and polypropene. Measurements were made with a balance-rheometer system Dr. Kepes and a capillary viscosimeter. Three experimental parameters, η0, τ0 and h have been determined. Steady shear and oscillatory shear viscosity data have been compared. A plot of intrinsic viscosity vs. composition of blends shows a minimum. Variation of η0 and τ0 with temperature follow the Arrhenius law but h does not depend on temperature. 相似文献
20.
Mireille Canal-Raffin Beatrice L'Azou Beatrice Martinez Elisabeth Sellier Fawaz Fawaz Philip Robinson Celine Ohayon-Courtès Isabelle Baldi Jean Cambar Mathieu Molimard Nicholas Moore Patrick Brochard 《Particle and fibre toxicology》2007,4(1):1-13