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91.
徐乐 《沈阳工程学院学报(自然科学版)》2006,2(1):79-82
无线异步传输模式(ATM)网络通信系统将在宽带和多媒体个人通信得到广泛应用.提出一种用于无线ATM网络多媒体通信服务的呼叫允许控制(CAC)方案,它采用统计大量用户移动信息来估计未来业务需求和系统可用资源,并根据用户移动信息动态地调整用于潜在切换呼叫的资源预约,能有效利用无线频谱资源,增大系统容量. 相似文献
92.
Fibre-reinforced plastic (FRP) composites have been increasingly used in rehabilitation and strengthening of concrete structures.
Significant increases in stiffness and strength have been achieved by applying this technique. However, there is concern about
the ductility or toughness performance of FRP/concrete hybrid structures, which is critical in the application of this technology.
This paper presents a new theoretical method to predict the fracture resistance behaviour of FRP post-strengthened concrete
flexural beams. No slip between the FRP and plain concrete matrix is assumed and Mode I fracture propagation is considered.
The model is valid for a wide range of span-to-depth ratios and any crack length. The influence of the bridging stresses provided
by the fracture process zone (FPZ) at the tip of a fictitious fracture is examined. The effect of various material and geometric
parameters on the resistance curve and toughness of the hybrid structure is discussed, based on the numerical results from
the developed theoretical formulae. The results provide a useful insight into the strengthening/toughening and the design
of FRP sheet/concrete beam structures. 相似文献
93.
Dheerendra Kumar Dwivedi A. Sharma T. V. Rajan 《Materials and Manufacturing Processes》2005,20(5):777-791
In this paper, the influence of silicon particle morphology on mechanical properties of two piston alloys has been reported. Alloys having nominal composition Al-12%Si-1%Ni-0.8%Cu-0.6%Mg (LM13) and Al-17%Si-1%Ni-0.8%Cu-0.6%Mg (LM28) were prepared by melting and casting. The morphology of silicon crystals was changed using additives during the melt treatment and subsequently by heat treatment. Mechanical properties such as hardness, ductility, and tensile strength of experimental alloys were tested. Test results showed that the melt treatment and heat treatment of both the alloys increased the tensile strength, hardness, and ductility. However, the influence of melt treatment on mechanical properties was not as significant as that of heat treatment. Tensile strength and ductility of LM13 was found to be higher than the LM28 alloy under similar conditions. Hardness of LM28 was higher than the LM13 alloy. Optical and SEM studies showed a change in eutectic silicon morphology on melt treatment of LM13. However, change in morphology of primary silicon particles was not significant as for LM28. Heat treatment of both alloys caused spheroidization and better distribution of eutectic silicon crystals. Sharp-edged primary silicon particles were rounded off after the heat treatment of LM28. Scanning electron microscopy (SEM) of tensile fractured surfaces was carried out to study the influence of microstructure on fracture mode. Heat treatment of both alloys promotes dimple fracture. However, as-cast and melt-treated alloys show predominantly cleavage fracture. 相似文献
94.
The centrally cracked Brazilian disc specimen has been used by many researchers to study mode I and mode II brittle fracture in different materials. However, the experimental results obtained in the past from this specimen indicate that the fracture toughness ratio (KIIc/KIc) is always significantly higher than the theoretical predictions. It is shown in this paper that the increase in the ratio KIIc/KIc can be predicted if a modified maximum tangential stress (MTS) criterion is used. The modified criterion takes into account the effect of T-stress in addition to the conventional singular stresses. The fracture toughness ratio KIIc/KIc is calculated for two brittle materials using the modified criterion and is compared with the relevant published experimental results obtained from fracture tests on the cracked Brazilian disc specimen. A very good agreement is shown to exist between the theoretical predictions and the experimental results. 相似文献
95.
Slip initiation on frictional fractures 总被引:1,自引:0,他引:1
O. Mutlu 《Engineering Fracture Mechanics》2005,72(5):729-747
Direct shear tests and biaxial compression tests are conducted to investigate the onset of slip along a non-homogeneous frictional surface and to determine the effect of specimen thickness and confining stress on slip initiation and propagation. The specimens are made of two and three acrylic blocks with the contact surfaces between blocks having on their upper half a frictional strength smaller than on their lower half. This creates a “weak” surface on the upper half and a “strong” surface on the lower half. The specimens are then loaded in direct shear or biaxial compression with confining pressures ranging from 0.7 to 3.5 MPa. The onset of slip, slip propagation, and the stress field generated at the front and center of the blocks interfaces are monitored using a photoelastic technique where a thin photoelastic film is placed at the location where observations are made. The onset of slip at the weak-strong zone interface is treated as propagation of a frictional crack under Mode II loading. The critical stress intensity factor, KIIC, at the onset of slip is obtained from photoelastic techniques. The results show a weak dependency of KIIC on the normal stress applied and no influence of the specimen size for specimens thicker than 25.4 mm; for thinner specimens the KIIC values are smaller because the boundaries of the specimen prevent the full development of the stress field ahead of the crack tip. The experiments show a linear increase of the critical energy release rate with normal stress which is explained with linear elastic fracture mechanics theories. 相似文献
96.
~~重视心理因素在临床中的作用@李清华!400042重庆$重庆石油高等专科学校
@周宇玲$铁马集团职工医院~~~~ 相似文献
97.
连彬 《重庆科技学院学报(自然科学版)》2003,5(3):30-32
从高等职业技术教育特点入手 ,通过分析目标职业岗位群对人才的知识、能力、素质结构的要求 ,提出了高职旅游管理专业的培养目标与培养模式。 相似文献
98.
通过对泌阳凹陷前杜楼地区北部断块 98- 1井区资料的分析 ,设立隶属函数 ,建立模糊判别模式 ,对 98- 1区的 7个砂层进行模糊判别 ,获得了较好的效果。 相似文献
99.
The paper presents some results on global exponential stability of linear time invariant systems with different time scales. The full system is decomposed in two reduced ones by means of singular perturbations and a smooth approximation of a Variable Structure Control is synthesized for each of them using Reaching Law approach. The global closed loop stability is then proved for the whole system using Lyapunov methods and a particular state space decomposition. Moreover a literal form for ε∗ (a parameter which measures the minimum separation between time scales) is derived. 相似文献
100.
介绍了基于BS模式的网络教学系统的硬件网络拓扑结构设计以及软件的总体结构设计,并对关键子系统的设计做了说明。 相似文献