《Construction and Building Materials》2001,15(5-6):263-270

The patterns of failure in a pull-out test are visualized by an X-ray CT scanner to supply the basic data on the bond failure of rock bolts and cable bolts. In the pull-out test, a comparison was made between two types of cable bolts and rock bolts. From the results, it is shown that the microscopic failure mechanism is classified as the different failure mode. Then the supporting effect of rock bolts and cable bolts are discussed.  相似文献   

    

《International Journal of Impact Engineering》2005,31(6):755-767

The phenomena and the test results of dense fragment cluster impacting armor plate are briefly summarized. The test results indicate that the impulse and the rate of energy deposition on the target and the impacting duration of the fragment cluster are the most important factors, which induces the multi-fragment effects, i.e. synergistic effects, in the impacting process. Meanwhile, they are the characteristic parameters that distinguish the cumulative effects from the additive effects. The analytical methods are employed to investigate the cumulative effects and additive effects caused by the dense fragment cluster. Based on the analysis of the terminal effect of a single fragment, the extrusion-shear damage model of the target impacted by the fragment cluster is developed, and two criteria for the occurrence of the cumulative effect are given and applied to the test analysis. The dimensionless characteristic parameter of the fragment-cluster/target-plate system is also derived.  相似文献   

    

《Computational Materials Science》2005,32(1):66-84

The melting and softening behavior of nano-size silica (SiO₂) was studied using the molecular dynamics method. Energy supply was simulated by considering radiative heat transfer. The potential function of silica includes three-body interaction as well as two-body interaction. Initially, thermal treatment for making the amorphous state was performed for both thin film-type and sphere-type nano-size specimens. Then, pre-determined radiative energy, estimated by the spectroscopic concept of electromagnetic waves which are reflecting and refracting in the nano-size material, was applied to the specimen continuously. Depending on the temperature rise, each specimen exhibited softening or melting accompanied by dissociation of silicon oxide molecules. A change in the atomic structure was mainly recognized in the Si–O–Si bonding angle, which was effectively assessed using a novel parameter named the “B parameter”. By using this “B parameter”, both the strained state of SiO₄ tetrahedra and their interconnection become obvious simultaneously. Regardless of the specimen shape, the coordination number and the “B parameter” have a certain relationship depending on the characteristic atomic-scale local structure of silica, such as SiO₄, SiO₃, or SiO₂. It was found that a wide distribution of the “B parameter” for the Si–O–Si angle and increase in the distribution for the O–Si–O angle together indicate melting or softening of the nano-size silica.  相似文献   

    

《Materials Research Bulletin》2006,41(4):867-872

A novel green emitting phosphor, Tb³⁺-doped Ca₂GeO₄ was prepared for the first time by a solid-state reaction. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄ → ⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM). Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 and 550 nm under UV excitation. In addition, Al³⁺ or Li⁺ co-doping enhances the green emission from Ca₂GeO₄:Tb³⁺ by about 18 and 4 times, respectively, under UV excitation. The excellent luminescence properties make it a possible candidate for flat panel display application.  相似文献   

    

《Composites Part B》2003,34(6):527-538

Concrete bridge decks supported by main girders develop initial cracks in the longitudinal or transverse direction by applied loads. Therefore, it is important to consider the crack patterns and deflections if such decks are to be strengthened. This study investigated the effectiveness of strengthening using carbon fiber sheets. The experimental variables were the direction and the amount of strengthening material. To simulate the real behavior of the bridge deck, static structural tests were conducted on six specimens, with a built-in concrete girder on each side. The structural behavior was then observed through the crack pattern and the load–displacement relationship of each specimen. Also, the yield line theory that adopts the modified Johansen's yield criterion was applied to estimate the ultimate strength.  相似文献   

    

《Advanced Powder Technology》1999,10(1):51-64

An electrically conducting powder was produced by mixing bronze spheres with a small amount of carbon black powder. The potential difference across beds of this powder was measured under static conditions and vibration. The system was very sensitive and monitored changes during vibration cycles at rapid rates. Horizontal and vertical conductances were measured. Above a minimum vertical stress, the ratio of the two was constant. The conductance was related to vertical stress by a linear relationship with hysteresis, for both static conditions and vibration at small accelerations. A simple model has been proposed to describe this system. At high accelerations (< 10 m/s²) changes were much larger. There were permanent changes in conductance and the system was non-linear. The data demonstrate that the internal structure of a particle bed displays great sensitivity, hysteresis and a dependence upon stress history.  相似文献   

    

《Cold Regions Science and Technology》2004,38(2-3):93-101

The method of numerical analysis of the differential scanning calorimetry (DSC) thermogram obtained during warming makes it possible to obtain a complete curve of the unfrozen water content in frozen soil, including the highest temperature at which last ice crystals melt and the unfrozen water content becomes equal to the total water content. This is referred to as the freezing point of the soil–water system obtained on melting. Statistical analysis of 137 results obtained for 6 monomineral and homoionic model soils implies that, similarly to the freezing point obtained from the cooling curves, the soil freezing point obtained on melting strongly depends on the water content. An empirical equation, found basing on the reported results, has proved to be useful as a predicting tool with reference to 33 foreign data points obtained in the typical way (i.e., from the cooling curve).  相似文献   

    

《Cement and Concrete Composites》2006,28(9):790-799

This paper presents the results of an investigation of the properties of mortar in which a calcined clay was employed as a pozzolan. Mortars were prepared using either heat treated clay or ground waste clay bricks (from the same clay subjected to 1000 °C calcining) as a pozzolanic partial replacement for cement at replacement levels of 10%, 20% and 30%. The compressive strengths of the mortars were monitored up to 90 days and the resistance to sodium sulphate solution and synthetic seawater was monitored up to 300 days. The specimens were also monitored for weight changes. Partially replacing cement by ground brick or heat-treated brick clay gives early strengths that are lower than that of the control. At 90 days, however, the strengths are the same as or are greater than that of the control. Heat-treated clay is effective in reducing expansion during exposure of the mortar to sulphate solution and synthetic seawater. The rapidly cooled clay gives better performance, in terms of strength development and resistance to harmful solutions, than the slow cooled clay.  相似文献   

    

《Reliability Engineering》1987,17(1):1-8

In order to establish a feasible and useful reliability evaluation model for a network system of dependent components, the failure of a component is distinguished into many states artificially, according to the causes which bring about such a failure and the effects to the system in such a way that the failure rate of each state can be easily estimated. Such failure state of a component can be grouped into four types, single (stochastical independent), active, passive and common-cause failures.  相似文献   

    

《Materials Chemistry and Physics》1987,17(5):453-460

This study is devoted to the mechanical properties of asbestos-epoxy composites. Chrysotile fibres were first pretreated by means of an interfacial polymerization technique effecting eventually a poly (hexamethylene adipamide) coating on the asbestos surface. The interface characteristics were significantly altered and due to the well-known compatibility between epoxy and polyamide phase considerable deviation from the behaviour encountered when using untreated fibres was confirmed. Accordingly, while varying pretreated fibre content and also concentration of the polyamide coating, the tensile properties of the resulted composites were examined.  相似文献