粗粒土二维模型试验研究

 粗粒土是土石坝的主要填坝材料,其力学特性研究是土力学热点之一,一般采用三轴试验来研究粗粒土的力学性质,由于试验方法的限制,很难观察到三轴试验过程中颗粒的运动。为了获得试验过程中颗粒的运动规律,研究粗粒土的细观变形机理,设计并开展了粗粒土二维模型试验。二维模型试验过程中可以清楚地观察到颗粒的运动,能定性地分析试样的受力变形特征。试验结果表明：①峰值偏应力随侧压力的增大而增大,峰后略有软化现象,体变随应变的发展先剪缩后剪胀,侧压力越小剪胀性越明显;②抗剪强度包线呈很好的线性关系;③颗粒破碎率随侧压力的增大而增大,在很小的侧压力下,就有颗粒破碎发生;④试样破坏时有较明显的剪切带。模型试验的上述规律和三轴试验成果具有很好的一致性,说明二维模型试验能够反映三轴试验过程。     

Modelling the HRR-singularity with akin and conventional singular elements

A single edge notched plate of elastic-plastic material has been analysed using different finite element meshes and different singular crack tip element. Especially the Akin element was of interest since it gives a possibility to model the HRR-singularity.     

载荷作用下聚碳酸酯试件温升的实验研究

描述了红外辐射技术和热电偶用于测量聚合物材料变形时表面和内部温度的方法,在动态压缩中,用T型微丝热电偶测得了聚碳酸酯的内部温度变化;在准静态拉伸试验中,用红外热像仪获得了聚碳酸酯拉伸过程中的表面温度变化及表面温度场。结果表明,聚合物在准静态拉伸过程中,接近材料的屈服点时温度开始上升,在屈服点处试件表面温度最高,表面温度上升23℃至26℃,达到最高温度的时间与应变率有关;动态压缩时,试件中心温度上升最高,由里向外逐渐降低,试件内部温度与应变率和离表面的距离有关,在应变率为2500 s-1时,内部温度上升约42℃,有60%的塑性功转化为热。     

Surface damage of metallic glasses by argon ion bombardment

The surface damage of metallic glasses Fe₄₀Ni₄₀P₁₄B₆, Fe₄₀Ni₃₈Mo₄B₁₈, Fe₄₀Ni₄₀B₂₀, Fe₈₀B₂₀ and Ni₆₄Zr₃₆ under argon ion bombardment at room temperature has been investigated. Blister formation was observed in the dose range of 1 × 10¹⁷ to 1 × 10¹⁸ ions/cm². At higher doses, blisters disappeared with concurrent roughening of the bombarded surface. Erosional features like cones and pyramids are not observed. Argon induced blisters also disappeared on room temperature aging without any further bombardment after blister formation. Post-irradiation annealing at high temperatures (673 and 873 K) resulted in blister formation, severe surface exfoliation and pin-hole formation. The precipitation of the implanted argon into bubbles is also observed.     

Laboratory scale testing of extruded earth masonry units

There has been a resurgence in use of earth as a construction material largely driven by environmental concerns. Extruded earth masonry is a method of earth brick production that utilises existing fired brick manufacturing techniques. Extruded earth has distinct physical characteristics compared to other earthen building techniques. As industrial scale extrusion trials require large volumes of material, laboratory scale material development relies on samples prepared using alternative forming methods, such as moulding and compaction, which do not reliably reproduce the full-scale manufacturing process. The paper presents a representative method of manufacturing small scale extruded earth bricks. A suitable testing methodology is proposed, with varying curing conditions investigated. The small scale bricks are compared against equivalent large scale unfired earth bricks. The small scale bricks achieved a compressive strength of 3.39 MPa and with a corrected difference compared to the full scale bricks of 0.07 MPa; were found to be a reliable basis for laboratory scale investigation of material performance. The relationship that describes the effect of moisture content on strength exists for both small and large scale bricks.     

Short contact time catalytic partial oxidation of biogas – A comprehensive study on CO2 and N2 dilution

The short contact time catalytic partial oxidation of methane diluted with nitrogen and/or carbon dioxide to act as a surrogate for biogas conversion was carried out. Experiments were carried out under varying operating conditions to determine the possible use of the products in pyrolysis.Carbon dioxide has a larger effect on the product selectivities and back face temperature of the catalyst compared to nitrogen for equal dilutions. Carbon dioxide is consumed in the reactor whereas nitrogen is not. Since carbon dioxide likely takes part in endothermic reactions, the temperature of the catalyst is lower as is the conversion of methane and selectivity to carbon monoxide and hydrogen.The product stream is at an appropriate composition and temperature for subsequent use in a pyrolysis reactor. The presence of hydrogen and carbon monoxide will result in the removal of oxygen from bio-oils that are produced in the pyrolysis reactor.     

Fire risk perception and building evacuation by vulnerable persons: Points of view of laypersons,fire victims and experts

Fire risk perception and its influence on building evacuation were studied in order to improve building evacuation processes. The sample adopted in this study consisted of (i) laypersons, mostly elderly; (ii) healthcare professionals working with vulnerable individuals who live with disability on an everyday basis, for their point of view on disabled persons; (iii) fire victims for their experience (persons who suffered burns in a fire).Qualitative research was used to study fire risk perception and to understand the attitudes and behaviours of individuals. The information was collected during interviews following a questionnaire that combined questions of a general nature, questions referring to the fire and questions focused on the experience of evacuating a building.Results of this inductive, exploratory and qualitative method showed differences between the analysis of experts, the point of view of laypersons and the experience of fire victims. They also showed that risk perception is influenced by psychological, social, physical, political (here regulatory and normative) and cultural factors. Fire risk perception is based on the individual-environment-risk paradigm. Among the factors characterising risk perception, we noted the preponderant role of trust emerges, as well as that of the human environments (daily and emergency), the physical environment (building) and the climate of safety in which the event takes place. These different dimensions of fire risk perception show that it is a combination of psychometric and cultural paradigms. Building evacuation is seen as a psychological process involving both emotion and cognition.The resulting model aims to improve the understanding of a building evacuation process and to provide tools to anticipate crises.     

Experimental analysis of behavior and damage of sandwich composite materials in three-point bending. Part 2. Fatigue test results and damage mechanisms

The analysis of stiffness degradation and the identification of damage mechanisms during and after fatigue tests of sandwich panels with PVC foam cores have been performed. The sandwich panels with cross-ply laminates skins made of glass fiber and epoxy resin were manufactured by vacuum moulding and subjected to three-point bending tests. Two PVC cores of similar type but with differing densities were investigated. The effect of core density and thickness on the damage behavior was highlighted. Using the cyclic life criterion, fatigue curves were plotted according to two models and compared with those of the literature. It has been demonstrated that the sandwich SD 2, with the higher core density, withstands a higher load and possesses greater rigidity in static tests, combined with an enhanced fatigue resistance, when compared to sandwich SD 1 which has a lower core density. Translated from Problemy Prochnosti, No. 3, pp. 32–44, May–June, 2009.     

Elastic properties of porous oxide ceramics prepared using starch as a pore-forming agent

The elastic properties, in particular the tensile modulus (Young's modulus) and Poisson ratio, of porous alumina, zirconia, and alumina–zirconia composite ceramics are studied using the resonance frequency method and the results compared with theoretical predictions. Starch is used as a pore-forming agent, so that the resulting microstructure is essentially of the matrix-inclusion type (with large bulk pores, connected by small throats when a percolation threshold is exceeded). It is found that for this type of microstructure the porosity dependence of the Young's modulus is significantly below the upper Hashin–Shtrikman bound and the power-law prediction; it corresponds well, however, to a recently proposed exponential relation and to an empirical volume-weighted average of the upper and lower Hashin–Shtrikman bounds. Results for all three types of ceramics indicate that – in the porosity range considered, i.e. up to approximately 50% – the Poisson ratio depends only slightly on porosity.