张拉体系的几何构造分析

本文对张拉结构的力学特点进行了较为全面的介绍和相关内容的比较。张拉结构的平衡矩阵内容丰富 ,含括了特定结构的节点和杆件数目、结构拓扑条件以及其Euclidean几何定义等关于结构分析的诸多内容。通过对这一矩阵的分析 ,可以对张拉结构的几何构造以及预应力 (分布 )对张拉结构的几何稳定性 (刚度 )的影响两方面的问题有深入的认识     

钢筋混凝土锈蚀参数试验研究

基于大尺寸柱式试件的电化学试验结果,得出了平均锈蚀深度与最大裂缝宽度、平均锈蚀深度与最大坑锈深度的统计关系;探讨了在快速锈蚀条件下,按法拉第定律的电化学锈蚀控制方程来估算钢筋锈蚀深度的合理性。根据柱式拉伸试件的试验结果和有限元仿真分析,研究了轴向不均匀锈蚀对结构的影响。     

An experimental study on creep of welded tuff

This paper presents results of five creep tests conducted in uniaxial compression at room temperature. The test specimens were from the welded Topopah Spring tuff formation at Yucca Mountain, Nevada. The specimens exhibited brittle failure. Multiple stress levels were applied in steps to each specimen. Each stress level was maintained for 3 days or longer. The transient creep for all the stress levels can be well described by power functions. The transient creep is caused by an elastic aftereffect. The tuff does not show real steady-state creep. The so-called steady-state creep rate decreases with time. In general it is very low, typically in the range of 10⁻⁷ h⁻¹. For the first 50 h, the so-called steady-state creep rate may be described as a power function of stress. The specimen failed shortly after it entered into the accelerating creep phase.     

Failure envelope considering the ultimate tensile capacity of suction caissons in sand

Little analytical work has been done to elucidate the ultimate capacity of suction caissons under vertical tensile (V), lateral (H), and moment (M) loads in soils. In this paper, in order to reveal the effect of vertical tensile, lateral, and moment loads on the ultimate capacity of suction caissons in sand, an analytical investigation was made using a traditional bearing capacity theory. Taking account of the vertical equilibrium of an annular element of a skirt, through the vertical tractions inside and outside the skirt of a suction caisson when a vertical tensile load is applied, the vertical displacement of the soils adjacent to the skirt of the suction caisson was presented. The most appropriate bearing capacity equation for predicting the experimental results was shown for suction caissons having an embedment larger than a diameter in sand. For the deformation-load responses of suction caissons with various embedment ratios in sand, subjected to inclined tensile loads, there was a good agreement between the results obtained from laboratory tests and those predicted by the present method. The failure surfaces, considering the ultimate tensile capacity in the H-M, H-V, and M−V planes, and in the H-M−V space, for suction caissons in sand, were presented.     

Ti-xCr-yCu钛基材料的制备及组织性能研究

研究了Al-Cu-Li-(0.35Mg)-(0.2In)合金的拉伸性能、时效析出相类型及其分布。T6峰时效时,Al-Cu-Li合金的时效析出相为T1(Al2CuLi)和?? (Al2Cu)相。添加0.2%In时,T6态时效早期形成许多方块状的立方相Al5Cu6Li2,且随时间延长其尺寸保持稳定;同时,可促进? ?相析出;相应合金的时效响应加速,强度提高。同时添加In和Mg可抑制Al5Cu6Li2相析出,但促进T1相析出。In和Mg的复合微合金化效果小于2050铝锂合金中Ag和Mg的复合微合金化效果,因而In+Mg复合微合金化铝锂合金T6态强度低于Ag+Mg复合微合金化的2050铝锂合金。T8态时效时,时效前预变形产生的位错抑制了In元素单独添加和In+Mg复合添加的微合金化效果。     

科卡金矿边坡岩石力学试验

通过岩石单轴压缩试验,获得岩石的基本力学性质指标,分析岩石的破坏形式,利用声发射装置探讨岩石试件在压缩过程中内部能量的变化及破坏过程。结果显示,边坡岩石属于硬质岩,在外荷载达到抗压强度时,瞬间发生破坏,破坏后岩石呈碎块状,表明该岩石破坏类型为脆性破坏。     

高温碳化张力对碳纤维性能影响

在碳纤维生产过程中张力贯穿于整个工艺过程,张力控制的划分可分为两个部分,一是预氧化张力控制;二是碳化张力控制。借助在线张力仪详细研究了特定工艺条件下的高温碳化张力对6K碳纤维拉伸强度、弹性模量和密度的影响。     

Mechanical and electrochemical behavior of novel electrolytes based on partially stabilized zirconia for solid oxide fuel cells

In this study, 3 mol% yttria stabilized zirconia (3YSZ) is investigated as a SOFC electrolyte alternative to 8 mol% yttria stabilized zirconia (8YSZ). The mechanical and electrochemical properties of both materials are compared. The mechanical tests indicate that the thickness of 3YSZ can be reduced to half without sacrificing the strength compared to 8YSZ. By reducing the thickness of 3YSZ from 150 µm to 75 µm, the peak power density is shown to increase by around 80%. The performance is further enhanced by around 22% by designing of novel electrode structure with regular cut-off patterns previously optimized. However, the cell with novel designed 3YSZ electrolyte exhibits 30% lower maximum power density than that of the cell with 150 µm-thick standard 8YSZ electrolyte. Nevertheless, the loss in the performance may be tolerated by decreasing the fabrication cost revealing that 3YSZ electrolyte with cut-off patterns can be employed as SOFC electrolyte alternative to 8YSZ.     

Effect of hybrid polymer coating of Bioglass® foams on mechanical response during tensile loading

A simplified two-dimensional finite elements model was created for a polyvinyl alcohol (PVA) coated Bioglass^® strut undergoing tensile stresses (loading mode I). The strengthening contributions due to the infiltration of coating into surface cracks and coating's stiffness were evaluated in terms of stress intensity factor K_I and tensile stresses σ_yy in the proximity of the crack tip. The infiltration of the coating until the crack tip resulted as the most effective criterion for the struts strengthening. Bioglass^® based scaffolds were dip coated into PVA and PVA/microfibrillated cellulose (MFC) aqueous solutions and tested in tensile load. Coated samples exhibited remarkably higher tensile strength than non-coated ones, which further raised with the increased amount of MFC. Contact angle θ and linear viscosity η measurements of PVA/MFC solutions showed that MFC caused a reduction in θ and a drastic increase in η, indicating that a balance between these two effects must be achieved.     

Effect of microstructure and overaging on the tensile behavior at room and elevated temperature of C355-T6 cast aluminum alloy

The present study was focused on the microstructural and mechanical characterization of the Al–Si–Cu–Mg C355 alloy, at room and elevated temperature. In order to evaluate the influence of microstructural coarseness on mechanical behavior, samples with different Secondary Dendrite Arm Spacing (SDAS) (20–25 μm for fine microstructure and 50–70 μm for coarse microstructure), were produced through controlled casting conditions. The tensile behavior of the alloy was evaluated at T6 condition and at T6 with subsequent high temperature exposure (41 h at 210 °C, i.e. overaging), both at room and elevated temperature (200 °C). Microstructural investigations were performed through optical and electron microscopy.The results confirmed the important role of microstructure on the tensile behavior of C355 alloy. Ultimate tensile strength and elongation to failure strongly increased with the decrease of SDAS. Larger SDAS, related to lower solidification rates, modify microstructural features, such as eutectic Si morphology and size of the intermetallic phases, which in turn influence elongation to failure. Overaging before tensile testing induced coarsening of the strengthening precipitates, as observed by STEM analyses, with consequent reduction of the tensile strength of the alloy, regardless of SDAS. A more sensible decrease of tensile properties was registered at 200 °C testing temperature.