Femtosecond Ti: Sa ultra short-pulse laser irradiation effects on the properties and morphology of the zirconia surface after ageing

Femtosecond pulses from a Ti:Sapphire laser were used to irradiate specimens of yttria-stabilised (35% mol) tetragonal zirconia (Y-TZP) with the purpose of studying the effects of the irradiations on their surface properties and morphology after ageing. Zirconia disks were divided into eight groups (n = 32) according to their surface treatment and subsequent ageing: Control: no treatment; sandblasting: Al₂O₃ sandblasting 50 μm; and ultrashort laser pulses irradiation with 25 μJ pulses, considering two different scanning steps based on the width between two grooves. These groups were duplicated and submitted to ageing. The surfaces were analysed using scanning electron microscopy (SEM), and X-ray diffraction. A finite element analysis, a biaxial flexure test, as well as fractographic and Weibull analyses, were performed. The strengths of the disks were statistically different for the treatment factor, and the principal stresses seemed to be concentrated at the centre of the specimens, as predicted by the computer simulations. Ageing decreased the strengths for all groups and increased the Weibull modulus for the laser group with the 40 μm-width between two grooves. The sandblasting group presented the highest monoclinic phase peak. Although the most significant strength was found within the sandblasting group, the phase transformation was favourable to the laser groups. The Weibull modulus was higher for the laser group with the 60 μm-width between two grooves, confirming the highest homogeneity of its failure distribution. Regardless of the surface treatment, strength was decreased with ageing in all groups. The femtosecond Ti:Sa ultra-short pulse laser irradiation can be suggested as an alternative to the gold standard sandblasting in long-term Y-TZP zirconia rehabilitations, such as crowns and veneers.     

压电精密驱动柔性微夹钳设计

为了实现对微纳尺度下物件的精密夹持,建立了柔性微夹钳系统。并对该系统柔性夹钳设计、运动学、动力学和控制方法等进行研究。首先,利用柔性铰链设计方法设计了柔性微夹钳,利用伪刚体法建立了机械的伪刚体模型。接着,以伪刚体模型法建立了系统的运动学模型,即机械放大比和输入刚度等数学模型。然后,利用拉格朗日方法建立了系统的动力学方程,得出系统的自然振动频率。最后,通过ANSYS有限元方法对系统建立的模型进行了仿真分析和验证,此外,利用PID控制算法对微夹钳系统进行实验控制。实验结果表明:跟踪控制结果误差为2.4%;放大比为9.12倍。基本满足微纳尺度下的微夹持工作,其工作精度可达微米级别甚至纳米级别,符合设计要求。     

中美钢筋混凝土梁正截面承载力计算比较

从荷载组合和正截面受弯承载力计算两方面对钢筋混凝土梁正截面承载力计算的中国规范和美国规范进行了比较,并给出了比较结果,对了解我国的规范水平具有参考价值。     

开口截面钢-混凝土组合梁受扭的试验分析

为研究钢-混凝土组合梁在不同加载方式下的受扭性能,完成了6根钢-混凝土组合梁的弯扭试验和纯扭试验,其中2根梁的扭矩直接作用于工字钢梁上,其余4根梁则由钢梁和混凝土翼缘板作为整体共同受扭。试验结果表明,当扭矩直接作用于钢梁上时,混凝土翼缘板通过栓钉对钢梁的扭转提供约束,从而使钢梁的抗扭承载力比纯钢梁的提高2倍以上。在试验参数相同时,混凝土翼缘板和钢梁作为整体复合受扭时组合梁的开裂扭矩及极限抗扭承载力比扭矩直接作用于钢梁时的分别提高86%和39%。分析了两种不同加载方式下钢-混凝土组合梁受扭和受弯承载力的变化。建立了扭矩直接作用于钢梁上时极限扭矩的计算模型及计算公式。对整体受扭时组合梁的弯矩相关性进行了分析,并建立了相关曲线公式。计算结果与实测值吻合较好。     

钢筋混凝土梁剩余抗弯强度的灰色预测

运用灰色系统理论，对钢筋混凝土梁的不完全的高温静荷载试验曲线Ｔ－ＳＭ进行预预，并获得了高温后钢筋混凝土梁剩余抗弯强度，为估算高温后钢筋混凝土梁的剩余抗变强度提供了一种新的方法。     

关于FWD在路面弯沉检测中发展的探讨

介绍了路面弯沉检测的重要性，筒述了路面弯沉检测的发展，详细阐述了FWD的系统构成、工作原理以及FWD的测试过程，以更好地进行路面弯沉检测。     

开口截面钢-混凝土组合梁弯扭性能的理论分析与试验研究

对 3根不同扭弯比的开口截面组合梁弯扭进行试验分析得出组合梁的弯型和扭型两种破坏形态。将组合梁划分成三维 8结点实体单元 ,用有限元方法对组合梁在弯扭作用下的工作性能进行了弹性理论分析 ,建立了弯扭强度M -T相关公式。通过编制组合梁截面的弯矩 -曲率全过程计算程序 ,得出了混凝土翼板受力与截面弯矩之间的关系 ,从而阐明了弯扭共同作用下组合梁的受力机理 ,建立了极限状态的弯扭强度M -T相关公式 ,并分析了组合梁截面参数对相关曲线的影响。     

Displacement and curvature estimation for the design of reinforced concrete slender walls

Previous earthquakes, such as the 2010 Maule earthquake in Chile, have demonstrated the need to establish suitable predictors of compressive or tensile strains in concrete or steel in reinforced concrete shear walls, which can provide limit states or confinement requirements. Slender walls are commonly controlled by flexural deformations that can be divided into elastic and inelastic components. This study provides calibrated expressions for the elastic and inelastic components of flexural deformations using a fiber model for slender walls. These expressions are obtained for rectangular and T‐shaped walls. The elastic component is dependent on the axial load and the boundary steel reinforcement ratio. The impact of wall coupling is investigated, which requires a correction for the elastic component. The investigation of the inelastic component is based on a plastic hinge model, in which the length of the plastic hinge is a function of the lateral inelastic drift of the wall among other parameters. The traditional linear inelastic curvature distribution over the wall height is also modified for cases with steel reinforcement with a long yield plateau or low strain hardening, which results in a larger curvature at the wall base. The distribution is validated with experimental data from the literature. Copyright © 2016 John Wiley & Sons, Ltd.     

Modal testing as a means of quantitative monitoring of damage progression in a model FRP rehabilitated bridge deck system

Although substantial research has been conducted on the application of externally bonded fibre reinforced polymer (FRP) materials as a means of strengthening deficient and deteriorating concrete components most studies, and even field monitoring, have been at the component level. There is lack of data regarding the systems level response of strengthening. This paper reports on the results of an investigation of the effect of progressive strengthening of a slab-girder system through initial flexural strengthening of the decks followed by shear strengthening of the central girder. The progression of damage after each phase of loading was assessed through a process of forced vibration based modal testing. The paper focuses on modal testing and model updating procedures as a means of structural health monitoring and indicates that the process can be used effectively to accurately show changes in both local and global response through the different stages of loading. The procedures not only provide an assessment of damage progression and load redistribution in the rehabilitated components, but also enable an accurate representation of response at the systems and local (through support locations) levels.     

圆弧柔性铰链的优化设计

柔性铰链是高精度柔性机构的关键部件,其运动精度与运动范围影响着柔性机构的性能,本文对圆弧柔性铰链进行了柔度矩阵推导,并依据柔度方程进行优化设计。采用结构矩阵法建立了圆弧柔性铰链的柔度方程,对矩形截面的翘曲抗扭刚度进行推导,得到了约束扭转状态下的扭转柔度近似方程。为相对长度较小铰链的扭转刚度精确求解提供了依据。对比理论计算结果与有限元分析结果,结果显示扭转柔度的最大相对误差在10%左右,其余方向柔度相对误差低于6%,验证了柔度方程的准确性。采用正交试验直观分析法得到柔性铰链各设计参数对转动刚度的灵敏度,并利用多目标遗传算法对柔性铰链的转动柔度以及轴向刚度两个目标进行了参数优化。通过优化结果与设计经验选取参数的对比,发现优化后圆弧柔性铰链的弯曲柔度提升了5.12%,同时铰链的轴向刚度提升了4.72%,证明针对圆弧柔性铰链的优化设计具有明显效果。