高拱坝施工期温控参数敏感性分析

在混凝土高拱坝浇筑过程中,影响坝体施工期温度场及温度应力的因素有很多,因此选用适当的浇筑方案对于节约工程成本及提高坝体安全性有着重要意义。以孟底沟水电站工程为例,选用多种施工方案,并利用三维有限元方法进行仿真分析,分析了浇筑季节、浇筑层厚、间歇时间及浇筑温度等因素对坝体施工期的敏感性。结果表明,低温季节浇筑、在防止热量倒灌的前提下尽量减小浇筑层厚度、缩短间歇时间、降低浇筑温度有助于降低温度应力,提高坝体安全性。     

长江经济带环境污染治理投资对生态效率的影响研究

环境污染治理投资是生态环境保护的资金来源，其投资规模和投资形式对生态效率产生着重大影响。本文构建生态效率测度指标和非期望的超效率SBM模型，测定了长江经济带9省2市的生态效率水平，再利用Tobit模型量化研究环境污染治理投资的总量及各投资形式对生态效率的影响程度，得出长江经济带环境污染治理投资对生态效率具有正向影响但影响程度一般，3种环境污染治理投资类型中的当年完成环保验收项目环保投资对生态效率影响程度最大且显著。     

Quantitative method for estimating stain density in electron microscopy of conventionally prepared biological specimens

Stain density is an important parameter for optimising the quality of ultrastructural data obtained from several types of 3D electron microscopy techniques, including serial block-face electron microscopy (SBEM), and focused ion beam scanning electron microscopy (FIB-SEM). Here, we show how some straightforward measurements in the TEM can be used to determine the stain density based on a simple expression that we derive. Numbers of stain atoms per unit volume are determined from the measured ratio of the bright-field intensities from regions of the specimen that contain both pure embedding material and the embedded biological structures of interest. The determination only requires knowledge of the section thickness, which can either be estimated from the microtome setting, or from low-dose electron tomography, and the elastic scattering cross section for the heavy atoms used to stain the specimen. The method is tested on specimens of embedded blood platelets, brain tissue and liver tissue.     

膨胀剂对约束条件下UHPC早期抗裂性能影响的试验研究

超高性能混凝土(UHPC)在钢桥面铺装结构中由于铺装材料受到钢板、栓钉等的约束,加上材料本身水胶比小,更易收缩,早期容易承受拉应力导致开裂。通过在拌和过程中添加膨胀剂可以起到减小收缩的作用,但该方法对于约束条件下的UHPC铺装的早期抗裂性能提升是否有促进作用,仍需通过更多试验进行合理评估和深入研究。通过圆环法对3组不同配方的UHPC在均匀约束条件下的早期抗裂性能进行定量测试,并将试验数据进行回归分析和计算,得到了各组的平均应力发展速率,进而评估了各组的开裂风险等级。试验结果表明,通过在UHPC中加入适量膨胀剂,可使其最终收缩应力减小,并可降低其收缩应力发展速率,进一步降低其在约束条件下的开裂风险。     

Modeling of the electromechanical coupling between crack propagation and piezoelectric behavior in active layers of smart devices

In this article, a new computational approach is investigated to predict the crack propagation inside some smart structures equipped with surface-bonded piezoelectric layers; meanwhile, the electromechanical coupling is exploited. The current industrial need of analyzing rather irregular geometries motivates resorting to a numerical approach. Therefore, the finite element method (FEM) is used to predict both the fracture behavior and the coupled response of piezoelectric material through a suitable interoperation of the two computational environments, available in some commercial code like the ABAQUS^©. The two solutions are then coupled by means of a subroutine, in this case operated through the ISIGHT^© tool. After a preliminary analysis and a validation, results of some numerical simulations are shown to highlight some significant peculiarities of the coupled behavior of the piezoelectric material.     

水平裂缝对坚硬顶板失稳破断的影响规律研究

为了研究水力压裂形成水平裂缝后坚硬顶板的失稳破断规律,基于材料力学和关键层相关理论,结合数值模拟,对含水平裂缝坚硬顶板的变形破坏特征和失稳破断机制进行了研究。结果表明:当坚硬顶板存在水平贯穿裂缝时,无论上位与下位岩层是否发生同步运动,坚硬顶板的破断步距均小于其初始极限跨距。存在水平贯穿裂缝的坚硬顶板及其上覆岩层,会形成拉压复合破坏区,更易于发生失稳破坏。坚硬顶板块体咬合点区域的拉压复合破坏作用是造成块体局部失稳、回转加剧和整体破断的主要原因。     

热处理工艺对TC4钛合金冲击磨损性能的影响

研究了退火和固溶时效处理对热轧态TC4钛合金的力学性能和组织的影响,并考察了其冲击磨损性能。结果表明:退火处理后试样组织中转变β相增加,强度、塑性和韧性均较热轧态有所提升;而固溶时效处理后试样组织的晶粒细化且尺寸更为均匀,同时具有最高的强度,而塑性和韧性则较热轧态有所降低。经过10 h的冲击磨损试验后,退火态试样的磨损率最低,而固溶时效态试样的磨损率最高。通过磨损断口观察发现退火态试样表面冲刷犁沟较短,且终点处存在合金的塑性堆积,同时磨损面组织发生塑性变形,晶粒延展拉长。退火态试样较高的塑性和韧性有助于吸收冲击能量,因此表现出较好的耐冲击磨损性能。     

Warpage control method during surface forming process of plastic film-reinforced flexible decorative veneer

The plastic film of the new plastic film reinforced pliable decorative veneer (PRPDSV) is used as a flexible reinforcement material and an adhesive material. It has good water resistance, impermeability, simple preparation and finishing processes, and no formaldehyde release. However, warpage phenomenon during hot pressing has been a bottleneck problem restricting its industrial development. In order to solve this problem solve, the study proposed a concave, and convex molds method, established an elastic–plastic FEA model of hot pressing processes of the PRPDSV using concave and convex molds with static/general static solution module in the nonlinear ABAQUS, and researched the effect on the performances of the PRPDSV from the parameters of temperature, pressure, and mold curvature radius theoretically and verified experimentally. Analysis results showed that the surface forming temperature had a great effect on warpage control for PRPDSV. The higher the temperature is, the smaller the curvature radius of the corresponding mold will be and the better the warpage will be. The curvature radius of the molds had a significant effect on the warpage control. Under the conditions with the same hot pressing parameters, the smaller the curvature radius is, and the better control on the warpage for the PRPDSV will be.