Indirect measuring of crack growth by means of a key-curve-method in pre-cracked Charpy specimens made of nodular cast iron

The determination of dynamic crack resistance curves from single specimen fracture tests requires information about the crack advance during the experiment. Here, attention is focused on crack resistance curves for nodular cast iron based on experimental data from instrumented Charpy tests. In order to estimate the actual crack length a key curve method (KCM) is employed. On the other hand, the Charpy impact tests were realized numerically using finite element calculations in conjunction with a continuum damage model (CDM) to simulate ductile crack growth. The parameters of the CDM model were determined from the experimental data of single specimen fracture tests. Equivalence between the experimental and the numerical realization of a fracture test was ensured by validating the predictions of the numerical simulations by means of low blow fracture tests. Comparison between the crack advance predicted by the numerical simulations and the results obtained using the proposed KCM shows a sufficiently well agreement with the actual crack length. Furthermore, crack resistance curves obtained from single specimen tests using either standard estimation schemes in conjunction with the KCM or numerical simulations are compared with the predictions based on low blow fracture tests.     

横向撞击对竖直桩影响的动力分析

针对桩基础施工中使用机械清理桩头时经常遇到的撞击问题,把桩周土当作Winkler地基,运用弹塑性碰撞理论,由拉氏正变换和逆变换解析得到了桩顶受到横向冲击荷载时桩的瞬态横向动力响应;通过变换不同的桩土参数,对有限长桩和无限长桩的最大无量纲响应沿深度的变化曲线进行了分析比较.结合相应的工程实例,对竖直桩的配筋及所能承受的横向撞击速度的临界值(0.22 m/s)作了探讨,并提出了相应的施工改进措施,如控制撞击速度或调整桩身配筋等.     

合肥市"创景花园"环境影响评价思路

随着房地产业蓬勃发展,所带来的环境问题也日益显现,如项目选址不符合规划,对区域环境功能造成影响;设计布局不合理对生态和景观造成不良影响;施工管理不善产生弃土、扬尘,造成二次污染;施工噪声扰民等.因此,重视房地产开发建设项目环境管理,搞好环境影响评价工作,对促进房地产业健康发展,实现环境、经济同步增长具有积极的现实意义.本环境影响评价结合<环境影响评价技术导则>,通过对合肥"创景花园"住宅小区建设项目存在的主要环境问题分析,提出环境保护对策与建议.     

输电线路悬索式跨越架抗冲击性能影响规律研究

目前悬索式跨越架的设计未考虑动态冲击效应。为了探究悬索式跨越架在不同工程参数下抗导线冲击的影响规律,文中以悬索式跨越架承载索常用的超高分子量聚乙烯绳为例,建立了绳索受冲击的仿真模型。文中研究不同工程参数对跨越架在事故工况下(断线和跑线)的抗冲击性能影响规律,得到基于桁架单元的动力学仿真与试验的最小误差为0.67%。仿真结果表明:因牵引板的作用,断线对跨越架产生的冲击载荷大约为跑线的2～3倍;跨越架冲击载荷随落线高度而增加,但具有一定随机性,其弧垂变化水平在4～4.5 m;中间承载索和绝缘网安全系数较小;1 250 mm~2导线比630 mm~2导线的线密度、配套使用的牵引板大,故1 250 mm~2导线对跨越架的冲击较大。     

实时监控下堆石坝压实质量模糊综合评估

堆石坝填筑碾压质量采用事中和事后双控。事中碾压参数往往不能在全工作仓面上100%满足控制要求，且受坝料性质不均匀的影响，即便是相同的碾压参数，也可能会导致不同的压实质量。事后试坑检测采用有限个测点，难以客观反映整个施工仓面的压实质量；若单纯采用压实连续检测指标（如CV）控制，其与坝料压实质量之间也存在一定误差。文章利用大坝填筑碾压质量实时监控技术，在动态采集碾压参数和压实连续检测指标CV的基础上，采用Dempster-Shafer（D-S）证据理论，提出了一种综合考虑事中碾压参数、事后CV的压实质量模糊综合评价方法。此外，为了保证碾压区域无明显连续薄弱区，通过DBSCAN空间聚类分析，提出等效连续薄弱面积的概念，对压实质量薄弱区域空间分布进行定量评价。实例分析表明，此方法可以有效避免单独事中或事后评估的片面性，提高压实质量评估的全面性，为高堆石坝施工质量控制提供一种新的手段。     

综合能源系统级联失效及故障连锁反应分析方法

随着能源互联网及综合能源系统建设的不断深入，不同能源系统之间的关联耦合特性进一步加深。现阶段综合能源系统研究中对故障在综合能源系统内的传播影响分析不够深入，且未考虑不同能源子系统的故障连锁。针对此问题提出综合能源系统级联失效及故障连锁反应分析方法。首先，以综合能源系统为研究对象，从宏观层面分析了综合能源系统的故障连锁失效机理，同时分别对天然气系统、电力系统及热力系统的故障影响进行了细致分析；其次，分别从拓扑完整性和失效级联影响度2个维度提出了综合能源系统连锁故障影响评价指标，并梳理了连锁故障影响的分析流程；最后，通过构建综合能源系统的测试算例，验证所提方法的有效性与实用性。     

强夯法在工业厂房地基加固处理中的应用分析

结合桂林苏桥标准厂房工程案例,对强夯法在工业厂房地基加固处理中的应用进行探讨。结果表明,强夯法操作简单,地基加固效果比较好,可有效改善厂房地基的承载力及加固强度,满足施工要求。     

考虑光伏动态特性的功角电压交互失稳机理分析

在大容量直流和高比例新能源集中接入电网的背景下,研究了考虑光伏动态特性影响的直流大功率扰动引发功角电压交互失稳问题。首先,从理论上推导了两机等值系统发电机转子运动方程和电动机负荷运动方程;然后,分析了直流大功率扰动引发功角和电压交互作用导致系统失稳的物理机理;最后,进一步分析了光伏低电压穿越期间不同有功/无功特性对系统稳定性的影响规律,通过吉泉直流实际系统算例进行了仿真验证。研究结果表明,两侧发电机功角拉开和负荷母线电压跌落(电动机电阻减小)形成恶性循环最终导致系统失稳,不同的光伏低电压穿越有功/无功特性对系统稳定性的影响需要通过理论结合仿真综合分析。     

Analytical layer-element approach for wave propagation of transversely isotropic pavement

Asphalt pavements have been recognised as transversely isotropic multi-layered structures. In this paper, an analytical layer-element approach is utlised to solve the wave propagation of transversely isotropic multi-layered pavement structures under the falling weight deflectometer impact load. After the application of Fourier–Hankel transform, the Navier's equation for transversely isotropic layer by impulsive force are solved analytically. The global stiffness matrix equation of multilayered structures is further obtained by assembling the interrelated layer-elements, and the actual solution is achieved by numerical inversion of the Fourier–Hankel transform after the solution in the transformed domain is obtained. The layer-element of a single layer and the global stiffness matrix only contain negative exponential functions, which leads to a considerable improvement in computation ef?ciency and stability. Numerical examples are presented to demonstrate the accuracy of this method and to inversitgate the influence of the properties of transversely isotropic elastic materials on the load-displacement responses.     

Low velocity impact analysis of sandwich plates with functionally graded face sheets

This article deals with the study of low velocity impact response on sandwich plates with functionally graded face sheets. High-order sandwich plate theory is improved by considering the in-plane stresses of the core that usually are ignored in the analysis of sandwich structures. A new approach is used to reduce the equations of motion from 27 equations to 15 equations and then solving them for both unsymmetric and symmetric sandwich plates. The model is also checked by finite element simulation and by comparing with other references for validation. A parametric study is done for various geometrical and mechanical properties.