清水隧道围岩检测研究

目前铁路运营隧道不良状况严重,因此有必要采取可靠的检测方法来检测和评估隧道的实际状况,同时检测的数据也为隧道日常的维修保养及必要的整治工程提供了系统完整的依据.本文以清水隧道现场检测作为实例,通过对土压力、孔隙水压力、衬砌应变及围岩深部位移的检测分析了清水隧道存在的问题,并在出了若干工程建议.     

微生物及酶对己内酰胺的降解动力学研究

采用微生物菌株和从该菌株提取的粗酶液对己内酰胺进行降解，并对己内酰胺的降解动力学进行了研究．结果表明，初始己内酰胺的浓度越小，降解速率常数越大，半寿期越短，微生物的降解能力越强；由微生物提取的粗酶液（胞外酶）的Km值较小，对己内酰胺有较强的亲和力，可有效地降解己内酰胺。     

梁板壳有限单元中的各种闭锁现象及解决方法

对梁元和板壳单元中存在的各种闭锁现象进行详细的分析，对现有的一些解决方法的优劣性进行比较，以使人们对闭锁现象有更深入的认识，并能有效地消除或减轻它们的不利影响.分别在二维、三维梁元与板壳单元有限元公式中引入Hellinger-Reissner混合函数或降阶积分，以减轻或消除闭锁现象对单元计算精度的不利影响.通过4个算例来阐明闭锁现象随单元受力情况、单元厚度、单元网格划分的不同而对结构非线性分析结果所带来的不同程度的影响. 结果表明，闭锁现象对结构的数值分析结果影响显著，对以受弯为主而膜应力很小甚至为零的单元，膜闭锁现象非常严重，而对薄壁单元，剪切闭锁的影响特别严重；采用单元的混合公式或在协调元中采用降阶积分，可有效地消除单元的各种闭锁现象和插值函数的误差对单元计算精度带来的不利影响，能使单元计算精度和计算效率得到显著改善.     

角焊缝角变形的产生机制与固有剪切应变分量的双抛物面分布模型

以T形焊接接头为算例,结合热弹塑性有限元法和映射应变分量法,研究了角焊缝角变形的产生机制。结果发现:角焊缝产生角变形的主要根源是固有剪切应变,而不是传统思维认为的横向固有正应变,且角变形的大小与固有剪切应变的分布形式密切相关。基于一系列T形焊接接头的数值试验,提出了角焊缝固有剪切应变分量的双抛物面分布模型。     

A large deformation solid‐shell concept based on reduced integration with hourglass stabilization

In this paper a new eight‐node (brick) solid‐shell finite element formulation based on the concept of reduced integration with hourglass stabilization is presented. The work focuses on static problems. The starting point of the derivation is the three‐field variational functional upon which meanwhile established 3D enhanced strain concepts are based. Important additional assumptions are made to transfer the approach into a powerful solid‐shell. First of all, a Taylor expansion of the first Piola–Kirchhoff stress tensor with respect to the normal through the centre of the element is carried out. In this way the stress becomes a linear function of the shell surface co‐ordinates whereas the dependence on the thickness co‐ordinate remains non‐linear. Secondly, the Jacobian matrix is replaced by its value in the centre of the element. These two assumptions lead to a computationally efficient shell element which requires only two Gauss points in the thickness direction (and one Gauss point in the plane of the shell element). Additionally three internal element degrees‐of‐freedom have to be determined to avoid thickness locking. One important advantage of the element is the fact that a fully three‐dimensional stress state can be modelled without any modification of the constitutive law. The formulation has only displacement degrees‐of‐freedom and the geometry in the thickness direction is correctly displayed. Copyright © 2006 John Wiley & Sons, Ltd.     

Development of stress-modified fracture strain for ductile failure of API X65 steel

The present paper proposes ductile failure criteria in terms of true fracture strain (the equivalent strain to fracture) as a function of the stress triaxiality (defined by the ratio of the hydrostatic stress to the equivalent stress) for the API X65 steel. To determine the stress-modified fracture strain, smooth and notched tensile bars with four different notch radii are tested, from which true fracture strains are determined as a function of the notch radius. Then detailed elastic–plastic, large strain finite element analyses are performed to estimate variations of stress triaxiality in the tensile bars, which leads to true fracture strains as a function of the stress triaxiality, by combining them with experimental results. Two different failure criteria are proposed, one based on local stress and strain information at the site where failure initiation is likely to take place, and the other based on averaged stress and strain information over the ligament where ductile fracture is expected. As a case study, ligament failures of API X65 pipes with a gouge are predicted and compared with experimental data.     

复合荷载作用下完全叠接管节点热点应力的实验研究

通过实验研究了完全叠接管节点试件在复合荷载作用下的热点应力。首先研究了完全叠接管节点试件在轴力、平面内弯矩和平面外弯矩分别作用下的应变集中因子,结果表明在轴力和平面外弯矩作用下,该管节点试件的最大应变集中因子产生在靠近L支管的T支管的鞍部,而在平面内弯矩作用下,该管节点试件的最大应变集中因子则产生在L支管的冠跟部。随后,研究了完全叠接管节点试件在复合荷载作用下的热点应力,结果表明在复合荷载作用下最大热点应力可能出现在介于鞍部和冠部之间的任一位置。通过Gulati等和API所提出的复合荷载作用下的叠加方程与实验结果比较,发现Gulati等所提出的方程与实验结果吻合得很好,而API所提出的方程则偏于保守。     

Correlation of material constraint with fracture toughness of interface regions in a dissimilar metal welded joint

In this work, the constraint parameter A_p based on crack‐tip equivalent plastic strain was calculated by finite element analyses for the cracks located at different locations in two interface regions in a dissimilar metal weld joint (DMWJ). The capabilities of the parameter A_p for characterizing material constraint and establishing correlation of material constraint with fracture toughness of the interface region cracks have been examined. The results show that the parameter A_p can characterize material constraint effect caused by material mismatch and initial crack positions in the interface regions. Based on the A_p, the correlation lines and formulae of material constraint with fracture toughness of the interface region cracks in the DMWJ can be established, and they may be used for obtaining material constraint‐dependent fracture toughness for the interface region cracks. The results in this work combining with those in the previous studies indicate that the parameter A_p may be a unified constraint parameter that can characterize both geometry constraint (including in‐plane and out‐of‐plane constraints) and material constraint, and it may be used in accurate fracture assessments of welded components with different geometry and material constraints.     

塑性弯曲变形对金属组织性能影响的研究

本文在分析强烈塑性变形(severe plastic deformation)对金属材料组织性能影响的基础上,进一步研究金属材料经过反复塑性弯曲变形后,其内部组织性能的变化规律.以H85黄铜板材为对象,采用MARC有限元等方法计算不同弯曲半径与板厚之比(r/h,简称:径厚比)对金属材料内部累积应变的影响,同时通过金相组织分析和显微硬度测定,进一步确定其内部晶粒尺寸的变化规律.研究表明,金属板材经过反复塑性弯曲变形后,其内部累积应变量大小沿厚度分布随离中性层距离增加而增大、晶粒尺寸则随之变小、金属的显微硬度随之增加.而且随着径厚比(r/h)减小,其累积应变量效应越显著.