Optimum strain gage location for evaluating stress intensity factors in single and double ended cracked configurations

A general methodology has been proposed for calculation of optimum radial strain gage locations for measurement of the stress intensity factors using strain gage technique. The upper bound (r_max) of strain gage locations for complex single ended and double ended cracked configurations has been determined using the proposed method. Further, dependency of the r_max on the crack length to width ratio and on the state of stress is investigated. Numerical results obtained from the present investigation are observed to be in accordance with the theoretical predictions. Using the proposed approach the correctness of strain gage locations used by the earlier researchers is also verified.     

Room temperature nanoindentation creep of nanoscale Ag/Fe multilayers

This paper deals with room temperature indentation creep behavior of nanoscale Ag/Fe multilayers. The constant-load nanoindentation test results reveal that all the multilayers exhibit steady-state creep after transient creep occurring at first 150 s and decreasing periodicity leads to a decrease in the stress exponent and an increase in creep rate. The dependence of the stress exponent and creep rate on the periodicity indicates that the creep process is dominated by dislocation glide-climb mechanism and the increasing fraction of grain boundaries and interfaces provide effective diffusion paths for the creep climb that determines the whole creep rate.     

结构面对波形相关系数的影响

采用基于连续介质的块体离散元程序(CDEM)模拟结构面处应力波传播过程,用相关系数来描述应力波在结构面处发生的波形变化,研究了单结构面对波形变化的影响范围。研究表明:相关系数和透射系数在结构面处的变化规律是一致的,可以有效反映波形在结构面处的变化,单结构面对4倍波长范围内的测点波形有明显影响。     

粗短钢纤维混凝土动力性能研究

钢纤维混凝土(SFRC)的静力性能已被广泛研究,但有关动力性能方面的文献仍较少。SFRC的动力性能受钢纤维的特性(几何形状与强度)、钢纤维的掺量、分布以及基体混凝土性能的影响。为方便研究,借助于一个简化的细长杆模型,导出了粗短钢纤维变形运动时的基本微分方程。重点研究了动载作用下,大体积粗短钢纤维混凝土结构内部的应力分布。     

岩溶地质对隧道施工稳定性的影响评价

根据依托工程的工程地质特点,利用三维有限元数值模拟方法,选取典型断面,通过分析有溶洞与无溶洞两种工况下隧道开挖引起的隧道围岩的位移、应力等指标的变化,来评价溶洞对隧道稳定性的影响,指出岩溶离隧道顶部较近时,隧道开挖可能使顶板断裂而出现垮塌,从而造成突水突泥等地质灾害。     

工作面推进过程中支承压力的发展规律研究

W1303工作面是山西高河能源有限公司的首采工作面,通过对W1303工作面超前支护范围内的单体支柱压力进行监测,运用矿山压力与岩层控制理论进行分析,得出工作面推进过程中支承压力的发展规律。     

Stress distributions in a horizontal pressure vessel and the saddle supports

This paper presents analysis results of stress distributions in a horizontal pressure vessel and the saddle supports. The results are obtained from a 3D finite element analysis. A quarter of the pressure vessel is modeled with realistic details of saddle supports. In addition to presenting the stress distribution in the pressure vessel, the results provide details of stress distribution in different parts of the saddle separately, i.e. wear, web, flange and base plates. The effect of changing the load and various geometric parameters is investigated and recommendations are made for the optimal values of ratio of the distance of support from the end of the vessel to the length of the vessel and ratio of the length of the vessel to the radius of the vessel for minimum stresses both in the pressure vessel and the saddle structure. Physical reasons for favoring of a particular value of ratio of the distance of support from the end of the vessel to the length of the vessel are also outlined.     

低渗透气藏水平井气水两相产能研究

低渗透含水气藏开发过程中,水平井底见水不仅增加了地层流体渗流的复杂性,而且降低了水平井产量。以气水两相渗流理论为基础,建立了气水两相运动方程,定义气水两相启动压力梯度以及气水两相广义拟压力,考虑应力敏感、滑脱效应、紊流效应和表皮效应对气水同产水平井产能的影响,利用保角变换方法推导出低渗透气藏中水平井气水两相三项式产能新公式。通过实例计算,利用新公式计算的无阻流量结果与实际产能测试结果相对误差较小,仅为5.13%,说明新公式精确可靠,且敏感性分析表明,水平气井产水量随着滑脱因子以及水气质量比的增大而增大,而随着启动压力梯度以及应力敏感指数的增大而减小,但启动压力梯度对产水量影响较小,若生产压差较大,启动压力梯度可以忽略不计。     

An Integrated Fracture Mechanics Based Approach for Non-Linear Analysis of Lightly Reinforced Concrete Beams

A non-linear fracture mechanics based approach is proposed to depict a typical fracture mechanism from initiation to growth, eventually leading to failure. This concept is developed for a lightly reinforced beam in flexure. The proposed model integrates the existing methodology of a Stress Intensity Factor equilibrium equation with the bridging forces developed in concrete cover and rebar. The model and solution algorithm outlined presents an elaborate understanding of the mechanism involved and is significant in predicting the behaviour of flexural members. The analysis is performed using MATLAB programming. The proposed approach ensures a maximum tolerable crack length and crack width for flexural members to prevent a catastrophic failure. Such an approach has the potential to serve as an analysis and design tool for reinforced concrete components subjected to normal conditions and towards deciding rehabilitation and strengthening measures.     

3Cr13Mo钢板多参数YAG激光焊接残余应力和形变的仿真研究

通过500 W YAG激光机以焊接速度0.5~1.2 mm/s、电流150~200 A,脉冲宽度3.0~5.0 ms和频率18~40 Hz参数对5 mm 3Cr13Mo马氏体耐热不锈钢板(/%:0.28C,0.8Si,0.36Mn,0.030S,0.029P,12.10Cr,0.57Mo,0.45Ni)进行焊接试验,同时应用大型有限元软件ABAQUS开发建立焊接模型,对焊接过程中温度场、残余应力场和形变进行了数值模拟。研究结果表明,模拟值与实际测试值基本吻合,计算的焊接残余应力最大值集中在距焊缝0.1 mm的热影响环向区,在焊接电流150 A,脉冲宽度3.0 ms,频率18 Hz,焊接速度0.5 mm/s的工艺参数下,最大残余应力所引起的残余塑性应变量可达0.325。