C2S2法中剪切应变的理论分析及其数值模拟

C2S2(板材连续剪切变形技术)是一种针对于细化薄板材料晶粒尺寸的全新的材料加工技术,通过这种技术可以使板的晶粒度降低至亚微米级或者纳米级.介绍了板材连续剪切变形技术的基本原理,对其所产生的剪切应变进行了计算和理论分析,并采用了有限元软件MAFAP4.0对其成形过程进行了模拟,模拟结果表明:挤出角Φ、外弧角Ψ等因素对材料的变形量有不同程度的影响.     

预应力砼空心板端部开裂研究及处理

作者介绍了预应力砼空心板张拉后,在两端部底面出现长度不等的细微裂缝的原因及分析,提出了两种理论计算模型并进行了比较.     

低周疲劳损伤对老化船舶结构剩余极限强度的影响

为了分析低周疲劳累积损伤对老化船舶结构剩余极限强度的影响,应用连续介质损伤力学方法,将损伤耗散余势和塑性应变理论相结合,建立船舶结构剩余极限强度低周疲劳累积损伤模型,得到老化船舶结构极限强度随低周疲劳累积损伤衰减的规律.运用此模型,给出船舶常用Q235钢材和45钢材剩余极限强度随低周疲劳累积损伤衰减规律的工程应用经验关系式,验证了方法的合理性和实用性,为进一步分析低周疲劳对老化船舶结构极限强度的影响奠定了基础.     

Numerical Simulation of Shield Tunnelling Under a Historic Building Based on the Local Stiffness Correction Method (DMSM)北大核心CSCD

The district modified stiffness method (DMSM) considers the effect of joints and hand holes on the stiff-ness of the lining ring, assuming the stiffness around the joint and hand hole is to be reduced and the stiffness else-where is not changed. Considering the stiffness reduction of the lining ring caused by the segment’s circumferential joint, the internal force of the lining structure, the ground surface settlement and the displacement response of the surrounding soil body induced by shield driving are analyzed by an HS small strain constitutive model, and a 3D FEM model is established to analyze the interactions among the tunnel, soil body and building to apply to the dou-ble-line running tunnel of Shanghai Metro Line 11, which crosses under a historic building. In contrast, a 3D numeri-cal model based on the routine method (RMM) is set up and a comparison with the site measured data is conducted,with results indicating that they agree very well. The simulation results show that the existing building not only changes the surface settlement trough but also largely reduces horizontal displacement at the corresponding measuring points of the settlement trough; the distortion values of the existing building are related to the positions of the tunnel face and the location of the building; and the final distortion doesn’t decrease after completion of tunnel construction, but major residual distortion remains. This simulation method provides a reference for the control of disturbances during shield construction in soft rock. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

PREDICTION OF WELDING DEFORMATIONS BY FEM BASED ON INHERENT STRAINS

IntroductionIt is of importance to predict and control theresidual deformations caused by welding pro-cesses to ensure the accuracy of a welded produc-tion.Nowadays there are three ways to deter-mine the welding deformations:( 1 ) empiricalformulas or curves based on the experiments;( 2 ) thermo- elasto- plastic analysis by FEM;( 3)inherent strain method.The empirical formulasare only suited to the cases of simple plates orbeams that undergo a welding cycle close to theexperiment conditions. …     

FRP包裹混凝土圆柱统一约束模型

为进一步明确纤维增强复合材料(FRP)约束混凝土圆柱轴压性能影响因素及现有约束模型适用性,收集了混凝土强度在6.2～188.2 MPa范围内的普通混凝土、高强混凝土、超高性能混凝土、再生混凝土、海水海砂混凝土和工程水泥基复合材料等1049组普通FRP/大应变FRP包裹圆柱的试验数据.在统计分析基础上,基于最小二乘法建立...     

基于抗裂性能的水泥稳定碎石级配组成研究

运用级配设计理论和正交试验设计方法,针对水泥稳定碎石基层易产生裂缝这一缺陷,在总结已有研究成果的基础上,选取了多种典型集料级配设计方案,通过力学性能和物理性能试验,优选了抗裂性能良好的水泥稳定碎石集料级配设计方法和设计方案,并对水泥稳定碎石基层材料的合理级配组成进行了探讨。     

真空辅助压浆技术在有粘结后张预应力桥梁结构中的应用

在有粘结后张预应力桥梁结构中,预应力筋在高应力状态下的腐蚀成为工程界极为关注的敏感问题。真空辅助压浆技术是解决有粘结后张预应力筋防腐问题最有效的途径之一,压浆混合料的配制是最重要的技术,而真空压浆仅为辅助手段。     

基于Hoek-Brown准则的隧道围岩改进单元安全度分析

为了建立基于应变软化Hoek-Brown强度准则的围岩安全性评价方法,首先推导了Hoek-Brown准则与Mohr-Coulomb准则之间的关系,求得等效内摩擦角和黏聚力。其次将屈服接近度和破坏接近度进行变换统一到单元安全度量体系,进而总结了由Hoek-Brown应变软化参数表征的改进单元安全度（Zone Safety Index,ZSI）公式,实现了对单元的弹性、屈服和破坏状态的表达,并基于FLAC3D中FISH语言进行二次开发,编译了ZSI计算程序。随后,通过FLAC3D软件建立三维隧道模型,对该方法进行验证,并研究了Hoek-Brown准则参数对ZSI的影响规律。最后针对甄峰岭隧道大变形段的锚杆加固效果进行研究,利用ZSI法对大变形段不同长度锚杆加固方案进行安全稳定性对比分析,确定了较为合理的加固支护措施。研究结果表明：①ZSI小于1的区域与MIDAS的有效塑性应变区域基本一致,验证了ZSI程序的正确性,且ZSI可对岩体的弹性、屈服、破坏区域进行量化评价。②ZSI随地质强度指标GSI增加而增大,采用三次多项式进行拟合精度较高;随着单轴抗压强度σ_ci增大,ZSI呈指数方程增加,具有较高的相关性,扰动越大,单元安全度越小,表征围岩稳定性越差,ZSI随扰动因数D呈双曲线递减趋势变化;③ZSI法能够作为隧道初期支护方案优化和安全性评价的参考指标,对相关隧道的优化结果显示,3 m长注浆锚杆,同时加强其他支护结构能有效控制事故区的大变形,且安全性较好。     

弹塑性固有应变法在厚壁球面舱壁结构焊接中的应用

针对热弹塑性有限元法仅适用小规模焊接的弊端,采用弹塑性固有应变法对厚壁球面舱壁结构的焊接工艺进行模拟,并对球面舱壁结构的焊接工艺进行优化,最终给出球面舱壁结构合理的焊接工艺.在大型有限元软件ANSYS的基础上,通过开发的热弹塑性焊接计算程序得到单道焊缝焊接时的残余应变;通过残余应变等效,对球面舱壁的各焊缝处施加温度载荷;通过一次弹塑性有限元法得到厚壁球面舱壁结构的整体变形.通过开展不同焊接工艺下球面舱壁结构的焊接变形分析,给出厚壁球面舱壁结构合理的焊接工艺.