图解法测定压力容器残余应力的研究

电测法测定压力容器的残余应力,关键取决于屈服应力的确定。本文基于平面应力屈服条件,通过薄壁筒压力容器非膜应力部位的组合应力轨迹,用图解的方法研讨了测点的屈服应力。结果发现,残余应力和弯曲应力均可改变薄膜应力轨迹,以致组合应力部位的屈服应力不同于薄膜应力部位,但是,拉应力区域,第一主应力方向的Tresca屈服应力均为sσ。根据应力轨迹与屈服轨迹之交点的应力符合屈服条件的原理,通过分解薄壁筒焊缝的电测应力曲线,探讨了测点第二主应力方向的Tresca屈服应力以及用Mises屈服轨迹得到残余应力的方法。探究结果表明,压力容器的残余拉应力可以通过电测应力用图解方法得以测定,并且其测试精度可满足工程要求。基于平面应力屈服条件,研讨了压力容器非膜应力部位的组合应力轨迹,并根据应力轨迹与屈服轨迹之交点的应力符合屈服条件的原理,用薄壁筒的电测应力曲线,探究了图解法测定压力容器残余应力的可行性。结果表明,图解法可用于压力容器残余拉应力的测定,并且其测试精度可满足工程要求。     

封闭应力方向对巴西圆盘试验影响的数值模拟

为揭示封闭应力对巴西圆盘应力分布和破裂演化过程的影响,开展不同方向封闭应力对巴西圆盘破裂二维数值模拟研究。将封闭应力的区域等效成一个封闭的包裹体分布在岩体中,探究不同方向封闭应力对圆盘应力分布和裂纹扩展的影响。结果表明,施加封闭应力的部位出现局部应力变化明显高于未施加的区域,随着加载的进行,施加封闭应力区域的局部应力小于周围未施加封闭应力的区域;对比有无封闭应力存在时加载过程中最大米塞斯应力,得出当封闭应力与加载方向夹角为0°时最大,为20.78 MPa;当无封闭应力和封闭应力方向为0°时,圆盘中心起裂,封闭应力方向为30°,60°,90°时,圆盘的裂纹带发生倾斜并出现多条倾斜短裂纹,圆盘未中心起裂。     

高速轧机工作界面非稳态混合润滑过程多因素耦合辊缝力学特性研究

综合运用摩擦润滑理论、流体力学理论、轧制理论,建立了考虑动态辊缝非稳态润滑过程多因素耦合轧制界面力学模型.该模型综合运用了基于非稳态润滑过程的界面摩擦模型、工作辊运动模型、辊缝应力分布模型构成的界面薄膜约束多因素耦合模型.系统分析了非稳态混合润滑状态下,当压下率和表面粗糙度为定值时不同时刻工作区压应力和摩擦应力的分布情况,以及压下率为定值时工作区压应力、摩擦应力随表面粗糙度和后张应力变化的情况.结果表明:在压下率和表面粗糙度为定值时,当具有较大的后张应力时,工作区压应力和摩擦应力却较低,同时压应力梯度和摩擦应力梯度也相当小,摩擦应力在入口和出口边缘处达到最大,当后张应力减小时,辊缝间压应力和摩擦应力增加,压应力梯度和摩擦应力梯度较大;在压下率为定值而表面粗糙度为变量时,当后张应力较大时,表面粗糙度对工作区中的压应力和摩擦应力影响非常大,辊缝间压应力和摩擦应力随着表面粗糙度的增加而增加,当后张应力较小时,表面粗糙度对工作区中的压应力和摩擦应力影响不太明显.     

闪光对焊连接HRB400级钢筋疲劳试验与试验影响因素研究

基于闪光对焊连接的HRB400级高强钢筋,开展一系列疲劳性能试验,得到多组双对数双折线S-N曲线和疲劳应力幅;基于此对影响疲劳试验结果的试验频率、试验应力比、试验钢筋种类、焊接残余应力四个因素进行研究。研究结果表明:高、低频试验得到的疲劳应力幅有一定的差距,低频试验得到的疲劳应力幅比高频试验低约20MPa;应力比0.4时的疲劳应力幅比应力比0.2时的疲劳应力幅低,大直径的钢筋试件的疲劳应力幅较低,32mm直径的钢筋试件在应力比0.4时的疲劳应力幅与应力比0.2时的疲劳应力幅相差不大;闪光对焊连接HRB400高强钢筋试件的疲劳应力幅比HRBF400高强钢筋试件的疲劳应力幅高约10MPa~20MPa,且大直径钢筋试件的应力幅值差异较小。     

一种新的应力率定义

本文研究客观应力率的定义及表示,在放弃了客观应力率形式上的对称性以后定义了一类广义的非对称的客观应力率。从Cauchy应力原理出发,通过构造应力向量形式上和变形及变形率无关的客观导数,得到两种形式的应力率;它们表示作用在参考构形中单位物质面元应力向量的真实变化,这样就消除了应力率定义中的不确定性。用新应力率对次弹性体简单剪切进行了计算,得到的应力不振荡,且满足超弹性正应力-剪应力普适关系。     

应力分量变化范围的描述方程及其图形

过应力空间一点的不同斜面上的正应力、剪应力以及全应力会随着斜面的变化而变化。全应力的变化范围常用应力椭球方程和应力椭球面来描述。首次给出了过一点不同斜面上正应力、剪应力变化的描述方程及其三维图形。该方程和应力椭球方程共同构成了所有应力分量的描述方程。针对剪应力、全应力作用方向与斜面的法向并不一致的问题,给出了一种能够直接描述不同斜面上正应力、剪应力和全应力变化的三维图形,该图形能够非常直观地表示正应力、剪应力以及全应力数值的变化。     

结构拓扑优化应力敏度分析的伴随法

针对受应力约束的连续体结构拓扑优化问题,推导了应力敏度分析的伴随法公式;并以算例形式,将伴随法计算的应力敏度结果与差分法结果进行对比,验证了所推导公式的准确性,应力敏度分析结果表明了应力对设计变量的偏导数具有局部性特点。在此基础上,以受应力约束重量极小化为目标的结构拓扑优化为例,对比分析了应力一阶Taylor近似与满应力法的优化效果。结果表明:相比满应力法,应力一阶近似能使结构应力在更多的部分达到许用应力,得到的最优结构重量更轻。对设计变量数目巨大的应力约束连续体结构拓扑优化问题,由于应力约束数目可以通过准有效约束初选及不考虑删除单元的应力约束等方式减少,通常比设计变量数目小很多,应用应力敏度分析伴随法可以显著提高计算效率。     

多轴应力疲劳失效的基本准则

引言若机件各点的应力是交变应力,且各点或其中某些点的应力状态是复杂应力状态,机件在这种交变应力作用下的失效现象则称之为多轴应力疲劳现象,简称多轴应力疲劳.正像判断或预测金属材料开始产生塑性变形的条件称为屈服准则那样,人们把判断或预测发生多轴应力疲劳失效的规则(条件)称之为多轴应力疲劳失效准则.实际上,多轴应力疲劳失效准     

应力圆的解析与图解法证明

应力圆以严格的应力解析表达式为理论根据.作为几何图形,应力圆是应力状态直观形象的载体,人们可以通过作图的方法方便地获得描述应力状态的有关参数,即图解法,这在计算工具尚不发达的年代很有价值.然而,图解法存在的根本依据是应力圆所具有的特性,深入系统地研究这些特性,可以深刻地揭示应力圆的本质.为此,从应力圆的理论构成入手,深入分析应力圆的理论表达式与几何图形的有机联系,并对应力圆图解法进行系统证明.     

金属轧制过程辊缝非稳态混合润滑特性研究

根据Tsao和Sargent的混合润滑假设,建立了板带轧制时混合润滑状态下的非稳态润滑基本模型.系统分析了非稳态混合润滑状态下,基于正弦后张应力输入时,摩擦应力、压应力随时间和表面粗糙度变化的分布情况,以及基于某一压下率下在不同时刻表面粗糙度对摩擦应力、压应力分布的影响.结果表明:在较大的后张应力情形下,工作区中的压应力对表面粗糙度非常敏感,且随着表面粗糙度的增加相应增加;当后张应力减小时,压应力对表面粗糙度的敏感度下降.表面粗糙度对工作区中摩擦应力的分布有较大影响,当有较大后张应力输入时,辊缝间压应力相应较低,此时摩擦应力大小分布对表面粗糙度非常敏感,且随着表面粗糙度的增加而增加.与后张应力相比,表面粗糙度对摩擦应力的影响更为显著.     

Thermal analysis of a flow of immiscible couple stress fluids in a channel

An analytical study of the entropy generation rate and heat transfer in a flow of immiscible couple stress fluids between two horizontal parallel plates under a constant pressure gradient is performed. Both plates are kept at different and constant temperatures higher than that of the fluid. The Stokes couple stress flow model is employed. The classical no-slip condition is prescribed at the plates, and continuity of the velocity, rotation, couple stress, shear stress, temperature, and heat flux is imposed at the interfaces. The velocity and temperature distributions are found analytically, and they are used to compute the entropy generation number and Bejan number. The effects of the couple stress parameter and Reynolds number on the velocity, temperature, entropy generation number, and Bejan number are investigated. It is observed that the friction near the plates in couple stress fluids decreases as the couple stress increases.     

Mohr-Coulomb准则主应力回映算法及在地基问题的应用

针对Mohr-Coulomb准则在应力空间中存在奇异点的问题,提出了主应力空间应力回映算法。分析了多屈服面下塑性流动法则,给出了应力更新过程中应力回映区域的判定方法,推导了不同映射区域下塑性因子的Newton-Raphson迭代求解式和应力更新方程,建立了对应的一致切线模量表达式。利用C++语言,编制了弹塑性有限元求解程序,并对岩土地基问题进行求解,计算结果的比对证明了所编程序的可行性和精确性。     

Viscoelastic analysis of residual stress in quenched thermosetting resin beams

The residual stress generated by the molding process of thermosetting resins exerts serious influences upon their mechanical properties. This residual stress is generally classified by two groups: one produced by shrinkage in the curing reaction of monomers, the other produced by the nonuniformity of the temperature distribution in the cooling process. This paper is concerned with the theoretical and experimental analysis of the generation of residual stress of the latter type, using examples of rectangular beams of thermosetting resins quenched on both the upper and lower surfaces. First, a viscoelastic model is applied to make a qualitative prediction of the residual stress in quenched beams. Second, using linear-viscoelastic theory, fundamental equations are derived for the residual stress in a viscoelastic rectangular beam, where an unsteady and nonuniform temperature distribution is assumed in the direction of depth. The theoretical values of the residual stress in rectangular beams are calculated under various quenching conditions for two resins having different viscoelastic characteristics, i.e., epoxy and unsaturated polyester. The theoretical residual-stress distributions agree fairly well with the residual stress measured experimentally at every quenching condition for both resins. The qualitative prediction that the residual stress in quenched beams is compressive in the vicinity of the upper and lower surfaces and is tensile in the inner parts is confirmed. The relaxation modulus of epoxy resin changes more greatly with time and temperature than that of unsaturated polyester resin. The theoretical and experimental analysis shows that the residual stress for the former resin is larger than that for the latter. Therefore, it is concluded that the generation of residual stress is more significant where the relaxation modulus of resin changes greatly with time and temperature.     

Stress Separation of Interferometrically Measured Isopachics in a Perforated Plate

A method for the stress separation of interferometrically measured isopachics using an Airy stress function is proposed in this study. A Poisson equation that represents the relationship between the sum of principal stresses and an Airy stress function is solved using a finite element method. The Dirichlet boundary condition for solving the Poisson equation is determined by the approximation of an assumed Airy stress function along the boundary of the model. Therefore, the distribution of the Airy stress function is obtained from the measured isopachic contours. Then, the stresses are obtained from the computed Airy stress function. The effectiveness of the proposed method is validated by applying the proposed method to the isopachic contours in a perforated plate obtained by Mach-Zehnder interferometry. Results indicate that stress components around a hole in a plate can be obtained from isopachics by the proposed method.     

高地应力岩体多孔爆破破岩机制

深部岩体爆破破岩是爆炸荷载与高地应力共同作用的结果。基于一些简化假设，建立了一个高地应力岩体双孔爆破计算模型，采用光滑粒子流体力学-有限元方法耦合数值模拟方法，研究了高地应力作用下炮孔间裂纹的传播及贯通过程，分析了炮孔周围应力场动态演化过程与分布特征。研究结果表明:爆破引起的岩体开裂主要是环向动拉应力所致，地应力对岩体的压缩降低了炮孔周围环向动拉应力、缩短了环向动拉应力的作用时间，因而对爆炸致裂起抑制作用；静水地应力条件下多孔爆破时，垂直于炮孔连线方向传播的爆生裂纹更易受到地应力的抑制；对于高地应力岩体爆破，炮孔间的裂纹扩展长度随地应力水平的提高而减小，裂纹主要沿最大主应力方向扩展，因此沿最大主应力方向布置炮孔、缩短炮孔间距有利于炮孔间裂纹的连接贯通，形成良好的爆破开挖面。     

动脉压对静脉血管壁周向应力分布的影响

自体静脉是病变动脉管段常用的替代物。移植后因承受压力急剧升高引起的静脉管壁应力改变是影响移植手术的主要因素之一。为了比较移植前(静脉压作用下)和移植后(动脉压作用下)静脉管壁的周向应力分布，本文通过检测一定轴向伸长比条件下静脉管的p(压力)——V(容积)试验数据，利用3参数的应变能密度函数对实验数据进行拟合，进而求得静脉管壁的残余应力和沿血管壁的周向应力分布。对狗的股静脉和颈静脉的分析结果表明，在动脉压作用下静脉管壁周向应力将急剧增大。与处于静脉压环境相比，处于动脉压环境中的颈静脉管周向应力将增大差不多2个数量级。计算结果还显示，静脉管壁残余应力的数值虽然比动脉管壁的相应值小很多，但是与动脉管相同，血管壁残余应力依然对静脉管壁上的周向应力分布影响显著，残余应力的存在将大大削弱在静脉管内壁处的周向应力集中，使周向应力沿静脉管壁厚的变化梯度明显减小。     

Multi-scale analysis of subgrid stress and energy dissipation in turbulent channel flow

In present study, the subgrid scale （SGS） stress and dissipation for multiscale formulation of large eddy simulation are analyzed using the data of turbulent channel flow at Ret = 180 obtained by direct numerical simulation. It is found that the small scale SGS stress is much smaller than the large scale SGS stress for all the stress components. The dominant contributor to large scale SGS stress is the cross stress between small scale and subgrid scale motions, while the cross stress between large scale and subgrid scale motions make major contributions to small scale SGS stress. The energy transfer from resolved large scales to subgrid scales is mainly caused by SGS Reynolds stress, while that between resolved small scales and subgrid scales are mainly due to the cross stress. The multiscale formulation of SGS models are evaluated a priori, and it is found that the small- small model is superior to other variants in terms of SGS dissipation.     

Determination of Periodic Changes in the Stress State of Grounds from Variations in Infrared Radiation Flux

Examples of the records of variations with time in the signal from an infrared radiometer caused by the stress variations in the ground specimen and synchronous readings of strain gauges used to calculate stress variations are given. An algorithm of processing these records is constructed. A satisfactory coincidence of the stress variations in time determined with the use of synchronous radiation and tensometric measurement data is shown. The results show the efficiency of the infrared diagnostics of periodic changes in the stress state of grounds.     

DEFORMATION RIGIDITY OF ASSUMED STRESS MODES IN HYBRID ELEMENTS

The new methods to determine the zero-energy deformation modes in the hybrid elements and the zero-energy stress modes in their assumed stress fields are presented by the natural deformation modes of the elements. And the formula of the additional element deformation rigidity due to additional mode into the assumed stress field is derived. Based on, it is concluded in theory that the zero-energy stress mode cannot suppress the zero-energy deformation modes but increase the extra rigidity to the nonzero-energy deformation modes of the element instead. So they should not be employed to assume the stress field. In addition, the parasitic stress modes will produce the spurious parasitic energy and result the element behaving over rigidity. Thus, they should not be used into the assumed stress field even though they can suppress the zero-energy deformation modes of the element. The numerical examples show the performance of the elements including the zero-energy stress modes or the parasitic stress modes.     

循环荷载作用下饱和粘土中的有效应力原理的实验研究

有效应力原理是土力学中的经典理论,在土动力学中,有效应力原理的应用基本上是沿用土静力学中的方法,即通过建立合理的孔压模式,利用有效应力原理对土体的破坏进行分析。但是通过动三轴试验发现,在动三轴不固结不排水试验中,整个试验过程中孔压不发生变化,土体强度却发生了明显的衰减。这种现象利用有效应力原理无法得到合理的解释。针对这种现象,本文建议引入损伤变量D,作为反映土体结构变化的参数,对有效应力原理进行修正。经过修正后的有效应力原理反映了在循环荷载作用下,循环扰动造成的结构损伤对有效应力的影响,可以合理地解释动力作用下土体中孔压和有效应力相互转换,以及土体强度衰减的原因。