陶瓷/硬质合金/陶瓷夹层复合片应力分析模型

推导了由于热膨胀系数不同 ,在热压烧结陶瓷 /硬质合金夹层复合片内引起的残余应力计算公式 ;分析了夹层复合片产生热裂纹的原因及影响因素 ,所得结论对研制陶瓷

正交异性钢桥面板肋-面板焊缝疲劳验算的应力分析模型评估

以天津塘沽海河大桥的正交异性钢桥面板为例,建立钢箱梁节段的有限元分析(FEA)模型、简化FEA模型和基于钢箱梁节段的子模型进行肋-面板焊缝疲劳应力分析模型的评估。计算结果表明:对于远离纵腹板处的肋-面板焊缝,通过提高简化FEA模型中横隔板高度和约束横隔板底部翼缘的方式可减小与钢箱梁节段FEA模型结果的误差;对于靠近纵腹板处的肋-面板焊缝,所有简化FEA模型的应力计算结果均低于钢箱梁节段FEA模型的结果,且误差超过23%。基于钢箱梁节段的三跨子模型可以准确地给出钢桥面板任意位置的肋-面板焊缝的疲劳应力。它具有钢箱梁节段FEA模型的计算精度和简化FEA模型的计算效率,因此它可作为正交异性钢桥面板任意位置处肋-面板焊缝疲劳应力分析的准确和高效计算模型。

创建应力分析模型过程中的技巧

介绍了利用三维工程绘图pro／E软件创建工程机械关键零部件应力分析模型的方法。

载重轮胎复合结构的非线性有限元模拟和增量分析(二)

1．2．5．1应力分析 当应用于简化成旋转简体、膜体和壳体的轮胎结构时，大多数应力分析模型是以经典技术或有限元技术为基础的。在过去几年已经报道了用于分析轮胎在不同负荷条件下的应力、应变和变形场的大量以有限元为基础的轮胎模型。经典分析方法可以求解能彻底理解轮胎性能的多组微分方程，而有限元技术则可模拟实际轮胎轮廓的几何形状和研究轮胎各层具有代表性的材料性能。

QT500表面等离子喷涂8YSZ热障涂层TGO的残余应力状态及数值分析

分别采用超音速火焰喷涂（HOVF）和等离子喷涂（APS）在QT500球墨铸铁基体上制备Co Ni Cr Al Y粘结层（BC）和8YSZ陶瓷隔热层（TC）,研究了试样在1050℃高温环境中经过2.5、8、15、50、100 h恒温氧化后体系的应力情况。利用扫描电子显微镜（SEM）对热生长氧化物（TGO）的微观形貌进行观察与分析,并用拉曼荧光光谱仪（RFS）分析了其应力的分布及变化规律,并通过力学模型进行了残余应力的数值计算。结果表明：由陶瓷层与粘结层之间的热失配而导致TGO中产生残余压应力,其最大值范围为1.9557-1.9603 GPa;残余压应力在高温氧化初始阶段逐渐减小,至15 h达到最小值,随之逐渐增大后趋于稳定;在恒温阶段,θ-Al2O3转变为α-Al2O3所引起的体积收缩是TGO中残余应力减小并趋于稳定的直接原因。

不良地质下穿越既有管线顶管施工技术应用

为解决城市轨道交通建设中大型管线因受周边环境条件的制约与限制无法迁改的情况,通过施工前利用有限元建立土体模型分析周边土体变化对管线受力的影响;利用BIM可视化的特点绘制出工程的三维图,为相关项目管理人员的沟通交流提供信息平台;在顶管顶进过程中,通过“掘进控制技术”、“管线静态实时监测技术”,控制沉降;严格控制出土量,防止超挖而使地面出现塌陷;同时采用将膨润土与聚丙烯酰胺等高分子材料混合溶液拌和而成的新型固态泥浆,减少管顶的摩擦。现场实践表明,采用该技术确保了顶管机顺利安全通过既有管线,可节约成本约300万元。

大型泄洪排沙闸预应力闸墩结构模型试验研究

本文详细描述某抽水蓄能电站泄洪排沙闸大型预应力闸墩结构模型试验的模型比尺与材料选择、混凝土配合比、模型制作、结构受力性能测试构件的布置和测试系统、加载系统以及试验流程等研究过程。对试验数据进行归纳、整理和分析,得到在各种预定工况下的预应力预压效果和闸墩颈部、闸墩与锚块接触处及锚块等控制部位的受力状态,研究在超载情况下闸墩结构的承载能力,提出进一步改进结构设计的建议。

含未焊透缺陷压力管道的安全评定

未焊透是压力管道焊接接头常见缺陷之一，目前我国在用工业管道定期检验规程中对未焊透管道的定级较为保守，为了减少对未焊透缺陷的返修，需要进行科学而适用的压力管道缺陷安全评定，本文针对弯头焊缝位置处含未焊透缺陷的管道，建立管系应力分析模型，利用有限元对未焊透部位进行局部应力分析及应力线性化；采用考虑影响因素更为全面的平面缺陷简化评定方法，对管道的安全状况进行了评估，结果表明该管道在评定周期以内可安全运行。

轴向和转动约束不锈钢柱的耐火性能研究

英国研究人员开展了高温下轴向和转动约束不锈钢柱结构耐火性能数值模拟的改进方法研究。建立的有限元模型形成连续耦合的热应力分析模型,包括传热模型、屈曲分析几何材料非线性应力分析。有限元模型对文献报道的试件失效温度和耐火时间的平均预测误差为2%~6%,达到了较高的预测精度。

Analytical solution to rock pressure acting on three shallow tunnels subjected to unsymmetrical loads

According to the interaction of three shallow tunnels with large section, the analytical solution to rock pressure has been derived and discussed. The load model is given when the bilateral tunnels are excavated. According to the model, the stresses of three tunnels and single tunnel are calculated and compared to analyze the distribution characteristics, where the stresses are influenced by controlling factors of clear distance, covering depth and inclination angle of ground surface. The results show that, in general, the bias distribution is more serious. Therefore, it is significant to settle down the load model of three shallow tunnels so as to determine the measure of reinforcement and design the structure of support. The model and results can be used as a theoretical basis in designation and further research of the three shallow tunnels.

Kinetic Model and Simulation Analysis for Toluene Disproportionation and C9-Aromatics Transalkylation

A new kinetic model for commercial unit of toluene disproportionation and C9-armatiocs transalkylation is developed based on the reported reaction scheme.A time based catalyst deactivation function taking weight hourly space velocity(WHSV)into account is incorporated into the model,which reasonably accounts for the loss in activity because of coke deposition on the surface of catalyst during long-term operation.The kinetic parameters are benchmarked with several sets of balanced plant data and estimated by the differential variable metric optimiza- tion method.Sets of plant data at different operating conditions are applied to make sure validation of the model and the results show a good agreement between the model predictions and plant observations.The simulation analysis of key variables such as temperature and WHSV affecting process performance is discussed in detail,giv- ing the guidance to select suitable operating conditions.

CONFINING PRESSURE EFFECT ON ACOUSTIC EMISSIONS IN ROCK FAILURE

Based on the phenomenon that acoustic emissions (AE) generated by rock mass increase suddenly because of underground excavation, time sequence of AE rate in rock failure has been discussed by using statistical damage theory. It has been demonstrated that how the influence of confining pressure on the deformation behavior and AE characteristics in rocks can be inferred from a simple mechanics model. The results show that loading confining pressure sharply brings out increasing of AE. On the other hand, few AE emits when confining pressure is loaded sharply, and AE occurs again when axial pressure keeps on increasing. These results have been well simulated with computer and show close correspondence with directly measured curves in experiments.

Dynamic probabilistic analysis of stress and deformation for bladed disk assemblies of aeroengine

In order to describe and control the stress distribution and total deformation of bladed disk assemblies used in the aeroengine, a highly efficient and precise method of probabilistic analysis which is called extremum response surface method(ERSM) is produced based on the previous deterministic analysis results with the finite element model(FEM). In this work, many key nonlinear factors, such as the dynamic feature of the temperature load, the centrifugal force and the boundary conditions, are taken into consideration for the model. The changing patterns with time of bladed disk assemblies about stress distribution and total deformation are obtained during the deterministic analysis, and at the same time, the largest deformation and stress nodes of bladed disk assemblies are found and taken as input target of probabilistic analysis in a scientific and reasonable way. Not only their reliability, historical sample, extreme response surface(ERS) and the cumulative probability distribution function but also their sensitivity and effect probability are obtained. Main factors affecting stress distribution and total deformation of bladed disk assemblies are investigated through the sensitivity analysis of the model. Finally, compared with the response surface method(RSM) and the Monte Carlo simulation(MCS), the results show that this new approach is effective.

THEORY ANALYSIS AND EXPERIMENT STUDY ON THE FRACTURE PROPAGATION UNDER BLASTING LOAD

This paper theoretically analyzed and discussed the fractures’ initiation, propagation and arrest of grooved borehole blasting under the function of explosion, and provided the optimistic values of blasting parameters. The stress intensity factor and velocity of crack propagation were measured through dynamic caustics measuring system.

Geometry effect on mechanical properties of woven fabric composites

The effects of geometry on mechanical properties in woven fabric composites were explored. Two types of composites, including one-layered and two-layered composites, were designed and studied. For one-layered composites, inter-strand gap effects on the mechanical properties were studied, while three cases of geometries with inter-strand gaps in two-layered composites were evaluated. A woven fiber micromechanics analytical model called MESOTEX was employed for theoretical simulation. The predicted results show that the inter-strand gap and simple variation of the strand positions in a repeating unit cell significantly affect the mechanical properties of woven fabric composites.

Test analysis of stress characteristics on reinforcing rock slope with group anchorage cable

To research the reinforcement effect of a rock slope with group anchorage cables and the stress characteristics of pre-stressed anchorage cables in the fractured surface, the rock slope calculated model of a wedge block within the double-slide face was established by using the finite difference software according to the actual slope project combined with indoor model test. The pre-stress loss rule of the anchorage cable and the distribution of axial force and the force-transferring mechanism of the anchorage cable were analyzed during simulation. Also, based on the displacement contour and the safety factor of the calculated results, the quantitative analysis for the reinforcement ef- fect of the rock slope with group pre-stressed anchorage cable was discovered. The results computed by the software conform with the data in the experiment, which can prove the effectiveness and correctness of parameter selection and model building. Keywords group anchorage reinforcement, rock slope, joint fissure, pre-stressed anchorage cable, stress characteristics

Nonlinear static response of piezoelectric plates considering electro-mechanical coupling

Nonlinear static analysis of piezoelectric plates has been carried out using nonlinear finite element method considering electro-mechanical coupling,The geometrical nonlinearity has been taken into account and electric potential is assumed to be quadratic across the plate thickness,The governing equations are obtained using potential energy and Hamilton's principle that includes elastic and piezoelectric effects.The finite element model is derived based on constitutive equation of piezoelectric material accounting for coupling between elasticity and electric effect using higher order plate elements,Results are presented for piezoelectric plate under different mechanical boundary conditions,Numerical results for the plate are given in dimensionless graphical forms.Effects of boundary conditions on linear and nonlinear response of the plate are also studied.The numerical results obtained by the present model are in good agreement with the available solutions reported in the literature.

Effective grouting area of jointed slope and stress deformation responses by numerical analysis with FLAC^(3D)

To study the grouting reinforcement mechanism in jointed rock slope, first, the theoretical deduction was done to calculate the critical length of slipping if the slope angle is larger than that of joint inclination; Second, the numerical calculation model was founded by FLAG^3D, so as to find the stress and deformation responses of rock mass in the state before and after grouting, the analysis results show that the range between the boundary of critical slipping block and the joint plane that passes the slope toe is the effective grouting area （EGA）. After excavation, large deformation occurs along the joint plane. After grouting, the displacements of rock particles become uniform and continuous, and large deformations along the joint plane are controlled; the dynamic displacement can re- flect the deformation response of slope during excavation in the state before and after grouting, as well as the shear location of potential slip plane. After grouting, the dynamic displacement of each monitoring point reaches the peak value with very few time steps, which indicate that the parameters of the joint plane, such as strength and stiffness, are improved; the stress field becomes uniform. Tensile area reduces gradually; whole stability of the slope and its ability to resist tensile and shear stress are improved greatly.

Stress Transfer Modeling at the Interface of Cemented Prosthesis and Femur

Objective：To model the stress transfer at the interface of the cemented prosthesis and femur, an axisymmetric model of the interfacial stress transfer was established. Methods ： Assuming that the prosthesis, the cement and the femur were concentric cylinders with linear elastic and isotropic properties, distributions of the axial stresses in the prosthesis, the cement and the femur as well as the interfacial shear stresses at the prosthesis/cement interface and the cement/femur interface in the axial direction were obtained from the established axisymmetric stress transfer model. Results ： Interfacial failure was the main form for the prosthesis/cement/femur structure under external loads. Considering the residual thermal stresses, it was more likely to produce the mixed failure form than the pure shear failure form. Since the cement had a relatively high thermal expansion coefficient, the thermal effect accelerated the interface failure and thus aggravated the stress shielding effect. Due to a relatively high thermal residual temperature difference, the interfacial debonding and femur failure was more likely to occur for the cobalt-chromium alloy prosthesis material than the Ti-6A1-4V alloy prosthesis material. Conclusion： Assuming that the prosthesis, the cement and the femur are concentric cylinders with linear elastic and isotropic properties, distributions of the axial stresses in the prosthesis, the cement and the femur as well as the interfacial shear stresses at the prosthesis/cement interface and the cement/femur interface in the axial direction was obtained using the basic equations of axisymmetric elastic mechanics when the prosthesis bears the compressive stresses. Interface failure is the main failure form for the prosthesis/cement/femur structure under external loads. The thermal effects accelerate the failure of the prosthesis/cement interface and the cement/femur interface and the relaxation of the prosthesis, and then aggravates the stress shielding effect of the femur. Also, the thermal effects decrease the efficiencies of the interfacial stress transfer to some extent since it alleviates the failure of the interface and the femur, which was confirmed by the clinical results.

烧结应力研究进展

就烧结应力的产生、理论值计算等方面进行阐述,并利用能量法、曲率法、力平衡法计算烧结应力的思路,综述烧结应力发展的历史和研究进展。以等粒径颗粒模型的烧结应力研究为基础,建立非等径颗粒烧结应力分析模型,用计算机模拟烧结的真实条件,对非等径颗粒粉末冶金材料或梯度粉末冶金材料的烧结应力进行分析,这是未来该类材料烧结应力研究的主要方向。