环形激光二极管抽运棒状激光器中瞬态温度和热应力分析

直接从激光二极管发光强度的角分布出发,采用光线追迹方法获得激光棒内的热沉积分布,在此基础上采用热传导模型和热力模型,比较了不同抽运功率、不同棒半径下达到稳态温度分布的时间,并且对稳态和瞬态热应力进行了详细模拟计算。结果表明,采用环形激光二极管阵列侧面抽运的棒状激光器中的热效应问题十分严重,不同的抽运结构参量下,温度分布不同;达到稳态所需时间随棒半径增大而增加,而不受抽运功率的影响;抽运功率越大,棒内温差增大,热应力也越大;热破坏主要集中于激光棒中心区域和表面区域。     

Finite element simulation of wave propagation in an axisymmetric bar

An accurate solution for high-frequency pulse propagation in an axisymmetric elastic bar is obtained using a new finite element technique that yields accurate non-oscillatory solutions for wave propagation problems in solids. The solution of the problem is very important for the understanding of dynamics experiments in the split Hopkinson pressure bar (SHPB). In contrast to known approaches, no additional assumptions are necessary for the accurate solution of the considered problem. The new solution helps to elucidate the complicated distribution of parameters during high-frequency pulse propagation down the bar as well as to estimate the applicability of the traditional dispersion correction used in the literature for the analysis of wave propagation in a finite bar. Due to the dimensionless formulation of the problem, the numerical results obtained depend on Poisson's ratio, the length of the bar and the pulse frequency, and are independent of Young's modulus, the density and the radius of the bar.     

CFETR纵场磁体线圈内馈线结构设计与分析

介绍了中国核聚变工程试验堆(CFETR)纵场磁体线圈馈线系统内馈线的结构,它由外盒体、万向节、 超导母线与冷却管路以及内部支撑架等子部件组成。在纵场磁体线圈内馈线工况下,对其进行了结构设计,并通 过有限元分析,获得了内馈线工作状态下的应力和位移分布云图。结果表明,最大应力与最大位移变形均满足设 计使用要求。      

Fracture Analysis in Orthotropic Thermoelasticity Using Extended Finite Element Method

In this paper, a method for extracting stress intensity factors (SIFs) in orthotropic thermoelasticity fracture by the extended finite element method (XFEM) and interaction integral method is presented. The proposed method is utilized in linear elastic crack problems. The numerical results of the SIFs are presented and compared with those obtained using boundary element method (BEM). The good accordance among these two methods proves the applicability of the proposed approach and conforms its capability of efficiently extracting thermoelasticity fracture parameters in orthotropic material.     

Numerical-experimental hybrid method for stress separation in digital gradient sensing method

A numerical-experimental hybrid method for the stress separation in the digital gradient sensing (DGS) method is proposed in this study. In the proposed hybrid method, boundary conditions for a local finite element model, that is, nodal force along boundaries are inversely determined from experimental values obtained by the digital gradient sensing method. The hybrid method follows two stages. In stage 1, the DGS method measures the Cartesian stress gradient components directly and, subsequently, the sum in Cartesian stresses at all interesting points on the surface; stress sum are used to compute the unknown boundary conditions for the local model. In stage 2, the individual stress components are calculated by the direct finite element method using the computed boundary conditions from stage 1. The effectiveness is demonstrated by applying the proposed method to a stress concentration problem involving concentrated load acting on an edge of a large planar sheet. The individual stress components thus determined are summed and compared with analytical stress sum, confirming the effectiveness and accuracy of the proposed technique.     

Wave structure analysis of guided waves in a bar with an arbitrary cross-section

Both dispersion curves and wave structures, which are displacement distributions on a bar cross-section, are essential for guided wave NDEs. Theoretical dispersion curves and wave structures for a bar with an arbitrary cross-section are derived in this paper using a special modeling technique called the semi-analytical finite element method (SAFEM). The guidelines for guided wave NDEs of bar-like structures are also shown based on wave structure and modal analysis. First, the relationship between the dispersion curves and their corresponding wave structures were obtained for a square rod. Modes with longitudinal vibration have higher group velocities and torsional modes have constant phase and group velocities. Next, the relationship between the dispersion curves and wave structures for a rail are detailed. The rail is used to represent a bar with a complex cross-section. Similar to the square rod results, the rail's longitudinal modes have higher group velocities. However, the rail contains modes with local vibration. Finally, single mode detection and excitation techniques are introduced. A single mode can be obtained by detecting and exciting with a weighted function that corresponds to a specific mode's wave structure.     

Nonlinear constitutive behavior of ferroelectric materials

The ferroelectric specimen is considered as an aggregation of many randomly oriented domains. According to this mechanism, a multi-domain mechanical model is developed in this paper. Each domain is represented by one element. The applied stress and electric field are taken to be the stress and electric field in the formula of the driving force of domain switching for each element in the specimen. It means that the macroscopic switching criterion is used for calculating the volume fraction of domain switching for each element. By using the hardening relation between the driving force of domain switching and the volume fraction of domain switching calibrated, the volume fraction of domain switching for each element is calculated. Substituting the stress and electric field and the volume fraction of domain switching into the constitutive equation of ferroelectric material, one can easily get the strain and electric displacement for each element. The macroscopic behavior of the ferroelectric specimen is then directly calculated by volume averaging. Meanwhile, the nonlinear finite element analysis for the ferroelectric specimen is carried out. In the finite element simulation, the volume fraction of domain switching for each element is calculated by using the same method mentioned above. The interaction between different elements is taken into account in the finite element simulation and the local stress and electric field for each element is obtained. The macroscopic behavior of the specimen is then calculated by volume averaging. The computation results involve the electric butterfly shaped curves of axial strain versus the axial electric field and the hysteresis loops of electric displacement versus the electric field for ferroelectric specimens under the uniaxial coupled stress and electric field loading. The present theoretical prediction agrees reasonably with the experimental results. Supported by the National Natural Science Foundation of China (Grant No. 10572138)     

Thermal Stress Analysis of a Continuous and Pulsed End-Pumped Nd:YAG Rod Crystal Using Non-Classic Conduction Heat Transfer Theory

In this paper, temperature distribution in the continuous and pulsed end-pumped Nd:YAG rod crystal is determined using nonclassical and classical heat conduction theories. In order to find the temperature distribution in crystal, heat transfer differential equations of crystal with consideration of boundary conditions are derived based on non-Fourier’s model and temperature distribution of the crystal is achieved by an analytical method. Then, by transferring non-Fourier differential equations to matrix equations, using finite element method, temperature and stress of every point of crystal are calculated in the time domain. According to the results, a comparison between classical and nonclassical theories is represented to investigate rupture power values. In continuous end pumping with equal input powers, non-Fourier theory predicts greater temperature and stress compared to Fourier theory. It also shows that with an increase in relaxation time, crystal rupture power decreases. Despite of these results, in single rectangular pulsed end-pumping condition, with an equal input power, Fourier theory indicates higher temperature and stress rather than non-Fourier theory. It is also observed that, when the relaxation time increases, maximum amounts of temperature and stress decrease.     

Simulation on thermoelastic stress field and laser ultrasound waveform in non-metallic materials by using FEM

The thermoelastically generated stress and ultrasound fields in non-metallic materials by laser illumination are presented by using finite element method (FEM). The model accounts for the effects of thermal diffusion and optical penetration, as well as the finite width and duration of the laser source. The numerical results show that the strength and feature of the force source can be related to the heat input and certain material properties. The relationships between the stress waves and the ultrasound waveforms, particularly the precursor, are analyzed. The typical surface acoustic waves (SAWs) and the bulk waveforms at the epicenter are presented to illustrate the generated field and provide insight to the relevance of different mechanism taken into account in the model. PACS 02.70.Dh; 43.35.+d; 42.62.-b     

变截面杆共轴撞击数值分析及其应用前景

 为对弹性杆共轴撞击这一应力波基础问题进行扩展研究,基于非线性动力学软件LS-DYNA建立了有限元模型,分析了共轴撞击的变截面杆的形态参数对波形的影响规律,探讨了应力波产生的机理,并对其应用前景进行了展望。结果表明,由于变截面效应,一定形态参数的变截面杆共轴撞击可以得到具备波阵面平滑上升,较长的前沿升时和消除了波形振荡等特性的应力波;该特性是变截面杆撞击这一过程的内在属性,主要由变截面段的最小半径控制,变截面段长度仅对局部形态产生影响,对加载速度的变化不敏感;半无限长的变截面杆共轴撞击规律可在应力波加工等领域应用。由此可见,该规律对基础性理论进行了扩展,应用前景广阔。     

APPROXIMATE TRANSMISSION EQUIVALENCE OF ELASTIC BAR TRANSITIONS UNDER 3-D CONDITIONS

Transmission of quasi-longitudinal elastic waves through elastic bar transitions between uniform and collinear bar segments is studied by means of three-dimensional (3-D) finite element analysis. The aim is to examine, through an example, to what extent two geometrically different transitions which are transmission-equivalent in a one-dimensional (1-D) context may retain this property under 3-D conditions. The difference between the two transitions is assessed from the difference between 3-D results for reflected waves, while the presence of 3-D effects is judged from the difference between 3-D finite element and 1-D analytical results for transmitted waves. It is found that two smooth and significantly U001different elastic bar transitions which are transmission-equivalent in a 1-D context may retain this property with good approximation under significantly 3-D conditions, well beyond those under which 1-D theory can be used for prediction of wave shapes. This extends the domain of potential applications in areas such as percussive drilling correspondingly.     

A continuous vibration theory for rotors with an open edge crack

In this paper a new continuous model for flexural vibration of rotors with an open edge crack has been developed. The cracked rotor is considered in the rotating coordinate system attached to it. Therefore, the rotor bending can be decomposed in two perpendicular directions. Two quasi-linear displacement fields are assumed for these two directions and the strain and stress fields are calculated in each direction. Then the final displacement and stress fields are obtained by composing the displacement and stress fields in the two directions. The governing equation of motion for the rotor has been obtained using the Hamilton principle and solved using a modified Galerkin method. The free vibration has been analyzed and the critical speeds have been calculated. Results are compared with the finite element results and an excellent agreement is observed.     

Finite element modelling for fatigue stress analysis of large suspension bridges

Fatigue is an important failure mode for large suspension bridges under traffic loadings. However, large suspension bridges have so many attributes that it is difficult to analyze their fatigue damage using experimental measurement methods. Numerical simulation is a feasible method of studying such fatigue damage. In British standards, the finite element method is recommended as a rigorous method for steel bridge fatigue analysis. This paper aims at developing a finite element (FE) model of a large suspension steel bridge for fatigue stress analysis. As a case study, a FE model of the Tsing Ma Bridge is presented. The verification of the model is carried out with the help of the measured bridge modal characteristics and the online data measured by the structural health monitoring system installed on the bridge. The results show that the constructed FE model is efficient for bridge dynamic analysis. Global structural analyses using the developed FE model are presented to determine the components of the nominal stress generated by railway loadings and some typical highway loadings. The critical locations in the bridge main span are also identified with the numerical results of the global FE stress analysis. Local stress analysis of a typical weld connection is carried out to obtain the hot-spot stresses in the region. These results provide a basis for evaluating fatigue damage and predicting the remaining life of the bridge.     

A Green-Naghdi Model in a 2D Problem of a Mode I Crack in an Isotropic Thermoelastic Plate

In this article, the generalized thermoelastic theory under Green and Naghdi models are used to study the thermoelastic interaction in an isotropic material containing a finite crack inside the material. The crack boundary is due to a prescribed temperature and stress distribution. Based on the Green-Naghdi type II and type III models, the formulation is applied to generalized thermoelasticity with an appropriate choice of parameters. Numerical solutions of the displacement components, temperature, and stress components are obtained using the finite element method. The results have been verified numerically and are represented graphically. Comparisons were made with expected results from Green and Naghdi model of type III and Green and Naghdi model of type II.     

ITER磁体重力支撑系统的应力强度分析

用ANSYS有限元软件,分析了ITER重力支撑系统的静力情况。采用实体单元建立有限元模型,分析了磁体重量、热载荷、地震和电磁力多种工况下的应力分布及位移变形,获得的最大应力强度和最大位移均在许用应力及允许位移范围内。为进一步优化ITER重力支撑系统提供了重要的参考数据。     

A Mode I Crack Problem for a Thermoelastic Fibre-Reinforced Anisotropic Material Using Finite Element Method

In this article, the theory of generalized thermoelasticity with one relaxation time is used to investigate the thermoelastic fiber-reinforced anisotropic material with a finite linear crack. The crack boundary is due to a prescribed temperature and stress distribution. By using the finite element method, the numerical solutions of the components of displacement, temperature and the stress components have been obtained. Comparisons of the results in the absence and presence of reinforcement have been presented.     

声表面横波压力传感器的电极质量负载效应分析方法

针对声表面横波(Surface Transverse Wave,STW)压力传感器,提出了一种考虑叉指电极质量负载的有限元和微扰理论结合分析方法。首先构建包含叉指电极的有限元模型,通过计算电极表面的面电荷得到器件的等效输入导纳,由导纳谐振点处提取STW传播声场,然后根据微扰理论,由STW传播声场以及压力引起的传感器结构的应力应变,得到包含电极质量负载影响的STW传感器的灵敏度。以一种基于ST-90°X石英材料的点压式STW压力传感器为例进行了理论计算,电极厚度为0.17 μm和0.21 μm时,计算灵敏度分别为-54.9 kHz/bar和-21.7 kHz/bar,说明电极质量负载对于传感器有较大影响。制作电极厚度为0.17 μm的传感器进行测试,得到-57 kHz/bar的压力灵敏度,实验结果和理论结果吻合,证明计算方法的有效性。      

Adaptive sparse polynomial chaos expansion based on least angle regression

Polynomial chaos (PC) expansions are used in stochastic finite element analysis to represent the random model response by a set of coefficients in a suitable (so-called polynomial chaos) basis. The number of terms to be computed grows dramatically with the size of the input random vector, which makes the computational cost of classical solution schemes (may it be intrusive (i.e. of Galerkin type) or non intrusive) unaffordable when the deterministic finite element model is expensive to evaluate.To address such problems, the paper describes a non intrusive method that builds a sparse PC expansion. First, an original strategy for truncating the PC expansions, based on hyperbolic index sets, is proposed. Then an adaptive algorithm based on least angle regression (LAR) is devised for automatically detecting the significant coefficients of the PC expansion. Beside the sparsity of the basis, the experimental design used at each step of the algorithm is systematically complemented in order to avoid the overfitting phenomenon. The accuracy of the PC metamodel is checked using an estimate inspired by statistical learning theory, namely the corrected leave-one-out error. As a consequence, a rather small number of PC terms are eventually retained (sparse representation), which may be obtained at a reduced computational cost compared to the classical “full” PC approximation. The convergence of the algorithm is shown on an analytical function. Then the method is illustrated on three stochastic finite element problems. The first model features 10 input random variables, whereas the two others involve an input random field, which is discretized into 38 and 30 ? 500 random variables, respectively.     

保偏光纤双折射分析及全光纤拍长测试方法比对研究

理论分析了保偏光纤双折射效应,应用有限元法建立了保偏光纤的三维模型,得到了其横截面上的应力分布及归一化的双折射参数。选择3种全光纤构成的纯光学系统进行对比拍长测试实验,实验结果和理论模型计算结果十分吻合,并对比研究了几种测试方法的优缺点。选定一种光路结构简单有效的双折射测试系统,对高双折射光子晶体光纤进行测试,测得了其归一化的双折射参数,并计算得其拍长约为1.2mm。研究结果对不同复杂结构保偏光纤的建模理论分析和拍长性能测试及高双折射光子晶体光纤设计制作后的性能测试有一定的实用价值。     

激光加热的微塑性成形有限元模拟

针对难成形材料微构件成形困难的特点,提出基于激光双面加热的微塑性成形方法。采用有限元分析软件ABAQUS,建立了基于激光加热的微镦粗圆柱形工件的热力耦合有限元模型,并对激光加热后工件的温度场分布和微塑性成形进行了模拟和应力分析。结果表明,采用激光双面加热的方法可以为微塑性成形建立合适的温度场,激光加热状态下的微塑性成形力明显降低,提高了微塑性材料的成形性能,拓宽了微塑性成形技术的应用范围。