Modeling Angle Beam Ultrasonic Testing Using Multi-Gaussian Beams

This paper proposes a new approach to modeling angle beam ultrasonic testing that can predict pulse-echo signals, in an absolute and computationally efficient manner, from various reflectors in steel welded joints. This approach relies on a model of the entire ultrasonic measurement process, a model which requires one to solve three subsidiary problems; 1) determination of a system efficiency factor, 2) evaluation of the ultrasonic beam field around the flaw, and 3) calculation of the scattering from the reflector. Here, solutions are offered for each of those three subsidiary problems. To solve the first problem we employ the specular reflection from the cylindrical part of a STB-A1 (Standard Test Block in compliance with Japanese Industrial Standards Z 2347) (equivalently IIW (International Institute of Welding) type 1) standard block to determine the system efficiency factor. To solve the second problem, we calculate the ultrasonic wave field at the flaw with a highly efficient multi-Gaussian beam model. For the third problem, we treat the scattering from a reflector by high frequency approximations. We explicitly give the solutions to all three of these subsidiary problems for counter bore, crack, and side-drilled hole reflectors. Experimental results that validate this approach are also given.     

Untersuchungen zum Elektronenstrahl‐Randschichtumschmelzen einer sprühkompaktierten übereutektischen eisenhaltigen Al‐Si‐Legierung

The present study shows the influence of two different electron beam deflection techniques on surface deformation, microstructure and hardness after an electron beam surface remelting of a spray‐formed hypereutectic aluminium alloy (AlSi17Fe5Cu4Mg). Due to the specific rapid heating and cooling rates on the one hand and the high content of alloying elements on the other hand, the surface microstructure was modified by phase formation, grain refinement and an oversaturation of aluminium solid solution. As a result the hardness was threefold increased (284 HV 0.1) compared to the untreated base material (104 HV 0.1). This hardness increase was significantly higher than the level of the conventional heat treatment (e. g. age hardening approx. 170 HV 0.1). The remelting process largely influenced the wear behaviour under abrasive (scratch test) and abrasive‐adhesive (pin‐on‐disc test) load conditions. Remelted surface layers generated by meander deflection technique showed the most improvement regarding their wear performance.     

复合材料梁的脱层识别

本文作者研究了具任意脱层复合材料梁的单参数振动反分析。基于弹性理论,建立了复合材料脱层梁的基本方程式。对脱层梁进行了分区处理,方便地描述了脱层长度、脱层位置。利用边界条件、区间位移连续性条件和弯矩剪力平衡条件建立了反分析的特征方程式。综合考虑系统的一阶固有频率和一阶振型,通过反分析特征方程式求出某一待定参数。为工程无损检测提供理论依据。     

Nonlinear non-classical microscale beams: Static bending, postbuckling and free vibration

This paper initiates the theoretical analysis of nonlinear microbeams and investigates the static bending, postbuckling and free vibration. The nonlinear model is conducted within the context of non-classical continuum mechanics, by introducing a material length scale parameter. The nonlinear equation of motion, in which the nonlinear term is associated with the mean axial extension of the beam, is derived by using a combination of the modified couple stress theory and Hamilton’s principle. Based on this newly developed model, calculations have been performed for microbeams simply supported between two immobile supports. The static deflections of a bending beam subjected to transverse force, the critical buckling loads and buckled configurations of an axially loaded beam, and the nonlinear frequencies of a beam with initial lateral displacement are discussed. It is shown that the size effect is significant when the ratio of characteristic thickness to internal material length scale parameter is approximately equal to one, but is diminishing with the increase of the ratio. Our results also indicate that the nonlinearity has a great effect on the static and dynamic behaviors of microscale beams. To attain accurate and reliable characterization of the static and dynamic properties of microscale beams, therefore, both the microstructure-dependent parameters and the nonlinearities have to be incorporated in the design of microscale beam devices and systems.     

Analytical solution for three-dimensional model predicting temperature in the welding cavity of electron beam

This paper provides an analytical solution for three-dimensional model predicting temperature in the welding cavity of electron beam. It is not easy to measure the temperature on the keyhole of electron-beam welding. Therefore it is essential to develop an analytical model that can accurately predict the temperature in the keyhole. In this study, the keyhole produced by an electron beam is assumed to be a paraboloid of revolution and the intensity of electron beam is supposed to be Gaussian profile. In order to obtain an analytical solution, the parabolic coordinate system is utilized to analyze the temperature in the keyhole and the parameter approximating convection is proposed to account for the effect of convection of molten metal. Considering the momentum balance at the bottom of the keyhole but neglecting the absorption in the plume, an analytical solution is developed for semi-infinite workpieces. As compared with other analytical solutions, the analytical solution obtained by this model provides the temperature distribution more consistent with the experimental data. The effects of various parameters on the temperature distribution in the keyhole are also discussed in this study.     

三维机织复合材料的一种梁单元细观力学模型

根据三维机织复合材料中纤维束排列和变形的周期性特点,推导了一种细观梁单元模型。该模型考虑了纤维束的拉 (压) 弯耦合效应和纤维束之间的相互作用,可以描述纤维束和基体中的细观应力分布,并得到宏观的力学性能。针对一种典型的三维机织复合材料,首先根据编织参数,确定其细观几何结构,取最小周期的一段纤维束作为分析胞元,用上述细观梁单元分析了该段纤维束在面内拉伸荷载下的细观应力分布,计算出平均模量, 并用材料试验和细观实体有限元对本模型进行了检验,结果与本文的预测吻合良好。研究表明,拉、弯耦合效应引起的纤维束中的细观弯曲应力同平均轴向应力相比,不可忽略。      

Lattice modelling of the failure of particle composites

Three-phase particle composites are modelled by a beam lattice. The second, hard phase (particle) is a linear elastic material. However, to improve the representation of the lattice model, tension softening of the matrix and/or the interface between the particle and the matrix is introduced. Moreover, as each beam element in the lattice is short and deep, instead of using the Euler-Bernoulli theory, beam elements based on the Timoshenko theory are introduced to enhance accuracy. Finally, the effect of finite deformations is also investigated due to the large displacements and/or rotations likely to be involved with the evolution of the damage. Numerical results for particle composites are presented and discussed.     

复合材料圆管构件的等效模型研究

本文针对任意壁厚的复合材料圆管构件的等效弹性模量和剪切模量提出了高阶理论计算方法,它考虑了构件的横向剪切效应以及层合材料的三维本相关系,并且对三种缠绕方式的等效模量进行了预测,预测结果与经典层合报理论和实验的预测结果吻合较好,该方法可用于复合材料杆件结构的设计中。     

钢筋混凝土剪力墙多垂直杆单元模型力学性质分析及其改进

分析了多垂直杆单元的力学性质,证明了与之等效的梁单元的转角和横向位移的位移函数均为一次式,且该梁单元在求弯曲横向位移时,需采用1节点数值积分。讨论了多垂直杆单元模型转动中心c值的含义,认为c值反映了数值积分的求积节点或假设剪切应变插值点的变化,会对单元的刚度产生影响,并对c值的取值范围提出了合理建议。提出了竖向弹簧布置的改进方式,按高斯点布置代替均布方式时,能够用较少的弹簧得到更为精确的结果,提高了计算速度。最后,从横向位移模式和剪应力不均匀分布两个方面提出了改进多垂直杆单元模型的新构想。     

Modeling and analysis for the development of Lightweight Piezoceramic Composite Actuators (LIPCA)

This paper focuses on the modeling and analysis of Lightweight Piezoceramic Composite Actuators (LIPCA) for developmental purposes. A simple analytical model and a numerical model for predicting the displacement of the actuators due to both an applied input voltage and transverse load to the piezoelectric ceramic layer are presented. The analytical model describing the laminated beam actuation results in two primary design parameters, an actuation coefficient of a laminated beam C_ulb and the bending stiffness of a laminated beam EI_lb. The C_ulb is a parameter when maximum displacement is required. The bending stiffness affects the displacement performance when a transverse load is applied to the actuators. An experiment was performed to verify the proposed laminated beam model. The numerical model, a NASTRAN finite element model, is used to assess the effect of initial dome heights of actuators on the displacement. An increase in the initial dome height produces a positive effect for the low anisotropic actuators and gives a negative effect for the high anisotropic actuators. In conclusion, the results indicate that designing to maximize the C_ulb, the EI_lb, and the initial dome height of the low anisotropic actuators could generate LIPCA-type actuators with larger displacement and higher force.     

微谐振式压力传感器的差动输出设计与建模

提出一种应用于微谐振式压力传感器的敏感结构,其一次敏感元件为矩形硅膜片,膜片的上表面架设有三个两端固支的硅谐振梁,间接感受压力作用,根据膜片上不同位置设置的硅谐振梁的固有频率对于压力变化有不同的变化规律的特点,实现对被测压力的差动输出检测。针对这种结构,建立被测压力与谐振梁固有频率的数学模型。设计实际尺寸参数进行计算分析,得出谐振梁的分布位置和几何参数对其振动特性的影响规律,给出了由差动输出解算压力的公式,验证了所提出的结构的设计思想和优化参数的可行性。     

压电驱动器非线性模型研究

本文通过对压电驱动器的软件计算结果与实验结果的差异进行研究总结,利用变形后压电驱动器中各个结构部分的应力应变分布特点,结合复合层合材料力学、梁力学模型和压电材料非线性模型理论构造出压电薄片与基体材料的简化耦合模型,从而建立结构的非线性模型。模型计算结果比软件计算结果更符合实验结果，并且形式比前人的更简单，物理意义清晰明确。再利用该模型对不同结构参数下的压电驱动器性能进行分析，直观地反应出压电驱动器各结构参数对驱动器性能的影响。     

Ultrasonic Beam Models for Angle Beam Surface Wave Transducers

ABSTRACT

Explicit three-dimensional (3D) point source and multi-Gaussian beam models are obtained for the Rayleigh waves generated by a surface wave angle beam transducer using an angular plane wave spectrum approach. Simulations show that the multi-Gaussian surface wave beam model agrees well with the point source model while being computationally more efficient. The theoretical predictions obtained with the models are also compared to the experimental measurement results where good agreement with the models is found for both on-axis and off-axis field comparisons.     

The Asymptotic Expansion Load Decomposition elastoplastic beam model

A new higher‐order elastoplastic beam model is derived and implemented in this paper. The reduced kinematic approximation is based on a higher‐order elastic beam model using the asymptotic expansion method. This model introduces new degrees of freedom associated to arbitrary loads as well as eigenstrains applied to the beam. In order to capture the effect of plasticity on the structure, the present elastoplastic model considers the plastic strain as an eigenstrain imposed on the structure, and new degrees of freedom are added on the fly into the kinematics during the incremental‐iterative process. The radial return algorithm of J₂ plastic flow is used. Because of the constant evolution of beam kinematics, the Newton‐Raphson algorithm for satisfying the global equilibrium is modified. An application to a cantilever beam loaded at its free extremity is presented and compared to a three‐dimensional reference solution. The beam model shows satisfying results even at a local scale and for a significantly reduced computation time.     

Micromechanics models for the elastic constants and failure strengths of plain weave composites

In this paper, two models are presented for plain weave composites. One is finite element analysis (FEA) model for elastic constants, namely, sinusoidal yarn model. Another is analytical model for failure strengths, namely, sinusoidal beam model. The FEA model is generated by interfacing an in-house computer code with FEA software strand6, and the analytical model is developed using the theory of elasticity. Numerical studies are carried out using the present models to investigate the effects of some major geometrical parameters on the properties of plain weave composites. It is concluded that the failure strengths are closely related to the fiber volume fraction of a yarn, and the mechanical properties are closely related to the overall fiber volume fraction of the composites. An experimental testing program is conducted for T300/934 plain weave composites to validate the developed models. A good agreement exists between the predicted and measured results.     

基于振型控制的变厚度梁的优化设计研究

提出了计算梁弯曲振动的新方法。从弯曲变形的角度出发,利用有限差分的方法,建立了梁弯曲振动的计算模型,模型同时适用于等厚度梁和变厚度梁。使用不同类型的梁对模型的准确性进行了验证,结果表明模型具有较好的计算精度。同时,尝试使用该模型进行梁的振型优化设计,对模型做适当的变形后,就可以以梁的频率和振型作为目标,通过数值方法来获取最佳的厚度分布值。最后用一个实例对方法进行了验证,结果表明利用该模型进行梁的振型优化设计是可行的。     

一种用于水声运动目标成像的空间散射模型

水声成像过程中为了分析所接收的运动目标回波、理解接收信号的形成机理,提出了一种用于该情况的空间散射模型,并利用此模型仿真了"T"型阵成像声呐接收的回波信号。对信号的分析说明了空间散射模型的正确性。以空间散射模型为基础,利用傅里叶变换波束形成算法对不同条件下的球体目标进行了水声成像,并分析了成像性能。性能分析说明了水声目标大小、距离等因素对成像的影响情况,还特别强调了在运动情况下目标的成像情况。以上工作完成了对"T"型阵水声成像过程的模拟,为成像过程回波信号研究和成像声呐研制提供了理论基础和仿真手段。     

Kerbspannungen sind Biegespannungen – was sind gute und böse Kerben?

Notch stresses are bending stresses – what are good and bad notches? The origin of a stress concentration in an engineering component can be explained by the imagination of superimposed bending stress. The curved surface of a notch can also be seen as the concave side of a heavily curved beam under bending. The nonlinear stress distribution of the beam under bending superimposes with the nominal stress and causes the stress concentration. In order to avoid such stress concentrations the increase of stress along the notch contour has to compensate with the decrease of the nominal stress. A multi‐linearized model demonstrates the interaction between the flow of stresses and the increase of the cross‐section of the component.     

基底隔震建筑的剪切梁动力模型

本文提出了基底隔震结构的分布参数剪切梁模型，给出了该模型下的自由频率方程及任意阶振型函数的解析表达式。与现有的一阶刚体模型、二阶质点模型、多质点模型及时程分析法相比较，采用本模型可以更清楚、更全面地反上部结构与基础隔震参数的相互关系，且易于为工程设计人员所接受。     

无粘结预应力高性能粉煤灰混凝土桥梁收缩与徐变变形试验研究

结合洛湛线的建设,以8根不同掺量的高性能粉煤灰混凝土无粘结预应力桥梁的收缩、徐变试验为基础,研究了不同掺量高性能粉煤灰混凝土在荷载长期作用下收缩、徐变性能及其上拱随时间的变化规律,探讨了温度、湿度等环境因素对不同掺量高性能粉煤灰混凝土收缩、徐变的影响。300多天的实验观测结果表明:高性能粉煤灰掺量20%～40%混凝土梁不但具有良好的工作性能和力学性能,而且长期性能良好,与同强度的未掺高性能粉煤灰的梁相比,其后期强度和抗压弹性模量增大,收缩徐变减小,具有良好的社会和经济效益。