区域性阴极保护数学模型算法的改进

用边界元法（ＢＥＭ）求解区域性阴极保护的数学模型,以往采用矩形单元离散,步骤比较复杂,工作量大,当被保护体的几何形状适宜进行柱面单元划分且同柱面单元截口线上的电位可视为近似相同时,采用柱面单元离散,可减少模型中节点的数量,缩短计算周期,利用可变误差多面体寻优时,以往对阴极极化曲线的拟合过于简单,寻优的平稳性较差,对阴极极化曲线进行分段性拟合,可使寻优过程更加平稳,按上述方法编制的程序ＢＥＭＵ已用于     

Modelling of the electrochemical machining process by the boundary element method

This paper describes the development and application of the boundary element method to model the machining of simple milling and turning features. The 3D model uses linear triangular elements to discretise the workpiece and tool surfaces. Highlights of the program include the use of analytical integration to calculate the element matrices rather than numerical, and the automatic refinement of the mesh as the workpiece is progressively machined. The program has been tested for milling slots using a rectangular tool and for turning a thin-walled tube. It is shown that there is good agreement between the predicted and experimental results.     

A new non-contacting non-destructive testing method for defect detection in concrete

A new non-destructive testing (NDT) method for defect detection in concrete structures is presented. The method is based on the dynamic response of flawed concrete structures subjected to impact loading. Conversely to similar NDT techniques, such as the impact-echo method, the present method uses non-contacting devices for both impact generation (a shock tube producing shock waves) and response monitoring (laser vibrometers measuring concrete surface velocity). Experimental and numerical (finite element) studies have been carried out for concrete specimens containing artificial defects (penny-shaped cracks parallel to the free surface) with varying length and depth. According to the experimental and numerical results, it appears that the present method enables an effective detection of defects, particularly in the range of shallow defects.     

Evaluation of the BEASY program using linear and piecewise linear approaches for the boundary conditions

The boundary element method (BEM) was used to study galvanic corrosion using linear and logarithmic boundary conditions. The linear boundary condition was implemented by using the linear approach and the piecewise linear approach. The logarithmic boundary condition was implemented by the piecewise linear approach. The calculated potential and current density distribution were compared with the prior analytical results. For the linear boundary condition, the BEASY program using the linear approach and the piecewise linear approach gave accurate predictions of the potential and the galvanic current density distributions for varied electrolyte conditions, various film thicknesses, various electrolyte conductivities and various area ratio of anode/cathode. The 50‐point piecewise linear method could be used with both linear and logarithmic polarization curves.     

Nondestructive evaluation of concrete quality and integrity in composite columns

This paper summarizes the results obtained from the studies aimed at determining the feasibility of using the impact-echo technique for nondestructive evaluation of concrete quality and integrity in composite columns. Both numerical and experimental studies are carried out to gain a thorough understanding of the transient impact response of composite columns with/without flaws. Results obtained from these studies show that the impact response of a solid composite column is composed of a number of cross-sectional modes of vibration generated by multiple wave reflections between close proximity of boundaries. The frequency of the fundamental mode can be used to determine the P-wave speed in concrete. The presence of flaws disrupts the spectral pattern associated with the solid case. A shift of the fundamental frequency to a lower value is the key to identifying the presence of a flaw. In addition, the spectrum will also show a high amplitude peak at the frequency corresponding to the depth of the flaw.     

Detection and classification of flaws in concrete structure using bispectra and neural networks

The problem addressed in this paper is the detection and classification of flaws in concrete structure. It is known that higher-order spectra contain information not present in the power spectrum and can suppress Gaussian noise. Thus estimates of higher-order spectra have been shown to be useful in certain signal processing problems. This paper is concerned with the feature extraction from bispectra for concrete flaw detection. Impact-echo experiments are carried out for three different types of flaw in concrete structure. For each monitoring signal, after bispectral estimation, features are selected from the modules of bispectra in the primary region. For automatic interpretation, a multilayer back-propagation neural network is used as a classifier. Both clean data and data with additive white Gaussian noise are used for training and testing. The classification results obtained experimentally demonstrate that this method has good detection rates in varying environments.     

Study and experimental validation of the calculation of the ECT signal induced by a minute crack using a FEM–BIM combination

A combination of the boundary integral (BIM) and finite element (FEM) methods is presented for the calculation of the signal induced by small cracks. This approach—by preserving the attractive properties of both methods—allows considering a large variety of probe structures while the computation time remains low, especially if the signal of a complete scan is calculated. To validate the calculation results, experiments are carried out using a large number of minute cracks. The good agreement obtained between the measured and calculated data shows the applicability of the presented method.     

Flexible Sheet Forming Technology by Double-sided Simultaneous Shot Peen Forming

The exceptionally flexible forming technology shot peen forming is used primarily on large, three-dimensionally curved sheet metal in the aircraft and aerospace industries. Depending on the kinetic shot energy, both convex and concave curvatures will be generated. The most recent development, double-sided simultaneous shot peen forming, brings about a higher productivity of the entire process. FEM simulations of single and multiple impacts are presented in order to evaluate the characteristics of concave curvatures generated by both single and double-sided peen forming.     

Analysis of eddy currents in a bar containing an embedded defect

The eddy current distribution is studied in a metal bar containing an embedded defect inserted within an encircling coil. Furthermore, the impedance change of the coil regarding the characteristics of the defect is determined. The defects investigated are nonmetallic inclusions and embedded cracks which may occur during the manufacturing processes of bars. To simulate these problems, a two-dimensional transverse-electric model is proposed, and then a set of coupled surface integral equations are formulated systematically. Since the magnetic field is unknown along the boundary of the defect, an additional boundary condition derived from Maxwell's equations is used. Using the boundary element method (BEM), these integral equations are solved in terms of nodal unknowns-current density. After the current distribution is obtained, the impedance changes of the coil caused by the defects are calculated vs. the configuration of defect for various frequencies. If the inclusion is circular and located at the center of the bar, good agreements are found by comparing the BEM solutions with the analytical ones. An auxiliary surface integral equation is also derived to further determine the currents on both sides of the crack.     

Capacity of the remanent magnetism method to detect fractures of steel in tendons embedded in prestressed concrete

Sudden collapses of structural components due to fractures of the prestressing steel have occurred. The paper describes the successful application of a nondestructive testing method to identify defective structures. The remanent magnetism method makes it possible to localize fractures of single prestressing steel bars in postensioned tendons. The tendons need not be accessible at any point, not even at the jacking ends. The ferromagnetic properties of the prestressing steel are used in this process. Characteristic magnetic leakage fields are caused by fractures. The magnetic field, measured at the concrete surface along the projection of the tendon profile, allows conclusions concerning existing fractures. Also the extent of damage (number of broken steel bars) can be evaluated.     

Die land optimization of section extrusion by finite element method

1　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｔｈｅｅｘｔｒｕｓｉｏｎｏｆｓｅｃｔｉｏｎｓｗｉｔｈｆｌａｔ ｆａｃｅｄｄｉｅｓ ,ａｓｔｈｅｓｅｒｉｏｕｓｆｒｉｃｔｉｏｎｏｎｔｈｅｍａｔｅｒｉａｌ/ｔｏｏｌｉｎｔｅｒｆａｃｅａｎｄｔｈｅｂｉｇｄｉｆｆｅｒｅｎｃｅｉｎｇｅｏｍｅｔｒｙｂｅｔｗｅｅｎｔｈｅｅｘ ｔｒｕｄｅｄｓｅｃｔｉｏｎａｎｄｔｈｅｂｉｌｌｅｔ ,ｎｏｎ ｕｎｉｆｏｒｍｍｅｔａｌｆｌｏｗｏｃｃｕｒｓｉｎｔｈｅｄｅｆｏｒｍａｔｉｏｎｚｏｎｅ .Ｔｈｉｓｍａｙｒｅｓｕｌｔ,ｄｅ ｐｅｎｄｉｎｇｏｎｔｈｅｃｏｍｐｌ…     

Finite element analysis of die wear in hot forging processes

Design optimization of hot forging dies requires an accurate estimation of die wear. The presented paper introduces a finite element model for wear estimation that includes the process related thermal effects on hardness of the tool material. Fundamental investigations concerning the hardness evolution due to thermal softening of the tool material are presented. To obtain necessary data for model calibration by means of statistical analysis, optical measurements are performed on several industrial forging dies. The introduced model is proved to be applicable in wear estimation of hot forging dies over a large number of operating cycles.     

模切板刀片复合弯曲成形中的回弹研究

复合弯曲成形是一种高柔性的板料成形工艺。运用有限元方法分析了模切板刀片的复合弯曲成形,对成形过程中的回弹进行了研究。建立了外环转角与弯曲回弹角的度的关系。分析了内环圆角半径与对回弹的影响,对模切刀片的成形具有一定的指导意义。     

Analysis of workpiece thermal behaviour in cut-off grinding of high-strength steel bars to control quality and efficiency

Cut-off grinding is a machining process for separating various components and materials. The application of this trimming technology for high-strength steel bars leads to thermally induced defects such as grinding burrs and residual stresses. By means of a developed and empirically validated FE model it is possible to control the temperature distribution in the workpiece. The implementation of a CBN grinding wheel along with the optimization of the cutting parameters allows a significant decrease of the thermal load in the machined bar. As a consequence, thermal defects are reduced, thus leading to a high-quality trimming process.     

Modelling vibration transmission in the mechanical and control system of a precision machine

The relative vibration between tool and workpiece factors significantly to the performance of a precision machine. This paper develops a model for predicting the vibration transmission from two major excitation sources, ground vibration and fluid bearing force, to the tool and the workpiece position through the mechanical and control system of a precision machine. We synthesised the frequency response functions obtained from a finite element analysis of the machine to create transmissibility matrices that define the dynamic behaviours of the electromechanical system. The validity of the developed model was checked by comparing the measured relative vibrations to the results calculated from the measured excitations.     

Rapid computation of eddy current signals from narrow cracks

An existing boundary element method model for eddy current inspection of ideal or narrow cracks is revised. Using some lately devised concepts on efficiently and rapidly simulating canonical eddy current geometries, we show how this model can be made easier to implement and faster to calculate. The approach is largely based on a novel method for rapidly calculating the Green's function and reducing the matrix fill-time, and also on a similar method for rapidly computing the incident electric field. As a result, the model has been made an order of magnitude faster than the existing one without sacrificing accuracy. We pay attention to numerical analysis details and analyze issues that so far have not been clarified. The validity of our approach is also verified by the experiment. Although we have tested the model against published data, we have also produced our own precision measurements for surface and through-the-thickness slots in plates with the coils performing scans along and across the slots at various frequencies.     

Simulation of galvanic corrosion of magnesium coupled to a steel fastener in NaCl solution

The galvanic corrosion of magnesium alloy AZ91D coupled to a steel fastener was studied using a boundary element method (BEM) model and experimental measurements. The BEM model used the measured polarization curves as boundary conditions. The experimental program involved measuring the total corrosion rate as a function of distance from the interface of the magnesium in the form of a sheet containing a mild steel circular insert (5 to 30 mm in diameter). The measured total corrosion rate was interpreted as due to galvanic corrosion plus self corrosion. For a typical case, the self corrosion was estimated typically to be ～ 230 mm/y for an area surrounding the interface and to a distance of about 1 cm from the interface. Scanning Kelvin Probe Force Microscopy (SKPFM) revealed microgalvanic cells with potential differences of approximately 100 mV across the AZ91D surface. These microgalvanic cells may influence the relative contributions of galvanic and self corrosion to the total corrosion of AZ91D.     

ANALYSIS OF DISTRIBUTIONS OF RESIDUAL STRESS AND STRAIN BENEATH A NOTCH AFTER ROLLING

The fatigue property of the notched part can be improved significantly by introducingcompressive residual stress resulting from surface plastic deformation at the notch.Theresidual stress and strain distributions beneath the notch is predicted by using finite elementmethed (FEM) of large strain elasto-plastic analysis in this paper.It is investigatedwheather the rolling process could be replaced by a plane-strain indenting with a model inthe analysis.The effects of material strength.notch radius r.and indentation and depth Δhon the distribution of residual stress and strain are discussed.The agreement of predictedand experimental results is good enough.     

2VQS发动机气缸罩冲压成形数值模拟分析

本文应用Ｌｓ－Ｄｙｎａ３ｄ非线性有限元件对桑塔纳２０００型轿车ＶＱＳ发动机气缸罩冲压成形过程进行了详尽的有限元模拟分析，通过与实测结果的比较、表明有限元预测结果可靠的。     

装甲车车内声学响应分析

装甲车的振动噪声控制一直是理论和工程领域不断研究的课题,其车内噪声直接影响作战人员的作战水平,进行装甲车内部噪声的研究十分必要。首先分别建立并分析了装甲车车内空腔模型以及考虑结构和空气之间相互作用的声固耦合模型,通过对比耦合前后的声学模态振型图,得出车体结构对空腔声学特性有一定的影响;然后使用边界元法对整车声固耦合模型进行声学响应分析,得到驾驶员右耳处的声压分布情况;最后对声压峰值的频率点进行板件声学贡献量分析,为改善车内的声学特性提供了参考依据。