随焊冲击抑制6061-T6铝合金接头软化行为研究

6061-T6铝合金焊后软化最严重的区域为焊接热影响区,易造成铝合金构件整体强度下降。为了抑制焊接接头的软化现象,通过新参数直流反接TIG焊以及随焊冲击实验对焊接接头进行强化,并通过维氏硬度计、扫描电子显微电镜、能谱分析仪和电化学工作站对冲击试样进行分析。结果发现:随焊冲击后焊接热影响区软化行为减弱,晶界析出的G.P区、Mg2Si、CuAl2以及β相的尺寸和聚集程度变小,晶粒得到细化。焊接热影响区冲击区腐蚀电流小于未冲击区,塔菲尔斜率大于未冲击区,抗腐蚀性能增强。

Aligned Solidification Structure of the MnBi Phase in Semisolidified Bi-Mn Alloy with a Static Magnetic Field

The solidification structure of Bi-3 wt pct Mn alloy grown up in the semisolid zone under the influence of a staticmagnetic field (up to 1.0 T) and the relation of the magnetic property with the solidification structure have beeninvestigated experimentally. It was shown that the primary phase MnBi crystals in the alloy aligned and oriented alongthe direction of the applied magnetic field. The orientating tendency and the average length of the elongated MnBicrystals increased with the increase of the applied field and the solidification time. Moreover, the remanence of thealloy along the aligned direction of the MnBi phase in the case of solidification with a magnetic field was apparentlyanisotropic and nearly double of that without the magnetic field. This indicated that the MnBi crystals orientedand aligned along their easy magnetization axis. A model was proposed to explain the alignment and orientationgrowth of the MnBi crystals in a magnetic field in terms of the magnetic anisotropy of the crystals and the magneticinteraction between them.

Partition of Unity for a Class of Nonlinear Parabolic Equation on Overlapping Non-Matching Grids

A class of nonlinear parabolic equation on a polygonal domain Ω R2 is inves- tigated in this paper. We introduce a finite element method on overlapping non-matching grids for the nonlinear parabolic equation based on the partition of unity method. We give the construction and convergence analysis for the semi-discrete and the fully discrete finite element methods. Moreover, we prove that the error of the discrete variational problem has good approximation properties. Our results are valid for any spatial dimensions. A numerical example to illustrate the theoretical results is also given.

Multi-Purpose Forensics of Image Manipulations Using Residual-Based Feature

The multi-purpose forensics is an important tool for forge image detection.In this paper,we propose a universal feature set for the multi-purpose forensics which is capable of simultaneously identifying several typical image manipulations,including spatial low-pass Gaussian blurring,median filtering,re-sampling,and JPEG compression.To eliminate the influences caused by diverse image contents on the effectiveness and robustness of the feature,a residual group which contains several high-pass filtered residuals is introduced.The partial correlation coefficient is exploited from the residual group to purely measure neighborhood correlations in a linear way.Besides that,we also combine autoregressive coefficient and transition probability to form the proposed composite feature which is used to measure how manipulations change the neighborhood relationships in both linear and non-linear way.After a series of dimension reductions,the proposed feature set can accelerate the training and testing for the multi-purpose forensics.The proposed feature set is then fed into a multi-classifier to train a multi-purpose detector.Experimental results show that the proposed detector can identify several typical image manipulations,and is superior to the complicated deep CNN-based methods in terms of detection accuracy and time efficiency for JPEG compressed image with low resolution.

Higher Order Triangular Mixed Finite Element Methods for Semilinear Quadratic Optimal Control Problems

In this paper,we investigate a priori error estimates for the quadratic optimal control problems governed by semilinear elliptic partial differential equations using higher order triangular mixed finite element methods.The state and the co-state are approximated by the order k Raviart-Thomas mixed finite element spaces and the control is approximated by piecewise polynomials of order k(k≥0).A priori error estimates for the mixed finite element approximation of semilinear control problems are obtained.Finally,we present some numerical examples which confirm our theoretical results.

Effect of seed particles content on texture formation of Si_3N_4 ceramics by gel-casting in a strong magnetic field

In this paper, the textured Si3N4 ceramics were prepared by adding seed particles during gel-casting in the magnetic field of 6 T, followed by pressureless sintering. The effect of pH on the stability and dispersibility of Si3N4 slurry and the effect of seed particles content on texture formation of SiaN4 ceramics were both studied. Those results showed that the slurry with good stability and dispersibility was obtained when pH was about 11.6. The a or b-axis of Si3N4 particles or crystals was aligned parallel to the direction of the magnetic field in the magnetic field of 6 T. The degree of texture of Si3N4 ceramics further increased during sintering. With the increasing of additional β-Si3N4 particles in the magnetic field of 6 T, the degree of texture increased from 0.19 without seed particles to 0.76 with 9% （mass fraction） seed particles. The increase of seed particles content promoted the texture formation of Si3N4 ceramics.

A Quadratic Triangular Finite Volume Element Method for a Semilinear Elliptic Equation

In this paper we extend the idea of interpolated coefficients for a semilinear problem to the quadratic triangular finite volume element method.At first we introduce quadratic triangular finite volume element method with interpolated coefficients for a boundary value problem of semilinear elliptic equation.Next we derive convergence estimate in H1-norm,L2-norm and L¥-norm,respectively.Finally an example is given to illustrate the effectiveness of the proposed method.

Study on the liquid metal flow field in FC-mold of slab continuous casting

The flow pattern and the velocity distribution of a liquid metal in the flow control mold （FC-mold） were investigated with a mercury model by analogy to the molten steel during continuous casting. The velocity measurement was conducted by the ultrasonic Doppler velocimeter （UDV） under various magnetic distributions and flux densities. The impingement intensity and the scouring intensity of the liquid metal to the narrow wall of the mold were calculated based on the measured data, and the influence of the magnetic flux density on the liquid metal flow in the mold was analyzed. The results showed that the surface of the liquid metal became more active when only the lower magnet was assembled, and the surface fluctuation was suppressed when further applying the upper magnetic field. It was indicated that when the upper and lower magnetic flux densities were 0.18 T and 0.5 T, respectively, the optimum conditions could be obtained, under which the free surface fluctuation could be suppressed, and a flow recirculation could rapidly form.