Effect of combined magnetic field on the eliminating inclusions from liquid aluminum alloy

The effect of electromagnetic field on the removal of inclusions in the aluminum alloy was investigated. Primary silicon particles precipitating from the solidification of Al-Si hypereutectic alloy were regarded as inclusions. An experimental apparatus applied with both rotating magnetic field (RMF) and traveling magnetic field (TMF) was employed to study the distribution of silicon particles in Al-Si alloy under magnetic field. The results showed that combined magnetic field (CMF) consisting of RMF and TMF eliminated the silicon particles from the molten alloy. Compared with TMF or RMF, CMF increased the separating effectivity substantially. It was proposed that CMF provided a highly effective approach for metal purification.     

金属磁记忆技术表征应力集中、残余应力及缺陷的探讨

对应力集中、残余应力及缺陷三者之间的关系进行讨论,举例分析磁记忆信号对不同应力集中程度、疲劳裂纹及残余应力的反映.结果表明:金属磁记忆技术适宜表征铁磁材料存在磁导率急剧变化的位置;磁记忆信号能否表征残余应力还需要进一步的深入研究.     

螺旋磁场对Sn-Sb合金成分偏析的影响

为了深入研究螺旋磁场解决重力偏析的效果及作用机理,本文选用低熔点Sn-Sb合金,分析不同励磁电流下螺旋磁场对铸锭宏观成分偏析的影响,并与常规条件下及相同工艺参数旋转磁场条件下的凝固组织进行比较.结果表明,螺旋磁场的电磁力分布特点有利于在铸锭内部形成更大区域的均匀搅拌,相比于旋转磁场可以更好地改善铸锭成分的宏观偏析;随着励磁电流的增大,两种磁场改善偏析、细化凝固组织的效果更好;当螺旋磁场励磁电流为100 A时,基本消除铸锭上、下部位由于重力作用导致的成分偏差,β相(SnSb)变得细小且均匀分布在基体内.在金属熔体凝固的过程中施加螺旋磁场可消除重力偏析,效果优于旋转磁场.     

Remote Field Eddy Current Control Using Rotating Magnetic Field Transducer: Application to Pressure Tubes Examination

The remote field eddy current (RFEC) technique is used to investigate the possibility of detecting the discontinuities practiced on pressure tubes samples from nuclear reactors, pressurized heavy water reactors (PHWR) type. In this article, we propose to develop the RFEC using the technique of rotating magnetic field (RMF). A method for calculating the field generated by the eddy current transducer with RMF using propagator matrix was developed. The experimental measurements are realized for artificial discontinuities practiced in pressure tubes samples.     

Variation of Residual Magnetic Field of Defective U75V Steel Subjected to Tensile Stress

Variation of the stress‐induced magnetic field of the U75V rail steel under tension was investigated in this research. Various magnetic responses were registered by a magnetometer in the elastic and plastic deformation stages, which can be explained by the microstructural changes in magnetic domains. Two types of defective specimens were also tested to correlate the stress concentration with the magnetic field. It is found that the tangential component of the magnetic field B_x is much more sensitive to local stress concentration than the normal component B_z. The tangential component B_x reaches a peak value at the rupture position, and the peak magnitude is proportional to the concentrated stress caused by the defect. This observation is different from the Q235 steel, whose tangential component B_x and the normal component B_z are equally effective. Such discrepancy might be due to that U75V fails in a more brittle pattern than the Q235 steel. The average value of the B_x along the loading axis can determine the overall stress state of the structure, while the peaks in the B_x curve tell the local stress concentration caused by cracks and dislocation.     

Grain refinement of horizontal continuous casting of the CuNi10Fe1Mn alloy hollow billets by rotating magnetic field (RMF)

Rotating magnetic field (RMF) is used in horizontal continuous casting of CuNi10Fe1Mn alloy hollow billets. The result shows that the formerly inhomogeneous columnar grain macrostructure turns into homogeneous equiaxed grain with the application of RMF. The microstructure without RMF transforms from coarse and disordered dendrites to dense dendrites which have obvious orientation, while the microstructure with RMF from center to edge displays the evolution from spherical grains to disordered dendrites without orientation. The mechanical properties are improved remarkably.     

Relaxation element method in calculations of stress state of elastic plane with the plastic deformation band

On the basis of relaxation element method an analytical representation of the band of localized plastic deformation, as the defect with its own internal stress field in the plane under tensile loading, is given. The influence of orientation of the band with respect to tensile axis on the stress concentration in the plane is analyzed.     

Magneto stress analysis of a strip with a semi elliptical notch under uniform magnetic field

Two dimensional solutions of the magnetic field and magneto elastic stress are presented for a magnetic material of a thin strip with a semi-elliptical notch subjected to uniform magnetic field. The strip is a finite plate of a simply connected region. A linear constitutive equation is used for the stress analysis. According to the electro-magneto theory, only Maxwell stress is caused as a body force in a plate. Therefore, the magneto elastic stress is analyzed using Maxwell stress. In the present problem, as a result, the plane stress state does not arise, and the σ_z in the direction of the plate thickness and the shear deflection (anti-plane shear stress) arise for soft ferromagnetic material. The stress σ_z in the plate is strong compressive stress for a soft ferromagnetic material. A rational mapping function is used for the stress analysis, and the each solution is obtained as a closed form. No further assumption of the plane stress state that the plate is thin is made for the stress analysis, though Maxwell stress components are expressed by nonlinear terms. The rigorous boundary condition is completely satisfied without any linear assumptions on the boundary. The anti-plane shear stress causes Mode III stress intensity factor when the notch is a crack. Stress concentration values are investigated for a notch problem, of which expression is given. Figures of the anti-plane shear stress distribution, Mode III stress intensity factor, and stress concentration values are shown.     

18CrNi4A钢力-磁效应的ANSYS模拟

采用大型有限元分析软件ANSYS建立18CrNi4A试样及其周围空气层的有限元模型,对其进行地磁场中拉伸载衙下的力-磁效臆有限几模拟,得出试样应力分布网以及试样表面切向和法向漏磁场分布结果;磁场下应力集中对磁记忆信号的影响进行分析;最后,将模拟结果与实际试验结果进行比对,得出分析结果,为磁记忆检测技术的机理和试验的深入研究提供依据.     

Remote Control of Mechanical Forces via Mitochondrial‐Targeted Magnetic Nanospinners for Efficient Cancer Treatment

In cells, mechanical forces play a key role in impacting cell behaviors, including adhesion, differentiation, migration, and death. Herein, a 20 nm mitochondria‐targeted zinc‐doped iron oxide nanocube is designed as a nanospinner to exert mechanical forces under a rotating magnetic field (RMF) at 15 Hz and 40 mT to fight against cancer. The nanospinners can efficiently target the mitochondria of cancer cells. By means of the RMF, the nanocubes assemble in alignment with the external field and produce a localized mechanical force to impair the cancer cells. Both in vitro and in vivo studies show that the nanospinners can damage the cancer cells and reduce the brain tumor growth rate after the application of the RMF. This nanoplatform provides an effective magnetomechanical approach to treat deep‐seated tumors in a spatiotemporal fashion.     

外应力对Terfenol-D棒的应变和磁感应强度的影响

超磁致伸缩材料Terfenol-D是一种新型的功能材料,以Terfenol-D为核心元件设计各种换能器时,磁场H和应力σ是必须考虑的因素.研究了一定偏置磁场下外加压应力对Terfenol-D棒的应变和磁感应强度的影响.首先测试了在一定的偏置磁场下外压应力和应变的关系,结果表明偏置磁场一定时,应变和应力之间的关系复杂,可用磁性材料技术磁化理论来解释.其次又测试了一定偏置磁场下的外加动态应力和磁感应强度的关系,测试结果表明一定的偏置磁场下,外加压应力增加,磁感应强度减小;偏置磁场为5kA/m时,磁感应强度达到最大值.该实验结果可以为基于Terfenol-D的换能器件的设计提供技术支持.     

Liquid metal model experiments on casting and solidification processes

This paper is concerned with laboratory studies using liquid metals with T _melt ≤ 300°C to model the flow of metals in industrial processes. Considering three selected examples the main features of such cold models are described. In the first instance we examine an aluminium alloy investment casting process. The requirement of reducing high flow velocities was achieved by the application of a static magnetic field. Local velocity measurements as well as integrated flow rate determination were carried out using eutectic InGaSn (T _melt = 10°C). Secondly, model experiments were performed on the electromagnetic stirring of liquid metals in a cylindrical cavity. We applied a rotating magnetic field (RMF) and a travelling magnetic field and recorded flow maps by means of ultrasonic Doppler velocimetry. With the goal of an efficient 3D-mixing, measurements were made using a combination of both field types with promising results. Thirdly, we report on systematic studies of the effect of an RMF on the solidification of a PbSn alloy. Directional solidification experiments demonstrate the influence of the electromagnetically driven convection on the resulting microstructure.     

铁磁构件应力集中的有限元分析和磁记忆检测

应用ANSYS软件对平板中心裂纹构件的应力分布进行有限元分析,不仅得出了符合积分理论解的精度较高的分析结果,并且通过对加载构件表面漏磁场的测量,验证了应力集中与磁记忆效应之间的规律,进一步探讨了磁记忆检测在铁磁构件损伤预诊断中应用的可行性.     

应力生长FeCoSiB非晶薄膜的磁各向异性研究

采用应力生长方法，制备出受压应力和张应力作用的FeCoSiB非晶磁弹性薄膜，研究了薄膜中的应变大小对FeCoSiB薄膜的磁滞回线、剩磁、应力诱导各向异性场等磁特性的影响．结果表明，无应变薄膜在薄膜面内呈现各向同性，而有应变的薄膜呈现出明显的各向异性。张应力诱导的各向异性与应力方向平行，而压应力形成垂直于应力方向的磁各向异性。各向异性场随应变的增大而线性增大。     

Influence of Slot Defect Length on Magnetic Flux Leakage

A key issue, which influences the applications of magnetic flux leakage testing, is defect quantification. There have been many research on the relationship between width, depth and magnetic flux leakage of slot defect. However, the length factor is often ignored. The relationship between characteristics of defect leakage field and defect length was investigated. The magnetic flux leakages of a series of plate specimens with the same width, same depth and different length slot defects were tested under the same magnetizing conditions. Testing results show that defect length is an important parameter needed to consider in quantifying defects.     

应力场强法中场径参数的研究

针对应力场强法中场径计算方法存在争议且不易求取的问题,基于应力场强法假设,研究了场径参数计算方法的理论依据;在考虑场径求取可行性的基础上,提出一种在任意载荷条件下确定试件场径的方法.给出了场径的求取步骤,选取6块不同应力集中系数的缺口试件在4种应力比下,按照步骤求取场径.对场径计算结果拟合并作图,由图所示分析影响场径大小的因素.得出结论:在相同应力比下,场径与应力集中系数呈很强的线性关系;在相同应力集中系数下,场径与应力比呈很强的二次曲线关系.通过实例对所提出的方法进行了验证,结果表明:由提出方法确定的场径计算得出的疲劳寿命更贴近于试验寿命,在保证安全的基础上提高了疲劳寿命预测的准确性.     

磁流变液的流体动力学理论

在外加磁场作用下,磁流变液从牛顿流体变成了Bingham体,超过屈服应力开始流动,其的流变性(弹性、塑性、粘性)、磁化性、导电性、传热性以及其它的机械性质和物理学性质皆发生显著的改变.研究磁流变液在外加磁场作用下,流场分布规律随磁场强度变化的动态特性,建立磁流变液的流体动力学理论,对开发和设计磁流变器械至关重要.本文运用物理学和流体力学的基本理论,结合本构方程,考虑磁场对磁流变液的流动的影响,建立了磁流变液力磁耦合的流体动力学模型,给出了描述磁流变液流动的基本方程组.     

Thermal Residual Stress Distribution in Carbon Fiber/Novel Thermal Plastic Composite

Thermal residual stress is one of the major factors affecting composite mechanical performance. In this paper, a 3-D FEA technique was utilized to analyze the thermal residual stress distribution in Carbon fiber/PPESK composite. Parabolic failure criterion was used to predict composite potential failure zone. Results indicate that, thermal residual stress distributions in different parts of the composite are different. At composite free end zone, the maximum thermal residual stress is located at fiber surface; in composite inner zone, the maximum stress is located in the matrix; at composite defect zone, stress concentration is located at defect surface. Thermal residual stress at composite free end zone will lead to fiber–matrix interfacial de-bonding. Thermal residual stress concentration at composite defect zone will decrease composite mechanical performance.     

Theoretical and experimental determination of magnetic stress intensity factors of a crack in a double cantilever beam specimen

This paper presents the results of an experimental and theoretical investigation of the magnetic fracture behaviour of double cantilever beam (DCB) specimens. DCB tests were conducted on ferritic stainless steel SUS430 in the bore of a superconducting magnet at room temperature. A simple experimental technique using strain gauges was used to determine the stress intensity factor. The experiments show the predicted increase in the stress intensity factor with increasing magnetic field. The theoretical analysis is based on a beam‐plate theory for magnetoelastic interactions in a soft ferromagnetic material. Numerical calculations are carried out, and the stress intensity factor is obtained for several values of magnetic field. A comparison of the stress intensity factor is made between theory and experiment, and the agreement is good for the magnetic field considered.     

Effect of stress concentration on magnetic flux leakage signals from blind-hole defects in stressed pipeline steel

Stress-dependent magnetic flux leakage (MFL) signals of the normal surface component (radial) MFL signal from blind-hole defects in pipeline steel were investigated. Three different stress rigs with uniaxial stress and field configurations were used. A double-peak feature in the MFL signal was defined quantitatively by a saddle amplitude, which was taken as the difference between the average of the double peaks and the corresponding saddle point. Results indicated that the saddle amplitude increased linearly with increasing tensile surface stress and decreased, or did not exist, for increasing compressive surface stress. Finite-element calculations indicated that stress concentration also increased with increasing defect depth. The measurements and analysis demonstrate that the stress-dependent saddle amplitude behavior in the radial MFL signal is associated with surface-stress concentrations near the blind-hole defects.