软磁复合材料铁芯电机特性的仿真研究

为了发挥软磁复合材料的高电阻率,低损耗,易于再利用的特点,仿真模拟将其应用在永磁电机的铁芯上.以12槽4极直流电机为仿真对象,把三维计算问题转化成二维模型,用JMAG软件对电机进行建模,阐述SMC与硅钢片铁芯差异,先用两种材料进行仿真,结果说明只靠替换铁芯材料对电机性能改进并不会产生很大改善,改进模型,得出不同延伸高度铁芯延伸长度增加引起的电流和转矩特性与功率变化的关系.利用所建模型将Somaloy500的软磁复合材料与50CS800的硅钢片制备的铁芯进行模拟实验,结果表明:相同条件下软磁复合材料铁芯的效率要更高一些.最低转速时效率增加5%,最高转速时效率增加10%;软磁复合材料铁芯模型抑制电流输出,各向同性的优势明显.结论为SMC材料在低转速电机的开发中依旧能够发挥优势,实现电机性能的提高.     

Loss behavior of viscoelastic sandwich structures: A statistical-continuum multi-scale approach

This work presents a multi-scale model of viscoelastic constrained layer damping treatments for vibrating plates/beams. The approach integrates a finite element (FE) model of macro-scale vibrations and a statistical-continuum homogenization model to include effects of micro-scale structure and properties. The statistical-continuum homogenization model makes the micro- to macro-scale transition to approximate the effective behavior of the heterogeneous core by using n-point probability functions. A simple sound transmission model is used to show the effect of material microstructure on the sound transmission loss of the sandwich structure. The damping behavior resulting from the presence of voids and negative stiffness regions in the core material is modeled. This study clearly shows that, it is of high interest to research either material structures or processing techniques which lead to negative stiffness behavior. The results also poignantly show that the proposed multi-scale model yields insight on heterogeneous material behavior leading to increased damping properties and ultimately enhances the ability to design sandwich beam/plates.     

A Theoretical Framework for Core Material Properties Identification in Cellular Solids using Novelty Detection

Abstract:  This paper presents a novelty detection-based technique to identify core material properties of honeycombs and cellular structures. A numerical model (finite element) representing full scale and/or reduced size of the cellular solid is used to generate transmissibilities between topological homologous points at cells in different locations. In order to make the procedure robust against noise, these transmissibilities are artificially corrupted. This step is representative of a series of experimentally obtained measurements which automatically return information relating to the size and shape of data noise along with the mean measurement. The next stage, both in this paper and in the proposal for the experimental approach, is to generate several further sets of transmissibilities from the finite element model; the only difference being that the core material properties are altered from the original values. A novelty detection framework is then adopted to find a similarity measure between each of these 'test' transmissibilities and the original set thereby identifying the material properties. Although this work is concerned with identifying only one material property, the methodology extends to identifying several properties.     

7075铝合金高速搅拌摩擦焊材料流动行为及性能研究

目的 针对7075–O铝合金高焊速、高转速搅拌摩擦焊接缺陷多、质量差等问题,研究焊接接头材料流动对焊缝性能的影响。方法 选用焊接速度1 000 mm/min,搅拌转速分别为1 000、1 200、1 600、1 700 r/min的条件对7075–O铝合金板进行搅拌摩擦焊接,分析不同焊接工艺参数下焊接接头的显微组织及力学性能。同时,利用Fluent软件模拟7075–O铝合金搅拌摩擦焊接过程中的材料流动场分布,分析焊接材料流动与缺陷形成的关系。结果 利用7075–O铝合金三维流动模型,预测出高焊速条件下焊缝前进侧形成一个低压区,孔洞等缺陷易出现在此区域,数值模拟预测与试验结果吻合。在高焊接速度1 000 mm/min、焊接转速1 200 r/min时,焊缝表面光滑平整,焊核区域的硬度分布更加均匀。结论 随着搅拌转速从1 000 r/min增大到1 700 r/min,热输入量逐渐增大,孔洞缺陷由隧道型孔洞转变为不连续的小孔。同时,随着搅拌转速的增大,焊缝高硬度区域的宽度先增大而后降低。当搅拌转速为1 200 r/min时得到了优质的焊接接头,焊缝焊核区硬度分布均匀,硬度值最高为176HV。     

核-壳型聚合物乳液对照像性能的促进和稳定作用

人工合成聚合物被广泛应用于卤化银感光材料,改善其物理力学性能。经过试验发现,特殊设计,合成的核－壳型聚合物乳液用于 化银感光材料涂层中,不仅能提高胶片的物理力学性能,对照像性能也能产生促进和稳定作用;在胶片的人工老化过程中,对照像性能,尤其是反差和感光度的衰退起到明显的抑制作用,特别适用于高感、高反差印刷制版胶片。在大量应用试验的基础上,对其作用机理作了有益的探讨。     

A high-order theory for the analysis of circular cylindrical composite sandwich shells with transversely compliant core subjected to external loads

A new model based on the high order sandwich panel theory is proposed to study the effect of external loads on the free vibration of circular cylindrical composite sandwich shells with transversely compliant core, including also the calculation of the buckling loads. In the present model, in contrast to most of the available sandwich plate and shell theories, no prior assumptions are made with respect to the displacement field in the core. Herein the displacement and the stress fields of the core material are determined through a 3D elasticity solution. The performance of the present theory is compared with that of other sandwich theories by the presentation of comparative results obtained for several examples encompassing different material properties and geometric parameters. It is shown that the present model produce results of very high accuracy, and it is suggested that the present model, which is based on a 3D elasticity solution for the core material, can be used as a benchmark in future studies of the free vibration and buckling of circular cylindrical composite sandwich shells with a transversely compliant core.     

High-order free vibration analysis of sandwich plates with both functionally graded face sheets and functionally graded flexible core

Free vibration analysis of functionally graded material sandwich plates is studied using a refined higher order sandwich panel theory. A new type of FGM sandwich plates, namely, both functionally graded face sheets and functionally graded flexible core are considered. The functionally graded material properties follow a power-law function. The first order shear deformation theory is used for the face sheets and a 3D-elasticity solution of weak core is employed for the core. On the basis of continuities of the displacements and transverse stresses at the interfaces of the face sheets and the core, equations of motion are obtained by using Hamilton’s principle. The accuracy of the present approach is validated by comparing the analytical results obtained for a degradation model (functionally graded face sheets and homogeneous flexible core) with ones published in the literatures, as well as the numerical results obtained by finite element method and good agreements are reached. Then, parametric study is conducted to investigate the effect of distribution of functionally graded material properties, thickness to side ratio on the vibration frequencies.     

Approximate elastic-plastic analysis of the static and impact behaviour of polymer composite sandwich beams

An elastic-plastic beam bending model has been developed to simulate the post-upper skin failure energy absorption behaviour of polymer composite sandwich beams under three-point bending. The beam skins consist of woven and chopped strand glass, while the core is a resin impregnated non-woven polyester material known as Coremat. A polyester resin was used for the construction. The theoretical model consists of a central hinge dominated by a crushing core and tensile elastic strains in the lower skin. Experimental measurements of the non-linear force-deflection characteristics for the beam are compared to the theoretical predictions from the model, and it is shown that the shear crushing of the core has an important effect on the behaviour of the beam. The model shows that the most important material properties are the lower skin tensile failure strain and the core crushing strength. Dynamic effects are included in the model in the form of a strain rate dependence of the core crushing stress and the strain rate dependence of the failure strain in the lower skin. The increase in material strength with strain rate gives rise to an improved energy absorption capacity for the beam under impact loading.     

Moisture diffusion in composite sandwich structures

The mechanical properties of polymer core materials in sandwich structures are often degraded by moisture that is absorbed during storage. To date, there is no reliable model to predict the amount of moisture that is present in these sandwich core materials. A multi-layer diffusion model applicable to these sandwich structures is described in this report. Inputs to this model are: (1) diffusivities of core and face sheet materials as functions of temperature, (2) moisture saturation data as a function of relative humidity, and (3) sandwich structure exposure history. The output is a prediction of the amounts of moisture in the core material and face sheets as a function of time.

In order to validate this model, moisture diffusion experiments were performed on a sandwich material consisting of graphite–epoxy face sheets and a core of Rohacell^® polymethacrylimide 200WF foam. Samples of this material were dried, and then hydrated at either 32 °C or 65 °C at either 83% or 100% relative humidity. The face sheets were separated from the core and each component was weighed, dried, and weighed again in order to determine the moisture distribution in the sandwich structure. The results were then compared with the model predictions.     

Consideration of Core Segregations on the Formability of Bearing Steel

In this paper the influence of core segregations on the formability of workpieces made of bearing steel is analysed and discussed on the basis of compression tests. First the necessary material properties and flow curves, taken at different regions of the bar stock material, were investigated. The core segregation material shows significantly higher flow stress at higher strain rates than the surrounding segregation‐free material. Further a strong influence of the forming temperature on the flow stress was found. On basis of these findings an FEM‐model was developed, that considers the core segregation properties, its shape and position. The results of the compression simulation with this model show a clear impact of the inhomogeneous material properties on the stress distribution.     

The influence of correlating material parameters of gradient foam core on free vibration of sandwich panel

For the sandwich panel with mass density gradient (DG) foam core, the Young's modulus of the core varies with the mass density along the thickness direction. To characterize the correlative effect of Young's modulus and mass density of the DG closed-cell foam material, a simplified formula is presented. Subsequently, based on a high-order sandwich plate theory for sandwich panel with homogeneous core, a new gradient sandwich model is developed by introducing a gradient expression of material properties. Finite element (FE) simulation is carried out in order to verify this model. The results show that the proposed model can predict well the free vibration of composite sandwich panel with the gradient core. Finally, the correlating effects of material parameters of the DG foam core on the natural frequencies of sandwich panel are investigated. It is found that the natural frequencies of sandwich panels decrease as the gradient changes of the DG foam cores increase under the condition of that the core masses keep constant.     

Surface layer stiffness effects on fracture of polymer multilayers: a linear elastic model

A tough thermoplastic polymer may show a transition to brittle behaviour when a skin of different properties forms on, or is painted or bonded onto, its free surfaces. A small-scale yielding, linear elastic analysis of the core material, in combination with an axisymmetric plate analysis of the skin, is used here to explore the role in this phenomenon of skin-core modulus inequality. When applied to the homogeneous (equal modulus) case, this very simple constraint model appears to provide independent support for the ASTM thickness criterion for plane-strain LEFM test validity. When applied to previously published impact fracture data from inhomogeneous (polyethylene-polypropylene) sandwich plates, the model successfully explains the shift in brittle-tough transition temperature precipitated by bonding a polypropylene skin to a polyethylene core. The model offers specific predictions for the effect, on transition temperature shift, of variables such as skin thickness and core properties; these predictions remain to be verified.     

Optimal design and parameter estimation of frequency dependent viscoelastic laminated sandwich composite plates

Recent developments in optimization and parameter estimation of frequency dependent passive damping of sandwich structures with viscoelastic core are presented in this paper. A finite element model for anisotropic laminated plate structures with viscoelastic frequency dependent core and laminated anisotropic face layers has been formulated, using a mixed layerwise approach, by considering a higher order shear deformation theory (HSDT) to represent the displacement field of the viscoelastic core, and a first order shear deformation theory (FSDT) for the displacement fields of adjacent laminated face layers. The complex modulus approach is used for the viscoelastic material behaviour, and the dynamic problem is solved in the frequency domain, using viscoelastic material data for the core, assuming fractional derivative constitutive models. Constrained optimization of passive damping is conducted for the maximisation of modal loss factors, using the Feasible Arc Interior Point Algorithm (FAIPA). Identification of the frequency dependent material properties of the sandwich core is conducted by estimating the parameters that define the fractional derivative constitutive model. Optimal design and parameter estimation applications in sandwich structures are presented and discussed.     

纸木复合蜂窝材料蠕变性能研究

主要是利用四元件Burger模型对纸木复合蜂窝材料蠕变性能进行研究,其中蠕变实验采用三点弯曲的加载方式.研究结果表明:四元件模型可以用来模拟纸木复合蜂窝材料的短期蠕变行为;瞬间弹性变形和延迟弹性变形均随着应力水平的加大而加大;参数A和B、 C和D关联度大小依次为B＞D＞C,该材料的瞬时弹性变形和延迟弹性变形之间联系紧密.建议可通过单板与纸板直接胶合来提高纸木复合蜂窝复合材料的胶接性能.     

Guides “bimorphes” d''ondes ultrasoniques “bimorph” ultrasonic wave guides”

An analysis of the dispersion of elastic waves is presented for two types of long ultrasonics wave-guides that we qualify of “bimorph”: (i) a “three-layer” guide made of two different materials and (ii) a “clad core” guide built up of a rectangular core surrounded by a cladding, the materials of the rod and cladding having different properties. An analytical model is proposed to describe the extensional, flexural and torsional motions in “bimorph” wave guides having two geometrical and material symmetry axes. The asymptotic behaviour of the model allows one to select the material properties which lead to modes guided essentially either in the central layer or in the core of the bimorph guide. Moreover, the dispersive properties of a “bimorph” can be controlled through the choice of geometrical and material parameters.     

Elastic/plastic indentation hardness and indentation fracture toughness: The inclusion core model

A new model for determining elastic/plastic indentation is presented. This model generalizes Johnson's incompressible core model to a compressible material and allows the indentation pressure to be transmitted via a misfitted inclusion core beneath the indenter which is surrounded by a hemispherical plastic zone. The internal stress field inside the core is obtained by applying Eshelby's spherical inclusion problem together with Hill's spherical-cavity expansion analysis. The plastic deformation considered here exactly ensures compatibility between the volume of a material displaced by the indenter and that accommodated by expansion. The analysis explains the essential relationships between the dimensions of the indentation and plastic zone and the dominant material properties; yield stress, hardness and elastic modulus. The solution is extended to evaluate the indentation fracture toughness by taking into account the reduced half-space constraint by the image force.     

Multiscale modelling of the composite reinforced foam core of a 3D sandwich structure

A key objective dealing with 3D sandwich structures is to maximize the through-thickness stiffness, the strength of the core and the core to faces adhesion. The Napco^® technology was especially designed for improving such material properties and is under investigation in this paper. In particular, the potential of the process is characterized using a micromechanical modelling combined to a parametric probabilistic model. An experimental analysis is further detailed and validates the theoretical estimates of the core-related elastic properties. It is readily shown that the technology is able to produce parts with significantly improved mechanical properties. Finally, thanks to the probabilistic aspect of the modelling, the study allows to establish a link between the randomness of the process and the uncertainties of the final mechanical properties. Thus, the present approach can be used to optimize the technology as well as to properly design structures.     

A new scheme of many-body potentials for hcp metals

A nonspherical symmetric model of embedding atom potential is schemed for hexagonal close-packed (hcp) metals. The empirical embedding energy function and core–core repulsion used in this paper are based on the embedded atom theories of Daw–Baskes (D–B) and Finnis–Sinclair (F–S). The cohesive energy, vacancy formation energy, bulk modulus and elastic constants of five hcp metals are calculated and compared with the experimental data. The results show that it is useful in the calculations of mechanical and cohesive properties of hcp metals and can be used in computer simulations of the study of material properties with molecular dynamic method.     

Thermo-mechanical load interactions in foam cored axi-symmetric sandwich circular plates – High-order and FE models

This work presents analytical and finite element analysis (FEA) results of the thermo-mechanical non-linear response of an axi-symmetric circular sandwich plates with a compliant foam core. The study investigates the load–thermal interaction response of a sandwich panel where the properties of the core are temperature dependent and degrade as the temperatures are raised. It presents briefly the governing equations for a sandwich plate based on the principles of the high-order sandwich panel theory (HSAPT) which incorporates the effects of the vertical flexibility of the core material as well as the effects of temperature independent/dependent mechanical properties of the foam core. The effects of the thermal degradation of core material on the thermo-mechanical non-linear response of a simply supported circular sandwich plate are studied through the analytical and FE models. The difficulties involved in non-linear geometrical FE modeling of sandwich panels with a compliant “soft” core with temperature-dependent mechanical properties are discussed. The HSAPT model predictions are compared very well with FE result. An important conclusion of the study is that the interaction between mechanical loads, temperature induced deformations, and degradation of the mechanical properties due to elevated temperatures, may seriously affect the structural integrity of foam cored sandwich plates.