A single cone-cap plasticity with an isotropic hardening rule for powder materials

In this paper, a new single cone-cap plasticity with an isotropic hardening rule is presented for powder materials. A general form is developed for the cap plasticity, which can be compared with some common double-surface plasticity models proposed for powders in literature. The constitutive elasto-plastic matrix and its components are derived based on the definition of yield surface, hardening parameter and nonlinear elastic behavior, as a function of relative density of powder. Different aspects of the model are illustrated and the procedure for determination of powder parameters is described. Finally, the applicability of the proposed model is demonstrated in numerical simulation of triaxial and confining pressure tests.     

Influence of hardening rule on prediction of cyclic plasticity in pressurized thin tubes subjected to cyclic push-pull

The paper considers the cyclic plastic behaviour of a thin-walled tube subjected to steady internal pressure and cyclic reversed axial push-pull. Tubes under such a loading combination are known to exhibit continued strain growth in the hoop direction. The steady-state behaviour of the tube is investigated using a number of hardening rules within the framework of time-independent plasticity theory. Isotropic hardening and Prager kinematic hardening are considered first and shown to yield no strain growth at the steady state. When a kinematically hardened yield surface is assumed to translate in the direction of the stress rate vector, considerable steady-state strain growth is predicted in the hoop direction. Consideration of two-surface plasticity theory yields also large steady-state strain growth. Closed-form analytical expressions are derived for growth rates and ranges of cyclic plasticity for all hardening rules considered. Contours of strain growth are plotted for practical ranges of primary and secondary stresses using representative material properties. Comparison with limited test data indicate that the predicted steady growth rate is larger than about four times observed rate.     

A new slide rule for electron microscopy

The principle and the mechanism of a new slide rule is explained and its possible application to solving all of the tasks in electron microscopy with respect to the calculation of sizes, magnifications etc.     

一种新型发泡机的实验研究

把气泡雾化喷嘴与现今流行气泡发生器原理相结合,提出了一种新型发泡机,并详细介绍了新型发泡机中气泡雾化器的设计方法和绕流筒的选择,最后给出了此新型发泡机的实验结果.并与其它方式发出的气泡做了比较,并有较满意的结果.     

A new structure for enhanced transmission through a two-dimensional metallic grating

The spectral response of metallic two‐dimensional periodic structures in which circular apertures are engraved has been extensively studied. We show that in such devices transmission can be highly enhanced by partially shutting the central parts of each aperture in order to make a periodic array of subwavelength coaxial structures.     

On the explosive hardening of one end of a metallic block

Aluminium and mild steel plates were subjected to shock loading on one end by detonating Metabel explosive sheet. The residual stresses in the principal directions were measured using the X-ray, back reflection method, through the specimen thickness.Macro- and micro-structural analyses and micro-hardness surveys of the unloaded specimens were made to examine how the influence of explosive thickness decays with distance from the loaded surface. A central fracture under explosive loading is explained by reference to unloading waves.     

A new approach for rule extraction of expert system based on SVM

Based on the SVM’s excellent generalization performance, a new approach is proposed to extract knowledge rules from Support Vector Clustering (SVC). In this method, the first step is to choose the features of the sample data by using Genetic Algorithm for improving the comprehensibility of the knowledge rules. Then the SVC algorithm is adopted to obtain the Clustering Distribution Matrix of the sample data whose features have been chosen. Finally, hyper-rectangle rules are constructed using the Clustering Distribution Matrix. To make the rules more concise, and easier to explain, hyper-rectangle rules are simplified further by using rules combinations, dimension reduction and interval extension. In addition, the SMOTE (Synthetic Minority Over-sampling Technique) algorithm is adopted to resample fault samples in order to solve the serious imbalance problem of samples. The UCI datasets are used to validate the new method proposed in this paper, the results compared with other rules extraction methods show that the new approach is more effective. The new method is used to extract knowledge rules for aero-engine oil monitoring expert system, and the results show that the new method can effectively extract knowledge rules for expert system, and break through the bottleneck in expert system knowledge dynamic acquisition.     

一种新型金属硬密封蝶阀的设计

针对金属硬密封蝶阀的双向密封问题,基于液压元件设计中的油缸活塞原理,设计了一种在动水作用下带移动密封不锈钢圈的新型金属硬密封蝶阀。对基本结构进行了分析,确定了采用双偏心结构的设计;对正向承压比压、反向承压比压、金属密封圈的移动距离进行了计算,有效地解决了双偏心金属硬密封蝶阀的反向承压问题;对密封副材料选择进行了分析,有效地保证了密封效果和比压要求。     

Ratcheting behavior of cylindrical pipes based on the Chaboche kinematic hardening rule

In this study, cyclic loading behavior of thick cylindrical pipes are described. Effects of internal pressure level and axial strain amplitude on the ratcheting rate under different types of loading histories are investigated. The kinematic hardening theory based on the Chaboche model is used to predict the plastic behavior of the structures. An iterative method is developed to analyze the structural behavior under cyclic loading conditions based on the Chaboche kinematic hardening model.     

The plastic collapse of sandwich beams with a metallic foam core

Plastic collapse modes of sandwich beams have been investigated experimentally and theoretically for the case of an aluminium alloy foam with cold-worked aluminium face sheets. Plastic collapse is by three competing mechanisms: face yield, indentation and core shear, with the active mechanism depending upon the choice of geometry and material properties. The collapse loads, as predicted by simple upper bound solutions for a rigid, ideally plastic beam, and by more refined finite element calculations are generally in good agreement with the measured strengths. However, a thickness effect of the foam core on the collapse strength is observed for collapse by core shear: the shear strength of the core increases with diminishing core thickness in relation to the cell size. Limit load solutions are used to construct collapse maps, with the beam geometrical parameters as axes. Upon displaying the collapse load for each collapse mechanism, the regimes of dominance of each mechanism and the associate mass of the beam are determined. The map is then used in optimal design by minimising the beam weight for a given structural load index.     

Comparison of the work hardening of metallic sheets in bending-unbending and simple shear

Constitutive equations for sheet metals are important input data for the numerical simulation of forming processes. Their identification usually comes from uniaxial tensile tests at several orientations to the rolling direction and from equibiaxial tests. To characterize the kinematic part of the work hardening, strain path reversals are needed and different mechanical tests have been developed, such as tension-compression and simple shear. The aim of this work is to investigate the influence of the database used for identification, by using either bending-unbending or simple shear for strain path reversal. This study is performed both on an aluminum alloy and a TRIP steel. The presented results show that, for a limited strain range, the experiments are consistent.     

Characterization of the three-dimensional structure of a metallic foam during compressive deformation

X‐ray microtomography has been employed to collect three‐dimensional images of aluminium closed‐cell foam, enabling the internal structure to be characterized in three dimensions. An experimental technique and image analysis approach has been developed, and is described, in terms of the labelling of cells and the extraction of quantitative data such as the cell volume and cell compression. An in situ compressive deformation experiment has been performed on a single sample in order to illustrate the approach. The effect of the three‐dimensional cellular structure on the mechanisms of deformation suggests not only the position of large cell volumes to be very important in the local concentration of stress, but also the distribution of cell volumes of immediate neighbours.     

Application of a continuum constitutive model to metallic foam DEN-specimens in compression

The behavior of double-edge notched specimens of metallic foams in compression is studied numerically. To model the constitutive behavior of the metallic foam, a recently developed phenomenological, pressure-sensitive yield surface [1] is used. Compressive yielding in response to hydrostatic stress is incorporated through a dependence on the plastic Poisson ratio ν^p. Results are presented in terms of limit load F_lim, as a function of notch depth, a/W, and the plastic Poisson ratio ν^p. For incompressible plastic behavior, ν^p=0.5, the results show notch-strengthening due to constrained plastic deformation near the crack/notch-tip. For fully compressible plastic behavior (no lateral expansion on uniaxial compression, ν^p=0), no notch-effect is observed. The validity of using a continuum model for the analysis of metallic foam notched specimens is discussed.     

A plasticity theory for porous solids

A plasticity theory is developed for a solid weakened by numerous cracks or voids. The treatment is completely isotropic and would be suitable whenever the voids are nearly spherical or where the direction of cracks is completely random. Using simple models an explicit representation for a second-order yield surface parameterized by the void fraction is presented. The resulting constitutive law is shown to be of the hypoelastic type and simple examples are treated. An approximate expression for a deformation theory is also discussed.     

Influence of hardening rule on the elasto-plastic behaviour of a simple structure under cyclic loading

The modes of cyclic elasto-plastic deformation of a two-bar structure with unequal areas and lengths under the simultaneous action of sustained mechanical load and cyclic thermal history are investigated analytically using three types of elasto-plastic material models: perfectly plastic, linear kinematic hardening and linear isotropic hardening. This simple structure is shown to exhibit much of the behaviour of interest in design of structural components subjected to repeated thermal loads: viz, elastic shakedown, reversed plasticity and ratcheting. The cyclic plastic behaviour of the structure is developed in closed form and the effects of strain hardening, hardening rule and geometrical parameters of the two-bar assembly on the deformation modes are critically examined.     

Evaluation of cyclic plasticity models of multi-surface and non-linear hardening by an energy-based fatigue criterion

This study examines the performance of four constitutive models according to capacity in predicting metal fatigue life under proportional and non-proportional loading conditions. These cyclic plasticity models are the multi-surface models of Mroz and Garud, and the non-linear kinematic hardening models of Armstrong-Frederick and Chaboche. The range of abilities of these models is studied in detail. Furthermore, the plastic strain energy under multiaxial fatigue condition is calculated in the cyclic plasticity models by the stress-strain hysteresis loops. Using the results of these models, the fatigue lives that have set in the energy-based fatigue model are predicted and evaluated with the reported experimental data of 1% Cr-Mo-V steel in the literature. Consequently, the optimum model in the loading condition for this metal is chosen based on life factor.     

A new penalty parameter update rule in the augmented lagrange multiplier method for dynamic response optimization

Based on the value of the Lagrange multiplier and the degree of constraint activeness, a new update rule is proposed for penalty parameters of the ALM method. The theoretical exposition of this suggested update rule is presented by using the algorithmic interpretation and the geometric interpretation of the augmented Lagrangian. This interpretation shows that the penalty parameters can effect the performance of the ALM method. Also, it offers a lower limit on the penalty parameters that makes the augmented Lagrangian to be bounded. This lower limit forms the backbone of the proposed update rule. To investigate the numerical performance of the update rule, it is embedded in our ALM based dynamic response optimizer, and the optimizer is applied to solve six typical dynamic response optimization problems. Our optimization results are compared with those obtained by employing three conventional update rules used in the literature, which shows that the suggested update rule is more efficient and more stable than the conventional ones.