弹性体材料微塑性变形与称重传感器非线性

本文提出了弹性体材料微观组织的微塑性变形是产生传感器非线性的原因之一的新观点。通过对载荷、微塑性变形、应变、输出之间的关系在原理上进行分析,探讨了弹性体材料微塑性变形对称重传感器非线性的影响规律以及进程输出曲线的形状特点,并指出控制钢材成份和改进热处理工艺以减少软质相是缩小非线性的途径。     

Surface asperity deformation under bulk plastic straining conditions

The paper is concerned theoretically and experimentally with the flattening of asperities by tools in metal-forming processes, a topic important to lubrication in metal forming. It specifically studies the plane strain compression process. It proposes kinematically admissible velocity fields for the crushing of asperities on a plastically flowing foundation and by adjusting independent variables of the fields predicts the actual flows by an energy minimization method. The theoretical predictions are compared with plane strain compression tests on aluminium samples with surfaces abraded in the direction of bulk plastic flow (the condition that the modelling describes). Both theory and experiment predict that asperities are crushed at the start of bulk plastic compression, to generate a real area of contact a certain fraction of the tool area depending on the contact friction and aspect ratio of the flow field, between 0.75 and 0.95 according to theory and between 0.6 and 0.8 according to experiment; but that with further bulk compression these contact fractions do not change. Despite these quantitative differences, it is felt that the method developed in this paper could usefully be extended to study asperity behaviour in other forming processes such as drawing or rolling.     

The plastic extension of a chain of rings due to an axial impact load

The plastic response of a chain of circular rings due to an axial tensile impact load was investigated both experimentally and in part, analytically. Chains were built-up from circular aluminium rings and subjected to axial impact loading at one end. High-speed photography was employed to record the development of the deformation process. It was found that plastic collapse was progressively transmitted to neighbouring rings in the manner of a plastic wave. To investigate the situation analytically, a simplified approach was adopted which assumed rigid-perfectly plastic behaviour of the ring material and arrived at an equation of the same form as the classical one-dimensional elastic wave equation.     

Dynamic instability analysis of a non-autonomous system subjected to moving impulsive non-conservative load

When a force is applied tangentially on the main axis of beam-type structure, it is well known that the system becomes non-conservative. Dynamic instability of tube excited by moving follower force discretely and periodically is investigated. The effective stiffness of system becomes non-stationary due to time-dependent follower force. Floquet theory is employed to examine the heteroparametric instability regions in the system parameter space. It turns out that there exist two type of instability that are due to parametric and combination resonances, which are confirmed through numerical simulation. Unique features which occur in parametric vibration are also discussed.     

Large plastic deformation of beams of angle-section under symmetric bending

The large deflection flexural behaviour, particularly in plastic range, of beams of right-angle section under four-point symmetric bending is investigated thoroughly. Experiments were carried out for symmetric bending of aluminium alloy L-beams to observe the global load-deflection characteristics, as well as the distortion of cross-sections. The effect of supporting condition in the four-point bending on the global behaviour of the L-beams was also examined experimentally. By considering the geometrical change of beam and the plastic energy dissipations due to the global bending of beam and the angular distortion of cross-sections, a rigid, linear hardening model is proposed. The model is capable of predicting the crosssectional distortion and the structural softening behaviour observed in the experiments with a reasonable accuracy.     

加筋平托盘均布载荷作用下的变形研究

根据板的小变形理论,对平托盘次要结构进行简化,将加筋平托盘面板看成厚度变化的加筋平板,利用在均布载荷条件下板的变形公式,解出了此时的加筋板变形挠度解,并通过改变加筋板各几何参数,得到了加筋板不同的刚度分布,进而分析对最大变形的影响。研究表明,加筋板各几何参数在不同的取值范围对板的最大变形贡献有差异。为筋的厚度与面板厚度之间尺寸的协调设计提供了依据,对平托盘在结构尺寸的初期设计,如何分布配置材料具有一定的实际指导意义。     

Analytical approximations to large post-buckling deformation of elastic rings under uniform hydrostatic pressure

This paper presents analytical approximations to large post-buckling deformation of a circular, elastic, and inextensional ring under uniform hydrostatic pressure. By combining the Newton's method with the method of harmonic balance, we establish analytical approximations to large deformation of the ring. Unlike the classical method of harmonic balance, the linearization is performed prior to proceeding with harmonic balancing thus resulting in a set of linear algebraic equations instead of one of non-linear algebraic equations. We are hence able to establish analytical approximate solutions. These approximate solutions show excellent agreement with the exact solution, and are valid for small as well as large difference of the curvatures of the undeformed and the deformed ring.     

Mechanics of nonmonotonic plastic deformation

Dimensionless invariants for assessing the stress–strain state in specific stamping operations are analyzed. Their influence on the stability of plastic deformation is discussed.     

Dynamic model for the calculation of smooth solids,taking account of plastic deformation

A dynamic model describing the introduction of a smooth rigid sphere in a uniform elastoplastic hardened solid is considered. On the basis of the model, numerical-analytical formulas describing the behavior of a solid in the elastoplastic region of contact interaction are proposed. These formulas allow the influence of the dynamic load on the indentation depth to be taken into account.     

Dynamic deformation under a modified split Hopkinson pressure bar experiment

This paper presents a modified split-Hopkinson pressure bar (SHPB) technique. The dynamic stress-strain behaviors were estimated at room temperature and subzero temperature to −75°C by using the conventional SHPB and compared with a modified SHPB technique. A computer simulation using a finite element algorithm is also performed to study the dynamic material responses. Furthermore, we attempt to find a proper material constitutive law by using the simulation process. It is suggested that the modified SHPB test used in this study can be successfully utilized to offer an experimental condition of a higher strain rate than that obtained from the conventional SHPB test.     

内压作用下斜接管容器塑性极限载荷的数值研究

对三台具有斜接管的圆柱形容器(θ=30°,45°,60°)在内压作用下的塑性变形特征及塑性极限载荷进行了三维非线性有限元数值研究.结果表明:斜接管与筒体截交区纵向截面的锐角侧材料首先进入塑性状态.截交区附近出现明显的塑性变形,纵向截面内发生径向收缩,而横向截面出现明显的径向鼓胀,接管与筒体间的夹角减小.结果同时提供了三台容器的极限载荷值,为该类容器的分析设计提供了依据和参考.     

The stability of plastic deformation in tension

Different concepts of the term “stability” are discussed and the resulting stability conditions in tension are derived. Particular importance is given to the relation between stability and the type of heterogeneities that may occur in tensile specimens. It is shown that a general instantaneous criterion of stability, in terms of the deformation properties of the material, cannot be formulated. However, if finite deformations are considered it is possible to derive general necessary criteria, which depend, of course, on the definition of stability adopted.The results obtained can explain the experimental observations concerning the phenomenon of necking in tensile tests, particularly its “weak” relation to the point of maximum load.     

复杂载荷变刚度静不定梁通用力学模型及变形方程

对复杂载荷下变刚度静不定梁建立了一种通用力学模型，得出梁任一截面的变矩方程。通过对变矩方程的积分和积分后方程的递推，推导出梁任意截面的转角和挠度变形的一般方程，并给出工程计算实例。该方程易于采用计算机处理，为复杂载荷下变刚度静不定梁程序化求解提供基础。     

Finite plastic deformation of a circular membrane under hydrostatic pressure—I: Rate-independent behaviour

The large strain behaviour of a circular membrane under uniform hydrostatic pressure is examined for materials with transversely isotropic plastic properties. Time-independent material response is assumed, and both flow theory and deformation theory of plasticity are considered.A variational principle is first applied to derive the governing equations for the pressurized membrane. It is shown that a special solution previously given by Hill[7] for isotropic materials can readily be extended to certain transversely isotropic membranes.A finite element solution based on Hill's extremum principle[24] is then developed to study the influence of anisotropy on the finite deformation behaviour of the membrane. Conditions where localized-necking bifurcations become possible are also discussed.     

塑料模具的动态仿真

对Pro/E软件中的塑料顾问模块进行阐述,并以CD盒的冷流道注射模具浇注系统为例,对注射过程中注射压力、时间、填充质量以及温度变化情况进行模拟分析,分析结果对实际加工具有指导意义.     

Static contact under load between nominally flat surfaces in which deformation is purely elastic

In considering the contact between two rough surfaces, an asperity-based model has been obtained by applying the most general Hertzian equations for elastic deformation to the random surface model of Longuet-Higgins. For a given separation, general formulae for the expectations and variances of the load and real contact area and for the mean number of contacts are given, whilst for the variance of the number of contacts an upper bound has been derived. The formulae, involving analytically intractable integrals, have been evaluated in a special case by Monte Carlo techniques.     

Contact friction in the deformation zone during ultrasonic surface plastic deformation

It is shown that the introduction of torsional ultrasonic oscillations in the deformation source reduces the work of the frictional forces in comparison with the application of radial and longitudinal ultrasound or the absence of ultrasound. The application of torsional ultrasound to the deforming element reduces the contact-friction coefficient by a factor of 20–60, as against a factor of two or less when radial and longitudinal ultrasound is applied to the contact zone. With increase in the rolling rate and decrease in oscillation amplitude of the deforming element, the effectiveness of ultrasound application declines.     

Surface plastic deformation of an applied metal layer

The deformation of an applied surface layer of austenitic metal is considered. The optimal reduction is established.