可压缩材料平面应变滑移线场的数值解和边界条件

简要介绍了可压缩材料平面应变滑移线理论。导出了滑移线场应力和速度数值解。处理了应力边界条件，阐明了应力和速度间断规律。举例说明了边界条件处理和数值解步骤。     

用统一平面应就滑移线场理论求解厚壁圆筒的极限荷载

用统一平面应变滑移线场理论，得到了拉压性能不同材料的厚壁圆筒的极限荷载统一解，它也可以适用于拉压强度相等的材料，能充分发挥材料性能，减轻结构重量，取得多方面的经济效益。     

可压缩烧结材料平面塑性变形

本文简要介绍了可压缩烧结材料平面应变滑移线理论。应用该理论和滑移线场数值解确定了可压缩烧结材料平板镦粗时，在宽高比ｗ／ｈ≥ｔｇ（π／４＋θ／２）、接触摩擦系数非零和工件相对密度任意给定的条件下的塑性区、压板压力分布和最大滑动摩擦系数。用烧结铜试样粗糙平板镦粗实验进行了验证。     

半无限体压入简化滑移线场的上限模式的通解

本文导出光滑平冲头压入半无限体的简化滑移线场的上限模式的通解。此通解不仅包含已报道的简化滑移线上限模式解，而且其极限值就是滑移线解。     

FM法锻造的模拟研究

本文利用激光云纹技术[1]模拟了砧宽比（2W/H0）为0.4、0.6、0.8时的平面FM法锻造过程，采用按云纹图修正理论滑移线场的方法[2]，提出了更接近实际的FM法滑移线场，从修正的滑移线场和云绀方图分别得到了变形区静水压应力和等效应变分布，并与普通锻造法的结果进行了比较，结果表明，两种锻造方法在锻件心部产生的最大等效应变相差不大，但EM法产生较大的静水压应力，对消除锻件内部孔洞型缺陷有利。     

用统一平面应变滑移线场理论求解厚壁圆筒的极限荷载

用统一平面应变滑移线场理论,得到了拉压性能不同材料的厚壁圆筒的极限荷载统一解,它也可以适用于拉压强度相等的材料,能充分发挥材料性能,减轻结构重量,取得多方面的经济效益。     

各向异性强化材料的滑移线场理论

1.前言滑移线场的理论和方法是求解塑性平面应变问题最有效的方法之一.一般定义最大剪应变速率方向的迹线为滑移线。经典的滑移线场理论所得到的沿α、β两族滑移线的应力方程为dp+2Kdθ=0(1—1)式中p为静水压力,K为剪切屈服应力,θ为x轴方向与主应力σ_1方向的夹角.速度方程为     

确定塑性平面应变滑移场方向的一个简便方法

滑移线理论是解决塑性平面应变问题的一个重要方法。只要作出滑移场,决定了α线和β线的方向,同时确定场内任意一点的平均应力σ,则可以通过Hencky方程     

滑移线教学中粗糙平冲头压入半无限体的非Prandtl解探讨

针对经典教材滑移线理论教学中光滑平冲头和粗糙平冲头压入半无限体计算结果相同问题,构建了粗糙平冲头压入半无限体的非Prandtl滑移线场。与Prandtl场解相比,摩擦的存在使单位接触压力和应力状态影响系数增加了11%,与光滑平冲头压入半无限体计算结果相比,x方向的应力增加约82%,计算结果更能准确反映摩擦使变形力增加的塑性理论,有助于学生理解滑移线法以及滑移线理论的研究和应用。     

和界面接触的刚性线夹杂对SH波的散射

利用积分变换方法，得出了两相材料中单位简谐力的格林函数。根据简谐集中力的格林函数得出了和界面接触的刚性线的散射场。利用无穷积分的性质，把和界面接触刚性线的散射场分解为奇异部分和有界部分。通过分解后的散射场建立了和界面接触剐性线在SH波作用下的Cauchy型奇异积分方程。根据所得奇异积分方程和刚性线的散射场得到了刚性线端点的奇异性阶数及奇性应力。应用刚性线端点的奇性应力定义了刚性线端点的应力奇异因子。对所得Cauchy型奇异积分方程的数值求解，可得刚性线端点的应力奇异因子。     

纯钼烧结体压缩变形本构模型建立

基于可压缩连续材料的屈服准则和塑性本构关系,推导了粉末烧结材料的压缩变形屈服条件,采用真空烧结技术制备了不同密度的钼,通过在MTS810实验机上进行单向压缩试验,研究了在不同的初始密度,变形温度和应变速率的条件下,纯钼烧结休压缩变形流变应力的变化规律.建立了其流变应力的经验回归模型,进而确定了纯钼烧结材料压缩变形的屈服...     

Micromechanical analysis of friction anisotropy in rough elastic contacts

Computational contact homogenization approach is applied to study friction anisotropy resulting from asperity interaction in elastic contacts. Contact of rough surfaces with anisotropic roughness is considered with asperity contact at the micro scale being governed by the isotropic Coulomb friction model. Application of a micro-to-macro scale transition scheme yields a macroscopic friction model with orientation- and pressure-dependent macroscopic friction coefficient. The macroscopic slip rule is found to exhibit a weak non-associativity in the tangential plane, although the slip rule at the microscale is associated in the tangential plane. Counterintuitive effects are observed for compressible materials, in particular, for auxetic materials.     

A finite strain constitutive model for metal powder compaction using a unique and convex single surface yield function

Constitutive modelling of metal powder compaction processes is a challenge in view of realistic simulations. To this end, the article under consideration has two objectives: the first goal is to present a new unique and convex single surface yield function for pressure dependent materials, which is also applicable to other areas of granular materials such as soils or concrete. The flexibility is shown at various materials. The yield function is based on a log-interpolation of two known simple yield functions. A convexity proof of the new yield function is provided. The second objective is to propose a new rate-independent finite strain plasticity model for metal powder compaction, which is based on the multiplicative decomposition of the deformation gradient into an elastic and a plastic part with evolution equations for internal variables representing the basic behaviour of powder materials under compaction conditions. These variables are used for the evolution of the yield function in order to represent the compressible hardening behaviour of powder materials. On the basis of the constitutive model, the material parameters are identified at experimental data of copper powder.     

Constitutive Models for Compressible Nonlinearly Elastic Materials with Limiting Chain Extensibility

Constitutive models are proposed for compressible isotropic hyperelastic materials that reflect limiting chain extensibility. These are generalizations of the model proposed by Gent for incompressible materials. The goal is to understand the effects of limiting chain extensibility when the compressibility of polymeric materials is taken into account. The basic homogeneous deformation of simple tension is considered and simple closed-form relations for the deformation characteristics are obtained for slightly compressible materials. An explicit first-order approximation is obtained for the lateral contraction and for the Poisson function in terms of the axial extension which is shown to be valid for each of two specific compressible versions of the Gent model. One of the main results obtained is that the effect of limiting chain extensibility is to stiffen the material relative to the neo-Hookean compressible case. Mathematics Subject Classifications (2000) 74B20, 74G55.     

Static crack resistance of iron‐based sintered powder materials

A boundaryvalue problem of static crack resistance of structurally heterogeneous sintered materials is formulated within the framework of the structurally phenomenological approach. A numerical algorithm for modeling the mechanical behavior of structurally heterogeneous cracked powder materials is proposed. Crack resistance of some structurally heterogeneous powder materials is estimated. The anomalous character of the crack resistance revealed is studied with the use of fractography. Theoretical findings are supported by results of mechanical cracking tests.     

High-order time integration applied to metal powder plasticity

The present article treats two objectives. In the first investigation attention is focused on the application of time-adaptive finite elements formulated on the basis of a high-order time integration procedure on a constitutive model for compressible finite strain viscoplasticity for metal powder. In this connection, it has to be emphasized that the integration procedure is not only applied to the evolution equations on Gauss-point level but on the total system of differential–algebraic equations resulting from the application of the vertical line method on the quasi-static finite element equations. The specific application emerges from the field of metal powder compaction. Particular studies are carried out using stiffly accurate, diagonally implicit Runge–Kutta methods in combination with the Multilevel-Newton algorithm for solving the DAE-system. In this respect, the effort vs. accuracy behavior is investigated which is also related to order reduction known in elastoplasticity. The second topic treats the local stress algorithm for taking into account the yield function based finite strain viscoplasticity model, where the classical Newton–Raphson method fails. This is the reason why most constitutive models of powder materials are implemented into explicit finite element codes. Thus, the proposed investigations compare different methods in view of a stable and efficient integration process in implicit finite element formulations.     

Investigation of metal extrusion and axial compression of compressible media by means of a modified slab method

Summary A modified slab method for the investigation of the axisymmetric forming of compressible materials is introduced. It is based on the elementary slab method, the main difference being the additional variable relative density, describing the porosity. The material itself is modeled as rigid-plastic, with a yield condition given by [6]. Reasonable assumptions lead to a model for the forward extrusion and axial compression of powder metals. The results achieved with appropriate material parameters for copper powder correspond with experimental experience. Received 18 February 1997; accepted for publication 14 July 1997     

Experimental investigation on capillary force of composite wick structure by IR thermal imaging camera

A novel sintered–grooved composite wick structures has been developed for two-phase heat transfer devices. With ethanol as the working fluid, risen meniscus test is conducted to study the capillary force of wick structures. Infrared (IR) thermal imaging is used to identify and locate the liquid meniscus. The effects of sintered layer, V-grooves and powder size on capillary force are explored. The results show that the capillary force of composite wick structures is larger than that of grooved and sintered ones. Interaction wetting between groove and sintered powder happens during the liquid rise in composite wick, which provides an additional source of capillary force. It exhibits a variation of capillary force of composite wicks with different powder size due to the difference of open pore size and quantity in sintered porous matrix.     

一种非线性强度准则及转换应力法

岩土材料在二维破坏模式下具有较强烈的曲线形态,在一般剪应力与正应力空间中提出用幂参数曲线来表达上述曲线,该曲线与摩尔圆的外切点即对应为破坏应力点,则利用该点的外切直线斜率的反正切值来得到有效滑移角.对于三维单元体,共存在三个有效滑移角,利用三个有效滑移角确定出空间有效滑移面.基于岩土材料为摩擦型材料这一基本特性,利用空间有效滑移面上的应力比为一定值作为衡量材料破坏与否的判断准则,基于上述思路推导得到了t强度准则,在偏平面上,t准则开口形状为介于Von-Mises圆形曲线到SMP曲边三角形形态.在子午面上,引入开口的幂函数作为反映静水压力效应以及剪切破坏的曲线,而闭口的水滴型屈服面函数作为反映体积压缩屈服曲线,反映了岩土材料的压剪耦合特性.基于所提出的t强度准则, 推导了变换应力公式,可将以$p,q$为应力量的二维模型简单方便的转换为三维应力状态本构模型.通过强度以及多种应力路径的测试对比,验证了所提t准则及基于该准则的变换应力公式的合理性.      

On Compressible Materials Capable of Sustaining Axisymmetric Shear Deformations. Part 4: Helical Shear of Anisotropic Hyperelastic Materials

Conditions on the form of the strain energy function in order that homogeneous, compressible and isotropic hyperelastic materials may sustain controllable static, axisymmetric anti-plane shear, azimuthal shear, and helical shear deformations of a hollow, circular cylinder have been explored in several recent papers. Here we study conditions on the strain energy function for homogeneous and compressible, anisotropic hyperelastic materials necessary and sufficient to sustain controllable, axisymmetric helical shear deformations of the tube. Similar results for separate axisymmetric anti-plane shear deformations and rotational shear deformations are then obtained from the principal theorem for helical shear deformations. The three theorems are illustrated for general compressible transversely isotropic materials for which the isotropy axis coincides with the cylinder axis. Previously known necessary and sufficient conditions on the strain energy for compressible and isotropic hyperelastic materials in order that the three classes of axisymmetric shear deformations may be possible follow by specialization of the anisotropic case. It is shown that the required monotonicity condition for the isotropic case is much simpler and less restrictive. Restrictions necessary and sufficient for anti-plane and rotational shear deformations to be possible in compressible hyperelastic materials having a helical axis of transverse isotropy that winds at a constant angle around the tube axis are derived. Results for the previous case and for a circular axis of transverse isotropy are included as degenerate helices. All of the conditions derived here have essentially algebraic structure and are easy to apply. The general rules are applied in several examples for specific strain energy functions of compressible and homogeneous transversely isotropic materials having straight, circular, and helical axes of material symmetry.