STRENGTH CRITERION FOR PLAIN CONCRETE UNDER MULTIAXIAL STRESS BASED ON DAMAGE POISSON’S RATIO

A new unified strength criterion in the principal stress space has been proposedfor use with normal strength concrete (NC) and high strength concrete (HSC) in compression-compression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. Thestudy covers concrete with strengths ranging from 20 to 130 MPa. The conception of damagePoisson's ratio is defined and the expression for damage Poisson's ratio is determined basically.The failure mechanism of concrete is illustrated, which points out that damage Poisson's ratiois the key to determining the failure of concrete. Furthermore, for the concrete under biaxialstress conditions, the unified strength criterion is simplified and a simplified strength criterion inthe form of curves is also proposed. The strength criterion is physically meaningful and easy tocalculate, which can be applied to analytic solution and numerical solution of concrete structures.     

Micro-mechanical approximation to the stress field around an inclined fiber of FRCC

Matrix spalling or crushing is one of the important mechanisms of fiber-matrix interaction of fiber reinforced cementitious composites (FRCC). The fiber pullout mechanisms have been extensively studied for an aligned fiber but matrix failure is rarely investigated since it is thought not to be a major affect. However, for an inclined fiber, the matrix failure should not be neglected. Due to the complex process of matrix spalling, experimental investigation and analytical study of this mechanism are rarely found in literature. In this paper, it is assumed that the load transfer is concentrated within the short length of the inclined fiber from the exit point towards anchored end and follows the exponential law. The Mindlin formulation is employed to calculate the 3D stress field. The simulation gives much information about this field. The 3D approximation of the stress state around an inclined fiber helps to qualitatively understand the mechanism of matrix failure. Finally, a spalling criterion is proposed by which matrix spalling occurs only when the stress in a certain volume, rather than the stress at a small point, exceeds the material strength. This implies some local stress redistribution after first yield. The stress redistribution results in more energy input and higher load bearing capacity of the matrix. In accordance with this hypothesis, the evolution of matrix spalling is demonstrated. The accurate prediction of matrix spalling needs the careful determination of the parameters in this model. This is the work of further study.     

希尔新屈服准则另一简化形式的外凸范围及m值对屈服轨迹的影响

本文根据泰勒公式推导出了屈服而外凸的一般条件。在而内同性的情况下,研究了文献[1]中所推荐的新屈服准则的外凸性,讨论了屈服轨迹随 m 值的变化规仲以及屈服轨迹的变化对板枓压延性分析的影响。     

The National Soil Information System (NASIS): Designing soil interpretation classes for military land-use predictions

The focus of the National Cooperative Soil Survey is shifting from producing static, printed soil survey reports to providing a dynamic resource of soils information for a wide range of needs. The National Soil Information System (NASIS) is the core component of this vision and is designed to manage and maintain soil data from collection to dissemination. NASIS supports this conceptual shift in three important areas: (1) collection of new information in compliance with standards, (2) application of expert knowledge to make information usable for a variety of purposes, and (3) dissemination of information to a wide variety of users. This paper demonstrates the use of NASIS for evaluating the suitability of military lands for vehicle related land-use activities.     

Prediction of incipient shear band trajectories in a thick wall cylinder explosion test

A simple but precise and physical mechanism-based mathematical expression is proposed to predict shear band trajectories in thick wall cylinders subject to external surrounding pressure. The expression is based on the Coulomb-Mohr fracture criterion and can be applied to various compression-sensitive materials, especially ceramics. The predicted result closely matches the experimental observations, which makes this method quite useful in testing material behavior. This expression also permits the extraction of the parameter μ in the Coulomb-Mohr criterion from experimental observations. Furthermore, no pre-assumptions or after-test measurement are necessary in order to carry out the prediction. The only two values needed to conduct the prediction are the initial inner radius and the friction coefficient μ. A comparison between the newly proposed model and existing theory is made to reveal their relations and demonstrate the effectiveness of the newly derived mathematical expression.     

Electroelastic analysis of a piezoelectric finite wedge with mixed type boundary conditions under a pair of concentrated shear forces and free charges

The antiplane problem of a piezoelectric finite wedge with mixed type boundary conditions (i.e. traction free-electrically grounded or clamped-electrically insulated) assumed on the circular edge is studied in this paper. Using the first and second kinds of the finite Mellin transforms, the stress and electrical displacement in the piezoelectric finite wedge subjected to a pair of concentrated shear forces and free charges are derived analytically. The singularity orders and all generalized intensity factors can also be obtained. After being reduced to the crack problem, the energy density theory is applied to study the effects of the boundary conditions on the circular edge and the wedge radius on the fracture behaviors of the cracked piezoelectric medium. The problem can be further degenerated to several simple problems and the results agree well with those of previous studies.     

Stability of annular flow and slugging

In this work we propose an effective viscosity criterion for the stabilization of annular gas-liquid and liquid-particle flows and an inertial mechanism which drives waves into slugs in slugging gas-liquid flows. Annular flow is stable when the fluid having the higher effective viscosity occupies the core region and the lower viscosity fluid is in the annulus. The eddy viscosity criterion is shown to be very consistent with published work on annular flow transitions in horizontal and vertical gas-liquid flows. It also applies to a variety of liquid-solid and gas-solid flows. In the second part of the paper we propose a mechanism for explaining the growth of initially small waves and initiation of slugs in gas-liquid flow.     

Instability of an Unbounded Elastic Plate in a Gas Flow

The stability of an unbounded plane elastic plate in gas moving on one side of the plate and at rest on the other is analyzed. The gases are inviscid and in general different. The plate is under tension and has flexural stiffness. It is shown that the system is always unstable to plane sinusoidal perturbations with wave vector parallel to the velocity. As limiting cases, a tangential discontinuity between the two gases and unilateral flow past a plate with constant pressure on the opposite side are considered. In these cases, the conditions of stability to plane perturbations are non-trivial and are investigated below.     

材料持久极限曲线的逼近和疲劳与屈服强度校核的判据

本文根据材料的对称循环持久极限σ－１和静载强度极限σｂ，提出脉动循环持久极限σ０的估算公式．在此基础上，结合材料持久极限曲线，建立了塑性材料构件在应力循环特性ｒ＞０情况下对其进行疲劳或屈服强度校核的判据．     

复合材料层合板的HOFFMAN塑性区尺寸因子

本文在Hoffman强度准则的基础上,采用复合材料层合板第K层中心穿透裂纹尖端附近的应力分量,得到一个计算复合材料层合板Hoffman塑性区尺寸因子的公式.