The cutting of soil by narrow blades

The available models for predicting the forces acting on a narrow soil cutting blade have required separate measurements of the shape of the three-dimensional soil failure pattern ahead of the blade. It is proposed that a three-dimensional model consisting of straight line failure patterns in the soil can be used to predict both the draft forces and the volume of soil disturbed in front of a narrow blade. Limit equilibrium mechanics equations are written for the soil wedges in terms of an unknown angle of the failure zone and the theoretical draft force is minimized with respect to this angle. Force factors are thus found which are of the type to fit Reece's general earthmoving equation, but which vary with the width to depth ratio of the blade as well as with the rake angle of the blade and the friction angle of the soil. In addition the approximate geometry of the three-dimensional failure pattern in the soil is predicted for varying blade shapes and soil strengths. This allows the design of simple tools on the basis of their draft force requirements and their soil cutting efficiency. The draft force predictions and failure geometry calculations are shown to have considerable verification by experimental results.     

Inverse problem of fracture mechanics for a disk fitted onto a rotating shaft

A plane problem of fracture mechanics for a circular disk fitted onto a rotating shaft is considered. The disk is assumed to be fitted tightly onto the shaft, and there are N randomly located straight-line cracks of length 2l_k (k = 1, 2, ..., N) near the inner surface of the disk. The interference between the disk and the rotating shaft, providing minimization of fracture parameters (stress intensity factor) of the disk, is theoretically studied on the basis of the minimax criterion. A closed system of algebraic equations is constructed, which allows the problem of optimal design to be solved. A simplified method of minimization of disk fracture parameters is considered. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 201–209, July–August, 2009.     

The inception and evolution of earthmoving soil mechanics

Soil and test conditions important to earthmoving machinery have been found to be significantly different from all other fields of endeavour with the partial exception of tillage studies. This could be the subject of a long dissertation. Broadly, however, soil conditions which produce critical mobility problems are much too soft and/or wet to be of concern to the earthmoving contractor who has to meet rigid specifications on acceptable types and moisture contents of fill soils. Occasional soft spots are considered as nuisances instead of indicators of the need for major design compromises.

Civil engineers are concerned with the same types of soil, but in a vastly different context. They must design soil structures which will never reach initial soil failure. Earthmoving processes, on the other hand, must accept soil failures in many different forms and degrees and utilize post-failure soil strength to perform their tasks efficiently.

Tillage studies display many important similarities to earthmoving studies, particularly in regard to the types of soil failures of importance. They are, in reality, merely another form of earthmoving; by definition, if nothing more. Earthmoving processes can range into much stronger soils, but this alone is insufficient to set them apart.

The term Earthmoving Soil Mechanics was introduced in 1962⁽²⁰⁾. This paper more clearly defines the implications of the new terminology and illustrates the first successful application of soil mechanics and model analysis principles in the earthmoving industry.     

A dynamic model for soil cutting by blade and tine

A dynamic model for soil cutting resistance prediction by blade and tine was developed, taking account of shear rate effects both on soil shear strength and soil-metal friction, besides the conventional soil slice inertia, for both brittle and flow failure of soil. The model was verified with a series of tests in a soil bin with a blade and a tine, and the results were acceptable.     

国外土力学本科教学探讨——以挪威科技大学为例

 教材建设、课堂教学以及实验教学是工科本科生培养的一个重要环节, 本科教材编写 和教学也要与时俱进, 不断创新、发展和提高. 土力学作为土木工程等专业一门重要专业基 础课程, 一直受到各相关高校普遍重视. 文中从教材编写、教材内容、国外课堂教学以及实 验教学等方面阐述了国外土力学教学的特色, 希望能对国内的土力学教材编写和课程教学有 一定的参考.     

Finite element analysis of plane soil cutting

This study develops the finite element method (FEM) of solution to provide a theoretical means for determination of soil performance under the actions of a cutting blade—and the forces required to promote cutting. The developed FEM takes into account the effect of progressive and continuous cutting of the clay soil at the tip of the blade, with possible development of failure zones in the soil whenever the shear strength of the soil is exceeded. The solution provides detailed information on stress and deformation fields in the soil, together with tangential and normal pressures developed at the blade soil interface Correspondence between theoretically computed displacement fields and measured values has been obtained. In addition, the theoretically computed and experimentally measured values for forces developed in blade thrust are seen to be in close agreement.     

如何用好土力学——对青年土木工程师谈土力学的理论与应用

针对青年学生和年轻的土木工程师在工程实践中如何使用好土力学的理论这一问题进行了讨论.指出了土力学理论与其它土木工程结构理论的根本区别,以及工程经验和判断力的重要性,并就工程经验和判断力以及如何进行培养展开了讨论.本文还对如何阅读土力学文献和如何选择土力学数学模型进行了论述.最后还列出了Casagrand[2]对实际应用土力学理论的要求.     

Large rotating states of a conducting elastic wire in a magnetic field: subtle symmetry and multiparameter bifurcation

In this paper we consider large-amplitude, steadily rotating states of a flexible, nonlinearly elastic, current-carrying wire in a magnetic field. Our formulation leads naturally to a multiparameter bifurcation problem. A detailed local analysis is ostensibly intractable, due to the presence of the rotation group SO(2). However, we identify an additional, more subtle symmetry, which enables a standard local bifurcation analysis via group-theoretic methods. In contrast to well known methods of local equivariant bifurcation theory, we first exploit the group invariance of the full problem (before performing a local reduction) to construct a reduced problem that is also amenable to a global analysis, which we provide.Supported in part by the U.S. Army Research Office through the Mathematical Sciences Institute of Cornell University, Contract DAAG29-85-C-0018, and by the Air Force Office of Scientific Research, Grant No. AFOSR-88-0222.     

The dynamic calibration of a hot wire by means of a sound wave

Hot wires of various design, operated by the constant resistance method, were calibrated by means of a plane sound wave of 2500 Hz. This is achieved by locating a small open resonance tube axially in a homogeneous incompressible airflow. Its third harmonic is excitated by superimposing a coaxial, damped, progressive, plane wave on the main airstream. The hot wire to be calibrated is situated in an anti-node of the particle velocity. The amplitude at this station is known from the pressure gradient of the standing wave measured at two small holes in the wall by a probe microphone. This device in turn is calibrated in a specially developed “pistonphone”. Numerical results of the diverse designs are communicated; an absolute accuracy of ±2% is achieved.     

Measurement and interpretation of space-time correlation functions and derivative statistics from a rotating hot wire in a grid turbulence

A family of autocorrelation functions and derivative statistics are measured by a rotating hot wire in a grid turbulence. The autocorrelation functions, at various probe radii and speeds, can be rescaled with the probe effective velocity suggesting that Taylor's hypothesis is satisfied. The effects of the random convecting speed and the temporal change which would violate the hypothesis are however effectively removed in computing the autocorrelation functions. For the derivative statistics, it is shown that the eulerian temporal derivative statistics can be determined from the time derivative statistics measured by the moving probe at two different speeds based on the principle of Galilean invariance. The Reynolds number dependence of the eulerian temporal derivative mean square values suggests that the main contribution comes from the nonlinear acceleration terms in the limit of high Reynolds number.     

Thinking of several problems in soil mechanics teaching

在给本科生讲授土力学及与学生的讨论中,作者从教学的角度对几个小问题进行了思考.这些思考包括：将不易理解的知识形象化;通过对比强化土的力学特性;土力学中的归一化思想与线性化简化;学生对工程量取值范围的感觉;以及两个相近问题的辨析思考.作者将如上的思考体会在文中通过实例一一介绍,期待前辈及同行的批评与指导.     

土力学教学实践中几个小问题的思考

在给本科生讲授土力学及与学生的讨论中,作者从教学的角度对几个小问题进行了思考.这些思考包括：将不易理解的知识形象化;通过对比强化土的力学特性;土力学中的归一化思想与线性化简化;学生对工程量取值范围的感觉;以及两个相近问题的辨析思考.作者将如上的思考体会在文中通过实例一一介绍,期待前辈及同行的批评与指导.     

The stability of a compressed rotating rod

The classical stability problem of a compressed hinged elastic rod rotating with constant angular velocity about the axis that passes through the hinges is considered. It is assumed that the compressive force is constant and the line of its action coincides with the axis of rotation of the rod. The stability of a solution of the nonlinear problem that describes deformation of the rod under the action of the compressive force and the distributed centrifugal load is studied within the framework of the stability theory of dynamic systems with distributed parameters. The buckling paramcters of the problem are determined. Calculation results are given. Technology Institute, Altai State Technical University, Biisk 659305. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 4, pp. 190–197, July–August, 2000.     

The mechanical behavior of a wire rope with an independent wire rope core

A new model for simulating the mechanical response of a wire rope with an independent wire rope core is presented. The rope is subjected to both an axial load and an axial torque. In contrast with previous models that consider the effective response of wound strands, the present model fully considers the double-helix configuration of individual wires within the wound strand. This enables to directly relate the wire level stress to the overall load applied at the rope level. The model assumes a fiber response of individual wires. Two alternative kinematics of the wires are considered, and are used to predict the elastic response of the rope. The postulated kinematics are theoretically validated and the predicted rope response is in agreement with new experimental data. The new model enables the extraction of the stress at the wire level that can be used in turn to estimate global features of the rope such as force interaction between wires, rope stiffness, strength, and fatigue life.     

Stratification of a gas by an incandescent wire

The propagation of a shock wave in a gas in which there is a wire rendered incandescent by a pulsed electrical discharge enables one to discover the stratified structure in space acquired by the gas as a result of nonuniform heating.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 175–176, July–August, 1984.     

Experimental study of frontal resistance force in soil cutting

The paper presents an experimental study of the frontal resistance forces in soil cutting, with emphasis on their dependence on tool displacement during the loading and unloading stages under quasistatic and dynamic regimes. Laboratory tests on undisturbed soil, using specially developed equipment, showed that:During the loading stage, at pre-limiting levels of the frontal resistance force, the soil undergoes both reversible and residual deformations.At the onset of the unloading stage, the restoring force undergoes a downward jump.The limiting value of the frontal resistance force increases considerably in the cutting velocity interval of 0.1 to 3–5 mm/s; at higher velocities, up to 25 mm/s, this force slowly. At the initial velocity of 3 m/s, the limiting value of the frontal resistance force exceeds by about 20% its counterpart appearing at the velocity of 0.1 mm/s.The frontal resistance force is linearly related to the tool width and non-linearly to the depth of cutting.