J. Maciejewski

Laboratory optimization of the soil digging process

A new idea for the optimization of digging using earth-working machinery is presented and experimentally verified. This idea is based on the conclusions derived from previous papers presented by the same authors, that the soil cutting trajectories incorporating the generated shear band as a part of them are the optimal ones. Dividing the whole excavation task into several repeatable cycles for which the soil free boundary before and after the experiment are similar the optimization of a single cycle plays a significant role in the energetic efficiency of the whole task. A single cycle of the working process is defined using several basing parameters. The influence of each parameter on the specific unit energy of the process was experimentally verified. Finally, a set of values for the discussed parameters is recommended for the particular soil and tool shape.

Failure Criteria and Compliance Variation of Anisotropically Damaged Materials

The damage state is usually described by introducing damage tensor of the second or fourth order. An alternative approach would be based on damage distribution function specifying the damage state on any physical plane. This approach is assumed in the paper. First, the limit state failure condition for a material element is specified by assuming crack density distribution on physical planes. The critical plane approach is next used and the limit condition is obtained in the parametric form with the plane orientation vector to be determined from the maximization of the failure function. The resulting failure condition is applied to the analysis of directional strength evolution of uniaxially compressed specimens with varying orientation of principal stress and damage tensor axes. The damage evolution in a stressed element can also be described by postulating the damage state on the physical plane and its growth due to increasing stress or strain. The damage growth function is assumed and the resulting damage distribution is specified. The associated compliance variation is next determined by accounting for the effect of frictional slip at compressed crack interfaces and opening modes for crack under tensile tractions.

Critical Plane Approach to Analysis of Failure Criteria for Anisotropic Geomaterials

Numerous geomaterials such as rock and soil exhibit structural anisotropy related to material fabric elements such as crack pattern, bedding, layering, contact arrangements, among others. The fundamental problem is associated with the specification of effective properties of the representative material element, accounting for microstructure and defect distribution. The present work is aimed at the derivation of failure criteria for materials with anisotropic microstructure, such as crack pattern, microlaminate structure, or grain contact arrangement. The assumed density distribution function specifies the microstructure used in deriving the failure criteria and damage evolution rules for specified deformation histories. The state of a material is described by the damage density distribution on the physical planes. The critical plane approach is used with account for a damaged and an intact area fraction. The maximum of failure function is specified for all potential failure planes and critical plane orientation is determined. The derived failure condition is applied to study strength evolution for triaxially compressed specimens with varying orientation of principal stress and damage tensor axes. Also a general stress state is considered and the representative failure condition is derived. The application of failure criteria to particular cases is discussed. In particular, the limit states are specified for engineering problems, such as embedded anchor plate pull-out and rigid tool penetration into the material.

Experimental and Numerical Investigations of the Effects Associated to Complex Loading Combinations

The paper presents experimental results concerning evaluation of an influence of cyclic torsion on stress variations during monotonic deformation carried out on the X10CrMoVNb9-1 steel. All strain controlled tests were performed at room temperature using thin-walled tubular specimens. The experimental programme contained selected combinations of monotonic and cyclic loadings, i.e. the torsion-reverse-torsion cycles were superimposed on the monotonic tension. It is shown that such cycles associated with monotonic tension caused essential variations of tensile stress. A significant decrease of the axial stress was visible. A single specimen method for yield surface determination was used to evaluate variations of yield point at different combinations of tension and torsion. The yield surface concept was also used to check permanency of the stress reduction during tension assisted by cyclic torsion. The effects observed during monotonic and cyclic loading combinations were theoretically described using the Maciejewski-Mroz model. It enabled to predict kinematic and isotropic softening or hardening of the material in question. The results exhibited that the model can be used successfully to simulate material behaviour during various combinations of monotonic and cyclic loadings.

Analysis of Energy Consumption of Crushing Processes – Comparison of One-Stage and Two-Stage Processes

Abstract This paper presents experimental comparison of two machine crushing technologies: one-stage and two-stage. The study was carried on a model double-toggle jaw crusher which allows crushing forces, energy and toggle displacement to be measured. The main aim of the work was to determine the energy consumption of crushing process assuming a given level of fragmentation. Studies were performed on three rocks: granite “Strzegom”, limestone “Morawica” and sandstone “Mucharz”. The material tested had a cubic shape and average dimension of 90 mm. One-stage crushing was carried out for outlet slot er = 11 mm, and two-stage crushing for er = 24 mm and 11 mm. In the tests special design of variable profile moving jaw was used and fixed jaw was flat. The analysis of the results shows that taking into account energy consumption, it is better to use two-stage crushing process. For given materials energy consumption in the two-stage crushing process was reduced by 30%.

Evaluation of Influence of Crushing Plates Shape on “Mucharz” Sandstone Crushing Process

This paper presents the results of laboratory tests and evaluation of influence of crushing plates shape on rock crushing process performed on double-toggle jaw crusher. Machine is equipped with diagnostic system that monitors operation of the crusher. Measuring system consists of sensors which are able to determine displacement of moving jaw, forces acting on toggle plate, changes of angular velocity and torque on machine driveshaft. This system allows data acquisition and analysis of acquired signals. The most important parameters that describe crushing process are: crushing forces and specific energy. These parameters were used to evaluate the influence of plates shape in “Mucharz” sandstone crushing process. Tests were carried out on a set of eight plates of different shapes and notches arrangement, i.e., flat plates, plates with triangular profile, plates with coaxial and non-coaxial notches arrangement and plates with constant and variable t scale profiles. Studies show that the plates with triangular profile and variable pitch compared to the flat plates have a positive effect on particle size distribution, loads in the crusher’s working space (crushing forces values), and crushing energy. The product has much less fine fractions for profiled plates but overall process performance decreases comparing to flat plates.

Study on Load Distribution in the Working Space of Lever Crusher

This paper presents laboratory jaw crusher stand equipped with special construction measuring system which allows to determine the load distribution in crusher’s working space. This system consists of nine independent segments, equipped with strain gauges to measure normal and tangential forces and moments. Additionally, crusher’s construction allows to measure forces acting on toggle plate and displacement of moving jaw, changes of rotary velocity and torque on machine driveshaft. In this research exemplary tests results of rock crushing processes realized on three sets of crushing plates were analyzed. Studies were carried out on flat, profiled plates with parallel teeth and plates with variable profile. Analysis of results shows significant differences in the quality of the process depending on the type of used plates. Plates with variable profile are favorable from load distribution and the crushing energy point of view.

Analysis of Deformation and Damage Processes in Soil-Tool Interaction Problems

The processes of interaction of earth-working machines with soils are related to large inelastic deformation inducing soil structure variation with dilatancy, compaction and critical states developing during the process. The effects of hardening, softening, strain localization in shear or tensile rupture bands accompany the machine tools operation in the cohesive soil. The aim of this contribution is to provide simplified incremental analysis of some typical processes, such as soil cutting, digging, filling, and compaction among others, by applying constitutive models relevant to the type of process. The aim of analysis is to predict the deformation modes, forces interaction and energy required for the process, and also to generate optimal process control in order to minimize some parameters of soil-tool interaction.