Numerical Study Of Interaction Between The Bucket Of Excavator And Soil

The wicked construction environment and complicated loads have led to the working device of excavator bearing intense changing actions with a high degree of randomness and complexity during construction,which has placed great demands on the reliability and durability of the working device of excavator.And as part having direct contacts with excavated material of the working device of excavator,the bucket has been directly under the influence of these actions,which is defined as the load spectrum in engineering.So it's of great significance for the structural design and optimization of excavator to study the load spectrum of bucket and master its rules and characteristics.Based on discrete element method for particulate materials,taking the WK-75 bucket for example,the paper has chosen “Linear Contact Model” as contact constitutive relation to build up the three-dimensional numerical model of process of bucket digging excavated material by adopting PFC calculation software which uses wall elements to simulate bucket and clump elements to simulate excavated material.Through calculation and post-processing,the load spectrum of bucket,the curve of mass of material in bucket and the information about doing work of bucket,as well as the conditions of force acting on teeth of bucket during a whole cycle of bucket excavating material,have been obtained and analyzed.In addition,based on principles of control variable method,the paper has simulated the operation process of such bucket which has five kinds of number of teeth and three types of digging track,whose influence on the load spectrum has been discussed and analyzed.DEM simulation has achieved the visualization of the operation process of bucket,which allow the operation process and the information about flow of material to be observed directly.And the operation process is mainly made up of two parts: the early cutting stage and the late lifting stage.During the whole process,the load spectrum of bucket is always fluctuating up and down randomly with varying magnitude,which presents typical randomness and complexity,especially in the early cutting stage this characteristic is particularly evident.The doing work of bucket proves the distribution regulation of the digging resistance from another angle: due to intense fluctuation and variation of the load spectrum in the early cutting stage,the work speed and quantity is very fast and quite large.On the contrary,the work in the late lifting stage is slow and less.As the first tool for bucket excavating material,the teeth have enduring complicated loads with varying magnitude,whose fluctuation is so strong that there is no obvious regularity to be found among the loads every tooth enduring in the early cutting stage.The influence of difference of teeth number upon the load spectrum has been mainly reflected in distribution and magnitude,especially in the early cutting stage there exist overlaps and crossovers among the load spectrum.Meanwhile,resulting from difference of teeth number,the max distinction among the peak mass of material inside the bucket is not greater than 7%,while the max distinction among the final mass of material inside the bucket is not more than 9.7%,which proves that the main function of teeth is to destroy the integrity of accumulated materials rather than improve degree of filling up materials of bucket from another perspective.The diversity of digging track has significant effects on the time the peak value of the load spectrum appeared that the decomposed trajectory is much earlier to peak than the ideal trajectory.Moreover,this diversity has resulted in the difference among the peak value of the load spectrum being not more than 12.2%.In the fluctuating stage after peak,the load spectrum of the ideal trajectory behaves better,whose changes of distribution is more stable and final degree of filling up materials is higher.In addition,by comparing and analyzing their expenditure of energy per ton,it is discovered that both of cost-effect is almost the same.So the ideal trajectory with higher final degree of filling up materials should be chosen on equal conditions in practice.