Study On Static Stress Distribution Characteristics In Silos

Silos are widely used in energy,chemical and grain industries.In static conditions,the stress in the silo differs from that of fluid.Due to the powder compaction and the nonuniform stress distribution in the static silo,the rat holes,arching and central flow often occur during the loading and discharging process.Although many experimental research and theoretical analysis have been carried out on the silo.While the stress distribution of the powder in the silo is still not fully understand.Therefore,this paper studied the stress distribution and its influencing factors in the static silo.The effects of the material properties and silo geometric parameter on the mechanism of stress distribution in the silo were explored.In order to obtain the influence of material properties on the powder flowability,the ShearTrac-II shearing system was used to study the flow behavior of the material at the different type,particle size and the external moisture content of the glass bead,corn flour and anthracite.The results showed that the internal friction angle and cohesive force of corn flour were largest than those of glass bead and anthracite.With the decrease of the particle size,the internal friction angle and the cohesive force increased.Therefore,the powder shear force rose and the flow function decreased under the same compaction stress with the decrease in the particle size.The internal friction angle decreased with the increase of the external moisture content.With the increase of external moisture content,the cohesive force of wet granules increased while the flow function decreased because of capillary force.As the external moisture content reached to 6.8%,the powder appeared to be stagnant.The distributions of horizontal stress,vertical stress and wall normal stress of the glass bead were obtained in the three-dimensional plexiglass silo.The results showed that the wall normal stress gradually increased with the height from the outlet.The stress in the cylinder segment tended to decrease.The peak of the stress appeared at the junction.The horizontal stresses at the junction combination of silo were differ slightly and were smaller than wall normal stress.While at the top of the silo,the horizontal stress distribution showed the opposite trend.The vertical stress in the silo gradually decreased from the center to the wall at the junction.The vertical stresses in the remaining planes were substantially equal.The peak of the vertical stress appeared in the center of the silo.Experimental studies on static stress distribution of glass bead,corn flour and anthracite in three-dimensional silos were examined.The material type and average particle size had weak effect on the distribution of horizontal stress.In the cross-section of the cone section at the junction,the wall normal stress of the anthracite was the largest and the wall normal stress of the corn flour was the smallest.The higher the external moisture content,the smaller the wall normal stress of anthracite.The wall normal stress was large with the rough material surface and the low external moisture content in the cross-section of the cylinder section at the junction.With the increase of the cone angle of the silo,the horizontal stress and the wall normal stress in the cross-section of the cylinder section at the junction reduced.The wall normal stress in the cross-section of the cone section at the junction increased and the horizontal stress had little change.In the cross-section of the cylinder section at the junction,the vertical stress was affected by the material bulk density and the friction between the particles and the wall surface.The larger the particle size and the greater the external moisture content,the greater the vertical stress of the anthracite.The difference between the vertical stress of the anthracite with larger particle size and the smaller particle size gradually increased from the center of the silo to the wall.The cone angle had weak effect on the vertical stress.