Shengqiang Jiang

Numerical study of concrete mixing transport process and mixing mechanism of truck mixer

– The purpose of this paper is to establish a new two-phase Discrete Element Method (DEM) model to investigate the movement of fresh concrete which consists of mortar and aggregate. The established DEM model was adopted to simulate the mixing process of fresh concrete based on the commercial software package PFC3D. The trajectories of particles and particle clusters were recorded to analyze the mixing behavior from different scales. On one hand, the macro-scale movement was obtained to make the mixing process visualization. On the other hand, the relative micro movement of the single particle and particle clusters was also monitored to further study the mixing mechanism of the fresh concrete. , – A new two-phase DEM model was designed to simulate the movement of fresh concrete which consists of mortar and aggregate. The linear-spring dashpot model was used to model all the contacts between particle and particle/wall to characterize the viscidity of fresh concrete. Moreover, two sets of parallel bond models were employed to characterize the contact between the mortar particles and mortar/coarse aggregate particles, namely the pbond1 and pbond2. The hybrid treatment enables the current DEM model to handle the yield behavior. , – The mixing process of fresh concrete is mainly composed by the transportation in the x-direction and the overturn and fall off in the y- and z-directions. With these movements in different directions, the concrete particles can be fully mixed in the mixing drum. , – A new two-phase DEM model was proposed and used to simulate the mixing process of fresh concrete. The outcomes of the simulation would be helpful for making the transporting truck visualization and the movement behavior of fresh concrete observable. The model can provide dynamic information of particles to reveal the interaction mechanism of fresh concrete in the truck mixer which is extremely difficult to obtain on-line in physical experiments or building site.

Numerical study on the discharging homogeneity of fresh concrete in truck mixer: Effect of motion parameters

ABSTRACT An adequate discharging homogeneity of fresh concrete is the benefit of avoiding segregation and pipe blocking. In this article, the discrete element method was used to simulate the discharging process of fresh concrete in truck mixer. GB/T 9142 was used to examine the discharging homogeneity through five samples. It was found that the content of coarse aggregate is higher in the first and fifth samples but lower in the third sample than the standard C30 fresh concrete. The homogeneity of the second and fourth samples is higher than the others. These findings are consistent with experimental observations. Moreover, the standard deviation was proposed to scale the discharging homogeneity of mixture, which could present more comprehensive information besides the five samples used in GB/T 9142 standard. The effect of mixing speed, mixing time, discharging speed, and oblique angle on the discharging homogeneity was further discussed. The numerical results reveal that the discharging homogeneity of fresh concrete increases when the mixing speed increases from 1 to 2.5 rev/min, but decreases when the mixing speed further increases from 2.5 to 3 rev/min. The discharging homogeneity increases with the decrease of discharging speed, the oblique angle, and the transport mixing time.

The Analysis of the Flexible Load Sharing Structure of the Ring Gear in Planetary Transmission

Based on the problem that the tooth root stress increased under the thin rim and the deformation of the inner ring gear is not enough under the thick rim, this paper proposes a new flexible load sharing structure of the internal ring gear, which can further improve the deformation of the internal ring gear by the combination of bolts and elastic cotter pins, So that the teeth stress can meet the design requirement while improving the load performance. However, an optimized space existed for the system deformation with flexible internal load, the design of the bolt and elastic cuff also requires strength analysis. In this paper, ABAQUS finite element analysis of the flexible radius, pin thickness and pin number on the stress and deformation of bolts and elastic pin are studied to explore the maximum deformation and reasonable combination of the structural parameters by an orthogonal simulation, the sensitivity analysis is carried out for the bolt deformation, the stress for the bolt and elastic pin. The research of this paper can provide theoretical guidance for the design of planetary gear box ring gear.

A Numerical Study of the Effect of Loading Profiles on Mixing/Segregation of Particles in the Truck Mixer via DEM

Discrete element method (DEM) was employed to study the mixing of two sizes of particles in a truck mixer. The effects of five different loading profiles on the mixing/segregation of particles were discussed. The contact ratio between particles was adopted to quantitatively analyze the particle mixing/segregation degree. The simulation results revealed that the motion of particles in the radial direction is more intense than in the axis one, which leads to the radial mixing/segregation faster and more obvious. It was also indicated that different initial states in the radial direction have little influence on the final mixing states, but the influence in the axial one cannot be ignored. The small particles are more likely to get into the big particle clusters, which can lead to the increase of the mixing/segregation in both axial and radial directions.