Modelling Of Crack Propagation in Flexible Pavement Using X-FEM Method

A research aim was to achieve a finite element model for predictive pavement cracking implementing ABAQUS software ver.6.12.1. A simulation model for pavement structure was implemented to analyze the propagation of cracks within flexible pavement. The X-FEM method adopted in this research based on the functions of interpolation that can characterize the displacements near the crack zone, initial crack was defined at the bottom of asphalt layer. The estimated results illustrated that X-FEM was efficient for the simulation of cracks in pavement structures without the need for re meshing during crack propagation evolution process. Finally, inclusive simulation results probed the considerable effect for improvement of bonding layers to enhance the service life of pavement in terms of decreasing the rate of crack propagation. The crack was propagated upwards from depth end of asphalt layer to pavement surface and deviated from center of applied pressure with an inclination of almost 300 in the third upper zone of asphalt layer while the pre-crack point was always located in the bottom of asphalt layer in pavement model because of the different characteristics of their bonding bases. In the crack zone the permanent deformation was increased gradually from the crack edge along vertical direction of crack spread due to tensile stresses concentration at the crack zone. The action of horizontal and vertical stresses affect crack propagation and growth vertically to the direction of higher horizontal tensile stresses, and along direction of higher compression vertical stresses.

MANUFACTURING OF SANDWICH PANELS AND ITS VERIFICATION BY NUMERICAL SIMULATION

This paper deals with the manufacturing of a parallel hydroformed sandwich panel, which is used as a reinforcement for solar panels. The forming process can cause excessive thinning and cracking. Therefore, PAM-STAMP software is used for the analysis of defects. The outputs of the numerical simulation provide information, such as failure pressure, critical areas or limiting deformations. The comparison of the numerical simulation with the experimentally obtained data is created for the validation of these outputs. The comparative criteria are the failure pressure, the crack zone, and the thickness distribution. Subsequently, the results can be used for a design optimization of the sandwich panel.

MECHANICAL PROPERTIES OF CEMENT CONCRETES INCORPORATING GROUND TIRE RUBBER

This article proves the possibility of replacing aggregates in concrete mixtures with rubber, which is obtained by grinding used car tires. It was found that the replacement of crushed coarse aggregate in the amount of 10 vol.% with ground rubber from used car tires increases the bending strength by 23% The compressive strength does not change significantly. When working in the subcritical stage of deformation (until the macrocrack shifts), concrete with the replacement of the coarse aggregate is preferred, as the energy consumption of which for elastic deformation (We) exceeds the base concrete. Analysis of the supercritical stage of deformation (macrocrack propagation) reveals that the replacement of fine and coarse aggregates negatively affects the value of total energy consumption for local static deformation in the main crack zone (Wl), which is by 1.35 and 1.14 times lower than the control concrete.

Numerical Analysis for the Caving Characteristics of Rock Mass with Inclined Joints in Caving Mining

In caving mining, the successful initiation and propagation of caving require one low-dip joint set. However, not every mine has a low-dip joint set. The Hemushan Iron Mine in China was taken as the engineering background, and the caving characteristics of rock mass with inclined joints were analyzed based on the synthetic rock mass (SRM) model. First, the inclined joints were investigated in the Hemushan Iron Mine. Second, model parameters were determined based on the geological conditions of the mine, and seven models were established. Third, the caving process was simulated, and caving characteristics were monitored. For rock mass with inclined joints after undercutting, the research showed that the crack zone was significant, and the crack zone existed not only around the undercut area but also further away in the model. The stress concentration areas dispersed in the model except for the top of the undercut area. The caving line was not a standard arch, and the highest point of the caving line was biased towards the direction of the undercut. Under the same undercut width, with the decrease of joint length in the joint system, the number of cracks decreased, the degree of stress concentration became weaker, and the height of the caving line decreased.

Discrete Element Simulation Analysis of the Bending and Toppling Failure Mechanisms of High Rock Slopes

The high rock slope situated in the Southwest stope of Taiping Mining, Inner Mongolia, is subject to dumping failure due to its instability. The dumping body rock layer of this stope shows obvious bending and lowering of the head. The overturning angle of the rock strata can reach 46°, and tension dislocation along the rock joint can be observed in exposed sections and at the bedding and lithologic interface. The sliding surface also displays a broken line morphology. Through evaluation of regional rock integrity parameters and rock soft and hard parameters, rock-mass strength based on Hoek Brown strength estimation criteria can be developed. Based on the discrete element method, the geological model of layered excavation of the thin layer slope can be constructed. Combined with indoor and outdoor assessments, the characteristics of toppling deformation of the thin layer open-air slope can be studied and summarized. In this study, simulation analysis showed that under first excavation conditions, a crack-, dump-, and antislip zone was formed. The rock in the crack zone formed a “<”-shaped fracture along the slope surface that was squeezed towards the bottom of the slope. In the lower dumping area, the deflection angle gradually increased with excavation, and the deformation range and levels in the antislip area increased with excavation. Following the third excavation, the antisliding zone disappeared and the toppling line changed from a broken line to a straight line. In the final state, the slope collapsed as a whole, with the collapse of the dumping body penetrating the top to the foot of the slope.

Groundwater Inrush Control and Parameters Optimization of Curtain Grouting Reinforcement for the Jingzhai Tunnel

Based on the systematic study on the characteristics of water and mud inrush during the excavation of Jingzhai tunnel, the mechanism of water inrush seepage transformation caused by excavation disturbance is analyzed. By means of electromagnetic geophysical prospecting, the potential water bearing area of the tunnel was analyzed. The constitutive model of rock mass and grouting parameters are considered in the numerical simulation. The law of tunnel crack initiation and expansion under different curtain grouting parameters is proposed. The characteristics of seepage water inrush caused by excavation are described. It is considered that there are three stages in the seepage characteristics of tunnel: incubation, sudden, and stable. Numerical simulation was used to analyze the crack propagation track and water inflow characteristics under the grouting thickness of 3 m, 5 m, and 7 m. When the curtain grouting thickness was 3 m, the fracture field penetrated the curtain grouting area. The dominant seepage channel is formed, which greatly increases the probability of water inrush. When the curtain thickness is 5~7 m, the expansion of the crack zone can be controlled basically, so that the fracture and water bearing rock layer cannot form a seepage channel. At last, the grouting scheme of 6 m thick grouting and 20 m advanced grouting was selected, and the water seepage was reduced by 83%.

Thermal vision of fracture behavior on acrylic composites

The aim of this work was to investigate thermal properties of acrylate-based composite combined with alumina-based particles. The composites were made of poly (methyl methacrylate) (PMMA) modified with dimethyl itaconate (DMI) as a matrix. As reinforcement were used alumina particles (Al2O3) and alumina doped with iron oxide (Al2O3-Fe) modified with 3-aminopropyl-trimethoxylane (AM) and flax oil fatty acid methyl esters (biodiesel - BD). According to the thermal conductivity measurements, the highest thermal conductivity values had the composite with alumina particles with the highest alpha phase content. With the addition of modified alumina particles to PMMA/DMI matrix mechanical properties were improved (tensile strength, modulus of elasticity and elongation at break). Composite with 3 wt. % Al2O3-Fe-AM particles had the most improved mechanical properties. It was noticed that this composite, compared to PMMA, had the lowest temperature in a crack zone (10.28%) and that is due to the better stiffness and highest thermal conductivity. The results indicated that the Sobel fractured surface area is related to the crack energy, which is reflected by the temperature of sample monitored by thermal vision.

Investigation of causes of XCMG QY25К lorry-mounted crane accident

The article conducted a study of the causes of the accident of the XCMG QY25K lorry-mounted crane. Visual inspection of the emergency boom (boom in a critical condition) was carried out with the analysis of the state of the material in the broken section. The microstructure of steel in the crack zone was investigated. Chemical analysis of steel with a determination of the mass fraction of chemical elements was performed. Studies of the strength and hardness of material samples were carried out. Theoretically, the maximum tensile and compressive stresses in the section of the failed boom are determined. Comprehensive analysis of the obtained theoretical and experimental research results made it possible to establish the true cause of the accident of the lorry-mounted crane.

Modeling the Flow of Crude Oil in Cracked Pipeline

The form of transportation of energy from the sources to the consumers is the concern of the researchers across the world, this is due to the consequences upon the failures. Some of these failures causing economical losses and environmental damages. Both are worth to be investigated and studied to reduce the risks and losses. In this paper the effects of cracks in pipelines has been investigated, it is found that the crack is causing the decrease in pressure. Several pipes were used in the experiment, one without crack and the rest with different crack size. The pressure drop in the area around the crack (named crack zone) was bigger in the up and down stream zones. Computational fluid dynamics CFD package ANSIS (Fluent) was used in the analysis and the results presented. Because the fluid used in the research is crude oil, so the paper is mainly for the benefit of the oil and gas industries and the pipeline designers and manufacturers.