Papers by Keyword: Crack Propagation

Abstract: Maximum normal stress criterion can be used to determine the cracking angle in the uniform and non-uniform zone. According to this theory, the propagating process of the crack in non-uniform composite material is simulated based on the finite element method. The results show that the crack advances wave-like and basically along the direction perpendicular to the maximum normal stress, which is of great guiding significance for the fracture resistance of such kind of structure.

Abstract: Ceramic materials has approximate color and translucency with natural tooth, which is unmatched by other restorative materials. Because of its beautiful appearance, good physical and chemical properties, all-ceramic crown restorations are more widely used. However, due to the brittleness of ceramics and the stress mismatch between different materials, failure phenomenon is often observed during the service period of all-ceramic crowns. The failure process and mechanism are not clear, in this paper, the force performance of all-ceramic crowns is analyzed using the RFPA (realistic failure process analysis) system. The crack initiation, propagation and failure process of all-ceramic crown can be clearly observed and the research results provide guidance for clinical application.

Abstract: Based on the mesoscopic damage theory and the finite element method, a numerical code RFPA was applied to investigate the rock fragmentation by three TBM cutters loaded one after another in different time interval. The whole process of crack initiation and propagation was successfully simulated by the cutters loaded with different step intervals. The time interval of the disc cutters has significant influence on the fracture patterns and the rock breaking efficiency. The simulated results show that there are three types of breakage mode of the rock subjected to compression by the cutters.

Abstract: Laboratory experiments and numerical simulations, using Particle Flow Code (PFC2D ), were performed to study the behavior of marble under tri-axial loading and pre-existing fissure uniaxial compression. The laboratory tri-axial compression results of marble was analyzed, and the calibration of the micro-properties of BMP (Bonded particle model ) in PFC2D with the test data was carried out successfully. The pre-existing fissure was simulated by smooth joint contact, and the cracking propagation mode of pre-existing fissure was carried out with the calibrated BMP properties and single smooth joint contact. The simulation show that the tensile crack firstly initiated along the vertical direction to pre-existing fissure, and then gradually departs towards the direction of axial stress, and finally develops along the direction of axial during compression. The numerical simulation coincide with our understanding of fracture mechanics.

Abstract: Roller is a main tool and consumption parts for steel rolling. With analysis test on the fatigue property of roller, the development incentives of crack propagation were realized, the service life of roller was improved and the cost of Production was reduced in a large extent. Roller is a circular column, which do fixed-axis rotation under combined action of roll pressure, bearing reaction, Support roller reaction force and torsion. The failure types of roll such as flaking, fracture and crack. Simulate and analysis on damage of the roller crack by the fracture mechanics of knowledge and ANSYS, which shown that compressive was large with the ring and axial and compressive was small with the radial direction, so the compressive of radial direction the analysis had little effect on roll surface.

Abstract: The situation that the grouting borehole doesn’t intersect with natural fractures of rock masses is often met in practical grouting project. Hence, it’s very necessary to discuss whether the rock masses around borehole will split under the grouting pressure and the corresponding splitting orientation. After the splitting crack finishes propagation, we can estimate whether it will penetrate with original fractures, and it’s favorable for grouting theory analysis and numerical simulation and so on. According to this, the splitting criterion and splitting orientation are proposed with and without considering ground stress, respectively. In the meantime, under the situation of splitting, the singularity of crack-tip’s stress field is simulated by 6 nodes singular isoparametric element through secondary development of large-scale finite element analysis software-ANSYS. The stress intensity factor is introduced and the propagation of the splitting crack is simulated to obtain the final propagation length, which has significant guiding meaning to grouting theory and the practical grouting projects.

Abstract: The fatigue life of crane steel structure will inevitably decrease in the course of work, which directly affects the work of crane. So the correct fatigue life evaluation is necessary. Based on crack propagation theory, a framework of assessing remaining fatigue life of crane metal structures is built in this paper. Moreover, in order to descript the analysis process, an example about fatigue life estimation of a shipbuilding gantry crane whose maximum hoist 100 ton was shown. During assessment of remaining fatigue life of aged crane structure, some important indexes were inspected such as corrosion，strength and defection in focused weld joints, besides of finite element simulation of structure. The results can also be used to evaluate the whole metal structure of this crane.

Abstract: Leak before break(LBB) is an important analysis method for insuring the structure safety and reliability of nuclear reactor. Now LBB technology is widely used in nuclear power plant design. It has a good development in foreign countries, but domestic research is relatively little. The study of crack propagation is core of LBB analysis. In this paper the Molecular dynamics simulations of crack propagation for material of pipes in China Experimental Fast Reactor(CEFR) were studied. The temperature on the flaw in the top of the model has a significant effect, and the position of the flaw would affect the damage form and the damage position of material analyzing the deformation of models. For the same model, temperature has a significant effect on crack propagation process. The analysis of this paper has a guiding role for the LBB analysis of pipes from microcosmic angle.

Abstract: In this paper, the thermal fatigue damage phenomenon in the comprehensive temperature environment is studied by means of thermal fatigue damage mechanics and FEM technology, the thermal-stress analysis modal under the comprehensive thermodynamic boundary conditions is established, the regularities of distribution of temperature fields, thermal stress fields effected by the comprehensive coupled variables are investigated. According to the modify of material characteristics under the high-temperature alternating thermal impact conditions and the integrated influences of environment, mechanical parameter and material microstructure to the fatigue fracture, numerical modal of thermal fatigue crack initiation and propagation are developed, so the characteristics of thermal fatigue crack propagation are studied, which are verified by the experiments, it is very significant to study thermal damage question of working equipments in the similar conditions.

Abstract: The fatigue fractography and surface of A7075 aluminum alloy was investigated by means of optical microscope, scanning electron microscope and technology of metallurgic replica. The results show that the fatigue crack generally initiated in the surface or near the surface of the sample area, such as hole and inclusion. The crack propagation regions under high stress amplitude was characterized by furrow and hollow, and obviously presented fine ripple vein. While lots of fatigue striations and sidesteps with the holes and secondary cracks generated in the crack propagation regions of low stress amplitude. Fatigue transient breaking area is a mixed fracture of brittle and ductile fracture. In the fatigue crack propagation stage, with the increasing of cycle times, secondary cracks gradually merged into primary crack on the path of crack propagation. The dislocation of crack tip,grain boundaries and different grain orientations have great influence on the path of crack growth, which can make cracks bending.