Papers by Keyword: Maximum Principal Stress

Abstract: This study aims at analyzing the influence of the maximum principal stress on Tungsten Carbide Steel die core in an extrusion die which caused the crack of die core, and then adjusts the dies assembly method in order to improve the service life of die. In this study, combining FEM simulation software with Taguchi Method L₉(3⁴) is to choose the cobalt content for die core materials, and the quantity of shrink fit while assembling the die core and die case as the reference parameters. When carrying out the simulation process, compared the changes of the maximum principal stress of the die core caused by the plastic deformation of die materials to achieve the minimum expected value as the goal be chosen the most optimal die combination. Then, the results obtained are to make dies in trial and mass-production practically; as a result, it can be achieved that the die life is improved from the original 1000pcs to 150000pcs, which is more 150 times better than before.

Abstract: Based on geological conditions of working face 25110 in YiMa coal mine, the ground stress distribution around thrust fault is simulated by using FLAC^3D. In the fault profile, the intersection of fault footwall profile and the middle of coal seam tendency dip profile, ground stress distribution are analyzed. Distress is not continuous because of faults. Coal and rock show different stress states under high stress because of different physical and mechanical properties, and the maximum principal stress and the minimum principal stress distribute consistently with the z axis and the x axis. It provide basis on optimal design of outburst prevention of coal seam with impulsion pressure risk.

Abstract: In first mine of Chagannaoer, 2# coal seam, the mainly mined out layer, was 22.00m thickness in average. In order to meet the requirements of production ability, the mine was planned to apply mining technology of fully mechanized caving. Good or bad of top coal’s caving was an important prerequisite which decided the mining technology of top coal caving could be chosen or not. Due to lack of producing mines in this region and no experience to refer, we simulated the mining process of 2# coal seam using numerical software of FLAC3D, and gained evolution laws of stress and displacement of top coal and overlying strata and expansion laws of plastic zone. Through analysis, we got that the top coal damaged seriously and the top coal could be caved smoothly. Relying on the geological conditions of site, we verified the simulated results with method of fuzzy comprehensive evaluation. Combined with the research results, we decided that 2# coal seam’s caving was better and was convenient for top coal caving, so it was suitable for caving mining in 2# coal seam in first mine of Chagannaoer.

Abstract: Recent earthquakes indicate that tunnels can not be considered as structures invulnerable to earthquakes, especially in areas crossing a fault. Seismic damage, such as falling, fissure and dislocation of the tunnel lining may happen at location of fault. Under the action of earthquake, two kinds of loads may occur, which are the fault movement and the function of seismic wave. In order to analyze the seismic damage to cross-fault tunnel, the seismic characters under each kind of load are studied by using finite element method. Some meaningful conclusions have been achieved. Under the condition of strike-slip fault, the stress of tunnel concentrated at the position of fault, and the stress in both active and driven plate is small. The influence degree of reverse fault is between the other two kinds of faults. By enhancing the lining materials stiffness, the displacement of tunnel decreased, but the peak acceleration and first principle stress of it increased and the position of max-displacement also changed.

Abstract: In this study AZ31 sheet with a thickness of 1.2mm and diameter of 52mm was simulated to press into a dish by a finite element method(FEM) software, which to obtain better processing of plastics forming of magnesium alloy by varying die parameters. In order to find the way of development on drawing property and to formulate the rational stamping processing, simulations have been applied on the maximum principal stress various with round radius of dent die and round radius of punch and die gap. Simulation results show that: to obtain a dish of 29mm diameter, a sheet of AZ31 magnesium with a thickness of 1.2mm and diameter of 52mm has been drawn, the fracture occurring at the corner of dish wall bottom. the ability of drawing varies with the round radius of dent die, which better radius is 3.8 mm. In the same way better round radius of punch is 3.0 mm, while better half gap is 1.8mm. Experiments also show that high diameter ratio has been increased with the various of die parameters and forming ability of material has been developed. It is reliable of simulation of finite element method.

Abstract: Fatigue is one of the most common failure mode in hydraulic excavator boom. To find the most fatigue dangerous operating state of boom and effectively improve the life of the structure, a new method is proposed for the estimation of fatigue life under all operation states. In the case of unknown the history of loading, firstly find out the hinged support force under all boom poses, then calculate the stress of every point of the boom under the actions of each group hinged support force via finite element method, and finally simulate all operating states through the poses combination, conducts analysis of multiaxial fatigue life in the maximum principal stress as the nominal stress, calculates the life and the most dangerous operating state in all points, and compares to obtain the most dangerous position and the life of the boom. The results of contrast analysis showed that: the most dangerous zone of the excavator boom calculated by the life estimation method of all operating states coincide with the actual destruction situation. The life of the structure can be greatly improved after a simple reasonable improvement of the parts.

Abstract: Interfacial delamination is a recognized failure mode in Integrated circuits (ICs). A major cause for this failure is the mismatch of Thermal Expansion Coefficients, Young’s modulus, and Poisson’s ratios of the package materials. Here, the influence of delamination between epoxy and dielectric layers on pattern shift and passivation cracking in IC package under aeronautical conditions, mainly temperature and load cycles, is studied by maximum plastic strain and maximum principal stresses theory using a certain 2D FEM model with different delamination length “L_c.right”. Delaminations are easy to introduce more dangerous impact to the package, because the IC microstructures endure serious thermo-mechanical loading under aeronautical working conditions. The method can be used to find the dangerous designed structure schedules and will provide a basis for selecting passivation materials of aeronautical IC packages.

Abstract: This paper presents our effort to reduce thermo-mechanical failures related IC packaging reliability problems. These reliability problems are driven by the mismatch between the different material properties. First of all, finite element analysis are adopted to investigate the influence of encapsulation structures and material properties on the stress distribution in dielectric layers and plastic strain distribution in die for a typical stacked package of IC microstructures. Results show that thinner package body, lower thermal stress and smaller plastic strain can be realized in this micro-structure with the different design geometry parameters and materials properties. Secondly, it was also found that the transition layer of TiN between the die and dielectric layer has a pronounced influence on decreasing the local stress in the passivation layer by comparison analysis. These studies would be beneficial to improve the reliability of stacked IC micro-structure packages.

Abstract: he transition fillet regions linking the bell crank and the crank-arm and linking the crankarm and the bearing journal are the regions where the strength is the weakest in crankshaft. Based on a crank-shaft model, the effect of the geometric parameters on maximal principal stress at the two transition fillet regions was analyzed using FEM and software ANSYS8.0. It was concluded that the maximal principal stress at the two transition fillet regions is related not only to the transition fillet radius but also to the bell crank length and the crank-arm width.

Abstract: The passivation cracking of Micro-structures of IC packages is studied by maximum principal stress theory using a certain 2D FEM model with different design parameters, pitch of lines, width of line, thickness of epoxy, thickness of dielectric layer, thickness of glue, the glue material’s yielding stress and Aluminium yielding stress (following as “d”, “w”, “t_epo”, “t_Teos”, “t_glue” “sy_glue” and “sy_al” respectively). For different critical process steps, the final process temperature is acted as a representative parameter to analyze its impact. Furthermore, Response Surface Model (RSM) of principal stress is established using any two design parameters. Results show that “d”, “w”, “t_epo”, “sy_glue” and “sy_al” will have great influence on passivation cracking while “t_Teos” have a little impact.