Papers by Keyword: Limit Load

Abstract: At present the orthotropic pressurized metal structure is generally used as the isotropic one, ignoring the anisotropic characteristics of material caused during rolling process. At the same time, the elastic stress analysis design method is commonly used in pressure vessel, and the load capacity coming from plasticity of material has not been utilized. Therefore, elastic-plastic analysis of orthotropic pressurized structure is of great theoretical significance and engineering value. In present paper the limit load of orthotropic titanium cylindrical shell under internal pressure was studied. By finite element method with twice elastic slope criterion the variations of limit load for orthotropic and isotropic titanium cylindrical shells under different diameter-thickness ratios were investigated. The effect of orthotropic mechanical property on limit load of titanium cylindrical shell was discussed. At the same time, the difference of limit loads between orthotropic and isotropic titanium cylindrical shells was compared. The calculation results show that the limit loads of orthotropic and isotropic titanium cylindrical shell increase with the diameter-thickness ratio, and the limit load of orthotropic titanium cylindrical shell increases more obviously. Additionally, if the yield strength of isotropic cylindrical shell is the same as or close to the yield strength of circumferential direction for orthotropic titanium cylindrical shell, the difference of limit load is smaller. While the yield strength of isotropic cylindrical shell is much different from the yield strength of circumferential direction for orthotropic titanium cylindrical shell, the difference of the limit load is higher.

Abstract: In order to evaluate the safety and integrity of piping with local wall-thinning at elevated temperature, a numerical method for plastic limit load of modified 9Cr-1Mo steel piping is proposed in the present paper. The limit load of piping at high temperature is defined as the load-carrying capacity after the structure has served for a certain time period. The power law creep behavior with Liu-Murakami damage model is implemented into the commercial software ABAQUS via CREEP for simulation, and the Ramberg-Osgood model is modified to consider the material deterioration effect of modified 9Cr-1Mo steel by introducing the creep damage factor into the elasto-plastic constitutive equation. For covering the wide ranges of defect ratios and service time periods, various 3-D numerical examples for the piping with local wall-thinning defects, and creep time are calculated and analyzed. The limit loads of the defected structures under high temperature are obtained through classic zero curvature criterion with the modified Ramberg-Osgood model, and the typical failure modes of these piping are also discussed. The results show that the plastic limit load of piping containing defect at elevated temperature depends not only on the size of defect, but also on the creep time, which is different from the traditional plastic limit analysis at room temperature without material deterioration.

Abstract: Pressure vessel contained with different nozzles which caused geometric discontinuity of the pressure vessel wall, which resulted in stress concentration around the nozzle. There may be the chances of failure of vessel junction, which was attributed to the high stress concentration. Therefore, detail stress distribution analysis need to be done for pressure vessel with the nozzle. Determination of limit pressure at different location on lateral nozzle by using finite element method. Lateral nozzle was subjected to internal pressure and in-plane bending moment. Results found that plastic hinge occurred in the nozzle-vessel junction area shoulder. Plastic limit loading increased with the increasing of outside diameter and wall thickness of branch pipe when the size of primary piping was constant value, whereby the influence of outside diameter of branch pipe was more remarkable. Moreover, engineering estimation formulas of plastic limit in-plane bending moment was obtained based on plastic limit loading database.

Abstract: In this paper, the elastoplastic stress analysis of a novel parabola-arc-shaped head subjected to internal pressure has been carried out using finite element method. Limit loads and burst pressures are obtained for various geometric parameters and compared with the conventional torispherical and ellipsoidal heads. For the same middle diameter and thickness, the novel parabola-arc-shaped head shows better mechanical performance than the torispherical head. The burst pressure is mainly determined by the size of cylinder and the burst always occurs in cylinder. The head can improve the burst load when the cylinder is relatively short. The improvement of the novel parabola-arc-shaped head is almost the same as the ellipsoidal head, while the torispherical head is slightly inferior. As the novel parabola-arc-shaped head can be more easily formed with less material consumed compared to the conventional ones, it should thus be applicable in engineering practice.

Abstract: The local wall thinning(LWT) is a kind of common volume defect in pressure pipe. The limit loads of elbows with LWT under pressure, bending moment, torque and their combined loads have been studied in detail by orthogonal experimental design and finite element method. The results have shown that the influence of depth and circumferential length of LWT on the limit load is more obvious compared to that of axial length when an elbow is under pressure, bending moment or torque. The change of limit bending moment and torque with the depth of LWT and circumferential length is significant for an elbow under combined bending moment and torque. At last, the safety assessment equations for elbow under combined in-plane closing bending moment and torque were proposed by regression analysis.

Abstract: Increasing the beam cross section is a kind of traditional and universal strengthening methods of civil structure. The mechanical performance test were studied on the mechanics performance and deformation of four reinforced concrete beams in this study. The results show that increase of the cross section and tensile area at the bottom of the steel could effectively improve the performance of mechanical. The beam crack load, yield load, ultimate load and bending strength are increasing with cross section and mechanical. By simulating the relationship bwteen load and deflection. It is concluded that The finite element simulation of reinforced concrete beam with the reasonable concrete unit and reinforced unit can meet the demand of practical engineering.

Abstract: This paper discusses the plastic limit load of elbows without defects and with local thinned area (LTA) in the extrados under combined pressure and in-plane closing bending moment. Finite element analysis (FEA) and experiments have been used. The results of FEA show that, for the elbows without defects, when the ratio of pressure to the limit pressure (P/PL) is smaller than 0.469, the limit moment of elbows increases with the increasing pressure; when the ratio (P/PL) is bigger than 0.469, the limit moment of elbow decreases with the increasing pressure. For the elbows with LTA, the FEA results show that with different LTA the variation of the limit load of elbows to the pressure is different. Perhaps, the limit moment of elbows always decreases with the increasing pressure. It is also likely that the limit moment of elbows increases with the increasing pressure and then decreases with the increasing pressure. The results of FEA are consistent with the experimental results. By fitting the results of FEA, the safety assessment figure for elbows under combined pressure and in-plane closing bending moment is drawn.

Abstract: As the important airborne equipment of casualty aeromedical evacuation, the structure design of aeromedical evacuations stretcher bracket not only has to meet the mounting interface in the civil aviation aircraft and meet the medical rescue requirements during the casualty evacuation, and also has the good bearing capacity of limit load. A structure design of frame-type aeromedical evacuations stretcher bracket is presented in this paper. Based on the finite element method (FEM), the ultimate bearing capacity of the bracket attachment of this structure is analyzed with nonlinear mechanics, and then the intensity and stiffness under the case combinations of limit load are simulated and analyzed to ensure the good security and reliability of the stretcher bracket during the casualty aeromedical evacuation.

Abstract: The bucket is a metal entity, linked to a machine called DRAGLINE, used for loading the different sizes of granular materials in large quantities. Each bucket is provided with six teeth which in contact with materials to be discharged, in order to extract the mineral. These teeth are connected to the bucket via a semi-rigid connection. In operation, except for the wear phenomenon "normal", some teeth break after a few hours of operation at the fixed portion in the singularity region (radius of curvature equal to zero). We observed via elastic numerical simulation in quasi-static regime, performed using PATRAN and NASTRAN software, that hot spots are located at the singularity region. We also used this numerical calculation for analyzing the effect of the variation radius of curvature on the stress concentration factor by plotting the variation of this factor vs of said radius. To deepen, we repeated the same study but this time considering the material of the tooth as elastic perfectly plastic for seeking the limit load. For each value of the radius of curvature, was plotted the variation of the elasto-plastic external force according to the displacement of the front end of the tooth, knowing that the other end is fixed.

Abstract: Based on phenomenological method, the paper carried out experimental study for a kind of typical bolted joint structure, three kinds of testing specimens was designed, from the test result, the phenomenological model was obtained and the nonlinear mechanics behavior was comprehended, at last, the phenomenological model was verified experimental and numerical