Key Engineering Materials Vols. 353-358

Abstract: Structural analysis of automotive engine cover under vibration excitation is performed by finite element analysis (FEA) in order to identify the critical area of the structure. Assembly load due to the tightening of the bolts as well as the vibration excitation were considered to describe the actual loading condition. Natural frequencies of the system were extracted considering the damping effect of the structure. Dynamic analysis was performed based on the extracted natural frequency of the system. Experimental modal analysis (EMA) and measurement of strains were performed to verify the results of the analysis. Analysis results correlated closely with the experimental results. Analysis and experiments showed that contribution of the assembly load should not be ignored to predict the structural failure of the engine cover.

Abstract: A spacer grid assembly is one of the main structural components of the nuclear fuel assembly of a Pressurized light Water Reactor (PWR). The spacer grid assembly supports and aligns the fuel rods, guides the fuel assemblies past each other during a handling and, if needed, sustains lateral seismic loads. The ability of a spacer grid assembly to resist these lateral loads is usually characterized in terms of its dynamic and static crush strengths, which are acquired from tests. In this study, a finite element analysis on the dynamic crush strength of spacer grid assembly specimens is carried out. Comparisons show that the analysis results are in good agreement with the test results within an 8 % difference range. Therefore, we could predict the crush strength of a spacer grid assembly in advance, before performing the dynamic buckling test. And also a parametric study on the crush strength of a spacer grid assembly is carried out by adjusting the weld penetration depth for a sub-sized spacer grid, which also shows a good agreement between the test and analysis results.

Abstract: The structural response and behavior of steel joint under fire condition are analyzed in this paper. A simplified model for moment-rotation relationship of the end-plate bolted connections at elevated temperatures is proposed. This model is convenient and effective to describe the characteristics of extended end-plate joint and can be applied to evaluate the structural response and fire-resistant performance under static-load and thermal effects. The results of finite element analysis and related experiment are also used to validate the proposed model. It is found that the initial rotational stiffness and limit loading-capacity of steel joint components are affected significantly by the degradation of materials and the dimensions of components.

Abstract: In this paper, full-scale reinforced concrete slabs are analyzed under thermal-mechanical loads in fire conditions. The rectangular one-way slabs including a simply supported slab and a three-span continuous slab are concerned in the analysis. Finite element simulation is carried out by using the ABAQUS program to evaluate the non-uniform temperature distributions in thickness of the slabs and to analyze the deformation and stress redistribution of the slabs at elevated temperatures. Sequentially coupled thermal and structural analyses are performed to simulate the responses of the slabs in fire conditions. Deformation and strength of the slabs under thermal and mechanical loads are discussed. The numerical results are compared with the experimental ones and good agreements are observed. The analysis results show that the main reinforcement ratio has significant effects on the deformation and strength of the slabs at elevated temperatures and the three-span continuous slab has better performance of fire-resistance than the simply supported slab.

Abstract: Fatigue fracture behavior of a hybrid joint beam for the tilting car body was evaluated in comparison to the case of static fracture. Specimen beams of the hybrid joint part attached in the real tilting car body were fabricated for the bending test. Characteristic fracture behaviors of hybrid joint beam specimens under cyclic transverse loads were very different from the case under static loads. Static transverse load caused shear deformation and fracture in the honeycomb core region, while cyclic transverse load brought about delamination along the interface between composite skin and honeycomb core layers as well as fracture of the welded joint. Fracture characteristics obtained by the transverse fatigue tests were reflected for improving the hybrid joint structure in the real tilting car body.

Abstract: A simple spline integral equation method is presented in this paper for the axisymmetrical bending of circular plates with variable thickness. Firstly, the fundamental solution of a second-order differential equation is derived. With the slope of the deflection surface taken as an unknown function, an integral equation is then established for circular plates with variable thickness. The integral equation is solved numerically by cubic spline interpolation and the deflection and bending moment at any point within the circular plate are obtained. Finally, the validity of the proposed method is verified with the analytical solution obtained from the literature.

Abstract: The nonlinear finite element method (FEM) was applied to the analysis of the strain distribution in
-shaped seal rings acted by internal pressure or the combined action of internal pressure and axial displacement. The results indicate that the maximum Mises equivalent strain exists at the juncture between the exterior surface of the loop and that of the knuckle when the ring is acted by axial compression displacement and relatively large internal pressure, which is in agreement with the practical work conditions of the rings. According to the plastic limit analysis method, the limit internal pressure should be determined based on the strained condition of the juncture between the exterior surface of the loop and that of the knuckle of the ring by using twifold elastic slope criterion. The formulae for calculating the limit internal pressure of the rings were also derived by regression analysis of the FEM results. These formulae can be used in the limit design and the safety assessment of
-shaped rings.

Abstract: Die wear is regarded as a crucial factor which affects die life and quality of products. In hot extrusion process, finite-element method (FEM), BP neural network and genetic algorithm were combined together to optimize extrusion die profile which yielded more uniform wear depth distribution on die profile. A method of B-spline function interpolation was used to describe extrusion die profile. The temperature, pressure and velocity field of nodes that lied on extrusion die profile were gained by FEM simulation. Wear depth of extrusion die profile was calculated by modified Archard theory. The results were used to train BP neural network, so that nonlinear mapping relations between reference points of die profile and wear depth were obtained. In order to gain uniform wear depth, genetic algorithm was applied to optimize extrusion die profile. Optimum result, compared with common conical die profile, reduced wear depth of extrusion die and improved service life. At the same time, the optimal result accorded with practical conditions.

Abstract: A simple and efficient spline integral equation method is presented in this paper for the axisymmetrical bending of circular plates with large deflection. Based on two second-order differential equations in terms of the slope of the deflection surface and the radial displacement of the circular plate, two integral equations are derived. The circular plate is then equidistantly divided into a circular plate element and a series of annular plate elements along its radial direction and the slope of the deflection surface and the radial displacement are both approximated by cubic spline interpolation. The two integral equations are solved numerically and the displacements and internal forces at any point within the circular plate can be obtained. Finally, some numerical results are presented for illustrating the validity of the proposed method. It can be concluded that the proposed numerical method can be used to analyze circular plates with large deflection with reasonable accuracy.

Abstract: This paper proposes two concepts in order to estimate the stability of surrounding rockmass of deep tunnel, one is YAI (yielding approach index) which is used to denote the stability difference among the zones in surrounding rockmass whose stress states are close to yielding, the other is FD (failure degree) which focuses on the estimation of failure degree of the zones in surrounding rockmass and can be calculated by the equivalent plastic strain when failure occurs. Finally, a numerical analysis on the excavating process of a deep tunnel is performed, and YAI and FD are used to estimate the stability states of rockmass. The accurate estimation on plastic field and the proper evaluation on stability state indicate that these two concepts are rational and of perfectly practical use.