Fangyuan Cui

Bio: Fangyuan Cui is an academic researcher. The author has contributed to research in topics: Stiffness & Surface roughness. The author has an hindex of 2, co-authored 5 publications receiving 12 citations.

Stiffness Calculation Method and Stiffness Characteristic Analysis of Bolted Connectors

Abstract: At present, few scholars have studied the effect of surface roughness on assembly stiffness. The influence of the joint surface stiffness on the overall stiffness is neglected. In this paper, a new method for calculating the stiffness of bolted joints is presented. The effect of joint surface stiffness on the overall stiffness is considered. Firstly, the relationship between load and displacement between cylinder and cylinder (including the joint surface with certain roughness) is studied, and the stiffness characteristic expression of the joint surface is obtained; the results are compared with the traditional stiffness calculation theory, and then, the influence of bolt connection surface on bolt connection is studied and compared with the stiffness calculation results of traditional bolt connection. The results show that the theoretical model presented in this paper is more practical.

Elasto-plastic analysis of the contact region between a rigid ellipsoid and a semi-flat surface:

Abstract: When the load acting on a mechanical structure is greater than the yield strength of the material, the contact surface will undergo plastic deformation. Cumulative plastic deformation has an import...

Stiffness Calculation Model of Thread Connection Considering Friction Factors

Abstract: In order to design a reasonable thread connection structure, it is necessary to understand the axial force distribution of threaded connections. For the application of bolted connection in mechanical design, it is necessary to estimate the stiffness of threaded connections. A calculation model for the distribution of axial force and stiffness considering the friction factor of the threaded connection is established in this paper. The method regards the thread as a tapered cantilever beam. Under the action of the thread axial force, in the consideration of friction, the two cantilever beams interact and the beam will be deformed, these deformations include bending deformation, shear deformation, inclination deformation of cantilever beam root, shear deformation of cantilever beam root, radial expansion deformation and radial shrinkage deformation, etc.; calculate each deformation of the thread, respectively, and sum them, that is, the total deformation of the thread. In this paper, on the one hand, the threaded connection stiffness was measured by experiments; on the other hand, the finite element models were established to calculate the thread stiffness; the calculation results of the method of this paper, the test results, and the finite element analysis (FEA) results were compared, respectively; the results were found to be in a reasonable range; therefore, the validity of the calculation of the method of this paper is verified.

Inverse Identification of Virtual Material Parameters Using Surface Response Methodology

Abstract: The virtual material model is now widely applied for modeling the dynamical performance of assembled structures since it can effectively represent the complicated contact behavior of joint interfaces despite being relatively simple to create. In this study, a virtual material model is adopted for modeling the dominant physics of a bolted joint subject to a set of pretightening conditions. The unknown virtual material parameters are acquired by an inverse identification procedure that uses the surface response methodology. The greatest advantage of this approach is the ease with which it acquires the joint parameters without taking apart a built-up structure to do special measurements on each separated component. Intricate theoretical calculations can also be avoided when this method is used. This study addresses the responses of virtual material parameters under different pretightening considerations. Predictions based on the identified virtual material parameters are compared with the corresponding results obtained using the analytical method. The correlation between the two sets of results at all preload levels is promising, which indicates the successful identification of the virtual material parameters.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Nonlinear effects on the stiffness of bolted joints and nonlinear effects on the stresses and deformations of bolted joints

Abstract: Axisymmetric finite element modeling of bolted joints was performed to show the effects of the magnitude as well as the radial location of the externally applied load on the member separation radius and the stress on the surface between the two members. The separation radius was found to be nonlinearly related to changes in the magnitude as well as position of the external load. A 27-percent decrease for 24-mm bolts to 39-percent decrease for 8-mm bolts in the separation radius resulted with changes in the load magnitude. The external load varied from zero to the maximum that could be sustained before joint separation for steel members. The change in separation radius for the aluminum members, cast iron members, and a combination of the two materials was on the order of 2--10 percent. For the minimum and maximum external load, the separation radius decreased by 5 and 12 percent, respectively, with an increase in radial position of the external load. The stress was found to be higher near the bolt for larger external loads and also when the radial location of the external load was increased.

A Theoretical Model for the Normal Contact Force of Two Elastoplastic Ellipsoidal Bodies

Abstract: To model the mechanical behavior of granular materials, a reliable description of the material properties is indispensable. Individual grains are usually not perfectly spherical. In batteries, for instance, lithium nickel manganese cobalt oxide (NMC) is a frequently used material, consisting out of particles with possibly ellipsoidal like shapes. As particles may plastically deform under increasing stresses, the paper presents a theoretical model for the normal contact force of elastoplastic ellipsoidal bodies for the use in the context of mechanical discrete element method (DEM). The model can be considered as extension of the elastic, elastic-plastic, fully plastic Thornton model by using a more general description to incorporate elliptical contact areas. The focus is on a normal contact force description as continuous function of time for all regimes, elastic, elastoplastic, and fully plastic loading, as well as unloading from elastoplastic loading, while the evolution of the plastic contact area is not considered here. All underlying formulae to describe the force-displacement relationship for the static contact problem are derived, partly based on finite element analysis (FEA). To verify the new model, FEAs are performed and their results compared with the model predictions.

Modeling and Analysis of the Stiffness Distribution of Host–Parasite Robots

Abstract: The stiffness distribution (SD) of robot has a great influence on the robot pose accuracy, but the calculation efficiency and accuracy of stiffness distribution are still low. This study presents a finite element fitting method with an extremely small number of computational cells. It was developed based on experimental results of robot stiffness. This method can be employed to establish single- and multi-source fitted SD (FSD) (S-FSD and M-FSD) models for host–parasite (H–P) robots. The computational efficiency and correctness of the FSD models were verified by case studies. The configurations of six evolutionary mechanisms of an H–P robot were subjected to an SD analysis. A comparison of the six configurations shows that adding parasitic branched chains can improve the SD of the H–P robot to varying degrees. In particular, the most notable improvement was for H–P mechanism. Specifically, by averaging the stiffness of all positions, the average-stiffnesses of H–P mechanism in the $x$ -, $y$ -, and $z$ -directions were 104.10%, 1427.78%, and 1101.62% of those of the host mechanism, respectively. In the SD diagram, the medium- and high-stiffness regions of mechanism F are large and distributed in a banded pattern between the highest pose point and the furthest pose point, whereas its low-stiffness region is small and concentrated near the nearest pose point.

A Model accounting for Stiffness Weakening of Curvic Couplings under Various Loading Conditions

Abstract: Curvic couplings are frequently used in aeroengine rotors. The stiffness of the curvic couplings is of guiding significance to the engineering design of aeroengine rotors as it is significantly different from that of continuous structures. In this paper, definitions and relations of the structure parameters for a curvic coupling are firstly introduced. Based on this proposed mechanical framework, a novel mechanical model accounting for the stiffness weakening under shearing, compression, bending, and torsion is developed for curvic couplings. In this model, a three-spring system, which consists of two types of springs, is adopted to describe the equivalent stiffness of a pair of meshing teeth of curvic couplings. The spring stiffness is obtained by employing the plane strain analysis of a discretized tooth with trapezoid pieces. Subsequently, the stiffness matrix of curvic couplings is deduced based on the deformation compatibility of each tooth and the force balance of the whole structure. A series of analyses of curvic couplings with various structure types are performed to demonstrate the mechanism behind the proposed model, and the results are verified against those obtained from finite element analyses. It is shown in this study that the pressure angle is the major factor affecting the stiffness of curvic couplings, while the compression stiffness and bending stiffness are more sensitive than other stiffnesses. Furthermore, the stiffness of curvic couplings is considerably smaller compared to that of continuous structures, indicating the importance of appropriate modelling of stiffness weakening in the design of aeroengine rotors.