Papers by Author: Lan Liu

Abstract: A mathematic model of ball screw was constructed which was based on the elastic contact deformation theory. The helix angle was considered and the formula of axial elastic deformation was deduced in this study. Furthermore, a finite element model of ball screw was established and its elastic deformation results were also acquired. And the effect of contact angle on axial elastic deformation was analyzed by theoretic method and FEA. The study shows that the axial elastic deformation of ball screw changes with the contact angle. The deformation will decrease by the contact angle increasing, and the positional accuracy of the ball screw is improved.

Abstract: Coupled molecular dynamics simulation and finite element method, a multiscale method is used to model nanoscale sliding contacts problems. According to an experimental sample, 4 textured surfaces with different asperity shapes are designed. Through the friction forces comparisons between smooth surface and textured surfaces, the effects of texture shapes are investigated, and 2 better textured surfaces are discovered to reduce friction forces.

Abstract: A multiscale method coupled molecular dynamics simulation and finite element method is used to investigate two dimensional nanoscale sliding contacts between a rigid cylindrical tip and an elastic face centered cubic copper substrate with textured surface, in which adhesive effects are considered. Two series of nanoscale surface textures with different asperity shape, different asperity heights and different spacing between asperities are designed. Through the friction forces comparisons between smooth surface and textured surfaces, a better shape is advised to indicate that asperity shape plays an important role in friction force reduction. With proper asperity height and proper spacing between asperities, surface textures can reduce friction forces effectively.

Abstract: Surface texture, as one of the typical surface integrity characteristics, plays a vital part in efficiently and systematically evaluating the surface integrity and relevant mechanical properties of machined parts. Commonly used 2D surface roughness parameters are formularized and discussed in this paper. And 3D characterization technique is also illustrated through measuring and describing a machined surface with an optical profiling system. The relationship between surface texture and the fatigue property of final machined parts are discussed by employing the quantity of effective stress concentration factor which could be expressed by the standard surface roughness parameters and measured averaged root radius of surface texture’s valleys. This research emphasizes the indispensable role of the surface texture in evaluating surface integrity and corresponding functional performance of machined parts.

Abstract: Groundbreaking work and past standard of surface integrity regarding description, measurement and evaluation of machined components are retrospected. Typical surface integrity characteristics such as surface topography, macro and microstructure, microhardness and residual stress distribution are preferentially adopted for quantitatively describing and systematically evaluating of surface integrity. Corresponding processing conditions and fatigue performance along with surface integrity characteristics are also detailedly classified and digitally defined through meaningful data sets. A framework of surface integrity model for machined components is subsequently proposed and preliminarily established by understanding the nature of surface integrity and its relation with processing parameters and fatigue properties. This pilot study offers a conceptual model as well as some feasible operational approaches for control of surface integrity in cutting technology and consequent improvement of the fatigue life for machined components.

Abstract: In this paper, an insect-based flapping-wing flying microrobot was built which can successfully fly in the sky. The unsteady aerodynamics associated with this microrobot was studied by using the method of computational fluid dynamics (CFD). On the basis of numerical simulation, the Fluid-Structure coupling mechanics for flexible flapping-wings were studied and discussed. According to the practically developed flapping-wing microrobot, a 2-D simulation model for flexible flapping-wings was established. Fluid-Structure coupling deformation and the effects of this model on the aero dynamic performance were analyzed, which have offered a theoretical basis for design of the aircraft with flexible flapping-wing. In order to verify the results of numerical simulation, aerodynamic performance tests have been conducted for the rigid and flexible flapping-wings in a low turbulence and low Reynolds number wind tunnel.

Abstract: The performance simulation report of product is an important basis for resource distribution and estimate in design process. In order to acquire data rapidly, an automated generated solution of performance simulation report is presented. It can be applied not only in mechanical product but also in other fields. The technology architecture of management system for performance simulation report is constructed, which is based on SOA. And the data management is accomplished by relational database and Java content repository. The BIRT tool engines encapsulate the main step of creating report, then the performance simulation report can be demonstrated by Web browser. At last, an engineer application of multidisciplinary simulation has been implemented and it demonstrated the validity and practicability of the solution.

Abstract: In order to implement collaborative work in enterprises, it is important to exchange and share data during product design process. According to the characteristics and types of simulation data for mechanical properties analysis, an effective data management method is presented. Based on the functional framework of collaborative simulation environment, a new database system has been designed by combining relational database and content repository. The content repository for simulation data has been established and designed by user-defined node type whose model is a simple hierarchy. In this repository, simulation metadata have been stored as node properties. Furthermore, simulation data files can be stored in node which facilitates the upload and download of files. In the mean while, simulation flow data can be stored in relational database. An engineering application is employed to demonstrate the feasibility and practicability of the data management system.