Baotong Li

Multidiscipline Topology Optimization of Stiffened Plate/Shell Structures Inspired by Growth Mechanisms of Leaf Veins in Nature

Biological structures with preeminent performance in nature endow inexhaustible inspiration for creative design in engineering. In this paper, based on the observation of the natural morphogenesis of leaf veins, we put forward a simple and practical multidiscipline topology optimization method to produce the stiffener layout for plate/shell structures. This method simulates the emergence of complex branching patterns copying the self-optimization of leaf veins which always try to grow into a configuration with global optimal performances. Unlike the conventional topology optimization methods characterized by “subtraction mode,” the proposed method is based on the “addition mode,” giving great potential for designers to achieve more clear stiffener layout patterns rather than vague material distributions and, consequently, saving computational resources as well as enhancing availability of design outputs. Numerical studies of both static and dynamic problems considered in this paper clearly show the suitability of the proposed method for the optimal design of stiffened plate/shell structures.

Integration of geometric variation and part deformation into variation propagation of 3-D assemblies

This paper introduces a novel modelling method for variation propagation calculation of 3-D assemblies taking into account geometric variation and part deformation, which are neglected in most models in tolerance analysis. Initially, numerical studies are carried out in order to illustrate the characteristics of strain distribution in components and contact forces on the mating surfaces of a 3-D assembly. According to these characteristics, a linear equivalent model using springs to represent the elastic mating surfaces with geometric variation was presented. Then, the equilibrium criterions corresponding to actual contact situations and iterative searching algorithm of the equilibrium status of contacting were developed. The proposed modelling and calculation method were finally applied to the assembly of two machined parts, on which finite-element analyses and experimental tests were conducted to validate the effectiveness and accuracy. This linear contact model also shows an important advantage on modelling and calculating efficiency, which enable the practical application to variation propagation calculation in both tolerance design and assembly process.

Application of ultrasound technique to evaluate contact condition on the faying surface of riveted joints

Contact area and pressure distributions on the faying surfaces of riveted joints are critical to fretting fatigue crack. However, these contact conditions are hard to evaluate by experimental methods. This study proposed an application of ultrasound technique to quantify contact area and pressure distribution on the faying surface of riveted joints. This ultrasound method consists of the ultrasonic reflection map measurement of the faying surface, and a parallel calibration procedure to establish the relationship between ultrasonic reflection and contact pressure. In this way, the contact area and pressure distributions of riveted joints installed with different riveting forces were investigated. The results show that the contact pressure increases rapidly with the squeeze force, while the contact area spreads slightly at the same time. The mean pressure profiles of the ultrasonic results were compared with the results of a finite element model for the riveted joints. The comparison shows that the mean pressure profiles are consistent with the numerical results.

A Noise Evaluation Based Wiener Deconvolution Method for Contact Parameters Measurement Using Ultrasound

Ultrasound method is an extremely useful tool in contact parameters identification for joint surface widely used in engineering product. Wiener filter is commonly used to ultrasonic reflection map to reduce the influences of the blurring effect introduced by ultrasonic beam size on the measurement accuracy, but the results are not good enough because it is difficult to estimate the signal-to-noise ratio of reflection map. In this paper, a noise evaluation based Wiener deconvolution approach is developed to handle this problem. The noise power spectrum of reflection map is estimated through the steel-air contact area of the joint surface, and an evaluation of the ratio of noise power spectrum and signal power spectrum is obtained based on the noise variance and the experimental reflection map. To verify the efficiency of the developed approach, a sphere-plate contact interface is selected as a concrete case in which different Wiener deconvolution approaches are applied for evaluation of contact parameters. The results are compared with simulation results produced by a finite element model (FEM). The comparisons show that the contact parameters obtained by the proposed approach are more accurate than that obtained by commonly used Wiener filter approaches.Copyright

Distortion Optimization of Engine Cylinder Liner Using Spectrum Characterization and Parametric Analysis

In an automotive powertrain system, the cylinder liner is one of the most critical components which possesses the intricate structural configurations coupled with complex pattern of various operational loads. This paper attempts to develop a concrete and practical procedure for the optimization of cylinder liner distortion for achieving future requirements regarding exhaust emissions, fuel economy, and oil consumptions. First, numerical calculation based on finite element method (FEM) and computational fluid dynamics (CFD) is performed to capture the mechanism of cylinder liner distortion under actual engine operation conditions. Then, a spectrum analysis approach is developed to describe the distribution characteristic of operational loads (thermal and mechanical) around the circumference of a distorted cylinder bore profile; the FFT procedure provides an efficient way to implement this calculation. With this approach, a relationship between the dominant order of distortion and special operational load is obtained; the design features which are critically relative to cylinder liner distortion are also identified through spectrum analysis. After characterizing the variation tendency of each dominant order of distortion through parametric analysis, a new design scheme is established to implement the distortion optimization. Simulation results indicate that a much better solution is obtained by using the proposed scheme.

The Slippage Analysis at Bearing Surface of Bolted Joints due to Cyclic Transverse Loads

Bolted joints are widely used in mechanical structures due to their easy installation and maintenance. However, self-loosening of bolted joints caused by cyclic transverse loads has remained unsolved. In this study, the parametric finite element (FE) model is established to simulate the self-loosening. The slippage state at bearing surface and thread surface is investigated based on the FE model. Moreover, the influences of transverse frequency, amplitude, friction coefficient and initial preload on residual preload are discussed under a certain amount of time; the variations in back-off angle of nut and residual preload with time are analyzed under multi transverse loops. The results show that thread surface undergoes complete slip prior to the bearing surface, which provides theoretical guidance for looseness-proof design of bolted joints to some degree. The FE model can also be used to design the initial preload and predict the connections life under given vibration environment.Copyright

A New Method to Analyze Three-Dimensional Non-Repetitive Run-Out (3D-NRRO) of Angular Contact Ball Bearings

As ultra-precision index of high-precision ball bearings, the value of three-dimensional non-repetitive run-out (3D-NRRO) directly influences the rotation accuracy in complex mechanical system. Reducing 3D-NRRO contributes to improve the quality of manufacturing in machining tools. This paper develops five-freedom model to analyze the 3D-NRRO of an angular contact ball bearing caused by geometrical errors of the rings raceways and the balls. In the model, the variation of contact angle caused by centrifugal force of balls is taken into consideration, and the geometrical errors of rings raceway and balls are described by Fourier series. Meanwhile, based on Hertzian contact theory and the solution method of dimensional chains, the 3D-NRRO analytical program has been developed, the value of 3D-NRRO analysis is shown. From the results, the relationship between the 3D-NRRO and the geometrical errors of rings raceway and balls are analyzed quantitatively. Findings of this paper provide theoretical supports to reduce or control the 3D-NRRO by optimizing manufacturing process of bearing components.Copyright