Lian Hong Zhang

Investigation of Residual Stress in Green Compacts of Metal Powder Using X-Ray Diffraction

Residual stresses in green compacts have a significant influence on the quality of the compact and post-compaction processes like part handling. In this study, the latest European and American standard for residual stress measurement by X-ray diffraction have been used to obtain more exact residual stresses in surface of green compacts as experimental evidence for simulation. The influence of kinds of powders, compacting pressure and friction on residual stresses in green compact has been studied.

Kinematic Modeling of the Gear Shaping Based Novel Cutting Area Analytical Method for Large Gear Shaper

Large gear is widely used as a key component of heavy machineries. Gear shaping is the most commonly process of large gear manufacturing. For the design of large gear shaper, the determination of its main driving force depends on the empirical formula. However, its result has shown that the main driving force is much larger than what really needs, which produces a lot of waste. A novel analytical method is proposed in this paper. According to this method, the cutting area can be calculated precisely, and the design of main driving force will be more reasonably, it also provides the theoretical foundation for the design of large gear shaper.

Optimization of Channel Dimensions in the Flow-Field for PEMFC

This paper focuses on the improvement of the distribution uniformity and consumption rate of the hydrogen (H2) in proton exchange membrane (PEM) fuel cells via optimization of the channel dimensions in the flow-field of bipolar plates. Based on the half-cell model for the anode side numerical simulation is carried out with computational fluid dynamics software Fluent. The method of DOE (Design of Experiment) is used in the simulation, and the results show that channel depth is the most influential factor to H2 consumption rate, channel width comes second, and land width has the least influence.

Experimental Study of Assembly Clamping Pressure on Performance of PEM Fuel Cells

The compression induced by the assembly of proton exchange membrane (PEM) fuel cells causes partial deformation of the gas-diffusion layers (GDLs) and, consequently, influences the performance of PEM fuel cells. In order to investigate how assembly pressure affects electric efficiency of PEMFC, performance of PEMFC experiments with a miniature self-humidifying, breathing PEMFC stack are conducted under different clamping pressures. The polarization and power efficiency curves of PEMFC under different clamping pressures show that the best performance can be obtained at the allowable lower limit of working parameters. The research shows that the effect of assembly clamping pressure is significant, and the low clamping pressure is beneficial to improve the performance of the PEMFC stack while keeping sealing. The experimental results indicate that a clamping pressure of 1MPa improves the fuel cell performance in this paper.

Residual Stress in Powder Metallurgy Green Compact

Residual stress in green compact is an important factor to influence the quality of the compact and corresponding powder metallurgy product. To understand the residual stress, a finite element model is set up to simulate the single and double action pressing, unloading and ejecting of powder compacting process. Results show that compaction type has significant influence on the rule of residual stress state and the double action pressing is more helpful to reduce the risk of cracking than the single action pressing. Also better lubricant condition is beneficial to improve residual stress in the green compact.

Parameter Design of Cylinder Gear Pairs with Small Number of Teeth

Gear transmission with a small number of teeth is widely used as a key component of mopeds, motorcycles, electric bicycles and so on. A parameter design of cylinder gear pairs with small number of teeth was put forward, which was carried out by establishing a optimization model and selecting the preliminary parameters of gear pairs, and then adjusting the parameters according to the meshing interference conditions and the strength theory. The parameters of the compact gear pairs, which meet transmission quality requirements and strength condition tested by finite-element analysis, can be obtained ultimately. The feasibility and rationality of this method are verified by case.

A Dynamic Contact Model of Rough Surfaces Based on the Microscopic Contact Analysis of Asperities

Dynamic contact model of rough surfaces can provide the theoretical basis for analyzing the microscopic damage of surfaces in wear process and constructing the analytical wear model to predict wear. A dynamic contact model of sliding rough surfaces is innovatively constructed based on the characterization of the contact asperities on rough surfaces in this paper. Firstly, an asperity model of rough surface is set up according to the surface topography parameters and the static contact parameters is evaluated in the light of statistics contact theory; Then the contact characteristic of surface topography in sliding is analyzed and a series of equivalent contact models are proposed; Finally, the dynamic contact model of rough surfaces is established and from which the dynamic contact parameter of rough surfaces is formulated. The dynamic contact model can be further improved to analyze the friction fatigue wear of sliding pairs and provide reference for tribology design of mechanical surfaces.

Finite Element Analysis of the Strength of Ladder Type Structure of the Deep-Water AUV

Autonomous underwater vehicle (AUV) is one of the current research hotspots in the field of robotics. It has abroad application prospect in the oceanographic survey, resource exploration and military fields. The AUV presented in this paper is mainly used for investigating the deep water oil and gas resources and works in underwater 3000 meters. It carries a series of measuring equipment, such as battery, sensors and pressure-resistant cabins, to engage in exploration tasks. When the AUV is lifted in water or in air, the loads acted on the main frame of AUV are different. In order to realize lightweight design and save buoyancy within the allowable range of the material strength, this paper puts forward a novel ladder type construction with two longitudinal beams and five crossbeams made of stainless steel, and analyzes the forces sustained by the main frame when lifted. Compared with traditional aluminum welding structure frames, the advantages of the trapezoid frame of the deep water AUV are as follows: large effective capacity, strong bearing capability and convenient maintenance. At the same time, using GRP hulls can improve the total structural strength significantly. The validity of the design and analyze is verified by recent at-sea trails.

Wet Modal Analysis of a Deep-Sea Autonomous Underwater Vehicle

When cruising underwater, the Autonomous Underwater Vehicle (AUV) oscillation will affect some sensors’ measuring precision. In this paper, the method of equivalent entities is used to build the AUV’s solid model, and the AUV’s fluid-solid coupling system together with its wet modal is analyzed using ANASYS software. In addition, the AUV’s bending mode and breathing mode under different depths are discussed, which will reflect the changing trends of AUV vibration frequencies during operation. The conclusion can provide the theoretical basis for the AUV structure design when certain measuring task is performed using sensors.

Analytical Model Study of Ellipse Crank Arm Final Upset Forging Force on Slab Method

According to the structure of the crank arm, the conformal mapping method was adopted to transform the elliptical section map of it to the round. Then by the slab method an analytical model for final upsetting force of the crank arm was established, which is a derivation based on assumptions of axisymmetric plastic forming status. Finally, a simulation was implemented in case of the second crank of crankshaft 6G32. Accordance to it the accuracy of the analytical model was examined. Further more the causes of the data deviation from the model and the simulation were analyzed in this thesis.