【作者】 吴立鸿；

【导师】 龙思远；

【作者基本信息】 重庆大学 ， 材料加工工程， 2005， 硕士

【摘要】 节能降耗、提高性能已经成为当今汽车、摩托车发展的一种必然趋势。轮毂作为车辆上的高速运动部件,重量减轻可以有效的降低能耗、改善整车的加速及制动性能、提高驾乘舒适性及安全性。采用轻量化材料实现轮毂的更新换代是实现这一目的有效途径。镁合金最轻的商用金属结构材料,与现行的轮毂用铝合金相比,具有比重小、价格低、比强度高、阻尼减振性能突出等优点,用于摩托车轮毂能降低车辆自重及燃油消耗,降低车辆的振动和噪声,提高车辆加减速的动力学特性。现有轮毂的结构都是针对钢和铝合金设计的,由于镁合金与钢、铝合金的机械性能差别较大,因此必须对原结构轮毂的服役应力状态进行分析,以确保材料替代后的服役性能。为实现轮毂材料的更新换代、推动镁合金在轮毂上的合理应用,本研究应用有限元法,对150 摩托车铝、镁两种材料的轮毂进行了服役应力分析。分析结果表明: 1)研究的轮毂采用倾角式辐板结构、过渡圆角较小,导致服役峰值应力集中出现在轮辐与轮鼓、轮辐与轮辋间的过渡部位;轮毂其余部分应力分布均匀、变化缓和。2)由于镁合金弹性模量较低,可通过较大的弹性变形实现整体承载,对于相同结构尺寸的轮毂,当材料从铝合金改为镁合金后,服役应力峰值从36.4MPa 降低到27.1MPa,降幅达25.6%,应力集中程度趋于缓和,交变幅度变小,整体应力分布变得更均匀。3)针对镁合金疲劳强度低的特性,通过改倾角式辐板为直辐板及增大辐板与轮鼓、辐板与轮圈之间的过渡圆角等结构优化措施,将服役应力峰值从27.1MPa 降低到23.1MPa,进一步提高了镁合金轮毂的服役可靠性与安全性。上述研究结果为镁合金轮毂结构再设计提供了理论依据。采用该理论设计和制造的挤压铸造镁合金轮毂在减重30% 的基础上,通过了国家权威机构的台架实验检测和企业在川藏和青藏路上进行的道路试验。检测结果表明:镁合金能够显著提高摩托车的性能,并降低油耗14%以上。更多还原

【Abstract】 Oil consumption reduction and performance enhancement have become the development trend of road vehicles, especially of motorcycles. Due to their nature of high-speed motion and rotation, weight reduction of the wheels is the most efficient way to reduce the oil consumption, to improve the accelerating and braking performance, enhance the riding comfort of a road vehicle. Naturally, use of light weight materials on the wheels is the most straight-forward way to achieve the goal. In comparison with most widely used aluminum alloys, magnesium alloys are the lightest commercialized metallic material for structural applications. Mg alloys possess the attractive properties desired by motorbikes, such as low density, low cost, higher specific strength, good casting properties, out-standing damping capability. When used as wheel material, Mg alloys are able to reduce mass of the wheels, to absorb vibration, to damp noise emission, to reduce oil consumption, to enhance acceleration and braking performance and the resultant riding comfort. However, the Mg alloys cannot be directly used on the commercial wheels because Mg alloys possess material properties considerably differing from those materials, such as steel or Al alloys, to which the wheel is designed for. To ensure the performance and safety, the service condition of the wheels has to be analyzed and the structure of the Mg wheels have to redesigned to in accordance with the materials properties of Mg alloys. To promote a scientific understanding on the effect of material substitution and structural features on the service condition of wheels, numerical analyses of stress and strain distribution in wheels of both 356 Al alloy and AM60B Mg alloy under service condition were performed, and the 150 Mg wheel structure was redesigned and optimized with finite element method (FEM). The obtained important results were high-lighted as follows: 1) The use of tilted supporting bar and the small transition curve in 150 wheel gives rise to stress concentration at transition segments. The stress distribution in the rest part of the wheel is even. In the rest of the wheel, the stress level is comparatively low and the strain distribution is uniform. 2) Replacement of Al alloy A365 with Mg alloy AM60, service stress distribution in the wheel becomes more uniform, the peak value of the concentrated stress reduced from 36.4MPa to 27.1MPa, down by 25.6%. The stress distribution in the wheel as a whole trends to become more uniform and variation during a service cycle becomes much smaller. This is because the low elastic modulus of Mg alloy permits the wheel structure to undergo more intensive elastic deformation, witch, in turn, transfers the load more widely to the whole wheel, creating a pattern of ‘Global Load Sharing’. 3) Considering the fact that Mg alloy has a lower fatigue strength, the tilt angle between the hub and spoke and the transition curves at both ends of spokes were modified during structure optimization so that the peak service stress was further reduced from 27.1MPa to 23.1MPa, down by 14.8%, to strengthen the service reliability and safety. Guided by the above results, 150 motorbike Mg alloy wheels were redesigned and produced with a patented novel squeeze casting process with 30% weight saving. Their service properties were tested in the laboratory of an authorized organization and by a 8000 km tough road-test via Sichuan-Tibet and Tibet-Qinghai country road organized by Loncin motorbike company. It is evident that the Mg alloy wheel possesses significantly improved service performance and an oil consumption reduction of more than 14%.更多还原