导　　师： 郝志勇

学科专业： 080204

授予学位： 博士

作　　者： ;

机构地区： 浙江大学

摘　　要： 镁合金是一种新型的轻金属材料,由于其重量轻、比刚度和比强度高、阻尼吸震性能及压铸性能好等优点,越来越广泛地在汽车产品上得到应用。 针对某型乘用汽车开展了镁合金的应用研究。分析了仪表板横梁原始结构的刚度、强度、模态等性能。采用压铸工艺设计镁合金压铸结构替换原钢质仪表板横梁总成,零件数量由50个减少到7个,缩减率为86/%。通过对镁合金压铸结构进行相关性能分析,发现结构设计产生的问题。对结构进行结构设计改进,初步提高刚度性能。采用基于多物理量的结构灵敏度分析及质量最小化的优化模型进行镁合金压铸结构的优化设计,在满足各项机械性能要求的同时,镁合金替代件的质量比原钢质结构减轻了46.6/%。 对镁合金组合板件进行了隔声性能分析。根据单层板声阻抗结果和夹层板的阻抗转换定理得到双层板隔声量的推理结果。分析了组合板空气夹层厚度变化、不同厚度板件配置、单个板件厚度变化等多种情况对组合板件隔声性能的影响。通过自行设计的混响箱,在消声室内对组合板件进行混响声场条件下的噪声衰减性能的实验研究,比较了混响声场下不同组合板件的声学性能。 对前围板进行了镁合金材料替换研究,重点考查了隔声性能的变化。在低频段采用FEM//BEM/(有限元-边界元/)法对不同材质前围板进行隔声性能比较,发现该结构由镁合金替换钢质材料后,重量减轻但隔声性能并未下降,在某些频段甚至更加良好。对前围板孔洞密封是保障结构隔声性能的前提。通过施加声学包装,发现在计算频域中的低频处产生隔声性能恶化现象,同时分析结果表明吸声材料并非越厚越好。采用FE-SEA法进行中高频段隔声性能分析,发现钢的隔声性能优于镁合金,同时通过对关键区域进行声学包装设计,能产生明显的声学优化效果。 采用ATV法/(声传递向量法/)进行声贡献量分析,得到贡献量最大板块,通过模态分析,确定了隔声低谷的声传递路径。根据分析结果对关注频率段的主要声透射区域及相邻板块进行结构改进,发现其中一块隔声量变化明显。以优化第一阶模态为目标,对该区域进行拓扑优化设计。结果表明,隔声低谷现象虽然得到了改善,但高频段声学性能有所下降。对此现象,需要结合声学包装进行该频段的声学优化。 建立了整车车内声场SEA/(统计能量分析/)模型。通过对前围板材料进行替换,计算驾驶员耳旁噪声,发现3mam镁合金前围板在高频处相对于1mm钢制前围板的耳旁噪声大。将复合前围板的每层材料厚度作为设计变量,以轻量化为目标,进行车内声场优化。通过MMA/(移动渐近线/)法和GA/(基因遗传法/)法进行优化比较,得出结论GA法能得到全局解。经过对车内耳旁噪声优化迭代计算后,和原钢质复合前围板相比,复合结构重量下降9.93kg,减重46.3/%。耳旁噪声优于钢制复合前围板产生的声学结果,实现了低噪声轻量化设计。 Magnesium alloy is a new kind of widely used light metal materials. Due to its light weight, high stiffness and strength, excellent damping performance and so on, the material has a very wide range of application on vehicle. Magnesium alloy has good die casting performance, so the magnesium alloy die casting is adopted for the lightweight design and relevant performance analysis. Magnesium alloy die casting parts is designed based on the die casting process, so as to replace the dashboard beam assembly, to reduce the original number of parts from50components to seven. Die casting structure and original structure is compared by stiffness, strength and modal analysis. The multiple parameters sensitivity optimization model is built, and it optimizes structure's performance to meet the requirements. The weight is lighter than the original structure by46.6/%, realizing the lightweight design. Sound insulation performance analysis was carried out on the magnesium alloy double-layer board. According to the acoustic impedance ratio of single plate when it is with the bending vibration and impedance transformation theorem, sound insulation calculation formula for double-layer plate is obtained. The effect of factors like the panel thickness, air layer thickness and placement order of plates with different thickness on the sound insulation performance component is analyzed. With the self-designed reverberation chamber, in the anechoic room, the sound transmission loss test is carried out towards the double-layer plate in the reverberation condition, and the influence of these parameters of factors mentioned above towards the structure's performance are tested. The material of the dash substituted with the magnesium alloy, analysis was carried out on the sound transmission loss performance of the dash panel. In low frequency band, by the method of FEM//IBEM, dash panel made of different materials are compared, and the sound insulation performance it is found that magnesium alloy after replacing steel materials gives better sound insulation performance, with more than30/%reduction in weight. Good structural acoustic performance is guaranteed by sealing the dash panel hole. By applying acoustic package, sound insulation performance degradation is found at low frequency in the calculation of the frequency domain. Meanwhile, the analysis results show that sound performance of the structure is not better as the absorption material is getting thicker. By the FE-SEA method for middle and high frequency sound insulation performance analysis, it is found that the sound insulation performance of steel is better than that of magnesium alloy, meanwhile by acoustic package design of key areas, obvious acoustic optimization results can be made. By ATV method for analyzing acoustic contribution, the plate with biggest contribution is found. And by the modal analysis, the sound transfer path of the sound transmission valley is determined. According to the results of the analysis, structure adjustment is carried out in the plates that are adjacent to each other in the main acoustic transfer area. It is found that the change is obvious in one plate. By optimizing this area with topology optimization with aim of optimizing the first mode frequency, the defect of sound transmission valley has been alleviated meanwhile the acoustic performance has dropped in the high frequency. Therefore, acoustic optimization in corresponding frequency should be carried out along with the sound treatment. SEA model for Vehicle interior sound field analysis is set up, and by the substitution of the dash panel material, parotic noise is calculated, which leads to the result that the model with3mm thick Mg dash panel has higher noise level than the one with1mm thick steel dash panel. Treat the thickness of each layer of the composite dash panel as design variables, with the lightweight design as the goal, to optimize interior sound field. With the comparison of using MMA method and GA method to optimize the model, the conclusion is that GA method can offer global solution. After optimization iterations, the weight of the dash panel is11.52kg lighter than the original magnesium composite dash panel which is decreased by38.2/%. Compared with steel composite dash panel, weight of optimized one is decreased by46.3/%. Parotic noise is better than that of the model with steel composite dash panel, realizing lightweight design as well as low noise request.

关 键 词： 镁合金 压铸 结构优化 轻量化 隔声 声学包装 耳旁噪声

分 类 号： [U462]

领　　域： [机械工程] [交通运输工程] [交通运输工程]