Accelerated Life Prediction of Machine Structures Under Fatigue Spectrum Loads

9812703 Yen本项目旨在开发机器和结构使用寿命预测的设计过程。 本研究的主要任务有三：（a）发展变幅疲劳载荷下寿命预测的加速表征理论;（B）利用（a）中发展的理论通过复杂的计算机模拟来预测机器的寿命;（c）通过机器的动态测试来验证分析和计算模型。 在所有情况下，将使用真实条件下的疲劳载荷谱。项目中开发的加速表征技术基于以下观察结果：不同疲劳条件（频率、应力和温度）下的材料退化过程具有相同的一般特征，但在时间上有所变化。 这种时间上的变化允许人们使用在较短时间间隔内获得的数据来预测长期疲劳寿命。 基于所提出的理论，疲劳失效取决于应变能密度向临界值的累积。 这样的公式允许一个地址的加载顺序或任何任意组合的负载上的疲劳寿命的影响。 为了证明所提出的将材料与机器联系起来的寿命预测概念的有效性，将设计和建造一个概念性的地面车辆（CGV）。 CGV将由短切纤维增强复合材料制成。 CGV的研究包括对车辆在真实载荷历史下的动态响应进行计算模拟和实验验证。 计算研究的最终结果是使用这里开发的理论预测CGV的寿命（通过应力和应变数据）。 在计算模拟研究中，将进行CGV的几何建模和应力分析。这项研究依赖于从实验中提取的真实负载和计算模型预测之间的收敛性检查。机器结构的动态响应的实验验证将包括CGV的设计和制造以及一系列的结构动态测试。 为了提取真实的装载数据，CGV将在实际地形上行驶，车载数据采集系统。随后，将系统响应数据转换为疲劳谱载荷，用于实验室试验。 该项目的结果可以将材料选择/评估、CAD/CAM/FEA/仿真和耐久性/失效分析链接到生命周期设计综合中。

9812703YenThis project intends to develop a design process for service life prediction of machines and structures. There are three major tasks in this study: (a) develop an accelerated characterization theory for the life prediction under variable amplitude fatigue loads, (b) use the theory developed in (a) to predict the life of a machine through an elaborate computer simulation, (c) verify the analytical and computational models with the dynamic testing of a machine. In all cases, the fatigue load spectrum under real-life condition will be used.The accelerated characterization technique to be developed in the project is based on the observation that the material degradation processes under different fatigue conditions (frequency, stress, and temperature) have the same general characteristics but are shifted in time. This shift in time allows one to predict the long-term fatigue life using the data obtained over shorter time intervals. Based on the proposed theory, the fatigue failure is governed by the accumulation of strain energy density toward a critical value. Such a formulation allows one to address the effects of loading sequence or any arbitrary combination of loads on the fatigue life. In order to demonstrate the validity of the proposed life prediction concept that links materials to machines, a conceptual ground vehicle (CGV) will be designed and built. The CGV will be made of a chopped-fiber reinforced composite material. The investigation of CGV includes conducting both computational simulation and experimental verification of the dynamic response of a vehicle under a real-life loading history. The end result of the computational study is to predict the life (through stress and strain data) of the CGV using the theory developed here. In the computational simulation study, the geometrical modeling and stress analysis of the CGV will be conducted. This study relies upon the convergence check between the real-life loading extracted from the experiments and that predicted by the computational model. The experimental verification of the dynamic response of machine structures will include the design and fabrication of a CGV and a series of structural dynamic tests. To extract the real-life loading data, the CGV will be driven on the actual terrain with an on-board data acquisition system. Later, the system response data will be translated into the fatigue spectrum load for the laboratory test. The results of this project can link material selection/evaluation, CAD/CAM/FEA/Simulation, and durability/failure analyses into a life cycle design synthesis.