This 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.
