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Vehicle Holding Device(VHD) has a role that holding the launch vehicle on its launch pad until the engine therust reaches a steady condition. The analytical study of shape parameters and dynamic characteristics of hydraulic cylinders is carried out. The contraction of cylinder is considered as the major factor of releasing mechanism. Through the analysis, the decreasing of cylinder slit size and increasing initial charging pressure increase the contraction force. Through the transient analysis, cylinder load, displacement and inner pressure distribution are confirmed. The cylinder contraction force is converged to the cylinder external force when the cylinder starts to move. Also, the pressure distribution in the hydraulic cylinder is constant.

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A fatigue life is one of the key design factors for crawler excavators because they are usually operated in a very harsh working condition. In order to evaluate the fatigue life, the fatigue loads in various working conditions should be decided in advance. In case of the attachments such as boom and arm, the forces at the bucket tip due to digging and lifting are primary fatigue loads, which can be calculated relatively easily using design specifications. However, the forces at the track need to be considered additionally for the upper and lower frames. And it is almost impossible to measure the forces at track in a field test. In this study, a dynamic model of excavator including track system is implemented and dynamic load simulations are carried out to investigate the distribution of the reaction forces at each roller for the typical working scenarios. The model and the simulation technique are verified by comparison with the results of measurement in view of weight balance, cylinder forces, accelerations of counter weight and stresses at concerned points. The normalized distribution of the reaction forces at each roller in digging and lifting working mode are presented and the distribution is expected to be used as the baseline of fatigue load estimation for the upper and lower frames of various class crawler excavators. To get the multibody dynamic simulation results by the excavator motion, we used the commercial software such as Recurdyn for kinematic and dynamic modeling. Especially the track modeling of the excavator is composed using Track_LM module of the Recurdyn. And stress analysis of the frame is carried out using the NX-Nastran program.

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