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The tube-array structures coupled both with the fluid and the axial load is focused. In a heat exchanger, the tubes are frequently affected by cold and hot fluid shock waves. Thus, tubes are often found to be vibrated and even to be worn out. This vibration may not only alter the performance of the tubes but also introduce the damage in the heat exchanger. In this work, the dynamic properties of coupled tube-array structures with the axial loads are investigated. Futher, the tube-array structures in a heat exchanger, consisting of periodic cooling tubes are also considered to simulate as a coupled periodic structure system. It is found that each tube of the system is weakly coupled to the adjacent tube via water. By using the Galerkin method, the equations of the coupled system with the fluid effect can be derived. Numerical results reveal that the axial load and fluid effects may influence the dynamic properties of a fluid coupled tubearray structures system of a heat exchanger significantly.

The buckling and the critical speed of a micro drill in a drilling process were investigated in this study. The trend towards higher density printed circuit boards (PCB), requires smaller holes, down to 0.3 mm in diameter, to be drilled through the board. Due to the micro scale, the drilling fracture is frequently found in a micro drilling process. In all drilling fracture cases, fractures caused by buckling are most frequently found, because of the super high spinning speed and the micro scale. To improve the quality, produce a higher production rate and avoid the drill breakage, the buckling load and critical speed in the micro drilling process must be studied. A stepped pre-twisted beam is used to simulate the micro drill. A moving WinklerType elastic foundation is used to approximate the drilling process. A time dependent vibration model for drilling is presented. In an actual engineering application, the drill fracture is frequently found in a micro drilling process. In many cases, it would be caused by the time dependent buckling. The investigation on the buckling and critical speed properties in the micro drilling process to depress the time dependent buckling is presented in this work. The effects of rotating speed, pre-twisted angle and thrust force on the buckling and critical speed of the micro drill are considered. The numerical analysis indicates that the buckling load is reduced suddenly as the micro drill moves into a work piece.

The trend toward higher-precision manufacturing technology requires more micro-machining, such as micro-milling. The dynamic characteristics of the micro-milling process must be studied to improve quality, produce a higher production rate, and avoid micro-mill breakage. A dynamic model of a micro-stepped mill with time-dependent cutting-boundary conditions was studied to understand the dynamic characteristic of a micro-mill in the milling process. This work presents the dynamic model and numerical analyses on vibration in micro-milling. An experiment’s result is used to validate the accuracy of the above model. A stepped pre-twisted beam was used to simulate the micro-end mill. The time-dependent boundary and cutting force were used to approximate the milling process. Consequently, a time-dependent vibration model in a micro-milling process is presented. The effects of the rotation speed, cutting depth and boundary stiffness on the dynamic characteristics were considered. Both numerical and experimental analyses indicate that the vibration amplitude was reduced as the micro-mill moved into a work piece.