Abstract:

By using sine sweep and random vibration experiments, the dynamic response of two layers stacked packaging units of computers is investigated with different input acceleration spectral shapes, different input intensities of acceleration power spectral density (PSD) and different constraints. Acceleration sensors and I-scan system are respectively used to measure the acceleration response of computers and the dynamic force between the stacked boxes. The sine sweep experiment results show that the resonance frequency, resonance acceleration response of computer and peak of dynamic pressure ratio between boxes are obviously influenced by the constraint to stacked packaging units. The random vibration experiment results show that the acceleration PSD of the upper computer is mainly controlled by the first resonance frequency, and the acceleration PSD of the lower computer controlled together by the first and second resonance frequencies. The acceleration response of the upper computer in the first resonance region is much bigger than that of the lower computer; The product response of stacked packaging units is mainly subject to the excitation PSD in the resonance region, rather than that in the non-resonance region; The dynamic pressure PSD between boxes is mainly controlled by the first resonance frequency. The probability density function of force level-crossing between contact surfaces is of Weibull distribution; Strengthening the constraint to stacked packaging units can effectively suppress the pitch motions of boxes, and will make the boxes undergo a larger and broader force levels.

Key words: dynamic response, force level-crossing, power spectral density, random vibration, stacked packaging units