Experimental studies of welding effects on damping for undersea warfare applications

Abstract

Damping in structures has historically been of great importance in nearly all branches of engineering endeavors, and it also happens to be one of the most difficult parameters to predict. The purpose of this research is to study the effects that welding has on damping. Measurements and comparisons of the damping ratios of two welded stiffened plates, two flat plates and one machined stiffened plate are undertaken. The frequency response and natural frequencies of five steel structures are determined experimentally. A finite element model is created for three of the structures to determine the natural frequencies and associated mode shapes. The damping ratios are then determined using the half-power point method. The results show that at frequencies less than 500 Hz, welding tends to cause the damping ratio to increase. The experimental and numerical results show that the mode shapes that experience the highest degree of stress at a weld are associated with the natural frequencies with the highest damping ratio. These results may lend to better understanding of the effects of welding on damping and assist in obtaining better empirical approximations of damping for use in ship shock computer simulations.