Changes in sound phenomena of a beam due to rib and weld properties

Abstract

Experiments will show how rib and weld discontinuities on a beam effect wave propagation and far-field sound radiation. Numerous aluminum and steel beams were constructed using a different rib and weld configuration. The beam dimensions were 5 cm × 0.635 cm × 2.44 m and the ribs had T-shaped cross sections of slightly varying dimensions. The beams were then suspended and sound pressure 2.5 cm from the beam surface was measured with a microphone. By changing the physical construction of the attachment area of the ribs it was possible to isolate and analyze the effects of the different construction parameters. Also, the existence and effect of residual stresses in the beams due to the construction process was investigated. Analysis of the data showed that both the ribs and the welds produced changes in the far-field sound radiation and the phase speed of the propagating waves. Also, the geometry and the means of attachment of the rib affected the sound field. Transmission and reflection coefficients were calculated, along with travel times of the waves, to verify the changes in phase speeds that were found. [Work supported by ONR, Contract No. N00014-93-1-0493.]