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The use of mechanical vibrations to relieve residual stresses in engineering components is increasing in use. Several vibratory conditioning systems are commercially available. When the technique was considered for treatment of fabricated structures at Larsen and Toubro Limited, residual stress measurements were made to determine the effectiveness of the treatment. A bedplate structure was vibrated by means of a commercially available variable-frequency vibrator. Residual stresses were measured near a weld location in the structure before and after treatment. Stress relief of about 30 to 57 % was noted. During the vibratory treatment, surface strains were monitored; at resonance the applied surface strain amplitude was measured to be about 600 microstrains. Subsequent to machining, the bedplate showed good stability of dimensions. A stainless steel bowl assembly was fabricated with carbon steel cooling jackets. The bowl contained heavy weldments but could not be thermally stress relieved prior to machining. The bowl was treated by vibrations and the close tolerances on the machined dimensions were satisfied. Both the components described have been installed on site and have maintained dimensional stability.
welded joints, residual stress, vibrations, vibratory conditioning, stress relief, stress measurement
Nagendra Kumar, BV
Machinery Development, Larsen and Toubro Ltd., Powai Works, PRDH, Bombay,