Effect of experimental pre-stress and residual stress on modal behaviour

Considerable research effort has been expended demonstrating the existence of variability in dynamic response characteristics of nominally identical structures. It is accepted that, however precisely the tolerances are defined for the finished product, the method by which these are achieved vary from one component to the next. It is inevitable that residual stresses within the component will arise and correspond to the severity of the manufacturing process. In addition, poorly defined tolerances will lead to lack of fit in redundant structures, causing geometry and stress-stiffening alterations due to the internal loads. The work presented in this paper considers the development of residual and prestresses in two simple structures under laboratory conditions. The residual stresses are introduced to the material through standard manufacturing processes. By the use of annealing the influences of the local stresses are identified. The source of variability due to the annealing process is compared with inconsistencies introduced by the measuring process. The second example considers the dynamic influence of introducing known loads within a redundant frame structure. The likely effects of imposed pre-stress and work hardening of structures during their working life are discussed.