Guided wave structural health monitoring is a challenging problem, in part because of the complexity of signals received in a real structure containing geometrical features and boundaries. Signals scattered from damage can be one or two orders of magnitude smaller in amplitude than the direct arrival. Detection of these small, scattered signals is often accomplished by comparing signals of interest to one or more baseline signals recorded from the undamaged structure. Previous work by many researchers has shown that homogeneous temperature changes as small as a few degrees Celsius can mask damage unless compensation is made. Here we consider the impact of applied loads on complex guided wave signals because such loading effects may be unavoidable in the in situ environment. Experiments were performed and are described where data from a spatially distributed array of piezoelectric sensors are recorded as a function of applied uniaxial load before and after introduction of simulated damage via an attached mass. Load-dependent signal changes in both short and long time regimes are considered, and their impact on structural health monitoring is discussed.
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