Evaluation of mean loading effects on vibration-based active airframe damage detection

Although mean loading is critical in the design of airframes, current structural health monitoring methods have not fully addressed the effects of mean loading on damage detection capability. In this study, an active vibration-based damage detection method was used to evaluate a damaged joint condition on a stiffened aluminum panel, a prototypical airframe feature. Interrogation frequencies and force levels were chosen based on the sensitivity of the induced nonlinear structural response to changes in active drive conditions. Repeated tests quantified the measurement uncertainty, to assess detection confidence at each damage increment. Adding static loading to the damage location had the effect of decreasing detection sensitivity, under constant drive conditions. However, adjusting drive amplitude and drive frequencies showed that significant sensitivity could be regained under tensile and compressive loading. Results indicate that the nonlinear vibration-based approach shows potential for application to relevant airframe structures, even when considering important static and operational load conditions.