Ideal process design approach for hot metal working

Xifan Wang


Structural health monitoring (SHM) methods are being explored as techniques to assess the integrity of mechanical, civil, and aerospace structures. Most of these methods detect or quantify damage by comparing current structural state measurements to stored baseline measurements collected from an undamaged structure. These baseline dependent methods assume that measured signals will not change when exposed to varying environmental and usage conditions. To avoid limitations of this assumption, baseline-free techniques such as vibro-acoustic modulation (VAM) are being explored. VAM is a nonlinear vibration technique in which the structure of interest is excited using a combination of specific frequencies and the response recorded. The VAM technique assumes that an undamaged structure can be represented by a linear system while the representation of a damaged structure must include nonlinearity. A nonlinearity is assumed to result in the generation of sideband responses. To demonstrate the use of VAM to detect fatigue cracking, experimental testing has been performed on existing damaged and undamaged specimens, as well as on fatigue specimens where cracks have been initiated and grown. Initial testing of the damaged and undamaged specimens provides validation for using VAM as a baseline-free SHM technique. Subsequent measurements during fatigue testing confirm this result. Two rectangular coupons were fatigue cycled to initiate and grow cracks. The VAM method detected cracks at 6.42 percent and 12.24 percent damaged cross-sectional area. Potential advantages and limitation of the use of VAM for fatigue crack detection are discussed, and recommendations for additional research efforts to improve or refine the technique are given.