Structural buckling can lead to failure, but beyond the initial onset of buckling there exists a stable region within which
there may be no material damage, the structure retains the load carrying capacity, and can recover fully elastically when
unloaded. Reclaiming this region as valid design space requires the full understanding of changes in the structure that
take place in this post buckled region that precede failure. In addition, there is also a critical need for a monitoring
technique that can measure the extent of excursion of a given structural element into the post buckled region and ensure
that there is sufficient margin of safety. Such a monitoring technique based on vibration characteristics of buckled
structures is proposed in this paper. In this research, to determine the feasibility of such an approach, the natural
frequencies and mode shapes of an aluminum shear panel were monitored while the panel was undergoing different
levels of buckling under uniform edge shear. The changes seen in frequencies and mode shapes were found to a measure
indicative of the level of buckling deformation.
Among different failure modes observed in structures, loss of stability due to buckling is a major concern. Buckling may
be induced because of overload or as a consequence of other types of failures in the structure. This paper examines two
techniques, namely, vibration based analysis, and stress wave propagation analysis for detecting this onset of instability.
The responses of a bar and a plate are used to illustrate the effectiveness of the two approaches. These analyses were
performed through finite element simulations and limited experiments. Changes in vibration frequencies and mode shapes are found to provide good indications of the impending failure as well as its progress. Changes in the wave propagation characteristics showed some limited success in detecting the incipient buckling.
Most structural health monitoring analyses to date have focused on the determination of damage in the form of crack growth in metallic materials or delamination or other types of damage growth in composite materials. However, in many applications, local instability in the form of buckling can be the precursor to more extensive damage and unstable failure of the structure. If buckling could be detected in the very early stages, there is a possibility of taking preventive measures to stabilize and save the structure. Relatively few investigations have addressed this type of damage initiation in structures. Recently, during the structural health monitoring of a wind turbine blade, local buckling was identified as the cause of premature failure. A stress wave propagation technique was used in this test to detect the precursor to the buckling failure in the form of early changes in the local curvature of the blade. These conditions have also been replicated in the laboratory and results are reported in this paper. A composite column was subjected to axial compression to induce various levels of buckling deformation. Two different techniques were used to detect the precursors to buckling in this column. The first identifier is the change in the vibration shapes and natural frequencies of the column. The second is the change in the characteristics of diagnostic Lamb waves during the buckling deformation. Experiments indicate that very small changes in curvature during the initial stages of buckling are detectable using the structural health monitoring techniques. The experimental vibration characteristics of the column with slight initial curvatures compared qualitatively with finite element results. The finite element analysis is used to identify the frequencies that are most sensitive to buckling deformation, and to select suitable locations for the placement of sensors that can detect even small changes in the local curvature.
Most structural health monitoring analyses to date have focused on the determination of damage in the form of crack growth in metallic materials or delamination or other types of damage growth in composite materials. However, in many applications local instability in the form of buckling can be the precursor to more extensive damage and unstable failure of the structure. If buckling could be detected in the very early stages, there is a possibility of taking preventive measures to stabilize and save the structure. Relatively few investigations have addressed this type of damage initiation in structures. Recently, during the structural health monitoring of wind turbine blades, local buckling was identified as the cause of premature failure. Results from this investigation suggested that stress waves could be used for detecting the early signs of change in the local curvature that precedes buckling type of failure in this structure. These conditions have been replicated in the laboratory and detailed investigation on the ability of low frequency vibrations to detect the buckling displacement has been carried out. The experiment was performed on a composite bar. The results clearly show that low frequency vibrations could be used to detect the onset of buckling in which the local deflection is only of the order of 0.25 inches.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.