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I Negru, GR Gillich, ZI Praisach, M Tufoi, N Gillich. Natural frequency changes due to damage in composite beams. Journal of Physics: Conference Series, 628, 2015.

Abstract: Transversal cracks in structures affect their stiffness as well as the natural frequency
values. This paper presents a research performed to find the way how frequencies of sandwich
beams change by the occurrence of damage. The influence of the locally stored energy, for ten
transverse vibration modes, on the frequency shifts is derived from a study regarding the effect
of stiffness decrease, realized by means of the finite element analysis. The relation between the
local value of the bending moment and the frequency drop is exemplified by a concrete case. It
is demonstrated that a reference curve representing the damage severity exists whence any
frequency shift is derivable in respect to damage depth and location. This curve is obtained, for
isotropic and multi-layer beams as well, from the stored energy (i.e. stiffness decrease), and is
similar to that attained using the stress intensity factor in fracture mechanics. Also, it is proved
that, for a given crack, irrespective to its depth, the frequency drop ratio of any two transverse
modes is similar. This permitted separating the effect of damage location from that of its
severity and to define a Damage Location Indicator as a sequence of squared of the normalized
mode shape curvatures.

Keywords: damage detection, crack, frequency shift, vibration

Posted by Gilbert-Rainer Gillich

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