ON CRACK IDENTIFICATION AND CHARACTERIZATION IN A BEAM BY NONLINEAR VIBRATION ANALYSIS

The weakly non-linear character of a cracked vibrating beam is exploited for the purpose of determining crack location, depth and opening load. The approach is motivated by examining the response of a bilinear spring-mass system to excitation at two frequencies, such that the difference between the two frequencies is the resonant frequency of the system. The numerically generated steady state response of the system clearly betrays the presence of the bilinear spring, even if the difference between the compressive and tensile stiffness is very small. The same idea is applied to a cracked beam forced at two frequencies, with the crack providing a local bilinear stiffness in the beam. The numerically generated steady state response shows the effect of the opening and closing of the crack. The prominence of this non-linear effect is then correlated with crack position and depth. It is shown that the non-linear effect is maximized if a static load is also placed on the beam that would cause the crack to be on the verge of opening, thus determining the opening load.