Delamination Detection Of Fiber Reinforced Composite Laminated Beams Using Modal Data

Fiber-reinforced polymer(FRP)composite laminates have been widely and popularly used in various engineering disciplines,such as aeronautical,marine,and automotive industries,due to their outstanding mechanical properties,such as lightweight and ease of manufacture.However,delamination or interlaminar damage is susceptible to occur because of the low inter-laminar fracture toughness of the matrix,which may significantly reduce the stiffness of the FRP laminates and then lead to a severe loss of structural integrity.Meanwhile,delamination is usually not visible from the surface.Therefore,it is necessary to develop a reliable and efficient method for delamination detection.Present work focuses on assess delamination in composite laminated cantilever beams by using the change ratio of modal data and an experience-based learning algorithm.A reverse detection method based on vibration modal data is proposed to quantify the location,size and interface layer of delamination damage in FRP composite laminated cantilever beams.The methods for delamination identification proposed in this paper are validated both numerically and experimentally.(1)In the numerical case,three types of objective functions are studied and compared,including the function using frequency change ratio only(F-based method),the function using modal shape change ratio only(MS-based method)and their combination function(F&MS-based method);Three-dimensional finite element models of intact and delaminated cantilever beams were established and their modal data were extracted.The effects of modal data of order 4,6,8 and 10 on delamination identification structures were compared;Three other algorithms(CMFOA,PSO and SSA)are compared for delamination identification of cantilever laminated beams;The robustness of F-based method and F&MS-based method is studied and compared.(2)The cantilever beam specimens without damage and with delamination damage were designed and manufactured,and the measured frequency and mode shape values of the specimens were obtained through modal tests.Then the measured data were used in the F-based and F&MS-based method to predict the delamination damage in the FRP cantilever beam specimens(experimental verification).Numerical results show that the proposed F&MS-based method can obtain excellent results in the three delamination variables(position,size and interface layer)of the composites.It is confirmed that the addition of mode shape information can significcantly improve the accuracy of interface layer prediction;The convergence speed and recognition accuracy may not improved with the increase of modal datasince they are generally related to the measured noise level;The F&MS-based method is not sensitive to the measurement noise even under the noise as high as 7% for frequency data 10% for mode shape data;In comparison to other three state-of-the-art optimization algorithms including CMFOA,PSO,and SSA,the proposed EBL is able to obtain more competitive results in delamination detection of laminated beams.The experimental results further indicated that the F&MS-based method can accurately detect the delamination in composite laminates.