Inverse determination of local variations of constituent level elastic parameters of FRP composite plates

Abstract

ABSTRACTA novel technique for the determination of local variations in the constituent level elastic parameters of fibre reinforced plastics composite plates has been presented from experimentally measured natural frequencies and mode shapes or frequency response functions (FRF) using finite element model updating technique. The constituent level elastic parameters, i.e. the fibre and matrix stiffnesses for a ‘patch area’ having different elastic properties from the rest of the structure have been estimated quantitatively. The location and extent of this patch can be predicted a-priori from careful comparison of mode shapes. The methodology uses the correlations between the experimentally measured frequencies and mode shapes or FRFs and their corresponding values from finite element predictions of the ‘patch plate’. The objective function, consisting of the weighted differences in the undamped eigenvalues as well as the normalized mode shapes or FRFs of the two models, is minimized in the least square sense using a gradient-based inverse eigen-sensitivity method implemented through a computer program. The methodology has been demonstrated through a numerically simulated example first, followed by a real experimental case study. Results indicated that the efficiency and the robustness of the algorithm depend upon the accuracy of the acquired modal data.