Search

Modal parameter identification is adversely affected by the mass loading of the transducer in experiments, especially when multi-transducers are arranged on the lightweight structure. In order to remove the coupling effects of transducers on each measurement point, a hierarchical multi-transducers eliminations method based on Sherman–Morrison theory is investigated. The method consists of two steps: (1) Decomposition: multiple elimination is decomposed into multi-levels, the relationship of the frequency response functions between each level is illustrated in the tree diagram; (2) Elimination: according to the relationship between each level, the measured frequency response functions are modified level by level. Numerical simulation is conducted by employing a three-degrees-of-freedom spring-mass system and the robustness is verified in the noise case. Experimental investigations are undertaken by employing a lightweight cantilever beam: Laser Doppler vibrometer is adopted to obtain measured frequency response functions without transducer mass loading effect, which are regarded as the target data. The initial frequency response functions are obtained in the case, in which multi-accelerometers are arranged and the effects should be removed. The result shows that the method can effectively decouple the frequency response functions due to transducers. In the elimination process, it is necessary to delete duplicate information (frequency response functions), which can greatly reduce the amount of calculation. And the effects of multi-transducers mass can be removed and the corrected frequency response functions are in quite good agreement with the target values. [ABSTRACT FROM AUTHOR]

Uncertainties are generally included in elastic parameters of the fiber reinforced textile composites. An approach on predicting the statistical characteristics of elastic modulus of braided composites using vibration test data is proposed in this paper. The method consists of two main steps, firstly estimate the initial mean values of the orthotropic elastic parameters by adopting the homogenization method, and then identify the variability of the elastic constants using a stochastic model updating algorithm with the first-order perturbation approach, the uncertain parameters are assumed as the summation of mean value and a deviation term with zero mean. A braided composite panel is employed in numerical simulations to verify the proposed method, the random samples of experimental modal data are simulated with the Latin Hypercube Sampling technique based on a reference finite element model, which is constructed by using deterministic updated elastic parameters. Results show that the mean value and standard deviation of the uncertain effective parameters of braided composite can be identified from modal data using the proposed stochastic identification method. [ABSTRACT FROM AUTHOR]

The honeycomb sandwich composite material has been widely applied in engineering due to its excellent mechanical performance. The elastic properties of honeycomb core is of crucial importance in efficient mechanical analysis. An approach on determining the equivalent elastic modulus of honeycomb core using experimental modal data is proposed in this paper. Based on analytically predicted elastic constants of the pure core, the initial finite element model of a honeycomb panel is constructed using a three-layer sandwich theory; according to errors that exist in analytically estimated equivalent parameters and the sensitivity analysis of modal frequencies with respect to system parameters, the out-of-plane shear moduli G cxz and G cyz are selected to be determined. Consequently, the two parameters are determined by minimizing an objective function which is formulated with vibration test and numerical modal data. Comparative investigations are conducted to illustrate that the initial values of the parameters with physical significance play an important role in the identification procedure. The presented method can provide accurate and reliable predictions of material constitutive parameters of honeycomb core. [ABSTRACT FROM AUTHOR]