Estimation of dynamic paramaters for viscoelastic materials by longitudinal vibration testing using pulse method
In this paper, two methods based on longitudinal vibration testing of a thin bar are proposed for measuring the dynamic parameters of the viscoelastic materials in a wide frequency region. First, an inverse method by FEM based on resonance measurement is presented, in which the measured response of longitudinal vibration is asymptotically approached by the forward calculated response from the finite element computation, then the dynamic parameters can be obtained. Second, an improved wave propagation measurements based on free end longitudinal vibration signal is described. In which the dynamic parameters in the frequency range of 1kHz to 5kHz are calculated from the vibration velocity ratio between the long bar and the short bar.
Bond stresses in a randomly vibrating sandwich plate: Multi-modal theory
Abstract The excitation of sandwich plates by the acoustic coincidence effect is first discussed. A Fourier analysis is then carried out to find the bond normal stress in a sandwich plate excited by general random noise pressures. The general solution is then restricted to the plane wave excitation of a sandwich beam. The effect of inclining the plane waves at the correct angle for coincidence effect excitation is discussed and calculations are made for a sandwich beam of typical dimensions. It is found that, compared with normal incidence plane wave excitation, coincidence effect excitation can produce larger stresses. It is particularly noteworthy that several of the higher order modes of vibration of the beam can be excited in a near coincidence condition at the same angle of plane wave incidence. This is because the flexural wave velocity in sandwich plates is almost independent of frequency at shorter wavelengths.
Evaluation of buckling load and dynamic performance of steel shear wall retrofitted with strips made of shape memory alloy
One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.