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.
Women and Politics in Early Tudor England
Political historians working on the early Tudor period have traditionally concentrated on institutions – monarchy, council, parliament, courts, and administrative bodies – that excluded women. The very definition of politics underlying the dominant historiography has thus made it seem both natural and inevitable to write history as if the world of high politics, the world that really counted, were exclusively male.