Sensitivity Assessment of the Nonlinear Resonant Ultrasonic Spectroscopy for Concrete Damage Detection

Nonlinear Resonant Ultrasound Spectroscopy is a nondestructive acoustic method which is able to measure the bulk hysteretic nonlinearity. This method monitors the shift of the resonant frequency in response of variations in the excitation frequency amplitudes. Measurements were performed on concrete samples exposed to temperatures of 200, 400, 600, 800, 1000, 1200 °C. The elastic modulus values are given to compare the Nonlinear Resonant Ultrasound Spectroscopy (NRUS) sensitivity. These are calculated from the measured velocities of ultrasonic pulses (linear acoustic method) and from the bulk density. The strengths of the samples obtained by destructive methods are also given. Based on these results, the NRUS method can be described as a very sensitive indicator of damage in concrete.

Dynamics of a Damping Device Based on Ishlinsky Material

In present paper we consider the damping properties of the oscillating system with hysteretic nature. The mathematical model of considered system is based on the operator approach for the hysteretic nonlinearity on the example of Ishlinsky material. Such a converter is a continual analogue of the set of stops connected in parallel. In the frame of the paper we compare the various approaches to modeling of damping systems. Namely, together with the hysteretic damper we consider the so-called nonlinear viscous damper which is a generalization of a standard linear damper with dependence on the velocity. The mathematical model of the considered system is formulated in terms of second order ordinary differential equation with hysteretic nonlinearity (namely, the operator-type nonlinearity). In comparison with the phenomenological models of hysteresis (such as Bouc-Wen model) that are often used in the modeling, the Ishlinsky model allows to " feel" the hysteretic nature of the material on the physical level. The major result of the presented paper is the comparison both the hysteretic and viscous (including the linear and nonlinear cases) dampers. Such a comparison is made in terms of transmission functions that reflect the "efficiency" of suppression of the external perturbations by the force transmission from an external source to the load. The results of numerical simulations showed the high efficiency of hysteretic damper both in and outside the resonance region (at the same time it is well known that the linear viscous damper has a weak efficiency outside the resonance region). The disadvantage of the hysteretic damper lies in the fact that its ability to dump the relative motion of the system under external forces is insignificantly reduced outside the resonance region.

Dynamics of a Upright Pole Coupled with Nonlinear Hysteretic Isolators under Harmonic Base Excitation

Leady isolator shows hysteretic nonlinearity. The isolation efficiency of leady isolator is an important problem in many engineering structures. In this paper, vibrations of a ceramic upright pole coupled with four leady isolators under harmonic base excitation are studied. A hysteretic force-deformation model of leady isolator is derived from experimental results. With this model, the vibration of the pole in rotation is studied. The frequency response is obtained analytically by employing harmonic balance method. The analytical results are agreed well with numerical results. The vibration of the pole is decreased greatly by leady isolator, especially near resonant case. The influences of system parameters on vibration response and resonant peak are discussed in detail.

Discrete hysteretic sine-Gordon model: soliton versus hysteresis

In this work we consider a nonlinear dynamical system which is a set of nonlinear oscillators coupled by springs with hysteretic blocks (hysteretic sine-Gordon model). The hysteretic nonlinearity is modeled using the phenomenological Bouc-Wen model). The wave processes (solitonic solutions) in such a system are investigated taking into account the hysteretic nature of the coupling.