Index of content:
Volume 136, Issue 2, August 2014
- NONLINEAR ACOUSTICS 
Quantitative linear and nonlinear resonance inspection techniques and analysis for material characterization: Application to concrete thermal damage136(2014); http://dx.doi.org/10.1121/1.4887451View Description Hide Description
Developed in the late 1980s, Nonlinear Resonant Ultrasound Spectroscopy (NRUS) has been widely employed in the field of material characterization. Most of the studies assume the measured amplitude to be proportional to the strain amplitude which drives nonlinear phenomena. In 1D resonant bar experiments, the configuration for which NRUS was initially developed, this assumption holds. However, it is not true for samples of general shape which exhibit several resonance mode shapes. This paper proposes a methodology based on linear resonant ultrasound spectroscopy, numerical simulations and nonlinear resonant ultrasound spectroscopy to provide quantitative values of nonlinear elastic moduli taking into account the 3D nature of the samples. In the context of license renewal in the field of nuclear energy, this study aims at providing some quantitative information related to the degree of micro-cracking of concrete and cement based materials in the presence of thermal damage. The resonance based method is validated as regard with concrete microstructure evolution during thermal exposure.
136(2014); http://dx.doi.org/10.1121/1.4884758View Description Hide Description
The mechanism of generating backward dragging forces on objects standing in the path of a single, translationally invariant, symmetric acoustic Bessel beam is studied. This paper aims to provide mechanical and structural conditions for the emergence of negative axial forces based on the elastodynamic response of acoustically penetrable objects and beam's nonparaxiality parameter. An extensive numerical study has been performed for various liquid and solid elastic cases to illustrate the validity of the proposed eigenfrequency-based conditions. Results have revealed the existence of a complex but interpretable link between the emergence of negative radiation forces on spheres illuminated by zero-order Bessel beams and the eigenfrequencies of the particle. Considerable progress has been made in elucidating these relationships, which may lead to the development of predictable and robust single-beam acoustic handling devices.