Nonlinear Acoustic Spectroscopy Research Articles

The Possibility of Using Nonlinear Acoustic Spectroscopy with a Single Excitation Signal for Testing of Concrete Elements Damaged by High Temperature

This paper focuses on the use of nonlinear acoustic spectroscopy with one excitation signal for NDT of concrete parts exposed to high temperature. The rate of the temperature rise, the highest achieved temperature, time of exposure to elevated temperature and the cooling rate has an influence on the overall damage of concrete structures affected by fire. The test specimens described in this paper have been heated for various periods of time and at a different temperature. Nonlinear acoustic spectroscopy method was performed before and after heat load.

Nonlinear Acoustic Spectroscopy and Frequency Sweep Ultrasonics: Case on Thermal Damage Assessment in Mortar

An exhaustive study on thermal damage of Portland cement-based materials is addressed. Damage carried out at different temperatures on concrete between 40 and $$525\,^{\circ }\hbox {C}$$ were assessed by means of microstructural, physical and nondestructive tests. Microstructural analysis (thermogravimetry and scanning electron microscopy) showed the principal changes of the Portland cement hydrated products for the different analysed temperatures. Compressive and flexural strengths remained constant or even increased at a low heating temperature range, while the mass loss increases. Dilatometry analysis revealed important information about deformation incompatibilities between the paste and the aggregate. These results have been correlated with nondestructive tests: nonlinear impact resonance acoustic spectroscopy (NIRAS) and ultrasonic measures. The dynamic modulus and ultrasonic pulse velocity have closely predicted the linear stiffness decay of the specimens. However, hysteretic parameter from NIRAS analysis exhibited a different trend from stiffness-related parameters, keeping constant until $$250\,^{\circ }\hbox {C}$$ and suffering a huge increasing for 400 and $$525\,^{\circ }\hbox {C}$$ . Ultrasonic attenuation computed with a broadband ultrasonic signal (chirp) revealed interesting information about scattering components inside the material, and is sensitive to interfacial transition zone between aggregate and paste in a large range of frequencies. The correlation between microstructural, mechanical and nondestructive techniques were carried out successfully. Nonlinear vibration and ultrasonic attenuation are non-conventional parameters that gave specific information about a complex damage process, such as a thermal attack in highly heterogeneous materials (e.g. Portland cement composites).

Nonlinear Acoustic Spectroscopy Method for Nondestructive Testing of Thermally Damaged Concrete

Most concrete structures are subjected to a range of temperature corresponding to normal environmental temperatures. However, there are important cases where concrete structures may be exposed to much higher temperatures (e.g., jet aircraft engine blasts, building fires, chemical and metallurgical industrial applications in which the concrete is in close proximity to furnaces, and some nuclear power-related postulated accident conditions). Exposure of concrete to high temperatures affects its mechanical properties. In this paper we examine the dependence of the fundamental frequency on temperature to which the concrete beams were heated. Fundamental frequencies were obtained by an innovative method used Pseudorandom Binary Sequence of Maximum Length as a perturbation signal. For the verification of the results the Ultrasonic Pulse Velocity in concrete were also measured and flexural bending strengths were determined. The results show method with Pseudorandom Binary Sequence of Maximum Length as a perturbation signal as a very promising for non-destructive testing of thermally damaged concrete.

Non-linear Ultrasonic Spectroscopy as an Assessment Tool for the Structure Integrity of Concrete Specimens

On the basis of non-linear effect studies, new diagnostic and defectoscopic methods have been designed which are based on the elastic wave non-linear spectroscopy. The non-linear ultrasonic spectroscopy brings new prospects into the acoustic non-destructive testing of material degradation. Poor material homogeneity and, in some cases, the shape complexity of some units used in the building industry, are heavily restricting the applicability of "classical" ultrasonic methods. These linear acoustic methods focus on the energy of waves, which are reflected by structural defects, variations of the wave propagation velocity, or changes in the wave amplitude. However, none of these "linear" wave characteristics is as sensitive to the structure defects as the specimen non-linear response. In this way, non-linear methods thus open new horizons in non-destructive ultrasonic testing, providing undreamed-of sensitivities, application speeds, and easy interpretation. One of the fields in which a wide application range of non-linear acoustic spectroscopy methods can be expected is civil engineering. It is predicted that these advanced techniques can contribute a great deal to the improvement and refinement of the defectoscopic and testing methods in the building industry. The present paper deals with analyzing one of the non-linear ultrasonic defectoscopic methods from the viewpoint of its application to the concrete specimen structural integrity evaluation. Both intact specimens and specimens subject to various kinds of stress have been tested. The effect of structural defects on the elastic wave propagation has been studied.

The Possibilities of Nonlinear Ultrasonic Spectroscopy for the NDT in Civil Engineering

Current methods of non-destructive ultrasonic material testing are based on the analysis of elastic wave reflection, absorption and interference. These methods are difficult to apply to inhomogeneous building materials showing tiny cracks and defects distributed throughout the specimen bulk, or in the cases where the defect size is comparable with the wavelength. Analysis of these phenomena occurring in intricate shapes is also difficult. To cope with such problems, application of wave propagation related nonlinear effects and higher harmonic signal generation in the defect vicinity is advisable. Due to the presence of defects, the atomic potential energy ceases to be exactly harmonic. Second and third harmonic frequencies arise. In this domain, methods employing the nonlinear acoustic spectroscopy apply. These novel defectoscopic methods are based on the nonlinear behaviour of current defects and inhomogeneities regarding the elastic wave propagation processes. Unlike the electromagnetic and acoustic emission methods, which only allow the localization of currently emerging cracks and defects, the non-linear ultrasonic defectoscopy is all-defect-sensitive, thus constituting a method applicable to characterizing the quality and reliability of materials.

NDT of Mechanical Damaged Concrete Specimens by Nonlinear Acoustic Spectroscopy Method

Current research and development of non-linear ultrasonic spectroscopy methods shows these methods to be very promising for material testing and defectoscopy in the near future. Our experiments focused on the testing of lightweight concrete specimens using the single-frequency excitation method. We studied the concrete specimens' structure after having been stressed by a mechanical force. Measurements were realized before and after mechanical loading.

NDT of Reinforcement Corrosion Using Ultrasonic Spectroscopy

Corrosion of built-in steel reinforcement ranks among the most serious mechanisms of bridge structure degradation. There are many reasons for the corrosion to occur: failures occurring during the bridge construction, consequences of traffic load, or, simple, ageing of the structures. Visual inspection of a bridge provides general information on the bridge condition. However, it cannot provide any information on the internal structure and integrity of the reinforced concrete or pre-loaded elements of the bridge in question. This is why non-destructive diagnostic methods are acquiring growing importance, helping researchers to properly evaluate the condition of a bridge and decide upon the most convenient methods for maintenance, repair or refurbishment of the bridge in question or its parts and schedule them accordingly.In this domain, methods employing the non-linear acoustic spectroscopy (NEWS - Nonlinear Elastic Wave Spectroscopy) achieved rush advancement recently. They are based on the fact that a non-linearity, which is due to the presence of a defect, makes an extraordinary indicator of the structure damage. These new, non-destructive methods appear to be promising for application to a wide range of materials featuring relatively heavy non-homogeneities, and for a large span of sites, from micro-chip to bridge structures. The present paper deals with an experimental study of the application of non-linear ultrasonic spectroscopy methods to the detection of steel reinforcement corrosion and its consequences for reinforced concrete specimens subjected to corrosion induced degradation cycles.

Nonlinear acoustic spectroscopy of local defects in geomaterials

General approaches to solving the problem of nonlinear acoustic spectroscopy of defects in geomaterials are considered. Expressions that relate the nonlinear response (scattering at combination frequencies) to the position, orientation, and nonlinear characteristics of narrow cracks are obtained. The expressions describe a broad class of nonlinear interactions at a crack. The nonlinearity caused by the contact of uneven rough edges of a crack is analyzed in detail. The results of the analysis are compared with the results obtained earlier from considering micromechanical models and with experimental data. The satisfactory agreement between the theoretical and experimental values of Landau’s moduli suggests that the mechanism of contact nonlinearity may manifest itself in the process of fracture of polycrystalline rock, when narrow cracks with uneven edges are formed. Numerical examples demonstrate the possibility of determining the orientation and position of a narrow crack. The procedure of solving the problem of crack localization is illustrated by the example of a crack in a thin rod. The importance of taking into account the phase data in the determination of the crack coordinate is pointed out.

Nonconventional approaches to ultrasonic assessment of skeletal system

Conventional bone ultrasonometry is based on the transmission mode measurement of the linear acoustic parameters of bone (speed of sound and broadband attenuation). It is a well-established technique specifically for osteoporosis diagnostics though it is highly limited in its applications. It cannot be used for the assessment of the hip bone which is the most important area in characterization of the skeletal system and can hardly be used in pediatric applications, particularly in neonatology, for the assessment of newborns and premature and low-birth-weight infants skeletal systems, which became especially vital during the last few decades. There are several new ideas on acoustic assessment of the skeletal sites hardly accessible by the conventional bone ultrasonometry and on principles of the acoustic characterization of bone quality, fracture risk evaluation, and monitoring of therapeutic interventions. New approaches are based on the use of the ultrasound radiation pressure for the remote generation of acoustic waves in bones, on the use of various modes of guided acoustic waves having a propagation speed dependent on both the elasticity modulus and the bone thickness, on the use of geometrical dispersion of sound velocity for bone characterization, and the use of principles of nonlinear acoustic spectroscopy for remote bone testing. [Work supported by NIH.]

Nonlinear acoustic spectroscopy applied to damage detection of elastic structures

The strong linkage between damage and nonlinear elasticity of materials leads to much research in the field of nonlinear response of mechanical structures. The aim of this work is to demonstrate the relevance of nonlinear acoustic spectroscopy for damage detection in elastic structures. The proposed method consists of the observation of linear and nonlinear responses to harmonic excitations of the structure: the damage detection and localization are obtained from an array of sensors. The nonlinear response amplitude is proportional to the local nonlinearity (failure nonlinear elastic response). A dual frequency method has been demonstrated for cracked beam excited by two force sources located at different points; the theoretical analysis comes from the Green function method applied to each overtone displacement field, the crack elastic response is handled by a nonlinear force/displacement behavior. Small scale experiments are presented for aluminum and concrete beams and the experimental results confirm the capability of nonlinear acoustic spectroscopy for detection and monitoring of damaged structures. [Work supported by European Community.]

Nonlinear acoustic spectroscopy on the real squashing collective mode in 3He-B

We have excited the real squashing (RSQ) collective modes in 3He-B with two simultaneous ultrasound pulses, yielding two-phonon absorption (TPA). We also detected TPA using single-frequency high-intensity sound pulses. The Zeeman splitting of the parametrically excited RSQ mode has been demonstrated. We checked the dispersion relations of the J=2 + modes in zero magnetic field and extracted the collective mode velocities directly from experiments.