Nonlinear Resonant Ultrasound Spectroscopy Research Articles

비선형 초음파공명 특성을 이용한 미세균열 탐지

기존 비파괴평가 기술의 결함 탐지 한계를 극복하기 위하여 비선형 초음파공명 특성을 이용한 미세 균열 진단 기술을 개발하였다. 가진 전압에 따른 초음파공명 주파수의 천이현상과 정규화 공명 진폭 감소 현상을 비선형 초음파공명 특성 파라미터로 제안하였으며 이를 실험적으로 확인하였다. CT 시편에 피로시험을 통하여 미세한 자연 균열을 생성하였으며 피로 사이클 단계마다 초음파공명주파수와 정규화 공명진폭의 변화를 측정하였다. 무결함 또는 10 <TEX>${\mu}m$</TEX> 정도의 매우 미세한 균열이 존재하는 시편에서는 초음파공명 주파수 천이현상이나 정규화 공명 진폭의 변화가 나타나지 않는 반면에 30 <TEX>${\mu}m$</TEX>급 이상의 미세 균열 시편에서는 균열 크기가 증가함에 따라 초음파공명주파수의 천이 현상이나 정규화 공명 진폭의 감소량이 증가함을 확인하였다. In order to overcome the detection limit by the current nondestructive evaluation technology, a nonlinear resonant ultrasound spectroscopy(NRUS) technique was applied for detection of micro-scale cracks in a material. A down-shift of the resonance frequency and a variation of normalized amplitude of the resonance pattern were suggested as the nonlinear parameter for detection of micro-scale cracks in a materials. A natural-like crack were produced in a standard compact tension(CT) specimen by a low cycle fatigue test and the resonance patterns were acquired in each fatigue step. As the exciting voltage increases, a down-shift of resonance frequency were increases as well as the normalized amplitude decrease. This nonlinear effects were significant and even greater in the cracked specimen, but not observed in a intact specimen.

Nonlinear resonant ultrasound spectroscopy is sensitive to the level of cortical bone damage

The objective of the study was to evaluate the sensitivity of nonlinear resonant ultrasound spectroscopy (NRUS) measurements to the accumulation of damage in cortical bone by fatigue or by controlled crack propagation. Two groups of human cortical bone specimens were prepared from the femoral mid-diaphysis. The specimens from the first group were taken through a progressive fatigue protocol consisting of four steps of cyclic four-point bending. The specimens from the second group were taken through a toughness protocol consisting of initiation and controlled propagation of a stable crack induced by 4-point bending mechanical loading. Our results evidenced a progressive increase of the normalized nonlinear elastic parameter during fatigue testing or during toughness experiments. While in specimens subjected to mechanical fatigue cycling the relative variation of nonlinear elasticity was significantly related to the relative variation of the number density of small cracks assessed with micro-computed tomogr...

J042015 オーステナイト系ステンレス鋼SUS304のクリープ損傷評価への非線形超音波スペクトロスコピー法の適用

In this paper, we describe the change of nonlinearity by the nonlinear resonant ultrasound spectroscopy (NRUS) during creep damage in an austenitic stainless steel, JIS-SUS304, under 120MPa, 973 K. which is a resonance-based technique exploiting the significant nonlinear behavior of damaged materials. In NRUS, the resonant frequency of an object is studied as a function of the excitation level. As the excitation level increases, the elastic non-linearity is manifest by a shift in the resonance frequency. NRUS exhibits high sensitivity to microstructural change of damaged materials. We use an electromagnetic acoustic transducer (EMAT) to monitor NRUS of bulk shear wave propagating in the thickness direction of the sample. The EMAT operates with the Lorentz-force mechanism and is the key to establish a monitoring for microstructural change during creep with high sensitivity. Furthermore, use of EMAT makes contactless transduction possibility. We also monitor the change of linear ultrasonic characterizations, shear-wave attenuation and velocity. NRUS exhibits much larger sensitivity to the damage accumulation than the velocity. This measured NRUS showed a peak at 50 % of the total life. We interpreted these phenomena in terms of dislocation mobility and restructuring, with support from scanning electron microscope (SEM) and transmission electron microscope (TEM) observations. The NRUS evolution as creep progress is related to the microstructure change, especially, dislocation mobility. This is supported by TEM observation for dislocation structure. This technique has potential to assess the damage advance and to predict the creep life of metals.

J042042 非線形三波相互作用法による金属材料の疲労過程中の非線形超音波挙動の変化

In this study, we applied non-contacting NRUS (Nonlinear resonant ultrasound spectroscopy), and nonlinear three-wave interaction methods with non-contacting transducer, EMAT (Electromagnetic acoustic transducer) to evaluation of fatigue damage in pure copper plates subjected to zero-to-tension fatigue loading. They are resonance-based techniques exploiting the significant nonlinear behavior of damaged materials. In NRUS, the resonant frequency of an object is studied as a function of the excitation level. As the excitation level increases, the elastic nonlinearity is manifest by a shift in the resonance frequency. In nonlinear three-wave interaction method, two intersecting ultrasonic waves produce a scattered wave when the resonance condition is satisfied. The wave amplitude is measured. NRUS and nonlinear three-wave interaction methods exhibit high sensitivity to micro-structural change of the damaged material. They rapidly increase from 60 % of fatigue life to the fracture. The change of the nonlinear acoustics in three-wave interaction methods sensitivity is higher than that in NRUS. These noncontact resonance-EMAT measurements can monitor the evolution of the nonlinear acoustics throughout the fatigue life and has a potential to assess the damage advance and to predict the fatigue life of metals.

J042014 非線形超音波共鳴理論の構築

J042014 非線形超音波共鳴理論の構築

High-accuracy acoustic detection of nonclassical component of material nonlinearity

The aim is to assess the nonclassical component of material nonlinearity in several classes of materials with weak, intermediate, and high nonlinear properties. In this contribution, an optimized nonlinear resonant ultrasound spectroscopy (NRUS) measuring and data processing protocol applied to small samples is described. The protocol is used to overcome the effects of environmental condition changes that take place during an experiment, and that may mask the intrinsic nonlinearity. External temperature fluctuation is identified as a primary source of measurement contamination. For instance, a variation of 0.1 °C produced a frequency variation of 0.01%, which is similar to the expected nonlinear frequency shift for weakly nonlinear materials. In order to overcome environmental effects, the reference frequency measurements are repeated before each excitation level and then used to compute nonlinear parameters. Using this approach, relative resonant frequency shifts of 10(-5) can be measured, which is below the limit of 10(-4) often considered as the limit of NRUS sensitivity under common experimental conditions. Due to enhanced sensitivity resulting from the correction procedure applied in this work, nonclassical nonlinearity in materials that before have been assumed to only be classically nonlinear in past work (steel, brass, and aluminum) is reported.

Carbonation assessment in concrete by nonlinear ultrasound

The carbonation process results in a change in the elastic properties of concrete, resulting in a variation of standard acoustic indicators such as wave speed. However, this evolution is too low to ensure an efficient carbonation assessment. The present communication focuses on the feasibility of carbonation assessment in concrete by applying Nonlinear Resonant Ultrasound Spectroscopy (NRUS). The results show that the nonlinear parameter is significantly affected by the presence of carbonation, which is interpreted with respect to the evolution of concrete microstructure in the presence of this pathology.

Localization of material defects using nonlinear resonant ultrasound spectroscopy under asymmetric boundary conditions

The position of microscopic defects in a one-dimensional bar is analyzed by means of the nonlinear resonant ultrasound spectroscopy technique under asymmetric boundary conditions. Experimental results on cementitious material confirm the feasibility of the method to locate nonlinear scatterers. Good agreement between the real damage position and the inferred experimental prediction is obtained based on information about the nonlinear frequency shift and about the amplitude ratio of the third and fifth harmonic for the fundamental resonance mode.

Microdamage evaluation in human trabecular bone based on nonlinear ultrasound vibro-modulation (NUVM)

The primary aim of this work is to investigate the potential of nonlinear ultrasound for microdamage detection in human bone. Microdamage evaluation in human bone is of great importance, because it is considered a significant parameter for characterizing fracture risk. Experiments employing nonlinear acoustic vibro-modulation were carried out in human femoral trabecular specimens removed during surgery. A frequency mixing (inter-modulation) was observed between an ultrasound wave, propagating in the bone, and a low-frequency vibration applied directly to the bone specimens. The appearance of side frequencies, which are related to the vibrational excitation, around the fundamental ultrasound frequency manifests the modulation nonlinear phenomenon. Instead of inducing microdamage by mechanical fatigue loading, specimens with different degree of osteoporosis were used. The experiments demonstrated that osteoporotic bone exhibits stronger nonlinearity compared to healthy bone presenting significant increase of the modulation amplitude with increasing degree of osteoporosis. The obtained results indicate that, in contrast to conventional hysteretic nonlinearity, dissipative acoustic nonlinearity can be of significance in the generation of nonlinear modulation effects. In the proposed technique the size and the shape of samples are not crucial compared to nonlinear resonant ultrasound spectroscopy (NRUS). Furthermore, the method is sensitive to the presence of microdamage, non-invasive, easy to implement and most important, it can be proved valuable tool for in vivo bone damage characterization.

Nonlinear ultrasound can detect accumulated damage in human bone

Bone micro-damage is commonly accepted as a relevant parameter for fracture risk assessment, but there is no available technique for its non-invasive characterization. The objective of this work is to study the potential of nonlinear ultrasound for damage detection in human bone. Ultrasound is particularly desirable due to its non-invasive and non-ionizing characteristics. We show results illustrating the correlation of progressive fatigue of human bone samples to their nonlinear dynamical response. In our experiments, damage was induced in 30 samples of diaphyseal human femur using fatigue cycling. At intervals in the cycling, the nonlinear response of the samples was assessed applying Nonlinear Resonant Ultrasound Spectroscopy (NRUS). The nonlinear parameter α, which in other materials correlates with the quantity of damage, dramatically increased with the number of mechanical testing cycles. We find a large spread in α in the pristine samples and infer that the spread is due to damage differences in the sample population. As damage accumulates during cycling, we find that α is much more sensitive to damage than other quantities measured, including the slope and hysteresis of the load/displacement curve, and the dynamic wavespeed. To our knowledge, this study represents the first application of the concept of nonlinear dynamic elasticity to human bone. The results are promising, suggesting the value of further work on this topic. Ultimately, the approach may have merit for in vivo bone damage characterization.

Understanding the effect of boundary conditions on damage identification process when using non-linear elastic wave spectroscopy methods

This paper presents an experimental campaign aimed at understanding the limitations and capabilities of non-linear elastic wave spectroscopy (NEWS) non-destructive technique (NDT) methods in the presence of variable boundary conditions. In particular, the objective was to understand if the contact between the structures under investigation and the clamps used to hold the structures could generate non-classical non-linear effects that could affect the damage detection process by producing false-positive indications of defects presence. Two different techniques were analysed with varying degree clamping torque. The first approach evaluates the resonance frequency shift as a function of the external load amplitude, and it is called non-linear resonant ultrasound spectroscopy (NRUS). The second method used, called non-linear wave modulation spectroscopy (NWMS), monitors the generation of sidebands and harmonics when the structure is excited by a double tone external load. The results showed that the non-classical hysteretical non-linear effects were dependent on the boundary conditions, highlighted by the presence of resonance shift and harmonics and sidebands in an undamaged sample. This research shows that more work is needed to demonstrate the effectiveness of the methods and the ease of implementation in a structural health monitoring system and further research studies and methodology development are needed to discern non-classical non-linear effects generated by contacts between mating parts (clamps and sample) from that generated due to the presence of damage.

Multi-mode nonlinear resonance ultrasound spectroscopy for defect imaging: An analytical approach for the one-dimensional case

A nonlinear version of the resonance ultrasound spectroscopy (RUS) theory is presented as an extension of the RUS formalism to the treatment of microdamage characterized by nonlinear constitutive equations. General analytical equations are derived for the one-dimensional case, describing the excitation amplitude dependent shift in the resonance frequency and the generation of harmonics resulting from the interaction between bar modes due to the presence of either localized or volumetrically distributed nonlinearity. Solutions are obtained for classical cubic nonlinearity, as well as for the more interesting case of hysteresis nonlinearity. The analytical results are in excellent quantitative agreement with numerical calculations from a multiscale model. Finally, the analytical formulas are exploited to infer critical information about damage position, degree of nonlinearity, and width of the damage zone either from the shifts in resonance frequency occurring at different excitation modes, or from the shift and the harmonics predicted at a single mode. Unlike other techniques, the multi-mode-nonlinear RUS method does not require a spatial scan to locate the defect, as it lets different excitation modes, with different vibration patterns, probe the structure. Two general methods are suggested for inverting experimental data.

Applying nonlinear resonant ultrasound spectroscopy to improving thermal damage assessment in concrete

Nonlinear resonant ultrasound spectroscopy (NRUS) consists of evaluating one or more resonant frequency peak shifts while increasing excitation amplitude. NRUS exhibits high sensitivity to global damage in a large group of materials. Most studies conducted to date are aimed at interrogating the mechanical damage influence on the nonlinear response, applying bending, or longitudinal modes. The sensitivity of NRUS using longitudinal modes and the comparison of the results with a classical linear method to monitor progressive thermal damage (isotropic) of concrete are studied in this paper. In addition, feasibility and sensitivity of applying shear modes for the NRUS method are explored.

Bone micro-damage assessment using non-linear resonant ultrasound spectroscopy (NRUS) techniques: A feasibility study

Non-linear resonant ultrasound spectroscopy (NRUS) is a technique exploiting the significant non-linear behavior of damaged materials, related to the presence of damage. This study shows for the first time the feasibility of this technique for damage assessment in bone. Two samples of bovine cortical bone were subjected to a progressive damage experiment. Damage accumulation was progressively induced in the samples by mechanical testing. For independent assessment of damage, X-ray CT imaging was performed at each damage step, but only helped in the detection of the prominent cracks. Synchrotron micro-CT imaging and histology using epifluorescence microscopy were performed in one of the two samples at the last damage step and allowed detection of micro-cracks for this step. As the quantity of damage accumulation increased, NRUS revealed a corresponding increase in the non-linear response. The measured change in non-linear response is much more sensitive than the change in elastic modulus. The results suggest that NRUS could be a potential tool for micro-damage assessment in bone. Further work has to be carried out for a better understanding of the physical nature of damaged bone, and for the ultimate goal of in vivo implementation of the technique where bone access will be a challenging problem.

Nonlinear resonant ultrasound spectroscopy (NRUS) applied to damage assessment in bone

Nonlinear resonant ultrasound spectroscopy (NRUS) is a resonance-based technique exploiting the significant nonlinear behavior of damaged materials. In NRUS, the resonant frequency(ies) of an object is studied as a function of the excitation level. As the excitation level increases, the elastic nonlinearity is manifest by a shift in the resonance frequency. This study shows the feasibility of this technique for application to damage assessment in bone. Two samples of bovine cortical bone were subjected to progressive damage induced by application of mechanical cycling. Before cycling commenced, and at each step in the cycling process, NRUS was applied for damage assessment. For independent assessment of damage, high-energy x-ray computed tomography imaging was performed but was only useful in identifying the prominent cracks. As the integral quantity of damage increased, NRUS revealed a corresponding increase in the nonlinear response. The measured change in nonlinear response is much more sensitive than the change in linear modulus. The results suggest that NRUS could be a potential tool for micro-damage assessment in bone. Further work must be carried out for a better understanding of the physical nature of damaged bone and for the ultimate goal of the challenging in vivo implementation of the technique.

Elastic nonlinearity and damage detection in quasibrittle materials using single mode nonlinear resonant ultrasound spectroscopy (SIMONRUS)

A promising tool for NDT of quasibrittle materials has been developed and applied in the field of damage detection. The technique focuses on the acoustic nonlinear response of the material’s resonance modes when driven at small wave amplitudes. A diagnostic method was constructed to quantify the acoustic nonlinearity of homogenous and isotropic samples in bench-top resonance experiments. The analysis of the data is supported by a phenomenological model based on the Preisach model of hysteresis. Six material parameters—two linear and four nonlinear—can be extracted from a simple set of amplitude-dependent resonance experiments, and completely define the material state of the sample. The characterization procedure is applied to damage detection in slate plates. Linear and nonlinear parameters were measured for progressive fatigue induced by cyclic mechanical loading. A rapid increase of the nonlinear parameters was observed early in the loading process and only a small to modest variation of the linear parameters. Near failure, the nonlinear coefficient deduced from the softening of the modulus increased by a factor of 1000. Similar observations were made when analyzing the second and third harmonics. Presently, linear and nonlinear behavior of slate exposed to natural and accelerated hygrothermal aging is being monitored.