Modeling and Measuring All the Elements of an Ultrasonic Nondestructive Evaluation System I: Modeling Foundations

Abstract

A comprehensive model of an ultrasonic nondestructive evaluation (NDE) flaw measurement system is developed that combines models for the electrical components (pulser/receiver, cabling), electromechanical components [transducer(s)], and the acoustic/elastic processes present in the materials being inspected, including the scattering of ultrasonic waves from a flaw. This model is called the electroacoustic measurement (EAM) model. Here, in Part I, the underlying modeling foundations of the EAM model are described in detail and the use of the EAM model is demonstrated in a transducer design study. This EAM model provides a new, powerful tool for analyzing virtually any element in the measurement process. In Part II it will be shown that this power can be extended to characterizing typical commercial measurement systems through the use of models and purely electrical measurements of the system components.     

Optimization of Periodic Permanent Magnet Configuration in Lorentz-Force EMATs

The relative merits of three different periodic permanent magnet (PPM) configurations are investigated for the generation of SH₀ waves with a Lorentz-force electromagnetic acoustic transducer (EMAT) on a 60-mm diameter aluminum pipe. Such transducers are often used for checking the integrity of pipelines. It was found that minimizing lift-off by using magnets machined to the same curvature as the pipe increased the magnitude of the generated wave by over 70%, compared to the use of a PPM with a single planar surface. A less expensive and more versatile alternative is to use a PPM for which the two lines of magnets are angled with respect to each other to realize closer average proximity to the pipe surface. Numerical simulations and experiments indicated that the amplitude of a SH₀ wave with this magnet configuration would still be approximately 60% higher than the reference case of a PPM with a single planar surface.     

Spatial localization of stress-perturbing wave generated by anelectromagnetic acoustic transducer

A new apodization of electromagnetic acoustic transducer has been proposed to generate the stress perturbing wave, which has a spatially localized magnitude distribution. According to the acoustoelastic effect, a stress perturbing wave radiated into metals gives rise to an ultrasound velocity change that corresponds to the deviation of the stress in the metal. In ultrasonic measurements, it is desirable to use a narrow beam in order to obtain a high resolution. A transducer has been constructed which has a Sinc function apodization. To compare with other types of electromagnetic acoustic transducers, including a Limited Bessel-type transducer, numerical simulations are performed. It is shown that the proposed transducer provides the optimum characteristics of the spatially localized magnitude distribution. Furthermore, experimental results are presented to confirm the numerical predictions     

Numerical Analysis for Eddy Current Characteristics of Magnetically Saturated Ferromagnetic Tubes

Abstract

Magnetic saturation is applied to ferromagnetic tubes inspected by the encircling or inner coil because suppressing magnetic noise is important for the eddy current testing technique. Eddy current signal characteristics in magnetically saturated tubes are different from those in nonmagnetic tubes. In ferromagnetic tubes, defect signal phase angle is not useful for estimating defect depth because it does not depend on the defect depth. In this paper, numerical eddy current analysis has been done in order to explain the relationship between the defect depth and the phase angle in magnetically saturated tubes. This analysis is performed as follows: 1) The magnetic permeability near the defect is calculated as the non-linear magnetostatic problem. 2) The eddy current distribution is calculated as the linear magnetodynamic problem using the incremental permeability value calculated in step 1. The numerical analysis results reveal that the permeability around the defect remains inhomogeneous and it causes the unique eddy current characteristics. Based on these calculated results, a quantitative evaluation method of determining defect depth is proposed. After determining the defect shape by using signal characteristics obtained from the strongly magnetizing state, the defect depth can be estimated by using the signal amplitude.     

Numerical simulations of an electromagnetic acoustictransducer-receiver system for NDT applications

The development of a multistage numerical model of an electromagnetic acoustic transducer (EMAT), with particular emphasis on an EMAT receiver, is presented. The model includes five separate modeling states: static magnetic field simulation of an electromagnet; pulsed eddy current distribution of a generic meander-line coil suspended over a conducting specimen; Lorentz force distribution due to the interaction of the static magnetic field with the eddy current distributions; acoustic wave generation and propagation based on the dynamic Lorentz forces; and acoustic wave detection by an EMAT receiver. In particular, it is shown how the transient particle displacement fields are converted into an induced voltage response as part of the EMAT receiver system. Numerical simulations show that the voltage response is dependent on the wire spacing of the receiver coil     

Modeling and Measuring All the Elements of an Ultrasonic Nondestructive Evaluation System I: Modeling Foundations

A comprehensive model of an ultrasonic nondestructive evaluation (NDE) flaw measurement system is developed that combines models for the electrical components (pulser/receiver, cabling), electromechanical components [transducer(s)], and the acoustic/elastic processes present in the materials being inspected, including the scattering of ultrasonic waves from a flaw. This model is called the electroacoustic measurement (EAM) model . Here, in Part I, the underlying modeling foundations of the EAM model are described in detail and the use of the EAM model is demonstrated in a transducer design study. This EAM model provides a new, powerful tool for analyzing virtually any element in the measurement process. In Part II it will be shown that this power can be extended to characterizing typical commercial measurement systems through the use of models and purely electrical measurements of the system components.     

Ultrasonic Transducer Sensitivity and Model-Based Transducer Characterization

Abstract

It is shown that the role that an ultrasonic piezoelectric transducer plays in both generating and receiving ultrasound in an ultrasonic nondestructive evaluation (NDE) measurement system can be completely described in terms of the transducer's electrical impedance and open-circuit, blocked force receiving sensitivity. Furthermore, it is shown that both of these quantities can be obtained experimentally via a model-based approach and purely electrical measurements. The measurement of sensitivity uses a method originally developed for lower-frequency acoustic transducers. However, it is shown that at the higher frequencies found in ultrasonic NDE applications electrical cabling effects play an important role and must be compensated for in determining the transducer sensitivity. Examples of experimental measurement results using these new approaches are given.     

Impulse Modeling of the Rayleigh Wave Propagation Generated by a Spherical Focused Transducer

In order to characterize materials locally by means of the Rayleight wave analysis, a new modeling of acoustic microscopy in the case of an impulse excitation is presented. The usualV(z) representation established for a given frequency component, is extended to the case of a broadband excitation of the transducer. Therefore, the time-dependant acoustic response of the material,s(z,t), is mainly composed of two echoes: the specular and the Rayleigh contributions which are resolved in time. In the first part, we demonstrate that the acoustic response can be represented by the time convolution product between the acoustic signal detected at the focus on an ideal reflector, and a function depending onz andt variables. This last function is connected to the tranducer emission profile, which includes the diffraction effects, and the reflectance of the material. In the second part, the modeling is discussed with regard to experimental data on several materials and takes into account the attenuation phenomena. Experimental results and computations are shown to be in a good agreement.     

Nucleation of 4He Crystal at Melting Pressure by Acoustic Waves

No Heading When an acoustic wave pulse of several msec was applied to superfluid ⁴He at melting pressure, ⁴He crystal was nucleated on the transducer and rapidly disappeared after the pulse. We measured thresholds of the acoustic wave power which induced a nucleation in the temperature range between 0.09 K and 1 K. The treshold of the nucleation exhibited no temperature dependence below 0.3 K. The nucleation was not induced above 0.6 K even if the injected acoustic pulse was strong. 0.6 K is close to the inversion temperature at which the direction of the force by acoustic wave was inverted on the solid-liquid interface of ⁴He [Phys. Rev. Lett. 90, 075301 (2003)]. Our observation indicates that the effect of acoustic radiation pressure contributes to the heterogeneous nucleation by acoustic waves.PACS numbers: 67.80.–s, 68.08.–p, 81.10.–h, 43.25.Qp.     

Interdiffusion in ternary Fe–Cr –Al alloys with variable molar volume

Abstract

For interdiffusion profiles obtained at 1000ºC in the Fe-rich corner of the ternary system Fe –Cr – Al the evaluation of these profiles with the method proposed by Dayananda and Sohn in 1999 has been performed. Further, an alternative mathematical model is presented which directly yields element mobilities and Kirkendall velocities from experiments if the Gibbs free energy of the system is given as a function of composition, temperature and pressure. Computer simulations show that, interestingly enough, already fairly weak deviations from (thermodynamic) ideality will lead to pronounced up-hill diffusion effects for the majority component, i.e. Fe.     

Meso-scale modeling of hypervelocity impact damage in composite laminates

ObjectivesThis paper presents an approach to numerical modeling of hypervelocity impact on carbon fiber reinforced plastics (CFRP).MethodsThe approach is based on the detailed meso-scale representation of a composite laminate. Material models suitable for explicit modeling of laminate structure, including fiber-reinforced layers and resin-rich regions, are described. Two numerical impact tests with significantly different impact energies were conducted on thermoplastic AS4/PEEK materials with quasi-isotropic layups. Simulations employed both SPH and Finite element methods.ResultsResults of simulations are verified against experimental data available from the literature and demonstrate good correlation with the experiments.ConclusionsDeveloped modeling approach can be used in simulations where post-impact damage progression in composite material is of the main focus.     

管件电磁成形数值模拟方法及缩径变形分析

随着电磁成形工艺应用的发展,需要强有力的数值模拟方法来预测成形过程,并用来指导成形系统设计.归纳了现有的电磁成形模拟方法及各自的特点,讨论了模拟中存在的问题和面临的挑战.应用FEM软件ANSYS对铝合金管件电磁缩径成形进行了数值模拟,研究了管件均匀缩径变形规律.变形管坯轮廓验证了电磁缩径成形的模拟结果.     

Piezoelectric tubes and tubular composites for actuator and sensor applications

Piezoelectric actuators and sensors made with a tubular structure can provide a great agility of effective response in the radial direction. For a radially poled piezoelectric tube, the effective piezoelectric constant in that direction can be tuned to be positive, zero or negative by varying the ratio of the outer radius (R _o) to the inner radius (r _o) of the tube. For a suitable ratio of R _o/r _o, this effective constant can also be changed in sign or set to zero by adjusting the d.c. bias field level for tubes made of electrostrictive materials. Therefore, one can make a piezoelectric transducer with all the effective piezoelectric tensile constants having the same sign. End-capped thin-walled tubes also exhibit an exceptionally high hydrostatic response, and the small size of the tubular structure makes it very suitable for integration into a 1–3 composite which possesses low acoustic impedance and high hydrostatic response.     

Doppler-Based Airborne Ultrasound for Detecting Surface Discontinuities on a Moving Target

Abstract

This paper presents a novel concept based on the acoustic Doppler effect for detecting defects on the surface of a rapidly moving object. The proof-of-concept tests show the feasibility of this approach. By impinging and detecting airborne ultrasound on a rotating target with surface notches, the Doppler effect was clearly observed in the spectral domain at the time when the transducer passed over the flawed zone. For continuous monitoring, the gated spectral magnitude is used to discriminate the signals returned from a flawed region against those from sound regions. In addition, two real-time signal processing techniques are proposed.     

DESIGN OPTIMIZATION FOR ROBUSTNESS USING QUADRATURE FACTORIAL MODELS

Abstract

This paper describes a robust optimization methodology for designs involving either complex simulations or actual experiments. The methodology adopts a new objective function that consists of the Expected Performance (EP) and the weighted Deviation Index (DI). The proposed Quadrature Factorial Model estimates the expected performance and the standard deviation of a design. This scheme greatly reduces the number of experiments and provides superior results for systems with significant interaction effects and nonlinear variations. The proposed methodology is applied to the design of helical gears with minimum transmission error. The robust optimum shows a significant reduction of the expected transmission error compared with previous studies, while maintaining the insensitivity to manufacturing errors and load variation.     

Calculation of the characteristics of an electromagnetic temperature transducer

The main characteristics of an electromagnetic transformer transducer for the noncontact determination of the temperature of nonmagnetic cylindrical articles are considered. Translated from Izmeritel'naya Tekhnika, No. 1, pp. 53–56, January, 1997.     

Comparison of fully coupled modeling and experiments for electromagnetic forming processes in finitely strained solids

In fracture and fragmentation research the technique of electromagnetic forming, which uses electromagnetic (Lorentz) body forces to shape metallic parts, is finding significant use due to the high velocity, high strain rate loading it can impart without contact on workpieces. The same process is also becoming increasingly relevant for manufacturing processes in sheet metal forming, where this technique offers several advantages: speed, repeatability, non-contact loading, reduced springback and considerable ductility increase in several metals. Current modeling techniques for these coupled electromagnetic and thermomechanical processes are not based on coupled variational principles that can simultaneously account for electromagnetic and mechanical effects. Typically, separate solutions to the electromagnetic (Maxwell) and motion (Newton) equations are combined in staggered or lock-step methods, sequentially solving the mechanical and electromagnetic problems. To address this issue, Thomas and Triantafyllidis (J Mech Phys Solids 57:1391–1416, 2009) have recently introduced a fully coupled Lagrangian (reference configuration) variational principle, involving the magnetic field potential and the displacement field as independent variables. The corresponding Euler-Lagrange equations are Maxwell’s and Newton’s equations in the reference configuration under the eddy current approximation. This novel approach is used here to simulate free expansion experiments of AA6063-T6 aluminum tubes. A viscoplastic constitutive model, developed independently by the authors (Thomas et al. Acta Mater 55:2863–2873, 2007) for necking experiments in tubes of the same aluminum alloy, is used in the simulations. The measured electric currents and tube deformation—the latter obtained by Photon Doppler Velocimetry—show reasonably good agreement with the corresponding simulations, which are obtained using a variational integration numerical scheme that results in an efficient staggered solution algorithm.     

Remote Field Eddy Current Technique: Phantom Exciter Model Calculations

Abstract

High resolution results of finite element calculations for remote field eddy current “phantom exciter” simulations of slit defect interactions using single through wall transit are presented. These show that fine circumferential slits cause almost no field perturbations in the case of nonferromagnetic tubes but big perturbations in ferromagnetic tubes where high magnetic H fields occur in the slits. Defect-induced magnetic field perturbations must therefore be considered in addition to eddy current perturbations when ferromagnetic materials are inspected, particularly in the case of fine slits orthogonal to the magnetic field direction. Additional details seen are the funnelling of energy into slits in ferromagnetic pipes and precursor disturbances of fields approaching defects. It is suggested that these are due to the reflection of the electromagnetic waves dictates by boundary conditions at the near side defect boundary.     

基于感知的城市开放空间声环境评价指标研究

文章从人群主观感知角度出发，针对人口、交通密集型城市开放空间声环境质量评价进行研究，以期从大量的物理、心理声学特征中提取出“有效特征参量”，拓展现有声环境评价指标。该研究基于对上海市开放空间复合混杂的整体声环境特征分析以及实验室主观评价实验，构建了“特征参量”-“主观满意度”样本集，进而提出双重相关系数评估方法，定量评估17种物理、心理声学特征参量间的内在相互影响，以及它们对人群声主观感知的影响，筛选出适应于城市整体声环境主观评价的“有效特征参量”：等效连续A声级LA、噪声中值与环境本底值的差值L50-L90以及尖锐度S，其中，LA是影响声环境主观满意度的决定性因子，它与满意度Sat的负相关性达到88%,L50-L90对Sat的负相关性为25%,S与满意度Sat的正相关程度为33%。进一步，基于它们与满意度Sat的相关系数，计算出3个“有效特征参量”影响“主观满意度”权重系数：0.6,0.17以及0.23。     

Formulation Optimization of a Hydrocolloid Dressing

Abstract

A methodology of mixture experiments has been applied to the formulation of a multicomponent hydrocolloid dressing. Using an extreme vertices statistical design, a semi-occlusive dressing composed of dextran, phospholipid, glycerol and sodium lauryl sulphate has been formulated, which checks evaporative water loss (EWL) from the excised wound surface of rats to an optimum level.