摘要:

This paper presents a source model for laser ultrasonic generation in non‐metals in the thermoelastic regime. It is shown that the waveforms can be directly related to the optical absorption depth of the material. The longitudinal component due to the buried source is shown to be a bipolar pulse which can be modelled by convolving the temporal form of the laser pulse with the optical absorption profile and its time delayed inverted reflection from the free surface. The heated disc is surrounded by cold constraining material so the radial in‐plane forces have Heaviside like time dependence whereas the vertical component only exists during the initial fast rise of the free surface and therefore can be modelled as a delta function. The predications of the model are compared for a TEA CO2laser generation in a plastic, an Excimer laser in glass and a Nd:YAG laser in silicon. This model also explains difference between constrained and unconstrained surfaces for the first time, in the constrained case the vertical force is related to the integral of the laser pulse profile and has Heaviside like time dependence. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570154

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In recent work at Northwestern University, Multiplexed Two‐Wave Mixing Interferometers (MTWM) have been developed. These systems are able to perform optical detection of ultrasonic motion over an array of points simultaneously. Optical phase gratings are used to create a detection‐array of laser beams that are directed to the specimen. The detection array can be arranged in several ways on the test object. The scattered beams from the detection‐array are collected and combined with a single reference beam in a photorefractive crystal to form a multiplexed two‐wave mixing configuration. Each of the output beams from the photorefractive crystal is imaged on to a separate element of a photodetector array. The resulting MTWM system is capable of providing simultaneous optical detection (with high spatial resolution and sub‐nanometer displacement sensitivities) at several points on a test object. The MTWM system can be used in several modes for laser ultrasonic NDE of flaws and materials characterization. In this paper we present recent advances and applications of this technology. An application of the MTWM system for fast recovery of Lamb wave dispersion curves is presented. We obtain the dispersive time‐domain Lamb wave signals at multiple source‐to‐receiver distances. Following the algorithm of Alleyne and Cawley, these time‐position domain signals are transformed to the frequency‐wavenumber domain using a 2D FFT technique. The MTWM system enables rapid characterization of Lamb wave dispersion. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570155

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Wide area imaging devices offer many speed and flexibility advantages to NDE applications. They can be reconfigured quickly to accommodate a variety of part geometries and sizes and can be deployed without precise fixturing for the sensor or the part. When the part to be inspected is large or complicated (with many bends); applications use several sensors or move a single sensor to multiple viewpoints to complete an inspection. An operator must then review several images for a single part, spatially relate indications across disparate images, and assume the collection of images completely covers the part. We describe a system that uses laser‐ultrasound as a wide area, imaging device. The system also uses a structured light range camera — typically used to measure shape — to locate the part in the work cell. We describe how camera calibration, photogrammetry, triangulation, and registration techniques are used to define coordinate frames that allow us to relate the data from the laser‐ultrasound imaging device to a CAD model of the part. We then map the ultrasound data from various viewpoints onto the CAD model, creating a natural 3D coordinate frame for the operator to relate indications and evaluate scan coverage. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570156

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The pulsed eddy current (PEC) technique is widely used to detect and quantify flaws in conducting plates .This method has been used to test materials subjected to heat treatment. Material properties such as conductivity show a marked change with temperature. As the heat diffuses into the material, the probe output changes owing to the changing material properties. Hence, it becomes difficult to obtain consistent results when searching for defects. Such problems can be effectively tackled by combining thermal and pulsed eddy current analysis for getting a reference data for the signals acquired from the probe. In this paper, a model is presented which combines transient thermal analysis and PEC Finite Element Model to track the probe output changes occurring during Laser based heat treatment of thin sheet conducting materials. The first step encompasses modeling of the laser treatment process using a three dimensional Finite Difference method .Properties of the material such as conductivity and specific heat capacity changes with temperature. Such parameters can be averaged over the temperature range of the laser treatment process and used in the model. The thermal model can also be extended to heterogeneous materials like Carbon reinforced composites. The temperature distribution in the material which is obtained from the thermal model is used as the input data for the axisymmetric PEC Finite element analysis. Hence the probe output can be tracked over the entire time interval. This forms an effective basis for combining the physics of two diffusive phenomena, i.e. thermal and pulsed eddy current in the NDE and control of such processes. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570157

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A computer simulation has been developed to evaluate eddy‐current probes containing magnetic field sensor arrays for the detection and evaluation of hidden corrosion. The simulation is used to assess probes that incorporate magneto‐resistive or Hall devices in a closely‐spaced, linear array. These probes will allow rapid data acquisition over a track width determined by the length of the array. The benefit of the simulation is that adjustments to the virtual probe parameters are easily made allowing improvements in sensitivity, imaging capability and resolution. A number of probe designs have been studied in this way including the “racetrack” probe. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570158

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The influence of corrosion on ultrasonic and electromagnetic nondestructive evaluation results has been simulated for 2‐layer aluminum aircraft fuselage. Simulations have been performed with respect to ultrasonic time‐of‐flight measurements aiming on the detection of corrosion at the backwall of the first aluminum layer. Calculations of the eddy current probe response have been performed, where the thickness of the first and second layer and also the probe‐to‐specimen lift‐off at several eddy current operating frequencies have been varied. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570159

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This paper indicates that eddy current is induced not only by induction electric field but also by electric potential gradient. The potential gradient plays a major role in inducing eddy current around discontinuities in the test material. The potential is generated by conversion of induction electric field where the eddy current is smaller than that induced by induction electric field. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570160

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We apply our proprietary volume‐integral eddy‐current code, VIC‐3D©, to the solution of challenging NDE problems that involve ferromagnetic anomalies or workpieces. These include problems with “wear scars and permeable crusts” in steam‐generator tubing, characterization of coatings with electrical and magnetic layers, and flaws in ferromagnetic workpieces. Validation of the code by the use of benchmark experiments will also be described. Finally, we will explain the development of the mathematical model in terms of volume‐integral equations through the use of Amperian currents for magnetic effects. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570161

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Iowa State University’s pulsed eddy‐current system has been redesigned to be smaller, more sturdy and easier to install and operate. Improvements have been made to the electronic circuits, the computer interface, the enclosure design and to the software. Changes have resulted in a much more user‐friendly system that it portable and can be installed quickly and easily in the field. As part of an evaluation of the new system, bond‐thickness measurements on specimens supplied by Cessna were carried out. Results were found to be in good agreement with those obtained by direct measurement. Additional experiments were carried out on corrosion specimens from SAIC Ultra Image Inc. Using data from these specimens a calibration‐based approach to flaw quantification is demonstrated. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570162

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This paper demonstrates the crack detection of thick‐walled non‐magnetic metal plates by eddy current testing, which used to be difficult because of the skin effect generally. For the purpose, this paper proposes a novel eddy current testing probe for cracks in thick‐walled plates and evaluates the capability of the present probe. The probe was designed, based on the numerical computation using 3D fast eddy current code. The advantages of the present probe are strong eddy current on the back of specimens and small decay of eddy current in the thickness direction. Through experiments, we confirmed that this probe can detect the back artificial defect on INCONEL718 specimen with thickness of 7.0mm and 304 Stainless steel specimen with thickness of 8.0mm. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570163

出版商:AIP    

年代:1903

数据来源: AIP