摘要:

We are developing a microwave radar sensing and imaging system to detect and locate gas leaks in natural gas pipelines. The underlying detection principle is radar backscattering from the index‐of‐refraction inhomogeneities introduced by the dispersion of methane in air. An essential first step in the development effort is modeling to estimate the radar cross section. This paper describes the modeling results and the experimental efforts underway to validate the model. For the case of leaks from small holes in a pressurized gas pipeline, we modeled the gas dynamics of the leak jet to determine the plume geometry and the variation of methane concentration in air as a function of distance from the leak source. From the static and dynamic changes in the index of refraction in the turbulent plume, the radar backscatter cross sections were calculated. The results show that the radar cross sections of the leak plumes should be detectable by special‐purpose radars. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570174

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A scanning microscope based on a high transition temperature Superconducting Quantum Interference Device (SQUID) was used to detect incipient fatigue failure in ferritic stainless steel. The results show the development of localized peaks in remanent magnetization prior to the formation of visible fatigue cracks, that is, in region 2 of fatigue damage. Because of the combined magnetic and spatial resolution of the SQUID microscope, these local changes can be detected well before there is any dramatic change in the overall magnetization of the specimen. An interesting secondary result is that, while the SQUID microscope also detects small cracks, until these have a significant crack opening (more than a few microns) the dominant contribution to the local magnetization peak is the damage associated with the crack (presumably, the damage that created the crack) rather than the crack itself. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570175

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Work in Thermosonics (Vibration Thermography) has demonstrated the ability to make cracks in metals, delamination in composites and disbonds visible to Infrared Thermography. A basic question of what energy levels are needed to “activate” the discontinuities remains as an impediment to a universal understanding and use of the technique. A specific strain gage configuration to measure only differential movement between the sides of a crack was compared with laser vibrometry measurements of the surface movement and crack infrared emittance levels of simple samples. Measurements were made to measure the effect of varying some of the operating parameters and the relationship of the measurements to crack visibility. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570176

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We describe recent developments in sonic infrared (IR) imaging. The sonic IR imaging NDE technique uses a single short pulse of sound to cause cracks to heat up and become visible in the infrared. Results of recent experiments on metal aircraft structures and composite test samples with natural and simulated defects are presented in this paper. Examples of defects in metals include cracks originating under fasteners and cracks in mechanical parts. Examples of defects in composites include fatigue cracks, pillow inserts, pull‐tab disbonds, skin‐to‐core disbonds, etc. Both 20kHz and 40kHz ultrasonic excitation sources were used for studying the frequency effect. Vibrational behavior of surfaces near the defects was monitored and correlated with the IR signals. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570177

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Extensive work has been done in the past characterizing the effects of high power ultrasonic energy on material properties. More recently high amplitude ultrasonic signals have been used in combination with infrared camera systems to detect the presence of flaws in materials. Defects such as cracks in metals, exfoliation and generalized corrosion in metals, delamination in composites and disbonds have been detected using this technique. Presently no systematic study has been developed that addresses the limitations and advantages of this technique. The authors would like to present some initial results on this technique that try to determine the effects that sample geometry, crack length and contact area have on the thermographic signal. For this purpose, the authors have developed a test fixture that allows the control of several of the experimental parameters for the optimization of the thermosonic signal. Results are presented in this paper. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570178

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We describe recent experiments in sonic infrared (IR) crack detection in an F‐110 fan disk. This technique uses a single short pulse of sound to cause cracks to heat up and become visible in the infrared. A low frequency (15 to 40 kHz) ultrasonic transducer fills the sample with sound that causes frictional heating at crack interfaces. We show that the technique can be applied to quite large and irregularly shaped objects like an aircraft engine disk without exciting acoustic mode patterns which might hide cracks in nodal regions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570179

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The paper shows that the acousto‐thermal principal is capable of characterizing microstructure changes due to fatigue in Ti‐6Al‐V4. The results are discussed in terms of internal friction and compared to low frequency, high stress thermographic characterization and nonlinear acoustics. The dislocation structure of the fatigued titanium alloy was characterized by transmission electron microscopy. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570180

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Thermosonics is a hybrid ultrasonic — thermal technique in which the sample is excited using a low frequency ultrasonic wave. A finite difference model was constructed to study the heat transfer characteristics through the material into which different source characteristics can be introduced. Various types of heat sources that might be created due to friction were mathematically generated for various excitation velocities of the ultrasound source and the corresponding predicted thermal images are obtained. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570181

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The use of elastic waves in combination with thermal waves allows to separate structural information about investigated components from defect specific thermal signatures. Ultrasound Burst Phase thermography (UBP) is an defect‐selective and fast imaging tool for damage detection. This contribution presents results obtained on various kinds of problems related to modern automobile production (crack detection in grey cast iron and aluminum, characterization of adhesive‐bonded joints etc.). Advances resulting from frequency modulated ultrasound excitation will be presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570182

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Standard radiography simulators are based on the attenuation law complemented by built‐up‐factors (BUF) to describe the interaction of radiation with material. The assumption of BUF implies that scattered radiation reduces only the contrast in radiographic images but does not image object structures itself. This simplification holds for a wide range of applications like weld inspection as known from practical experience. But only a detailed description of the different underlying interaction mechanisms is capable to explain effects like mottling or others that every radiographer has experienced in practice. The application of the N‐Particle Monte Carlo code MCNP is capable to handle primary and secondary interaction mechanisms contributing to the image formation process like photon interactions (absorption, incoherent and coherent scattering including electron‐binding effects, pair production) and electron interactions (electron tracing including X‐Ray fluorescence and Bremsstrahlung production). Additionally it opens up possibilities like the separation of influencing factors and the understanding of the functioning of intensifying screen used in film radiography. The paper intends to discuss the opportunities in applying the Monte Carlo method to investigate special features in radiography in terms of selected examples. It is important to note that the use of Monte Carlo methods is a laboratory type of technique for basic investigations because of the enormous computing power that is needed. For in‐field applications such as for inspection planing simplified models are of much greater importance and increasingly in use. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570183

出版商:AIP    

年代:1903

数据来源: AIP