Search results for "Laser ultrasound"
showing 10 items of 14 documents
Laser-Generated Acoustic Signal Interaction with Surface Flaws on Rail Wheels
2005
Long- and short-range acoustic-signal interaction with surface-breaking cracks and geometric boundaries of the rail-wheel tread area are presented in this article. Ultrasonic signals are generated using a laser-line source of varying length and distance from a crack and are detected with a 1-MHz contact transducer to map the sound field behind the crack in the near, intermediate, and far fields of the insonified region. The factors that affect the behavior of a laser-generated surface acoustic wave propagating along the tread area of a rail wheel are discussed. A signal normalization method is proposed to help in sensing the presence of a crack from the transmitted signal unaffected by the …
Proof of concept of wayside railroad wheel inspection using a laser-air hybrid ultrasonic technique
2003
Non-destructive inspection of railroad wheels is performed in maintenance shops, where wheels are removed and inspected individually. No technique is yet available to the railroad industry to perform wayside inspections of wheels on a moving train. The characteristics of laser and air-coupled ultrasound are discussed to justify the use of a laser-air hybrid ultrasonic technique. Laser generation of ultrasound is combined with air-coupled detection to provide a flexible non-contact and remote technique that would enable the railroad industry to perform wayside inspections of moving railroad wheels. The present paper describes Proof of Concept set-up and results of the experiments performed a…
Defect Detection in Additively Manufactured Components: Laser Ultrasound and Laser Thermography Comparison
2018
Despite continuous technological advances in additive manufacturing, the lack of non-destructive inspection techniques during the manufacturing process is a limit for the industrial breakthroughs. Additive manufacturing is mainly used in industrial sectors where the zero defect target is crucial. The inclusion of the integrity assessment into the additive manufacturing process would allow corrective actions to be performed before the component is completed. To this end, the development of in-process monitoring and processing techniques is of great interest.This work proposes and compares two remote non-destructive inspection techniques: laser ultrasound and laser thermography. The two techn…
Inspection of additive-manufactured layered components
2015
Laser powder deposition (LPD) is a rapid additive manufacturing process to produce, layer upon layer, 3D geometries or to repair high-value components. Currently there is no nondestructive technique that can guarantee absence of flaws in LPD products during manufacturing. In this paper a laser ultrasonic technique for in-line inspection of LPD components is proposed. Reference samples were manufactured from Inconel and machined flaws were created to establish the sensitivity of the technique. Numerical models of laser-generated ultrasonic waves have been created to gain a deeper understanding of physics, to optimize the set-up and to verify the experimental measurements. Results obtained on…
Detection of disbonds in multilayer structures by laser-based ultrasonic technique
2008
Adhesively bonded multi-layer structures are frequently used, mostly in the aerospace industry, for their structural efficiency. Nondestructive evaluation of bond integrity in these types of structures, both after manufacturing and for periodic inspection during service, is extremely important. A laser-based ultrasonic technique has been evaluated for non-contact detection of disbonds in aluminum multi-layer structures. Two configurations have been used to detect disbonded areas: pitch-catch with unidirectional guided wave scan and through-transmission with bidirectional scan. Guided wave scanning was done with a laser line source and air-coupled transducer sensing at 500 kHz, 1 ;MHz, and 2…
Numerical study for a new methodology of flaws detection in train axles
2013
Train loads and travel speeds have increased over time, requiring more efficient non-destructive inspection methods. Railway axles are critical elements; despite being designed to last more than 20 years several cases of premature failure have been recorded. Train axles are inspected regularly, but the limits associated to the traditional inspection technologies create a growing interest towards new solutions. Here a novel non-destructive inspection method of in-service axles based on non-contact data collection is presented. The propagation of surface waves, generated by a thermo-elastic laser source, is investigated using a finite element method based on dynamic explicit integration. Coup…
Influence of laser beam profile on the generation of ultrasonic waves
2011
The different ultrasonic fields generated in metallic materials by a laser beam with flat and Gaussian profile are investigated experimentally and using the finite element method (FEM). A high power laser beam irradiating a solid surface produces elastic waves with a mechanics that depends on many parameters, including the profile of the laser beam. The influence of the beam profile is investigated with the FEM analysis, considering the temperature dependence of material properties.
Rail track field testing using laser/air hybrid ultrasonic technique
2003
Nondestructive testing methods used for the testing of rail in tracks worldwide can be limited by discontinuity location or orientation within the rail. Vertical split head and rail base cracks are among those types of discontinuities that are difficult to detect, which in some cases may result in a reail failure in service. A noncontact and remote hybrid ultrasonic technique has been developed by combining laser generation with air coupled detection of ultrasonic signals in rails. The test apparatus mounts on a railroad pushcart and tests are performed in motion with all components kept above the running surface of the rail track. Tracks have been tested for vertical split head and rail ba…
PROPAGAZIONE DI ONDE DI RAYLEIGH LUNGO SUPERFICI CURVE: UNO STUDIO NUMERICO E SPERIMENTALE
2014
Il fenomeno della propagazione delle onde di superficie lungo confini rettilinei (superfici piane) è stato studiato adeguatamente. Tuttavia le indagini riguardanti la loro propagazione in superfici cilindriche sono limitate e risultano insufficienti ai fini di un loro utilizzo nelle tecniche d’ispezione non distruttive (NDE), nonostante possano essere di grande interesse per svariate applicazioni. E’ stato dimostrato sperimentalmente che l’onda superficiale subisce un cambiamento di fase durante la sua propagazione lungo una superficie cilindrica. Un approccio numerico è stato sviluppato per studiare questi effetti per diversi materiali, curvature e frequenze. I risultati numerici e sperime…
Surface waves on cylindrical solids: numerical and experimental study.
2013
The use of Rayleigh waves enables the solution of several important inspection problems. Propagation of surface waves along straight boundaries has been properly studied but investigations about their propagation on cylindrical surfaces are not sufficient, despite they can be still of interest for NDE applications. It has been proved experimentally that a surface wave pulse suffers a phase shift during its propagation along a cylindrical surface. A numerical approach has been developed to efficiently study these effects for different materials, curvatures and frequencies. This study can help the scientific community to better understand the phenomenon, quite complex and not yet fully explor…