Search results for "Laser ultrasonics"

Laser Ultrasonics Inspection for Defect Evaluation on Train Wheel

2019

Abstract Passengers’ safety and in-service life of wheelset axles play an important role in railway vehicles. For this reason, periodic inspections are necessary. Among non-destructive techniques, ultrasonic ones are widely applied in this field. The main disadvantage of conventional ultrasonic techniques is that the overall inspection of wheels requires the train to be put out-of-service and disassembly each part, which is time-consuming and expensive. In this paper, a non-conventional non-contact laser ultrasonic inspection for train wheels is proposed. The proposed method uses a laser interferometer to receive the ultrasonic wave without contact. The receiving system allows choosing the …

Inspection of Laser Powder Deposited Layers

2014

Laser Ultrasonics Inspection of Train Wheel - Evaluation of Optimized Setup

2021

In the railway field, the safety of passengers and the service life of train components are a crucial issue. For this reason, continuous periodic inspections by non-destructive techniques are required. Among these, ultrasonic tests are widely used in this field, even though the conventional ultrasound techniques have the disadvantage of requiring the disassembly of the wheels and of putting the train out of service. This procedure is expensive and time-consuming and can be neglected if non-contact ultrasonic techniques are used. In this work, the authors present an experimental research on some defects, artificially obtained on a railway wheel supplied by Trenitalia Spa, by adopting three d…

Digital signal processing for rail monitoring by means of ultrasonic guided waves

2007

Recent train accidents have reaffirmed the need for developing rail defect detection systems that are more effective than those used today. One of the recent developments in rail inspection is the use of ultrasonic guided waves (UGWs) and non-contact probing techniques to target transverse-type defects. Besides the obvious advantages of non-contact probing, that include robustness and a potential for large inspection speed, such a system can theoretically detect transverse defects under horizontal shelling or head checks. This paper demonstrates the effectiveness of digital signal processing to enhance the damage detection sensitivity of the non-contact system. The method proposed here comb…

Laser induced decohesion of coatings: probing by laser ultrasonics.

2002

The aim of the present study is to investigate a conventional laser-ultrasonics technique for the determination of intrinsic properties of oxide coatings and their adhesion strength on a metallic substrate. The good agreement between experiments and computations in an epicenter configuration allows determining the longitudinal wave velocity as well as the Young's modulus of the oxide coatings versus the porosity. For a critical value of the laser energy, a breakdown at the coating-substrate interface is generated by the laser irradiation. The critical tensile stress field developed at the coating/substrate interface, which leads to the interfacial fracture, can be easily calculated. The val…

Evaluation of viscoelastic constants of metallic materials by laser-ultrasonics at elevating temperature

2002

The main objective of this study is the determination of elastic moduli and viscosity coefficients of metals at elevating temperature up to melting point. More specifically, it involves the analysis of the propagation of acoustic waves generated and detected simultaneously by laser-ultrasonic for the measurement of longitudinal and shear velocities. This preliminary work primarily concerns Tin (Sn) metal known for its low melting point and attenuation coefficient.

Simultaneous laser generation and laser ultrasonic detection of the mechanical breakdown of a coating–substrate interface

2001

Abstract The present study deals with information that could be obtained by real-time contactless monitoring of the normal displacement, due to the propagation of the longitudinal waves generated by nanosecond pulsed laser irradiation, through a transparent and porous ceramic coating deposited on a metallic substrate. These displacements were recorded in real-time at the rear surface of the specimens using a laser heterodyne interferometer and were correlated with the different steps of laser/material interaction (thermoelastic interactions, fracture of the coating–substrate interface and coating expulsion). An analytical model was developed to establish a relation between the longitudinal …

Triple resonant four-wave mixing: A microwatt continuous-wave laser source in the vacuum ultraviolet region at 120 nm

2012

We present a vacuum ultraviolet laser source by four-wave mixing in mercury vapour based on solid-state laser systems. Maximum powers of 6μW were achieved with an increase of four orders of magnitude in efficiency.

Observability of the Risken–Nummedal–Graham–Haken instability in Nd:YAG lasers

2003

Multilongitudinal mode instability in ring Nd:YAG lasers is theoretically analyzed. After we review the way in which the standard two-level laser theory applies to this laser we extend the theoretical treatment to include transverse effects. We do this by taking into account the finite transverse section of the active medium and by assuming a Gaussian transverse distribution for the intracavity field. Finally we demonstrate that multimode emission develops whenever the intracavity field waist diameter is almost equal to the active rod diameter. We conclude that continuous-wave diode-pumped Nd:YAG lasers with low cavity losses are good candidates for the observation of the Risken–Nummedal–Gr…

Laser-ultrasonics: a non-contact method to link the acoustic attenuation to metal damping properties up to the melting point

2004

The objective of this work is to describe the viscoelastic behavior of metals up to their melting temperature by measuring the velocity and the attenuation of ultrasonics waves. For that purpose, a technique called laser-ultrasonics has been optimized for the high temperature domain and the solid to liquid transition. This paper is especially applied to the viscoelastic characterization of tin, from room temperature up to the melting point.