During the last decade, significant advances in the field of remote detection of ultrasound have taken place Optical systems with increasing sensitivity for monitoring ultrasound on samples with optically rough surfaces have been developed, so that some designs are now moving from the research laboratory into industrial environments In this review, a range of optical techniques is presented These techniques are analysed regarding their use for the measurement of ultrasonic waves They include the use of optical self-mixing, phase modulators and photorefraction-based interferometers For the case of established instruments such as two-beam interferometers and Fabry-Perot interferometers, various newly developed configurations with associated ultrasonic transfer functions are described Many interferometers have broadband frequency responses that extend up to several hundred megahertz Some systems offer in-plane ultrasonic measurement, whilst most offer out-of-plane measurements Emphasis is placed on their potential for industrial applications, taking into account the likely sample-surface roughness and environmental vibration

https://iopscience.iop.org/article/10.1088/0957-0233/10/11/201/pdf

Optical remote measurement of ultrasound

One approach to testing the suitability of an adhesive joint for a particular application is to build and test to destruction a representative sample of the joint. In this way the best adhesive and surface treatment for a given application can be found. To reduce the costs of this approach, the designer will wish to call on previous experience with adhesives, surface treatments, and joint designs so as to reach a high probability of success before he builds and tests a structural prototype. If structures are expensive, it will be difficult to justify more than a very limited series of prototype tests before production begins. During the production phase, and also in service with critical structures, it is essential to use nondestructive tests to assess the quality and fitness for purpose of the product. The nondestructive test will not measure strength directly but will measure a parameter which can be correlated to strength. It is therefore, essential that a suitable nondestructive test is chosen and that its results are correctly interpreted. In this paper, typical defects found in adhesive joints are described together with their significance. The limits and likely success of current physical nondestructive tests are described, and future trends outlined.

Nondestructive testing of adhesively-bonded joints

The rapid non-destructive inspection of large composite structures

This work describes two separate applications of air-coupled ultrasonic nondestructive evaluation (NDE) for rapid inspection of aerospace components. First, air-coupled transducer arrays are used for through transmission scanning of relatively large preproduction test samples. In this case a focused array system was designed to facilitate faster inspection rates and at the same time match the resolution and performance of available water jet apparatus. The second approach is geared toward in situ inspection and involves single-sided scanning using a dual transducer configuration for generation of surface, shear, and Lamb waves within the test specimen. In both cases, the difficulties of practical air-coupled inspection are discussed and the design solutions presented for each application. Piezocomposite transducer technology, in conjunction with narrow-band low-noise electronics, constitutes the basis for achieving the required signal to noise ratio (SNR) to ensure robust operation within the industrial environment. A number of scan images, performed on realistic samples, are shown and the results compared with those obtained using alternative methods. Excellent image quality is demonstrated from real time scanning and without recourse to any off-line data processing.

Applications of through-air ultrasound for rapid NDE scanning in the aerospace industry

This paper describes the application of the capacitive imaging technique to the inspection of composite materials. The fundamental theory of the capacitive imaging technique was briefly described. Experiments using prototype capacitive imaging probes were also carried out. The proof-of-concept results indicated that the capacitive imaging technique could be used to detect cracks and delaminations in the glass fibre composite, defects in the aluminium core through the glass fibre face as well as surface features on the carbon fibre specimens.

Non-destructive evaluation of composite materials using a capacitive imaging technique

Practical considerations for the rapid inspection of composite materials using laser-based ultrasound

Current techniques for automated ultrasonic inspection of airframe structures can only be used to examine limited areas which have large radii of curvature. Manual inspection techniques are required in areas having small radii. Laser-based ultrasound (LBU) offers the potential to rapidly inspect large-area composite structures having contoured geometries, without restriction to large radii of curvature [1–4]. The key components that comprise an LBU rapid inspection system are the generation and detection lasers, a 2D scanner and a suitably fast data acquisition system. These must be integrated to provide an areal scan rate of at least 100 ft2/hr based on a 0.5″ × 0.5″ pixel size. In this paper results are presented of an investigation of the relative merits of using a CO2 laser versus a Nd:YAG laser for thermo-elastic ultrasonic generation in composite materials. In our previous studies, ultrasonic C-scan images of components were acquired with the LBU system by mechanically translating the test specimen in front of the stationary generation and detection laser beams [2–4]. If the scan is to be done rapidly, this technique becomes increasingly difficult and more expensive as the mass of the part increases. To fully realize the high speed scanning potential of a same side laser-in/laser-out inspection system, it is necessary to deflect the laser beams across the part surface. An implementation of angular scanning of the generation and probe laser beams across the part surface is described. A data acquisition scheme that has been used to demonstrate data acquisition rates of 33 waveforms/sec (for 200 point waveforms) is also described.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1302&context=qnde

Rapid Inspection of Composites Using Laser-Based Ultrasound

Laser-based ultrasound (LBU) has a number of distinct advantages compared with conventional contact piezoelectric transducer systems. The LBU technique is noncontacting and the laser beams conform to the part surface so that couplant nonuniformities and the need for maintaining normality to, and fixed distance from, the part are eliminated. The LBU technique thus potentially allows rapid, and close to 100%, inspections of complexly contoured surfaces. Various laser techniques used to generate and receive ultrasonic waves have been reviewed by several authors [1–2]. While the generation and detection procedures employed by LBU are distinctly different from systems employing piezoelectric transducers, once ultrasound is generated by a laser, it propagates into a material and interacts with defects in precisely the same way. Thus, laser-based ultrasound can provide inspection resolution comparable to that which can be obtained using commercially available ultrasonic squirter systems, which require water coupling to the part.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=2963&context=qnde

Inspection of Components Having Complex Geometries Using Laser-Based Ultrasound

: The design, implementation, and proof-of-concept demonstration of a fiber-based Cassegrain optical scanning system was completed. Optical generation and detection with the fiber-based Cassegrain optical scanning system over 100-m lengths of optical fiber was demonstrated. High peak power, Q-switched Nd:YAG laser pulses (>45 mJ/pulse at 532 nm) through optical fiber in a robust manner was successfully delivered. This program established the absolute thermoelastic generation efficiency for four different laser wavelengths and eight different material/boundary conditions.

/pdf/laser-based-ultrasound-for-remote-and-limited-access-16fapxn31o.pdf

Laser-Based Ultrasound for Remote and Limited-Access Inspection Applications

Phase I of “Research on Intelligent Processing of Carbon-Carbon Composites” is a two year program to develop enabling technologies for real time control of the carbonization process for resin matrix composites. The research has three related foci: in situ material property sensors; process models; and intelligent control architecture. The research has, to date, 1) developed control strategies at three levels of sophistication that use sensors and models to complete carbonization more rapidly while still reducing losses; 2) developed a control architecture that integrates those sensors and models; 3) conducted successful in situ tests of chemical and physical property sensors; 4) developed a high temperature eddy current sensor (not yet tested in situ); 5) developed considerable kinetic data on the carbonization reactions, described the basic reaction paths and their relation to physical properties qualitatively, and developed a kinetic equation for the lowest temperature family of carbonization reactions, the production of water from hydroxyl groups; 6) defined the modeling strategy for calculating gas pressure and the experimental strategy for developing models for matrix strength. In the following, we describe the general problem and the issues in modeling and control to provide a context for the sensor results.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=2374&context=qnde

Robert C. Addison

Papers

Practical considerations for the rapid inspection of composite materials using laser-based ultrasound

Rapid Inspection of Composites Using Laser-Based Ultrasound

Inspection of Components Having Complex Geometries Using Laser-Based Ultrasound

Laser-Based Ultrasound for Remote and Limited-Access Inspection Applications

Sensors for Carbonization Control