Ultrasonic inspection technique

Fokker Bond Tester. An ultrasonic inspection technique commonly used for aircraft structures is based on ultrasonic spectroscopy [2]. Commercially available instruments (bond testers) used for this test operate on the principle of mechanical resonance in a multi-layer structure. A piezoelectric probe shown in Figure 3b, excited by a variable frequency sine signal is placed on the surface of the inspected structure. A frequency spectrum in the range of some tens of kHz to several MHz is acquired by the instrument, see Figure 3a. 

A number of different types of ultrasonic inspection techniques using pulsed ultrasound waves from 2.25 to 10 MHz can be applied to bonded structures.25 The most common methods are as follows ... 

For detection of more localized corrosion, such as crevice corrosion or SCC, other ultrasonic inspection techniques may be useful. Baseline data generated at the time of installation will also be helpful in evaluating results. One benefit derived from this type of inspection technique is that it can often be conducted with little or no interference with production. Periodic planned visual inspection of equipment utilized under conditions likely to cause stress cracking is also an effective technique, especially when combined with non-destructive inspection techniques such as dye penetrant inspection. It may be necessary to remove coatings or insulation from the equipment surface to facilitate inspection. 

Development of signal processing techniques for ultrasonic inspection techniques for the detection and sizing of cracks in relevant austenitic components. 

On-line monitoring, inspection and maintenance development of innovative techniques for monitoring of corrosion conditions and material damage and of improved ultrasonic inspection techniques ... 

Figure U.l Ultrasonic inspection techniques, (a) Contact pulse echo with a search unit combining a transmitter and receivers, (b) Contact through transmission. Transmitting search unit on top and receiving search unit on the bottom, (c) Immersion pulse echo with search unit (transmitter and receiver) and part inspected under water, (d) Immersion through transmission with both search units (transmitter and receiver) and part under water, (e) Immersion reflector plate. Same as (c) but each unit requires a reflector plate below the part being inspected. (Ref Hagemaier, D.J., End Product Nondestructive Evaluation of Adhesive Bonded Metal Joints , Adhesives and Sealants, vol. 3, Engineered Materials Handbook, ASM International, Materials Park, OH, 1990)...

Basic ultrasonic experimental techniques to help understand the ultrasonic inspection techniques for adhesive bond inspection can be found in Krautkramer [11] and more detail on theoretieal aspects of wave propagation in Rose [12]. 

Light, G.M. and Bloom, E.A., Use of dry-coupled ultrasonic inspection techniques for evaluation of bondline quality. In Nondestructive Evaluation of Materials and Composites, SPIE Proceedings Vol. 2944, Scottsdale, AZ, Dec. 3-5,1996. 

Nondestructive testing. An ultrasonic inspection technique is available for the detection of flaws in plate, piping, and tubing. The water-immersed pulse-echo ultrasound equipment has been adapted to highspeed use. Eddy-current, dye-penetrant, and radiogr.aphic inspection methods are also used as required. The inspected materials have included Inconel, austenitic stainless steel, INOR-8, and the Hastelloy and other nickel-molybdenum-ba.se alloys. 

Therefore, the establishment of the Non-Destructive Inspection technique to understand the presence of the defect on the bonding interface by the ultrasonic wave etc. accurately is demanded. And, the reliability of the product improves further by feeding back accurate ultrasonic wave information obtained here to the manufacturing process. 

In co-operation with LM Glasfiber, a complete section of a rotor blade was produced with a number of well defined defects in order to perform an initial sensitivity test by means of ultrasound, vibrations techniques and real-time radiography. Based on the results of this initial test it was found that automated ultrasonic inspection was the best suited teclmique. In co-... 

The coin-tap test is a widely used teclinique on thin filament winded beams for detection of disbonded and delaminated areas. However, since the sensitivity of this teclinique depends not only on the operator but also on the thickness of the inspected component, the coin-tap testing technique is most sensitive to defects positioned near the surface of the laminate. Therefore, it was decided to constructed a new scaimer for automated ultrasonic inspection of filament winded beams. A complete test rig illustrated in figure 6 was constructed in order to reduce the scanning time. While the beam rotates the probe is moved from one end to the other of the beam. When the scarming is complete it is saved on diskette and can then be evaluated on a PC. The scanner is controlled by the P-scan system, which enables the results to be presented in three dimensions (Top, Side and End view). 

Defects such as hot tears or laps, quench cracks, localized overheating during stress rehef, and corrosion may occur during the tubemaking process (154). Magnetic particle, ultrasonic, and visual inspection techniques are used to ensure that relatively few tubes enter service with significant defects. 

An overall assessment as to the reliability of inspection techniques (NOT), including ultrasonics, is given by Silk". ... 

Corrosion may be monitored by measuring changes in thickness with time using ultrasonic thickness gages. An automated ultrasonic inspection system has been devised and used in monitoring corrosion in nuclear waste containers and typical variations in ultrasonic indications in corroded and uncorroded areas have been recorded successfully. Major types of equipment inspection by ultrasonic technique has been done in mill components, power equipment, jet engine parts, aircraft components, railway materials, automotive components and other machinery components. 

Ultrasonic examination is currently the most commonly used NDT method for inspection of composites. It presents desirable features such as providing information about defects situated deeply inside a material, but equally this method has several limitations. Flaws modify ultrasonic parameters such as wave velocity, refraction, reflection, scattering, and intensity, thus affecting the efficiency of ultrasound in defect location. In order to fully understand the concept of ultrasonic testing, it is necessary to use some mathematics, which will be kept to a minimum. The principle, advantages, and limitations of ultrasonic NDT techniques for composite inspection are described next. 

In summary, it can be said that ultrasonic testing is a well-established method but difficult to implement with composites, mainly because of their heterogeneity, anisotropy, and multiple layers. The repeatability of the technique is also often limited signal interpretation remains uncertain or difficult, and further improvements arc required. Complex geometries and nonplanar surfaces are difficult to inspect and tend to complicate signal interpretation, defect detection, and ultrasonic inspection in general. 

Two years ago an experiment was carried out by the UK Atomic Energy Authority on the Prototype Fast Reactor at Dounreay, to establish whether ultrasonic imaging could be carried out beneath the sodium. The success of this experiment has given confidence in the eventual use of ultrasonics for under sodium inspection. Under-soUium ultrasonics cannot as yet match inspection techniques that can be applied in a more amenable situation. However it seems likely that it can provide the equivalent of visual examinations. 

Ultrasonic C-scan n. A non-destructive inspection technique for reinforced plastics in which the energy absorbed from a short ultrasonic pulse is measured. This is quantitatively different for sample containing delaminations, voids, or too little or too much reinforcement, than for solid samples of the correct composition. 

Examinations will include liquid penetrant or magnetic particle techniques when surface examination is specified, ultrasonic or radiographic techniques when volumetric examination is specified, and visual inspection techniques will be used to determine surface condition of components and for evidence of leakage. Specific techniques, procedures and equipment, including any special techniques or equipment will be in accordance with the requirements of IWA-22 00 of ASME Section XI and will be defined in the in-service inspection program. 

Resonetics Inc. of Nashua, NH has successfully machined simulated voids in silicon nitride specimens with an Excimer laser. Two longitudinally ground and lapped tensile specimens have been provided to them with plans for machining 100 each of 10,20, 50, and 100 mm voids. One of these IQIs was provided to Panametrics, Inc. for use in development of their surface wave technique for ultrasonic inspection of cylindrical specimens. 

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