In this process the amplitude height is usually referred to artificial reference reflectors or it is compared to an idealized circular reference reflector according to the DGS-method.
Ultrasonic Inspection Basics Download As PDFFrom: Composites Part A: Applied Science and Manufacturing, 2014 Related terms: Non-Destructive Testing Radiographic Testing Transducer Delamination Elastic Moduli Enzyme Textile Fiber View all Topics Download as PDF Set alert About this page Non-destructive evaluation (NDE) of aerospace composites: methods for testing adhesively bonded composites B.Ehrhart,. C. Bockenheimer, in Non-Destructive Evaluation (NDE) of Polymer Matrix Composites, 2013 9.4.6 US methods US methods are without a doubt the most versatile NDT method.
A very large diversity of US methods are available, and in use, for the inspection of composite parts. The common principle of these techniques is the generation of a US pulse (1 to 25 MHz) which propagates into the material, to be reflected or attenuated by an obstacle (defects, inhomogeneities, interphases). The propagation behaviour of US waves into the material is linked directly to intermolecular forces and mechanical behaviour. US waves are particularly sensitive to the differences of impedance within the structure and so, for all US techniques involving contact of a transducer that functions as an actuator andor sensor, the use of a coupling medium (such as water, oil or gel) is required to minimise signal loss. Once the US wave has been reflected or transmitted, a sensor detects it, delivering information such as intensity (defect size, adhesive properties) and time of flight in the inspected part (depth of obstacle). The choice of this sensor is a compromise between test frequency and sensor size. The US field generated in the structure by the transducer must deal with a complex interference area in the near field of the transducer. ![]() The entire surface of bonded structures is generally scanned in order to provide information about the precise size and location of any defects. Two main modes exist: the pulse-echo mode where the actuator is also the sensor; and the transmission mode where a separate actuator and sensor are used. Different coupling methods are available to suit all inspection needs: contact measurements with the sensor on the surface; immersion measurements (usually in water tanks); squirter measurements (flow of water onto the surface to avoid complete immersion); air-coupled US measurements (without a coupling medium); and laser stimulated US measurements. Finally, a large variety of sensor sizes, orientation, and geometry, enable different US wave directions, and beam pressure to travel in particular directions in the bonded part. This variety of sensors enables the generation of longitudinal, transversal and Lamb waves for the detection of various defect orientations and geometries. US techniques have benefited from numerical reconstruction processes to eliminate parasitic signal changes, especially due to coupling issues, thickness variations and composite plies arrangements. Spatial resolution and quantification has been improved in methods such as phased array or sampling phased array, where the combination of sensors can be electronically triggered for angular scanning and focusing variations. US inspection is a standardised NDT technique in all aeronautic manufacturers. Ultrasonic Inspection Basics Skin Disbonds InIts application ranges from the inspection of skin disbonds in honeycomb core sandwich structures of composites, porosity in bond lines, delaminations and disbonds in bonded parts, to the precise position, size and geometry of defects in the complete part. However, despite the universal use of ultrasonics, this NDT technology is unable to detect changes in adhesive bond strength, a fact that is well known. The US waves can nevertheless yield information regarding the morphological and elastic features at the interface of adhesive bonds, by their behaviour in the inspected material. Ultrasonic Inspection Basics Full Chapter URLView chapter Purchase book Read full chapter URL: DEFECT DIAGNOSIS IN FORGED ROTORS BY MEANS OF ULTRASONIC IMAGING METHODS E. NUSSMLLER,. W. MLLER, in Non-Destructive Testing 1989, 1989 OUTLINE OF THE PRESENT SITUATION Conventional examination method Ultrasonic examination of large forgings such as rotor shafts and similar components is still mainly done manually today. The interpretation of indications is usually carried out by an operator observing the echoes displayed on the screen. ![]()
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