Advanced Materials Research Vols. 13-14

Abstract: Measurement apparatus intended for use in potentially explosive atmospheres in Europe, must comply with the EC Directive 94/9/EC, also known as “ATEX directive”. The conformity must be verified by a so called ATEX Certificate. In the frame of the EC-funded research project „Corrosion testing of tank ships“, AE-field tests on board large tank ships were executed. Intrinsically safe certified AE sensors were temporarily immersed through a potentially explosive atmosphere from the tank top through manholes into the liquid contents. Ship owners and involved classification societies insisted on the availability of a system certificate confirming intrinsic safety for the used sensors and isolation barriers and also for the whole installation for protection from the risk of a lightning strike into a signal cable running over deck. For this certification process, all details of installation, such as cabling, earthing, over voltage protection, etc., have been decided, explained and examined. This paper presents some basics of explosion protection with its terminology and the new “Product Family ISAFE“.

Abstract: The use of AE for testing the integrity of structures has a long history but its use for continuous monitoring of structures is not so well established. In a world of ageing infrastructure the need for methods of continuous monitoring is increasing so that the operation, maintenance and repair of structures can be more effectively managed. The extent to which AE will play a role in this obviously depends upon how effective it is in providing the wanted information in a timely manner to those who need it. However, other crucial aspects in its adoption will be the ease with which it can be used (e.g. specified, installed, interpreted) as well as its reliability and lifetime costs. With these considerations in mind, a multi-channel monitoring system has been developed called SIMPALTM. Throughout its development, field trials have been conducted with the aim of exploring the practical usefulness of a simpler kind of AE system. This paper provides an overview of the approach taken in developing the system and presents data gathered during proving trials and from its practical application to structures such as bridges.

Abstract: Conventional methods of acquiring and using acoustic emission (AE) discard the raw signal waveform after extracting signal features from it. The main reason for this is the number of bytes required to save hundreds of thousands of AE waveforms, using a modern high speed multichannel system the hard-drive may be quickly filled. One side effect of this “feature extraction” approach is that information is thrown away with the wave-form. The advent of systems capable of acquiring AE waveforms on all channels has opened up the opportunity to use this extra data to get more information about the source and the transmission path. This paper describes the use of acoustic emission waveforms to aid source discrimination, and presents data acquired during pressure testing of a slug-catcher.

Abstract: Acoustic Emission is a very powerful tool for health monitoring of structures and mechanical components, especially due to its sensitivity, which is very useful at the early stages of damage evolution. Evaluation of its potential on rotating structures such as gearboxes, is studied in the present paper. A new concept of transducer mounting is realized in a single stage in-house built gearbox. The acoustic emission signature of the healthy gears is acquired. Then artificial defects are seeded and the acquisition is repeated. The signals are afterwards analyzed and the assessment of the applicability of the method becomes possible. Given the present experimental setup, health monitoring of gearboxes using acoustic emission is considered to be of rising potential.

Abstract: Non-destructive monitoring of damage accumulation in woven-fabric carbon/carbon composites is a topic of high interest due to the increased use of such materials in structural components for the aerospace, automobile and defense industries. Acousto-ultrasonics (AU) is a non-destructive technique that utilizes two typical acoustic emission sensors one as a pulser and the other as a receiver. During tensile load-unload-reload tests the pulser emits an ultrasonic pulse, which in the form of elastic wave propagates through the test specimen and is captured by the receiver. As damage accumulates into the material structure the ultrasonic pulse interacts with the damaged microstructure and changes its characteristics often in a subtle not obvious manner. Consequently, sophisticated signal processing methods are needed to extract the hidden information from the recorded AU waveforms in order to identify the type of damage and quantify its severity. The diffuse field decay rate method and wavelet-based methods were applied in order to process the AU waveforms and extract damage sensitive parameters. Two types of C/C composites with different interface concepts were tested and the applied technique elucidates the damage evolution developed during cyclic loading and associated with the different interface concepts.

Abstract: The investigation reported in this paper was centered on the application of the Acoustic Emissions (AE) technology for characterising the defect sizes on a radially loaded bearing. The aim of this investigation was to ascertain the relationship between the duration of AE transient bursts associated with seeded defects to the actual geometric size of the defect. It is concluded that the geometric defect size can be determined from the AE waveform.

Abstract: An empirical investigation is undertaken in order to assess the potential of the AE technique for the detection of seal-to-rotor rubbing in steam turbines. Rubbing was induced at various axial locations along a 4 ½ tonne test rotor, rotating at 3000 rpm and supported by 7” (178mm) journal bearings. This paper examines the capabilities of bearing mounted AE transducers for the detection of seal-to-rotor rubbing.