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|Title: ||The development of condition monitoring strategies and techniques appropriate to mechanical structures.|
|Authors: ||Drummond, Gordon|
|Supervisors: ||Watson, John|
|Issue Date: ||Nov-2004|
|Publisher: ||Robert Gordon University|
|Citation: ||DRUMMOND, G. R., WATSON, J. F. and TAYLOR, R. M., 2001. The non destructive evalution of wire ropes - utilizing acoustic emission techniques. In: Fleet maintenance symposium. San Diego.|
DRUMMOND, G. R., FRASER, K. F., LITTLE, J. L., WATSON, J. F. and CAMPBELL, P., 2002. Assessing the structural integrity of crane booms using acoustic emission. In: 25th European Conference on Acoustic Emission Testing. Prague.
DRUMMOND, G. R., MILLS, C. J., WATSON, J. F. and WALTER, T., 2003. Using wide band acoustic emission to determine the condition of rolling element bearings. In: 57th meeting of MFPT Society: Impact of prognostics on organisational success. Virginia Beach.
DRUMMOND, G. R., CAMPBELL, M. and WATSON, J. F., 2003. Talking structures. In: International Conference of Maintenance Societies. Perth, Australia.
DRUMMOND, G. R., 2004. Assessing the structural performance of cranes. In: 9th North Sea Offshore Cranes Conference. Aberdeen.
DRUMMOND, G. R. and WATSON, J. F., 2004. An investigation into the comparison of maintenance strategies past, present and future by enhancing periodic proof testing with acoustic emission to generate reliable through life structural integrity assurance. In: 26th European Conference on Acoustic Emission Testing. Berlin.
|Abstract: ||Recent legislation, LOLER, removed the compulsion of periodical proof testing of lifting
equipment to ascertain its "fitness for purpose". It has become the responsibility of a
competent person to assess equipment's fitness for purpose and ability for continued safe
use. This thesis reviews the technologies available to the competent person to enable
him/her to come to an informed decision regarding the condition of mechanical
structures. It was identified that an optimal methodology would interrogate structural
integrity whilst the equipment performed its intended function. Coupling a means of
assessment with the equipment's operation allows the investigator to focus on only
defective conditions that will limit the future operation. Such an approach of condition
monitoring structural integrity as opposed to employing traditional methods of inspection
that are essentially failure finding tasks permits the discrimination between benign and
malignant defects. Restorative and replacement activities can therefore take place based
upon the likelihood of equipment's functional failure.
The supplementary monitoring of Acoustic Emission (AE), with the established industrial
practice of proof testing, was considered to provide data to monitor structural integrity
and provide the basis upon which a structure can be re-qualified for future service. The
nature of failure of engineering materials was examined which identified failure modes
such as corrosion, creep and fatigue resulted in a progressive degradation of a localised
area. The AE is a proportion of energy released during such deterioration. Further it was
determined that the rate at which the deterioration increased was non-linear.
Within a laboratory environment wire ropes with seeded faults were subjected to a
simulated life during which the qualitative and quantitative nature of the AE was
investigated.It was found that the quantity of the emission generated during proof tests
was indicative of the severity of the induced defect. This substantiated the claim that AE
could be used to enhance the proof test and provide a means by which a condition
assessment could be made at intervals throughout the life of a structure.
A series of five case studies explored the use of AE on a variety of differing in-service
mechanical structures, mostly lifting equipmept. The case studies were conducted on
pad-eyes,link-plates, cranes, both Electrical Overhead Travelling (EOT) and pedestal
cranes and finally, an underwater vehicle pressure hull. The approach of using the
combination of AE with a proof test was verified in the cases of pad-eyes and EOT
cranes. In the instance of link plates, simultaneous measurement of strain and AE during
a load test demonstrated the ability of AE to detect localised yielding. During the
destruction test of a pedestal crane boom section, various conventional methods of AE
evaluation were utilised to investigate which would provide the most reliable condition
indicator; it was found that Intensity Analysis generated the most effective trendable
A study on a pressure hull with known fatigue cracks that were subjected to both static
and dynamic testing whilst monitoring with AE was conducted. The fatigue cracks were
sized pre and post the trial using Time of Flight Diffraction (ToFD). During the trial Alternating Current Potential Drop (ACPD) was used to detect any growth as it occurred.
Such techniques were used to substantiate claims AE could detect a propagating defect.
When the AE is viewed in conjunction with ACPD results and the measurements attained
with the ToFD it was clear that all three techniques concluded that crack growth occurred
at two sites.
Finally the investigation returns to a laboratory to exarnine the robustness of the
technique through the life of a mechanical structure. The objective being to identify if
periodical measurement of AE taken during the course of the life of the structure would
repetitively generate information pertaining to the identification of the flaw as well as the
severity of the flaw as it initiates and propagates through to failure. A power law was
fitted to the data acquired during the proof tests. The use of a power law was considered
appropriate due to the previously identified non-linear nature of material failure. A
Scanning Electron Microscope was used to visually examine the fracture surfaces. It was
found that increasing increments between striations on the fracture surface illustrated the
non-linear increase of crack extensions during fatigue and corroborated the
appropriateness of fitting a power law to the proof test data.
Such an investigation permitted the conclusion that the approach of fitting a power law to
the discrete energies from sequential proof tests is an appropriate method of attaining a
trendable condition indicator. The competent person could employ such a methodology
for the purposes of attaining information upon which an informed decision can be made
on the continued safe use of mechanical structures.|
|Appears in Collections:||Theses (Engineering)|
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