Product category:
Testing and Calibration Services and Information
News Release from: AV Technology | Subject: Structural monitoring
Edited by the Engineeringtalk Editorial
Team on 14 December 2007
Structural monitoring improves life on
the buses
Tests validate theoretical structural integrity predictions for Optare's Tempo and Versa buses under a wide range of operational conditions.
AV Technology has completed a comprehensive series of structural monitoring tests on two buses designed and manufactured by Optare The onboard tests, carried out at the Millbrook Proving Ground in Bedfordshire, have been used to validate theoretical structural integrity predictions for the company's Tempo and Versa buses under a wide range of operational conditions
This article was originally published on Engineeringtalk on 7 Jul 2003 at 8.00am (UK)
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Optare, which manufactures buses at sites in Leeds and Rotherham, is one of the most respected names in the UK bus and coach industry, and the company claims its vehicle design, award winning styling and proven operational efficiency all combine to put their bus operators one step ahead of their competitors.
Using integral construction technology, each design is conceived to optimise operational productivity and to provide a "great travelling experience for passengers".
AVT has extensive experience in the application of strain gauges and sensors for measuring and recording the behaviour of vehicles and structures under real life operational conditions.
Its part of the project involved the installation of a range of measuring sensors, including single- and three-element rosette strain gauges, displacement transducers and accelerometers.
These were located at various positions on the buses and connected into a multichannel HBM data acquisition system, mounted inside the vehicle and powered by the onboard battery.
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The buses were put through their paces at Millbrook during four days of arduous testing.
The vehicles were subjected to more than twelve different test conditions and surfaces including inclines, adverse cambers, rough tracks, speed and twist humps, the infamous bone-shaking Belgian Pave and potholes.
To ensure comprehensive results, tests on the buses were repeated in both the unladen and fully laden gross vehicle weight conditions (12 tonnes for the Versa and 17 tonnes for the Tempo.) Rather than use a conventional separate chassis-body concept for its vehicles, Optare has pioneered the development of a single fully integrated body and chassis construction.
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This offers a number of important advantages, including the ability to provide passengers with a more user-friendly lower entry/exit facility.
The strain gauges were bonded to the stainless steel welded structure at approximately 30 predetermined positions as defined by Optare's finite element analysis.
Strain data from these positions were analysed to determine the minimum and maximum strain levels as well as fatigue levels experienced by the structure under each test condition.
The vehicle has a fully welded integral structure and therefore results from each strain gauge position were analysed for fatigue failure using BS7608 and the relevant weld class.
(Weld analysis assumes the weld will contain inherent defects which will propagate if exposed to significant stress and the analysis carried out gives the estimated life to failure within selected confidence limits.
It is usually based on a standard weld classification which takes into account weld size and type, together with weld geometry and loading configurations).
The draw-wire displacement transducers, which have a measuring range of +/-50mm, were installed diagonally across the vehicle at the front, middle and rear planes to measure any diagonal displacement of the structure.
Accelerometers were installed over the front and rear axles to measure vertical, lateral and longitudinal road input accelerations, together with cornering and braking loads.
The data sampling rate was set at 1200 samples per second per channel, with the option to increase it to 2400 samples per second.
All data analysis was performed using nCode nSoft data analysis software, including nCode Fatimas fatigue analysis software.
The acceleration and displacement data were reviewed in conjunction with strain data to understand the behaviours of the structure.
Analysed data were supplied to Optare so that the company could carry out a correlation exercise between actual measured strains and stresses compared with those predicted by in-house finite element analysis.
AVT's Senior Engineer Simon Hirst is clear in the role his company's data acquisition and analysis plays in vehicle development and as he explains: "The purpose of practical tests is to increase confidence in the theoretical analysis and to help eliminate structural problems before future designs are prototyped".
"Given the huge amount of data collected during such tests, it is important that we supply our clients with information in a suitable format so that they can readily interpret and integrate the results within their own systems".
"Our data analysis techniques allow us to quantify and extract key information so that we provide clients with a comprehensive, yet manageable data overview".
Optare's Engineering Manager, Colin Hunt, is pleased with the overall way the tests were conducted and he concludes: "The results from the Millbrook tests showed good correlation with our theoretical values and no structural design parameters needed to be changed".
"Although finite element analysis is an important part of our ongoing development programme, practical testing is equally important and we will continue to combine both disciplines so that we continually improve our designs for future generations of vehicles". Request a free brochure from AV Technology ...
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