Tag Archives: infra-red

Out of the valley of death into a hype cycle?

Fig 5 from Middleton et al with full captionThe capability to identify damage and track its propagation in structures is important in ensuring the safe operation of a wide variety of engineering infrastructure, including aircraft structures. A few years ago, I wrote about research my group was performing, in the INSTRUCTIVE project [see ‘INSTRUCTIVE final reckoning‘ on January 9th, 2019] with Airbus and Strain Solutions Limited, to deliver a new tool for monitoring the development of damage using thermoelastic stress analysis (TSA) [see ‘Counting photons to measure stress‘ on November 18th, 2015].  We collected images using a TSA system while a structural component was subject to cycles of load that caused damage to initiate and propagate during a fatigue test. The series of images were analysed using a technique based on optical flow to identify apparent movement between the images which was taken as indication of the development of damage [1]. We demonstrated that our technique could indicate the presence of a crack less than a millimetre in length and even identify cracks initiating under the heads of bolts using experiments performed in our laboratory [see ‘INSTRUCTIVE update‘ on October 4th, 2017].  However, this technique was susceptible to errors in the images when we tried to use low-cost sensors and to changes in the images caused by flight cycle loading with varying amplitude and frequency of loads.  Essentially, the optical flow approach could be fooled into identifying damage propagation when a sensor delivered a noisy image or the shape of the load cycle was changed.  We have now overcome this short-coming by replacing the optical flow approach with the orthogonal decomposition technique [see ‘Recognising strain‘ on October 28th, 2015] that we developed for comparing data fields from measurements and predictions in validation processes [see ‘Million to one‘ on November 21st, 2018] .  Each image is decomposed to a feature vector and differences between the feature vectors are indicative of damage development (see schematic in thumbnail from [2]).  The new technique, which we have named the differential feature vector method, is sufficiently robust that we have been able to use a sensor costing 1% of the price of a typical TSA system to identify and track cracks during cyclic loading.  The underpinning research was published in December 2020 by the Royal Society [2] and the technique is being implemented in full-scale ground-tests on aircraft structures as part of the DIMES project.  Once again, a piece of technology is emerging from the valley of death [see ‘Slowly crossing the valley of death‘ on January 27th, 2021] and, without wishing to initiate the hype cycle [see ‘Hype cycle‘ on September 23rd, 2015], I hope it will transform the use of thermal imaging for condition monitoring.

Logos of Clean Sky 2 and EUThe INSTRUCTIVE and DIMES projects have received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 685777 and No. 820951 respectively.

The opinions expressed in this blog post reflect only the author’s view and the Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains.

References

[1] Middleton CA, Gaio A, Greene RJ & Patterson EA, Towards automated tracking of initiation and propagation of cracks in Aluminium alloy coupons using thermoelastic stress analysis, J. Non-destructive Testing, 38:18, 2019.

[2] Middleton CA, Weihrauch M, Christian WJR, Greene RJ & Patterson EA, Detection and tracking of cracks based on thermoelastic stress analysis, R. Soc. Open Sci. 7:200823, 2020.

Condition-monitoring using infrared imaging

If you have travelled in Asia then you will probably have experienced having your health monitored by infrared cameras as you disembarked from your flight.  It has been common practice in many Asian countries since long before the COVID-19 pandemic and perhaps will become more usual elsewhere as a means of easily identifying people with symptoms of a fever that raises their body temperature.  Since, research has shown that infrared thermometers are slightly more responsive as well as quicker and easier to use than other types of skin surface thermometers [1].  In my research group, we have been using infrared cameras for many years to monitor the condition of engineering structures by evaluating the distribution of load or stress in them [see ‘Counting photons to measure stress‘ on November 18th, 2015 and  ‘Insidious damage‘ on December 2nd, 2015].  In the DIMES project, we have implemented a low-cost sensor system that integrates infrared and visible images with information about applied loads from point sensors, which allows the identification of initiation and tracking of damage in aircraft structures [2].  I reported in December 2019 [see ‘When seeing nothing is a success‘] that we were installing prototype systems in a test-bench at Empa.  Although the restrictions imposed by the pandemic have halted our tests, we were lucky to obtain data from our sensors during the propagation of damage in the section of wing at Empa before lockdown.  This is a landmark in our project and now we are preparing to install our system in test structures at Airbus once the pandemic restrictions are relaxed sufficiently.  Of course, we will also be able to use our system to monitor the health of the personnel involved in the test (see the top image of one of my research team) as well as the health of the structure being tested – the hardware is the same, it’s just the data processing that is different.

The image is a composite showing images from a visible camera (left) and processed data from infrared camera overlaid on the same visible image (right) from inside a wing box during a test at Empa with a crack extending from left to right with its tip surrounded by the red area in the right image.  Each nut in the image is about 20 mm in diameter and a constant amplitude load at 1.25 Hz was being applied causing a wing tip displacement of 80 mm +/- 15 mm.

The University of Liverpool is the coordinator of the DIMES project and the other partners are Empa, Dantec Dynamics GmbH and Strain Solutions Ltd.

The DIMES project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 820951.

 

The opinions expressed in this blog post reflect only the author’s view and the Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains.

References

[1] Burnham, R.S., McKinley, R.S. and Vincent, D.D., 2006. Three types of skin-surface thermometers: a comparison of reliability, validity, and responsiveness. American journal of physical medicine & rehabilitation, 85(7), pp.553-558.

[2] Middleton, C.A., Gaio, A., Greene, R.J. and Patterson, E.A., 2019. Towards automated tracking of initiation and propagation of cracks in aluminium alloy coupons using thermoelastic stress analysis. Journal of Nondestructive Evaluation, 38(1), p.18.

When seeing nothing is a success

In November I went to Zurich twice: once for the workshop that I wrote about last week [see ‘Fake facts and untrustworthy predictions’ on December 4th, 2019]; and, a second time for a progress meeting of the DIMES project [see ‘Finding DIMES’ on February 6th, 2019].  The progress meeting went well.  The project is on schedule and within budget. So, everyone is happy and you are wondering why I am writing about it.  It was what our team was doing around the progress meeting that was exciting.  A few months ago, Airbus delivered a section of an A320 wing to the labs of EMPA who are our project partner in Switzerland, and the team at EMPA has been rigging the wing section for a simple bending test so that we can use it to test the integrated measurement system which we are developing in the DIMES project [see ‘Joining the dots’ on July 10th, 2019].  Before and after the meeting, partners from EMPA, Dantec Dynamics GmbH, Strain Solutions Ltd and my group at the University of Liverpool were installing our prototype systems to monitor the condition of the wing when we apply bending loads to it.  There is some pre-existing damage in the wing that we hope will propagate during the test allowing us to track it with our prototype systems using visible and infra-red spectrum cameras as well as electrical and optical sensors.  The data that we collect during the test will allow us to develop our data processing algorithms and, if necessary, refine the system design.  The final stage of the DIMES project will involve installing a series of our systems in a complete wing undergoing a structural test in the new Airbus Wing Integration Centre (AWIC) in Filton, near Bristol in the UK.  The schedule is ambitious because we will need to install the sensors for our systems in the wing in the first quarter of next year, probably before we have finished all of the tests in EMPA.  However, the test in Bristol probably will not start until the middle of 2020, by which time we will have refined our algorithm for data processing and be ready for the deluge of data that we are likely to receive from the test at Airbus.  The difference between the two wing tests besides the level of maturity of our measurement system, is that no damage should be detected in the wing at Airbus whereas there will be detectable damage in the wing section in EMPA.  So, a positive result will be a success at EMPA but a negative result, i.e. no damage detected, will be a success at Airbus.

The DIMES project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 820951.

 

The opinions expressed in this blog post reflect only the author’s view and the Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains.

Finding DIMES

A couple of weeks ago I wrote about the ‘INSTRUCTIVE final reckoning’ (see post on January 9th).  INSTRUCTIVE was an EU project, which ended on December 31st, 2018  in which we demonstrated that infra-red cameras could be used to monitor the initiation and propagation of cracks in aircraft structures (see Middleton et al, 2019).  Now, we have seamlessly moved on to a new EU project, called DIMES (Development of Integrated MEasurement Systems), which started on January 1st, 2019.  To quote our EU documentation, the overall aim of DIMES is ‘to develop and demonstrate an automated measurement system that integrates a range of measurement approaches to enable damage and cracks to be detected and monitored as they originate at multi-material interfaces in an aircraft assembly’.  In simpler terms, we are going to take the results from the INSTRUCTIVE project, integrate them with other existing technologies for monitoring the structural health of an aircraft, and produce a system that can be installed in an aircraft fuselage and will provide early warning on the formation of cracks.  We have two years to achieve this target and demonstrate the system in a ground-based test on a real fuselage at an Airbus facility.  This was a scary prospect until we had our kick-off meeting and a follow-up brainstorming session a couple of weeks ago.  Now, it’s a little less scary.  If I have scared you with the prospect of cracks in aircraft, then do not be alarmed; we have been flying aircraft with cracks in them for years.  It is impossible to build an aircraft without cracks appearing, possibly during manufacturing and certainly in service – perfection (i.e. cracklessness) is unattainable and instead the stresses are maintained low enough to ensure undetected cracks will not grow (see ‘Alan Arnold Griffith’ on April 26th, 2017) and that detected ones are repaired before they propagate significantly (see ‘Aircraft inspection’ on October 10th, 2018).

I should explain that the ‘we’ above is the University of Liverpool and Strain Solutions Limited, who were the partners in INSTRUCTIVE, plus EMPA, the Swiss National Materials Laboratory, and Dantec Dynamics GmbH, a producer of scientific instruments in Ulm, Germany.  I am already working with these latter two organisations in the EU project MOTIVATE; so, we are a close-knit team who know and trust each other  – that’s one of the keys to successful collaborations tackling ambitious challenges with game-changing outcomes.

So how might the outcomes of DIMES be game-changing?  Well, at the moment, aircraft are designed using computer models that are comprehensively validated using measurement data from a large number of expensive experiments.  The MOTIVATE project is about reducing the number of experiments and increasing the quality and quantity of information gained from each experiment, i.e. ‘Getting Smarter’ (see post on June 21st 2017).  However, if the measurement system developed in DIMES allowed us to monitor in-flight strain fields in critical locations on-board an aircraft, then we would have high quality data to support future design work, which would allow further reductions in the campaign of experiments required to support new designs; and we would have continuous comprehensive monitoring of the structural integrity of every aircraft in the fleet, which would allow more efficient planning of maintenance as well as increased safety margins, or reductions in structural weight while maintaining safety margins.  This would be a significant step towards digital twins of aircraft (see ‘Fourth industrial revolution’ on July 4th, 2018 and ‘Can you trust your digital twin?’ on November 23rd, 2016).

The INSTRUCTIVE, MOTIVATE and DIMES projects have received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 685777, No. 754660 and No. 820951 respectively.

The opinions expressed in this blog post reflect only the author’s view and the Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains.

Sources:

Middleton CA, Gaio A, Greene RJ & Patterson EA, Towards automated tracking of initiation and propagation of cracks in Aluminium alloy coupons using thermoelastic stress analysis, J. Non-destructive Testing, 38:18, 2019