Invited speakers

  • Integrating full-field experimental imaging techniques for on-site inspections and stress based non-destructive evaluation

        Professor Janice Barton, University of Southampton, UK

   
 

Thermoelastic stress analysis (TSA) [1] and digital image correlation (DIC) [2] are two well known, complementary full field stress / strain measurement tools. Both provide data relating to the stress or strain change on the surface of a component. In the case of TSA the sum of principal stresses is obtained, whereas for DIC component strains are obtained. The principles underlying the measurements are very different for the two techniques and accordingly each technique has its strengths and weaknesses. For example, DIC provides the individual strain components but is limited in spatial resolution so areas with high strain gradients, such as around defects, are not well resolved. TSA in contrast has high spatial resolution but can only provide the sum of the principal stresses, making it difficult to implement in the context of failure criteria. However the information provided is complimentary, thereby giving independent measurements which together offer a richer understanding of the mechanical and thermal behaviour of the component or material being tested.

The presentation focusses on the development and implementation of TSA as a new stress based non-destructive evaluation approach. On-site tests are described, which consisted of the inspection of several welds along thick walled high pressure steam drains during a scheduled outage period at a coal fired power station (EDF, West Burton) on pipework. To excite the thermoelastic response, it is necessary to apply a cyclic load, which is usually done with a test machine in a laboratory setting. To deploy on-site it was necessary to develop a device to produce a small load sufficient to elicit the thermoelastic response. It was demonstrated that TSA inspections were very efficient, and the equipment was proved to be robust in the difficult service environment, with data collection and analysis taking a matter of minutes identifying stress concentrations close to welds. The presentation shows that TSA can be used effectively as a tool to rapidly inspect defects, which could be used in conjunction with other inspection techniques such as ultrasound.

A key challenge is how to most effectively combine DIC and TSA. TSA relies on a dynamic cyclic load, using a lock-in algorithm to extract the amplitude of the thermal response, DIC is most commonly applied to static loading. Recent work has shown that it is possible to use the same lock-in approach in DIC to extract strain, enabling standard low frame rate cameras with high spatial resolution to be used without the need for load-camera synchronisation. An example of how the techniques can be combined involves the inspection of discontinuous fibre compression moulded composite materials Here, a significant limitation is the heterogeneous mechanical properties at the mesoscale which adds complications to predicting the mechanical behaviour and thereby potentially reducing the uptake in the composite industry. To understand the mechanisms contributing to material heterogeneity, DIC and TSA are used to link the material heterogeneity with the surface response detected by DIC and TSA. To address the need for fast online inspection in a production environment, this work also demonstrates the capability of combining TSA with vibrational excitation of a component to capture surface stress heterogeneity.

 

  • Vibration energy harvesting: fundamentals and applications
    Professor Steve Beeby, University of Southampton, UK
   
  Vibration energy harvesting (VEH) involves the conversion of kinetic energy, in the form of vibrations, into electrical energy for use in powering autonomous sensor systems. It is an applied technology and the the design of the harvesters is fundamentally linked to the frequency spectrum and amplitude of the vibrations. The application also imposes physical constraints (space limitations and form factor), reliability requirements and, for commercial solutions, cost constraints on the entire system (harvester, power conditioning electronics, energy storage and load electronics). This talk will provide a brief overview of the fundamental principles of VEH and illustrate these through example harvesters and systems developed at the University of Southampton and at Perpetuum Ltd. These examples will include fixed frequency electromagnetic harvesters for industrial applications, piezoelectric harvesters designed for use in helicopter health and usage monitoring systems (HUMS) and a wireless condition monitoring system for the rail industry powered by Perpetuum’s vibration energy harvester. Finally, the suitability of different types of energy harvester (linear, bistable and Duffing type non-linear) for use in real applications will also be explored. 

 

  • Towards a population-based approach to structural health monitoring

          Keith Worden, University of Sheffield, UK

   
 

One of the problems with data-based Structural Health Monitoring (SHM) in practice is that data from damaged structures are scarce. This means that analysis is often confined to novelty detection, or unsupervised learning generally. The idea of population-based SHM is that data acquired on one structure might be used to help inferences for a different structure. This means that damage data from one structure might aid supervised learning over a population of similar structures. The basic ideas of such a population-based approach will be discussed with illustrations from the monitoring of an offshore wind farm.

Speaker Biographies

  Janice Dulieu-Barton is a full Professor of Experimental Mechanics at the University of Southampton in the UK. She received her PhD from the University of Manchester in 1993 where she started her research on the topic now known as ‘Thermoelastic stress analysis’.  She has published around 320 papers with 120 in archival journals, edited 11 conference proceedings and produced 8 book chapters. Janice’s expertise is in imaging for data rich materials characterisations and assessments of structural performance, with a focus on lightweight structural design particularly composite structures. She has won numerous grants that have allowed her to develop novel approaches in experimental mechanics, with as special focus on the development of infra-red imaging recently covering on high speed data capture, new approaches to residual stress analysis and strain-based NDE.  Most recently ‘Structures 2025’, an EPSRC strategic equipment grant, which will enable imaging to be used at full structural scale. Janice has served many roles within the British Society for Strain Measurement, where she is a fellow and has been chairman of the Society and its technical committee. She edited the journal ‘Strain’ and has been involved in its development since 2000. Janice is a fellow of the Institute of Physics where she served on council for many years and chaired the Stress and Vibration Group and the Applied Physics Division. Janice has organised and chaired numerous conferences, seminars and workshops for the IOP and other organisations covering a variety of topics. In 2016 she was elected as a Fellow of the US Society for Experimental Mechanics (the only non- US female to be awarded this honour). Most recently she was chairman of the 16th International Conference on Experimental Mechanics in 2014, which attracted over 500 international delegates to Cambridge in the UK. 
     
 

Professor Keith Worden began academic life as a theoretical physicist, with a degree from York University and a PhD in Mechanical Engineering from Heriot-Watt University eventually followed.

A period of research at Manchester University led to an appointment at the University of Sheffield in 1995, where he has happily remained since.

Keith's research is concerned with applications of advanced signal processing and machine learning methods to structural dynamics. The primary applications are currently in the aerospace and renewable energy industries.

Key dates

  • Revision of proceedings (committee)
    Early September 2018
  • Early registration deadline:
    5 June 2018
  • Registration deadline:
    26 June 2018

More information

Authors of accepted abstracts will have the option to publish their papers in IOP Publishing’s Journal of Physics: Conference Series and/or in the special edition Advances in Computational Stress and Vibration Analysis, of the European Journal of Computational Mechanics (EJCM).