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. 

 

  • Dynamic adaptive recursive concurrent multi-scale modelling in impact mechanics
    Professor Nik Petrinic, University of Oxford, UK
   
  The design against rapidly applied mechanical load upon engineering structures arising from short-lasting events such as explosions or collisions represents often one of the most critical aspects of all new engineering projects.  All final designs are currently assessed using elaborate numerical simulations, but their ability to meet the design requirements, in which both the global structural response and detailed stress analysis that respects all material characteristics and manufacturing processes are addressed, still remains a challenge due to massive computational requirements even for geometrically very small products.  The research into concurrent multi scale modelling which is capable of simulating the response of the structure at large (global) level simultaneously with accurately representing the behaviour of materials (ingredients) at the smallest relevant (local) level is the new backbone of the adopted integrated experimental-modelling approach presented in this paper.  In particular, initial results of stress wave propagation phenomena are presented, by focusing on the impulsive excitation and emphasizing the issues related to the communication between the length scales during the concurrent simulations, in order to demonstrate the ability of the algorithms to maintain the energy balance throughout the calculations. A new three-dimensional multi-scale adaptive method for explicit formulation is introduced, that allows a computationally efficient simulation of dynamic problems.  The introduction of the different spatial and temporal scales only on as/where needed basis, removes the limitation of those approaches which rely upon a-priori knowledge of the “hot-spots”, hence simulating de-facto the whole domain at the lowest scale of interest. The results of simulations show that considerably larger problems could be solved more efficiently by the developed dynamic adaptive recursive concurrent multi scale modelling approach, while guaranteeing that both the global and local responses are at least as accurate as “brute-force” approach would show, if such computing power was available.
   
  • Towards a population-based approach to structural health monitoring
    Keith Worden, University of Sheffield, UK


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 Nik Petrinic graduated in Structural Mechanics in 1988 at the University of Zagreb.  He completed his PhD in Computational Mechanics at the University of Swansea in 1996 and became a lecturer at the University of Oxford in 1998.

Professor Petrinic lectures on topics in Engineering Materials, Solid Mechanics and Structures. His research activities are focused on the development and integration of experimental and numerical methods for predictive engineering design in Impact Engineering.  His particular interests include temperature and strain rate dependent constitutive material behaviour including strain localisation, damage and fracture, as well as contact interaction for multi-body systems.  He has 25 years of research experience in the field of dynamic behaviour of solid materials, systems and structures as principal investigator/collaborator on an intricate portfolio of projects funded by UK, EU and US government research and defence agencies as well as directly by industry world-wide, during which time he has been advisor to over 30 post-doctoral research assistants/associates and over 35 post-graduate students (exclusive of those visiting from other academic, research and industrial establishments world-wide).

Professor Petrinic heads Oxford’s Impact Engineering Team which operates within the Impact Engineering Laboratory where corresponding research and technology-transfer projects funded by government agencies and industry are hosted.  He is the Deputy Director of the oldest Rolls-Royce’s University Technology Centre in Solid Mechanics and the newly awarded Royal Academy of Engineering Research Chair in Impact Engineering.

     
 

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

  • Paper submission deadline:
    28 May 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).