Computational Mechanics and Design Group

Department of Civil & Structural Engineering

Prof. Harm Askes

Professor of Computational Mechanics

Contact

h.askes@sheffield.ac.uk
+44 (0) 114 222 5769

Department of Civil and Structural Engineering
Sir Frederick Mappin Building
Mappin Street, Sheffield, S1 3JD

Profile

Harm Askes obtained his MSc degree in Civil Engineering from Delft University of Technology (Netherlands) in 1995. He also studied psychology and philosophy at Leiden University (Netherlands). In 2000 he was awarded a PhD from Delft University of Technology for his work in computational methods for failure analysis, followed in 2013 by a DEng from the University of Sheffield for his overall research accomplishments.

From 1999 until 2004 he was an Assistant Professor at the Faculty of Civil Engineering in Delft, where he was teaching Structural Mechanics and carrying out research in the field of Computational Mechanics. In September 2004 he was appointed Professor of Computational Mechanics at the Department of Civil and Structural Engineering of the University of Sheffield. He has also been the Head of Department since 2009.

His research interests are the modelling of engineering structures and materials. The two main themes are Numerical Methods and Mechanics of Materials:

Numerical Methods:

Error estimation and mesh adaptivity are required for efficient and accurate finite element analysis. Recent work focuses on applications to failure analysis and is carried out with Dr Canh Le Van, Prof. Matthew Gilbert and Dr Tanyada Panachet (Khon Kaen University, Thailand).

Constraint equations are an essential ingredient of many mathematical models. Recent work includes the use of negative penalty functions in terms of stiffness as well as inertia, carried out with Jack Hetherington, Prof. Antonio Rodriguez-Ferran (Universitat Politecnica de Catalunya, Spain) and Prof. Sinniah Ilanko (University of Waikato, New Zealand).

Mechanics of Materials:

Gradient-enriched continuum theories can be used to capture a range of microstructure-driven phenomena such as wave dispersion, size effects and strain localisation. The formulation of such gradient theories is pursued in collaboration with Prof. Andrei Metrikine of Delft University of Technology (Netherlands), Prof. Elias Aifantis of Aristotle University of Thessaloniki (Greece) and Prof. Antonio Rodriguez-Ferran of the Universitat Politecnica de Catalunya (Spain).

Following up on the previous item, the implementation of gradient theories is normally not straightforward due to the higher-order continuity requirements. Flexible finite element implementations are developed for straightforward implementation in existing software packages.

Recent activities and achievements

  • Executive Committee of the UK Association of Computational Mechanics in Engineering (2005-present)
  • Editorial Advisory Panel of the Proceedings of the ICE "Engineering and Computational Mechanics'' (2007-2011)
  • Associate Editor of the Journal of the Mechanical Behavior of Materials (2007-present)
  • Visiting Professor of the Universitat Politecnica de Catalunya (Barcelona, Spain) (2005-2006, 2008-2012)
  • Visiting Professor of Aalto University (Finland, formerly Helsinki University of Technology) (2006, 2011)
  • Senate Award for Departmental Leadership in Learning and Teaching in July 2013
  • Voted "Best Lecturer" of the Department by graduating students in June 2008

Qualifications

DEng, Numerical Methods and Mechanics of Materials, University of Sheffield, 2013
PhD, Computational Mechanics, Delft University of Technology, Netherlands, 2000
MSc, Civil Engineering, Delft University of Technology, Netherlands, 1995

Software

Research project(s)

Dynamic constraint modelling

In this project, we develop new penalty methods for use in fast transient dynamic problems, simulated with time-domain integrators. A problem that has plagued the community for many decades is that the usual stiffness-type penalties tend to decrease the critical time step of conditionally stable time integrators such as the...

Project deep carbon: verification and governance of environmental carbon sequestration

Carbon dioxide storage in deep geological formations is part of a technological approach for mitigating greenhouse gas emissions while maintaining the security and stability of the world’s energy systems. Subsurface storage is the final element to the Carbon Capture and Storage (CCS) chain, where the major issues are in understanding...

Dynamics of micro-trusses

We study the mechanical behaviour of micro lattices (also known as micro-trusses) under a range of loading conditions. Where applicable, we apply homogenisation and continualisation principles to derive higher-order gradient theories with a transparent interpretation of the emerging internal length scales. Under elastic loading conditions, the emergence of stop bands...

Publication(s)

(2017). The influence of random microstructure on wave propagation through heterogeneous media. International Journal of Fracture, 204 (1), pp. 114-120. (Full Text).
(2017). Reducible and irreducible forms of stabilised gradient elasticity in dynamics. Mathematics and Mechanics of Complex Systems, 5 (1), pp. 1-17. (Full Text).
(2016). A new multi-scale dispersive gradient elasticity model with micro-inertia: Formulation and 0-finite element implementation. International Journal for Numerical Methods in Engineering, 108 (5), pp. 485-512. (Full Text)., Abstract: Motivated by nano-scale experimental evidence on the dispersion characteristics of materials with a lattice structure, a new multi-scale gradient elasticity model is developed. In the framework of gradient elasticity, the simultaneous presence of acceleration and strain gradients has been denoted...
(2016). Microstructural length scale parameters to model the high-cycle fatigue behaviour of notched plain concrete. International Journal of Fatigue, 82 (3), pp. 708-720. (Full Text)., Abstract: The present paper investigates the importance and relevance of using microstructural length scale parameters in estimating the high-cycle fatigue strength of notched plain concrete. In particular, the accuracy and reliability of the Theory of Critical Distances and Gradient Elasticity are checked...
(2016). Gradient elasticity: a new tool for the multiaxial high-cycle fatigue assessment of notched components. (pp. 21-26). (Full Text)., Abstract: In this paper, the accuracy of gradient elasticity in estimating the fatigue strength of engineering components, characterised by the presence of stress risers and subjected to multiaxial high-cycle fatigue loadings, is assessed. In particular, a new approach, based on the combination of the Ru-...
Jadallah O, Bagni C, Askes H, Susmel L (2016). Microstructural length scale parameters to model the high-cycle fatigue behaviour of notched plain concrete. International Journal of Fatigue, 82 (2), pp. 708-720. (Full Text).
(2016). Gradient elasticity: a transformative stress analysis tool to design notched components against uniaxial/multiaxial high-cycle fatigue. Fatigue & Fracture of Engineering Materials and Structures, 39 (8), pp. 1012-1029. (Full Text).
(2016). Energy absorption in lattice structures in dynamics: Experiments. International Journal of Impact Engineering, 89 (2), pp. 49-61. (Full Text).
(2016). Ductile fracture of Q460 steel: Effects of stress triaxiality and Lode angle. Journal of Constructional Steel Research, 123 (EN4), pp. 1-17, Abstract: The ductile fracture characteristics of Chinese Q460 high strength structural steel under quasi-static condition were studied by using mechanical tests of four types of notched specimens. The influence of stress state on fracture mechanism of the material was investigated by observing the fracture...

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