Professor Harm Askes

MSc, PhD, DEng.

Interdisciplinary Engineering

Head of Interdisciplinary Engineering

Professor of Computational Mechanics

CIV Harm Askes
h.askes@sheffield.ac.uk
+44 114 222 5769

Full contact details

Professor Harm Askes
Interdisciplinary Engineering
Room D08
Sir Frederick Mappin Building
Mappin Street
Sheffield
S1 3JD
Profile

My research helps to make structures safer, more efficient, and more resilient.

Professor Harm Askes

Professor of Computational Mechanics

Harm's research interests are concerned with modelling the behaviour of engineering structures and materials.

He develops simulation tools to emulate this behaviour, allowing predictions that would be impossible through physical testing. This helps in making structures safer, more efficient, and more resilient.

In his free time, Harm enjoys reading comics and modern European history, cooking and running. He has published one novel (in Dutch) and has been a life-long fan of AFC Ajax 1981-1987, 1993-2004 and 2009-2014.


Qualifications
  • 2017-present: Head of Interdisciplinary Engineering
  • 2013: DEng higher doctorate
  • 2009-2017: Head of the Department of Civil and Structural Engineering
  • 2004-present: Professor of Computational Mechanics
  • 1999-2004: Assistant Professor, Delft University of Technology, Netherlands
  • 1995-1999: Research Assistant (PhD 2000), Delft University of Technology, Netherlands
  • 1993-1994: Philosophy studies, University of Leiden, Netherlands
  • 1992-1993: Psychology studies, University of Leiden, Netherlands
  • 1990-1995: Civil Engineering studies (MSc 1995), Delft University of Technology, Netherlands

(all Sheffield unless indicated otherwise)

Research interests

Harm's research interests are concerned with modelling the behaviour of engineering structures and materials. He develops simulation tools to emulate this behaviour, allowing predictions that would be impossible through physical testing. This helps in making structures safer, more efficient, and more resilient.

His two main themes are

Numerical Methods

  • Critical time step estimates for use in explicit time integrators.
  • Penalty methods in dynamics to enforce constraint conditions.

Mechanics of Materials

  • Wave propagation through micro-structured materials.
  • Gradient-enriched continuum theories.
 
Publications

Edited books

  • Susmel L, Askes H & Gilbert M (Eds.) (2016) Proceedings of the Department of Civil and Structural Engineering, University of Sheffield - The Annual Postgraduate Research Student Conference – 2016. Italian Group of Fracture. View this article in WRRO RIS download Bibtex download

Journal articles

Chapters

Conference proceedings papers

  • Susmel L, Bagni C & Askes H (2016) Gradient elasticity: a new tool for the multiaxial high-cycle fatigue assessment of notched components. Proceedings of the Department of Civil and Structural Engineering, University of Sheffield - The Ann (pp 21-26) View this article in WRRO RIS download Bibtex download
  • AA.VV. (2015) Proceedings of the Department of Civil and Structural Engineering, University of Sheffield – The Annual Postgraduate Research Student Conference 2015. The Annual Postgraduate Research Student Conference 2015 (pp 1-61). Sheffield, UK, 15 April 2015 - 15 April 2015. View this article in WRRO RIS download Bibtex download
  • Lincoln DL, Askes H, Smith CC, Cripps JC & Bennett T (2014) Coupled two-component flow in deformable fractured porous media with application to modelling geological carbon storage. Numerical Methods in Geotechnical Engineering - Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014, Vol. 2 (pp 989-994) RIS download Bibtex download
  • Bagni C, Askes H & Susmel L (2014) Finite Element Technology for Gradient Elastic Fracture Mechanics. Procedia Materials Science, Vol. 3 (pp 2042-2047) View this article in WRRO RIS download Bibtex download
  • Susmel L & Askes H (2012) On the multiaxial fatigue assessment of thin welded joints: A preliminary investigation. Gruppo Italiano Frattura (pp 167-176). Italy, 1 March 2012 - 3 March 2012. RIS download Bibtex download
  • Hetherington J, Rodriguez-Ferran A & Askes H (2012) Bipenalty methods for single-point and multi-point constraints in computational dynamics. Civil-Comp Proceedings, Vol. 99 RIS download Bibtex download
  • Askes H (2011) Gradient elasticity theories and finite element implementations for static fracture. Characterisation of Crack Tip Stress Fields (1st IJFatigue & FFEMS JointWorkshop) (pp 136-142). Forni di Sopra RIS download Bibtex download
  • Hetherington J, Rodríguez-Ferran A & Askes H (2011) Controlling the critical time step with the bi-penalty method. ECCOMAS Thematic Conference - COMPDYN 2011: 3rd International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering: An IACM Special Interest Conference, Programme RIS download Bibtex download
  • Askes H & Tyas A (2010) Physical motivation for mass scaling in explicit dynamics. 18th UK ACME conference (pp 53-56). Southampton RIS download Bibtex download
  • Hetherington J & Askes H (2010) A bipenalty formulation for interface elements. 18th UK ACME conference (pp 57-60). Southampton RIS download Bibtex download
  • Le CV, Askes H & Gilbert M (2010) A stabilized meshfree equilibrium formulation for lower-bound limit analysis. 18th UK ACME conference (pp 169-172). Southampton RIS download Bibtex download
  • Askes H, Caram s-Saddler M & Rodriguez-Ferran A (2010) The bipenalty method for explicit time integration. Engineering Computational Technology. Valencia RIS download Bibtex download
  • Askes H & Gitman IM (2010) Review and Critique of the Stress Gradient Elasticity Theories of Eringen and Aifantis. MECHANICS OF GENERALIZED CONTINUA, Vol. 21 (pp 203-210) RIS download Bibtex download
  • Askes H, Gitman IM & Bennett T (2009) Dynamic implementation of implicit gradient elasticity. Euromech Colloquium 510. Paris RIS download Bibtex download
  • Rodriguez-Ferran A, Tamayo-Mas E, Bennett T & Askes H (2009) A continuous-discontinuous model for softening and cracking based on non-local gradient elasticity. COMPLAS X. Barcelona RIS download Bibtex download
  • Rodriguez-Ferran A, Tamayo-Mas E, Bennett T & Askes H (2009) A continuous-discontinuous model for softening and cracking based on non-local gradient elasticity. COMPLAS X. Barcelona RIS download Bibtex download
  • Askes H, Gitman IM & Bennett T (2009) Dynamic implementation of implicit gradient elasticity. Euromech Colloquium 510. Paris RIS download Bibtex download
  • Askes H, Gitman IM & Bennett T (2007) Formulation and finite element implementation of dynamically consistent gradient elasticity. 15th UK National ACME conference. Glasgow RIS download Bibtex download
  • Uthman Z & Askes H (2007) A hyperelastoplastic ALE formulation based on spatial and material forces. 15th UK National ACME conference. Glasgow RIS download Bibtex download
  • Bennett T & Askes H (2007) Wave dispersion in heterogeneous materials using a C0-implementation of gradient elasticity. Modelling of Heterogeneous Materials (with applications in Construction in Biomedical Engineering) (pp 194). Prague RIS download Bibtex download
  • Gitman IM & Askes H (2007) Higher-order homogenisation methods for continua with internal length and internal time. 10th European Mechanics of Materials Conference (pp 129-135). Kazimierz Dolny RIS download Bibtex download
  • Bennett T & Askes H (2007) Numerical modelling of high frequency wave dispersion in heterogeneous materials. 10th European Mechanics of Materials Conference (pp 63-69). Kazimierz Dolny, Poland RIS download Bibtex download
  • Eurviriyanukul S & Askes H (2007) Equilibration of configurational forces in the tendon layout optimisation of pre-stressed concrete structures. 15th UK National ACME conference. Glasgow RIS download Bibtex download
  • Gitman IM, Askes H & Sluys LJ (2007) A coupled-volume approach to the multi-scale modelling of quasi-brittle materials. Materials Science Forum, Vol. 539-543 (pp 2582-2587). Vancouver, Canada, 4 July 2006 - 8 July 2006. RIS download Bibtex download
  • Gutierrez MA & Askes H (2006) Parametrisation of the Newmark time integrator for non-linear solid dynamics. 3rd European Conference on Computational Mechanics. Lisbon RIS download Bibtex download
  • Askes H, Gutierrez MA & Rodriguez-Ferran A (2006) Novel nonlocal continuum formulations. Part 1: Gradient elasticity based on nonlocal displacements and nonlocal strains. 3rd European Conference on Computational Mechanics. Lisbon RIS download Bibtex download
  • Uthman Z & Askes H (2006) A hyperelastodynamic ALE formulation based on spatial and material forces. 3rd European Conference on Computational Mechanics. Lisbon RIS download Bibtex download
  • Gitman IM, Askes H & Sluys LJ (2006) Multi-scale modelling of quasi-brittle material. Euro-C 2006: Computational Modelling of Concrete Structures. Austria RIS download Bibtex download
  • Gitman IM, Askes H & Sluys LJ (2005) Size effects and representative volumes. ICOSSAR (pp 403-410). Rome RIS download Bibtex download
  • Gitman IM, Askes H & Sluys LJ (2005) Multi-scale modelling and representative volumes: linear-elasticity and softening. International Conference on Fracture. Turin RIS download Bibtex download
  • Gitman MB, Gilman IM & Askes H (2003) On the stochastic stability of deformation processes. APPLICATIONS OF STATISTICS AND PROBABILITY IN CIVIL ENGINEERING, VOLS 1 AND 2 (pp 291-295) RIS download Bibtex download
  • Gitman IM, Askes H, Sluys LJ & Stroeven M (2003) Multiscale modelling of granular materials. COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES (pp 67-70) RIS download Bibtex download
  • Askes H, Metrikine AV & Naaktgeboren H (2003) A dynamically consistent gradient model derived from a discrete microstructure: higher-order stiffness and higher-order inertia. COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES (pp 43-51) RIS download Bibtex download
  • Chang CS, Askes H & Sluys LJ (2002) Higher-order strain/higher-order stress gradient models derived from a discrete microstructure, with application to fracture. ENGINEERING FRACTURE MECHANICS, Vol. 69(17) (pp 1907-1924) RIS download Bibtex download
  • Askes H & Rodriguez-Farran A (2000) An rh-adaptive strategy based on domain subdivision and error assessment. Finite Elements: Techniques and Developments (pp 95-102) RIS download Bibtex download

Theses / Dissertations

  • Askes H (2000) Advanced Spatial Discretisation Strategies for Localised Failure - Mesh Adaptivity and Meshless Methods. Delft University of Techology. RIS download Bibtex download

Dictionary/encyclopaedia entries

Previous funded projects
Dynamic contraint 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 central difference scheme.

We resolve this by the simultaneous use of stiffness-type penalties and inertia-type penalties - termed the “bipenalty method” - which allows for high accuracy in constraint imposition across a wide variety of problem types without the need to decrease the time step of an analysis.

Fundamental considerations relate to the stability and accuracy of the method, the derivation of mathematical proofs for suitable ratios of the two types of penalties, and the development of robust algorithms for the selection of penalty parameters.

Practical applications include the imposition of support conditions, the simulation of crack propagation with interface elements, and the modelling of contact-impact.

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 storage site capacities and the potential for leakage from the confined formation.

As a result there are research demands on prediction, monitoring and risk assessment in order to ensure optimal and safe practice.

Project Deep Carbon is a collaborative project involving research activities in the departments of engineering, physics and law, covering numerical modelling, particle detection, tomography and legislation.

The CMD group input is the development a new numerical simulator for geological carbon storage prediction in order to aid monitoring and risk assessment. The emphasis of this numerical research code is on coupling geomechanics and multiphase fluid flow.

UK Government CCS initiatives

Dynamics of miscro-tissues

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 and wave filters is of interest in the design of materials for insulation purposes. Under post-peak loading conditions, the interest is on designing truss materials with maximum capacity to absorb blast and impact waves.

In order to quantify energy absorption capacity of micro-trusses during blast, impact and ballistic attacks, a series of quasi-static and impact experiments will be performed on micro-truss samples.

Additive layer manufacturing techniques where a structure is built up progressively by the selective melting of specific regions in successive layers of metal powder will be used to manufacture these samples with different unit cell geometries in order to maximise the freedom in creation of potentially complex micro-truss structures.

Following the experiments, the multi-purpose nonlinear finite element analysis program LS-DYNA will be used to simulate the response mechanisms of micro-trusses. This will allow us to explore further the impact behaviour of micro-trusses and to clarify strain-rate sensitivity of such structures.

Theory of critical distance and gradient mechanics

This project aims to develop novel finite element software based on the combined use of the Theory of Critical Distance (TCD) and Gradient Mechanics suitable for performing the static and high-cycle fatigue assessment of notched/cracked components subjected to in-service complex systems of forces.

Even though they are designed to address two different problems, the most interesting feature of the above two theories is that both make use of a length scale that is intrinsic to the material: the TCD uses a critical distance, which is treated as a material property, to perform the strength analysis, whereas Gradient Mechanics employs a scale length to perform the stress analysis.

In spite of the evident analogies, so far such theories have never been attempted to be coupled consistently. However, a unification has many potentials for scientific breakthroughs: it would take full advantage, on one hand, of the TCD’s accuracy in estimating static and high-cycle fatigue strength of notched/cracked components and, on the other hand, of the computational efficiency of Gradient Mechanics in determining equivalent stress fields whose distribution fully depends on the actual value of the adopted length scale.

In this scenario, aim of the present joint project is then to reformulate the Gradient Mechanics concepts to develop the governing equations of specific bi- and tri-dimensional finite elements which can be used to determine the stress fields in the vicinity of the crack initiation sites, the strength analysis being directly, but implicitly, performed according to the TCD.