Upcoming Seminars

Cohesive-Zone Models for the Numerical Simulation of Interfacial Crack Initiation and Growth Accounting for Friction and Rate Dependence

• Tuesday 19th February, 1pm
• Room 816 Rankine Building
• Giulio Alfano – Brunel University

Abstract

In many engineering applications structural failure involves initiation and
propagation of cracks along interfaces. Examples include cracks in dams,
mortar-joint failure in brick masonry, delamination or fibre-matrix debonding
in composites, debonding of adhesive joints, frictional slipping of steel bars
in concrete, among many others. Despite the different materials and scales
involved, these problems share common features and, therefore, they can be
treated with similar approaches. In particular, for many of them the failure
process involves a region which is thin enough to be effectively lumped on a
zero-thickness interface surface for modelling purposes. Furthermore a finite
process zone can be identified around the propagating crack, where cohesive
stresses on the interface gradually decrease from a peak value to zero. In the
early sixties these observations led to the development of cohesive-zone models
(CZMs), which introduce nonlinear relations between stresses and displacement
discontinuities on interfaces. The link between this approach and fracture
mechanics lies in the energy dissipated per unit of surface, which for CZMs is
made equal to the fracture energy. In this talk the attention will be focused
on some CZMs recently developed by the speaker and some of his co-workers to
couple interface damage with friction or rate-dependence. It will be shown how
both cases can be studied within the same modelling framework based on simple
but physically justified assumptions, whereby the contribution of adhesion
energy, frictional dissipation and viscous dissipation can be separately
accounted for. Comparisons between experimental and numerical results will be
presented to validate the effectiveness of the models. Finally, the outlook for
future research will be discussed.

Insights of a Process Scientist in the Water Industry in Northeast Scotland

• Thursday 21th February, 1pm
• Room 451 Rankine Building
• Beata Tschirch. Scottish Water

Abstract

This presentation will focus on my work as a process scientist in the Northeast Scotland with the emphasis on waterquality problems and challenges in the region. Northeast raw water sources have a distinctive quality, which dictate the treatment solutions applied at treatment works. Treatment challenges such as fluctuating quality of sources, manganese and pesticide removal, algal blooms, disinfection by-products, bacteriological contamination and nitrification in networks will be presented based on examples from Grampian Water Treatment Works andSupply Systems. The purpose of this presentation is to discuss the treatment and distribution challenges in this region and explore possibilities for collaborative research between Glasgow University and Scottish Water.

Previous Seminars

• Tuesday 27th November at 1pm, David Gregoire, Coupling between damage and permeability in porous geomaterials in the context of CO2 storage and petroleum engineering
  
  Abstract
  
  One of the key challenges in geomechanics in the context of CO2 storage and petroleum engineering is the assessment of the tightness of storage facilities or the enhancement of the production capacitiesof non conventional reservoirs. The LFC-R Geomechanics group aims at aproper understanding of the various mass transfer mechanisms of thefluid-solid interactions and of the mechanical response of the solidphase. Our research focuses on fluid flow in submicron- andmicro-porous materials with evolving microstructure followingmultidisciplinary and multi-scale approaches.The first step toward a better understanding of the coupling betweendamage and permeability in such porous geomaterials, is to enhance thesolid phase description of damage and failure. Therefore the firstpart of the talk will be dedicated to the study of fracture and damagein solid quasi-brittle geomaterials. We will present how a new wellcontrolled experimental database presenting for the same material sizeeffect for different geometries may be useful to test the relevance ofmacro/meso-scale models. Mesoscale models are here used to understandthe deficiencies and the path to follow to improve classical nonlocalmacroscale models.The second part will aim to characterize the coupling between theevolving microstructure, the permeability properties and the globalmechanical loading in the context of CO2 storage and non conventionalreservoirs. We will present how static or dynamic loadings mayinteract with the microstructure and change the intrinsic permeabilityof the material.
   
• Thursday, 23 Aug, at 1pm Robert N. Simpson Isogeometric Boundary Element Methods using advanced Computational Geometry Discretisations
  
  Abstract
  
  'Isogeometric' formulations are receiving increasing attention within the fields of solid mechanics, fluid mechanics and computational geometry since the potential to make significant savings in time and cost for practical engineering simulations is great. The idea of using discretisations provided by Computer Aided Geometrical Design (CAGD) was proposed by T.J.R. Hughes et al. where Non-Uniform Rational B-Splines were primarily used, but the idea of using CAGD methods for analysis can be traced back even further. In the context of Boundary Element Methods (BEM), the 'panel' method essentially applies the same isogeometric concept for applications of wave-breaking resistance using a NURBS discretisation throughout. The use of such an approach is compelling, since both CAGD and BEM deal with quantities entirely on the boundary and allows analysis to proceed directly once a geometrical model is defined.
  
  The present talk discusses some recent developments for isogeometric BEM where in particular, the use of T-splines which overcome the significant limitations of NURBS in an analysis context are described. Certain unique aspects over conventional BEM formulations are detailed such as robust collocation algorithms and the requirement for semi-discontinuous bases for corners and edges. Several problems within the context of linear elasticity are illustrated, with the ability of the method to handle extremely complicated 3D geometries demonstrated.
  
  The talk also presents some new, unpublished work that illustrates the ability of isogeometric BEM to model complicated geometries in infinite domain problems. This is found to be a particularly attractive application of the method, where only a discretisation of the body surface is required. Several results are presented for exterior radiation and acoustic scattering problems where excellent agreement with closed-form solutions is obtained.
   
• Thursday, 5 Julay 2012 at 1pm, Domenico Gallipoli, A hysteretic soil-water retention model accounting for cyclic variations of suction and void ratio
  
  Abstract
  
  The seminar will present a water retention model capable of predicting the hysteretic response of soils during both wetting-drying cycles at constant void ratio and compression-swelling cycles at constant suction. In the proposed model two main surfaces, i.e. the main wetting and main drying surfaces, enclose the domain of attainable soil states in the degree of saturation – suction – void ratio space. Inside this domain, the variation of degree of saturation is governed by a reversible scanning law, which describes the transition from one main surface to the other. A simplified calibration procedure is presented to select the values of the four parameters defining the two main surfaces by using a minimum of two compression tests at constant suction and one drying test at constant mean net stress. Model computations are validated against results from laboratory tests on a compacted mixture of bentonite and kaolin. The proposed formulation is capable of capturing important soil features such as, for example, the influence of hydraulic hysteresis and deformation on the variation of degree of saturation and the dependency of water retention behaviour during compression on previous wetting-drying history. Moreover, during main wetting or main drying at high suction (i.e. at low saturation), the model correctly predicts a “virgin” retention line that uniquely relates water ratio and suction regardless of the current value of void ratio.  
   
• Thursday, 17 May , at 1pm Dr. Shangtong Yang, Concrete Crack Width under Combined Reinforcement Corrosion and Applied Load
  
  Abstract
  
  Corrosion of steel reinforcement in concrete is a well-known global problem that has caused widespread premature and unexpected failures of concrete infrastructure and significantly reduced its life expectancy. The corrosion induced concrete cracking is a complicated problem, involving a large number interactive contributing factors, such as the exposure environments, the quality of concrete, the detailing of structural elements and the stresses applied. It destroys the integrity of infrastructure, leading to eventual reduction of its load carrying capacity. The continual demands for greater load for infrastructure only exacerbate the problem. This makes the infrastructure increasingly vulnerable over time during its expected service life and poses a potential risk to the public. The presentation will talk about the development of an analytical method and a numerical method that can be used to predict the concrete crack width under this combined effect of corrosion and applied load.
   
• Thursday, 10 May , at 1pm, Dr. William Coombs, Dual-envelope unique Critical State model for fine-grained particulate
  
  Abstract
  
  One of the more successful and widely used constitutive formulations for fine-grained geomaterials (in particular, clay-like soils) is the isotropic modified Cam-clay (MCC) plasticity model. Central to this model (and subsequent extensions) is the concept of a Critical State (CS), initially proposed by Casagrande in 1936, where the medium undergoes unbounded distortions at constant stress and volume. Isotropic models are unable to account for the preferred orientation of the fabric which can have a pronounced influence on stiffness and strength. Thus a number of extensions to the MCC plasticity model have been proposed to represent this directional bias. However, these earlier anisotropic extensions to the MCC model failed to include both (i) a unique convex CS surface dependent on both the intermediate principal stress and Lode angle and (ii) hysteretic behaviour during unloading and reloading. Those shortcomings are addressed in the proposed hyperplastic formulation. The new model exhibits an asymptotic isochoric state which is uninfluenced by any initial or evolving anisotropy, and is independent of the path followed.This seminar will (i) present the key concepts underlying the model's theoretical development, (ii) detail the algorithmic treatment of the model, (iii) make comparisons with existing constitutive models and (iv) predict the point at which continuum idealisations of the material behaviour are no longer valid.
   
• Thursday, 3 May, at 1pm, Dr. Erakan Oterkus, Peridynamic Modeling of Materials and Structures
  Abstract
  
  In order to determine the deformation response of materials and structures subjected to external loading conditions, continuum mechanics was introduced by disregarding the atomic structure. The original continuum mechanics approach, classical continuum mechanics, has been successfully applied to numerous challenging problems. However, its governing equation, which is in partial differential form in space, faced a difficulty if there is any discontinuity in the structure since partial derivatives are not applicable in such a condition. In order to overcome this problem, various different approaches have been proposed such as Linear Elastic Fracture Mechanics, Extended Finite Element Method, etc. Some of these methods have their own limitations and others require some more research to convince the solid mechanics community. On the other hand, a new continuum mechanics approach, Peridynamics, was recently introduced with the intention that its governing equation is always valid whether there is any discontinuity in the structure or not, as opposed to the classical continuum mechanics, since its equation is an integro-differential equation. Moreover, it is in the class of non-local continuum mechanics so that all material points within the continuum can interact with each other by defining interaction forces. Thus, its mathematical structure becomes very much similar to molecular dynamics at the continuum level. This character of peridynamic theory makes this new approach a suitable candidate for multi-scale analysis of materials. Furthermore, its mathematical structure can also be applicable to other fields such as thermal, electric, etc., so that it may also be used as a single platform for multiphysics analysis of materials. Hence, in this seminar, a brief introduction of peridynamic theory will be given and its applications in various different areas will be presented.
   
• Friday 17th February 2012 1pm, Karin de Bosrst, Wood mechanics – across scales and disciplines
  
  Abstract
  
  Recent developments in the fields of physics, chemistry, and materials scienceallow to study wood at increasingly smaller length scales, and have given amuch deeper understanding of its structure at the nanoscale and the molecularinteractions upon mechanical loading or changes of environmental conditions.Combining multiscale modeling with computational simulations makes thisknowledge useful for timber engineering purposes. For instance, it enables toquantitatively assess the variability of the macroscopic material properties ofwood as typically observed for tests at the centimeter scale and to resolve the(thermo-hygro-mechanical) couplings at this scale.The multiscale modeling approach starts at the length scale of nanometers,where universal constituents with sample-independent properties, namelyhemicelluloses, lignin, and cellulose, are encountered. Their arrangement interms of a fiber-reinforced composite in the wood cell wall and the honeycombpattern of the wood cells is accomplished via a multistep homogenizationscheme. It is shown how this methodology can be applied to investigatestructure-property relations for hardwood in terms of its stiffness, and how totranslate failure and creep mechanisms observed at the microscale tocorresponding macroscopic properties of clear wood. Subsequently, constitutiveequations suitable for structural simulations can be derived. Finally, thesuitability of the proposed modeling strategy is discussed for the examinationof wood modification, degradation, and ageing. Examples of first successfulapplications in these fields underline the scientific potential and thepractical relevance of these topics as future research directions.
• 15th February 2012 1pm, Rene de Borst, A multi-scale approach to fluid flow in fracturing porous media
  
  Abstract
  
  In this contribution, we will develop a general numerical model for flow in progressively fracturing porous media. The theory includes flow inside stationary and propagating cracks. The flow inside the evolving crack can be in the tangential direction. This is achieved by a priori adopting a two-scale approach. At the fine scale the flow in the cavity created by the (possibly cohesive) crack is modelled using a sub-grid scale model. Since the cross-sectional dimension of the cavity is small compared to its length, the flow equations can be averaged over the width of the cavity. The resulting equations provide the momentum and mass couplings to the standard equations for a porous medium, which are assumed to hold on the macroscopic scale.The two-scale model which ensues, imposes some requirements on the interpolation of the displacement and pressure fields near the discontinuity. The displacement field must be discontinuous across the cavity. Furthermore, the micro-mechanics of the flow within the cavity require that the flow normal to the cavity is discontinuous, and in conformity with Darcy's relation which is assumed to hold for the surrounding porous medium, the normal derivative of the fluid pressure field must also be discontinuous from one face of the cavity to the other. For arbitrary discretizations, these requirements can be satisfied by exploiting the partition-of-unity property of finite element shape functions.To provide a proper setting, we will first briefly recapitulate the governing equations for a deforming porous medium under quasi-static loading conditions. The strong as well as the weak formulations will be considered, since the latter formulation is crucial for incorporating the micro-mechanical flow model properly. This micro-mechanical flow model will be treated next, and it will be shown how the momentum and mass couplings of the micro-mechanical flow model to the surrounding porous medium can be accomplished in the weak formulation. Time integration and consistent linearization of the resulting equations, which are non-linear due to the coupling terms and because of the cohesive crack model, complete the numerical model. Example calculations are given of a body with stationary cohesionless cracks and with a propagating cohesive crack. The calculations show that the influence of the presence of discontinuities on flow and deformation patterns can be significant.
• 15th September 2011, 1pm, Nick Loman, University of Birmingham, “Benchtop Sequencers and Bacterial Outbreaks”. Abstract Theme: Water & Environment

• 28th May 2011, 1pm, TBA, University of Glasgow, “Graduate Introductory Seminars”. Theme: Water & Environment

• 19th May 2011, 1pm, Room 816, Rankine Building Laura Rojas Solano, Universite de Pau et des Pays de l'Adour, Anglet, France “Macro and meso scale models to predict concrete failure and size effect”. Abstract Theme: Mechanics and Materials

• 14th May 2011, 1pm, Dr Russell J Davenport, University of Newcastle, “TBA”. Theme: Water & Environment

• 21st April 2011, 1pm, Kazi Hassan, University of Glasgow, “Graduate Introductory Seminars”. Theme: Water & Environment

• 7th April 2011, 1pm, Thi Minh Hue Le, University of Glasgow, “Stochastic modelling of unsaturated flow through embankments”. Abstract Theme: Mechanics and Materials

• 31 March 2011, 1pm, Room 816, Rankine Building: Jin Sun, University of Edinburgh, “Multiscale constitutive modelling of dense granular flow”. Abstract Theme: Mechanics and Materials

• 10 March 2011, 1pm, Room 816, Juan Carlos Rojas Vidovic, University of Glasgow, “Non-contact measurement of strains in soils subjected to wetting-drying cycles”. Abstract Theme: Mechanics and Materials

• 13 January 2011, 1pm, Room 816, Rankine Building, Dr Mike J Dempsey, Manchester Metropoliton University. “Expanded bed biofilm reactor technology for tertiary wastewater treatment” Abstract Theme: Water and Environment

• 6 January 2011, 1pm, Room 816, Rankine Building, Dr Andrew Free, University of Edinburgh. “Structure and Assembly of Microbial Communities in Natural, Semi-Natural and Engineered Environments” Abstract Theme: Water and Environment

• 16 December 2010, 1pm, Room 816, Rankine Building: Prof William T Sloan, University of Glasgow. “Strength, distribution of species, and optimal foraging morphology in fluvial biofilms” Abstract Theme: Water and Environment

• POSTPONED 9 December 2010, 1pm, Juan Carlos Rojas Vidovic, University of Glasgow, “Non-contact measurement of strains in soils subjected to wetting-drying cycles”. Abstract Theme: Mechanics and Materials

• POSTPONED 2 December 2010, 1pm, Room 816, Rankine Building: Jin Sun, University of Edinburgh, “Multiscale constitutive modelling of dense granular flow”. Abstract Theme: Mechanics and Materials

• 23 November 2010, 1pm, Room 816, Rankine Building: Dr John Harris, HR Wallingford, “Marine Scour - Lessons Learnt and Future Challenges”. Abstract Theme: Water and Environment

• 11 November 2010, 1pm, Room 816, Rankine Building: Prof. Qingquan Liu, Chinese Academy of Sciences - Beijing, “Hydraulic Modeling of Runoff and Sediment Yields in Small Watershed” Theme: Water and Environment

• 9 November 2010, 1pm, Room 816, Rankine Building: Francesca D'Onza, University of Glasgow, “Small to large deformations of unsaturated soils: An application to earth structures”. Abstract Theme: Mechanics and Materials

• 19 October 2010, 1pm, Room 816, Rankine Building: Prof. JiaQian Jiang, Glasgow Caledonian University, “Oxidation and Coagulation in Water and Wastewater Treatment”. Abstract Theme: Water and Environment

• 9 September 2010, 1pm, Room 816, Rankine Building: Lukasz Kaczmarczyk, University of Glasgow, “Lagrange Co-rotational formulation for 3d solids”. Abstract Theme: Numerical methods

• 19 May 2010, 1pm, Room 816, Rankine Building: Tomasz Koziara, University of Glasgow, “Shaking a nuclear plant core: solution strategies for large multi-body dynamic contact problems”. Abstract

• 5 May 2010, 1pm, Room 816, Rankine Building: Peter Grassl, University of Glasgow, “Modelling corrosion induced cracking in concrete. Abstract

• 4 March 2010, 1pm, Room 816, Rankine Building: Juan Carlos Rojas Vidovic, University of Glasgow, “Preparation of soil specimens for ESEM analysis”. Abstract

• 8 December 2009, 1 pm, Room 816, Rankine Building: Hikaru Nakamura, Nagoya University, Japan, “Fundamental analysis on evaluation for fire-proof performance of concrete”. Abstract

• 3 December 2009, 1pm, Room 816, Rankine Building: Alexander Menk, University of Glasgow, UK, “Lifetime Prediction for Solder Joints in Electronic Devices using X-FEM”. Abstract

• 12 November 2009, 1pm, Room 816, Rankine Building: Julien Vignollet, University of Glasgow, UK, “A biphasic swelling model for the nucleus pulposus of the intervertebral disc”. Abstract

• 8 September 2009, 9:30, Room 816, Rankine Building: Christian Hellmich, Vienna University , Austria, “Micromechanics of civil and bioengineering materials: current challenges in concrete and bone”. Abstract

• 3 September 2009, 1pm, Room 816, Rankine Building: Sam Frydman, Technion, Israel Institute of Technology, Israel, “Unsaturated soil mechanics: Critical review of physical foundations”. Abstract

• 17 August 2009: Jun Yang, Tsinghua University, Beijing, China, “Calculation Method and Application for the Time-History of Factor of Safety of Slopes Subjected to Seismic Load”. Abstract

• 3 August 2009, 1pm, Room 816, Rankine Building: Jiri Nemecek, Czech Technical University in Prague, “Nanoindentation of Heterogeneous Structural Materials”. Abstract

• 18 June 2009, 11am, Room 514, Rankine Building: Xiangyang Ju, Robert Gordon University, ” Digital image correlation for shape and displacement measurement”. Abstract

• 11 June 2009, 1pm, Room 816, Rankine Building: Daniel Balint, Imperial College, London, “Discrete Dislocation and Crystal Plasticity Analyses of Size Effects in Crystalline Materials”. Abstract

• 3 June 2009, 15:30pm, Room 816, Rankine Building: Sonia Garcia, U.S. Naval Academy in Annapolis, USA, “Engineering – Mathematics: bridging the gap”. Abstract

• 15 May 2009, 11am, Room 408, Rankine Building: Dmitriy Dikin, Northwestern University, Evanston, USA, “Experimental Mechanics at Nano Scale”. Abstract

• 2 April 2009, 1pm, Room 816, Rankine Building: Humberto Varum, University of Aveiro, Portugal, “Safety assessment and retrofit of existing RC buildings non-seismically designed”. Abstract

• 26 March 2009, 3pm. Room 601, Rankine Building: Yong Lu, University of Edinburgh, “Structural response to extreme dynamic loading: characteristics, modelling and some recent studies”. Abstract

• 12 March 2009, 1pm, Room 816, Rankine Building: Sarah Billington, Standford University, USA, “Ductile fiber-reinforced cement-based composites for seismic design and retrofitting”.

• 19 February 2009, 1pm, Room 816, Rankine Building: Markus Schmidt, Leipzig University of Applied Sciences, “Early age cracking and its influence on the durability of concrete structures”.

• 4 December 2008, Guy Houlsby, University of Oxford, “Hyperplasticity: a thermodynamic approach to plasticity theory”.

• 2 December 2008, Rod Jones, University of Dundee.

• 13 November 2008, Marcelo Sanchez, University of Strathclyde, “Analysis of Coupled Problems in Geo-Engineering”.