Keynotes Lectures

Generalized Finite Element Method: new trends and applications

Abstract

Recent trends towards improvement of the Generalized Finite Element Method (GFEM) robustness and its application on nonlinear analysis are addressed. Regarding the first aspect, the so called stable versions of the method are considered demonstrating its ability to put under control issues as numerical stability and accuracy. The use of flat-top partition of unities for constructing the augmented approximation space of the method is focused. Moreover, the issue of the error estimations for the GFEM is considered as well, then emphasizing a simple a-posteriori error estimator based on stress recovering. The stress recovering procedure is essentially an improvement of the classical ZZ approach for the Finite Element Method and is hereby denoted as ZZ-Block Diagonal.  Comparative analyses are presented aiming to assess features as recovered stresses accuracy, computational effort and error estimates. Furthermore, an innovative adaptive procedure for the GFEM guided by the error estimator employed as an indicator for both mesh refinement and selective enrichment is presented. Concerning applications, in line with the above mentioned developments, the use of the method for static and dynamic nonlinear structural analysis is addressed. Two dimensional problems including large deformations and contact effects are selected. Among the main findings, beyond the quality of the numerical results one can mention that the GFEM flat-top version preserves good conditioning of the system of equations even in presence of polynomial enrichment. Such an aspect is indeed a corner stone to guarantee numerical stability and accuracy.

Prof. Sergio P. B. Proença
São Carlos School of Engineering of the University of São Paulo (Brazil)

Graduation in Civil Engineering at Federal University of Paraná (1978), PhD in Structural Engineering at University of São Paulo (1988). Post-Doctoral period at the Politecnico di Milano, Italy. Visiting Scholar at the Department of Civil and Environmental Engineering of University of Illinois at Urbana-Champaign, USA. Full Professor of the Structural Engineering Department of the São Carlos School of Engineering. Research cooperations with Politecnico di Milano, Italy, Laboratoire de Mechanique et Technologie LMT-Cachan, France, Instituto Superior Tecnico of Lisbon and University of Illinois at Urbana-Champaign. Research activities on: Damage, Fracture Mechanics, nonlinear structural analysis, Generalized Finite Element Method.

Multiscale Modeling of Damage in Composite Materials:
From Molecular Dynamics Simulation to a Percolation Concept

Abstract

Damage in composite laminates often begins with the formation of a transverse crack, i.e., a crack that forms under application of a tensile force normal to fibers. This is followed by  multiplication of these cracks in an array of parallel cracks within plies, subsequently leading to delamination and fiber breakage. Experimental observations suggest that as precursor to transverse cracks, fiber/matrix debonding occurs first, followed by the interface cracks kinking out into the matrix and thereby linking up with other debonds. When sufficiently many debond cracks have coalesced, a continuous transverse crack is believed to form. This presentation will describe analyses at different scales, beginning with the molecular level of the epoxy matrix and continuing to the representative microstructural level where the transverse crack begins growing with its own driving force (energy release rate). By means of a molecular dynamics simulation, it will be shown that brittle cavitation under hydrostatic tension in epoxies is most likely the precursor to fiber/matrix debonding. The next level analysis considers the debond crack growth and kink-out as influenced by the neighboring debond cracks. Furthermore, statistically simulated representative volume elements (RVEs) are analyzed to reveal the effect of manufacturing induced nonuniformilty of fiber distribution on the debond initiation and subsequent transverse crack formation. A percolation concept is then used for predicting the conditions for multiple ply cracking.

Prof. Ramesh Talreja
Department of Aerospace Engineering, Texas A&M University (USA)       

Graduation in Civil Engineering at University of Bombay, India (1967). Master Science in Civil Engineering at Northeastern University, USA (1970). Ph.D in Solid Mechanics at The Technical University of Denmark (1974). Doctor of Technical Sciences (dr. techn.) at The Technical University of Denmark (1985). The Executive Council of the International Committee on Composite Materials (ICCM), an international, non-governmental, scientific and engineering organization, selected Prof. Talreja in 2013 to receive the highest recognition, the Scala Award, which carries with it the designation of World Fellow and Life Member of ICCM. He received the Outstanding Research Award in Composites in 2017 from American Society for Composites. He presented 145 invited/keynote/plenary lectures at conferences and 97 invited seminars at universities, research institutions and industry R&D labs. He served on over 50 Advisory Committees for international conferences. He is Consultant and Advisory Board Member for over 15 industry organizations. He is Reviewer for over 15 research funding organizations and for over 25 international journals. He was Professor of Aerospace Engineering at Georgia Institute of Technology (1991-2001). He was Department Head at Aerospace Engineering, Texas A&M University, and Division Chief at Aerospace Engineering, Texas Engineering Experiment Station (Sept. 2001- August 2003). He is Tenneco Professor of Engineering at Department of Aerospace Engineering, Texas A&M University since Sept. 2001. He was Distinguished Visiting Professor at US Air Force Academy (1999-2000). He was Editor-in-Chief of International Journal of Aerospace Engineering (2006-2009). He was Associate Editor of Mechanics of Materials journal (1999-2007). He is Editorial Board Member in 16 Journals.

A decohesive interface element for static and fatigue induce damage predictions in adhesively bonded joints under variable loads and debonding mode ratios

Abstract

Many methods exist for bringing together structural parts, in terms of the joining technique utilized. Conventional mechanical joints, such as bolted, pinned or riveted are preferred due to their simplicity and the disassembly ability that they offer for joining metal or composite materials. However, when a mechanical joint is loaded, local damage is induced at the fastener holes due to stress concentrations. This fact leads to the structural degradation of a joint and jeopardizes the structural integrity of the assembly structure. The demands for designing lightweight structures without any loss of stiffness and strength have turned many researchers and design engineers within the aerospace industry to seek for alternate joining methods. Thus, the field of structural adhesive bonding has matured with the development of a wide range of adhesives from the chemical industry. Adhesive bonding is a material joining process in which an adhesive, placed between the adherend surfaces, solidifies to produce an adhesive bond. This type of joining technology offers several advantages over conventional joining technologies such as reduction of production parts, higher strength/weight ratio, improved aerodynamic smoothness appearance and superior fatigue resistance. Within this context, a continuum damage mechanics based failure model that enables prediction of mixed-mode debonding growth in co-cured and co-bonded joints subjected to static and fatigue loadings will be presented in this talk. The proposed formulation has been developed for robust nonlinear finite element formulations based on explicit direct time integration schemes, particularly the central difference method. The failure model has been implemented as a user-defined material model into ABAQUS/Explicit finite element code.   Some case studies showing the model capabilities in terms of fatigue and static damage predictions at both coupon and sub-component levels will be also presented and discussed in this presentation.

Prof. Maurício Vicente Donadon
Instituto Tecnológico de Aeronáutica-ITA, Department of Aeronautics (Brazil)

Maurício Vicente Donadon is Professor of Aerospace Structures in the Department of Aeronautics at Technological Institute of Aeronautics in Brazil, where he has been since 2009. He received a B.S. in Mechanical Engineering from the Santa Catarina State University and M.S. in Mechatronics and Dynamic of Aerospace Systems from the Technological Institute of Aeronautics in Brazil. He received his Ph.D in Aeronautics from the Imperial College London-UK. His main research focuses on experimental, analytical and numerical aspects of failure in fiber-reinforced composites. Other interests include buckling, post-buckling and collapse of reinforced metallic and composite panels, smart materials, aeroelasticity, composite manufacturing processes, fracture mechanics, fatigue, structural dynamics, impact dynamics, nonlinear finite elements and design of wind turbine blades. He currently supervises with other academics several PhD and M.S. students at Technological Institute of Aeronautics in Brazil.

Buckling in analysis and design of structures in off-shore environment

Buckling of structural components is a fundamental verification in any engineering practice. However, some problems related to the buckling of slender elements as composite beams and flexible pipelines present still open aspects.

The buckling problem of pistons modelled as beams with not-uniform cross-section, needs a stronger effort than the classical Euler approach. Pistons strength strongly depends on buckling load and such information is a major requirement in the design process. Several analytical and experimental investigations of typical hydraulic cylinders have been carried out through the years but most of the available standards still use a linear approach with many simplifications. Limitations of current DNV standards for piston design in offshore technologies are discussed and comparisons with FEA and reference solutions are presented.

Flexible pipelines must be designed considering the extreme situation for which additional components are needed against severe loading and environmental conditions. Such structures are composed of several parts such as tensile armor which is needed in case of high tensile force, which increases with weight. The other common component termed pressure armor is used in deep waters and heavy components with high internal and external pressures. The stability of the pipe under pure tension is investigated by both theoretical and complex numerical 3D finite element nonlinear analysis. Longitudinal deformation depends on the contact pressure among layers and the theoretical model overcome this complexity giving comparable results with a fraction of the computational cost. In addition, homogenization methods can be introduced in order to investigate flexible pipelines with simple numerical tools that have more flexibility than simple theoretical formulations.

Prof. Nicholas Fantuzzi University of Bologna (Italy)

Dr. Nicholas Fantuzzi is a Senior Assistant Professor at the University of Bologna. He was graduated with grade 110/110 “cum laude” in Civil Engineering in 2009 and obtained his PhD degree in Structural Engineering and Hydraulics at University of Bologna in 2013. His research interests are: mechanics of solids and structures, fracture mechanics, implementation of numerical methods for the design of structures, application of composite materials in offshore engineering, and design and strengthening of offshore components with numerical simulations. He is currently working on the application of finite element and mesh-free methods in solids mechanics problems.

Natural and Synthetic Polymers – Constitutive Modelling and Applications in Biomechanics

Abstract

Connective tissues are hierarchically organized materials, in which arrangements of natural polymers, i.e. collagen macromolecules, are responsible for their load bearing capabilities. Thermoplastics, on the other hand, are technological synthetic materials formed by long carbon chains whose basic constituents, bond arrangements and spatial organization provide desired physical and macroscopic mechanical properties. When observed from a mathematical-mechanical representation point of view, both materials share similar basic concepts for their modelling: finite kinematics, inelastic deformation, rate and temperature dependency, anisotropy, damaging among other features.

Both materials are present in biomechanical applications. On one side: ligaments, tendons, skin, artery walls, cartilage; on the other side they appear in an increasingly growing field of polymeric implants: plates, screws, scaffolds, stents, low friction bearings, among others.

An overview and context addressing the modelling of thermoplastics for biomechanical applications will be discussed. Specific contributions on the field of bioabsorbable thermoplastics will be detailed. Concerning connective tissues, a particular attention is driven to their strongly organized microstructure, adequate for bridging among length scales. A sequence of studies on a typically well organized collagen structure will be presented, using to this end well established concepts of homogenization and multiscaling. Motivations to these studies focuses strain localizations, energy dissipation and corresponding clinical consequences on mechanotransduction mechanisms.

Prof. Eduardo Alberto Fancello
Universidade Federal de Santa Catarina

Eduardo Alberto Fancello has graduated as Mechanical-Electrical Engineering at the Universidad Nacional de Córdoba – Argentina (1987) and received his M.Sc. and D.Sc. degrees from COPPE – Universidade Federal de Rio de Janeiro – Brasil (1989 and 1993). He joined the Department of Mechanical Engineering of the Universidade Federal de Santa Catarina in 1994, and now occupyies the position of full professor. Visiting Scholar at the Mechanical and Aerospace Department of the University de Liege, Belgium (2005). He focuses his research and development activities on  a) constitutive modelling with emphasis on polymeric materials and biological tissues, b) numerical simulations of biomechanical systems and c) structural topology optimization.

Constitutive relations of materials with hereditary effects: Theory of viscoelasticity and viscoplasticity

Abstract

The durability of materials depends largely on material systems; usually long-term experimental tests should be performed for each material. Metals under high temperature levels experience the tendency to creep, i.e. they deform continuously under constant stress loading well below the yield stress. The same goes for the polymers at much lower temperatures, even under temperatures of 10 ºC or less. This is induced by internal changes endured by the materials that lead to time dependent properties. Not only the material stiffness decreases but also its strength, leading it to creep or combined creep-fatigue ruptures.

Even now, no unified theory of creep arisen to address properly the time-dependent properties of materials. These issues, in metals, have been put in evidence by turbine engines applied in nuclear power engineering and aircrafts, among others. Moreover, the structural applications of polymer matrix based composites in aeronautical, naval and civil constructions, becoming widespread, put a high pressure on durability assessment of these materials. Although these composite solutions, on short-term, may deliver a better mechanical performance; on a long-term basis it may be different.

The main goal is to provide an overview of time-dependent properties of metals and polymers. Constitutive laws employed to describe creep phenomena are revisited. Special attention is given to the viscoelastic and viscoplastic theories and their suitability to capture typical time-dependent behaviour, i.e. stress relaxation, creep and strain-rate dependency. Finally some remarks about creep failure, or time-dependent failure, are discussed and analysed.

Prof. Rui Miranda Guedes
Universidade do Porto

Rui Miranda Guedes received his MSc in Structural Engineering (1992) and PhD in Mechanical Engineering from the University of Porto (1997). In 1997 he joined the Mechanical Engineering Department of the University of Porto. He received his Habilitation in Mechanical Engineering from the University of Porto in 2012.

His research work has been developed on polymer based composite materials. His main interest is in durability and long-time prediction of mechanical behavior of composite structures. This includes modeling time-dependent behavior (viscoelastic/viscoplastic), hygrothermal effects and physical aging. More recently has been working in biodegradable medical devices for ligament repair. He acted as principal investigator in two research programs, funded by the Portuguese Science Foundation (FCT), to develop biodegradable solutions for augmentation devices used for repairing ligaments (ACL).

More recently, his research interests were directed to the crashworthiness enhancement of bus aluminium structures, under rollover compliance and frontal impact testing and modelling.