Keynotes Lectures

7th International Symposium on Solid Mechanics

Prof. Sergio P. B. Proença

University of Sao Paulo, Brazil

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.

Prof. Ramesh Talreja

Department of Aerospace Engineering, Texas A&M University (USA)  

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.

Prof. Maurício Vicente Donadon

Instituto Tecnológico de Aeronáutica-ITA, Department of Aeronautics (Brazil)

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.

Prof. Nicholas Fantuzzi

University of Bologna (Italy)

Buckling in analysis and design of uniform and stepped beams

Abstract

Buckling of beams is a classical verification in any engineering practice. However, some problems related to the buckling of slender uniform and stepped beams are still open. This talk focuses on the buckling problem of beams with uniform cross-sections and of pistons, modelled as beams with not-uniform cross-section which need a stronger effort than the classical Euler approach. Buckling of slender uniform beams is standardized by EC3 (Eurocode 3 in the European Union) and BS5950 (British Standards in the UK). In most cases, EC is more sophisticated than BS because it is an improvement of the latter. EC3 should be 8% more cost saving than BS5950 but many concerns have been placed on the EC for the buckling problem due to its inherent complexity, whereas BS is simple and direct. Thus, the aim of this research is to compare both codes with the Finite Element Analysis (FEA) and check if the complexity of Eurocodes is justified or not. Pistons are fundamental structural elements in any engineering practices. Their 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.

 

Prof. Nicholas Fantuzzi
University of Bologna (Italy)

Dr Nicholas Fantuzzi is an 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 method, differential quadrature method and mesh-free method for engineering problems.