Plenary Lecturers

Modeling Fiber-Reinforced Biosolids with Application to Artery Walls in Health and Disease

Abstract

Fiber-reinforced biosolids are composed of a matrix material that is reinforced by fibers of one or more families or by fiber distributions of different orientations. In biological fibrous tissues, such fibers are collagen, and the matrix material typically consists of elastic fibers. For example, the matrix for arterial walls can be considered an isotropic (neo-Hookean) material, while the collagen fibers, which are generally not perfectly aligned but are arranged in a more dispersed structure, generate anisotropy (for a review see, e.g., [1]). Collagen and elastic fibers form a unique microstructure that is particularly involved in the biomechanical response during a cardiac cycle and also continuously rearranges itself to adapt to (patho)physiological stimuli. It is important to note that the collagen and elastic fibers can be damaged/disrupted by various diseases.

This lecture will briefly summarize a dispersion model based on the bivariate von Mises distribution and used to construct a structure tensor. The latter is incorporated into a strain-energy function that accommodates both the mechanical and structural features of the material [2]. Based on the structural artery model, a patient-specific computer model of aortic dissection including fluid-structure interaction will be demonstrated, which enables the system behavior to be better understood and analyzed based on specific parameter changes [3]. The results suggest a strong connection between hemodynamics and aortic growth. The evaluated individual patient case serves as a crucial springboard to translate biomechanical computational models into clinical practice at a large scale. For a current, comprehensive review of aortic dissections see [4].

References
[1] G.A. Holzapfel, R.W. Ogden. Biomechanical relevance of the microstructure in artery walls with a focus on passive and active components. Am. J. Physiol. Heart Circ. Physiol., 315:H540-H549, 2018.
[2] G.A. Holzapfel, J.A. Niestrawska, R.W. Ogden, A.J. Reinisch, A.J. Schriefl. Modelling non-symmetric collagen fibre dispersion in arterial walls. J. R. Soc. Interface, 12:20150188, 2015.
[3] K. Bäumler, M. Rolf-Pissarczyk, R. Schussnig, T.-P. Fries, G. Mistelbauer, M.R. Pfaller, A.L. Marsden, D. Fleischmann, G.A. Holzapfel. Assessment of aortic dissection remodeling with patient-specific fluid-structure interaction models. IEEE Trans. Biomed. Eng., submitted.
[4] M. Rolf-Pissarczyk, R. Schussnig, T.-P. Fries, D. Fleischmann, J.A. Elefteriades, J.D. Humphrey, G.A. Holzapfel. Mechanisms of aortic dissection: from pathological changes to experimental and in silico models. Prog. Mater. Sci., in press.

MINI-CV

Gerhard A. Holzapfel is Professor of Biomechanics and Head of the Institute of Biomechanics at Graz University of Technology (TUG), Austria, since 2007. He is also Adjunct Professor at the Norwegian University of Science and Technology (NTNU), Trondheim, Norway, and Visiting Professor at the University of Glasgow, Scotland. Until 2013 he was Professor of Biomechanics at the Royal Institute of Technology (KTH) in Stockholm, Sweden, for 9 years (7 years as an Adjunct Professor). After his PhD in Mechanical Engineering in Graz he received an Erwin-Schrödinger Scholarship for foreign countries to be a Visiting Scholar at Stanford University (1993-95). He achieved his Habilitation at TU Vienna in 1996 and received a START-Award in 1997, which is the most prestigious research award in Austria for young scientists. In the following years (1998-2004) he was the Head of a research group on “Computational Biomechanics” at TUG. Among several awards and honors in the past years he is listed in “The World’s Most Influential Scientific Minds: 2014” (Thomas Reuters), he received the Erwin Schrödinger Prize 2011 from the Austrian Academy of Sciences for his lifetime achievements, and he was awarded the 2021 William Prager Medal and the 2021 Warner T. Koiter Medal.

Gerhard A. Holzapfel has authored a graduate textbook entitled “Nonlinear Solid Mechanics. A Continuum Approach for Engineering” (John Wiley & Sons), and co-edited seven books. He contributed chapters to 25+ other books, and published around 300 peer-reviewed journal articles. He is the co-founder and co-editor of the International Journal “Biomechanics and Modeling in Mechanobiology” (Springer-Verlag, Berlin, Heidelberg).

Variable amplitude fatigue life methodology for an airframe digital twin

Abstract

To incorporate aspects such as integrated design, manufacturability, inspectability, repairability or re-use, and to further decrease the structural weight of the aircraft while maintaining structural integrity and the highest level of safety, we see the need for a clean-sheet holistic structural design and integrity approach. Digital twin technology is the enabling technology for this approach that covers the whole life cycle of a structure, from multi-disciplinary design optimization to the end of the service life.

The certification process should be adjusted to allow for a gradual shift towards virtual full scale fatigue testing (FSFT), where the loads for virtual FSFT are not to be limited to a simplified spectrum concentrated at the actuator locations of the physical test, but should be distributed loads from simulated flights over a period of the entire design life, resulting in a more realistic fatigue spectrum. Accurate gust statistics with sufficiently small discretization combined with validated loads models including aeroelastic effects should be used to simulate flights over a period of the entire design life. When environmental conditions such as temperature and humidity are also incorporated in the simulated flights of the virtual FSFT, the virtual FSFT becomes a virtual service life test that will give the probability of failure of a given design for all different failure modes, e.g. static, fatigue, corrosion, creep, wear, etc. (see Figure 1).

Figure 1: Artist impression of a digital twin, i.e. a digital model of a specific aircraft that is enhanced with operational usage data and degradation models in such a way that this creates a digital copy of the physical state of that specific aircraft. The smaller cartoons to the bottom right represent environmental data that together with the operational usage data is taken as input for the model to determine the stresses at all structural elements.

Our presentation will explore how a new energy based fatigue crack growth rate equation can be used for variable amplitude fatigue life calculations during a virtual service life test. The energy based methodology does not require rainflow counting and gives a linear relationship between the strain energy density of a variable amplitude spectrum and the fatigue life (see Figure 2). The linear relationship allows for a fast and accurate screening of the fatigue resistance of an aerospace structure by determining the cumulative strain energy in each finite element of a finite element model at the end of a virtual service life test. During service the digital thread, which includes continuous load monitoring, contains the primary parameters that affect fatigue crack growth and the data is continuously compared with the virtual service life test data to determine if maintenance or inspections schemes have to be modified. Inspection results and Bayesian updating is used to adjust relevant probabilistic parameters of the structural risk assessment, which is the main the output of the structural digital twin.

Figure 2: Variable amplitude fatigue crack growth rate at Kref/E=4∙10^-4 √m as a function of the fatigue severity index (FSI), which is related to average strain energy density of a variable amplitude (VA) spectrum. Three specimens per spectrum are tested and a lower wing (LW) spectrum was used and different wing root bending moment (WRBM) spectra.

MINI-CV

Marcel Bos is heading the Platform Integrity & Life Cycle Support department of the Royal Netherlands Aerospace Centre NLR. He and his colleagues are responsible for monitoring the usage of the fleets of fixed wing and rotary wing aircraft of various aircraft operators, including the Royal Netherlands Air Force. This involves the collection and processing of large sets of aircraft and maintenance data, the development of degradation models and digital twins and the application of various data analysis approaches, including machine learning, in support of the fleet life management process.

From 2005 to 2017 Mr Bos was the Netherlands’ delegate to the International Committee on Aeronautical Fatigue and Structural Integrity (ICAF). In 2017 he was elected ICAF General Secretary.

Prediction of properties in fiber-reinforced composites using multiscale homogenization method

Abstract

The multiscale homogenization method is a powerful tool for predicting the properties of fiber-reinforced composites. This method allows for the accurate estimation of material behavior by considering different scales, from the microscale fiber-matrix interactions to the macroscale composite structure. Taking advantages of this technique, engineers can design composites with optimized strength, stiffness, and durability, tailored to specific applications. The predictive capability of the multiscale homogenization method not only enhances the understanding of composite materials but also streamlines the development process by reducing the need for extensive experimental testing.

MINI-CV

Reinaldo Rodríguez Ramos was born August 22, 1958 at Camaguey, Cuba. He is Full Professor of Mathematics at Faculty of Mathematics and Computer Sciences of University of Havana, Cuba. Dr. Rodriguez has served the University of Havana in several roles since 1987. Currently, more than 15 projects in composites-related fields are ongoing. He has advised 8 PhD students and more than 25 master’s students as well as more than 30 undergraduate students. Dr. Rodriguez has authored/co-authored more than 130 publications in composites science and technology including more than 40 proceeding papers.

His publication topics include: 3D Simulation, Active Force, Analytical Results,Anesthetic Procedures, Blinding Procedures, Cesarean, Current State Of Development, Degrees Of Freedom, Epidural Space, First Contact, Force Feedback, Force Model, Game Elements,Incompressible, Internal Pressure, Ligamentum Flavum, Loss Of Resistance, Mechanical Calculations, Mechanistic Model, Needle Insertion, Prototype Version, Serious Games, Skin Tissue, Stiffness Force, Subcutaneous Adipose Tissue.

Spinodal decomposition in mechanical metamaterials and systems with coupled chemomechanical interactions

Abstract

Many chemical and mechanical systems in nature exhibit micro- or nanostructural pattern formation with common topologies. A remarkable characteristic is their occurrence in systems, originally constituted of homogeneous mixtures that undergo spinodal decomposition, separating into two phases with wellestablished interfaces. In this talk, we examine some shared features, such as the non-convexity of free energy, inducing spinodal decomposition in various systems. Two specific examples are discussed.

The first is a mechanical metamaterial with microscale instabilities exhibiting capacity for repeatable extrinsic energy dissipation. Here, we highlight the development of a generalized standard model based on a quasi-convexified free energy framework that captures the homogenized behavior during the spinodal decomposition phase. The second system briefly introduced, block copolymers, involves chemomechanical coupling. We emphasize the current mathematical approaches used to analyze it.

Lastly, we explore another case of chemo-mechanical coupling: the embrittlement of steels due to hydrogen diffusion. The focus is on analyzing the configurational forces associated with crack propagation in the solvent. Special attention is given to how chemical potential non-homogeneity influences the evaluation of the J-integral and its impact on experimentally determining the fracture toughness of materials affected by hydrogen environments.

MINI-CV

Alfredo E. Huespe is a researcher of Conicet at CIMEC (Centro de Investigaciones en Mecánica Computacional), Conicet, National University of Litoral (UNL), Santa Fe, Argentina. He has served as a Professor of Mechanics at the Faculty of Chemical Engineering and as Director of the Materials Engineering career at the National University of Littoral, Argentina. He also served as a part-time professor in the Department of Strength of Materials and Structures in Engineering at the Escola Técnica Superior d’Enginyers de Camins, Canals i Ports (Civil Engineering School) of the Technical University of Catalonia, Barcelona, Spain. Additionally, he was a recipient of a Fulbright scholarship and a visiting scholar at Brown University, USA. He is currently a Visiting Professor in the Mechanical Engineering Program of COPPE at the Federal University of Rio de Janeiro, Brazil.

His research interests focus on Computational Fracture Mechanics, with over 20 years of experience, and the Computational Design of Mechanical and Acoustic Metamaterials. His recent work explores the analysis of Metamaterials with Bistable Mechanisms at the Microscale and problems involving significant chemo-mechanical interactions.

Optimal Redundancy of Structural Systems under Low Probability High Consequence Events 

Abstract

Typical structural systems have a high degree of static indeterminacy, but a low degree of redundancy. Abnormal loads resulting from low probability high consequence threats, like fires, landslides, accidental impact and explosions can produce localized damage. With lack of or with insufficient redundancy, localized initial damage may propagate, leading to the progressive collapse of the whole or of a disproportional part of the structure. On the other hand, strengthening the structure to produce alternate load paths (redundancy) has a significant impact in construction costs, with unknown cost-benefit relation. In this talk we address the problem from a risk-optimization perspective, which takes into account the possible system failure states of regular frame structures, as well as the corresponding costs of failure. A cost-benefit analysis is performed, comparing the strengthening cost with the reduction in expected failure costs, given local damage produced by abnormal loads. As a result, we obtain a break-even local damage or hazard probability, for which these costs are the same. For threats and hazards leading to local damage probabilities higher than the break-even value, structural strengthening is cost-effective. We show how the break-even probability changes with relevant problem parameters like strengthening cost, costs of failure, aspect ratio of the buildings, and extend of the strengthening measure. We show how the different failure propagation mechanisms compete for the limited strengthening budget, and we propose optimal design factors for beams and columns of regular frame buildings.

MINI-CV

Pesquisador nível 1 do CNPq desde 2013; nível 1B desde março de 2021. Membro do Comitê de Assessoramento de Engenharia Civil (CA-EC) do CNPq, 2021 a 2024. Possui graduação em Engenharia Mecânica pela Universidade Federal do Rio Grande do Sul (1996), Mestrado em Engenharia Mecânica pela Universidade Federal de Santa Catarina (1998), Doutorado em Engenharia Civil pela University of Newcastle, Australia (2003) e Livre-Docência pela Universidade de São Paulo (2013). Atualmente é Professor Associado do Departamento de Engenharia de Estruturas, Escola de Engenharia de São Carlos, Universidade de São Paulo, onde já formou 32* alunos na graduação e 33* mestres (*carga didática equivalente). Como orientador, concluiu a supervisão de nove pós-doutorandos, formou onze Doutores e dezenove Mestres (sendo duas co-orientações). É membro da Associação Brasileira de Engenharia e Ciências Mecânicas (ABCM), da Associação Brasileira de Métodos Computacionais em Engenharia (ABMEC) e membro do Comitê de Quantificação de Incertezas e Modelagem Estocástica da ABCM. É membro da Associação Brasileira de Análise de Risco, Segurança de Processo e Confiabilidade (ABRISCO). É consultor da FAPESP, CAPES e CNPq. Tem experiência nas areas de Engenharia Civil e Mecânica, com ênfase em Mecânica das Estruturas e Segurança das Estruturas. Atua principalmente nos seguintes temas: segurança das estruturas, confiabilidade estrutural, processos estocásticos, mecânica estocástica e otimização estrutural. É membro do Conselho Editorial dos periódicos Journal of the Brazilian Society of Mechanical Sciences and Engineering, ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Reliability Engineering & System Safety e Structural Safety.