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In precedent years mostly, though rarely nowadays, shear deformable structures were constructed across the globe. Also, the soil is deformed as a shear cantilever, which means that the shear forces and stresses are more prominent than the respective normal forces and stresses; thus, the dynamic soil–structure interaction of shear deformable bodies is an important aspect to be researched. In this article, the dynamic soil–structure interaction of shear deformable structures is investigated through nonlinear finite element modelling. The goal of this work is to enlighten the qualitative response of both soil and structures, as well as the differences between the sole structure and the soil–structure system. The Athens 1999 earthquake accelerogram is used, which is considered as a palm load (which means a load that is not periodic like the Ricker wavelets), in order to enlighten the importance of the investigation of palm loading. It is demonstrated that the total displacements of the soil–structure system are larger than the case of the sole structure, as expected when taking into account the dynamic soil–structure interaction. However, the residual displacements of the top are larger when a moderate soil thickness is assumed. Moreover, the output acceleration functions over time, comparing the same buildings as the sole building and as the soil-building system, have the same time function, but they are amplified with a constant value. As a consequence, the critical time of the maximum energy flux that is transmitted to the building is not dependent on the dynamic soil–structure interaction. [ABSTRACT FROM AUTHOR]

In precedent years mostly, though rarely nowadays, shear deformable structures were constructed across the globe. Also, the soil is deformed as a shear cantilever, which means that the shear forces and stresses are more prominent than the respective normal forces and stresses; thus, the dynamic soil–structure interaction of shear deformable bodies is an important aspect to be researched. In this article, the dynamic soil–structure interaction of shear deformable structures is investigated through nonlinear finite element modelling. The goal of this work is to enlighten the qualitative response of both soil and structures, as well as the differences between the sole structure and the soil–structure system. The Athens 1999 earthquake accelerogram is used, which is considered as a palm load (which means a load that is not periodic like the Ricker wavelets), in order to enlighten the importance of the investigation of palm loading. It is demonstrated that the total displacements of the soil–structure system are larger than the case of the sole structure, as expected when taking into account the dynamic soil–structure interaction. However, the residual displacements of the top are larger when a moderate soil thickness is assumed. Moreover, the output acceleration functions over time, comparing the same buildings as the sole building and as the soil-building system, have the same time function, but they are amplified with a constant value. As a consequence, the critical time of the maximum energy flux that is transmitted to the building is not dependent on the dynamic soil–structure interaction.

Subcutaneous tissue mechanics are important for drug delivery. Yet, even though this material is poroelastic, its mechanical characterization has focused on its hyperelastic response. Moreover, advancement in subcutaneous drug delivery requires effective tissue mimics such as hydrogels for which similar gaps of poroelastic data exist. Porcine subcutaneous samples and gelatin hydrogels were tested under confined compression at physiological conditions and strain rates of 0.01%/s in 5% strain steps with 2600 s of stress relaxation between loading steps. Force-time data were used in an inverse finite element approach to obtain material parameters. Tissues and gels were modeled as porous neo-Hookean materials with properties specified via shear modulus, effective solid volume fraction, initial hydraulic permeability, permeability exponent, and normalized viscous relaxation moduli. The constitutive model was implemented into an isogeometric analysis (IGA) framework to study subcutaneous injection. Subcutaneous tissue exhibited an initial spike in stress due to compression of the solid and fluid pressure buildup, with rapid relaxation explained by fluid drainage, and longer time-scale relaxation explained by viscous dissipation. The inferred parameters aligned with the ranges reported in the literature. Hydraulic permeability, the most important parameter for drug delivery, was in the range k 0 ∈ [ 0.142 , 0.203 ] mm 4 /(N s). With these parameters, IGA simulations showed peak stresses due to a 1-mL injection to reach 48.8 kPa at the site of injection, decaying after drug volume disperses into the tissue. The poro-hyper-viscoelastic neo-Hookean model captures the confined compression response of subcutaneous tissue and gelatin hydrogels. IGA implementation enables predictive simulations of drug delivery. [ABSTRACT FROM AUTHOR]

This work presents models and simulations of a numerical strategy for a time and cost-efficient virtual product development of a novel passive safety restraint concept for motorcycles. It combines multiple individual development tasks in an aggregated procedure. The strategy consists of three successive virtual development stages with a continuously increasing level of detail and expected fidelity in multibody and finite element simulation environments. The results show what is possible with an entirely virtual concept study—based on the clever combination of multibody dynamics and nonlinear finite elements—that investigates the structural behavior and impact dynamics of the powered two-wheeler with the safety systems and the rider's response. The simulations show a guided and controlled trajectory and deceleration of the motorcycle rider, resulting in fewer critical biomechanical loads on the rider compared to an impact with a conventional motorcycle. The numerical research strategy outlines a novel procedure in virtual motorcycle accident research with different levels of computational effort and model complexity aimed at a step-by-step validation of individual components in the future. [ABSTRACT FROM AUTHOR]

This paper introduces a Finite Element framework for large deformation adhesive contact between elastic bodies based on volume‐to‐volume interaction. A key component of this framework is a novel, customized arc‐length algorithm designed to follow the solution path through multiple snap‐through and snap‐back instabilities. Another new component is a k‐d tree based algorithm which significantly accelerates the computationally expensive volume‐to‐volume interaction calculations. This optimized Finite Element framework is then used to solve two‐body and three‐body elastic adhesive contact problems with realistic material and interaction parameters, using a 6‐12 Lennard‐Jones interaction potential. The improved efficiency of the k‐d tree based scheme makes it indispensable for interaction calculations. This paper also shows the importance of implementing adhesion‐specific customizations in the arc‐length solver. [ABSTRACT FROM AUTHOR]

Fibrin is a naturally occurring protein network that forms a temporary structure to enable remodeling during wound healing. It is also a common tissue engineering scaffold because the structural properties can be controlled. However, to fully characterize the wound healing process and improve the design of regenerative scaffolds, understanding fibrin mechanics at multiple scales is necessary. Here, we present a strategy to quantify both the macroscale (1–10 mm) stress-strain response and the deformation of the mesoscale (10–1000 µm) network structure during unidirectional tensile tests. The experimental data were then used to inform a computational model to accurately capture the mechanical response of fibrin gels. Simultaneous mechanical testing and confocal microscopy imaging of fluorophore-conjugated fibrin gels revealed up to an 88% decrease in volume coupled with increase in volume fraction in deformed gels, and non-affine fiber alignment in the direction of deformation. Combination of the computational model with finite element analysis enabled us to predict the strain fields that were observed experimentally within heterogenous fibrin gels with spatial variations in material properties. These strategies can be expanded to characterize and predict the macroscale mechanics and mesoscale network organization of other heterogeneous biological tissues and matrices. Fibrin is a naturally-occurring scaffold that supports cellular growth and assembly of de novo tissue and has tunable material properties. Characterization of meso- and macro-scale mechanics of fibrin gel networks can advance understanding of the wound healing process and impact future tissue engineering approaches. Using structural and mechanical characteristics of fibrin gels, a theoretical and computational model that can predict multiscale fibrin network mechanics was developed. These data and model can be used to design gels with tunable properties. [Display omitted] [ABSTRACT FROM AUTHOR]

We present an adaptive space-time phase field formulation for dynamic fracture of brittle shells. Their deformation is characterized by the Kirchhoff–Love thin shell theory using a curvilinear surface description. All kinematical objects are defined on the shell’s mid-plane. The evolution equation for the phase field is determined by the minimization of an energy functional based on Griffith’s theory of brittle fracture. Membrane and bending contributions to the fracture process are modeled separately and a thickness integration is established for the latter. The coupled system consists of two nonlinear fourth-order PDEs and all quantities are defined on an evolving two-dimensional manifold. Since the weak form requires C1-continuity, isogeometric shape functions are used. The mesh is adaptively refined based on the phase field using Locally Refinable (LR) NURBS. Time is discretized based on a generalized-α method using adaptive time-stepping, and the discretized coupled system is solved with a monolithic Newton–Raphson scheme. The interaction between surface deformation and crack evolution is demonstrated by several numerical examples showing dynamic crack propagation and branching.

The analysis of tissue mechanics in biomedical applications demands nonlinear constitutive models able to capture the energy dissipation mechanisms, such as damage, that occur during tissue deformation. Furthermore, implementation of sophisticated material models in finite element models is essential to improve medical devices and diagnostic tools. Building on previous work toward microstructure-driven models of collagenous tissue, here we show a constitutive model based on fiber orientation and waviness distributions for skin that captures not only the anisotropic strain-stiffening response of this and other collagen-based tissues, but, additionally, accounts for tissue damage directly as a function of changes in the microstructure, in particular changes in the fiber waviness distribution. The implementation of this nonlinear constitutive model as a user subroutine in the popular finite element package Abaqus enables large-scale finite element simulations for biomedical applications. We showcase the performance of the model in fracture simulations during pure shear tests, as well as simulations of needle insertion into skin relevant to auto-injector design. [ABSTRACT FROM AUTHOR]

This paper aims at comparing the use of different software environments for the study of a simple unreinforced masonry building through nonlinear static analyses. The presented results are part of a wider research project conducted within the ReLUIS consortium, and specifically within a research task whose purpose is providing practitioners with results and tools for an aware employment of commercial software packages for modelling masonry structures. In this study one of the benchmark structures of the research program is analysed; a two-story building characterized by rigid horizontal diaphragms, considering different configurations in terms of openings arrangements and effectiveness of ring beams, is subjected to seismic load conditions. Software packages considering two- and three- dimensional structural models are employed, and the obtained results are compared in terms of capacity curves and collapse mechanisms. One of the critical aspects on the basic assumptions made by software in terms of way to apply the horizontal loads is further investigated. In addition, the role of the shear strength is analysed correlating the mechanical properties to be adopted with micro- and macro- models. The considered models present very different features, and the analogies and differences obtained in the results are critically interpreted in view of the different hypotheses made by the software tools in terms of modelling strategies and adopted constitutive laws. [ABSTRACT FROM AUTHOR]

We propose a methodology for the validation of a numerical model of a railway interior with an inline seating layout arrangement, based on the use of multibody and finite element approaches for the analysis of the passive safety. We model the railway interior layout using a nonlinear finite element model of the passenger seats and all supporting structures. Multibody models of test dummies, appropriate to the identification of the injury mechanisms, are used as measuring tools of the human exposure to injury. The crash scenario model uses a crash pulse, which is the surrogate for the impact of the railway vehicle structure. Being the multibody dummy validated independently by the software vendor and the nonlinear finite element structural models built with detailed data, the validation of the complete layout involves the identification of the uncertain parameters used in the scenario construction and not of the parameters used in the independent models already validated. The interaction between the multibody and finite element is represented via a penalty contact force model, which, together with the dummy positioning data, provides the uncertain parameter set used in the validation process. An experimental test of the inline seating layout, carried with a physical prototype, provides the reference dynamic response for the validation of the numerical model. The injury levels measured with the dummies provide the reference injury criteria values used in the validation process. Following the model validation, we discuss the results obtained for the nominal crash scenario in the framework of the most relevant injury indices for railway passenger passive safety. [ABSTRACT FROM AUTHOR]

The objective of the research presented in this paper is to investigate the buckling behavior of a perforated thin-walled lipped channel beam subjected to combined load. A nonlinear finite element method was used to analyze the buckling behavior of the beam. Experimental tests were made to validate the finite element simulation. Three factors with three levels for each factor were chosen to examine their influence on the buckling behavior of the beam and these factors are: the shape of holes, opening ratio and the spacing ratio of . The finite elements outcome was analyzed by using Taguchi method to identify the best set of three-parameter combinations for optimum critical buckling load. The analysis of variance technique (ANOVA) was implemented to determine the contribution of each parameter on buckling strength. Results showed that the mode of buckling failure of the perforated beam is lateral-torsional buckling and the hexagonal hole shape, =1.7 and = 1.3 were the best combination of parameters that gives the best buckling strength. The results also showed that the shape of holes is the most influential on buckling behavior of the perforated beam for this case of loading.

Tissue expansion is a technique used clinically to grow skin in situ to correct large defects. Despite its enormous potential, lack of fundamental knowledge of skin adaptation to mechanical cues, and lack of predictive computational models limit the broader adoption and efficacy of tissue expansion. In our previous work, we introduced a finite element model of tissue expansion that predicted key patterns of strain and growth which were then confirmed by our porcine animal model. Here we use the data from a new set of experiments to calibrate the computational model within a Bayesian framework. Four 10 × 10 cm 2 patches were tattooed in the dorsal skin of four 12 weeks-old minipigs and a total of six patches underwent successful tissue expander placement and inflation to 60cc for expansion times ranging from 1 h to 7 days. Six patches that did not have expanders implanted served as controls for the analysis. We find that growth can be explained based on the elastic deformation. The predicted area growth rate is k ∈ [ 0.02 , 0.08 ] [ h − 1 ]. Growth is anisotropic and reflects the anisotropic mechanical behavior of porcine dorsal skin. The rostral-caudal axis shows greater deformation than the transverse axis, and the time scale of growth in the rostral-caudal direction is given by rate parameters k 1 ∈ [ 0.04 , 0.1 ] [ h − 1 ] compared to k 2 ∈ [ 0.01 , 0.05 ] [ h − 1 ] in the transverse direction. Moreover, the calibration results underscore the high variability in biological systems, and the need to create probabilistic computational models to predict tissue adaptation in realistic settings. Tissue expansion is a widely used technique in reconstructive surgery because it triggers growth of skin for the correction of large skin lesions and for breast reconstruction after mastectomy. Despite of its potential, complications and undesired outcomes persist due to our incomplete understanding of skin mechanobiology. Here we quantify the deformation and growth fields induced by an expander over 7 days in a porcine animal model and use these data to calibrate a computational model of skin growth using finite element simulations and a Bayesian framework. The calibrated model is a leap forward in our understanding skin growth, we now have quantitative understanding of this process: area growth is anisotropic and it is proportional to stretch with a characteristic rate constant of k ∈ [ 0.02 , 0.08 ] [ h − 1 ]. [Display omitted] [ABSTRACT FROM AUTHOR]

This work studied the effects of holes on the buckling characteristic of an open thinwalled lipped channel beam under a bending load. A nonlinear finite element method was utilised to examine the buckling behaviour of the beam. Experimental works were carried out to verify the finite element simulation. Three factors were chosen to examine their influence on the buckling of the beam. These factors namely, the holes' shape, perforated ratio (hole length to beam height) and spacing ratio (centre to centre distance between holes to beam height). The finite elements output was analysed by implementing the Taguchi method to distinguish the best group of three parameters collections for optimal strength of buckling. Whereas the analysis of variance technique (ANOVA) method was applied to specify the impact of each parameter on critical buckling load. Outcomes showed that the combination of parameters that gives the best buckling strength is the hole with a hexagonal shape, perforated ratio =1.7 and spacing ratio =1.3, and the holes' shape is the most effective factor. In addition, the study demonstrated that the hole's shape factor has the greatest influence on the buckling capacity. While the perforated ratio factor is the least influential. [ABSTRACT FROM AUTHOR]

Summary: The paper presents a computationally efficient algorithm to integrate a probabilistic, non‐Gaussian parameter estimation approach for nonlinear finite element models with the performance‐based earthquake engineering (PBEE) framework for accurate performance evaluations of instrumented civil infrastructures. The algorithm first utilizes a minimum variance framework to fuse predictions from a numerical model of a civil infrastructure with its measured behavior during a past earthquake to update the parameters of the numerical model that is, then, used for performance prediction of the civil infrastructure during future earthquakes. A nonproduct quadrature rule, based on the conjugate unscented transformation, forms an enabling tool to drive the computationally efficient model prediction, model‐data fusion, and performance evaluation. The algorithm is illustrated and validated on Meloland Road overpass, a heavily instrumented highway bridge in El Centro, CA, which experienced three moderate earthquake events in the past. The benefits of integrating measurement data into the PBEE framework are highlighted by comparing damage fragilities of and annual probabilities of damages to the bridge estimated using the presented algorithm with that estimated using the conventional PBEE approach. [ABSTRACT FROM AUTHOR]

Ductility in reinforced concrete (RC) beams subjected to bending is generally assessed on the basis of the one-dimensional (1D) beam theory through the moment–curvature relationship of its cross-section. The inhomogeneity of concrete, however, inevitably imposes a three-dimensional (3D) stress state in any RC structural member. The importance of this work is its different approach to assessing the ductility in RC beams, taking into account this triaxial stress state. A concrete model which has been well documented experimentally in the literature is used, in conjunction with an in-house 3D smeared fixed-crack finite element code. Simply supported beams under three-point monotonic loading are used as numerical examples. After validating the results with experiments, three important parameters which affect the ductility and strength of RC beams are investigated. These are the tension reinforcement ratio, the yield strength of tension reinforcement steel and the compression reinforcement ratio. It appears that, for the first two, the general trend remains the same as with the 1D approach of the Codes, whereas the third does not affect the ductility of the under-reinforced beams, contrary to the Codes. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Surfactants play an important role in various physiological and biomechanical applications. An example is the respiratory system, where pulmonary surfactants facilitate the breathing and reduce the possibility of airway blocking by lowering the surface tension when the lung volume decreases during exhalation. This function is due to the dynamic surface tension of pulmonary surfactants, which depends on the concentration of surfactants spread on the liquid layer lining the interior surface of the airways and alveoli. Here, a finite membrane element formulation for liquids is introduced that allows for the dynamics of concentration-dependent surface tension, as is the particular case for pulmonary surfactants. A straightforward approach is suggested to model the contact line between liquid drops/menisci and planar solid substrates, which allows the presented framework to be easily used for drop shape analysis. It is further shown how line tension can be taken into account. Following an isogeometric approach, NURBS-based finite elements are used for the discretization of the membrane surface. The capabilities of the presented computational model is demonstrated by different numerical examples – such as the simulation of liquid films, constrained and unconstrained sessile drops, pendant drops and liquid bridges – and the results are compared with experimental data. [ABSTRACT FROM AUTHOR]

Excessive mechanical stress following surgery can lead to delayed healing, hypertrophic scars, and even skin necrosis. Measuring stress directly in the operating room over large skin areas is not feasible, and nonlinear finite element simulations have become an appealing alternative to predict stress contours on arbitrary geometries. However, this approach has been limited to generic cases, when in reality each patient geometry and procedure are unique, and material properties change from one person to another. In this manuscript, we use multi-view stereo to capture the patient-specific geometry of a 7-year-old female undergoing cranioplasty and complex tissue rearrangement. The geometry is used to setup a nonlinear finite element simulation of the reconstructive procedure. A key contribution of this work is incorporation of material behavior uncertainty. The finite element simulation is computationally expensive, and it is not suitable for uncertainty propagation which would require many such simulations. Instead, we run only a few expensive simulations in order to build a surrogate model by Gaussian process regression of the principal components of the stress fields computed with these few samples. The inexpensive surrogate is then used to compute the statistics of the stress distribution in this patient-specific scenario. [ABSTRACT FROM AUTHOR]

The field of computational cardiology has steadily progressed toward reliable and accurate simulations of the heart, showing great potential in clinical applications such as the optimization of cardiac interventions and the study of pro-arrhythmic effects of drugs in humans, among others. However, the computational effort demanded by in-silico studies of the heart remains challenging, highlighting the need of novel numerical methods that can improve the efficiency of simulations while targeting an acceptable accuracy. In this work, we propose a semi-implicit non-conforming finite-element scheme (SINCFES) suitable for cardiac electrophysiology simulations. The accuracy and efficiency of the proposed scheme are assessed by means of numerical simulations of the electrical excitation and propagation in regular and biventricular geometries. We show that the SINCFES allows for coarse-mesh simulations that reduce the computation time when compared to fine-mesh models while delivering wavefront shapes and conduction velocities that are more accurate than those predicted by traditional finite-element formulations based on the same coarse mesh, thus improving the accuracy-efficiency trade-off of cardiac simulations.

Breast cancer is the most commonly diagnosed cancer type worldwide. Given high survivorship, increased focus has been placed on long-term treatment outcomes and patient quality of life. While breast-conserving surgery (BCS) is the preferred treatment strategy for early-stage breast cancer, anticipated healing and breast deformation (cosmetic) outcomes weigh heavily on surgeon and patient selection between BCS and more aggressive mastectomy procedures. Unfortunately, surgical outcomes following BCS are difficult to predict, owing to the complexity of the tissue repair process and significant patient-to-patient variability. To overcome this challenge, we developed a predictive computational mechanobiological model that simulates breast healing and deformation following BCS. The coupled biochemical-biomechanical model incorporates multi-scale cell and tissue mechanics, including collagen deposition and remodeling, collagen-dependent cell migration and contractility, and tissue plastic deformation. Available human clinical data evaluating cavity contraction and histopathological data from an experimental porcine lumpectomy study were used for model calibration. The computational model was successfully fit to data by optimizing biochemical and mechanobiological parameters through Gaussian process surrogates. The calibrated model was then applied to define key mechanobiological parameters and relationships influencing healing and breast deformation outcomes. Variability in patient characteristics including cavity-to-breast volume percentage and breast composition were further evaluated to determine effects on cavity contraction and breast cosmetic outcomes, with simulation outcomes aligning well with previously reported human studies. The proposed model has the potential to assist surgeons and their patients in developing and discussing individualized treatment plans that lead to more satisfying post-surgical outcomes and improved quality of life., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The nonlinear frequencies of pre-stressed graphene-based structures, such as flat graphene sheets and carbon nanotubes, are calculated. These structures are modeled with a nonlinear hyperelastic shell model. The model is calibrated with quantum mechanics data and is valid for high strains. Analytical solutions of the natural frequencies of various plates are obtained for the Canham bending model by assuming infinitesimal strains. These solutions are used for the verification of the numerical results. The performance of the model is illustrated by means of several examples. Modal analysis is performed for square plates under pure dilatation or uniaxial stretch, circular plates under pure dilatation or under the effects of an adhesive substrate, and carbon nanotubes under uniaxial compression or stretch. The adhesive substrate is modeled with van der Waals interaction (based on the Lennard-Jones potential) and a coarse grained contact model. It is shown that the analytical natural frequencies underestimate the real ones, and this should be considered in the design of devices based on graphene structures. [ABSTRACT FROM AUTHOR]

A broad-ranging plasticity model is constructed by combining Bigoni-Piccolroaz yield function with a sweeping expression of kinematic hardening. Subsequently, two explicit and implicit update algorithms are developed to compute the stress from the rate equations of the plasticity in an incremental elastoplastic finite element analysis. The integrations are based on Forward and Backward Euler schemes. Considering a number of varying materials and the associated plasticity models, the proposed formulations are examined by means of a comprehensive set of numerical investigations. These include investigations to verify the suggested strategies along with two numerical simulations carried out by implementing the algorithms in a nonlinear finite element code. The versatility of the formulae allows for an expansive choice of elastoplastic constitutive models with a simple adjustment of a few parameters. [ABSTRACT FROM AUTHOR]

In this contribution, a novel nonlinear formulation for the finite deformation analysis of shell-like structures made of dielectric polymers and subject to electrical loading is developed. The kinematics of mechanical deformation is described via a seven-parameter shell model. Moreover, a second-order Taylor expansion, containing three parameters, is proposed to approximate the electrical potential through the thickness of the shell. The combined mechanical and electrical parameters constitute a ten-parameter electro-shell model. After developing the variational formulation of the problem, a nonlinear finite element formulation for the numerical solution of the coupled electromechanical problem is also developed. The formulation is further enriched by the enhanced assumed strain method to alleviate locking in thin shells. Finally, the applicability of the proposed formulation in several benchmark examples is demonstrated. In particular, it is shown that the formulation can capture the results available in the literature with high accuracy. [Display omitted] • An electro-shell model for finite deformation of thin EAPs is developed. • The model involves seven mechanical and three electrical field variables. • A TL FE formulation for the solution of coupled electromechanical problem is developed. • Numerical results are in excellent agreement with those reported in the literature. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of abutment stoppers on the seismic response of motorway bridges in the longitudinal direction. A rigorous 3D finite element model of a representative overpass bridge, including the entire bridge-foundation-abutment-soil system, is developed and used as a benchmark. The effect of abutment stoppers is shown to be significant, and must therefore be considered for proper simulation of the seismic response of such bridges. Subsequently, the resistance mechanism of abutments triggered when the bridge deck collides on the stoppers is examined. The model is first validated against theoretical solutions. The abutment cantilever wall is subjected to slightly-but crucially-different loading when the deck collides on the stoppers: the loading is applied at the top of the abutment without any rotational restraint. To gain insights on the key parameters affecting the abutment resistance to such passive loading at the top, a dimensionless analysis and a comprehensive parametric study are conducted, employing an equivalent 2D model of the abutment. The latter is validated against the results of a rigorous 3D model. Based on the results of the parametric study, a simplified model accounting for the effect of abutment stoppers is developed. Its efficiency is assessed on the basis of slow-cyclic pushover and nonlinear dynamic time history analyses, using the full 3D model as a benchmark. Overall, the extended simplified model is shown to offer a reasonable approximation (excellent for cohesive soil) of the seismic performance of typical motorway bridges in the longitudinal direction. [ABSTRACT FROM AUTHOR]

A simple and effective corotational triangular facet shell finite element is proposed for the geometric nonlinear analysis of thin piezoactuated structures. The structures under investigation are laminated shells composed of elastic layers and sensory/active piezoelectric layers, perfectly bonded to each other. A polar decomposition based corotational framework is adopted. By filtering out large rigid body motions from structural displacements, this framework allows (i) to account for arbitrarily large displacements/rotations, provided strains are small, and (ii) to use existing and high-performance linear elements as core-elements. Within the classical laminated plate theory, the small strain core element formulation based on superposition of OPT membrane and DKT plate element is used, along with a layer-wise constant interpolation of the transversal component of the electric field. Numerical simulations dealing with benchmark problems and applications of technological interest prove accuracy and effectiveness of the proposed formulation. [ABSTRACT FROM AUTHOR]

This paper describes the development of a complete methodology for the aeroservoelastic modelling of horizontal axis wind turbines at the conceptual design stage. The methodology is based on the implementation of unsteady aerodynamic modelling, advanced description of the control system and nonlinear finite element calculations in the Samcef Wind Turbines design package. The aerodynamic modelling is carried out by means of fast techniques, such as the blade element method and the unsteady vortex lattice method, including a free wake model. The complete model also includes a description of a doubly fed induction generator and its control system for variable speed operation. The Samcef Wind Turbines software features a nonlinear finite element solver with multi-body dynamics capability. The full methodology is used to perform complete aeroservoelastic simulations of a realistic 2 MW wind turbine model. The interaction between the three components of the approach is carefully analysed and presented here. [ABSTRACT FROM AUTHOR]

A new nonlinear hyperelastic bending model for shells formulated directly in surface form is presented, and compared to four existing prominent bending models. Through an essential set of elementary nonlinear bending test cases, the membrane and bending stresses of each model are examined analytically. Only the proposed bending model passes all the test cases, while the other bending models either fail or only pass the test cases for small deformations. The proposed new bending model can handle large deformations and initially curved surfaces. It is based on the principal curvatures and their directions in the initial configuration, and it thus can have different bending moduli along those directions. These characteristics make it flexible in modeling a given material, while it does not suffer from the pathologies of existing bending models. Further, the bending models are compared computationally through four classical benchmark examples and one contact example. As the underlying shell theory is based on Kirchhoff–Love kinematics, isogeometric NURBS shape functions are used to discretize the shell surface. The linearization and efficient finite element implementation of the proposed new model are also provided. • The new model is objective, admits large deformations and captures anisotropic bending. • It allows to describe initially curved stress-free shells. • It is compared to existing bending models and it agrees with those at small deformations. • In contrast to existing models, it passes a proposed set of nonlinear bending test cases. • It allows for an efficient implementation within isogeometric shell FE. [ABSTRACT FROM AUTHOR]

This work presents models and simulations of a numerical strategy for a time and cost-efficient virtual product development of a novel passive safety restraint concept for motorcycles. It combines multiple individual development tasks in an aggregated procedure. The strategy consists of three successive virtual development stages with a continuously increasing level of detail and expected fidelity in multibody and finite element simulation environments. The results show what is possible with an entirely virtual concept study-based on the clever combination of multibody dynamics and nonlinear finite elements-that investigates the structural behavior and impact dynamics of the powered two-wheeler with the safety systems and the rider's response. The simulations show a guided and controlled trajectory and deceleration of the motorcycle rider, resulting in fewer critical biomechanical loads on the rider compared to an impact with a conventional motorcycle. The numerical research strategy outlines a novel procedure in virtual motorcycle accident research with different levels of computational effort and model complexity aimed at a step-by-step validation of individual components in the future., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2023.)

This paper presents a projection method for deriving membrane models from the corresponding three-dimensional material models. As a particular example the anisotropic Holzapfel–Gasser–Ogden model is considered. The projection procedure is based on the kinematical and constitutive assumptions of a general membrane theory, considering the membrane to be a general two-dimensional manifold. By assuming zero transverse stress, the Lagrange multiplier associated with the incompressibility constraint can be eliminated from the formulation. The resulting nonlinear model is discretized and linearized within the finite element method. Several numerical examples are shown, considering quadratic Lagrange and NURBS finite elements. These show that the proposed model is in very good agreement with analytical solutions and with full 3D finite element computations. [ABSTRACT FROM AUTHOR]

Interactive simulations in Virtual Reality, such as haptic interaction, are more and more used to test or optimize nonlinear mechanical systems subjected to large deformations. FE algorithms are often not suitable for such purposes due to the high computational burden and the long simulation times. This paper provides a modified version of the classic chain algorithm, referred to as modified chain algorithm (MCA), to overcome some convergency issues and reduce the simulation time. The proposed algorithm is able to reduce the number of iterations estimating two kind of average moment laws. The MCA is then integrated into a design optimization procedure for the synthesis of a double slider-crank compliant mechanism to be used as opening system for an adjustable bicycle saddle. Finally, a X-Y layered ABS prototype is manufactured by rapid prototyping technique and 3-D printer. Experimental setup to test the deflection of the prototype revealed in good accordance with results coming from the MCA. [ABSTRACT FROM AUTHOR]

The results of different nonlinear finite element models for eight simply supported reinforced concrete haunched beams designed to develop a shear failure under static loading are presented and discussed in this paper. Simplified nonlinear models in which the participation of the longitudinal steel reinforcement and stirrups is indirectly included were assessed using SAP2000. More complex nonlinear finite element models were assessed with ANSYS, in which longitudinal steel reinforcement and stirrups were modeled as built. Softening of concrete due to deformation was taken into account in the selected constitutive models using a failure surface with different peak compressive and tension stresses. Strain hardening for the steel reinforcement was considered using the Von Mises yield criterion. Perfect bond between concrete and steel was assumed. Shear–displacement curves for a specific section located at midspan of the beams were obtained from the finite element models and compared to those obtained from experimental testing. Also, crack patterns associated to different loads steps were obtained from ANSYS finite element models. It can be concluded that it is possible to obtain a reasonable correlation between analytical and experimental load–deformation curves and the main developed arch mechanism for RCHBs failing in shear using both simplified and detailed finite element models, which for practical purposes is more than acceptable. However, only a medium correlation between cracking patterns numerically obtained with detailed finite element models and those experimentally identified were observed, particularly for beams with shear reinforcement. [ABSTRACT FROM AUTHOR]

Data-driven methods are becoming an essential part of computational mechanics due to their advantages over traditional material modeling. Deep neural networks are able to learn complex material response without the constraints of closed-form models. However, data-driven approaches do not a priori satisfy physics-based mathematical requirements such as polyconvexity, a condition needed for the existence of minimizers for boundary value problems in elasticity. In this study, we use a recent class of neural networks, neural ordinary differential equations (N-ODEs), to develop data-driven material models that automatically satisfy polyconvexity of the strain energy. We take advantage of the properties of ordinary differential equations to create monotonic functions that approximate the derivatives of the strain energy with respect to deformation invariants. The monotonicity of the derivatives guarantees the convexity of the energy. The N-ODE material model is able to capture synthetic data generated from closed-form material models, and it outperforms conventional models when tested against experimental data on skin, a highly nonlinear and anisotropic material. We also showcase the use of the N-ODE material model in finite element simulations of reconstructive surgery. The framework is general and can be used to model a large class of materials, especially biological soft tissues. We therefore expect our methodology to further enable data-driven methods in computational mechanics. [Display omitted] • Data-driven modeling of nonlinear, anisotropic materials with automatically polyconvex energy functions. • Invariant inputs, energy outputs enable finite element implementation for large scale simulations. • Neural ODE model can interpolate analytical models and surpasses analytical models against experimental data. • Neural ODE model finds the closest convex function even when fed non-convex training data. • Demonstration of complex static equilibrium problems, e.g. reconstructive surgery. [ABSTRACT FROM AUTHOR]

This paper is aimed at studying the elastoplastic behavior of longitudinally stiffened girder webs subjected to patch loading and bending. The investigation is carried out by means of nonlinear finite element analysis to study the structural behavior of the girder components (flanges, web and stiffener) at ultimate limit state. Initial geometrical imperfections, plastic material behavior and large deflection effects are considered in the model. For the numerical model validation, the computer results from the simulations are compared with experimental results taken from the literature. A parametric study was carried out in order to investigate the influence of the applied bending moment and the relative location of the stiffener on the ultimate strength to patch loading. [ABSTRACT FROM AUTHOR]

This article presents a molecular dynamics (MD)-aided multiscale modeling framework that accounts for the nanoscale deformation kinetics and morphological irregularities in polymer with randomly-dispersed carbon nanotubes (CNTs). First, a novel coarse-grain MD approach is developed to generate large-size simulation domains comprising realistic aspect ratio CNTs and crosslinked molecular network of the bulk thermoset polymer. The coarse-grain approach can simulate the CNT dispersion state and cluster formation resulting from molecular-level interactions during the polymer curing process, several orders of magnitude faster than traditional all-atom MD approaches. Next, CNTs are approximated as equivalent solid fibers at the continuum level, and their cluster morphology is geometrically reconstructed using the information obtained from coarse-grain simulations. The reconstructed CNTs are embedded within a host polymer finite element simulation domain for multiscale homogenization. The polymer is modeled using a recently developed damage model that accounts for bond breakage information obtained from all-atom simulations. Standardized test specimens are also fabricated and characterized to support model calibration and hypotheses. The model predictions for effective properties correlated well with in-house and literature test results for different CNT weight fractions. The model also revealed critical mechanisms attributed to improved mechanical properties with increasing CNT aspect ratios. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Recently, a very general and novel class of implicit bodies has been developed to describe the elastic response of solids. It contains as a special subclass the classical Cauchy and Green elastic bodies. Within the class of such bodies, one can obtain through a rigorous approximation, constitutive relations for the linearized strain as a nonlinear function of the stress. Such an approximation is not possible within classical theories of Cauchy and Green elasticity, where the process of linearization will only lead to the classical linearized elastic body. In this paper, we study numerically the states of stress and strain in a finite rectangular plate with an elliptic hole and a stepped flat tension bar with shoulder fillets, within the context of the new class of models for elastic bodies that guarantees that the linearized strain would stay bounded and limited below a value that can be fixed a priori, thereby guaranteeing the validity of the use of the model. This is in contrast to the classical linearized elastic model, wherein the strains can become large enough in the body leading to an obvious inconsistency. [Copyright &y& Elsevier]

This paper provides an overview of recent advances in the computational modeling of the gecko adhesion mechanism. Several efficient modeling approaches are introduced that address the adhesion mechanism at various length scales, ranging from the molecular interaction at the Ångstrom scale to the toe description at the centimeter scale. In particular, detailed three-dimensional models for the gecko spatulae and setae are discussed. The emphasis here is placed on the computational efficiency of the presented contact formulations using coarse-graining and model order reduction. Different finite element methods, based on nonlinear structural mechanics, are considered to analyze the resulting models. Both continuum and beam formulations are discussed. In order to obtain an accurate description of peeling, a local finite element surface enrichment technique is presented. This paper also provides some ideas on future modeling approaches. [ABSTRACT FROM PUBLISHER]

In this paper, we present finite element formulations for general three-dimensional convex polyhedra for use in a common finite element framework that are well suited, e.g., for modeling complex granular materials and for mesh refinements. Based on an universally applicable interpolant for any convex polyhedron, different interpolation schemes are investigated in the context of nonlinear elastostatics. The modeling benefits and the numerical performance regarding the mechanical response and the computational cost are analyzed by several examples. [ABSTRACT FROM AUTHOR]

New designs of precast bridge parapets made with fibre reinforced concretes (FRC) were developed using nonlinear finite element calculations. A monolithic FRC parapet and a hybrid FRC parapet were designed. The latter parapet consisted of a shell of ultra-high performance FRC paired with a normal strength concrete core. Furthermore, two new anchorage systems were optimized for parapet installation on a new deck or for parapet replacement on an existing structure. Quasi-static tests showed that the load-carry capacity of the parapet designs exceed the PL-2 or TL-4 parapet specifications of CSA and AASHTO. The finite elements model developed in the project has satisfactorily reproduced the stiffness, ultimate strength, and failure mode of parapets. Additional numerical analyses were conducted for the hybrid parapet to provide design recommendations related to construction aspects and further optimizations. [ABSTRACT FROM AUTHOR]

The analysis of the biomechanics of growth and remodeling in soft tissues requires the formulation of specialized pseudoelastic constitutive relations. The nonlinear finite element analysis package ABAQUS allows the user to implement such specialized material responses through the coding of a user material subroutine called UMAT. However, hand coding UMAT subroutines is a challenge even for simple pseudoelastic materials and requires substantial time to debug and test the code. To resolve this issue, we develop an automatic UMAT code generation procedure for pseudoelastic materials using the symbolic mathematics package MATHEMATICA and extend the UMAT generator to include continuum growth. The performance of the automatically coded UMAT is tested by simulating the stress-stretch response of a material defined by a Fungorthotropic strain energy function, subject to uniaxial stretching, equibiaxial stretching, and simple shear in ABAQUS. The MATHEMATICA UMAT generator is then extended to include continuum growth by adding a growth subroutine to the automatically generated UMAT. The MATHEMATICA UMAT generator correctly derives the variables required in the UMAT code, quickly providing a ready-to-use UMAT. In turn, the UMAT accurately simulates the pseudoelastic response. In order to test the growth UMAT, we simulate the growth-based bending of a bilayered bar with differing fiber directions in a nongrowing passive layer. The anisotropic passive layer, being topologically tied to the growing isotropic layer, causes the bending bar to twist laterally. The results of simulations demonstrate the validity of the automatically coded UMAT, used in both standardized tests of hyperelastic materials and for a biomechanical growth analysis. [ABSTRACT FROM AUTHOR]