Commercial Finite Element Code Research Articles

A machine learning material model for structural adhesives in finite element analysis

The computational analysis of adhesives within finite element simulations is important for many engineering applications, from automotive structures to civil engineering. The underlying material descriptions are closed, analytically formulated models representing the stress-response of the material for given strains. In this publication, we investigate and present a methodology for adopting artificial neural networks for this purpose. The aim is to show feasibility and performance of such models to be able to uncouple the material description from fixed formulations to reap the benefits of neural networks for materials modelling. A methodology is presented for creating training data for a structural adhesive, whereby the data is obtained from specimen and from generic strain paths of a baseline material model. From this, feed-forward neural networks are trained and evaluated using machine learning tools as well as from an engineering perspective by pre-defined test strain paths. It is shown that, given the quality and the quantity of training data is adequate, the model is able to generalize with respect to the response. Especially, the coverage of complete strain space is shown to be crucial. A framework for using machine learning models in a commercial finite element code is presented, integrating models trained through high-level programming interfaces. This enables validating the performance and accuracy of such models in explicit simulations, which is shown to be a crucial step in evaluation of machine learning material models. The model is confirmed to be able to represent structural adhesives with high precision comparable to an analytical model and to generalize for unknown geometries and loading conditions. An approach to predict element failure with the machine learning model is shown and finally, the neural network model response is made explainable from an engineering point of view using feature importance.

Approximation of pre-twisted Achilles sub-tendons with continuum-based beam elements

Achilles sub-tendons are materially and geometrically challenging structures that can nearly undergo around 15% elongation from their pre-twisted initial states during physical activities. Sub-tendons’ cross-sectional shapes are subject-specific, varying from simple to complicated. Therefore, the Achilles sub-tendons are often described by three-dimensional elements that lead to a remarkable number of degrees of freedom. On the other hand, the continuum-based beam elements in the framework of the absolute nodal coordinate formulation have already been shown to be a reliable and efficient replacement for the three-dimensional continuum elements in some special problems. So far, that element type has been applied only to structures with a simple cross-section geometry. To computationally efficiently describe a pre-twisted Achilles sub-tendon with a complicated cross-section shape, this study will develop a continuum-based beam element based on the absolute nodal coordinate formulation with an arbitrary cross-section description. To demonstrate the applicability of the developed beam element to the Achilles sub-tendons, 16 numerical examples are considered. During these numerical tests, the implemented cross-section descriptions agreed well with the reference solutions and led to faster convergence rates in comparison with the solutions provided by commercial finite element codes. Furthermore, it is demonstrated that in the cases of very complicated cross-sectional forms, the commercial software ANSYS provides inflated values for the elongation deformation in comparison with ABAQUS (about 6.2%) and ANCF (about 9.4%). Additionally, the numerical results reveal a possibility to model the whole sub-tendons via coarse discretization with high accuracy under uniaxial loading. This demonstrates the huge potential for use in biomechanics and also in multibody applications, where the arbitrary cross-section of beam-like structures needs to be taken into account.

Residual Stress Enhancement by Laser Shock Treatment in Chromium-Alloyed Steam Turbine Blades.

In-service turbine blade failures remain a source of concern and research interest for engineers and industry professionals with attendant safety and economic implications. Very high-pressure shock impacts from laser shots represent an evolving technique currently gaining traction for surface improvement and failure mitigation in engineering components. However, the physical characteristics and effects of parameter variations on a wide range of materials are still not fully understood and adequately researched, especially from a computational point of view. Using the commercial finite element code ABAQUS©, this paper explores the application of laser shock peening (LSP) in the enhancement of residual stresses in Chromium-based steel alloyed turbine blade material. Results of the numerically developed and experimentally validated LSP model show that peak compressive residual stresses (CRS) of up to 700 MPa can be induced on the surface and sub-surface layers, while the informed varying of input parameters can be used to achieve an increase in the magnitude of CRS imparted in the peened material. Analysis of the hierarchy of influence of the five input parameters under investigation on residual stress enhancement reveals the laser shock intensity as the most influential, followed in descending order of influence by the exposure time, shot size, degree of overlaps, and the angle of shot impact.

Dynamic responses of submerged components in advanced reactors: experimental and numerical studies

The seismic design of an advanced nuclear reactor must consider the interaction of vessel internal components with the surrounding coolant: fluid–structure interaction (FSI). Available analytical solutions for FSI of submerged components do not accommodate multiple-component, intense seismic inputs and complex reactor and internal geometries. Physical testing of reactor vessels and internals to inform seismic design is impractical and cost-prohibitive, leaving the use of verified and validated, robust numerical models as the only plausible option for analysis and design. Physical data that could be used for validating such numerical models for multi-component shaking are not available. This article describes an experimental program performed on a 6-degree-of-freedom earthquake simulator to generate data that could support validation of seismic FSI numerical models for submerged components in commercial finite element codes. A scaled model of a base-supported reactor vessel with simplified representations of submerged internals was tested to generate submerged-component response histories for a range of seismic inputs. The generated data were used to validate numerical models in the finite element code LS-DYNA. Numerical models were validated for calculation of hydrodynamic pressure responses on internals, in-water frequencies of internals, and acceleration responses of internals. The generated data and the analysis recommendations could aid engineering analysts designing submerged components and systems for seismic effects.

Prediction of moisture diffusion and failure in glass/steel adhesive joints

Glass/steel adhesive joints are being used increasingly in the construction industry as they offer significant structural advantages over conventional mechanical fastener approaches. However, adhesive joints are also known to be sensitive to moisture diffusion into the bondline, which reduces the interfacial bonding strength for hybrid glass/steel substrates. The effect of moisture on the performance degradation of glass/steel adhesive joints has been successfully predicted assuming adhesive property degradation but requires experimental determination of the affected moisture ingress zone. This study utilizes a multi-physics numerical approach implemented via the commercial finite element code Abaqus 2020, which firstly simulates moisture ingress into the adhesive/glass interface and subsequently couples the diffusion effects with a cohesive zone modelling approach for damage initiation and propagation. The numerical predictions are calibrated against experimental data on glass/steel Double Cantilever Beam (DCB) specimens, which are bonded with a ductile methacrylate adhesive (Araldite 2047–1). The modelling approach is then validated against the experimental response of large double lap shear joints of a significantly different bondline geometry. It is demonstrated that the numerical model successfully predicts the critical exposure time for partial to complete joint degradation enabling the development of engineering guidelines for life-time prediction of various joint geometries.

Matrix-embedded metamaterials: Applications for the architectural heritage

A rather unexplored question and a very challenging problem consist in the synthesis and modeling of composite metamaterials consisting of at least two phases. The study of this problem may have a huge impact in the field of Civil Engineering, where such kind of composite materials found several applications, for instance, in application to architectural and civil engineering heritage. More precisely, the aim of this work is to study the mechanical properties of a fibrous metamaterial embedded in a softer matrix. Numerical simulations, obtained by means of a commercial Finite Element code, are carried out on a soft matrix reinforced by stiffer fibers arranged according to a geometry defined by the fiber directions and compared with results achieved using an effective model in which the micro-structure is homogenized. The role of the fibers and the matrix is reinterpreted with regard to these models. Finally, the employed models are calibrated to reproduce the mechanical behavior of a simple experiment.

Analysis of Side-Wall Wrinkling in Deep Drawing Processes

Wrinkling, developed due to compressive instability, is one of the main failure modes in deep drawing processes. Depending on the die geometry and blank holder force, it can be observed as flange wrinkling and/or side-wall wrinkling. In this study, side-wall wrinkling in cylindrical cup drawing process is investigated by using different constitutive models that are formed by using CPB06ex2, Hill’48, BBC2008-8p and BBC2008-16p yield criteria with isotropic hardening, and von Mises yield criterion with isotropic, kinematic and combined hardening. Numerical simulations are performed by implementing CPB06ex2, BBC2008-8p and BBC2008-16p models to a commercial finite element code through user subroutines. AA5042-H2 aluminium alloy is selected as a sheet material with 0.2083 mm thickness. In order to verify the developed models, the experimental results of the previous works for wrinkling profile and punch force evolution are employed. The results are compared and presented for the considered yield criteria.

Analysis of ESAFORM 2021 cup drawing benchmark of an Al alloy, critical factors for accuracy and efficiency of FE simulations

This article details the ESAFORM Benchmark 2021. The deep drawing cup of a 1 mm thick, AA 6016-T4 sheet with a strong cube texture was simulated by 11 teams relying on phenomenological or crystal plasticity approaches, using commercial or self-developed Finite Element (FE) codes, with solid, continuum or classical shell elements and different contact models. The material characterization (tensile tests, biaxial tensile tests, monotonic and reverse shear tests, EBSD measurements) and the cup forming steps were performed with care (redundancy of measurements). The Benchmark organizers identified some constitutive laws but each team could perform its own identification. The methodology to reach material data is systematically described as well as the final data set. The ability of the constitutive law and of the FE model to predict Lankford and yield stress in different directions is verified. Then, the simulation results such as the earing (number and average height and amplitude), the punch force evolution and thickness in the cup wall are evaluated and analysed. The CPU time, the manpower for each step as well as the required tests versus the final prediction accuracy of more than 20 FE simulations are commented. The article aims to guide students and engineers in their choice of a constitutive law (yield locus, hardening law or plasticity approach) and data set used in the identification, without neglecting the other FE features, such as software, explicit or implicit strategy, element type and contact model.

An Efficient Method for Predicting the Output Signal of an Eddy Current Probe Around the Edge of a Conductive Cylindrical Rod

We propose a semi-analytical model to predict the output signal of an eddy current probe around the edge of a conductive cylindrical rod. The proposed model is based on the truncated region eigenfunction expansion method and uses the second-order vector potential to formulate the resultant boundary problem. The use of appropriate boundary conditions on the truncation locations leads to less complex eigenvalue equations which remarkably increases the computation speed. The validity and computation efficiency of the proposed model are demonstrated by comparing the simulation results of several case studies with measurements and those obtained using a commercial finite element code.

Plasticity damage self-consistent model incorporating stress triaxiality and shear controlled fracture mechanisms – Model verification and validation

The plasticity damage self-consistent (PDSC) model is a damage model developed in the context of continuum damage mechanics in which the damage dissipation potential is formulated to account for damage contributions due to intervoid necking, shearing, and sheeting for an arbitrary stress state. The synergic action of different micromechanisms contributing to ductile fracture is accounted for by their dependence on the plastic deformation, stress triaxiality, third invariant of the deviatoric of the stress tensor, and unilateral conditions. In this work, the PDSC has been implemented in the commercial finite element code MSC MARC via user subroutines and used to predict ductile failure response under different stress state conditions. Firstly, the model implementation has been verified by comparing calculated damage evolution as a function of plastic strain, for prescribed combinations of stress triaxiality and Lode parameter under proportional loading, with an analytical solution. Successively, the model has been validated in predicting ductile fracture for Al6061-T6 in different specimen geometries and comparing with experiment results. Model capability to anticipate fracture initiation conditions, together with specimen global response, and ductile crack propagation also for complex load paths, is demonstrated.

Modeling the effect of backfill on dynamic fracture propagation in steel pipelines

In this paper, dynamic ductile fracture propagation simulations were conducted to study the use of smoothed particle hydrodynamics (SPH) for modeling the effects of backfill in pipeline burst simulations. The effect of SPH parameters on fracture velocity was studied using the Battelle Two-Curve Method (BTCM) approach of decoupling mechanics and gas decompression but characterizing propagation toughness by crack tip opening angle (CTOA) rather than Charpy absorbed energy (CVN). The backfilled pipe model was developed and studied using the commercial finite element code ABAQUS 2017. Ductile fracture propagation was simulated using a shell based constant CTOA model. The current study examined the numerical aspects of applying SPH through comparing results with literature. The effects of particle size, various backfill material properties, and backfill depth on the fracture velocity were examined. It was found that the particle size had a minor effect on the fracture velocity and should be selected in proportion to the diameter of the pipe being examined. The numerical study showed that increasing the density and shear modulus of the backfill material resulted in a reduction of the fracture velocity. The effect of backfill depth up to 1.4 m was also examined numerically and found to have little effect on the fracture velocity, agreeing well with literature. The present study illustrates the sensitivity of the fracture velocity to the various parameters used in SPH models.

Development, verification, and validation of comprehensive acoustic fluid‐structure interaction capabilities in an open‐source computational platform

AbstractThe acoustic fluid‐structure interaction (FSI) formulation is a practical numerical approach for the seismic analysis of fluid‐filled tanks. However, there are no verification and validation studies reported in the literature that demonstrate the ability of an acoustic FSI numerical model to predict responses important to structural and mechanical design for intense translational and rotational earthquake inputs. Herein, an acoustic FSI formulation is implemented in the open‐source Multiphysics Object‐Oriented Simulation Environment (MOOSE), and is formally verified and validated using analytical solutions and code‐to‐code verification, and experimental data, respectively. The analytical solutions are for small amplitude, unidirectional seismic inputs. The code‐to‐code verification utilizes a previously verified and validated Arbitrary Lagrangian‐Eulerian (ALE) numerical model in the commercial finite element code LS‐DYNA. The validation studies utilize a comprehensive data set assembled from results of 3D earthquake‐simulator tests of a fluid‐filled vessel. The acoustic numerical model in MOOSE is verified and validated for hydrodynamic pressures and support reactions except for cases that involve significant convective response. For small amplitude inputs, numerically predicted wave heights match those of the analytical solutions. The numerical model is not verified and validated for wave height calculations under intense 3D seismic inputs. The run times for the acoustic FSI simulations in MOOSE are an order of magnitude, or more, shorter than for the corresponding ALE simulations in LS‐DYNA. The utility of the MOOSE acoustic FSI implementation is demonstrated by seismic analysis of a building equipped with a fluid‐filled, advanced nuclear reactor.

Modeling the contribution of tire-reclaimed and industrial steels fibers on the strength and ductility of RC-frames structures

PurposeThis paper aims to model the performances of frames structures by comparing the predictions of ordinary control concrete (CC) and concretes reinforced by fibers. Two types of steel fibers were used in this work, industrial steel fibers (ISF) and tire-reclaimed fibers obtained by cutting virgin steel tire-cord to 50 mm, noticed virgin steel fibers (VSF). In total, 3% of VSF are used. The results obtained in this paper clearly show the contribution of fibers in improving the global and local behavior of the frames structures. VSF gives the same or better overall behavior as the use of industrial fibers for the same percentage of fibers, with the advantage that VSF contributes to the protection of the environment and limit the wastage of steel.Design/methodology/approachThis work was carried out using the commercial finite element code Abaqus/Explicit. The behavior of the different concretes used in this study was modeled by the concrete damage plasticity (CDP) constitutive law. The methodology adopted to complete this work consisted in identifying, by calibration of the available experimental results with the numerical predictions, the parameters of the corresponding CDP model for each of the concretes used in this work. To this end, the authors have successively identified the CDP parameters for the CC-V (control concrete used by Vecchio and Emara, 1992) used in frame structure (R + 1). Subsequently, the CDP parameters of the CC-T (control concrete used by Tlemat, 2004), the CVSF (concrete with virgin steel fibers) and the CISF-1 (concrete with industrial steel fibers type 1, ISF-1) are identified using the experimental results of beams under bending tests. Once the model parameters were determined for each concrete, the authors conducted a series of simulations to show the benefit of introducing claimed and industrial fibers in frame structure (R + 1) and (R + 2). This approach recommends the use of concrete reinforced with steel fibers, mainly 6% by mass of VSF and ISF-1, in place of ordinary concrete in new construction to increase the resistance of structures and contribute, if applicable, to the protection of the environment.FindingsThe main findings of this study can be summarized by: the strength and ductility of the frames structures made of concrete fiber are significantly increased. The use of tire-reclaimed steel fibers (VSF) gives the same or better overall behavior as the use of industrial fibers. In addition to their good mechanical contribution, the tire-reclaimed fibers contribute to the protection of the environment and limit the wastage of steel. The use of fibers reduces the cracking zones in concrete fiber frames structures. The usefulness of distinguishing the interstory displacement limits set by codes, in particular, uniform building code (UBC-97), for ordinary concretes and concrete reinforced with fibers is addressed.Originality/valueThe contribution of tire-reclaimed and industrial fibers on the strength and ductility of reinforced concrete-frames structures is addressed. The use of tire-reclaimed steel fibers gives the same or better overall behavior as the use of industrial fibers, the tire-reclaimed fibers having the advantage of contributing to the protection of the environment and limiting the wastage of steel. The paper also points to the usefulness of distinguishing the interstory displacement limits set by codes, in particular UBC-97, for ordinary concrete and concrete reinforced with fibers, in accordance to the predictions of the capacity curves.

Static and dynamic compressive and tensile response of highly stretchable polyurea

The mechanical response of highly stretchable polyurea elastomer at various strain rates is investigated via experiments, theoretical analysis, and numerical modeling. Experiments encompassing quasi-static and dynamic (SHPB/SHTB - split Hopkinson pressure/tension bar) mechanical tests, as well as drop-weight impact tests, are undertaken to identify the nonlinear and rate-dependent relationship between tensile/compressive true stress and deformation of the polyurea studied. Subsequently, a compressible visco-hyperelastic constitutive model for the material is established based on the summation of Cauchy stress components. The proposed model yields good agreement with experimental data, as well as a better description of the tensile response at stretch rates of 103 s−1 than other models (e.g., the YSL2000 model (Yang et al., 2000) and the SYLL2004 model (Shim et al., 2004)). The model is implemented in the commercial finite element code Abaqus/Explicit via a user-defined material (VUMAT) subroutine. Homogenous deformation modes of polyurea, i.e., uniaxial compression and tension, are accurately captured, and non-uniform deformation of polyurea, corresponding to impact by a hemispherically-tipped drop weight, which induces both compression and tension, is also well described. Finally, it is demonstrated that the proposed model is able to characterize the dynamic response of other polyureas reported in literature. The present study is helpful for the design and development of blast and impact-resistant polyurea protective coatings.

Analysis of dynamic fracture propagation in steel pipes using a shell-based constant-CTOA fracture model

In this paper, a finite element (FE) model with shell elements using a constant crack tip opening angle (CTOA) as fracture criterion was implemented for the simulation of dynamic fracture propagation in steel pipes. The new model was developed to improve computational efficiency over current CTOA models while retaining a high level of numerical accuracy. The commercial FE code ABAQUS was used to generate the meshes and perform the analyses. The proposed model was first used to reproduce data from an existing CTOA model of an American Petroleum Institute (API) X65 steel, matching the steady-state fracture velocity within a maximum difference of 5% while drastically reducing the computational time required. The model was then used to analyze recent experimental data from a full-scale pipe burst test of a Japanese Industrial Standard (JIS) steel STPG370, matching the crack velocity data within 4%. It was thereby demonstrated that FE analysis using this shell-based constant-CTOA model is an efficient method for describing dynamic fracture propagation in steel pipes and can be used as an engineering tool to develop fracture driving force based on CTOA.

A special finite element method applied to off-axis tunnel cracking in laminates

Off-axis oriented tunnel cracking in a laminated structure is modeled using a special 2D off-axis finite element formulation, thus replacing full 3D finite element simulations with much less demanding 2D simulations. The 2D off-axis element is formulated as a user element in the commercial finite element code ABAQUS, and the user element code is made available for the reader. The finite element formulation is used to predict the steady-state energy release rate and the mode-mixity for either one isolated crack or multiple interacting tunnel cracks in the central ply of a [0/θ/0/−θ]s layup. The laminate is loaded uni-axially or bi-axially, and analyses are presented for glass and carbon fiber composites for arbitrary layup angles θ. The 2D finite element model is found to give precise predictions when comparing the detailed simulations made by a full 3D finite element model. It is demonstrated that despite being a 2D method, the model rigorously provides detailed solutions for the out-of-plane deflection and strain. With a speed-up of more than four orders of magnitudes, it is thus possible to perform new, detailed, and very accurate studies of the dependency of laminate thickness as well as neighboring cracks on off-axis tunnel cracking.

Predictive Capability of a Finite Element Micro-Mechanical Model for Masonry Elements Reinforced Using CFRP

Different commercial Finite Element Codes proved to be able to describe the mechanical behavior of masonry materials externally reinforced by means of Carbon Fiber Reinforced Polymers (CFRP); the behavior of fracturing materials, characterized by low tensile strength, with adhered strips can be reproduced relying on parameters based on fracture mechanics and the theories of adhesion.In this report the comparison is made of previous experimental test results with numerical analysis, carried out on masonry panels reinforced with CFRP strips and subjected to out of plane actions. The comparison is especially addressed to the evaluation of the post peak branch; in addition to the slopes of the diagram in the pre-critic phase, available kinematic ductility and energy shares both prior and after the peak load were considered in order to interpret the capability of the micro-mechanical model implemented in the FEM Code to account for the local phenomena influencing the interaction between masonry and FRP strengthening systems.

Robust hybrid/mixed finite elements for rubber-like materials under severe compression

A new family of hybrid/mixed finite elements optimized for numerical stability is introduced. It comprises a linear hexahedral and quadratic hexahedral and tetrahedral elements. The element formulation is derived from a consistent linearization of a well-known three-field functional and related to Simo–Taylor–Pister (STP) elements. For the quadratic hexahedral and tetrahedral elements we derive (static reduced) discontinuous hybrid elements, as well as continuous mixed finite elements with additional primary unknowns for the hydrostatic pressure and the dilation, whereas the linear hexahedral element is of the discontinuous type. The elements can readily be used in combination with any isotropic, invariant-based hyperelastic material model and can be considered as being locking-free. In a representative numerical benchmark test the elements numerical stability is assessed and compared to STP-elements and the family of discontinuous hybrid elements implemented in the commercial finite element code Abaqus/Standard. The new elements show a significant advantage concerning the numerical robustness.

Equivalent linearization method improved by higher order statistics in modal space for geometrically nonlinear vibrations

In this paper, an equivalent linearization method considering higher order statistics based on nonlinear reduced order modeling techniques is proposed for the geometrically nonlinear random vibration problems of complex structures. Nonlinear reduced order models of the structures are constructed by leveraging the nonlinear analysis capabilities of commercial finite element codes, and an improvement to the Stiffness Evaluation Procedure method for determining the stiffness coefficients is achieved through the equivalence relation, leading to a notable reduction in computational cost with no further requirements for commercial finite element codes. The nonlinear terms are twice regulated equivalent, and then a regulated form of the stiffness coefficients is derived to introduce higher order statistics into the equations of motion. Then a linearized system obtained by the criterion of force error minimization is used to predict the random response of the original nonlinear system. The nonlinear problems are solved by the linearized system in the modal space, increasing computational efficiency significantly. Higher order statistical information of the response is introduced to improve the accuracy. Typical examples are used to verify the effectiveness of the proposed method, while its applicability is further demonstrated via the analysis of turbulence-excited composite laminates.

Ballistic impact response of reinforced honeycomb sandwich panels

Honeycomb sandwich panels are extensively adopted in a wide range of structures including aircraft, ships, automobiles, and infrastructure for being lightweight and occupying high out-of-plane compression and out-of-plane shear properties. They are evenly popular for their attractive energy absorption capability and resistance to ballistic impacts. Reinforcement of the hexagonal honeycomb panels is an efficient way to improve the impact resistance. However, a detailed study on the reinforcement types against ballistic impacts has not yet been reported. Therefore, the current research investigates the improvement of total energy absorption, ballistic limit velocity, and specific energy absorption (SEA) of three different reinforced hexagonal honeycombs, namely, triangular, circular, and hexagonal reinforcements against high-velocity blunt impacts. A parallel study is also carried out without any reinforcement and only thickening the cell wall of the non-reinforced hexagonal honeycomb panel. A numerical approach is adopted with commercial finite element code Ansys Explicit to analyze the virtual impact cases. The plate of the honeycomb panel is assumed as aluminum alloy Al-7075-T6, while the honeycomb core is made of Al-5083-H116. For both the alloy variants, Johnson-Cook flow stress parameters are utilized. For the projectile, a blunt cylindrical-shaped structural steel bullet is considered. It is found that, for the current investigations, triangular and circular reinforcements can significantly improve the overall ballistic performance of the sandwich panels with a penalty of weight increment. However, thickening the cell wall of the hexagonal core without any reinforcement exhibits the best ballistic performance.