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X-Frame core sandwich structures are fabricated with carbon fiber reinforced polymer (CFRP) face sheets and aluminum alloy cores. The hybrid combination enables composite face sheets to maximize specific flexural stiffness and X-Frame metal core to improve the impact resistance. The effects of impact energy, impact site and face sheet material type on the impact response and resulting damage state have are investigated experimentally and numerically. The low-velocity impact tests are carried out to study the impact response in terms of the impact load, absorbed energy and failure modes. Meanwhile, finite element analysis is implemented to simulate the impact behaviors and failure mechanisms by the VUMAT subroutine in ABAQUS/Explicit, using a progressive damage model based on the Hashin and Yeh delamination failure criteria. For comparison, all-metallic sandwich structures are also studied to better understand the influence of face sheet materials. These studies reveal that impact response and resulting damage state are strongly dependent on the impact energy and impact site. Composite sandwich structure absorbs more impact energy than aluminum sandwich structure for the perforation case, indicating that the former has better impact resistance. The predicted results of the low-velocity impact response are fairly consistent with the experimental measurements, which suggests that the numerical procedure could be a helpful tool in developing novel lightweight multifunctional structures. [ABSTRACT FROM AUTHOR]

The present study developed and implemented a new visco-hyperelastic model that is capable of predicting the time-dependent biomechanical behavior of the periodontal ligament. The constitutive model has been implemented into the finite element package ABAQUS by means of a user-defined material subroutine (UMAT). The stress response is decomposed into two constitutive parts in parallel which are a hyperelastic and a time-dependent viscoelastic stress response. In order to identify the model parameters, the indentation equation based on V-W hyperelastic model and the indentation creep model are developed. Then the parameters are determined by fitting them to the corresponding nanoindentation experimental data of the PDL. The nanoindentation experiment was simulated by finite element analysis to validate the visco-hyperelastic model. The simulated results are in good agreement with the experimental data, which demonstrates that the visco-hyperelastic model developed is able to accurately predict the time-dependent mechanical behavior of the PDL. [ABSTRACT FROM AUTHOR]

A numerical investigation was carried out to analyze in details the perforation process of target AA5754-O Aluminum plate when subjected to normal impact at low (up to 25 ms − 1 ) and moderate velocities (ranged between 25 − 50 ms − 1 ). A fully coupled elasto-visco-plastic-damage model is implemented into a user-defined material (VUMAT) subroutine for the commercial finite element code ABAQUS/Explicit. The strain rate effect is considered. Comparison between isotropic J 2 and orthotropic Hill yield criteria associated with isotropic and mixed non-linear isotropic/kinematic hardening was conducted. A parametric study of the effect of anisotropy, plate thickness and impactor nose shapes on ballistic limit and petal forming is carried out. A good agreement is found between numerical and experimental results conducted by other researchers. [ABSTRACT FROM AUTHOR]

The objective of this paper is to assess the reliability and effectiveness of the method of finite spheres, a truly meshless overlapping finite element method, for the solution of practical three-dimensional linear elasticity problems. Advantages include simplified discretization and the elimination of element distortion. The method is implemented in the ADINA finite element program through a user-supplied element subroutine. The solutions of three increasingly complex three-dimensional problems are studied (1) to establish the reliability of the method for practical linear elasticity problems and (2) to assess the effectiveness of the method as compared to the standard finite element method. The solutions indicate that the method of finite spheres is between one and two orders of magnitude more expensive in computational time than the standard finite element method. This is still a promising result since there are significant time savings for the method of finite spheres during the pre-processing phase, particularly in the discretization of complicated three-dimensional geometries and because the overlapping sphere elements can be directly coupled to traditional finite elements. [ABSTRACT FROM AUTHOR]

The simulation of progressive collapse of a power transmission tower-line system subjected to extremely strong earthquakes is studied in this paper. A three-dimensional finite element model is established for the coupled system that combines three towers and four span lines based on a practical project. The birth to death technique is adopted to simulate the progressive collapse of the system by using the user subroutine VUMAT in ABAQUS. The simulation of progressive collapse of the transmission tower-line system under either single-component or multi-component earthquake excitations is conducted. The collapse path, fracture position and collapse resistant capacity of the transmission tower are investigated. The result shows that the effect of multi-component seismic excitations should be taken into account in simulation of progressive collapse of the transmission tower, since the behavior of towers under multi-component excitations is different from that of single-component excitations. In addition, incremental dynamic analysis (IDA) is carried out to verify the results obtained herein. The present result should prove useful to the seismic design of power transmission towers. [ABSTRACT FROM AUTHOR]

Chaboche kinematic hardening, Yoshida–Uemori, and homogenous anisotropic hardening (HAH) models were evaluated in terms of their prediction capability of flow stress and evolutionary r-value under loading path changes. The first two models are based on kinematic hardening, whereas the HAH model is based on distortional hardening. Continuous compression–tension (CT) tests with pre-strains for dual-phase 780 and transformation-induced plasticity (TRIP) 780 steel sheets were conducted. For the initial anisotropy described by the Yld2000-2d model, uniaxial tension tests for three material orientations and a biaxial test were performed. During the CT tests, both stress and r-value variations with plastic strain were measured. All the models were implemented into the finite element software ABAQUS using user material subroutines. Experimentally, both sheets exhibited typical anisotropic hardening features such as the Bauschinger effect, transient hardening, and long-range softening. The TRIP 780 exhibited small work-hardening stagnation. In addition, the evolutionary r-value during the second loading was significant. The three models could predict most of the features in the stress–strain curves during the second loading. However, only the HAH model could predict the experimentally observed r-value evolution. This evolutionary r-value predicted by the HAH model could be explained by distortion of the yield locus during the first loading and its rapid recovery toward the initial yield locus shape. [ABSTRACT FROM AUTHOR]

Braided textile composite exhibits an efficient mechanism to distribute loads throughout its structure and have excellent impact resistant properties. Despite many works in the past, the successful prediction of braided textile composites strength still remains a challenge today. In this paper, a numerical simulation model based on a meso-scale approach is presented to predict the strength and damage behavior of braided textile composites. A meso-scale homogenized representative unit cell was built for the study using finite element analysis (FEA) method. 3D-Hashin and Stassi failure criteria were respectively selected for the yarn and the pure matrix, and coded in a subroutine in Abaqus finite element solver to study the individual constituents damages. From the different numerical studies, the failure mechanisms were observed to change with the braiding angle. The meso-scale computed results were also seen to agree closely with experimental and simulation results computed using a micro-mechanics failure approach. [ABSTRACT FROM AUTHOR]

Lateral-torsional buckling (LTB) is an ultimate limit state that can occur in the hogging moment regions of continuous composite steel and concrete beams. This limit state is characterised by the buckling of the steel profile compressed flange (bottom flange) about the minor axis, together with a distortion of the steel profile web. The European Standard EN 1994-1-1:2004 provides an approximate procedure for LTB design that is applicable to continuous composite beams, but only those with a plane web steel profile. The most important step of this procedure is the determination of the elastic critical moment. In this paper, a finite element analysis (FEA) model was developed using the software ANSYS to determine the elastic critical moments of continuous composite steel and concrete beams with corrugated sinusoidal-web steel profiles, which were evaluated against numerical data from the literature. Ultimately, a study involving 45 models was conducted based on FEA modelling, and a procedure for predicting the elastic critical moment of composite beams with sinusoidal-web steel profiles was proposed. [ABSTRACT FROM AUTHOR]

In this work, the thermal and mechanical responses of shape memory alloys are studied under different loading and boundary conditions. To this end, a common one-dimensional constitutive model for shape memory alloys capturing both pseudoelasticity and shape memory effect is implemented into ABAQUS commercial finite element package via a user material subroutine. The main benefit of this one-dimensional user material is its capability to simulate any mechanical as well as thermal loading path. Hence, it can be utilized in finite element simulation of any complicated smart structure consisting of shape memory alloy wires. To validate the proposed numerical approach, its predictions are shown to be in a good agreement with those obtained by analytical and other approved numerical solutions under different thermal and mechanical loading and boundary conditions. Since shape memory alloys are integrated into many applications as actuation elements, the actuation response of an axial shape memory alloy actuator heated from one end is studied using finite element method. Finally, the developed user material is employed in finite element simulation of a smart landing gear as a real-world smart structure. [ABSTRACT FROM AUTHOR]

In this paper, progressive debonding of the blade root joint of a 660 kW wind turbine under cyclic loading is studied. Progressive fatigue debonding of this adhesive joint is analyzed using cohesive zone interface modeling. The blade is subjected to various loadings such as aerodynamic forces, centrifugal force, weight, and force due to the change in wind direction. A user defined material subroutine is used in the ANSYS finite element code to predict both the crack (debonding) initiation and propagation in the adhesive joint under variable amplitude fatigue loading. The required material properties such as the critical strain energy release rate and the Paris law constants are characterized experimentally through the well-known tests for different fracture modes: double cantilever beam (DCB) for mode-I (opening mode), end notch flexure (ENF) for mode-II (shearing mode) and mixed mode bending (MMB) for mixed mode conditions. These tests are performed for composite to aluminum interfaces, which are representative of the actual material used in the manufacturing of the wind turbines blades. The experiments are performed under both static and fatigue loading. The predicted initiation and progressive damage results from numerical analyses are verified by experimental results for simple joints. It is illustrate that the maximum length of the deboned area after a typical overloading is about 8% of the total height of the root joint and during the fatigue loadings it would increase to about 40% of the total height after 1 month normal operation. The developed numerical analysis tool can then be used to predict the debonding initiation and propagation in the root joint of the wind turbine blades. [ABSTRACT FROM AUTHOR]

In this paper the complex thermomechanical behaviour at the tool – workmaterial interface in machining has been analysed. The contact behaviour is formulated in the frame of a Lagrangian Finite Element approach. The thermomechanical laws governing the tool – workmaterial interface in machining have been implemented via the VUINTER subroutine of ABAQUS/Explicit FE code. Using this interface, velocity dependent heat partition coefficient of the frictional heat has been implemented. Numerical results (calculated heat flux transmitted into the tool and cutting force) have been compared to experimental ones for different cutting conditions, which are in good agreement. It is shown that different couples of the heat partition and heat transfer coefficients can give the same heat flux transmitted in the tool. In addition, with the new developed VUINTER subroutine, it is possible to implement any mathematical model governing the friction and heat exchange for simulations of complex contact behaviours. [ABSTRACT FROM AUTHOR]

Abstract: Fibre-reinforced polymer-based composite materials fail due to a wide variety of interacting damage mechanisms, which require complex constitutive models in order to develop Finite Element (FE) predictive analysis. In this paper, a constitutive behaviour model based on Continuum Damage Mechanics (CDM) is proposed for the simulation of fabric-reinforced composites. The model uses simplified loading functions in order to minimise the computational time required to obtain the numerical solution. To reduce the influence of mesh refinement on the numerical solutions, the Crack Band Model (CBM) algorithm is implemented. In this way, the energy dissipated at each point in the material is regularized for the different damage mechanisms. This newly-formulated constitutive model is implemented by means of a user-defined material subroutine in Abaqus/Explicit FE code. The model is validated by comparing the results of FE predictions with experimental data from open hole specimens, under quasi-static tensile loading conditions. A good correlation between the numerical and experimental results is achieved when using a bilinear cohesive law, for different combinations of hole diameter and specimen width. [Copyright &y& Elsevier]

Abstract: This paper investigates the response of composite sandwich beams with honeycomb core subjected to low-velocity impact by using a finite-element model implemented in Abaqus/Explicit code. The face-sheets behaviour was modelled through a VUMAT subroutine, in which a failure model based on Hou failure criteria was implemented. The aluminium honeycomb core behaviour was defined as an elastic–plastic material. A series of low-velocity impact tests were carried out to validate the numerical model. Good agreement, in terms of contact-force histories, energy histories, absorbed energy, and failure of the sandwich beam was observed between the experimental data and the numerical results. The contribution of both the face-sheets and the core to the energy absorption process was analysed separately. It was found that the core controlled the energy absorption of the sandwich beams at the lowest impact velocities studied; however, at higher impact velocities the face-sheets were more involved. [Copyright &y& Elsevier]

Highlights: [•] Presents asynchronous variational integrators in the context of finite elements with continuous strain fields. [•] Illustrates an enhanced interpretation of the current space–time front. [•] Provides a strategy for estimating the critical time step size using CAG elements, nodal integration or SFEM. [Copyright &y& Elsevier]

Abstract: A potential-based cohesive zone model, so called the PPR model, is implemented in a commercial software, e.g. ABAQUS, as a user-defined element (UEL) subroutine. The intrinsic cohesive zone modeling approach is employed because it can be formulated within the standard finite element framework. The implementation procedure for a two-dimensional linear cohesive element and the algorithm for the PPR potential-based model are presented in-detail. The source code of the UEL subroutine is provided in for educational purposes. Three computational examples are investigated to verify the PPR model and its implementation. The computational results of the model agree well with the analytical solutions. [Copyright &y& Elsevier]

Abstract: This paper shows that the generalized finite element method with global–local enrichment functions (GFEMgl) can be implemented non-intrusively in existing closed-source FEM software as an add-on module. The GFEMgl is based on the solution of interdependent global (structural) and local (crack) scale problems. In the approach presented here, an initial global scale problem is solved by a commercial finite element analysis software, local problems containing 3-D fractures are solved by an hp-adaptive GFEM software and an enriched global scale problem is solved by a combination of the FEM and GFEM softwares. The interactions between the solvers are limited to the exchange of load and solution vectors and does not require the introduction of user subroutines to existing FEM software. As a results, the user can benefit from built-in features of available commercial grade FEM software while adding the benefits of the GFEM for this class of problems. Several three-dimensional fracture mechanics problems aimed at investigating the applicability and accuracy of the proposed two-solver methodology are presented. [Copyright &y& Elsevier]

This paper deals with the design of Ni47Ti44Nb9 shape memory alloy (SMA) tightening components. The tightening of an SMA ring on an elastic pipe is analyzed using the finite element code ABAQUS® and a UMAT subroutine developed by the authors to model the specific behavior of Ni47Ti44Nb9 SMA. Main features of the thermomechanical model implemented in this UMAT routine are briefly recalled. Numerical predictions are validated using experimental tightening pressures obtained on a test bed developed in this work. The validation strategy is documented and the results for different ring thicknesses are presented. This finite element tool is then applied to a parametric study of the influence of ridges on the tightening pressure. Eventually, geometrical defects like out of roundness are considered. [ABSTRACT FROM PUBLISHER]

Abstract: This article is concerned with implementing the Arlequin method into the commercial finite element software ABAQUS and demonstrating its versatility in various typical applications. According to the basic idea of the Arlequin method, the particular formulations for the ABAQUS user element are presented. A unified method for calculating coupling matrices is proposed in an obvious and straightforward way. The user element subroutines for coupling two relatively independent models with different or same dimensions are developed. Four numerical examples are considered: One is to demonstrate the coupling of elements with the same element type but different grid density by the Arlequin method, and the other three examples involve different types of elements. The numerical results justify the correctness of the codes developed for the user defined elements as well as the feasibility of the Arlequin method which is successfully integrated into ABAQUS. [Copyright &y& Elsevier]

Abstract: In this paper, we introduce an implementation of the extended finite element method for fracture problems within the finite element software ABAQUSTM. User subroutine (UEL) in Abaqus is used to enable the incorporation of extended finite element capabilities. We provide details on the data input format together with the proposed user element subroutine, which constitutes the core of the finite element analysis; however, pre-processing tools that are necessary for an X-FEM implementation, but not directly related to Abaqus, are not provided. In addition to problems in linear elastic fracture mechanics, non-linear frictional contact analyses are also realized. Several numerical examples in fracture mechanics are presented to demonstrate the benefits of the proposed implementation. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to describe an efficient method to connect two independent softwares so as to jointly use best qualities of each software around a complex problem solved by the finite element method (FEM). This connection makes it possible to extend quickly and easily the applicability of new models developed in academic softwares, by their simultaneous use with commercial softwares. This is particularly interesting when these models are very difficult to implement directly in commercial softwares. Most of the commercial FEM applications allow users to add additional features, physical models or boundary conditions via a programming interface. Within these user routines, access to internal data structures is possible, either through subroutine parameters and global variables, or via internal modules for reading and storing data. We use these capabilities to link the commercial software ABAQUS and an academic object-oriented C++ software HEREZH++, via the user-defined mechanical material behaviour (Umat). In this interface, HEREZH++ computes the mechanical behaviour of material and the code coupling performs a communication procedure between ABAQUS and HEREZH++. This paper describes this architecture which allows to implement easily original behaviour law in the commercial ABAQUS code. The asynchronous code coupling is made with a named piped interprocess communication method and an interface written in c/C++. Several test samples are presented to show the efficiency and accuracy of the proposed implementations concerning the computational time. In particular, an industrial test is carried out with an original behaviour model of elasto–visco-hysteresis which would have been very difficult to implement directly in ABAQUS. [Copyright &y& Elsevier]

Abstract: A finite-element-based inverse method has been developed to allow the characterization of the heterogeneity and nonlinearity in material properties of isotropic nuclear graphite using a single experimental test. The method is implemented into the commercial finite element code ABAQUS using its User Material (UMAT) Subroutine for ease of application. The program has been verified using simulated examples with idealized distributions of elastic modulus and the results showed rapid convergence with good accuracy. Finally, the method was applied to actual mechanical testing of nuclear graphite for which the heterogeneous distribution and nonlinearity of material properties were evaluated. [Copyright &y& Elsevier]

A mathematical algorithm which integrates the constitutive equations for the ductile fracture process in viscoplastic materials is described. The algorithm has been implemented in the finite-element commercial code ABAQUS by means of a constitutive USER subroutine. Based on the computational cell methodology proposed by Xia and Shih, the R-curves for pre-cracked Charpy specimens under different dynamic load conditions are obtained. In all cases it is observed that the mathematical algorithm is able to reproduce the increase in the material resistance to ductile tearing as the impact speed increases. [ABSTRACT FROM AUTHOR]

Abstract: The elasto-plastic constitutive equation accounting for isotropic hardening coupled with material damage has been implemented in the finite element code ABAQUS. A damage variable, which was defined in meso-scale, was used to reveal the effects of micro-defects within the material. With an explicit integration scheme, deep drawing of a mild steel square cup was simulated using the ABAQUS with a specially designed VUMAT subroutine. The three-dimensional brick element was adopted to build-up the finite element model, and the contact and friction between the blank and tool were taken into consideration. The forming process of deep drawing is a non-proportional loading one, so that the accumulated damage state variable depends on the strain path, or in other words, the loading history. The damage evolution and the wrinkle formation under the influences of Coulomb friction and the blank holding force were analyzed and discussed. Experiments have been conducted to investigate the effect of blank holding force on wrinkling, and determine the position of crack initiation. Experimental results are in good agreement with the predicted ones. [Copyright &y& Elsevier]

Asphalt paving layers, particularly the surface course, exhibit vertically graded material properties. This grading is caused primarily by temperature gradients and aging related stiffness gradients. Most conventional existing analysis models do not directly account for the continuous grading of properties in flexible pavement layers. As a result, conventional analysis methods may lead to inaccurate prediction of pavement responses and distress under traffic and environmental loading. In this paper, a theoretical formulation for the graded finite element method is provided followed by an implementation using the user material subroutine (UMAT) capability of the finite element software ABAQUS. Numerical examples using the UMAT are provided to illustrate the benefits of using graded elements in pavement analysis. [ABSTRACT FROM AUTHOR]