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The present paper focuses on the design of FE for the numerical modelling of failure induced by differential straining in concrete at the meso-scale. The differential straining is here considered as a deformation field added to the mechanical strain field and coming from the solution of a mass transport problem for instance. This differential straining can be induced by changes in degree of saturation, drying shrinkage or fluid overpressure for example. The meso-structure is based on a two-phase 3D representation of concrete, where stiff aggregates are embedded into a mortar matrix. In order to explicitly take into account these aggregates without any mesh adaptation, a weak discontinuity is introduced into the strain field. In addition, a strong discontinuity is also added to take into account cracking. The FE implementation is performed within the Enhanced Finite Element Method (E-FEM). An operator split method equipped with a return mapping algorithm accounting for differential straining is implemented for the computation of the discontinuities values, treated as local variables. In regards to the operator split method proposed in this paper, a broad range of problems can be solved such as basic mass transport problems or failure problem induced both by mechanical loading and differential straining. This feature is an advantage for the design of FE for durability issues. Finally 1D simulations are presented to assess the FE implementation and the performance of the numerical method. We also demonstrate the capability of the method for solving and analyzing 3D mesoscale problems. [ABSTRACT FROM AUTHOR]

In this paper, we develop a domain-decomposed subspace and multigrid solver to analyze the stress distribution for large-scale finite element meshes with millions of degrees of freedom. Through the domain decomposition technique, the shape editing directly updates the data structure of local finite element matrices. Doing so avoids the expensive factorization step in a direct solver and provides users with a progressive feedback of the stress distribution corresponding to the mesh operations: a fast preview is achieved through the subspace solver, and the multigrid solver refines the preview result if the user needs to examine the stress distribution carefully at certain design stages. Our system constructs the subspace for stress analysis using reduced constrained modes and builds a three-level multigrid solver through the algebraic multigrid method. We remove mid-edge nodes and lump unknowns with the Schur complement method. The updating and solving of the large global stiffness matrix are implemented in parallel after the domain decomposition. Experimental results show that our solver outperforms the parallel Intel MKL solver. Speedups of Image 1 can be achieved for large-scale meshes with reasonable pre-computation costs when setting the stopping criterion of the multigrid solver to be 1e−3 relative error. [ABSTRACT FROM AUTHOR]

Shot peen forming is often used to form the aerodynamic configurations of aircraft integral wing panels. The component is traditionally regarded as perfectly constrained target in peen forming process. However, weak-stiffness of the component results in concomitant macroscopic bending and stretching deformations, and releasing of peening stresses. Subsequent peening stresses are induced by shot impacts based on the current released stresses. In this paper, a intermittently peening-releasing finite element simulation model is used to study peening stress evolution in lowrigidity plate. An algorithm is proposed to calculate the increment of subsequent peening stress by connecting current stresses to the peening stresses in perfectly constrained target.With the algorithm, the peen forming deformations of freely constrained plates are calculated by equivalently simulating the peen forming process. And strip peen forming deformations are calculated and compared with experimental data. The comparison shows the peening deformation of a low-rigidity component should be treated as an incremental process and the algorithm can be used to predict the deformation with good accuracy. [ABSTRACT FROM AUTHOR]

This paper presents the task to establish a new and as simple as possible algorithm and method for testing ankle-foot orthoses (AFO) durability. Finite element analysis of the AFO allowed estimate weak points in the structure of orthosis. It was found that in the spring part of the AFO 1047.8 N loading could cause fracture or crack in its structure. Maximal stresses 249.53 MPa were found at the critical point. Distribution of maximal forces was evaluated in all the dynamic conditions of the experiment. The major force acting on the critical point was identified during the jumps (~ 30 N). It does not exceed and is far from loading limits estimated in static simulation test. Created AFO testing method is sufficient for simple initial assessment. [ABSTRACT FROM AUTHOR]

In this paper, an 8-node hexahedral element based on multi-point integration is proposed in the dynamic explicit framework, with a new adaptive subdivision method adopted. By taking advantages of the assumed strain method, the volumetric and the shear locking of the element are successfully avoided. The locking-free hexahedral element is further applied to coining simulations. Due to large-scale elements and high non-linearity, it's difficult to carry out coining simulations in the context of the implicit framework, especially for a commemorative coin with fine patterns. Thus, an explicit algorithm for coining simulations is developed, which avoids time-consuming iterations and guarantees the computational convergence. Aiming at improving the simulation efficiency furtherly, a multi-layer one-to-four adaptive element subdivision strategy is proposed, with two subdivision criteria with respect to element geometry considered. In this way, the element number in the simulation is dramatically decreased, while the fine patterns of the coin are described exactly. Based on several numerical examples, the locking-free and hourglass-free properties of the proposed hexahedral element are validated, and the accuracy of the coining simulation algorithm is also demonstrated. [ABSTRACT FROM AUTHOR]

The paper proposes a stress-driven integration strategy for Perzyna-type viscoplastic constitutive models, which leads also to a convenient algorithm for viscoplastic relaxation schemes. A generalized trapezoidal rule for the strain increment, combined with a linearized form of the yield function and flow rules, leads to a plasticity-like compliance operator that can be explicitly inverted to give an algorithmic tangent stiffness tensor also denoted as the m-AGC tangent operator. This operator is combined with the stress-prescribed integration scheme, to obtain a natural error indicator that can be used as a convergence criterion of the intra-step iterations (in physical viscoplasticity), or to a variable time-step size in viscoplastic relaxation schemes based on a single linear calculation per time step. The proposed schemes have been implemented for an existing zero-thickness interface constitutive model. Some numerical application examples are presented to illustrate the advantages of the new schemes proposed. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In view of the shortcomings such as slow search speed, low optimization precision and premature convergence of artificial hummingbird algorithm, an enhanced artificial hummingbird algorithm based on golden sine factor named DGSAHA is proposed. Firstly, chaos mapping is used to generate the initial candidate solution to increase the diversity of the population, which lays the foundation for the global search. Then, perturb the individuals by means of the differential variation between individuals on the group, thereby enhancing the diversity of the population, preserving the excellent individuals, eliminating the inferior individuals, and guiding the search process to approach the global optimal solution, avoiding the phenomenon of premature convergence. Finally, the golden sine factor were introduced in the guided foraging stage is conducive to the full exploration of the global optimal solution, reducing the search space for individuals to approach the optimal solution. And, it facilitates the balance between "exploration" and "exploitation" of algorithm. Thereby, the accuracy and speed of the DGSAHA can be improved to a certain extent. 25 classic functions, the CEC2014 and CEC2019 benchmark functions were tested, and several representative meta-heuristic algorithms and its improved algorithm are compared for evaluate the validity of DGSAHA. Meanwhile, the dimensional scalability of the variable-dimensional test function is discussed. The results of non-parametric statistical analysis and performance index show that DGSAHA in this paper has better comprehensive optimization performance, significantly improves the search speed and convergence precision, and has strong ability to get rid of the local optimal solution. Finally, the performance of DGSAHA and the practicability of truss structure are answered by three engineering examples of plane and space truss topology optimization problem. This optimization problem considers not only the static constraints such as stress, displacement and buckling, but also the dynamic constraints of frequency and motion stability. In order to avoid singularity and unnecessary analysis, the stiffness, mass and load matrices are reconstructed in finite element analysis. A lighter truss structure than the existing solution is obtained. The validity, extensibility and practicability of the algorithm are further illustrated. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to present a constraint and corresponding algorithm enhancing the evolutionary structural optimization (ESO) method, aiming to circumvent its structure break down problem in some special cases, such as the tie-beam problem. Design/methodology/approach – A virtual soft material introduced to an element will change the stiffness of the element and may consequently change the stress distribution of that element and its neighbors. With this property, the virtual stiffness of the selected element is calculated and the threshold of the stress changes is derived. The stress threshold is used to evaluate the role of an element on the load path and therefore decide the contribution of the element to the structure. Adding this checking operation into the original ESO iterations enables validation of element removal. Findings – The reason for structure break down with the ESO method is that the element removal criterion of ESO only works for certain optimal objectives. It cannot guarantee that the structure does not fail. The proposed operation offers a stronger and stricter constraint condition for ESO’s element removal process, preventing the structure from breaking down in some special cases. Originality/value – The tests on several examples reported in the literature show that the proposed method has the same ability to achieve an optimum solution as the original ESO methods do, while avoiding incorrect deletion of structurally important elements. The benchmark tie-beam problem is solved successfully with this algorithm. The method can be used in other situations as well. [ABSTRACT FROM AUTHOR]

This paper aims to highlight the induced stress occurring under static load in the real-size optimized structure of the double bottom of a chemical tanker. Also, it shortly presents an algorithm of the constructive and functional optimization through the finite element method, numerical modeling of the double bottom structure for the real-size ship with continuous and discontinuous welding being due to be achieved. [ABSTRACT FROM AUTHOR]

Trajectory compression is an efficient way of removing noise and preserving key features in location-based applications. This paper focuses on the dynamic compression of trajectory in memory, where the compression accuracy of trajectory changes dynamically with the different application scenarios. Existing methods can achieve this by adjusting the compression parameters. However, the relationship between the parameters and compression accuracy of most of these algorithms is considerably complex and varies with different trajectories, which makes it difficult to provide reasonable accuracy. We propose a novel trajectory compression algorithm that is based on the finite element method, in which the trajectory is taken as an elastomer to compress as a whole by elasticity theory, and trajectory compression can be thought of as deformation under stress. The compression accuracy can be determined by the stress size that is applied to the elastomer. When compared with the existing methods, the experimental results show that our method can provide more stable, data-independent compression accuracy under the given stress parameters, and with reasonable performance. [ABSTRACT FROM AUTHOR]

• Extension to VCFEM is achieved through enhancements in stress functions. • A new X-VCFEM is proposed to model the interface and matrix cracking in composites. • The matrix crack propagation is determined by the maximum energy release rate. • The interface crack propagation is assessed on the base of a series of criteria. • A remeshing algorithm is constructed. In this paper, a new extended Voronoi cell finite element method (X-VCFEM), in which two new elements in the crack propagation process are proposed and a remeshing algorithm is constructed, is proposed to model the initiation and propagation of the interface crack and the matrix crack in particulate reinforced composites. In order to accurately capture crack-tip stress concentrations, some singular stress terms of Williams expansion in the vicinity of crack tips are introduced in the stress functions in X-VCFEM. The direction of the crack propagation in matrix is determined by the maximum energy release rate and the interface crack propagation along the interface or into the matrix is assessed on the base of a series of criteria relating to the critical normal stress and the critical hoop stress. Then several numerical examples are used to demonstrate the effectiveness of X-VCFEM by comparing with results obtained by the commercial software ABAQUS. At last, a numerical example is given for a complex structure with 20 randomly distributing inclusions to model the interfacial cracking and matrix cracking. It is certain that this method is a powerful way to model the interfacial and matrix damage of composites containing a great deal of inclusions and cracks. [ABSTRACT FROM AUTHOR]

The aim of this paper is the design a new one-step implicit and thermodynamically consistent Energy–Momentum (EM) preserving time integration scheme for the simulation of thermo-elastic processes undergoing large deformations and temperature fields. Following Bonet et al. (2020), we consider well-posed constitutive models for the entire range of deformations and temperature. In that regard, the consideration of polyconvexity inspired constitutive models and a new tensor cross product algebra are shown to be crucial in order to derive the so-called discrete derivatives, fundamental for the construction of the algorithmic derived variables, namely the second Piola–Kirchoff stress tensor and the entropy (or the absolute temperature). The proposed scheme inherits the advantages of the EM scheme recently published by Franke et al. (2018), whilst resulting in a simpler scheme from the implementation standpoint. A series of numerical examples will be presented in order to demonstrate the robustness and applicability of the new EM scheme. Although the examples presented will make use of a temperature-based version of the EM scheme (using the Helmholtz free energy as the thermodynamical potential and the temperature as the thermodynamical state variable), we also include in an Appendix an entropy-based analogue EM scheme (using the internal energy as the thermodynamical potential and the entropy as the thermodynamical state variable). • A new one-step implicit EM time integration scheme for nonlinear thermo-elasticity. • Four discrete derivatives are included in the algorithm. • Algebraic simplification in discrete derivatives with respect to existing algorithms. • Proof of thermodynamic consistency and of second order accuracy with respect to time. • Numerical examples demonstrate the robustness and applicability of the new EM scheme. [ABSTRACT FROM AUTHOR]

In this paper an inverse and iterative method for the identification of material behavior is presented, based on the Finite Element Model Updating (FEMU) strategy. The FE simulations are performed with a commercial FE software code, using a self-implemented elastic material model at finite strain. The iterative identification procedure is based on an experimental test (numerical) whose measured kinematic values are compared to the corresponding simulated ones. Through an optimization algorithm the material parameters are varied in a way that the least-squares sum of the kinematic values is minimized and the optimal material parameters yielding the material behavior are identified. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]