varunr14/newsummary huggingface dataset:
The cohesive zone model approach has been shown to be an effective approach for simulating fracture events . However CZM simulations of quasi static events using an implicit solver usually encounter numerical difficulties due to the nonlinear and softening behavior of CZM . To overcome the numerical difficulties an explicit solver which is intended for fast transient problems can be employed for quasi static events such as stable tearing crack growth . In the current study a CZM based approach is applied to simulate Mode I stable tearing crack growth events in Arcan specimens made of 2024 T3 aluminum alloy by using an explicit solver . The cohesive parameters obtained in a recent study that lead to good predictions for both Mode I and mixed mode I II conditions are used in the current study . In order to shorten the solution time two artificial acceleration techniques are employed acceleration by reducing the time period of the analysis and acceleration by increasing the mass density of the model . A careful convergence study is carried out to gain an understanding of the choice of proper values for the parameters in the artificial acceleration techniques for efficient and accurate simulation predictions and to provide practical experience for CZM simulations in explicit analysis . 


Highlights:
The CZM approach is applied to simulate stable tearing crack growth by explicit solver. A careful convergence study is carried out for selecting proper parameters in the artificial acceleration techniques. Simulation results are validated by experimental data. Valuable practical experience for CZM simulations in explicit analysis is provided.
This paper presents a new finite element formulation for the dynamic analysis of three dimensional beams . The formulation is based on the geometrically exact three dimensional beam theory in which the strain vectors are the only unknown functions of the arc length parameter . The classical Newmark time integration scheme extended to the multiplicative group of spatial rotations is used and properly adapted for the strain based formulation . The Generalized method is used to enforce a numerical dissipation of higher modes . The update procedure needed in the iteration process is discussed in detail . The exact linearization of the governing equations is also presented . The performance of the formulation is demonstrated with numerical examples . 


Highlights:
We study the dynamics of spatial beams based on strain measures. Strain measures are the only unknown functions of the arc length parameter. Additive interpolation of strains gives fully consistent displacement and rotation fields. Present formulation satisfies the equality of equilibrium and the constitutive internal forces. The linearization and the update procedure are novel and presented for the first time.
The treatment of locking phenomena in finite element analysis has been extensively studied over the last decades . Among other techniques the use of Enhanced Assumed Strain methods can lead to formulations that yield good results although sometimes computationally expensive . This is mainly due to the use of enhancing parameters element wise defined and related to the element topology integration scheme and even the problem itself to be solved . The subspace analysis framework is based on a mathematical technique where the constraints to be respected by the formulations are applied at each Gauss point of the finite element mesh . Although this methodology can be found in the literature for some locking pathology it was never applied before to the analysis of transverse shear locking in 3D finite elements . Therefore in the current work the authors expand the existing subspace methodology to take into account the occurrence of this type locking in solid elements . This analysis is developed for different integration schemes in order to assess their performances . Previous EAS formulations are analyzed and an alternative formulation for the EAS parameters is proposed and applied to a set of benchmark linear and nonlinear problems for solid and solid shell elements in order to evaluate the occurrence of locking phenomena and infer about their potential applications . 


Highlights:
Methodology that allows for the adequate choice of enhancing parameters for solid finite element. The developed framework is based on a mathematical technique of subspace analysis. The methodology was expanded to take into account the effects of shear locking. A formulation with in plane reduced integration and hourglass stabilization is presented.
A set of mechanism based constitutive equations was developed to model the effects of microstructure evolution on elastic plastic flow of Q235 steel . This set of equations is implemented into the finite element solver ABAQUS for multi pass shape rolling process simulation . The procedure for multi pass rolling simulation was developed a scheduled multi pass rough rolling process of H shape steel was carried out and the accuracy of the equations was validated by comparisons between the calculated mill load and measured ones . A numerical orthogonal experiment was designed to investigate the effects of rolling parameters on the microstructure evolution . 


Highlights:
A set of mechanism based unified constitutive equations was developed. Procedure for the multi pass rolling simulation was developed and a Scheduled 9 pass H shape rough rolling process was carried out. A numerical orthogonal experiment was designed to investigate the effects of rolling parameters on the microstructure evolution.
The fixed grid finite element method is introduced to approximate the effective moduli of particulate composite . The difficulty of domain discretization induced by the inclusions is avoided in the fixed grid finite element method as the discretization is independent of the inclusions . The elastic properties of every finite element are approximated by a weighted function and the volume fractions of the constituents in the element are taken as the weights . A simple scheme is proposed to approximate the volume fractions in every element . The validities of the fixed grid finite element method are verified by comparing the effective moduli obtained from the fixed grid finite element method with those obtained from finite element method . The anisotropy of particulate composite is discussed with the fixed grid finite element and the applicability of the fixed grid finite element method for composite with multiple irregular inclusions is illustrated . 


Highlights:
The fixed grid finite element method is introduced to approximate the effective moduli of particulate composite. A simple scheme is proposed to calculate the volume fraction of the constituents in every element. The validity of the method is verified for composites both with soft conclusions and with hard conclusions. The availability of the method for composite with multiple irregular inclusions is presented.
In the present paper a three dimensional elasticity approach is employed to investigate buckling of heterogeneous functionally graded plates under biaxial compression shear tension compression and shear compression load conditions . In this regard a formulation that employs a full compatible three dimensional Hermitian element with 168 degrees of freedom and guarantees continuity of the strain and stress components is used . It is known that all of the available famous commercial finite element softwares and the proposed series solutions satisfy continuity conditions of the displacement rather than the stress components . Buckling occurrence is detected based on checking both the instability onset and equilibrium criteria . Results are extracted based on a Galerkin type orthogonality . Therefore they are more accurate than those obtained based on the traditional Ritz method . The presented three dimensional finite element analysis and the extracted results are quite new . A vast variety of results including results of biaxial compression compression tension shear and shear compression load cases is considered and discussed in detail . 


Highlights:
Buckling under various biaxial normal and shear load combinations is investigated. The 3D elasticity theory rather than the approximate plate theories is used. A full compatible 3D Hermitian element with 168 degrees of freedom is used. The stress continuity is guaranteed in the present approach. Results are extracted based on a Galerkin type orthogonality.
Aeroelastic flutter is a dangerous failure mode and aircraft structural components are designed under a deterministic flutter margin . Meeting this safety factor may result in overly conservative structures however an alternative approach incorporates uncertainties into the computational models and imposes a maximum allowable flutter probability during the optimization process . This technique is demonstrated for the variable thickness design of an elastic panel subjected to supersonic flow . A performance measure approach based on the first order reliability method incorporates probabilistic flutter constraints during the search for a minimum mass panel . Optimization results are given for uncertainties in the panel s boundary conditions and for non deterministic thickness design variables . 


Highlights:
Structural optimization for aeroelastic flutter is dictated by an eigenvalue migration problem. Uncertain boundary conditions can be included in the design process for aerospace panels. An efficient compromise between safety and structural mass is obtained with RBDO. The optimal topological distribution of material differs for deterministic and uncertain panels.
In this paper finite element formulation of various four unknown shear deformation theories is presented for the bending and vibration analyses of functionally graded plates . The present theories have strong similarity with the classical plate theory and accounts for shear deformation effects without using any shear correction factors . A four node quadrilateral finite element is developed using Lagrangian and Hermitian interpolation functions to describe the primary variables corresponding to the in plane displacements and transverse displacement respectively . Material properties are assumed to be graded in the thickness direction according to a power law distribution in terms of volume fractions of the constituents . Convergence test and comparison studies are performed for thin and very thick plates to demonstrate the accuracy of the present formulation . 


Highlights:
A new plate element is developed for functionally graded plates. The present element is based on various four unknown shear deformation theories. Numerical examples are presented to verify the accuracy of the present element. The proposed element is capable of modeling both very thin and thick plates.
In this paper a fully coupled numerical model is developed for the modeling of the hydraulic fracture propagation in porous media using the extended finite element method in conjunction with the cohesive crack model . The governing equations which account for the coupling between various physical phenomena are derived within the framework of the generalized Biot theory . The fluid flow within the fracture is modeled using the Darcy law in which the fracture permeability is assumed according to the well known cubic law . By taking the advantage of the cohesive crack model the nonlinear fracture processes developing along the fracture process zone are simulated . The spatial discretization using the extended finite element method and the time domain discretization applying the generalized Newmark scheme yield the final system of fully coupled nonlinear equations which involves the hydro mechanical coupling between the fracture and the porous medium surrounding the fracture . The fluid leak off and the length of fracture extension are obtained through the solution of the resulting system of equations not only leading to the correct estimation of the fracture tip velocity as well as the fluid velocity within the fracture but also allowing for the eventual formation of the fluid lag . It is illustrated that incorporating the coupled physical processes i.e . the solid skeleton deformation the fluid flow in the fracture and in the pore spaces of the surrounding porous medium and the hydraulic fracture propagation is crucial to provide a correct solution for the problem of the fluid driven fracture in porous media where the poroelastic effects are significant . 


Highlights:
A fully coupled XFEM model is used for hydraulic fracture propagation of porous media. The governing equations of porous media are derived using the generalized Biot theory. The fluid flow within the fracture is modeled using the cubic law in the Darcy law. The cohesive crack model is used for the nonlinear fracture process zone. The fluid leak off and the length of crack growth are obtained during the solution.
In this investigation a coupling between a 3D solid shell element for the analysis of multilayered composite shell structures and a specific response surface method is proposed . The first part of the paper is dedicated to the finite element formulation of a developed composite 8 node solid shell element called SCH based only on translational degrees of freedom . The basis of the present finite element formulation is the standard 8 node brick element with tri linear shape functions . A particular attention is given to alleviate shear trapezoidal and thickness locking without resorting to the classical plane stress assumption . Assumed natural strain method and enhanced assumed strain method are used to improve the relative poor element behavior of a standard hexahedral displacement element . The anisotropic material behavior of layered shells is modeled using a fully three dimensional elastic orthotropic material law in each layer including the thickness stress component . The second part of the paper will focus on an adaptive response surface method for the structural optimization problem . The response surfaces are built using moving least squares approximations and design of experiments by means of a specific method called Diffuse Approximation . Several numerical applications to composite multilayered shell structures are studied to show the applicability and effectiveness of the proposed procedure . Good results of analysis and optimization using the developed SCH solid shell element have been obtained in comparison with reference analytical solutions and with those obtained using the SC8R solid shell finite element available in ABAQUS code . 


Highlights:
We develop a new free locking Composite Hex Shell FE no stabilization is required. CPU time savings and better results with the Hex Shell FE compared to 3D bricks. 3D material law with failure criteria may be used with the Hex Shell FE model. New Strategy to reuse the DOE of previous iterations to reduce the FE simulations. A new RSM involving Diffuse Approximation model and pattern search optimization.
In this paper a new locking free element triangular thick plate element with 9 standard kinematic degrees of freedom and 6 additional degrees of freedom for shear strains for analyzing plate shell structures of thin or thick members is developed . With an appropriate use of independent shear degrees of freedom the shear locking problem is completely removed without inducing any numerical expediency such as reduced integration assumptions of strains stresses nor are additional efforts needed to stabilize spurious zero energy modes . Compared to existing triangular shear deformable plate elements that pass patch tests for both thick and thin plates the formulation of the present TTK9S6 element is very simple and perhaps as simple as possible . A number of numerical examples are tested showing the convergence and accuracy of the TTK9S6 element . 


Highlights:
We present a locking free element capable of analyzing plate shell structures without introducing any numerical expediencies. This new triangular shear deformable plate element passes patch tests either for thick or for thin plates. The proposed element has a simple formulation meanwhile it shows satisfactory convergence performance and possesses high accuracy.
During the past decade materials that display novel properties in the acoustic realm so called acoustic metamaterials have attracted much attention since these properties can provide promising opportunities to design new acoustic devices that can not be made with natural materials . Although acoustic metamaterials that exhibit negative mass density or negative bulk modulus and double negative acoustic metamaterials have been obtained experimentally by trial and error our aim is to develop a topology optimization method for the direct design of acoustic metamaterials based on the concept of local resonant mechanisms which ensures that the lattice constant is orders of magnitude functionally smaller than the corresponding sonic wavelength and avoids unwanted effects of Bragg scattering mechanisms . This paper proposes a level set based topology optimization method for the structural design of acoustic metamaterials that achieve an extremely negative bulk modulus at certain prescribed frequencies . Level set based topology optimization methods can directly provide clear boundaries in optimal configurations that avoid the presence of grayscales . The optimization problem is formulated for a two dimensional wave propagation problem with the objective being to minimize the effective bulk modulus at chosen target frequencies . An effective medium description based on S parameters is introduced to describe the acoustic metamaterial . Finite element method is used to solve the Helmholtz equation for acoustic waves sensitivities are obtained with the adjoint variable method and a reaction diffusion equation is used to update the level set function . Several numerical examples with prescribed target frequencies and different initial shapes are provided to demonstrate that the proposed method can provide clear optimized structures for the design of negative bulk modulus acoustic metamaterials . 


Highlights:
We propose a level set based topology optimization to design acoustic metamaterials using the Finite Element Method. We formulate the optimization problem using effective material properties. A two step optimization process enabled to handle the design of effective bulk modulus. In all examples we successfully obtain optimized shapes with negative bulk modulus.
A new approach for extracting stress intensity factors by the element free Galerkin class of methods through a modified crack closure integral scheme is proposed . Its primary feature is that it allows accurate calculation of mode I and mode II SIFs with a relatively simple and straightforward analysis even when a coarser nodal density is employed . The details of the adoption of the MCCI technique in the EFG method are described . Its performance is demonstrated through a number of case studies including mixed mode and thermal problems in linear elastic fracture mechanics . The results are compared with published theoretical solutions and those based on the displacement method stress method crack closure integral in conjunction with local smoothing technique as well as the M integral method . Its advantages are discussed . 


Highlights:
Adoption of modified crack closure integral MCCI in meshfree methods for evaluation of stress intensity factors SIFs . Comparison of MCCI technique with M Integral technique displacement method etc. Case studies on mixed mode crack problems involving remote loading crack face loading and thermal loading. Effect of enrichment functions order of Gauss integration domain of influence and nodal density on accuracy of SIFs.
This paper presents a decoupled Arbitrary Lagrangian Eulerian approach for the large deformation analysis of plane strain elastoplastic problems . In this decoupled approach the Eulerian step consists of first remeshing the deformed continuum and then remapping the state variables at the new quadrature points . Remeshing is performed without altering the element topology of the original mesh with the aid of the Spring Analogy Method enhanced with torsional springs . Before remeshing nodes at free boundaries are relocated using an analytical approach in order to preserve a good node distribution throughout the analysis . State variable remapping is achieved through the Radial Basis Point Interpolation Functions scheme . Large deformation elastoplastic analyses of two plane strain example problems are conducted using the presented ALE approach to test its robustness and effectiveness . The continuum is modeled as a Tresca or Mohr Coulomb elastic perfectly plastic material while the meshes consist of second order finite elements . The numerical results demonstrate that the present methodology is capable of predicting with adequate accuracy the load displacement response even in analyses involving very large translations of the loaded boundary . 


Highlights:
Remeshing is achieved using the enhanced Spring Analogy Method. State variable remapping is accomplished through the RBF interpolation scheme. We achieved very large deformation penetration simulations of plane strain elastoplastic problems. Obtained numerical results are in good agreement with limit analysis solutions.
This paper presents a novel Timoshenko beam element based on the framework of strain gradient elasticity theory for the analysis of the static bending free vibration and buckling behaviors of Timoshenko microbeams . The element proposed is a two node element which has 6 DOF at each node considering both bending and stretching deformations and 4 DOF considering only bending deformation . Unlike the classical Timoshenko beam element the current element satisfies the C 0 continuity and C 1 weak continuity and contains three material length scale parameters to capture the size effect . Finite element formulations are derived by utilizing the corresponding weak form equations . Convergence shear locking and comparison studies are carried out to examine the reliability and accuracy of the numerical solutions . The shear locking study shows that the present beam element is free of shear locking . Besides it is established that there is a good agreement between the present results with the results in existing literature . To further illustrate the applicability and accuracy of the new Timoshenko beam element the static bending free vibration and buckling problems of microbeams with various boundary conditions are covered by the analysis . The results show that such small size effects are significant when the beam thickness is small but become negligible with increasing beam thickness . Some results are believed to be the first known in the open literature and can be used as a benchmark for further studies . 


Highlights:
A new Timoshenko beam element is proposed. The current element satisfies the C 0 and C 1 weak continuities. Three material length scale parameters are contained in a stiffness matrix. This element is free of shear locking. Excellent agreement is achieved between the present results and literature.