Simulation Of Mechanical Behavior Research Articles

Three‐dimensional cohesive finite element simulations of mechanical behavior of polymer‐bonded explosives under quasi‐static tensile loading

AbstractMicrostructural features such as voids, microcracks and interfaces play an important role in the mechanical properties of polymer‐bonded explosives, which significantly decide the performance, safety and reliability. A series of micron‐scale 3D models were constructed, and a 3D cohesive finite element method in a commercial software was used to study the elastic properties and fracture development of HMX/Estane polymer‐bonded explosives under quasi‐static tension. The predicted Young's modulus of HMX/Estane PBX with particle volume fraction of 92.7 % at 0.01 s−1 is 2.24 GPa, which is only 7.4 % different from the experimental result. 3D models perform better than 2D models in the prediction of Young's modulus and Poisson's ratio, and the difference between 2D and 3D results can be up to 40 %. In addition, the effect of particle size on the mechanical properties is investigated. It is shown that 3D models can correctly describe the relationship of particle size with stress‐strain curves and fracture development of PBX. Results demonstrate that a 3D model is necessary in the study to delineate the relationships between microstructural features and the mechanical behavior of polymer‐bonded explosives.

Numerical simulation of mechanical behavior of rock samples under uniaxial and triaxial compression testsy

Purpose. The research aims to investigate how the load influences the ultimate compressive strength of rocks at failure. It uses both a uniaxial compression test, which involves incremental displacements, and a triaxial compression test, which applies varying confining stresses while maintaining a constant axial compression stress and incrementally increasing the displacement. Methods. To conduct the investigation, the researchers used RS2D, a rock-soil software, to examine the impact of different incremental displacements and confining stresses on the strength properties of various rock samples. The numerical analysis includes Fayum argillaceous sand, Sinai coal, Aswan granite, Assiut limestone, and Red-Sea phosphate. Findings. The research findings indicate that the ultimate compressive strength of rocks at failure is achieved with minor incremental displacements. Conversely, an increase in the confining stress leads to higher ultimate tensile strength, deviatoric stresses, and volumetric strain. However, the stress factor decreases in relation to the axial strain percentage. Originality. The simulator adopts Mohr-Coulomb failure criterion, presents and discusses the results in terms of stress-strain (σ-ε) curves, stress ratio (σ1/σ3), deviatoric stresses (σ1-σ3) and volumetric strain with respect to the percentage of axial strain. Practical implications. Using numerical modeling analysis, it becomes possible to reproduce the rock failure mechanisms observed in uniaxial and triaxial compression tests. This methodology has the potential to reduce the need for extensive experimental testing when assessing the tensile strength of rocks under different loads. As a result, both time and costs can be minimized.

Numerical simulation of mechanical behaviors and intergranular fracture of polycrystalline Nb3Sn and superconducting filaments

Given the importance of large-scale engineering applications of the superconducting compound Nb3Sn, both its use and performance under certain operating conditions have attracted the interest of applied superconductivity researchers and material scientists for several years now. Huge efforts are directed toward understanding the response to applied loads and predicting fracture damage within their internal microstructure; this is fundamental in the design of superconducting coils and magnets which must meet stringent requirements in terms of maximum thermal and electromagnetic loads. In this paper, the fracture behaviors in polycrystalline Nb3Sn and Nb3Sn filaments with composite structures are investigated using the micromechanical finite element (FE) models with Voronoi tessellation. First, the 2D and 3D Voronoi FE models of the polycrystalline Nb3Sn tensile tests are developed and validated to provide insight into the cracking behavior in the intergranular brittle fracture of polycrystalline Nb3Sn. A cohesive zone model is used to simulate crack propagation at the grain level model including grain boundary zones. It is found that the pre-existing cracks of polycrystals and martensitic phase transformation of grains significantly impact the fracture properties in polycrystalline Nb3Sn. Second, detailed FE models of powder-in-tube (PIT) and bronze route filaments with Voronoi structures for fracture analysis are then developed on the basis of experimental observations of sectional morphologies. The mechanism of crack initiation and propagation under tensile load have been investigated by analyzing the mechanical properties of each component and the characteristics of multi-scale composite structures of filaments. Furthermore, the damage situation is investigated in PIT filaments undergoing transverse compressive load. The proposed simulation method in this paper can be extended to the fracture and damage analysis of Nb3Sn superconducting wires with different layouts and fabrication processes.

Study on the Restoration of Class II Carious Cavities by Virtual Methods: Simulation of Mechanical Behavior.

The restoration of class II cavities is predominantly carried out with composite materials. Due to the high failure rate in restoring this type of cavity, composite materials with much-improved properties and new application techniques have been promoted. The study aimed to analyze the mechanical behavior of several topical composite materials (nanocomposites, nanohybrids and ormocer) using different application techniques. In a lower second molar, a class II occlusal cavity was prepared. As filling materials, we used the following combinations: Admira Fusion and Admira Fusion Flow, Grandio and Grandio Flow, Filtek Supreme XT and Filtek Supreme Flow. These were applied using a snow plow, injection molded and Bichacho techniques. Three-dimensional scanning of the molar with the prepared cavity was performed, and then scanning of each layer of added composite material was performed, obtaining three-dimensional models. The virtual molar models were analyzed with software specific to the finite element analysis method, where their physical-mechanical properties were entered and assigned to the components of the virtual molar. Simulations at high forces specific to bruxism were then carried out and analyzed, and compared. The values of displacements and strain, for all six analyzed situations, are relatively small (range from 5.25 × 10-6-3.21 × 10-5 for displacement, 6.22 × 10-3-4.34 × 10-3 for strain), which validates all three methods and the materials used. As far as the stress values are concerned, they are similar for all methods (250-300 MPa), except for the snow plow and injection-molded techniques using Grandio and Grandio Flow composites, where the maximum von Mises stress value was more than double (approximately 700 MPa). When using the combination of Grandio and Grandio Flow materials, the 1 mm thickness of the fluid composite layer was found to have a major influence on occlusal forces damping as opposed to 0.5 mm. Therefore, the Bichacho technique is indicated at the expense of the snow plow and injection-molded techniques. The composite materials used by us in this study are state-of-the-art, with clear indications for restoring cavities resulting from the treatment of carious lesions. However, their association and application technique in the case of Class II cavities is of clinical importance for resistance to masticatory forces.

Atomistic simulation of mechanical behavior of Cu/Cu3Sn solder interface with Kirkendall void under shear and tensile deformation

Atomistic simulation of mechanical behavior of Cu/Cu3Sn solder interface with Kirkendall void under shear and tensile deformation

Numerical Simulation of Mechanical Behavior of Gas Pipeline in High and Steep Slope

Long-distance natural gas pipelines can often pass through the common slope safely. However, when pipelines inevitably pass through high and steep slopes(HSS) for some reasons, it is difficult for engineers to predict the stress state of pipelines. Therefore, in order to investigate the safety of natural gas pipelines in HSS areas, the finite element simulation calculation model of the pipeline in HSS was established. The predicted numerical model shows that the maximum Von Mises stress and axial strain of the pipeline in the HSS area appear at the lower elbow of the pipeline, which should be paid more attention to in the risk assessment; The stress and deformation of the pipeline is mainly related with the wall thickness and internal pressure, appropriately increasing the wall thickness and reducing the internal pressure can improve the safety of HSS pipelines.

Erratum to: Experimental and Numerical Simulation of Mechanical Behaviour of Ultrafine Grained AA 2014 Al Alloy

Erratum to: Experimental and Numerical Simulation of Mechanical Behaviour of Ultrafine Grained AA 2014 Al Alloy

The fracture mechanical behavior simulation of calcium-deficient hydroxyapatite crystals by molecular dynamics and first-principles calculation

Natural hydroxyapatite provides certain strength and stiffness to biological bones, and most of the studies on the strength of bone tissues have been carried out on hydroxyapatite (HAP). However, the Ca/P ratio of hydroxyapatite in bones is actually about 1.50, and the natural hydroxyapatite belongs to calcium-deficient hydroxyapatite (CDHA) with Ca vacancy defects. Therefore, this work focused on the effect of Ca vacancy defects on CDHA crystals through investigating the generation and expansion of microcracks under uniaxial tensile loading by combining molecular dynamics and first principles method. A series of crystal models with different Ca vacancy ratios are constructed and find that Ca vacancies degrade the mechanical properties of hydroxyapatite. Meanwhile the fracture behavior of crystals is detailed and find that the cracks arise at vacancies and extend along the direction of vacancies. Also, first-principles calculation is performed to reveal the mechanism of crack formation in MD simulations. It is found that the decrease of Ca–O bonding of CDHA causes the decrease of the stability of the crystal structure by analyzing the DOS of HAP and CDHA, and the cracks originate from Ca vacancies. This work performs more realistic simulations of CDHA with calcium vacancy defects in actual bone tissue and directly reveals the development and progression of bone fragility at the nanometer scale.

Performance of different traditional and machine learning-based atomistic potential functions in the simulation of mechanical behavior of Fe nanowires

Characterization of nanoscale material properties using experimental methods is difficult due to their high costs and complexities. Hence, many researchers apply alternative techniques, such as atomic/molecular simulations, to overcome the limitations of experimental methods. A well-established method to study material behavior at nanoscales is molecular dynamics simulation. However, the accuracy of its results is highly dependent on the selection of appropriate potential functions/force fields modeling atomic interactions. This work investigates the effects of considering different potential functions on the mechanical characteristics of BCC Fe nanostructures using molecular dynamics simulations. Laboratory data are used to verify the calculated elastic properties of bulk structures. Furthermore, systematic simulations are performed to determine the elastic properties of nanowires under tensile loading, various potential functions, and different temperatures. According to the results, Ackland's potential function and experimental data are in excellent agreement. On the contrary, Asadi's potential function shows an opposite trend comparing other functions and experimental mechanical data. In addition, the potential function formulated based on artificial neural networks is capable to capture tension-induced necking phenomena in Fe nanowires.

Viscoelastic Characterization of a Thermoplastic Elastomer Processed through Material Extrusion.

Objective. We aim to characterize the viscoelastic behavior of Polyether-Block-Amide (PEBA 90A), provide reference values for the parameters of a constitutive model for the simulation of mechanical behaviors, and paying attention to the influence of the manufacturing conditions. Methods. Uniaxial relaxation tests of filaments of PEBA were used to determine the values of the parameters of a Prony series for a Quasi-Linear Visco-Elastic (QLVE) model. Additional, fast cyclic loading tests were used to corroborate the adequacy of the model under different test criteria in a second test situation. Results. The QLVE model predicts the results of the relaxation tests very accurately. In addition, the behavior inferred from this model fits very well with the measurements of fast cyclic loading tests. The viscoelastic behavior of PEBA under small strain polymer fits very well to a six-parameter QLVE model.

Simulation of Mechanical Behaviour of Woven Fabrics at the Scale of Yarns under Multi-Loading

The mechanical behaviour of textile structures is one of their most important characteristics as far as their end use is concerned. Textile structures, fabrics, or yarns are often considered as continuous mediums apart from the fact that they are composed of some discrete elements, individual fibres composing yarns and yarns composing fabrics. This is known as the transition scale, a very important lock to be considered, to evaluate the real structure behaviour. In this context, this work presents some simulations of the mechanical behaviour of a fabric where the yarn is a continuum material. Particular attention was paid to simultaneous loading in uniaxial or biaxial extension and shear loadings. The results of numerical simulations, which show the deformed fabric unit cell under multi-load conditions, are coherent with experimental observations and encourage the authors to continue the present work with parametrical and inverse case studies.

Experimental and Numerical Simulation of Mechanical Behaviour of Ultrafine Grained AA 2014 Al Alloy

Experimental and Numerical Simulation of Mechanical Behaviour of Ultrafine Grained AA 2014 Al Alloy

Hexagonal close-packed (hcp) alloys under dynamic impacts

Predictions on the mechanical behavior of metals and alloys with a hexagonal close-packed (HCP) lattice under dynamic influences in a wide range of temperatures are in demand for solving a wide range of applied problems. This article presents new results of numerical simulation showing the general similarity of the mechanical behavior of HCP titanium, zirconium, hafnium, and beryllium alloys under dynamic loadings in a wide range of temperatures. These alloys belong to the important isomechanical subgroup of HCP alloys. A model for numerical simulation of mechanical behavior of HCP alloys under dynamic loadings in a wide temperature range was proposed. The model takes into account the change in contributions to the flow stress from the mechanisms of twinning and dislocation slip in the considered subgroup of HCP alloys. A kinetic damage model was adopted to describe the damage evolution under complex stress conditions and under dynamic loading. Thus, it was possible to increase the accuracy of predicting the dynamic fracture under tensile loads including the spall fracture.

Simulation of mechanical behavior of carbonate gravel with hybrid PSO–SVR algorithm

Large-scale testing is one of the common methods used to study the mechanical behavior of carbonate gravels. However, due to the huge workload of larger-scale tests and a dimensional limitation of laboratory specimens, there are only a limited number of large-scale tests, and the mechanical behavior of carbonate gravels is not fully understood. In this study, a hybrid algorithm combining two techniques of artificial intelligence – particle swarm optimization and the support vector regression technique – are used to simulate soil behavior using on a dataset obtained from large-scale direct tests of carbonate gravels. Three types of single-output models have been developed, results show that the models developed by the proposed hybrid algorithm are highly accurate. In addition, one of the models used is to predict the shear strength of carbonate gravel under different normal stress. The results show that when the normal stress is larger than 600 kPa, the nonlinear shear strength model is more suitable for carbonate gravel with high particle breakage. Modeling the mechanical behavior of soil with artificial intelligence is thus a useful method to evaluate the mechanical properties of gravel economically and conveniently.

Molecular dynamics simulation of mechanical behavior and phase transformation of nanocrystalline NiTi shape memory alloy with gradient structure

Severe plastic deformation can lead to surface amorphization of nickel-titanium shape memory alloys (NiTi SMAs), and amorphous layer can be transformed into nanocrystalline layer by means of appropriate heat treatment. Consequently, molecular dynamics simulation is used to investigate mechanical behavior and phase transformation of nanocrystalline NiTi shape memory alloy with gradient structure, where surface layers possess the average grain sizes of 6, 9, 12 and 15 nm, respectively, and the middle layer possesses the average grain sizes of 20 nm. The maximum tensile stress and the irrecoverable strain decrease with the increase of the average grain size in the surface layers. As for the maximum tensile stress, the maximum value is 2.46 GPa and the minimum value is 1.92 GPa. As for the irrecoverable strain, the maximum value is 0.5%, and the minimum value is 0.25%. Amorphous phase and grain boundaries (GBs) have an important influence on the superelasticity of NiTi SMA. The degradation of superelasticity is mainly attributed to plastic deformation of the amorphous phase and the GBs.

Embedded-atom method potential for Ti<sub>2</sub>AlNb alloys

Molecular dynamics simulation is an effective computer simulation method. However, owing to the lack of suitable interatomic potential of multicomponent alloys, the application of molecular dynamics simulation is limited. The development of interatomic potential of multicomponent alloys has always been challenging. In this work, under the framework of EAM model, a construction method of interatomic potential suitable for ternary ordered alloys is proposed, and a new interatomic potential of Ti<sub>2</sub>AlNb alloys suitable for atomic-scale mechanical behavior simulation is developed. The potential can well reproduce the elastic constants of B2-Ti<sub>2</sub>AlNb, unrelaxation vacancy formation energy, substitutional atom formation energy, transposition atom formation energy, surface energy and cohesive energy of three ordered phase (B2, D0<sub>19</sub> and O phases ) in different volumes. To further test the potential functions, 1) the <i>E</i>-<i>V</i> curve of B2 phase is calculated, and the result is well consistent with Rose curve; 2) the melting transformation process of B2 phase is studied by molecular dynamics simulation, and the results roughly reflect the experimental fact. The present work provides a way to develop the interatomic potential of multicomponent alloys, and a option for the workers who simulate and calculate the Ti<sub>2</sub>AlNb alloys as well.

The Image-Based Finite Element Evaluation of the Deformed State

The article presents one of the possible approaches to modeling objects with anisotropic properties based on images of the study area. Data from such images are taken into account when building a numerical model. In this case, material inhomogeneity can be included by integrating the local stiffness matrix of each finite element with a certain weight function. The purpose of the presented work is to develop a finite element for the formation of a computational ensemble and simulation of mechanical behavior taking into account the data of two-dimensional medical images. To implement the proposed approach, we used the assumption that there is a correlation between the values in the image pixels and the elastic properties of the material. Meshing was based on a four-node plane finite element. This approach allows using the quantitative phase or scanning electronic images, as well as computed tomography data. A number of test problems for compression of elementary geometry samples were calculated. The distal part of the rat femur was considered as a model problem. A computed tomography scan of the sample was used to construct a numerical model taking into account the inhomogeneity of the material distribution inside the organ. The distribution field of the nodal displacements based on data obtained from the images of the study area is presented. Within the framework of a model problem, we considered how a computer tomograph resolution influences the quality of the obtained results. For this purpose, calculations were carried out based on compressed input medical images.

Mechanical behavior simulation of particulate-filled composite at meso-scale by numerical manifold method

Particulate-filled composite (PFC) is a kind of mixed multi-phase material with the grains highly embedded in the binders with ratio higher than 90%. Its good mixture capacity with the binder, in particulate or fibre form, leads to composite materials with intermediate properties that result from the combined action of the constituents. Due to the complexity of PFC meso-scopic composition and loading levels, it is difficult to reveal the deformation and damage mechanism of composites by traditional phenomenological macro-scale methods. In the present work, based on the PFC meso-structures with highly-filled grains, the numerical manifold method is utilized to simulate the meso-scale mechanical response of PFC at different loading levels. The effects of strain rates and temperatures on the meso damage morphology of PFC are studied. The damage evolution laws caused by interfacial debonding and micro-cracks in the meso structure are analyzed. Based on their isotropic assumption, the macroscopic equivalent damage evolution equations caused by these meso-scale damages are derived, respectively. The effects of loading levels on the mechanical characteristic parameters (such as modulus, failure strength, ultimate strain, etc.) are also discussed quantitatively. The specific mathematical expressions of the strain rate and temperature dependent properties under uniaxial tension/compression are statistically obtained. Two categories of constitutive models of coupling damage evolution equation with Johnson-cook and generalized Maxwell model are proposed to describe the macroscopic equivalent mechanical behavior of PFC.

Determining elastic constants of poplar wood (Populus deltoides) by ultrasonic waves and its application in the finite element analysis

ABSTRACT In simulation of wood mechanical behaviors, it is imperative to define elastic engineering parameters of the wood (three Young’s moduli, three shear moduli and six Poisson’s ratios). As regards, the determination of a set of nine independent elastic constants of wood by the experimental method is expensive and laborious and requires several specimens and test equipment and the literature is very rare and has a wide range in data. In this study, elastic engineering parameters of poplar wood (Populus deltoides) were determined by applying the ultrasonic waves and their first-ever application as input data in simulation of mechanical behavior of the poplar wood. Ultrasonic velocity measurements give a chance for the direct determination of the all orthotropic elastic constants using only little small stresses to the wood material. The commercial finite element program ABAQUSTM software package was used to model and analyze as linear orthotropic elastic materials. For validating the applicability and better and more accurate evaluation of engineering parameters were determined by ultrasonic wave propagation in simulation, both three-point bending and uniaxial tensile tests were examined. The ultrasonic technique for determination of elastic engineering parameters of poplar wood, as input data in the finite element method, leads to a very close correlation with the experiment results, which turns out that these data are reliable and applicable for the simulation of wood behaviors.

DEM simulation of mechanical behavior in one-dimensional compression of crushable ceramic pebble bed

The mechanical behavior in one-dimensional compression of a crushable ceramic pebble bed for the fusion reactor, which is under different crushing ratio assumptions (0% - 2%), was numerically investigated by the discrete element method (DEM) simulation. The crushed particle was modeled by a reduction of the particle radius, therefore, the instantaneous decrease of the local stress could be produced. To guarantee the mass conservation of the particles in the pebble bed, the sub-particle insertion process was conducted. Please note that this paper mainly deals with the post of failure of the particles, hence the pebble failure process was not captured. The results showed that the crushed particles could make the pebble bed softer, and with the same Li4SiO4 pebble bed strain, the bed stress decreased as the crushing ratio grew larger. The impact of the crushing ratio on the radial and axial local packing factor was limited on the oscillating amplitude without affecting the oscillating width. Besides, the effects of the coefficient of friction and restitution under different crushing ratios were investigated. At last, the analysis of changes in the average coordination number with the bed strain under different crushing ratios was performed.