Materials

Research

22 pages, 16027 KiB

Open AccessArticle

Optimization of Curvilinear Stiffener Beam Structures Simulated by Beam Finite Elements with Coupled Bending–Torsion Formulation

by Cesare Patuelli, Enrico Cestino, Giacomo Frulla and Federico Valente

Materials 2023, 16(9), 3391; https://doi.org/10.3390/ma16093391 - 26 Apr 2023

Cited by 1 | Viewed by 1326

Abstract

This research presents the application of a beam finite element, specifically derived for simulating bending–torsion coupling in equivalent box-beam structures with curvilinear stiffeners. The stiffener path was simulated and optimized to obtain an expected coupling effect with respect to four typical static load [...] Read more.

This research presents the application of a beam finite element, specifically derived for simulating bending–torsion coupling in equivalent box-beam structures with curvilinear stiffeners. The stiffener path was simulated and optimized to obtain an expected coupling effect with respect to four typical static load cases, including geometric constraints related to the additive manufacturing production method. The selected load condition was applied to the centroid of the beam section, and the structure performance was consequently determined. A variation in load position up to one-fourth of the beam width was considered for investigating the stiffener path variation corresponding to a minimum bending–torsion coupling effect. The results demonstrated the capability of such a beam finite element to correctly represent the static behavior of beam structures with curvilinear stiffeners and show the possibility to uncouple its bending–torsion behavior using a specific stiffener orientation. The simulation of a laser powder bed fusion process showed new opportunities for the application of this technology to stiffened panel manufacturing. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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17 pages, 6528 KiB

Open AccessArticle

New Damage Accumulation Model for Spall Propagation Mechanism in Bearing Raceways

by Ravit Ohana, Renata Klein, Roni Shneck and Jacob Bortman

Materials 2023, 16(4), 1750; https://doi.org/10.3390/ma16041750 - 20 Feb 2023

Cited by 1 | Viewed by 1754

Abstract

The aim of this study was to investigate the spall propagation mechanism in ball bearing raceways using physics-based models. Spalling is one of the most common types of bearing failures that can lead to catastrophic failure. This research takes a step forward toward [...] Read more.

The aim of this study was to investigate the spall propagation mechanism in ball bearing raceways using physics-based models. Spalling is one of the most common types of bearing failures that can lead to catastrophic failure. This research takes a step forward toward developing a prognostic tool for ball bearings. It is first necessary to understand the spall progression process in order to formulate a constitutive law of spall deterioration and to estimate the amount of remaining useful life. Fragment formation in the vicinity of the spall edge was found to consist of surface and sub-surface cracks that eventually coalesce, and a fragment is released from the raceway, based on naturally-developed spalls. Here, we describe a physics-based model, integrating a dynamic model with a finite element one to simulate this process. A continuum damage mechanics (CDM) approach and fracture mechanics tools were embedded into the finite element model to simulate the damage propagation. The formation of cracks in the vicinity of the spall (surface and sub-surface cracks) were studied using this effective stress CDM model, and the propagation of the cracks was examined using two approaches: a fracture mechanics approach and an accumulated inelastic hysteresis energy CDM approach. The latter also predicts the overall process of a single fragment release. The simulation results of the spall propagation models are supported by experimental results of spalls from both laboratory experimental bearings and an in-service Sikorsky CH-53 helicopter swashplate bearing. The results obtained show that the impact of the ball on the spall edge affects the crack propagation and the appearance of the surface and sub-surface cracks. Both release the residual stresses and cause crack propagation until a fragment is released. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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27 pages, 8380 KiB

Open AccessArticle

Elastic Critical Resistance of the Simple Beam Grillage Resulting from the Lateral Torsional Buckling Condition: FEM Modelling and Analytical Considerations

by Rafał Piotrowski, Andrzej Szychowski and Josef Vičan

Materials 2023, 16(4), 1346; https://doi.org/10.3390/ma16041346 - 5 Feb 2023

Cited by 4 | Viewed by 1515

Abstract

Transversely loaded beam grillages are quite often used in industrial construction. In order to produce a safe design of such structures, it is necessary to account for the lateral torsional buckling phenomenon, which reduces load-bearing capacity. To be able to calculate the relevant [...] Read more.

Transversely loaded beam grillages are quite often used in industrial construction. In order to produce a safe design of such structures, it is necessary to account for the lateral torsional buckling phenomenon, which reduces load-bearing capacity. To be able to calculate the relevant reduction factor, the elastic critical load must be determined. As regards the existing design practice for such structures, simplified conditions are assumed for the mutual restraint of the component beams. However, this approach does not correspond to reality. This study discusses the results of numerical investigations and analytical calculations concerning the effect of the elastic action of simple beam grillage (SBG) joints on the critical load, which results from the lateral torsional buckling (LTB) condition. The SBG was defined as a flat system of interconnected beams, unstiffened laterally and loaded perpendicularly to the grillage plane. The analysis covered H-shaped grillages with different span ratios of component beams, in which the main (coupling) beam was decisive for instability. The effectiveness of the use of closed-section stiffeners at the grillage joints was also investigated. The grillage elastic critical resistances (ECR) were determined for two variants of joint stiffening. The computations were performed by means of FEM numerical simulations. The spatial models were discretised with the following elements: (1) solid ones in Abaqus, (2) shell ones in ConSteel, and (3) thin-walled bars in ConSteel. The LTB critical moments of the weakest beam (critical beam), elastically restrained against warping and against lateral rotation (in the LTB plane), were computed using the analytical methods developed by the authors. To this end, the methods were proposed to determine the indexes of the critical beam elastic restraint in the adjacent stiffening beams. In the study, it was demonstrated that (1) taking into account the conditions of mutual elastic restraint and interaction of the component beams provides a more accurate assessment of the grillage ECR, (2) the use of closed-section stiffeners in the grillage joints increase the ECR compared with classic flat stiffeners, (3) the grillage ECR can be estimated based on the critical moment M_cr of the weakest beam (critical beam) when the conditions of its elastic restraint in joints are accounted for. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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17 pages, 8740 KiB

Open AccessArticle

Experimental Investigation of the Spall Propagation Mechanism in Bearing Raceways

by Ravit Ohana, Renata Klein, Roni Shneck and Jacob Bortman

Materials 2023, 16(1), 68; https://doi.org/10.3390/ma16010068 - 21 Dec 2022

Cited by 2 | Viewed by 1692

Abstract

This article investigates the spall propagation mechanism for ball bearing raceways by focusing on an experimental investigation of cracks that evolve in the vicinity of the spall edge. Understanding the spall propagation mechanism is an important step towards developing a physics-based prognostic tool [...] Read more.

This article investigates the spall propagation mechanism for ball bearing raceways by focusing on an experimental investigation of cracks that evolve in the vicinity of the spall edge. Understanding the spall propagation mechanism is an important step towards developing a physics-based prognostic tool for ball bearings. This research reflects an investigation of different spall sizes that propagate naturally both in laboratory experiments and in the field. By using a combined model of a rigid body dynamic model and a finite element model that simulates the rolling element–spall edge interaction, our results shed light on the material behavior (displacements, strains, and stresses) that creates an environment for crack formation and propagation. With the support of the experimental results and the rolling element–spall edge interaction model results, three stages of the mechanism that control fragment release from the raceway were identified. In Stage one, sub-surface cracks appear underneath the spall trailing edge. In Stage two, cracks appear in front of the trailing edge of the spall and, in Stage three, the cracks propagate until a fragment is released from the raceway. These stages were observed in all the tested bearings. In addition, other phenomena that affect the propagation of the cracks and the geometry of the fragment were observed, such as blistering and plastic deformation. We include an explanation of what determines the shape of the fragments. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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15 pages, 5105 KiB

Open AccessArticle

Mesoscale Models for Describing the Formation of Anisotropic Porosity and Strain-Stress Distributions during the Pressing Step in Electroceramics

by Radu Stefan Stirbu, Leontin Padurariu, Fereshteh Falah Chamasemani, Roland Brunner and Liliana Mitoseriu

Materials 2022, 15(19), 6839; https://doi.org/10.3390/ma15196839 - 1 Oct 2022

Cited by 2 | Viewed by 1419

Abstract

Porous ceramics are often produced by using pyrolisable additives to generate porosity during the sintering step. The examination of the experimental microstructures of the resulted porous ceramics revealed certain levels of anisotropy, even if the original soft additives used as pore forming agents [...] Read more.

Porous ceramics are often produced by using pyrolisable additives to generate porosity during the sintering step. The examination of the experimental microstructures of the resulted porous ceramics revealed certain levels of anisotropy, even if the original soft additives used as pore forming agents were spherical. The paper shows that anisotropic porosity may result in ceramics when using equiaxed soft polymeric additives for generating porosity, due to the deformation of soft inclusions during the pressing step. It has been found, by means of analytical and numerical calculations, that uniaxial pressing of a mixture of solid particles with contrasting mechanical properties (hard/soft) generates modifications in the shape of the soft phase. As a result, anisotropic shape distribution of the soft inclusions in the green ceramic body and elongated porosity in the final ceramic product are obtained. The elongated pores are statistically oriented with the major axes perpendicular to the pressing direction and will generate anisotropy-related functional properties. Analytical calculations indicate the deformation of a single soft inclusion inside a continuum solid. Further, by finite element simulations performed in 2D planes along the transversal and radial directions of the pressing axis, a bimodal angular distribution of the long axes of the soft inclusions has been found. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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17 pages, 4867 KiB

Open AccessArticle

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

by Festus Fameso, Dawood Desai, Schalk Kok, Dylan Armfield and Mark Newby

Materials 2022, 15(16), 5682; https://doi.org/10.3390/ma15165682 - 18 Aug 2022

Cited by 7 | Viewed by 1546

Abstract

In-service turbine blade failures remain a source of concern and research interest for engineers and industry professionals with attendant safety and economic implications. Very high-pressure shock impacts from laser shots represent an evolving technique currently gaining traction for surface improvement and failure mitigation [...] Read more.

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

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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28 pages, 7705 KiB

Open AccessEditor’s ChoiceArticle

Topology Optimization and Multiobjective Optimization for Drive Axle Housing of a Rear Axle Drive Truck

by Bin Zheng, Shengyan Fu and Jilin Lei

Materials 2022, 15(15), 5268; https://doi.org/10.3390/ma15155268 - 30 Jul 2022

Cited by 3 | Viewed by 3514

Abstract

As one of the important load-bearing components of a truck, the drive axle housing must meet the requirements of stiffness and strength. The traditional design method uses redundancy design to meet the performance requirements. The joint design between the three-dimensional mathematical model and [...] Read more.

As one of the important load-bearing components of a truck, the drive axle housing must meet the requirements of stiffness and strength. The traditional design method uses redundancy design to meet the performance requirements. The joint design between the three-dimensional mathematical model and finite element model is adopted, and the optimal design of the drive axle housing is realized based on topology optimization and multiobjective optimization. Firstly, the static analysis of the drive axle housing of a rear axle drive truck was carried out with four typical working conditions. It was concluded that the four working conditions all operate under the yield limit of the material, and it was found that the maximum equivalent stress of the four working conditions occurs at the step of the half-shaft casing. Among the four working conditions, the most critical one is the maximum vertical force working condition. Then, based on the maximum vertical force working condition, the fatigue life analysis is conducted, and the minimum fatigue life appears at the transition position of the half-shaft sleeve and the arc transition position of the main reducer chamber. The remaining parts can meet the design requirements. The overall safety factor of the drive axle housing is mainly between 1 and 5 when operating under this working condition. Then, through modal analysis, the first to sixth natural frequency and vibration modes of the drive axle housing are extracted. Based on the modal analysis, the dynamic characteristics of the drive axle housing are further studied by harmonic response analysis and random vibration analysis. Finally, two kinds of lightweight optimization schemes for the drive axle housing are given. Topology optimization reduces the mass of the drive axle housing by 17.4%, but the overall performance slightly decreases. Then, the five dimensional parameters of the drive axle housing are selected as design variables. The mass, maximum deformation, equivalent stress, service life, and the first-, second- and third-order natural frequencies are defined as objective functions. Through the optimal space-filling design method, the experimental designs are performed and the sample points are obtained. Based on the results of experiment design, the multiobjective genetic algorithm and response surface method are combined to optimize the objective functions. The analysis results show that the mass is reduced by 4.35%, the equivalent stress is reduced by 21.05%, the minimum life is increased by 72.28%, and the first-, second-, and third-order natural frequency are also increased to varying degrees. Two different optimization strategies are provided for the design of the drive axle housing. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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19 pages, 26825 KiB

Open AccessArticle

Influence of a Lighting Column in the Working Width of a W-Beam Barrier on TB51 Crash Test

by Radoslaw Wolny, Dawid Bruski, Marcin Budzyński, Lukasz Pachocki and Krzysztof Wilde

Materials 2022, 15(14), 4926; https://doi.org/10.3390/ma15144926 - 15 Jul 2022

Cited by 5 | Viewed by 1906

Abstract

Road equipment, such as, e.g., road safety barriers and lighting columns, are subject to certification according to the EN1317 standard to be allowed for use on European roads. In engineering practice, due to the terrain conditions, there are cases where other road equipment [...] Read more.

Road equipment, such as, e.g., road safety barriers and lighting columns, are subject to certification according to the EN1317 standard to be allowed for use on European roads. In engineering practice, due to the terrain conditions, there are cases where other road equipment is installed within the working width of road safety barriers. Such situations are not considered during the certification process. Hence, the aim of this study is to analyze the effect of a lighting column installed within the working width of the barrier on the results of the TB51 crash test. The full-scale crash test and numerical simulation of this event were conducted. In the full-scale crash test, as well as in the simulation, the lighting column prevented the barrier’s post from properly disconnecting from the guardrail, which resulted in the barrier failing to restrain and redirect the 13-t bus. The simulation was quantitatively compared to the experiment, where the correlation coefficient of ASI curves equaled 84%. The THIV curves differed significantly between the experiment and the simulation, which is explained within the paper. Next, simulations with and without the lighting column were compared. The ASI and THIV in the simulation without the column were 0.33 and 16.1 km/h, respectively. In the simulation with the column, the ASI and THIV were 0.44 and 17.7 km/h, respectively. The maximum roll angle of the vehicle in the simulation without the column was 2.01° and with the column was 5.96°. The main difference, however, was that the system without the lighting column within the working width of the barrier was capable of properly restraining and redirecting the vehicle. The specific mechanics underlying this behavior are described within the paper. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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16 pages, 10531 KiB

Open AccessEditor’s ChoiceArticle

The Application of a Hybrid Method for the Identification of Elastic–Plastic Material Parameters

by Beata Potrzeszcz-Sut and Agnieszka Dudzik

Materials 2022, 15(12), 4139; https://doi.org/10.3390/ma15124139 - 10 Jun 2022

Cited by 4 | Viewed by 1630

Abstract

The indentation test is a popular method for the investigation of the mechanical properties of materials. The technique, which combines traditional indentation tests with mapping the shape of the imprint, provides more data describing the material parameters. In this paper, such methodology is [...] Read more.

The indentation test is a popular method for the investigation of the mechanical properties of materials. The technique, which combines traditional indentation tests with mapping the shape of the imprint, provides more data describing the material parameters. In this paper, such methodology is employed for estimating the selected material parameters described by Ramberg–Osgood’s law, i.e., Young’s modulus, the yield point, and the material hardening exponent. Two combined identification methods were used: the P-A procedure, in which the material parameters are identified on the basis of the coordinates of the indentation curves, and the P-C procedure, which uses the coordinates describing the imprint profile. The inverse problem was solved by neural networks. The results of numerical indentation tests—pairs of coordinates describing the indentation curves and imprint profiles—were used as input data for the networks. In order to reduce the size of the input vector, a simple and effective method of approximating the branches of the curves was proposed. In the Results Section, we show the performance of the approximation as a data reduction mechanism on a synthetic dataset. The sparse model generated by the presented approach is also shown to efficiently reconstruct the data while minimizing error in the prediction of the mentioned material parameters. Our approach appeared to consistently provide better performance on the testing datasets with considerably easier computation than the principal component analysis compression results available in the literature. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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23 pages, 4285 KiB

Open AccessArticle

Design of a Practical Metal-Made Cold Isostatic Pressing (CIP) Chamber Using Finite Element Analysis

by Wentao Song and Weicheng Cui

Materials 2022, 15(10), 3621; https://doi.org/10.3390/ma15103621 - 18 May 2022

Cited by 1 | Viewed by 2651

Abstract

The fast development of deep-ocean engineering equipment requires more deep-ocean pressure chambers (DOPCs) with a large inner diameter and ultra-high-pressure (UHP). Using the pre-stressed wire-wound (PSWW) concept, cold isostatic pressing (CIP) chambers have become a new concept of DOPCs, which can provide 100% [...] Read more.

The fast development of deep-ocean engineering equipment requires more deep-ocean pressure chambers (DOPCs) with a large inner diameter and ultra-high-pressure (UHP). Using the pre-stressed wire-wound (PSWW) concept, cold isostatic pressing (CIP) chambers have become a new concept of DOPCs, which can provide 100% performance of materials in theory. This paper aims to provide a comprehensive design process for a practical metal-made CIP chamber. First, the generalized design equations are derived by considering the fact that the cylinder and wire have different Young’s moduli and Poisson’s ratios. Second, to verify the theory and the reliability of the CIP chamber, the authors proposed a series of FEA models based on ANSYS Mechanical, including a two-dimensional (2D) model with the thermal strain method (TSM) and a three-dimensional (3D) model with the direct method (DM). The relative errors of the pre-stress coefficient range from 0.17% to 5%. Finally, the crack growth path is predicted by using ANSYS’s Separating Morphing and Adaptive Remeshing Technology (SMART) algorithm, and the fatigue life is evaluated by using the unified fatigue life prediction (UFLP) method developed by the authors’ group. This paper provides a more valuable basis to the design of DOPCs as well as to the similar pressure vessels than the previous work. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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18 pages, 5467 KiB

Open AccessArticle

3D Finite Element Analysis of a Concrete Dam Behavior under Changing Hydrostatic Load: A Case Study

by Pavel Žvanut

Materials 2022, 15(3), 921; https://doi.org/10.3390/ma15030921 - 25 Jan 2022

Cited by 3 | Viewed by 3554

Abstract

In this study, a large arch-gravity Moste Dam was analyzed, where an automated system for the measurements of horizontal displacements of the upper part of the dam was established. Two-dimensional (2D) and three-dimensional (3D) analyses of dam behavior, taking into account the earth [...] Read more.

In this study, a large arch-gravity Moste Dam was analyzed, where an automated system for the measurements of horizontal displacements of the upper part of the dam was established. Two-dimensional (2D) and three-dimensional (3D) analyses of dam behavior, taking into account the earth pressures and the hydrostatic load, using the finite element method (FEM)-based computer program DIANA, were performed. The influence of lowering the water level of the reservoir by 6.2 m, on the horizontal displacements of the upper part of the dam, at stationary temperature conditions, was investigated. It was found that the results of the performed 2D and 3D FEM analyses fitted in very well with the result of experimentally determined measurement of horizontal displacements (which was 0.48 mm in the upstream direction) that was obtained using a hanging pendulum. An additional comparison of the results of 3D calculations showed that the finite element mesh density had a small effect on the calculated horizontal displacements. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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36 pages, 37970 KiB

Open AccessArticle

Methodology for Neural Network-Based Material Card Calibration Using LS-DYNA MAT_187_SAMP-1 Considering Failure with GISSMO

by Paul Meißner, Jens Winter and Thomas Vietor

Materials 2022, 15(2), 643; https://doi.org/10.3390/ma15020643 - 15 Jan 2022

Cited by 5 | Viewed by 5076

Abstract

A neural network (NN)-based method is presented in this paper which allows the identification of parameters for material cards used in Finite Element simulations. Contrary to the conventionally used computationally intensive material parameter identification (MPI) by numerical optimization with internal or commercial software, [...] Read more.

A neural network (NN)-based method is presented in this paper which allows the identification of parameters for material cards used in Finite Element simulations. Contrary to the conventionally used computationally intensive material parameter identification (MPI) by numerical optimization with internal or commercial software, a machine learning (ML)-based method is time saving when used repeatedly. Within this article, a self-developed ML-based Python framework is presented, which offers advantages, especially in the development of structural components in early development phases. In this procedure, different machine learning methods are used and adapted to the specific MPI problem considered herein. Using the developed NN-based and the common optimization-based method with LS-OPT, the material parameters of the LS-DYNA material card MAT_187_SAMP-1 and the failure model GISSMO were exemplarily calibrated for a virtually generated test dataset. Parameters for the description of elasticity, plasticity, tension–compression asymmetry, variable plastic Poisson’s ratio (VPPR), strain rate dependency and failure were taken into account. The focus of this paper is on performing a comparative study of the two different MPI methods with varying settings (algorithms, hyperparameters, etc.). Furthermore, the applicability of the NN-based procedure for the specific usage of both material cards was investigated. The studies reveal the general applicability for the calibration of a complex material card by the example of the used MAT_187_SAMP-1. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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19 pages, 9231 KiB

Open AccessArticle

Enhancing the Accuracy of Linear Finite Element Models of Vehicle Structures Considering Spot-Welded Flanges

by Luis Martins, Gregorio Romero and Berta Suarez

Materials 2021, 14(20), 6075; https://doi.org/10.3390/ma14206075 - 14 Oct 2021

Cited by 1 | Viewed by 1855

Abstract

Structural engineering simulations have required increasingly complex computational models to replace physical tests accurately. This work focuses on the numerical analysis of vehicle body structures, whose size and complexity make the use of very accurate nonlinear models unfeasible due to the prohibitive computational [...] Read more.

Structural engineering simulations have required increasingly complex computational models to replace physical tests accurately. This work focuses on the numerical analysis of vehicle body structures, whose size and complexity make the use of very accurate nonlinear models unfeasible due to the prohibitive computational costs involved. The purpose of this study is to find a new approach to model spot-welded joints in linear finite element models of thin-wall vehicle body structures, improving the accuracy of the model without increasing its complexity. Using a set of simplified nonlinear models, we fitted the stiffness and damping properties of these welded joints and used those adjusted values into a linear model of the entire vehicle body structure. The results were compared with experimental tests, showing a clear improvement in the accuracy of the modal and frequency responses provided by the linear finite element model, but keeping its initial complexity level. The adjusted model was then used in an optimization analysis to reduce the structure’s weight, leading to interesting cost savings and important reductions in the use of natural resources and carbon emissions. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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15 pages, 324 KiB

Open AccessArticle

Efficient Temporal Third/Fourth-Order Finite Element Method for a Time-Fractional Mobile/Immobile Transport Equation with Smooth and Nonsmooth Data

by Lijuan Nong and An Chen

Materials 2021, 14(19), 5792; https://doi.org/10.3390/ma14195792 - 3 Oct 2021

Cited by 1 | Viewed by 1617

Abstract

In recent years, the numerical theory of fractional models has received more and more attention from researchers, due to the broad and important applications in materials and mechanics, anomalous diffusion processes and other physical phenomena. In this paper, we propose two efficient finite [...] Read more.

In recent years, the numerical theory of fractional models has received more and more attention from researchers, due to the broad and important applications in materials and mechanics, anomalous diffusion processes and other physical phenomena. In this paper, we propose two efficient finite element schemes based on convolution quadrature for solving the time-fractional mobile/immobile transport equation with the smooth and nonsmooth data. In order to deal with the weak singularity of solution near

t = 0

, we choose suitable corrections for the derived schemes to restore the third/fourth-order accuracy in time. Error estimates of the two fully discrete schemes are presented with respect to data regularity. Numerical examples are given to illustrate the effectiveness of the schemes. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

15 pages, 5050 KiB

Open AccessArticle

Direct Computation of 3-D Stress Intensity Factors of Straight and Curved Planar Cracks with the P-Version Finite Element Method and Contour Integral Method

by Jianming Zhang, Rui Xu, Yong He and Wensheng Yang

Materials 2021, 14(14), 3949; https://doi.org/10.3390/ma14143949 - 15 Jul 2021

Cited by 3 | Viewed by 2672

Abstract

This paper presents direct computations of 3-D fracture parameters including stress intensity factors (SIFs) and T-stress for straight and curved planar cracks with the p-version finite element method (P-FEM) and contour integral method (CIM). No excessive singular element or enrichment function is required [...] Read more.

This paper presents direct computations of 3-D fracture parameters including stress intensity factors (SIFs) and T-stress for straight and curved planar cracks with the p-version finite element method (P-FEM) and contour integral method (CIM). No excessive singular element or enrichment function is required for the computation. To demonstrate the accuracy and efficiency of the proposed approaches, several benchmark numerical models of 3-D planar straight and curved cracks with single and mixed-mode fractures are considered and analyzed: a through thickness edge straight crack in a homogeneous material, a through thickness inclined straight crack, a penny-shaped crack embedded in a cube and a central ellipse shaped crack in a homogeneous cube. Numerical results are analyzed and compared with analytical solutions and those reported by the extended finite element method (XFEM) and the scaled boundary finite element method (SBFEM) in the available literature. Numerical experiments show the accuracy, robustness and effectiveness of the present method. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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12 pages, 2611 KiB

Open AccessArticle

Effect of Ankle Torque on the Ankle–Foot Orthosis Joint Design Sustainability

by Pruthvi Serrao, Vivek Kumar Dhimole and Chongdu Cho

Materials 2021, 14(11), 2975; https://doi.org/10.3390/ma14112975 - 31 May 2021

Cited by 4 | Viewed by 3157

Abstract

The ankle joint of a powered ankle–foot orthosis (PAFO) is a prominent component, as it must withstand the dynamic loading conditions during its service time, while delivering all the functional requirements such as reducing the metabolic effort during walking, minimizing the stress on [...] Read more.

The ankle joint of a powered ankle–foot orthosis (PAFO) is a prominent component, as it must withstand the dynamic loading conditions during its service time, while delivering all the functional requirements such as reducing the metabolic effort during walking, minimizing the stress on the user’s joint, and improving the gait stability of the impaired subjects. More often, the life of an AFO is limited by the performance of its joint; hence, a careful design consideration and material selection are required to increase the AFO’s service life. In the present work, a compact AFO joint was designed based on a worm gear mechanism with steel and brass counterparts due to the fact of its large torque transfer capability in a single stage, enabling a compact joint. Further, it provided an added advantage of self-locking due to the large friction that prevents backdrive, which is beneficial for drop-foot recovery. The design was verified using nonlinear finite element analysis for maximum torque situations at the ankle joint during normal walking. The results indicate stress levels within its design performance; however, it is recommended to select high-grade structural steel for the ankle shaft as the highest stresses in AFO were located on it. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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