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A special issue of Applied Mechanics (ISSN 2673-3161).

Deadline for manuscript submissions: closed (27 December 2023) | Viewed by 26965

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Prof. Dr. Filippo Berto

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Guest Editor

Department of Chemical Engineering, Materials and Environment, Sapienza University of Rome, 00184 Rome, Italy
Interests: fatigue and fracture behavior of materials; mechanical characterization; structural integrity of conventional and innovative materials
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Dr. Luis Reis

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Guest Editor

IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
Interests: fatigue testing; multiaxial fatigue; ultrasonic fatigue testing; additive manufacturing; product design
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Dr. Qing Peng

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Guest Editor

Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
Interests: multiscale modeling; nanomechanics; damage mechanics; nonlinear mechanics; physical mechanics; AI-mechanics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are pleased to announce that Applied Mechanics is now compiling a collection of outstanding papers in the field of material mechanics. We welcome contributions from the material mechanics research community, as well as recommendations from Editorial Board Members.

The purpose of this Special Issue is to publish a set of papers that typify the most exceptional, insightful, influential, and original research articles or reviews. We expect these papers to be widely read and highly influential within the field. All papers in this Special Issue will be collated into a printed book after the deadline and will be promoted.

We would also like to take this opportunity to call on more scholars to join the journal so that we can work together to further develop this exciting field of research.

Prof. Dr. Filippo Berto
Dr. Luis Reis
Dr. Qing Peng
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Mechanics is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

mechanics of materials
ceramics
metals
polymers
soft materials
electronic materials
strain
stress

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Published Papers (11 papers)

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Research

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25 pages, 8083 KiB

Open AccessArticle

Detailed Structural Analysis of Cylindrical Steel Tank Subjected to Various Seismic Peak Ground Values Using FSI Approach

by Yasir Zulfiqar, Asim Zulfiqar, Hafiz Waqar Ahmad, Umer Masood Chaudry, Muhammad Kashif Khan and Tea-Sung Jun

Appl. Mech. 2023, 4(3), 990-1014; https://doi.org/10.3390/applmech4030051 - 15 Sep 2023

Viewed by 3332

Abstract

The seismic analysis of ground-supported cylindrical steel tanks subjected to lateral harmonic displacement loadings has been carried out. This paper numerically evaluates the structural response of various tank geometries due to resonant seismic sloshing. The numerical investigation is performed using a two-way fluid structural interaction approach that couples computational fluid dynamics analysis with finite element transient structural analysis. The results of the analysis have been validated using Seismic Design Code (Eurocode 8, part 4). Regarding tank aspect ratio (H/D), five geometries covering slender, medium, and broad structures are analyzed under ten harmonic base excitations. All the geometries are excited at their first convective frequency, whose shape and magnitude are evaluated using modal analysis. The seismic response curves have been developed for each tank model, which reveal the complex and peculiar structural response. It is observed from the tanks’ seismic response that they undergo three transitional stress zones named safe, yielding, and failure zones. The critical loadings and failure duration have also been evaluated for each tank model. This will help to avoid future structural damage by designing liquid-containing structures based on evaluated seismic failure loads. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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16 pages, 5444 KiB

Open AccessArticle

Effects of Hybridization on Tensile, Flexural, and Damage Behaviors of Flax/Carbon Epoxy Composites

by Mohamed Habibi and Luc Laperrière

Appl. Mech. 2023, 4(2), 763-778; https://doi.org/10.3390/applmech4020039 - 13 Jun 2023

Cited by 2 | Viewed by 1607

Abstract

In recent years, the hybridization of natural fibers with synthetic fibers has received much attention. This paper conducted an experimental study on the tensile and flexural behavior of unidirectional carbon/flax fiber reinforced epoxy composites and single flax fibers. Four hybridization rates were considered for 16 reinforced layers in a symmetric staking sequence, with the carbon ply at the surface. The damage evolution under load increase was monitored using the acoustic emission (AE) technique. The Davies–Bouldin index and the K-means clustering algorithm were used to correlate the hybridization rates to the contribution of each damage mechanism to overall failure. AE monitoring of tensile and flexural behaviors showed that delamination and fiber breakage mechanisms dominate the composite failure, regardless of the hybridization rate. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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11 pages, 1642 KiB

Open AccessArticle

Machine Learning-Assisted Tensile Modulus Prediction for Flax Fiber/Shape Memory Epoxy Hygromorph Composites

by Tarik Sadat

Appl. Mech. 2023, 4(2), 752-762; https://doi.org/10.3390/applmech4020038 - 9 Jun 2023

Cited by 1 | Viewed by 2375

Abstract

Flax fiber/shape memory epoxy hygromorph composites are a promising area of research in the field of biocomposites. This paper focuses on the tensile modulus of these composites and investigates how it is affected by factors such as fiber orientation (0° and 90°), temperature (20 °C, 40 °C, 60 °C, 80 °C, and 100 °C), and humidity (50% and fully immersed) conditions. Machine learning algorithms were utilized to predict the tensile modulus based on non-linearly dependent initial variables. Both decision tree (DT) and random forest (RF) algorithms were employed to analyze the data, and the results showed high coefficient of determination R² values of 0.94 and 0.95, respectively. These findings demonstrate the effectiveness of machine learning in analyzing large datasets of mechanical properties in biocomposites. Moreover, the study revealed that the orientation of the flax fibers had the greatest impact on the tensile modulus value (with feature importance of 0.598 and 0.605 for the DT and RF models, respectively), indicating that it is a crucial factor to consider when designing these materials. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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39 pages, 68312 KiB

Open AccessArticle

A Numerically Efficient Method to Assess the Elastic–Plastic Strain Energy Density of Notched and Imperfective Cast Steel Components

by Michael Horvath, Matthias Oberreiter and Michael Stoschka

Appl. Mech. 2023, 4(2), 528-566; https://doi.org/10.3390/applmech4020030 - 27 Apr 2023

Cited by 3 | Viewed by 3296

Abstract

The fatigue strength of cast steel components is severely affected by manufacturing process-based bulk and surface imperfections. As these defect structures possess an arbitrary spatial shape, the utilization of local assessment methods is encouraged to design for service strength. This work applies the elastic–plastic strain energy density concept to study the fatigue strength properties of a high-strength cast steel alloy G12MnMo7-4+QT. A fatigue design limit curve is derived based on non-linear finite element analyses which merges experimental high-cycle fatigue results of unnotched and notched small-scale specimens tested at three different stress ratios into a unique narrow scatter band characterized by a scatter index of

1 : T_{Δ {\bar{W}}^{(t)}} = 2.43

. A comparison to the linear–elastic assessment conducted in a preceding study reveals a significant improvement in prediction accuracy which is assigned to the consideration of the elastic–plastic material behaviour. In order to reduce computational effort, a novel approximation is presented which facilitates the calculation of the elastic–plastic strain energy density based on linear–elastic finite element results and Neuber’s concept. Validation of the assessment framework reveals a satisfying agreement to non-linear simulation results, showing an average root mean square deviation of only approximately eight percent in terms of total strain energy density. In order to study the effect of bulk and surface imperfections on the fatigue strength of cast steel components, defect-afflicted large-scale specimens are assessed by the presented elastic–plastic framework, yielding fatigue strength results which merge into the scatter band of the derived design limit curve. As the conducted fatigue assessment is based solely on linear–elastic two-dimensional simulations, the computational effort is substantially decreased. Within the present study, a reduction of approximately 400 times in computation time is observed. Hence, the established assessment framework presents an engineering-feasible method to evaluate the fatigue life of imperfective cast steel components based on rapid total strain energy density calculations. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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14 pages, 2175 KiB

Open AccessArticle

Delamination Behavior of Highly Stretchable Soft Islands Multi-Layer Materials

by Philipp Kowol, Swantje Bargmann, Patrick Görrn and Jana Wilmers

Appl. Mech. 2023, 4(2), 514-527; https://doi.org/10.3390/applmech4020029 - 26 Apr 2023

Cited by 1 | Viewed by 1848

Abstract

Stretchable electronics rely on sophisticated structural designs to allow brittle metallic conductors to adapt to curved or moving substrates. Patterns of soft islands and stable cracks in layered silver-PDMS composites provide exceptional stretchability by means of strain localization as the cracks open and the islands strain. To investigate the reliability and potential failure modes, we study the initiation and propagation of delamination in dependence of structure geometry and quality of the metal-polymer bonding. Our numerical experiments show a well-bonded metal film to be under no risk of delamination. Even weakly bonded metal films sustain moderate strains well above the limits of classical electronic materials before the onset of delamination in the soft islands structures. If delamination occurs, it does so in predictable patterns that retain functionality over a remarkable strain range in the double-digit percent range before failure, thus, providing safety margins in applications. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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16 pages, 2544 KiB

Open AccessArticle

AFM Indentation on Highly Heterogeneous Materials Using Different Indenter Geometries

by Stylianos Vasileios Kontomaris, Andreas Stylianou, Georgios Chliveros and Anna Malamou

Appl. Mech. 2023, 4(2), 460-475; https://doi.org/10.3390/applmech4020026 - 18 Apr 2023

Cited by 7 | Viewed by 2455

Abstract

Hertzian mechanics is the most frequently used theory for data processing in Atomic Force Microscopy (AFM) indentation experiments on soft biological samples, due to its simplicity and significant scientific results previously published. For instance, using the Hertz model, it has been proven that there are significant differences in the mechanical properties of normal and cancerous tissues and that cancer cells’ invasive properties are correlated with their nanomechanical properties. However, many scientists are skeptical regarding the applicability of the Hertz theory to biological materials, as they are highly heterogeneous. The main critical question to be addressed is “what do we calculate” when fitting the force-indentation data to Hertz equations. Previous studies have shown that when using cylindrical, parabolic, or conical indenters, the fitting parameter is the average Young’s modulus. In this paper, it is demonstrated that it is also valid to fit equations derived from Hertzian mechanics to force-indentation data when testing soft, heterogeneous samples for any indenter geometry. The fitting factor calculated through this approach always represents the average Young’s modulus for a specific indentation depth. Therefore, Hertzian mechanics can be extended to soft heterogeneous materials, regardless of the indenter’s shape. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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18 pages, 6539 KiB

Open AccessArticle

Combining Digital Image Correlation and Acoustic Emission to Characterize the Flexural Behavior of Flax Biocomposites

by Mohamed Habibi and Luc Laperrière

Appl. Mech. 2023, 4(1), 371-388; https://doi.org/10.3390/applmech4010021 - 21 Mar 2023

Cited by 4 | Viewed by 2196

Abstract

Understanding the effect of staking sequences and identifying the damage occurring within a structure using a structural health monitoring system are the keys to an efficient design of composite-based parts. In this research, a combination of digital image correlation (DIC) and acoustic emission (AE) is used to locate and classify the type of damage depending on the stacking sequence of the laminate during flexural loading. As a first step, the results of the strain fields for unidirectional, cross-ply, and quasi-isotropic laminates were compared to discuss their global behavior and to correlate the different damage patterns with the possible failure mechanisms. The damage was then addressed using a comprehensive interpretation of the acoustic emission signatures and the K-means classification of the acoustic events. The development of each damage mechanism was correlated to the applied load and expressed as a function of the loading rate to highlight the effect of the stacking sequence. Finally, the results of DIC and AE were combined to improve the reliability of the damage investigation without limiting the failure mechanism to matrix cracking, interfacial failure, and fiber breakage, as expected by the unsupervised event clustering. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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18 pages, 8717 KiB

Open AccessArticle

Shear Deterioration of the Hierarchical Structure of Cellulose Microfibrils under Water Condition: All-Atom Molecular Dynamics Analysis

by Yukihiro Izumi, Ken-ichi Saitoh, Tomohiro Sato, Masanori Takuma and Yoshimasa Takahashi

Appl. Mech. 2023, 4(1), 230-247; https://doi.org/10.3390/applmech4010013 - 19 Feb 2023

Cited by 1 | Viewed by 2317

Abstract

This study aims to understand the mechanical properties of cellulose nanofibers (CNFs), a nano-sized material element of woods or plants. We develop all-atom (AA) molecular dynamics models of cellulose microfibrils (CMFs), which are the smallest constituent of CNFs. The models were designed for the process of structural failure or the degradation of a hierarchical material of multiple CMF fibers, due to shear deformation. It was assumed that two CMFs were arranged in parallel and in close contact, either in a vacuum or in water. The CMF models in water were built by surrounding AA-modeled water molecules with a few nanometers. Shear deformation was applied in the axial direction of the CMF or in the direction parallel to molecular sheets. Shear moduli were measured, and they agree with previous experimental and computational values. The presence of water molecules reduced the elastic modulus, because of the behavior of water molecules at the interface between CMFs as a function of temperature. In the inelastic region, the CMF often broke down inside CMFs in a vacuum condition. However, in water environments, two CMFs tend to slip away from each other at the interface. Water molecules act like a lubricant between multiple CMFs and promote smooth sliding. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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Review

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19 pages, 1305 KiB

Open AccessReview

Methods and Mechanical Properties of Polymer Hybrid Composites and Hybrid Polymer Composites: Influence of Ionic Liquid Addition

by Ahmad Adlie Shamsuri, Siti Nurul Ain Md. Jamil, Mohd Zuhri Mohamed Yusoff and Khalina Abdan

Appl. Mech. 2024, 5(1), 1-19; https://doi.org/10.3390/applmech5010001 - 20 Dec 2023

Cited by 2 | Viewed by 1449

Abstract

Polymer hybrid composites and hybrid polymer composites are distinct but interconnected composite classes, each with unique compositions and design philosophies. The mechanical properties of these composites are vital in advanced materials due to their impacts on performance, durability, and suitability for various applications. The addition of ionic liquids into these composites is a promising innovation in advanced materials. In this short review, various polymer matrices (e.g., thermosets, thermoplastics, and biopolymers), fillers (e.g., inorganic, carbon, organic, and metal), and ionic liquids (e.g., imidazolium- and phosphonium-based) used to fabricate polymer hybrid composites and hybrid polymer composites with added ionic liquids are identified. Furthermore, the addition of ionic liquids into these composites through different methods (e.g., magnetic stirring, mechanical stirring, solid grinding, etc.) is discussed. The influence of ionic liquid addition on the mechanical properties, specifically the tensile properties of these composites, is also shortly reviewed. The changes in the tensile properties, such as the tensile strength, tensile modulus, and elongation at break, of these composites are explained as well. The information presented in this review enhances the understanding of the methods applied to add ionic liquids into polymer hybrid composites and hybrid polymer composites, along with their tensile properties. In short, some ionic liquids have the capacity to enhance the tensile properties of hybrid polymer composites, and several ionic liquids can reduce the tensile properties of polymer hybrid composites. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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24 pages, 1410 KiB

Open AccessReview

Impact Testing on the Pristine and Repaired Composite Materials for Aerostructures

by Zoe E. C. Hall, Jun Liu, Richard A. Brooks, Haibao Liu and John P. Dear

Appl. Mech. 2023, 4(2), 421-444; https://doi.org/10.3390/applmech4020024 - 12 Apr 2023

Viewed by 2438

Abstract

Aircraft technologies and materials have been developing and improving drastically over the last hundred years. Over the last three decades, an interest in the use of composites for external structures has become prominent. For this to be possible, thorough research on the performance of composite materials, specifically the impact performance, have been carried out. For example, research of impact testing for pristine carbon-reinforced epoxy composites mentions matrix cracks, fibre fracture, and delamination as the failure modes that require monitoring. In addition, thorough testing has been carried out on composites repaired with an adhesive bond to observe the effects of conditioning on the adhesively bonded repair. The results suggest there are no major changes in the adhesive under the testing condition. By reviewing the impact testing on the pristine and repaired composite materials for aerostructures, this paper aims to illustrate the main findings and also explore the potential future work in this research scope. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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Other

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14 pages, 2491 KiB

Open AccessTechnical Note

Analytical Modeling for Mechanical Straightening Process of Case-Hardened Circular Shaft

by Shizhu Xing

Appl. Mech. 2023, 4(2), 715-728; https://doi.org/10.3390/applmech4020036 - 5 Jun 2023

Viewed by 1892

Abstract

Straightening has to be carried out in order to ensure the straightness of a shaft, as distortions exceed the tolerance limit. Since the straightening load is typically large enough to produce plastic and residual deformation, repeated straightening loading cycles are very likely to induce cracks or fractures on the case-hardened shaft surface. In this study, in order to minimize repeated straightening cycles, an analytical straightening model is developed which calculates optimum stroke displacements corresponding to measured straightness errors so as to achieve the desired residual deflections and eliminate straightness errors. First, the hardness variation in the shaft radial direction is considered in the analytical model. Then, the proposed theoretical model is validated by numerical simulations. The results suggest that the analytically predicted stroke displacements and residual deflections agree very well with the numerical results when using induction-hardened SAE 4140 steel, and this signifies that the analytical straightening model developed in this study is capable of providing predictions of straightening stokes. Full article

(This article belongs to the Special Issue Feature Papers in Material Mechanics)

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