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Research Progress on Mechanical Behavior of Polymers

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Physics and Theory".

Deadline for manuscript submissions: closed (30 September 2024) | Viewed by 9044

Special Issue Editors


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Guest Editor
Department of Mechanical Engineering, University of Coimbra, 3030-788 Coimbra, Portugal
Interests: Glass-fiber reinforced polymers; 3D printed polymers; fatigue of polymers; ageing effects
Special Issues, Collections and Topics in MDPI journals

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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
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Polymers offer a wide range of mechanical behaviours that profoundly affect their performance and determine their application in transforming healthcare, consumer goods, automotive, or aerospace industries, among others. Moreover, additive manufacturing has revolutionized polymer applications, allowing the creation of complex components with reduced waste and customized mechanical properties that depend on the materials used, process parameters, printing strategies, and post-processing. Therefore, prominent thermoplastics such as polylactic acid (PLA), polyethylene terephthalate glycol (PETG), or polyethylether ketone (PEEK), to name a few, are now widely employed for prototyping and making functional parts of consumer products, e.g., for biomedical, aerospatial, oil, and gas applications.

Hence, a thorough understanding of the mechanical properties of this class of engineering materials, either at room or at low/high temperatures, is crucial for designing durable polymer components.

In this Special Issue, we invite researchers and practitioners to contribute their expertise and insights to further our understanding of topics such as the yield strength, tensile strength, hardness, ductility, fracture toughness, fatigue, creep deformation, and failure mechanisms of recently developed or newly applied polymers.

Dr. Rui C. Martins
Dr. Ricardo Branco
Prof. Dr. Filippo Berto
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. Polymers is an international peer-reviewed open access semimonthly 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 2700 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

  • polymers
  • additive manufacturing
  • mechanical behaviour
  • structural integrity

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Published Papers (6 papers)

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Research

20 pages, 9028 KiB  
Article
Effects of Particle Size on Mechanical Properties and Forming Accuracy of Prosopis chilensis Powder/Polyethersulfone Composites Produced via Selective Laser Sintering
by Alaaeldin A. A. Abdelmagid, Aboubaker I. B. Idriss and Chun-Mei Yang
Polymers 2024, 16(13), 1786; https://doi.org/10.3390/polym16131786 - 25 Jun 2024
Viewed by 632
Abstract
Wood–plastic composites are becoming increasingly recognized for their sustainability and their potential for use in various production processes. Nevertheless, enhancing their mechanical strength continues to be a difficult challenge. The objective of this research was to improve the mechanical strength of wood–plastic composite [...] Read more.
Wood–plastic composites are becoming increasingly recognized for their sustainability and their potential for use in various production processes. Nevertheless, enhancing their mechanical strength continues to be a difficult challenge. The objective of this research was to improve the mechanical strength of wood–plastic composite components manufactured through selective laser sintering (SLS). This was achieved by integrating a sustainable composite material, Prosopis chilensis (PCP), with polyethersulfone (PES) to form a composite referred to as PCPC. This study showcased the effect of various PCP particle sizes on mechanical strengths, dimensional accuracies (DAs), and surface roughness of PCPC parts manufactured using AFS-360 SLS. Single-layer sintering was employed to assess PCPC powder’s formability with varying PCP particle sizes, and various tests were conducted to understand the materials’ thermal properties and analyze particle dispersion and microstructure. The results demonstrated that PCP particle sizes ≤ 0.125 mm significantly enhanced the mechanical strength, forming quality, and DA compared to other particle sizes and pure PES. Key findings for PCPC parts with PCP ≤ 0.125 mm included a bending strength of 10.78 MPa, a tensile strength of 4.94 MPa, an impact strength of 0.91 kJ/m2, and a density of 1.003 g/cm3. Post-processing further improved these parameters, confirming that optimizing PCP particle size is crucial for enhancing the mechanical properties and overall quality of PCPC parts produced via SLS. Full article
(This article belongs to the Special Issue Research Progress on Mechanical Behavior of Polymers)
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12 pages, 4480 KiB  
Article
Temperature and Strain Rate Related Deformation Behavior of UHMWPE Fiber-Reinforced Composites
by Chenhong Yi, Jianhui Xu, Lizhi Tian and Chun Zhang
Polymers 2024, 16(9), 1250; https://doi.org/10.3390/polym16091250 - 30 Apr 2024
Viewed by 1353
Abstract
As they possess the qualities of high specific strength, high specific modulus, high specific energy absorption, and excellent designability, ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced composites have gradually replaced traditional materials such as ceramics and steel plates as the main ballistic protection materials. [...] Read more.
As they possess the qualities of high specific strength, high specific modulus, high specific energy absorption, and excellent designability, ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced composites have gradually replaced traditional materials such as ceramics and steel plates as the main ballistic protection materials. Using an improved test method, the uniaxial tensile tests of UHMWPE fiber-reinforced composites at two strain rates of 10−4 s−1 and 10−2 s−1 and a temperature range from −20 °C to 80 °C are carried out to study the effects of strain rate and temperature on the tensile behavior of UHMWPE fiber-reinforced composites. The experimental results indicate that the tensile responses exhibit nonlinear characteristics and the sensitivity of strain rate and temperature. The yield strength and modulus decrease with increasing temperature and increase with the increase in strain rate. A phenomenological viscoelastic constitutive model composed of a nonlinear spring and a nonlinear Maxwell element is proposed to characterize the temperature and strain rate dependent deformation behavior of UHMWPE fiber-reinforced composites before yielding. The results show that the model can accurately predict the tensile nonlinear viscoelastic responses of UHMWPE fiber-reinforced composites before yielding over a wide temperature range under quasi-static loading. Full article
(This article belongs to the Special Issue Research Progress on Mechanical Behavior of Polymers)
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18 pages, 34923 KiB  
Article
Mechanical Properties and Performance of 3D-Printed Acrylonitrile Butadiene Styrene Reinforced with Carbon, Glass and Basalt Short Fibers
by Evgeniy Lobov, Ilia Vindokurov and Mikhail Tashkinov
Polymers 2024, 16(8), 1106; https://doi.org/10.3390/polym16081106 - 16 Apr 2024
Cited by 2 | Viewed by 1463
Abstract
This paper presents the results of experimental investigation of the mechanical characteristics of 3D-printed acrylonitrile butadiene styrene (ABS) and its modifications reinforced with different types of short-fiber fillers: carbon, glass, and basalt. Elastic modulus, tensile and bending strength, as well as fracture toughness [...] Read more.
This paper presents the results of experimental investigation of the mechanical characteristics of 3D-printed acrylonitrile butadiene styrene (ABS) and its modifications reinforced with different types of short-fiber fillers: carbon, glass, and basalt. Elastic modulus, tensile and bending strength, as well as fracture toughness were determined in series of mechanical tests for samples produced with different manufacturing parameters, such as nozzle diameter and infill angle. It was found that the use of ABS filament reinforced with the short fibers can significantly improve the mechanical properties of 3D-printed devices when the infill angle is oriented along the vector of the applied load. In such a case, the elastic modulus and tensile strength can be increased by more than 1.7 and 1.5 times, respectively. The use of a larger nozzle diameter led to the growth of tensile strength by an average of 12.5%. When the macroscopic load is applied along the normal to the printed layers, the addition of short fibers does not give much gain in mechanical properties compared to pure ABS, which was confirmed by both standard tensile and fracture toughness tests. The surface of the fractured samples was examined using scanning electronic microscopy, which allowed us to make conclusions on the type of defects as well as on the level of adhesion between the polymeric matrix and different types of short fibers. Full article
(This article belongs to the Special Issue Research Progress on Mechanical Behavior of Polymers)
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24 pages, 8722 KiB  
Article
Application of Neural Network Models with Ultra-Small Samples to Optimize the Ultrasonic Consolidation Parameters for ‘PEI Adherend/Prepreg (CF-PEI Fabric)/PEI Adherend’ Lap Joints
by Dmitry Y. Stepanov, Defang Tian, Vladislav O. Alexenko, Sergey V. Panin and Dmitry G. Buslovich
Polymers 2024, 16(4), 451; https://doi.org/10.3390/polym16040451 - 6 Feb 2024
Cited by 1 | Viewed by 1233
Abstract
The aim of this study was to optimize the ultrasonic consolidation (USC) parameters for ‘PEI adherend/Prepreg (CF-PEI fabric)/PEI adherend’ lap joints. For this purpose, artificial neural network (ANN) simulation was carried out. Two ANNs were trained using an ultra-small data sample, which did [...] Read more.
The aim of this study was to optimize the ultrasonic consolidation (USC) parameters for ‘PEI adherend/Prepreg (CF-PEI fabric)/PEI adherend’ lap joints. For this purpose, artificial neural network (ANN) simulation was carried out. Two ANNs were trained using an ultra-small data sample, which did not provide acceptable predictive accuracy for the applied simulation methods. To solve this issue, it was proposed to artificially increase the learning sample by including additional data synthesized according to the knowledge and experience of experts. As a result, a relationship between the USC parameters and the functional characteristics of the lap joints was determined. The results of ANN simulation were successfully verified; the developed USC procedures were able to form a laminate with an even regular structure characterized by a minimum number of discontinuities and minimal damage to the consolidated components. Full article
(This article belongs to the Special Issue Research Progress on Mechanical Behavior of Polymers)
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18 pages, 2438 KiB  
Article
On Cyclic-Fatigue Crack Growth in Carbon-Fibre-Reinforced Epoxy–Polymer Composites
by Silvain Michel, Neal Murphy, Anthony J. Kinloch and Rhys Jones
Polymers 2024, 16(3), 435; https://doi.org/10.3390/polym16030435 - 4 Feb 2024
Cited by 5 | Viewed by 1227
Abstract
The growth of cracks between plies, i.e., delamination, in continuous fibre polymer matrix composites under cyclic-fatigue loading in operational aircraft structures has always been a very important factor, which has the potential to significantly decrease the service life of such structures. Whilst current [...] Read more.
The growth of cracks between plies, i.e., delamination, in continuous fibre polymer matrix composites under cyclic-fatigue loading in operational aircraft structures has always been a very important factor, which has the potential to significantly decrease the service life of such structures. Whilst current designs are based on a ‘no growth’ design philosophy, delamination growth can nevertheless arise in operational aircraft and compromise structural integrity. To this end, the present paper outlines experimental and data reduction procedures for continuous fibre polymer matrix composites, based on a linear elastic fracture mechanics approach, which are capable of (a) determining and computing the fatigue crack growth (FCG) rate, da/dN, curve; (b) providing two different methods for determining the mandated worst-case FCG rate curve; and (c) calculating the fatigue threshold limit, below which no significant FCG occurs. Two data reduction procedures are proposed, which are based upon the Hartman-Schijve approach and a novel simple-scaling approach. These two different methodologies provide similar worst-case curves, and both provide an upper bound for all the experimental data. The calculated FCG threshold values as determined from both methodologies are also in very good agreement. Full article
(This article belongs to the Special Issue Research Progress on Mechanical Behavior of Polymers)
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16 pages, 6063 KiB  
Article
High-Cycle Fatigue Behaviour of Polyetheretherketone (PEEK) Produced by Additive Manufacturing
by Pedro Rendas, Alexandre Imperadeiro, Rui F. Martins and Bruno A. R. Soares
Polymers 2024, 16(1), 18; https://doi.org/10.3390/polym16010018 - 20 Dec 2023
Cited by 5 | Viewed by 2177
Abstract
Polyetheretherketone (PEEK) is the leading high-performance thermoplastic biomaterial that can be processed through material extrusion (ME) additive manufacturing (AM), also known as three-dimensional (3D) printing, for patient-specific load-bearing implant manufacture. Considering the importance of cyclic loading for load-bearing implant design, this work addresses [...] Read more.
Polyetheretherketone (PEEK) is the leading high-performance thermoplastic biomaterial that can be processed through material extrusion (ME) additive manufacturing (AM), also known as three-dimensional (3D) printing, for patient-specific load-bearing implant manufacture. Considering the importance of cyclic loading for load-bearing implant design, this work addresses the high-cycle fatigue behaviour of 3D-printed PEEK. In this work, printed PEEK specimens are cyclically loaded under stress-controlled tension–tension using different stress levels between 75% and 95% of printed PEEK’s tensile strength. The experimental results are used to document 3D-printed PEEK’s fatigue behaviour using Basquin’s power law, which was compared with previous fatigue research on bulk PEEK and other 3D-printing materials. As a pioneering study on its fatigue behaviour, the results from this work show that 3D-printed PEEK exhibits an above-average fatigue strength of 65 MPa, corresponding to about 75% of its tensile strength. Fracture surface analysis suggests that a transition can occur from ductile to brittle fracture with maximum stresses between 85% and 95% of the tensile strength. Evidence of crack propagation features on fracture surfaces under scanning electron microscope (SEM) observation suggests crack initiation in void defects created by printing deposition that propagates longitudinally through line bonding interfaces along layers. Considering this, 3D-printed PEEK’s fatigue behaviour can be strongly related to printing conditions. Further research on the fatigue behaviour of 3D-printed PEEK is necessary to support its use in load-bearing implant applications. Full article
(This article belongs to the Special Issue Research Progress on Mechanical Behavior of Polymers)
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