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Polymers
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Structural Integrity Assessment on Polymers and Composites
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Structural Integrity Assessment on Polymers and Composites

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

Deadline for manuscript submissions: closed (31 January 2024) | Viewed by 9192

Special Issue Editors

Dr. Francisco J. M. Q. de Melo

E-Mail Website
Guest Editor
Department of Mechanical Engineering, University of Aveiro, Aveiro, Portugal
Interests: computational mechanics; experimental techniques; fracture mechanics; damage; fatigue; FEM; aeronautics; railway infrastructure; transportation engineering
Special Issues, Collections and Topics in MDPI journals
Dr. Behzad V. Farahani

E-Mail Website
Guest Editor
Advance Monitoring and Structural Integrity Unit, Department of Mechanical Engineering, Faculty of Engineering, University of Porto, Porto, Portugal
Interests: numerical modelling; hydrogen embrittlement; experimental techniques; composites structures; fracture mechanics; damage mechanics; fatigue analysis; structural integrity assessment; material characterization
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In many engineering fields, structures are often subjected to various loading conditions that initiate and propagate defects in particular structural cracks. The development of fracture mechanics studies has enabled us to assess structural integrity and the adjustment of structural damage thresholds and to predict failure in damaged structures, extending their service life safely. These improvements may bring a positive social impact to the economy, public safety, and even the environment.

Fracture mechanics in polymers and composite materials has become a progressively concerning field as many industries transition to implementing these materials in many critical structural applications. As industries make the shift to implementing these materials, a greater understanding of structural integrity and failure mechanisms for the corresponding materials is required. Generally, polymers may reveal some inherently diverse behaviors compared to metals when cracks are subject to loading. This is largely attributed to their tough and ductile mechanical properties.

Microstructurally, metals contain grain boundaries, crystallographic planes, and dislocations, while polymers are made up of long molecular chains. In the same instance that fracture in metals involves breaking bonds, the covalent and van der Waals bonds need to be broken for fracture to occur. These secondary bonds (van der Waals) play an important role in the fracture deformation at the crack tip. Many materials, such as metals, use linear elastic fracture mechanics (LEFM) to predict behavior at the crack tip. For some materials, this is not always the appropriate way to characterize fracture response, and an alternate model is used. Elastic–plastic fracture mechanics relates to materials that show a time-independent and nonlinear behavior or, in other words, plastically deform. The initiation site for fracture in these materials can often occur at inorganic dust particles where the stress exceeds critical value.

The proposed Special Issue will gather original contributions in the form of research papers and reviews, demonstrating the latest developments and advances in the structural integrity assessment of polymeric materials subjected to a variety of loading conditions, which may result in damage, fracture, and failure occurrence. It will deal with applications from mechanical engineering to biomechanics, multiscale modelling with polymeric/composites structures, mathematical development, numerical simulations, experimental validations, proof of concept, structural/system design, performance verification and mechanical characterization in the field of biomechanics, automotive, pipes, tanks, packing materials, insulation, wood substitutes, adhesives, matrix for composites, and elastomers and any other potential topics in the industrial market.

Prof. Dr. Francisco J. M. Q. de Melo
Dr. Behzad V. Farahani
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

  • structural integrity
  • polymers
  • fracture
  • damage
  • fatigue
  • composites
  • numerical modeling
  • experimental mechanics
  • multiscale models
  • durability

Published Papers (6 papers)

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Research

17 pages, 3600 KiB  
Article
Elasto-Static Analysis of Composite Restorations in a Molar Tooth: A Meshless Approach
by Farid Mehri Sofiani, Behzad V. Farahani and Jorge Belinha
Polymers 2024, 16(4), 458; https://doi.org/10.3390/polym16040458 - 07 Feb 2024
Viewed by 627
Abstract
Dental caries and dental restorations possess a long history and over the years, many materials and methods have been invented. In recent decades, modern techniques and materials have brought complexity to this issue, which has created the necessity to investigate more and more [...] Read more.
Dental caries and dental restorations possess a long history and over the years, many materials and methods have been invented. In recent decades, modern techniques and materials have brought complexity to this issue, which has created the necessity to investigate more and more to achieve durability, consistency, proper mechanical properties, efficiency, beauty, good colour, and reduced costs and time. Combined with the recent advances in the medical field, mechanical engineering plays a significant role in this topic. This work aims at studying the elasto-static response of a human molar tooth as a case study, respecting the integral property of the tooth and different composite materials of the dental restoration. The structural integrity of the case study will be assessed through advanced numerical modelling resorting to meshless methods within the stress analysis on the molar tooth under different loading conditions. In this regard, bruxism is considered as being one of the most important cases that cause damage and fracture in a human tooth. The obtained meshless methods results are compared to the finite element method (FEM) solution. The advantages and disadvantages of the analysed materials are identified, which could be used by the producers of the studied materials to improve their quality. On the other hand, a computational framework, as the one presented here, would assist the clinical practice and treatment decision (in accordance with each patient’s characteristics). Full article
(This article belongs to the Special Issue Structural Integrity Assessment on Polymers and Composites)
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21 pages, 8285 KiB  
Article
Drilling of Cross-Ply UHMWPE Laminates: A Study on the Effects of the Tool Geometry and Cutting Parameters on the Integrity of Components
by Antonio Díaz-Álvarez, Marcos Rodríguez-Millán, Ignacio Rubio, Daekyum Kim and José Díaz-Álvarez
Polymers 2023, 15(19), 3882; https://doi.org/10.3390/polym15193882 - 25 Sep 2023
Cited by 1 | Viewed by 987
Abstract
Ultrahigh-molecular-weight polyethylene (UHMWPE) is used in the defence industry mainly owing to its properties, such as excellent dimensional stability, excellent ballistic performance, and light weight. Although UHMWPE laminates are generally studied under impact loads, it is crucial to understand better the optimal machining [...] Read more.
Ultrahigh-molecular-weight polyethylene (UHMWPE) is used in the defence industry mainly owing to its properties, such as excellent dimensional stability, excellent ballistic performance, and light weight. Although UHMWPE laminates are generally studied under impact loads, it is crucial to understand better the optimal machining conditions for assembling auxiliary structures in combat helmets or armour. This work analyses the machinability of UHMWPE laminates by drilling. The workpiece material has been manufactured through hot-pressing technology and subjected to drilling tests. High-speed steel (HSS) twist drills with two different point angles and a brad and spur drill that is 6 mm in diameter have been used for this study. Cutting forces, failure, and main damage modes are analysed, making it possible to extract relevant information for the industry. The main conclusion is that the drill with a smaller point angle has a better cutting force performance and less delamination at the exit zone (5.4 mm at a 60 m/min cutting speed and a 0.05 mm/rev feed) in the samples. This value represents a 46% improvement over the best result obtained in terms of delamination at the exit when using the tool with the larger point angle. However, the brad and spur drill revealed a post-drilling appearance with high fuzzing and delamination. Full article
(This article belongs to the Special Issue Structural Integrity Assessment on Polymers and Composites)
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21 pages, 6804 KiB  
Article
Damage Monitoring of Composite Adhesive Joint Integrity Using Conductivity and Fiber Bragg Grating
by Chow-Shing Shin and Liang-Wei Chen
Polymers 2023, 15(6), 1575; https://doi.org/10.3390/polym15061575 - 22 Mar 2023
Viewed by 1689
Abstract
Adhesive joints possess a number of advantages over traditional joining methods and are widely used in composite structures. Conventional non-destructive examination techniques do not readily reveal joint degradation before the formation of explicit defects. Embedded fiber Bragg grating (FBG) sensors and the resistance [...] Read more.
Adhesive joints possess a number of advantages over traditional joining methods and are widely used in composite structures. Conventional non-destructive examination techniques do not readily reveal joint degradation before the formation of explicit defects. Embedded fiber Bragg grating (FBG) sensors and the resistance of carbon nanotube (CNT)-doped conductive joints have been proposed to monitor the structural integrity of adhesive joints. Both techniques will be employed and compared in the current work to monitor damage development in adhesive joints under tensile and cyclic fatigue loading. Most of the previous works took measurements under an applied load, which by itself will affect the monitoring signals without the presence of any damage. Moreover, most FBG works primarily relied on the peak shifting phenomenon for sensing. Degradation of adhesive and inter-facial defects will lead to non-uniform strain that may chirp the FBG spectrum, causing complications in the peak shifting measurement. In view of the above shortfalls, measurements are made at some low and fixed loads to preclude any unwanted effect due to the applied load. The whole FBG spectrum, instead of a single peak, will be used, and a quantitative parameter to describe spectrum changes is proposed for monitoring purposes. The extent of damage is revealed by a fluorescent penetrant and correlated with the monitoring signals. With these refined techniques, we hope to shed some light on the relative merits and limitations of the two techniques. Full article
(This article belongs to the Special Issue Structural Integrity Assessment on Polymers and Composites)
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23 pages, 3789 KiB  
Article
Behavior of Hybrid Reinforced Concrete Bridge Decks under Static and Fatigue Loading
by Jared W. McRory, Fray F. Pozo-Lora, Zachary Benson, Raed Tawadrous and Marc Maguire
Polymers 2022, 14(23), 5153; https://doi.org/10.3390/polym14235153 - 26 Nov 2022
Viewed by 1708
Abstract
This paper presents a new bridge deck reinforcement alternative using hybrid reinforced concrete (Hybrid) consisting of Glass Fiber Reinforced Polymer (GFRP) rebar and alkali-resistant fiberglass composite macrofibers added to the concrete mixture. Fiberglass composite macrofibers are a miniaturized GFRP reinforcing bar that is [...] Read more.
This paper presents a new bridge deck reinforcement alternative using hybrid reinforced concrete (Hybrid) consisting of Glass Fiber Reinforced Polymer (GFRP) rebar and alkali-resistant fiberglass composite macrofibers added to the concrete mixture. Fiberglass composite macrofibers are a miniaturized GFRP reinforcing bar that is a composite of resin and glass fibers. An experimental testing program and analytical modeling were conducted to evaluate the structural performance at the service and ultimate limit states. Thirteen full-scale bridge deck specimens were constructed and tested under static and fatigue loading. The fatigue loading was applied up to two million cycles at a frequency of 4 Hz. Post-fatigue, the specimens were tested to failure to compare pre-and post-fatigue behavior. Simplified and moment-curvature analytical models were used to predict the specimens’ flexural strength at the ultimate level, and both were found to be accurate for predicting pre- and post-fatigue strength. Deflection and crack width were monitored throughout the fatigue loading, and these values were compared to the recommended AASHTO LRFD serviceability limits. Testing and analytical results showed that the Hybrid deck is a viable alternative to steel-reinforced and GFRP-reinforced bridge decks for flexural behavior. The service and ultimate level behavior of each bridge deck type was adequate as compared to the AASHTO LRFD service limits. The exceptional post-peak energy absorption demonstrated by the Hybrid adds ductility to previously elastic GFRP reinforced sections. Full article
(This article belongs to the Special Issue Structural Integrity Assessment on Polymers and Composites)
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22 pages, 7235 KiB  
Article
Experimental and Finite Element Simulation of Polyolefin Elastomer Foams Using Real 3D Structures: Effect of Foaming Agent Content
by Ehsan Rostami-Tapeh-Esmaeil, Amirhosein Heydari, Ali Vahidifar, Elnaz Esmizadeh and Denis Rodrigue
Polymers 2022, 14(21), 4692; https://doi.org/10.3390/polym14214692 - 03 Nov 2022
Cited by 5 | Viewed by 1931
Abstract
In this study, polyolefin elastomer (POE) foams were prepared without any curing agent using a single-step foaming technique. The effect of azodicarbonamide (ADC) content as a chemical foaming agent on the foams’ morphology and mechanical properties was studied using scanning electron microscopy (SEM), [...] Read more.
In this study, polyolefin elastomer (POE) foams were prepared without any curing agent using a single-step foaming technique. The effect of azodicarbonamide (ADC) content as a chemical foaming agent on the foams’ morphology and mechanical properties was studied using scanning electron microscopy (SEM), mechanical properties (tension and compression) and hardness. The results showed that increasing the ADC content from 2 to 3, 4 and 5 phr (parts per hundred rubber) decreased the foam density from 0.75 to 0.71, 0.65 and 0.61 g/cm3, respectively. The morphological analysis revealed that increasing the ADC content from 2 to 4 phr produced smaller cell sizes from 153 to 109 µm (29% lower), but a higher cell density from 103 to 591 cells/mm3 (470% higher). However, using 5 phr of ADC led to a larger cell size (148 µm) and lower cell density (483 cells/mm3) due to cell coalescence. The tensile modulus, strength at break, elongation and hardness properties continuously decreased by 28%, 21%, 16% and 14%, respectively, with increasing ADC content (2 to 5 phr). On the other hand, the compressive properties, including elastic modulus and compressive strength, increased by 20% and 64%, respectively, with increasing ADC content (2 to 5 phr). The tensile and compression tests revealed that the former is more dependent on foam density (foaming ratio), while the latter is mainly controlled by the cellular structure (cell size, cell density and internal gas pressure). In addition, 2D SEM images were used to simulate the foams’ real 3D structure, which was used in finite element methods (FEM) to simulate the stress–strain behavior of the samples at two levels: micro-scale and macro-scale. Finally, the FEM results were compared to the experimental data. Based on the information obtained, a good agreement between the macro-scale stress–strain behavior generated by the FEM simulations and experimental data was obtained. While the FEM results showed that the sample with 3 phr of ADC had the lowest micro-scale stress, the sample with 5 phr had the highest micro-scale stress due to smaller and larger cell sizes, respectively. Full article
(This article belongs to the Special Issue Structural Integrity Assessment on Polymers and Composites)
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19 pages, 5584 KiB  
Article
A Modified Mean Stress Criterion for Considering Size Effects on Mode I Fracture Estimation of Rounded-Tip V-Notched Polymeric Specimens
by Ali Reza Torabi, Mahdi Jabbari, Javad Akbardoost and Sergio Cicero
Polymers 2022, 14(7), 1491; https://doi.org/10.3390/polym14071491 - 06 Apr 2022
Viewed by 1507
Abstract
The aim of this paper is to assess the size and geometry effects on the mode I notch fracture toughness of polymeric samples containing rounded-tip V-shaped (RV) notches (V-notch with a finite radius at the notch tip). First, using a large number of [...] Read more.
The aim of this paper is to assess the size and geometry effects on the mode I notch fracture toughness of polymeric samples containing rounded-tip V-shaped (RV) notches (V-notch with a finite radius at the notch tip). First, using a large number of fracture tests on an RV-notched Brazilian disk and semi-circular bending polymeric samples with four different sizes, the size-dependent values of the notch fracture toughness are obtained. Then, the mean stress criterion is modified for characterizing the size-dependency of notch fracture toughness in polymeric samples. The resulting modified mean stress criterion considers higher order terms of the stress field when calculating the fracture process zone length around the tip of the defect. Additionally, the critical distance rc is assumed to be associated with the specimen size and a formula containing fitting parameters is utilized for considering this trend of rc. The comparison between the values of notch fracture toughness obtained from experiments and those predicted by the modified mean stress criterion shows that the suggested approach can provide accurate estimations of size-dependent values of notch fracture toughness in polymeric specimens containing RV notches. Full article
(This article belongs to the Special Issue Structural Integrity Assessment on Polymers and Composites)
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