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Special Issue "Metal-Polymer Multi-Material Structures and Manufacturing Techniques in Transportation"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (7 March 2020) | Viewed by 18700

Special Issue Editor

Prof. Dr. Sergio T. Amancio-Filho
E-Mail Website
Guest Editor
Institute of Materials Science, Joining and Forming, Graz University of Technology, BMK Endowed Professorship for Aviation, 8010 Graz, Austria
Interests: joining technology; additive manufacturing; materials science; metallurgy; polymer science; composites; metals and hybrid structures
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Special Issue Information

Dear Colleagues,

The reduction of greenhouse gas emissions—particularly from fossil-fuel-powered vehicles—by means of weight savings and leaner fuel consumption, helps to curb environmental impacts. Such environmental concerns and restrictions imposed by regulations have motivated scientists and engineers to design lighter structures without compromising reliability. The demand for lightweight structures has been growing across a wide range of engineering solutions, for transport, renewable power generation and construction industries. In general, for a variety of industries and specifically in the case of transport, where both weight savings and increased energy efficiency are pursued, the use of high-performance engineering polymers and composites (e.g., glass- and carbon-fiber reinforced polymers), has gained considerable importance in hybrid, multi-material structures. In addition to their advantage in specific strength, composites possess outstanding corrosion resistance, high strength and fatigue performances and thermal stability. Furthermore, the search for lightweight solutions has also fuelled the development of more advanced aluminum, titanium, magnesium and high strength steel alloys, reducing the overall weight of a structure while maintaining high mechanical performance. Therefore, the observed trend for achieving weight reduction is a mixed material design.

The field of metal-polymer multi-material structures has been growing at an increasing and particularly fast pace in recent years. Several techniques have been or are being developed with the aim of being used for additively manufacturing or joining dissimilar materials in cost efficient manners. Despite the benefits of using metals, high-performance polymers and their respective composite materials in a hybrid structure, the manufacturing of these dissimilar materials presents a great challenge due to their distinct physicochemical properties.

Over time, various joining techniques have been developed including adhesive bonding, mechanical fastening, welding-based technologies or combinations of one or more of these individual techniques—known as hybrid joining technologies. More recently, a new manufacturing field has been created to directly assemble metal-composite structures. These technologies involve the hybridization of metallic parts with polymer processing—such as injection over molding—or composite lamination techniques. These allow the fabrication of complex parts with improved mechanical performance and strength-to-weight ratios. Within this scope, one field that has great disruptive potential for contributing to the rise of hybrid structures is additive manufacturing. The possibility of using new materials and their combinations to additively manufacture hybrid components with complex geometries, has gained a momentum across several industries.

This Special Issue intends to review the state-of-the-art in joining and additive manufacturing of metal-polymer multi-material structures. Short communications, critical literature reviews, and technical papers addressing the correlations between microstructure, process, properties and mechanical performance are intended. The submission of manuscripts reporting on new joining and additive manufacturing processes as well as case-studies of real parts or applications in transportation are especially welcome. Examples of metal-composite multi-materials may include aluminium, titanium, magnesium, high and ultra-high strength steels combined with thermoset, thermoplastics and their composites. Manuscripts dealing with the fundamental understanding of the processing steps and material-related changes—e.g. microstructure, physical-chemical, corrosion resistance, natural and accelerated aging, crash and damage tolerance properties, on experimental, mathematical and computational areas will be considered for publication. New thermal joining techniques using, but not limited to, friction-, laser-, induction- and ultrasonic-based energy, as well as new 3D printing, wire-based and powder-based additive manufacturing techniques for direct assembly of metal-polymer multi-materials, will receive special attention in the reviewing process.

Prof. Dr. Sergio T. Amancio-Filho
Guest Editor

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. Materials 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 2300 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

  • Lightweight Structures
  • Joining Processes
  • Engineering Polymers
  • Fiber Reinforced Polymers
  • Polymer Composites
  • Multi-Material Structures
  • Metal-Polymer Connections
  • Additive Manufacturing

Published Papers (10 papers)

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Article
Durability of Metal-Composite Friction Spot Joints under Environmental Conditions
Materials 2020, 13(5), 1144; https://doi.org/10.3390/ma13051144 - 04 Mar 2020
Cited by 5 | Viewed by 1270
Abstract
The current paper investigates the durability of the single-lap shear aluminum-composite friction spot joints and their behavior under harsh accelerated aging as well as natural weathering conditions. Four aluminum surface pre-treatments were selected to be performed on the joints based on previous investigations; [...] Read more.
The current paper investigates the durability of the single-lap shear aluminum-composite friction spot joints and their behavior under harsh accelerated aging as well as natural weathering conditions. Four aluminum surface pre-treatments were selected to be performed on the joints based on previous investigations; these were sandblasting (SB), conversion coating (CC), phosphoric acid anodizing (PAA), and PAA with a subsequent application of primer (PAA-P). Most of the pre-treated specimens retained approximately 90% of their initial as-joined strength after accelerated aging experiments. In the case of the PAA pre-treatment, the joint showed a lower retained strength of about 60%. This was explained based on the penetration of humidity into the fine pores of the PAA pre-treated aluminum, reducing the adhesion between the aluminum and composite. Moreover, friction spot joints produced with three selected surface pre-treatments were held under outside natural weathering conditions for one year. PAA-P surface pre-treated specimens demonstrated the best performance with a retained strength of more than 80% after one year. It is believed that tight adhesion and chemical bonding reduced the penetration of humidity at the interface between the joining parts. Full article
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Article
Process-Related Changes in Polyetherimide Joined by Friction-Based Injection Clinching Joining (F-ICJ)
Materials 2020, 13(5), 1027; https://doi.org/10.3390/ma13051027 - 25 Feb 2020
Cited by 4 | Viewed by 1206
Abstract
This work presents a comprehensive study on the effects of the Friction-based Injection Clinching Joining (F-ICJ) process on the microstructure and local properties of the stake head. The manuscript evaluates the consequences on the quasi-static mechanical performance of hybrid joints of amorphous polyetherimide [...] Read more.
This work presents a comprehensive study on the effects of the Friction-based Injection Clinching Joining (F-ICJ) process on the microstructure and local properties of the stake head. The manuscript evaluates the consequences on the quasi-static mechanical performance of hybrid joints of amorphous polyetherimide (PEI) with aluminium AA6082. Through an overlay of microhardness map on a cross-polarized transmitted-light optical microscopy (CP-TLOM) image, two lower-strength microstructural zones in the PEI stake head were observed: a plastically-deformed zone (PDZ) and a thermo-mechanically-affected zone (PTMAZ). When compared to the base material, PDZ and PTMAZ have a reduction of 12%–16% and 8%–12%, respectively, in local mechanical properties. The reduced local strength was associated with distinct volumes of loosely packed PEI chains with unsteady chain conformation and thus larger free volume in the affected regions. The mechanical strength reduction is reversible through physical aging by thermal annealing the joints, which additionally shows that process-induced thermomechanical degradation of PEI by chain scission, as evidenced by size exclusion chromatography (SEC) analysis, does not appear to affect local mechanical strength. An evaluation of typical loading regimes of staked joints in lap shear (average ultimate force of 1419 ± 43 N) and cross tensile (average ultimate force of 430 ± 44 N) testing indicates that the process-induced changes of PEI do not compromise the global mechanical performance of such a structure. These findings provide a better understanding of the relationships between processing, microstructure, and properties for further F-ICJ process optimization. Full article
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Article
CFRP Thin-Ply Fibre Metal Laminates: Influences of Ply Thickness and Metal Layers on Open Hole Tension and Compression Properties
Materials 2020, 13(4), 910; https://doi.org/10.3390/ma13040910 - 18 Feb 2020
Cited by 9 | Viewed by 1753
Abstract
Thin-ply laminates exhibit a higher degree of freedom in design and altered failure behaviour, and therefore, an increased strength for unnotched laminates in comparison to thick-ply laminates. For notched laminates, the static strength is strongly decreased; this is caused by a lack of [...] Read more.
Thin-ply laminates exhibit a higher degree of freedom in design and altered failure behaviour, and therefore, an increased strength for unnotched laminates in comparison to thick-ply laminates. For notched laminates, the static strength is strongly decreased; this is caused by a lack of stress relaxation through damage, which leads to a higher stress concentration and premature, brittle failure. To overcome this behaviour and to use the advantage of thin-ply laminates in areas with high stress concentrations, we have investigated thin-ply hybrid laminates with different metal volume fractions. Open hole tensile (OHT) and open hole compression (OHC) tests were performed with quasi-isotropic carbon fibre reinforced plastic (CFRP) specimens. In the area of stress concentration, 90° layers were locally substituted by stainless steel layers of differing volume fractions, from 12.5% to 25%. The strain field on the specimen surface was evaluated in-situ using a digital image correlation (DIC) system. The embedding of stainless steel foils in thin-ply samples increases the OHT strength up to 60.44% compared to unmodified thin-ply laminates. The density specific OHT strength is increased by 33%. Thick-ply specimens achieve an OHC strength increase up to 45.7%, which corresponds to an increase in density specific strength of 32.4%. Full article
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Article
Effect of Metal Surface Topography on the Interlaminar Shear and Tensile Strength of Aluminum/Polyamide 6 Polymer-Metal-Hybrids
Materials 2019, 12(18), 2963; https://doi.org/10.3390/ma12182963 - 12 Sep 2019
Cited by 12 | Viewed by 1674
Abstract
Mechanical interlocking has been proven to be an effective bonding mechanism for dissimilar material groups like polymers and metals. Therefore, this contribution assesses several surface pretreatments for the metallic adherent. Blasting, etching, combined blasting and etching, thermal spraying, and laser structuring processes are [...] Read more.
Mechanical interlocking has been proven to be an effective bonding mechanism for dissimilar material groups like polymers and metals. Therefore, this contribution assesses several surface pretreatments for the metallic adherent. Blasting, etching, combined blasting and etching, thermal spraying, and laser structuring processes are investigated with regard to the achievable interlaminar strength and the corresponding surface roughness parameters. The experiments are carried out on EN AW-6082/polyamide 6 polymer-metal-hybrids, utilizing a novel butt-bonded hollow cylinder specimen geometry for determining the shear and tensile strength. The experimental results indicate that the surface roughness slope has a major impact on the interlaminar strength. A laser-generated pin structure is found to provide the best mechanical performance as well as the highest surface slope of all investigated structuring methods. Full article
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Article
Evaluation of Joint Formation and Mechanical Performance of the AA7075-T6/CFRP Spot Joints Produced by Frictional Heat
Materials 2019, 12(6), 891; https://doi.org/10.3390/ma12060891 - 17 Mar 2019
Cited by 14 | Viewed by 1683
Abstract
The development of lightweight hybrid metal–polymer structures has recently attracted interest from the transportation industry. Nevertheless, the possibility of joining metals and polymers or composites is still a great challenge. Friction Spot Joining (FSpJ) is a prize-winning friction-based joining technique for metal–polymer hybrid [...] Read more.
The development of lightweight hybrid metal–polymer structures has recently attracted interest from the transportation industry. Nevertheless, the possibility of joining metals and polymers or composites is still a great challenge. Friction Spot Joining (FSpJ) is a prize-winning friction-based joining technique for metal–polymer hybrid structures. The technology is environment-friendly and comprises very short joining cycles (2 to 8 s). In the current work, aluminum alloy 7075-T6 and carbon-fiber-reinforced polyphenylene sulfide (CF-PPS) friction spot joints were produced and evaluated for the first time in the literature. The spot joints were investigated in terms of microstructure, mechanical performance under quasi-static loading and failure mechanisms. Macro- and micro-mechanical interlocking were identified as the main bonding mechanism, along with adhesion forces as a result of the reconsolidated polymer layer. Moreover, the influence of the joining force on the mechanical performance of the joints was addressed. Ultimate lap shear forces up to 4068 ± 184 N were achieved in this study. A mixture of adhesive–cohesive failure mode was identified, while cohesive failure was dominant. Finally, a qualitative comparison with other state-of-the-art joining technologies for hybrid structures demonstrated that the friction spot joints eventually exhibit superior/similar strength than/to concurrent technologies and shorter joining times. Full article
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Article
Microstructure and Mechanical Performance of Additively Manufactured Aluminum 2024-T3/Acrylonitrile Butadiene Styrene Hybrid Joints Using an AddJoining Technique
Materials 2019, 12(6), 864; https://doi.org/10.3390/ma12060864 - 14 Mar 2019
Cited by 13 | Viewed by 2061 | Correction
Abstract
AddJoining is an emerging technique that combines the principles of the joining method and additive manufacturing. This technology is an alternative method to produce metal–polymer (composite) structures. Its viability was demonstrated for the material combination composed of aluminum 2024-T3 and acrylonitrile butadiene styrene [...] Read more.
AddJoining is an emerging technique that combines the principles of the joining method and additive manufacturing. This technology is an alternative method to produce metal–polymer (composite) structures. Its viability was demonstrated for the material combination composed of aluminum 2024-T3 and acrylonitrile butadiene styrene to form hybrid joints. The influence of the isolated process parameters was performed using the one-factor-at-a-time approach, and analyses of variance were used for statistical analysis. The mechanical performance of single-lap joints varied from 910 ± 59 N to 1686 ± 39 N. The mechanical performance thus obtained with the optimized joining parameters was 1686 ± 39 N, which failed by the net-tension failure mode with a failure pattern along the 45° bonding line. The microstructure of the joints and the fracture morphology of the specimens were studied using optical microscopy and scanning electron microscopy. From the microstructure point of view, proper mechanical interlocking was achieved between the coated metal substrate and 3D-printed polymer. This investigation can be used as a base for further improvements on the mechanical performance of AddJoining hybrid-layered applications. Full article
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Article
The Influence of Clamping Pressure on Joint Formation and Mechanical Performance of Ti6Al4V/CF-PEEK Friction-Riveted Joints
Materials 2019, 12(5), 745; https://doi.org/10.3390/ma12050745 - 04 Mar 2019
Cited by 5 | Viewed by 2150
Abstract
This work aims at investigating the influence of pre-set clamping pressure on the joint formation and mechanical strength of overlapping direct-friction-riveted joints. A pneumatic fixture device was developed for this work, with clamping pressure varying from 0.2 MPa to 0.6 MPa. A case [...] Read more.
This work aims at investigating the influence of pre-set clamping pressure on the joint formation and mechanical strength of overlapping direct-friction-riveted joints. A pneumatic fixture device was developed for this work, with clamping pressure varying from 0.2 MPa to 0.6 MPa. A case study on overlapping joints using Ti6Al4V rivets and woven carbon fiber-reinforced polyether-ether-ketone (CF-PEEK) parts were produced. Digital image correlation and microscopy revealed the expected compressive behavior of the clamping system and the continuous pressure release upon the joining process owing to the rivet plastic deformation and the polymer squeezing flow. Two preferential paths of material flow were identified through the alternate replacement of the upper and lower composite parts by a poly-methyl-methacrylate (PMMA) plate—the composite upward and squeezing flow between the parts which induced their separation. The ultimate lap shear forces up to 6580 ± 383 N were achieved for the direct-friction-riveted CF-PEEK overlap joints. The formation of a gap to accommodate squeezed polymer between the composite parts during the process had no influence on the joint mechanical performance. The increase in the clamping pressure for joints produced with a low friction force did not affect the joint-anchoring efficiency and consequently the joint strength. On the other hand, the combined effect of a high-friction force and clamping pressure induced the inverted bell shape of the plastically deformed rivet tip, a lower anchoring efficiency, and the delamination of the composite, all of which decrease the mechanical strength by 31%. Therefore, the higher the friction force and clamping pressure, the more defects would be generated in the composite parts and the more changes in the shape of the plastically deformed rivet tip, leading to a lower level of quasi-static mechanical performance. All the joints failed by initial bearing of the composite and final rivet pull-out. The findings of this work can contribute to further improvement of the clamping design for industrial application. Full article
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Article
Fundamentals of Force-Controlled Friction Riveting: Part II—Joint Global Mechanical Performance and Energy Efficiency
Materials 2018, 11(12), 2489; https://doi.org/10.3390/ma11122489 - 07 Dec 2018
Cited by 11 | Viewed by 2097
Abstract
The present work investigates the correlation between energy efficiency and global mechanical performance of hybrid aluminum alloy AA2024 (polyetherimide joints), produced by force-controlled friction riveting. The combinations of parameters followed a central composite design of experiments. Joint formation was correlated with mechanical performance [...] Read more.
The present work investigates the correlation between energy efficiency and global mechanical performance of hybrid aluminum alloy AA2024 (polyetherimide joints), produced by force-controlled friction riveting. The combinations of parameters followed a central composite design of experiments. Joint formation was correlated with mechanical performance via a volumetric ratio (0.28–0.66 a.u.), with a proposed improvement yielding higher accuracy. Global mechanical performance and ultimate tensile force varied considerably across the range of parameters (1096–9668 N). An energy efficiency threshold was established at 90 J, until which, energy input displayed good linear correlations with volumetric ratio and mechanical performance (R-sq of 0.87 and 0.86, respectively). Additional energy did not significantly contribute toward increasing mechanical performance. Friction parameters (i.e., force and time) displayed the most significant contributions to mechanical performance (32.0% and 21.4%, respectively), given their effects on heat development. For the investigated ranges, forging parameters did not have a significant contribution. A correlation between friction parameters was established to maximize mechanical response while minimizing energy usage. The knowledge from Parts I and II of this investigation allows the production of friction riveted connections in an energy efficient manner and control optimization approach, introduced for the first time in friction riveting. Full article
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Article
Fundamentals of Force-Controlled Friction Riveting: Part I—Joint Formation and Heat Development
Materials 2018, 11(11), 2294; https://doi.org/10.3390/ma11112294 - 15 Nov 2018
Cited by 12 | Viewed by 2914
Abstract
This work presents a systematic study on the correlations between process parameters and rivet plastic deformation, produced by force-controlled friction riveting. The 5 mm diameter AA2024 rivets were joined to 13 mm, nominal thickness, polyetherimide plates. A wide range of joint formations was [...] Read more.
This work presents a systematic study on the correlations between process parameters and rivet plastic deformation, produced by force-controlled friction riveting. The 5 mm diameter AA2024 rivets were joined to 13 mm, nominal thickness, polyetherimide plates. A wide range of joint formations was obtained, reflecting the variation in total energy input (24–208 J) and process temperature (319–501 °C). The influence of the process parameters on joint formation was determined, using a central composite design and response surface methodology. Friction time displayed the highest contribution on both rivet penetration (61.9%) and anchoring depth (34.7%), and friction force on the maximum width of the deformed rivet tip (46.5%). Quadratic effects and two-way interactions were significant on rivet anchoring depth (29.8 and 20.8%, respectively). Bell-shaped rivet plastic deformation—high mechanical interlocking—results from moderate energy inputs (~100 J). These geometries are characterized by: rivet penetration depth of 7 to 9 mm; maximum width of the deformed rivet tip of 9 to 12 mm; and anchoring depth higher than 6 mm. This knowledge allows the production of optimized friction-riveted connections and a deeper understanding of the joining mechanisms, further discussed in Part II of this work. Full article
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Correction
Correction: Falck, R. et al. Microstructure and Mechanical Performance of Additively Manufactured Aluminum 2024-T3/Acrylonitrile Butadiene Styrene Hybrid Joints by AddJoining Technique. Materials 2019, 12, 864
Materials 2020, 13(6), 1460; https://doi.org/10.3390/ma13061460 - 23 Mar 2020
Viewed by 898
Abstract
The authors wish to make the following correction to the paper [...] Full article
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