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Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Manufacturing Processes and Systems".

Deadline for manuscript submissions: closed (20 December 2021) | Viewed by 33351

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Dr. Maria Magdalena Pastor

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Department of Strength of Materials and Structural Engineering (RMEE), Barcelona School of Industrial Engineering (ETSEIB), Universitat Politècnica de Catalunya-Barcelona Tech (UPC), 08028 Barcelona, Spain
Interests: 3D printing; mechanical properties; strain measurement techniques; numerical modeling; structural design

Dr. Jordi Bonada

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Guest Editor

Department of Strength of Materials and Structural Engineering (RMEE), Barcelona School of Industrial Engineering (ETSEIB), Universitat Politècnica de Catalunya-Barcelona Tech (UPC), 08028 Barcelona, Spain
Interests: finite element analysis; numerical modeling; mechanical properties; frontal photopolymerization process; digital image correlation

Special Issue Information

Dear Colleagues,

Polymer-based additive manufacturing parts make up a significant and growing proportion of 3D printing, with increasingly diverse areas of application in the medical, aerospace, and automotive sectors.

Many factors, including materials and processes, and their expanding use as final or structural parts have contributed to this growth and have led to the need for specialized research in this field, which is of importance in many branches of engineering.

It is well known that several characteristics of printed parts, such as mechanical properties, depend on printing parameters. Therefore, analysis of the influence of manufacturing parameters on printed parts is a key factor in order to optimize the printing process as well as to predict and understand the material properties.

We encourage scientists and engineers to submit papers for inclusion in this Special Issue. There are no restrictions on the type of manufacture, polymer or field of application. Papers on theory, experiments, design, simulation, etc. will be considered for publication, and we expect that many will contain aspects of all of these.

A non-exhaustive list of possible items would be:

Process parameters
Experimental testing
Standards for testing
Anisotropy and asymmetry
Material constants characterization
Constitutive models
Mesostructure design and effects
Numerical simulation
Finite element analysis
Static and impact strength
Fatigue and fracture

Dr. Maria Magdalena Pastor
Dr. Jordi Bonada
Guest Editors

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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 2600 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

Additive manufacturing
Printing parameters
Mechanical properties
Material modeling
Numerical simulation
Experimental testing

Published Papers (10 papers)

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Research

12 pages, 3404 KiB

Open AccessArticle

Multiscale Soft Surface Instabilities for Adhesion Enhancement

by Vaisakh Vilavinalthundil Mohanan, Ho Yi Lydia Mak, Nishan Gurung and Qin Xu

Materials 2022, 15(3), 852; https://doi.org/10.3390/ma15030852 - 23 Jan 2022

Viewed by 2847

Abstract

Soft polymeric gels are susceptible to buckling-induced instabilities due to their great compliance to surface deformations. The instability patterns at soft interfaces have great potential in engineering functional materials with unique surface properties. In this work, we systematically investigated how swelling-induced instability patterns effectively improved the adhesive properties of soft polydimethylsiloxane (PDMS) gels. We directly imaged the formations of the surface instability features during the relaxation process of a swollen gel substrate. The features were found to greatly increase the adhesion energy of soft gels across multiple length scales, and the adhesion enhancement was associated with the variations of contact lines both inside the contact region and along the contact periphery. We expect that these studies of instability patterns due to swelling will further benefit the design of functional interfaces in various engineering applications. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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15 pages, 2503 KiB

Open AccessArticle

Influence of Infill Pattern on the Elastic Mechanical Properties of Fused Filament Fabrication (FFF) Parts through Experimental Tests and Numerical Analyses

by Jordi Bonada, Mª Magdalena Pastor and Irene Buj-Corral

Materials 2021, 14(18), 5459; https://doi.org/10.3390/ma14185459 - 21 Sep 2021

Cited by 12 | Viewed by 2544

Abstract

Fused Filament Fabrication (FFF) is one of the most extensive additive manufacturing technologies for printing prototypes or final parts in various fields. Some printed parts need to meet structural requirements to be functional parts. Therefore, it is necessary to know the mechanical behavior of the printed samples as a function of the printing parameters in order to optimize the material used during the manufacturing process. It is known that FFF parts can present orthotropic characteristics as a consequence of the manufacturing process, in which the material is deposited layer by layer. Therefore, these characteristics must be considered for a correct evaluation of the printed parts from a structural point of view. In this paper, the influence of the type of filling pattern on the main mechanical properties of the printed parts is analyzed. For this purpose, the first parts are 3D printed using three different infill patterns, namely grid, linear with a raster orientation of 0 and 90°, and linear with a raster orientation of 45°. Then, experimental tensile tests, on the one hand, and numerical analyses using finite elements, on the other hand, are carried out. The elastic constants of the material are obtained from the experimental tests. From the finite element analysis, using a simple approach to create a Representative Volume Model (RVE), the constitutive characteristics of the material are estimated: Young’s Moduli and Poisson’s ratios of the printed FFF parts. These values are successfully compared with those of the experimental tests. The results clearly show differences in the mechanical properties of the FFF printed parts, depending on the internal arrangement of the infill pattern, even if similar 3D printing parameters are used. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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17 pages, 6480 KiB

Open AccessArticle

Analysis of the Compression Behaviour of Reinforced Photocurable Materials Used in Additive Manufacturing Processes Based on a Mask Image Projection System

by Jordi Bonada, Pol Barcelona, Miquel Casafont, Josep Maria Pons, Jose Antonio Padilla and Elena Xuriguera

Materials 2021, 14(16), 4605; https://doi.org/10.3390/ma14164605 - 16 Aug 2021

Cited by 2 | Viewed by 1547

Abstract

Mask image projection based on stereolithography is an additive manufactured technology based on a Frontal Photopolymerization Process. Therefore, photocurable resins are used to build-up parts layer by layer. In this paper, alumina particles have been used as a reinforcement filler in order to improve the material stress-strain behaviour. In addition, the increment of the photoconversion ratio is a key factor to enhance the mechanical properties. Consequently, a numerical model has been used to determine the optimal printing parameters to enhance the elastic mechanical properties of printed parts according to the characteristics of photocurable materials. Stable and homogeneous reinforced materials have been obtained with an alumina content ranging from 5 to 15 wt%. Furthermore, the compression behaviour of reinforced materials has been analysed by means of experimental tests. The results show an enhancement of mechanical properties after the addition of reinforcement fillers, obtaining a maximum improvement in 10 wt% of solid load content. Finally, the influence of the sample’s orientation on the construction platform has been discussed. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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19 pages, 5492 KiB

Open AccessArticle

Cost-Effectively 3D-Printed Rigid and Versatile Interpenetrating Polymer Networks

by Osman Konuray, Arnau Sola, Jordi Bonada, Agnieszka Tercjak, Albert Fabregat-Sanjuan, Xavier Fernández-Francos and Xavier Ramis

Materials 2021, 14(16), 4544; https://doi.org/10.3390/ma14164544 - 12 Aug 2021

Cited by 6 | Viewed by 1964

Abstract

Versatile acrylate–epoxy hybrid formulations are becoming widespread in photo/thermal dual-processing scenarios, especially in 3D printing applications. Usually, parts are printed in a stereolithography or digital light processing (DLP) 3D printer, after which a thermal treatment would bestow the final material with superior mechanical properties. We report the successful formulation of such a hybrid system, consisting of a commercial 3D printing acrylate resin modified by an epoxy–anhydride mixture. In the final polymeric network, we observed segregation of an epoxy-rich phase as nano-domains, similar to what was observed in a previous work. However, in the current work, we show the effectiveness of a coupling agent added to the formulation to mitigate this segregation for when such phase separation is undesired. The hybrid materials showed significant improvement of Young’s modulus over the neat acrylate. Once the flexible, partially-cured material was printed with a minimal number of layers, it could be molded into a complex form and thermally cured. Temporary shapes were readily programmable on this final material, with easy shape recovery under mild temperatures. Inspired by repairable 3D printed materials described recently, we manufactured a large object by printing its two halves, and then joined them covalently at the thermal cure stage with an apparently seamless union. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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23 pages, 24583 KiB

Open AccessArticle

Structural Response Prediction of Thin-Walled Additively Manufactured Parts Considering Orthotropy, Thickness Dependency and Scatter

by Sigfrid-Laurin Sindinger, David Marschall, Christoph Kralovec and Martin Schagerl

Materials 2021, 14(9), 2463; https://doi.org/10.3390/ma14092463 - 10 May 2021

Cited by 6 | Viewed by 2651

Abstract

Besides the design freedom offered by additive manufacturing, another asset lies within its potential to accelerate product development processes by rapid fabrication of functional prototypes. The premise to fully exploit this benefit for lightweight design is the accurate structural response prediction prior to part production. However, the peculiar material behavior, characterized by anisotropy, thickness dependency and scatter, still constitutes a major challenge. Hence, a modeling approach for finite element analysis that accounts for this inhomogeneous behavior is developed by example of laser-sintered short-fiber-reinforced polyamide 12. Orthotropic and thickness-dependent Young’s moduli and Poisson’s ratios were determined via quasi-static tensile tests. Thereof, material models were generated and implemented in a property mapping routine for finite element models. Additionally, a framework for stochastic finite element analysis was set up for the consideration of scatter in material properties. For validation, thin-walled parts on sub-component level were fabricated and tested in quasi-static three-point bending experiments. Elastic parameters showed considerable anisotropy, thickness dependency and scatter. A comparison of the predicted forces with experimentally evaluated reaction forces disclosed substantially improved accuracy when utilizing the novel inhomogeneous approach instead of conventional homogeneous approaches. Furthermore, the variability observed in the structural response of loaded parts could be reproduced by the stochastic simulations. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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20 pages, 6857 KiB

Open AccessArticle

Feature Engineering for Surrogate Models of Consolidation Degree in Additive Manufacturing

by Mriganka Roy and Olga Wodo

Materials 2021, 14(9), 2239; https://doi.org/10.3390/ma14092239 - 27 Apr 2021

Cited by 4 | Viewed by 1835

Abstract

Surrogate models (SM) serve as a proxy to the physics- and experiment-based models to significantly lower the cost of prediction while providing high accuracy. Building an SM for additive manufacturing (AM) process suffers from high dimensionality of inputs when part geometry or tool-path is considered in addition to the high cost of generating data from either physics-based models or experiments. This paper engineers features for a surrogate model to predict the consolidation degree in the fused filament fabrication process. Our features are informed by the physics of the underlying thermal processes and capture the characteristics of the part’s geometry and the deposition process. Our model is learned from medium-size data generated using a physics-based thermal model coupled with the polymer healing theory to determine the consolidation degree. Our results demonstrate high accuracy (>90%) of consolidation degree prediction at a low computational cost (four orders of magnitude faster than the numerical model). Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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21 pages, 3240 KiB

Open AccessArticle

Modelling of Pore Collapse during Polymer Sintering: Viscoelastic Model with Enclosed Gas

by Florian Wohlgemuth, Dirk Lellinger and Ingo Alig

Materials 2021, 14(9), 2182; https://doi.org/10.3390/ma14092182 - 24 Apr 2021

Cited by 2 | Viewed by 1437

Abstract

Frenkel’s model for the late stage of coalescence of viscous particles has been extended to describe pore collapse in a viscoelastic melt during polymer sintering. The shrinkage of a pore in a polymer melt driven by surface tension is extended by taking into account the effects of trapped gas and gas transport out of the pore. Viscoelasticity has been shown to have a considerable impact on the time scale of the coalescence process. In addition, gas diffusion modifies the coalescence dynamics. Based on a parameter study, different regimes for the pore collapse have been identified. At the beginning of pore collapse, surface tension is considerably stronger than gas pressure within the pore. In this time interval (surface-tension-driven regime), the pore shrinks even in the absence of gas diffusion through the matrix. In the absence of gas transport, the shrinkage dynamic slows down and stops when the surface tension balances the gas pressure in the pore. If gas transport out of the pore is possible, surface tension and gas pressure are balanced while the gas pressure slowly decreases (diffusion-controlled regime). The final phase of pore collapse, which occurs when the gas pressure within the pore decreases sufficiently, is controlled again by surface tension. The limitations of the model are discussed. To analyze the interplay between different mechanisms and process steps during selective laser sintering, the respective time scales are compared using experimental data. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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9 pages, 2036 KiB

Open AccessArticle

Effects of 3D Printing-Line Directions for Stretchable Sensor Performances

by Chi Cuong Vu, Thanh Tai Nguyen, Sangun Kim and Jooyong Kim

Materials 2021, 14(7), 1791; https://doi.org/10.3390/ma14071791 - 05 Apr 2021

Cited by 10 | Viewed by 2680

Abstract

Health monitoring sensors that are attached to clothing are a new trend of the times, especially stretchable sensors for human motion measurements or biological markers. However, price, durability, and performance always are major problems to be addressed and three-dimensional (3D) printing combined with conductive flexible materials (thermoplastic polyurethane) can be an optimal solution. Herein, we evaluate the effects of 3D printing-line directions (45°, 90°, 180°) on the sensor performances. Using fused filament fabrication (FDM) technology, the sensors are created with different print styles for specific purposes. We also discuss some main issues of the stretch sensors from Carbon Nanotube/Thermoplastic Polyurethane (CNT/TPU) and FDM. Our sensor achieves outstanding stability (10,000 cycles) and reliability, which are verified through repeated measurements. Its capability is demonstrated in a real application when detecting finger motion by a sensor-integrated into gloves. This paper is expected to bring contribution to the development of flexible conductive materials—based on 3D printing. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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13 pages, 3339 KiB

Open AccessArticle

Towards Customized Footwear with Improved Comfort

by Rafaela Teixeira, Carlos Coelho, João Oliveira, Joana Gomes, Vera Vaz Pinto, Maria José Ferreira, João Miguel Nóbrega, Alexandre Ferreira da Silva and Olga Sousa Carneiro

Materials 2021, 14(7), 1738; https://doi.org/10.3390/ma14071738 - 01 Apr 2021

Cited by 10 | Viewed by 12766

Abstract

A methodology enabling the customization of shoes for comfort improvement is proposed and assessed. For this aim, 3D printed graded density inserts were placed in one of the critical plantar pressure zones of conventional insoles, the heel. A semi-automated routine was developed to design the 3D inserts ready for printing, which comprises three main stages: (i) the definition of the number of areas with different mesh density, (ii) the generation of 2D components with continuous graded mesh density, and (iii) the generation of a 3D component having the same 2D base mesh. The adequacy of the mesh densities used in the inserts was previously assessed through compression tests, using uniform mesh density samples. Slippers with different pairs of inserts embedded in their insoles were mechanically characterized, and their comfort was qualitatively assessed by a panel of users. All users found a particular pair, or a set, of prototype slippers more comfortable than the original ones, taken as reference, but their preferences were not consensual. This emphasizes the need for shoe customization, and the usefulness of the proposed methodology to achieve such a goal. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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16 pages, 2506 KiB

Open AccessFeature PaperArticle

Pozzolan Based 3D Printing Composites: From the Formulation Till the Final Application in the Precision Irrigation Field

by Nicola Schiavone, Vincent Verney and Haroutioun Askanian

Materials 2021, 14(1), 43; https://doi.org/10.3390/ma14010043 - 24 Dec 2020

Cited by 6 | Viewed by 2043

Abstract

A new eco-composite polymer for material extrusion fabrication based on fine fraction pozzolan waste was developed. In addition, the composite materials obtained were used to produce a self-watering pot with complex geometry and a permeable porous part to regulate the passage of water from the storage area to the roots of the plant. Moreover, the system was devised with a cover characterized by a UV-B barrier film. The results have shown the possibility of the 3D printing of complex geometric parts as microporous structures or thin films using a composite based on poly lactic acid (PLA) and pozzolan. The pozzolan has an effect of reinforcement for the composite and at the same time improves the cohesion between the layers of the part during printing. Full article

(This article belongs to the Special Issue Experimental Testing and Numerical Simulation of Polymer-Based Additive Manufacturing Parts)

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