An Investigation into Mechanical Properties of 3D Printed Thermoplastic-Thermoset Mixed-Matrix Composites: Synergistic Effects of Thermoplastic Skeletal Lattice Geometries and Thermoset Properties
<p>nTopology designs showcasing the thermoset phase (<b>left</b>), PLA thermoplastic phase (<b>middle</b>), and the resulting hybrid composite structure for Gyroid and Grid designs at 10% and 20% infill densities (<b>right</b>).</p> "> Figure 2
<p>Custom mold fabrication process involving 3D printing of customised CAD, silicon casting within the 3D printed mold, and the resulting flexible silicon mold. On the right, the PLA skeletons were kept in the silicon mould and the custom designed resin infiltration assembly dispensed the epoxy and polyurethane resin ‘on-demand’.</p> "> Figure 3
<p>Schematic representation of the process of developing hybrid mixed matrix composites (thermoset-thermoplastic).</p> "> Figure 4
<p>FTIR spectroscopy revealing the chemical structure of the skeleton PLA (<b>A</b>) and different thermoset matrix resins [epoxy (<b>B</b>) and polyurethane (<b>C</b>), both cured and uncured].</p> "> Figure 5
<p>Representative stress-strain curves for mixed matrix composites of epoxy with PLA and polyurethane with PLA for (<b>a</b>) Grid and (<b>b</b>) Gyroid infill designs. The uniaxial tensile behaviour of the baseline materials are shown in (<b>c</b>).</p> "> Figure 6
<p>Summary of the ultimate tensile strength (UTS) and % elongation of 3D printed PLA thermoplastic—epoxy and PU based thermoset mixed matrix composites. (<b>a</b>) demonstrates the UTS for the grid and gyroid infill designs with two infill densities for both types of resin infiltrations, while (<b>b</b>) showcase(ed the % elongation values of the same specimens. Young’s moduli of all the baseline and mixed matrix composites are represented in (<b>c</b>).</p> "> Figure 7
<p>Optical microscope images of the fractured surfaces after tensile tests. The top panel (<b>a</b>) shows the fractured interfaces of different mixed matrices with PLA–polyurethane system, while the bottom panel (<b>b</b>) represents the fracture behavior of the specimens with PLA–epoxy based mixed matrix composites after tensile tests.</p> "> Figure 8
<p>Scanning electron microscopy-based fractography studies for PLA skeletal lattice-based composites of epoxy and polyurethane matrices. Top panel (<b>a</b>,<b>b</b>) demonstrates the failure trend of PLA-polyurethane based mixed matrix composites, while the bottom panel (<b>c</b>–<b>f</b>) represents the brittle failure modes of the PLA-epoxy based composite systems.</p> ">
Abstract
:1. Introduction
2. Materials and Methods
2.1. Design of Mixed Matrices with Different Design Elements and Infill Density
2.2. 3D Printing of PLA Thermoplastic Skeleton and Silicon Based Thermoset Casting Molds
2.3. Thermoset Infiltration to Fabricate Mixed Matrix Composites
2.4. Chemical, Topographic and Physical Characterizations
3. Results
3.1. 3D Printing of PLA Patterns and Manufacturing of Mixed Matrix Composites
3.2. Fourier Transformed Infrared Spectroscopy Analysis
3.3. Mechanical Properties
3.4. Qualitative Assessment of the Fractured Surfaces
3.5. Fractography Study with SEM Image Analysis
4. Discussion
4.1. Influences of Infill Patterns and Infill Density on the UTS and % Elongation
4.2. Impact of the Various Resin Systems on the UTS and % Elongation
4.3. Influence of Thermoset Matrix on the Failure Behaviour of the Skeletal Lattice Thermoplastic
5. Conclusions
- Total eight variants of different TP-TS specimens comprising two different PLA-based skeletal lattice geometries (grid and gyroid), two varying infill densities (10% and 20%) of the same and two different resin systems (epoxy and polyurethane) were developed to figure out the best design and material combination for physically compatible mixed matrix composite.
- For a given infill pattern, higher infill density gave rise to higher surface area reflecting in the increased intake of resin (weight)
- Using qualitative FTIR spectroscopy, the signature peaks of the TP and the TS are identified whereas missing and/or decreased intensities of the peaks denoted the complete or partial curing for both the two-part resin systems.
- For both gyroid geometries, epoxy based mixed matrix composites demonstrated higher UTS compared to their polyurethane counterpart. This was explained in view of the higher stiffness of epoxy compared to relatively flexible polyurethane matrix. Grid geometries showed a mixed behavior.
- Higher elongation was recorded in the cases of gyroid patterned PLA skeleton-based composites with polyurethane resin system. The elongation increased with the infill density.
- This behavior was explained in the light of relatively flexible nature of the polyurethane matrix compared to the epoxy system, added with the gyroid geometry which being fully interconnected in the direction of stress application, distributed the load more efficiently prior to failure.
- From the optical microscope image analysis, ductile nature of failure was identified in the gyroid based geometries where typical “fiber pull-out” was noticed. All the grid-based composites (for both epoxy and polyurethane-based matrices) showcased brittle and sharp fracture. As the TS resins were confined in the isolated cells of the grid structure, there was no provision of the stress distribution like the continuous and interconnected gyroid structure. As a result, failure of any one cell dictated catastrophic failure of the entire structure, where more “progressive failure” was observed in the gyroid counterparts.
- Having higher area under curve for the 20% infilled gyroid patterns infiltrated with polyurethane resin, this composite system was believed to be the material with highest toughness. These mixed matrix composites can be used in high mechanical shock absorbing applications.
- Fractography revealed that thermoset matrix material properties (ductile or brittle) governed the failure modes of the thermoplastic lattice skeletons. While the PLA fibers demonstrated ductile failure when embedded in polyurethane matrix, brittle fracture was observed in the same PLA fibers in the PLA-epoxy system.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Infill Design | Grid | Gyroid | ||
Infill Density % | 10 | 20 | 10 | 20 |
Design Geometry | ||||
Weight, g (Thermoplastic) | 2 | 3 | 2 | 3 |
Surface Area, mm2 | 4665.5 | 7379.5 | 7640.8 | 8821.2 |
Weight, g (with Polyurethane Resin) | 8.2 | 8.35 | 7.5 | 7.65 |
Mixed Matrix (with Polyurethane Resin) | ||||
Weight, g (with Epoxy Resin) | 10.7 | 11 | 10.7 | 10.8 |
Mixed Matrix (with Epoxy Resin) |
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Khanjar, S.; Barui, S.; Kate, K.; Ajjarapu, K.P.K. An Investigation into Mechanical Properties of 3D Printed Thermoplastic-Thermoset Mixed-Matrix Composites: Synergistic Effects of Thermoplastic Skeletal Lattice Geometries and Thermoset Properties. Materials 2024, 17, 4426. https://doi.org/10.3390/ma17174426
Khanjar S, Barui S, Kate K, Ajjarapu KPK. An Investigation into Mechanical Properties of 3D Printed Thermoplastic-Thermoset Mixed-Matrix Composites: Synergistic Effects of Thermoplastic Skeletal Lattice Geometries and Thermoset Properties. Materials. 2024; 17(17):4426. https://doi.org/10.3390/ma17174426
Chicago/Turabian StyleKhanjar, Saleh, Srimanta Barui, Kunal Kate, and Kameswara Pavan Kumar Ajjarapu. 2024. "An Investigation into Mechanical Properties of 3D Printed Thermoplastic-Thermoset Mixed-Matrix Composites: Synergistic Effects of Thermoplastic Skeletal Lattice Geometries and Thermoset Properties" Materials 17, no. 17: 4426. https://doi.org/10.3390/ma17174426