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Additive manufacturing of multi-material composites
Dissertation   Open access

Additive manufacturing of multi-material composites

Ahmed Mahmoud Hossameldin Mahmoud Ibrahim
Doctor of Philosophy (Ph.D.), Drexel University
Jun 2024
DOI:
https://doi.org/10.17918/00010632
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Abstract

Additive manufacturing Fibrous composites Mechanical wear--Testing Thermosetting plastics Mechanical Engineering
Thermosetting polymers are well known for having remarkable strength and durability with respect to their weight, making them favorable over metals and alloys in a good number of industrial applications. However, these polymers are very brittle and will break shortly after damage is initiated in them (low toughness). This work aims to offer a resolution towards the strength/toughness trade-off by creating polymeric multi-material (MM) composites using an additive manufacturing (AM) vat photo-polymerization technique known as digital light processing (DLP). The first type of composites featured is called spatially resolved multi-resin structures, constituting a combination of resins, where DLP facilitates controlling resin choice and proportion, spatial location and domain size with no seams or surface artifacts and excellent material bonding. To synergistically combine strength and flexibility, rectangular bars of different geometrical structures (stacked, staggered and checkered) using a brittle methacrylate-based resin and a ductile urethane-based resin in pure and blended form were printed and mechanically tested. The results obtained emphasized the necessity of careful selection of resin combinations as well as the spatial arrangement pattern to achieve the desired synergistic effect. The second type featured is fiber reinforced polymeric composites (FRPCs), a class of materials widely used in so many modern applications nowadays, constituting high strength and modulus fibers embedded in a polymeric matrix, where fibers act as load carriers and the matrix keeps them oriented during loading. Despite their low cost and good in-plane properties (strength and stiffness), traditionally made FRPCs suffer from poor out-of-plane properties, and that makes them susceptible to delamination (poor interlaminar toughness). DLP printing can revolutionize making FRPCs as it allows high fiber loadings (near 30%) without serious operational issues like in other 3D printing techniques, as well as the facile addition of engineered polymeric interleaves in the form resin rich layers (RRLs) of controlled location, size and chemistry, which have been scientifically proven effective in ameliorating fiber composites' interlaminar toughness without sacrificing their overall strength. We demonstrated the efficiency of the technique by modifying a commercial 3D printer to produce near defect-free FRPCs with a novel methacrylate-based resin and random chopped glass fiber (GF) mats, where discrete resin layers of pre-determined number, height and location were easily incorporated. Mechanical testing results of printed sets showed that increase in resin layer thickness increases delamination resistance without sacrificing other important mechanical properties (tensile, flexure) thanks to improved mat consolidation, a unique feature of random chopped GF mats. Results also revealed that mat consolidation is considerably lower in DLP printing than in traditional FRPCs manufacturing (example: vacuum assisted resin transfer molding "VARTM"), thereby lower mechanical properties. This work shows the great promise DLP holds for the state-of-the-art. The ease of pattern control demonstrated in the first class opens the door for producing a wide array of topology optimized parts with location-controlled properties and increased service time, which can be of major significance for highly innovation demanding industries in terms of aesthetics and mechanical integrity (example: sports). The freedom of adding and controlling fiber and resin materials in demonstrated in the second class would be significant for high performance industries (examples: automotive, aerospace and construction), as further research and development on the current 3D printing systems would focus on automation, scale up and compression efficiency, leading to much more versatile, reliable, time and material efficient FRPCs production processes.

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