Stress-adapted fiber orientation along the principal stress directions for continuous fiber-reinforced material extrusion

Abstract

A proven method to enhance the mechanical properties of additively manufactured plastic parts is the embedding of continuous fibers. Due to its great flexibility, continuous fiber-reinforced material extrusion allows fiber strands to be deposited along optimized paths. Nevertheless, the fibers have so far been embedded in the parts contour-based or on the basis of regular patterns. The outstanding strength and stiffness properties of the fibers in the longitudinal direction cannot be optimally utilized. Therefore, a method is proposed which allows to embed fibers along the principal stresses into the parts in a load-oriented manner. A G-code is generated from the calculated principal stress trajectories and the part geometry, which also takes into account the specific restrictions of the manufacturing technology used. A distinction is made between fiber paths and the matrix so that the average fiber volume content can be set in a defined way. To determine the mechanical properties, tensile and flexural tests are carried out on specimens consisting of carbon fiber-reinforced polyamide. In order to increase the influence of the principal stress-based fiber orientation, open-hole plates are used for the tensile tests, as this leads to variable stresses across the cross section. In addition, a digital image correlation system is used to determine the deformations during the mechanical tests. It was found that the peak load of the optimized open-hole plates was greater by a factor of 3 and the optimized flexural specimens by a factor of 1.9 than the comparison specimens with unidirectional fiber alignment.

Interlaminar and translaminar fracture toughness of 3D‐printed continuous fiber reinforced composites: A review and prospect

“…Different fiber trajectories used in 3D‐printed CFRCs: (A) principal stress trajectories, 69 (B) Tailor woven trajectories, 68 and (C, D) asymmetrical and symmetric fluid flow streamlines 70 …”

“…As the fiber direction in the laminates was usually unidirectional and not designed to hinder cracks, the reinforcing performances of continuous fibers were not maximized. To redistribute loads, increase component stiffness, reduce stress concentration, and significantly increase the ultimate strength, different fiber trajectories are proposed, such as woven, principal stress, fluid flow streamlines, and others resulting from numerical optimization processes, [68][69][70] as shown in Figure 14. These fiber trajectory design methods might provide references for improving the fracture toughness of CFRCs.…”

“…Heat treatment was considered a good post-treatment method for improving product performance because it was significantly effective in reducing the porosity of composites. 73 He et al 46 found that the presence of voids in continuous carbon F I G U R E 1 4 Different fiber trajectories used in 3D-printed CFRCs: (A) principal stress trajectories, 69 (B) Tailor woven trajectories, 68 and (C, D) asymmetrical and symmetric fluid flow streamlines. 70 fiber-reinforced polyamide-based composites had a significantly negative impact on the initial fracture toughness of DCB specimens (continuous CF/PA6 filament used in specimen production was supplied by Markforged).…”

3D printing continuous natural fiber reinforced polymer composites: A review

“…58 The direction and distribution designs of continuous fibers could well control the mechanical properties of CNFRCs to meet the customized requirements. 59 In the existing literature, the 3D printing process, fiber surface treatment, and interfacial property optimization were studied to enhance the mechanical performances of CNFRCs. For instance, the selection of the printing parameters showed that decreases in layer height, printing speed, line spacing, and an increase in printing temperature could improve the mechanical properties of CNFRCs within a certain range of parameters.…”

“…CNFRC was designed to achieve high specific strength and customized performance by using continuous fiber to enhance the pure matrix's mechanical performance and control of anisotropy 58 . The direction and distribution designs of continuous fibers could well control the mechanical properties of CNFRCs to meet the customized requirements 59 . In the existing literature, the 3D printing process, fiber surface treatment, and interfacial property optimization were studied to enhance the mechanical performances of CNFRCs.…”