Modelling Fiber Orientation during Additive Manufacturing-Compression Molding Processes

The production of high-performance thermoplastic composites reinforced with short carbon fibers can be achieved by a novel “additive manufacturing-compression molding” technique. An advantage of such a combination is two-fold: controlled fiber orientation in additive manufacturing and less void content by compression molding. In this study, a computational fluid dynamics model has been developed to predict the behavior of printed layers during fiber-reinforced thermoplastic extrusion and subsequent compression molding. The fiber orientation was modelled with the simple quadratic closure model. The interaction between the fibers was included using a rotary diffusion coefficient that becomes significant in concentrated regimes. Finally, the second rank orientation tensor was coupled with the momentum equation as an anisotropic part of the stress term. The effect of different fiber orientation within printed layers was investigated to determine the favorable printing scenarios in the strands that undergo compression molding afterwards. The developed numerical model enables design of high-performance composites with tunable mechanical properties.Mechanical Engineerin

Experimental and Numerical Investigations on Dynamic Mechanical Properties of TPMS Structures

Triply Periodic Minimal Surface (TPMS) lattice structures have been of increasing interest due to their light weighting, enhanced mechanical properties, and energy absorption characteristics for automotive and biomedical applications. With the advent of additive manufacturing and geometric modeling software, TPMS lattices with complex geometries can be realized. In this work, TPMS lattice structures were fabricated with PLA using fused filament fabrication (FFF) and their dynamic properties are characterized through drop tower experiments. Although lightweight TPMS lattices are beneficial for their impact absorption capability, most of the existing works are limited to quasi-static compression, and dynamic impact tests are rarely performed. The current study investigates the stress-strain and energy absorption characteristics of TPMS lattices through drop tower testing and numerical modeling. Finite element modeling for TPMS lattices is carried out to validate the experimental responses. The mechanical properties, deformation, and failure mechanisms of TPMS lattices under dynamic impact are summarized for potential future applications.Mechanical Engineerin

ISOGEOMETRIC SHAPE OPTIMIZATION OF AUXETICS WITH PRESCRIBED NONLINEAR DEFORMATION

Ph.DDOCTOR OF PHILOSOPHY (FOE

Numerical modeling of fiber orientation in additively manufactured composites

Additive manufacturing has undergone a significant transformation, evolving from a mere prototyping technique to a reliable and proven manufacturing technology that can produce products of varying sizes and materials. The incorporation of fibers in additive manufacturing processes has the potential to improve a range of material properties, including mechanical, thermal, and electrical properties. However, this improvement is largely dependent on the orientation of the fibers within the material, with the properties being enhanced primarily in the direction of fiber orientation. As a result, accurately predicting and controlling the fiber orientation during the extrusion or deposition process is critical. Various methods are available to control fiber orientation, such as manipulating the nozzle shape, extrusion and nozzle speed, the gap between the nozzle and substrate, as well as fiber features like aspect ratio and volume fraction. At the same time, the presence and orientation of fibers can significantly impact the flow pattern and extrusion pressure conditions, ultimately affecting the formation of printed strands in a manner distinct from those without fibers. For that reason, our study utilizes computational fluid dynamics to anticipate and comprehend the printing conditions that would result in favorable fiber orientations and strand shapes, incl. corner printing. Our findings may be utilized to determine optimal toolpaths for 3D printing composites, as well as printing conditions that will facilitate the achievement of the desired fiber orientation within individual strands