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Growing age and different conditions often require the replacement of orthoses, and FDM-based 3D printing can produce them quickly with less investment. In today's market for orthotics, these characteristics are highly desired. Therefore, this study is fully focused on the optimization and strength analysis of FDM 3D-printed ankle–foot orthoses (AFO) fabricated using PLA and PLA reinforced with carbon fiber (PLA-C). An increase in ankle plantar-flexor force can be achieved by reinforcing thermoplastic AFOs with CFs. Specially designed mechanical strength tests were conducted at the UTM to generate force–displacement curves for stored elastic energy and fracture studies. The mechanical behavior of both AFOs was predicted with the help of an FEA. The model predictions were validated by comparing them with mechanical strength testing conducted under the same loading and boundary conditions as the FEA. In both the prediction and experimental analysis, the PLA-C-based AFOs were stiffer and could withstand greater loads than the PLA-based AFOs. An area of high stress in the simulation and a fracture point in experimentation were both found at the same location. Furthermore, these highly accurate models will allow the fabrication of AFOs to be improved without investing time and resources on trials. [ABSTRACT FROM AUTHOR]

• Examined rheological effects and revealing shear-thinning after 3 wt% CNTs. • Substantial increase in elastic modulus with CNTs in tensile test. • The Payne effect and non-linearity in fabricated nanocomposites were observed. • Storage modulus and strain rate sensitivity increases during DMA. • Fractography demonstrated CNTs effect for enhanced fracture resistance. Direct Ink Writing (DIW) revolutionizes 3D printing with carbon-based inks, offering design, complexity, and sustainability advantages. This study centers on formulating Polydimethylsiloxane (PDMS) and Multiwalled-Carbon Nanotube (CNT) nanocomposite-inks, assessing their rheological properties for DIW suitability and minimum reinforcement demands. Mechanical tests on DIW-fabricated samples are conducted under static and dynamic conditions substantiated by fractographic analysis. Rheological investigation confirms a 3 wt % reinforcement threshold for printability. Comparatively, 3.5 wt % CNT nanocomposites exhibit a substantial 143% increase in elastic modulus over neat PDMS. Dynamic mechanical analysis reveals heightened storage modulus with increasing CNT content, while fractography underscores localized areas resisting fracture, demanding elevated stress for breakage. [ABSTRACT FROM AUTHOR]

Direct ink writing (DIW) is a rapidly expanding additive manufacturing (AM) technique valued for its cost-efficiency and material adaptability. While DIW offers substantial process flexibility, achieving precise manufacturing demands a thorough understanding of its printability parameters. Key process variables such as printing speed, nozzle-bed gap, pulses for extrusion, and extrusion multiplier wield significant influence over the shape and dimensions of printed components. In this study, a machine learning model based on k-nearest neighbors is employed to predict dimensional accuracy. The model is trained using measured width and thickness data from printed rings, with flow and printing-speed tests defining parameter boundaries for printing. The final model demonstrates an accuracy of 81% and 74% for two PDMS-CNT composite ink compositions. The principal components analysis underscores the pivotal roles of the extrusion factor and printing speed in achieving superior geometric fidelity. Additionally, retraction-residual tests were conducted, revealing that the initial 10 seconds of extrusion hold critical importance as they can lead to distortions when traversing printed regions or perimeters, necessitating consideration in part design. To evaluate layer adhesion strength, a crucial aspect of AM, T-peel tests were performed. Furthermore, rheological tests provided insights into extrudability, printable reinforcing percentages, shape retention, and yield stress. Highlights • Rheological tests yield insights into minimum reinforcing% and shape retention. • Developed k-NN model predicts accuracy using measured printed rings' data. • PC analysis shows key roles of extrusion factor and print speed. • Retraction-residual tests reveal initial 10 seconds are critical. • Model validation results show 83.45% and 77.95% accuracy, close to prediction. [ABSTRACT FROM AUTHOR]