Recycling of carbon fibers enables a sustainable feedstock for industrial applications of high-performance composite materials. This allows light weighting with recycled carbon fibers due to their superior mechanical properties while reducing the high embodied energy and cost of virgin carbon fiber composites. This study optimizes a pyrolysis cycle for fiber recovery of an aerospace-grade thermoset prepreg and a cleaning (oxidation) step to minimize fiber degradation and left-over resin residue, enabling dispersion and alignment of the recycled, discontinuous fibers in the Tailorable Universal Feedstock for Forming alignment process. The study balances the influence of the optimized thermal cycle (pyrolysis + oxidation step) on recycled carbon fiber strength retention with the ability to disperse at the filament level to create aligned, recycled carbon fiber composite samples with high fiber volume fraction. The optimized thermal cycle for efficient fiber recovery applied a pyrolysis step at 500 °C for 4 h in an inert gas environment and an additional oxidation step at the same temperature for 100 min. This resulted in ~20% strength degradation of the fiber compared to the virgin fiber. The processed recycled composite achieved 44% fiber volume fraction with full modulus translation (~128 GPa) compared to the virgin continuous composite with strength translation (~870 MPa), reaching ~50%.

Manufacturing of large composite structures is labor-intensive and challenging. Traditional processing methods can be replaced by automated approaches such as Automated Tape Placement (ATP). The focal point of this effort is on thin-ply thermoset prepreg materials which have shown better resistance to damage tolerance under applied stress when compared to standard ply-thickness materials in recent times. However, composites processed by thin-ply materials require more placement iterations to achieve the same net volume of coverage as the standard ply-thickness materials. This can increase the probability of placement defects such as gaps and overlaps, which may degrade the mechanical performance of the composite. Modifications to the existing ATP system are made to address the issues of placement defects, which resulted in improved accuracy for thin ply placement. Unidirectional and quasi-isotropic panels are fabricated from 12’’ wide unidirectional prepreg sheet with the conventional hand layup (CHL) method for the baseline property comparison with panels fabricated by the ATP process using a ¼’’ wide slit tape. This paper investigates the effects of processing defects and material variability on the mechanical properties such as tensile, Open hole tension and Bearing tests of thin ply composites. In addition, the microstructure of the fabricated thin-ply composite panels is analysed using ultrasonic C-scans and confocal microscopy to examine the processing and material quality.

Wearable devices for gravity balancing have high potential for impact across domains, including neuromotor rehabilitation and occupational systems. Devices made from compliant mechanisms, optimized to achieve specific compensation moments at target joints, have proven effective, but thus far have solely been optimized towards gravity compensation and not other wearability criteria. In this work, we propose a multi-objective optimization framework, based on particle swarm optimization, to design a soft, gravity balancing shoulder orthosis, while taking into account wearability constraints such as undesired loading directions and device size. Using this custom framework, we pursued multiple stages of orthosis design and optimization, selecting multiple solutions to be translated to real-world prototypes. These solutions were realized via 3D printing with thermoplastic polyurethane and evaluated for mechanical performance on benchtop and in-vivo. In-vivo testing on 6 healthy individuals demonstrated relative reductions in muscle activity for the anterior deltoid and upper trapezius, by 53 % and 71 % respectively when operating the orthosis for static tasks within functional shoulder ranges of motion. Changes in muscle activation were also were observed across other muscles, including the posterior deltoid, as well as in dynamic tasks at different speeds.