Ultrasound-assisted 3D printing of glass fiber-reinforced polymers: Hierarchical fiber alignment and property enhancement

Particle-reinforced polymers attracted great attention in aerospace and automotive, where fiber alignment plays a critical role. Conventional manufacturing methods and magnetic/electric field-based fiber alignment techniques require certain filler geometries and electromagnetic properties, severely limiting their applicability. In this study, a novel ultrasound-assisted stereolithography additive manufacturing technique was developed, exploiting acoustic radiation forces generated from the acoustic property mismatches between fiber fillers and polymer matrix, manipulating multidirectional alignment of glass fibers and graphene particles during 3D printing. A method to quantify the fiber alignment level was developed and profound effects of ultrasonic driving voltage and fiber mass fraction on the fiber alignment rates were clarified, enabling up to 93.44 % orientation rate within the target angular range. Tensile testing of five fiber-aligned specimens revealed that the 0° unidirectionally aligned sample exhibited superior performance, with tensile strength increasing by 46.29 % compared to random-aligned samples and by 91.43 % compared with pure polymers. By integrating a rotating platform with the acoustic radiation force field, layer-by-layer fiber angle control was realized, facilitating the fabrication of complex 3D structures—including bionic flowers, character patterns, and intricate geometries. The developed technique was further validated using spherical nickel-coated graphite particles, attaining a 90.20 % orientation rate, expanding its potential for aligning particles with different geometries during 3D printing of particle-reinforced polymers.