| Summary: | Acoustic levitation techniques have been widely studied within the biological and medical disciplines, primarily to manipulate cells and molecules whose size range lies outside the capabilities of optical tweezers. Since, ultrasonic assembly has been applied more widely, with the trapping of micron- to millimeter-size objects of different shapes and sizes, and the formation of ordered arrays of particles having become possible. The research presented in this thesis investigates the feasibility of applying ultrasonic particle manipulation methodologies to manufacture short fibre reinforced polymer composites. A series of ultrasonic devices is developed allowing the manufacture of thin layers of anisotropic composite material. Strands of unidirectional reinforcement are, in response to the acoustic radiation force, shown to form inside various matrix media. The technique proves suitable for both photo-initiator and temperature controlled polymerisation mechanisms. To further explore key parameters in the design of ultrasonic devices, a number of linear acoustic models are developed. One- and two-dimensional finite element analysis are employed to study the resonance characteristics, compute the acoustic pressure, and calculate the acoustophoretic force on small spherical particles. A range of fibre architectures that can be generated with devices of up to eight transducer elements is explored by plane and spherical wave propagation methods. A separate study analyses the dynamic response of both an elastic sphere and cylinder placed in a standing wave field by solving the equations of non-linear fluid dynamics for arbitrary angles of radiation incidence. A comparison with analytical results shows good agreement in the limit of small particles. For large particles, the acoustic radiation force is further evaluated across a range of pressure amplitudes, and for a number of initial particle positions. Finally, a series of glass fibre reinforced composite samples constructed via the ultrasonic assembly process are subjected to tensile loading and the stress-strain response is characterised. Structural anisotropy is clearly demonstrated, together with a 43 % difference in failure stress between principal directions. The average stiffnesses of samples strained along the direction of fibre reinforcement and transversely across it were 17.66 ± 0.63 MPa and 16.36 ± 0.48 MPa, respectively.
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