Ultrasonic assembly of anisotropic short fibre reinforced composites

Abstract

We report the successful manufacture of short fibre reinforced polymer composites via the process of ultrasonic assembly. An ultrasonic device 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. A series of glass fibre reinforced composite samples constructed in this way 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±0.63MPa and 16.36±0.48MPa, respectively.

Counterpropagating wave acoustic particle manipulation device for the effective manufacture of composite materials

“…An area of developing interest is the ultrasonic assembly of composite materials [12], [13], [14], [15], [16], [17], [18], [19] and the related areas of metamaterial manufacture [20], [21]. In addition to producing a particular distribution of particles the manufacture of a composite material requires the additional step of curing the host materials to create a solid.…”

“…For example, the removal of ultrasonically assembled composite samples from inside the devices manipulation cavity is often achieved only with great difficulty, due to chemical bonding of the polymer to its surroundings. Furthermore, previous particle manipulation devices typically operate at a limited number of specific resonant frequencies, thus limiting the number of predetermined patterns that can be formed by a single device [12], [13], [14], [15], [16], [20], [17], [18], [19], [21].…”

3-D printed composites with ultrasonically arranged complex microstructure

“…Previous work has shown the effect of including unidirectionally aligned glass microfibres on the mechanical properties of a moulded resin sample. 20 Fibres of varying length scales were independently manipulated within a single part, and previous work has indicated that dynamic realignment of fibres is possible mid-layer. This real time control over microparticle inclusions enables 3D printing of functional composite materials without the necessity for complicated toolpaths which compromise print quality.…”

“…There are a number of existing methods capable of manipulating suspended particles, which make use of magnetic, electric and acoustic fields, as well as flow induced alignment techniques. 6,17,20 Electric and magnetic fields are generally only capable of producing nematic phases and would not allow complex structures to be realised. Magnetic field alignment also typically requires that the microparticles be pre-treated with superparamagnetic nanoparticles to increase their response to an incident magnetic field, which interfere with the intended effect of the microparticles.…”

“…2 Using ultrasonic manipulation to arrange particles within a resin system has been demonstrated in existing publications, 3,9,16,19 and mechanical characterisation of such parts demonstrated that structural anisotropy was achieved (8% stiffness and 43% strength anisotropy along the two principal directions). 20 More recently, 3D printing of components with unidirectional ultrasonically aligned microfibres has been demonstrated, as well as dynamically realigned orthogonal fibres within a single printed layer. 14 This method effectively separates the printing and microstructural formation processes, enabling greater freedom over the microstructures being formed.…”