Architected Flexible Syntactic Foams: Additive Manufacturing and Reinforcing Particle driven Matrix Segregation

TL;DR

This paper explores how hollow particle size influences the internal structure and mechanical properties of 3D-printed polyurethane syntactic foams, enabling tailored lightweight, high-performance materials for aerospace and marine applications.

Contribution

It reveals the role of particle size in controlling matrix segregation and mechanical responses during additive manufacturing of syntactic foams, a novel insight for material design.

Findings

Larger particles bridge gaps, increasing stiffness.

Smaller, stronger particles enhance densification and energy absorption.

Particle size controls microscale morphology and macroscale mechanics.

Abstract

Polymer syntactic foams are transforming materials that will shape the future of next-generation aerospace and marine structures. When manufactured using traditional processes, like compression molding, syntactic foams consist of a solid continuous polymer matrix reinforced with stiff hollow particles. However, polymer matrix segregation can be achieved during the selective laser sintering process with thermoplastic polyurethane (TPU). It is uncertain what role hollow particles play in forming this matrix segregation and its impact on the corresponding mechanical properties of syntactic foams. We show that the size of the hollow particles controls the internal microscale morphology of matrix segregation, leading to counter-intuitive macroscale mechanical responses. Particles with diameters greater than the gaps between the cell walls of the segregated matrix get lodged between and in the walls, bridging the gaps in the segregated matrix and increasing the stiffness of syntactic foams. In contrast, particles with smaller diameters with higher particle crushing strength get lodged only inside the cell walls of the segregated matrix, resulting in higher densification stresses (energy absorption). We show that stiffness and densification can be tuned while enabling lightweight syntactic foams. These novel discoveries will aid in facilitating functional and lightweight syntactic foams for cores in sandwich structures.