Sintering graded foamed beads: Compressive properties

Abstract

Designing the foam structures in terms of density and morphology gives the chance to tune their mechanical and functional properties to the specific application. Nowadays, this design has been leveled up by the introduction of graded foams which are characterized by spatially nonuniform densities and/or morphologies. Graded foams have proved superior compared to uniform one in numerous examples and loading conditions but in pure compressive loading, where properties such as the Young's modulus of graded foams are always inferior to uniform ones. When using sintered beads foams, macroscopic pure compression may induce local bending on the single bead, which can be exploited to induce stiffening. This thesis was investigated on both polystyrene and thermoplastic polyurethane samples made by foamed beads sintered in a cylindrical mold. The response to compressive tests of graded foams made by sintering beads having nonuniform cells structures was compared to the uniform counterparts. The results evidenced that, at same average density, foams had up to a 30% ca. of increase of the Young's modulus when the beads are characterized by a denser outer layer.

Topologically Optimized Graded Foams

“…[22] It has been exploited to produce samples with simple geometries, such as slabs or beads, and has proven to be efficient in targeting specific compressive properties of sintered foamed beads. [23] Accordingly, in the present work we introduce a novel procedure to design and produce a topologically optimized 3D gradedfoam structure through physical foaming. With the knowledge of the load conditions and constraints, as well as the mechanical properties of the expanded polymer, an optimized 3D density map is calculated with a topology optimization module within a finite element method (FEM) software.…”

“…[ 22 ] It has been exploited to produce samples with simple geometries, such as slabs or beads, and has proven to be efficient in targeting specific compressive properties of sintered foamed beads. [ 23 ]…”

Current Trend and New Opportunities for Multifunctional Bio-Scaffold Fabrication via High-Pressure Foaming

“…A preliminary experiment reported the use of the method to achieve complex shapes endowed with morphological gradients, such as a 1:10 scale human femur. The authors adopted polystyrene as a model polymer and polycaprolactone for the femur, showing the versatility of the method for any foamable biomedical thermoplastic [ 70 , 71 , 72 , 73 , 74 ]. Most recently, the gas foaming method with time-varying boundary conditions has been coupled with additive manufacturing, providing additional versatility in terms of porosity architecture [ 75 ].…”

Polymer Bead Foams: A Review on Foam Preparation, Molding, and Interbead Bonding Mechanism

“…Recently, some attempts have been made to prepare bead foam parts by synergizing the constrained expansion of foamed beads with simultaneous welding under high temperature conditions [23,[82][83][84]. Figure 11 shows the schematic of the in-mold foaming and molding (IMFM) process.…”