A preliminary study of cushion properties of a 3D printed thermoplastic polyurethane Kelvin foam

Abstract

The cells in conventional packaging foams have random size and orientation, and the energyabsorbing behaviour of these foams is determined by the collective contribution of different sizes of cells. In contrast to the random nature of stochastic foams, 3D printing technologies allow engineers to design and produce foams having engineered cellular structures. In this study, engineered cellular structures based on the classic Kelvin 1887 model were 3D printed in 30 × 30 × 30 mm thermoplastic polyurethane cubes with a repeating size of 216 unit cells.One hundred consecutive cyclic compression tests were performed to assess the 3D printed foam's resilience and energy absorption characteristics. The stress-strain curve of the 3D printed thermoplastic polyurethane foam indicated viscoelastic behaviour and a Mullins effect indicative of resilient rubber. A long wave buckling mode was observed during cyclic compression cycles due to the Kelvin structure. The cushion factor computed from the stress-strain curve was close to that of a metal spring with linear elasticity. The combination of the 3D printed foam's resilience, its much lower density than rubber, and the complete geometric freedom of the engineered cellular structures offer designers the potential to create high-performance cushion materials tailored for packaging applications.

Polyurethane Foams: Past, Present, and Future

“…Since additive manufacturing is being widely used, the PUFs industry must pay attention to this technology to avoid becoming obsolete. In fact, Changfeng Ge et al [ 27 ] have already reported a preliminary study of the properties of a 3D printed PUF and stated that these materials presented similar resilience properties to bulk rubber, but its density was four times lower than that of rubber. Moreover, this technology allows the possibility of printing products in customized sizes and shapes, which offers engineers an opportunity to design new cushion materials that are tailored for packaging applications.…”

Overview and comparison of modelling methods for foams

“…The polyhedron which is used as the base cell of the Kelvin foam is the tetrakaidecahedron consisting of 14 slightly curved faces and 24 vertices. 21,[78][79][80] In Simone et al (1998) 60 the analytical descriptions for the closed cell tetrakaidecahedral foam for calculating the Young's modulus and peak stress are given. It is important to note that the thickness is assumed to be constant in the whole foam cell wall.…”

Theory and practice of cushion curve: A supplementary discussion

“…When the foam is compressed to maximum σmax , the energy density e load can be obtained by calculating the area of the stress‐strain as illustrated in Figure . The e load in Figure is represented as the e indicated in Equations through …”

“…For example, the C* of expanded polyethylene (EPE) foam materials range from 3.95 to 4.70; the C* of the EPS is 2.50 . And if the cushioning materials is theoretically described with tangent elasticity, hyperbolic tangent elasticity, and linear elasticity, the C* are 2, 3.9, and 1, respectively …”