A facile method to fabricate auxetic polymer foams

This paper presents a new efficient method for manufacturing auxetic foams, a subcategory of metamaterials with intriguing mechanical properties. Unlike previous methods that require two steps involving heating or the use of a chemical solvent, the present method involves compressing the foam during the manufacturing process after cells have been formed in the die, but while the material remains soft. This one-step process is more time-efficient, energy-efficient, and flexible; it also requires fewer facilities and materials. After the manufacturing process, various mechanical properties of the auxetic foams were evaluated by compression tests (energy absorption, mean force, and maximum force) and indentation tests (stiffness, absorbed energy, and hysteresis energy). The results confirmed that the auxetic foams exhibited superior behavior compared with conventional foam at the same density. To further investigate the foam microstructures and deformation mechanisms, in situ compression tests were conducted; the macro behaviors of the foams were explained based on these observations. Overall, this paper presents a promising approach for the manufacturing of auxetic foams with improved mechanical properties that can be used in applications typically dominated by conventional foams.