Systematic and deep understanding of mechanical properties of the negative Poisson’s ratio convex-concave foams plays a very important role for their practical engineering applications. However, in the open literature, only a negative Poisson’s ratio effect of the metamaterials convex-concave foams is simply mentioned. In this paper, through the experimental and finite element methods, effects of geometrical morphology on elastic moduli, energy absorption, and damage properties of the convex-concave foams are systematically studied. Results show that negative Poisson’s ratio, energy absorption, and damage properties of the convex-concave foams could be tuned simultaneously through adjusting the chord height to span ratio of the sine-shaped cell edges. By the rational design of the negative Poisson’s ratio, when compared to the conventional open-cell foams of equal mass, convex-concave foams could have the combined advantages of relative high stiffness and strength, enhanced energy absorption and damage resistance. The research of this paper provides theoretical foundations for optimization design of the mechanical properties of the convex-concave foams and thus could facilitate their practical applications in the engineering fields.

The synthesized understanding of the mechanical properties of negative Poisson’s ratio (NPR) convex–concave honeycomb tubes (CCHTs) under quasi-static and dynamic compression loads is of great significance for their multifunctional applications in mechanical, aerospace, aircraft, and biomedical fields. In this paper, the quasi-static and dynamic compression tests of three kinds of 3D-printed NPR convex–concave honeycomb tubes are carried out. The sinusoidal honeycomb wall with equal mass is used to replace the cell wall structure of the conventional square honeycomb tube (CSHT). The influence of geometric morphology on the elastic modulus, peak force, energy absorption, and damage mode of the tube was discussed. The experimental results show that the NPR, peak force, failure mode, and energy absorption of CCHTs can be adjusted by changing the geometric topology of the sinusoidal element. Through the reasonable design of NPR, compared with the equal mass CSHTs, CCHTs could have the comprehensive advantages of relatively high stiffness and strength, enhanced energy absorption, and damage resistance. The results of this paper are expected to be meaningful for the optimization design of tubular structures widely used in mechanical, aerospace, vehicle, biomedical engineering, etc.

As a kind of metamaterial, the negative Poisson’s ratio foams, which expand (shrink) in the transverse direction when stretched (compressed) in the longitudinal direction, have many potential applications in fields such as aerospace and mechanical and biomedical engineering. In this paper, the out-of-plane crushing behaviors of four types of the orthogonal isotropic NPR convex-concave foams (CCF) were extensively studied using an electronic universal testing machine and Instron machine at different strain rates where each test was conducted at a constant compressive velocity under uniaxial compression. Strain rate effect on mechanical properties of these foams is experimentally studied. When the strain rate increases, the compressive force enhancement of the foams is obvious and varies with different specimens. The difference in energy absorption and deformation patterns for these foams between quasi-static and dynamic loading conditions is also analyzed. We find that the deformation patterns for the specimens are not only related to the compressive velocities but also the topologies of the specimens. The research in this paper is expected to be meaningful for the optimization design of the foam structures/materials widely used in the fields of aerospace and mechanical and biomedical engineering.