High Strain‐Rate Compression Experiments on Ni/Polyurethane Hybrid Metal Foams Using the Split‐Hopkinson Pressure Bar Technique

Abstract

Metal foams belong to the class of porous materials. This bio-inspired material class has gained an increasing interest over the last decades as a result of its versatile advantages in the field of lightweight constructions. [1][2][3] Metal foams exhibit a high energy absorption capacity under compression, based on a constant stress level over a large strain regime in the stress-strain curve. Hence, cellular materials are predominantly applied as energy absorbers in packaging, automotive, aerospace, and defence industry. [4] The stress-strain curve under compression loading is divided into three different regions. [5] The first region outlines an elastic deformation in the majority of the struts, nevertheless yielding occurs in isolated struts. Therefore, this region is referred to as pseudoelastic. [6] The end of the pseudoelastic region is achieved as soon as the first pore-layer collapses under the so-called plastic-collapse stress (PCS). Starting from this point, a nearly constant stress plateau emerges, where the remaining pore layers gradually collapse. In this damage stage, distinct flow plateaus emerge on the macroscale. The rising stress at the end of the stress plateau is subsequently generated by an increasing contact among the collapsed struts. This area of densification constitutes hereafter the third region of the stress-strain curve. [2] The particular shape of the stress-strain diagram is moreover based on the specific cellular microstructure of 3D interconnected pores. [7] Since the foams have to resist multiaxial static as well as dynamic loads during application, an analysis of potential strain-rate effects under compressive loading is essential. [3,[8][9][10][11] Strain-rate sensitivity in cellular materials is generally known to be based on four main criteria. [4] The first criterion affects exclusively closed-cell foams and open-cell fluid-filled foams, where the pore fluid moves slower in comparison to the surrounding framework. As a result, the pressure inside the pore rises and strain-rate effects occurs. The second criterion refers to the pore-framework itself. Calladine and English [12] observed microinertia effects in cellular materials depending on the particular deformation mode. While the first deformation mode is dominated by bending and shows no strain-rate sensitivity, the second deformation mode is subdivided into two distinct deformation steps, leading to an overall strain-rate sensitivity. The first step involves a plastic compression of the structure followed by a time-delayed rotation at the plastic flow hinges. [13] Thus, this effect does only depend on the structure of the specimen, however, the third criterion includes furthermore the material properties. According to Gibson and Ashby, [14] the strain-rate effects of metal foams are correlated with the properties of the strut material itself. The last criterion is based on the shock-wave propagation and enhancement, which occur solely for impact velocities above 50 m s À1 . [15] Previously, different results on strain-rat...

Entropy-Driven Design of Highly Impact-Stiffening Supramolecular Polymer Networks with Salt-Bridge Hydrogen Bonds

“…This high energy-dissipating behavior of the polyTA/arginine SPN stems from its high loss moduli (G″ = 0.25∼16.7 MPa from 0.1 to 100 Hz, Figure 2d), which represents the energy dissipated as heat at a specified frequency. 51 Furthermore, to examine the impact-stiffening behavior of the polyTA/arginine SPN in the high-speed regime, a split-Hopkinson pressure bar (SHPB) system, comprising a gas gun, a striker bar, an incident bar, and a transmitted bar, 12,20,24,52 was employed (Figure 4h). The initial high-speed stress wave (500 s −1 ) led to the elastic deformation of the SPN, exhibiting an ultrahigh modulus of ∼2 GPa (Figure 4i,j).…”

“…Furthermore, to examine the impact-stiffening behavior of the polyTA/arginine SPN in the high-speed regime, a split-Hopkinson pressure bar (SHPB) system, comprising a gas gun, a striker bar, an incident bar, and a transmitted bar, ,,, was employed (Figure h). The initial high-speed stress wave (500 s –1 ) led to the elastic deformation of the SPN, exhibiting an ultrahigh modulus of ∼2 GPa (Figure i,j).…”

Production of Electrolytic Composite Powder by Nickel Plating of Shredded Polyurethane Foam

“…The electrolytic technique is often used to obtain various materials because it is cheap and relatively simple, and nickel is widely used as electrode material in electrochemical processes. In the work of [ 41 ], the open-cell nickel/polyurethane hybrid metal foams were produced. However, to our knowledge, there is no information about research on nickel-polyurethane composite powder.…”