Impact Testing of Polymer‐filled Auxetics Using Split Hopkinson Pressure Bar

Abstract

In this paper, impact testing of auxetic structures filled with strain rate sensitive material is presented. Two dimensional missing rib, 2D re-entrant honeycomb, and 3D re-entrant honeycomb lattices are investigated. Structures are divided into three groups according to type of filling: no filling, low expansion polyurethane foam, and ordnance gelatine. Samples from each group are tested under quasistatic loading and dynamic compression using Split Hopkinson Pressure Bar. Digital image correlation is used for assessment of in-plane displacement and strain fields. Ratios between quasistatic and dynamic results for plateau stresses and specific energy absorption in the plateau are calculated. It is found out that not only the manufactured structures, but also the wrought material exhibit strain rate dependent properties. Evaluation of influence of filling on mechanical properties shows that polyurethane increases specific absorbed energy by a factor of 1.05-1.4, whereas the effect of gelatine leads to increase of only 5-10%. Analysis of the Poisson's function reveals influence of filling on achievable (negative) values of Poisson's ratio, when compared to unfilled specimens. The results for the Poisson's function yielded apparently different values as the assessed minima of quasi-static Poisson's ratio in small deformations are constrained by a factor of 15.

Static and dynamic compressive behaviour of 3D printed auxetic lattice reinforced ultra-high performance concrete

“…Compared with S-UHPC, lattice reinforced UHPC showed larger strain at peak stress and relatively more smooth curves, suggesting that PLA lattice reinforcement can delay the coalition of microcracks to generate and enlarger zone damage [80]. H-UHPC presented better stressstrain behaviour compared to T-UHPC, consistent with previous studies [16,53] that re-entrant honeycomb reinforced composites usually have better compressive performance than other lattice reinforced composites. 9.4% and 5.5% respectively reduction in compressive strength of P-UHPC.…”

“…It was found that the average plateau stress of 2D re-entrant reinforced composites filled with strain rate sensitive material under quasi-static compression was [79][80][81][82][83][84][85] MPa that was about 155% and 182% respectively higher than that of the equivalent 3D re-entrant and 2D missing rib composite. The dynamic average plateau stress of 2D re-entrant, 3D re-entrant and 2D missing rib lattice reinforced composites also was in the range of 121-123 MPa, 56-72 MPa and 52-57 MPa, respectively, presenting similar trends, while 2D re-entrant lattice has much better mechanical response during compression [53]. In recent years, apart from typical uniform auxetic lattice reinforced composites, the graded auxetic lattice reinforced composites were also explored, the specific energy absorption of which at up to 60% and 80% deformation was found to be around 61.2% and 65.2% lower than that of the corresponding uniform chiral lattice reinforced composite [57].…”

Recent advances in auxetics: Applications in cementitious composites

“…Several variant re-entrant 3D structures (Zhang et al, 2014, 2017; Proffit and Kennedy, 2020) have been studied for their potential in protective components using FEM. As identified from the differentiated increment (see Figure 8), it was concluded that SEA increased with impact loading rate non-proportionally and within critical threshold, after which wave-like propagation was always induced (Zhang et al, 2020; Boakye et al, 2020; Fíla et al, 2017). In addition, a reduction in peak stress and elongation of strain range for failure was also spotted simultaneously.…”

“…The study indicated that NPR reduced the initial yield stress under axial compression and enhanced initial yield strength under out-of-plane loads (Dhanasekar et al, 2016). The benefit of applying auxetic foam layers, to retrofit brittle masonry wall under compression, in-plane shear and out-of-plane flexure, was demonstrated by the (Fíla et al, 2017).…”

Finite-Element Modeling and Optimization of 3D-Printed Auxetic Reentrant Structures with Stiffness Gradient under Low-Velocity Impact

“…While a more instable deformation behavior with global shear and lateral distortion is observed for quasi-static loading due to the buckling of the cell walls, dynamic loading is observed to be more homogeneous, featuring a layer wise collapse with negligible lateral distortion (Fíla et al 2017). The dynamic deformation behavior is further reported to depend on the ductility of the base material.…”