Impact response of additively manufactured metallic hybrid lattice materials

Abstract

Additive manufacturing (AM) enables the design of new cellular materials for blast and impact mitigation by allowing novel material-geometry combinations to be realised and examined at a laboratory scale. However, design of these materials requires an understanding of the relationship between the AM process and material properties at different length scales: from the microstructure to geometric feature rendition to overall dynamic performance. To date, there remain significant uncertainties about both the potential benefits and pitfalls of using AM to design and optimise cellular materials for dynamic energy absorbing applications. This experimental investigation focuses on the out-of-plane compression of stainless steel cellular materials fabricated using selective laser melting (SLM), and makes two specific contributions. First, we demonstrate how the AM process itself influences the characteristics of these cellular materials across a range of length scales, and, crucially, how this influences the dynamic deformation. Secondly, we demonstrate how an AM route can be used to add geometric complexity to the cell structure, creating a versatile basis for future geometry optimisation. Starting with an AM square honeycomb (the reference case), we add porosity to the walls by replacing them with a lattice truss, while maintaining the same relative density. This geometry hybridisation is an approach uniquely suited to this manufacturing route. It is found that the hybrid lattice-walled honeycomb geometry significantly outperforms previously reported AM lattices in terms of specific strength, specific energy absorption, and energy absorption efficiency. It is also found that the hybrid geometry outperforms the benchmark metallic square honeycomb in terms of energy absorption efficiency in the intermediate impact velocity regime (i.e. between quasi-static loading and loading rates at which wave propagation effects begin to become pronounced), a regime in which the collapse is dominated by dynamic buckling effects.

Crushing Behavior of Graded Auxetic Structures Built from Inverted Tetrapods under Impact

“…As the deformation progresses along the specimen the stiffness of the specimen increases, thus increasing the engineering plateau stress. The plateau stress of the uniform (non‐graded) cellular structures is generally constant also at higher strain rates . The computational results are in a good agreement with the experimental measurements, also when considering the oscillations due to layer‐wise crushing.…”

Dynamic energy absorption characteristics of additively-manufactured shape-recovering lattice structures

“…It is also hypothesized that the inertia effect also contributes slightly to the different observed behaviors at different loading rates for both materials. According to Calladine and English, the inertia effects can change the collapse mode, and becomes more crucial in dynamic loadings for the structures that show softening as a result of buckling of the members with a sudden drop in their stress-strain graphs after an initial peak similar to what is seen here [62,63].…”

“…For a better prediction of the dynamic compressive responses of the cellular metamaterials, it is essential to probe the effects of major parameters that contribute to their energy absorption capability, such as strain rate, inertia effects, and material properties [37,[62][63][64]. In this research lattice structures with various relative densities were 3D printed and subjected to quasi-static at different strain rates as well as low-velocity dynamic loads, i.e.…”

An Examination of the Low Strain Rate Sensitivity of Additively Manufactured Polymer, Composite and Metallic Honeycomb Structures

“…It is well known that cellular material, such as foams, respond differently under shock/impact relative to a lower strain rate [9,17,18]. This is on account of dynamic factors, such as micro and macro-inertia, and wave effects at high strain rates that are not relevant at lower rates [9].…”