Designing Metallic Microlattices for Energy Absorber Applications

Abstract

Compressible media can mitigate impulsive loads due to their ability to absorb energy and lower the intensity of an impulse by extending its duration. A variety of cellular materials are currently used to protect persons or structures from impulsive loads in automotive, sporting, and defense applications. While foams are the most common energy absorption materials in use today, emerging capability to fabricate well-defined, ordered lattice structures offers opportunity to create new energy absorption materials with previously unachieved properties. [1] We use a novel approach to fabricate microlattices with a range of architectures and truss diameters in the 0.05->5 mm range. [2] Because the spatial configuration of voids and solid (referred to here as the cellular architecture) is not stochastic as in foams, microlattices offer much more control over their mechanical performance than other cellular materials. For example, the unit cell symmetry, truss angle, truss diameter, and node-to-node spacing can be controlled independently and the trusses can be solid or hollow. [3] Depending on the application, different performance characteristics are required of the energy absorbing material. The injury criterion, or damage threshold s th , determines the maximum allowable stress transmitted, s tr , through the energy absorber such that s tr < s th . For energy absorbers in direct contact with the human body the injury criteria is generally on the order of 1 MPa. [4,5] Safety standards often define limits on acceleration, e.g., 150 Gs at an impact velocity of 5.2 m s À1 for motorcycle helmets, [6] and the maximum acceleration is determined by the transmitted stress and the relevant mass by Newton's second law. Space limitations and light weight considerations typically call for a material with maximum energy absorption per unit volume and unit mass. These requirements call for a stress-strain performance with [*] Dr.

Energy dissipation mechanisms in hollow metallic microlattices

“…1,2 In particular, these materials have been designed for high mechanical efficiency (specific stiffness and strength), [3][4][5][6] sound absorption, 2 and impact protection. [7][8][9][10] When fabricated with open cell topology, cellular metals provide exceptional potential for multifunctionality, for example offering unique combinations of high specific stiffness and strength and active cooling. 11,12 These attractive properties can be further enhanced if periodic unit cell architectures are used rather than stochastic foams: a careful topological design of the architecture enables precise control on the load transfer from the macroscale to the unit-cell scale, resulting in order-of-magnitude improvements on specific stiffness and strength, among other properties.…”

Liquid marble: A novel liquid nanofoam structure for energy absorption

“…In the past, various types of materials have been developed for impact protection, such as cellular materials, 1,2 granular materials, 3,4 micro-trusses, 5,6 fiber reinforced composite materials, 7,8 and many others. However, several issues have limited the energy absorption performance of these conventional materials.…”

Superelasticity and reversible energy absorption of polyurethane cellular structures with sand filler

“…The energy absorption in one loading cycle (the enclosed area by the loading and unloading curves in Fig. 5) is about 3.4 MJ/m 3 which is in the same order of the advanced EAMS, such as metallic micro-lattice, Al foam and polymer foam [6,14]. During loading, the compressive stress of the sand filled hemi-ellipsoid is significantly larger than the value of its empty counterpart when the effective compressive strain is larger than 0.4.…”

“…Developing high performance EAMS has attracted extensive research interest for both scientists and engineers in recent years [1][2][3]. Cellular structures are perhaps the most widely employed platform of EAMS, due to their ability to absorb the impulsive energy and their compressibility to lower the intensity of an impulse by extending its duration [4][5][6][7]. The development, design, manufacturing and optimization of cellular structures have long been studied and reviewed [8,9].…”