Titanium Alloy Lattice Structures with Millimeter Scale Cell Sizes

Abstract

Cellular metals with stochastic cell structures (foams) [1] and related materials with periodic (lattice) cell topologies [2] have attracted significant interest because of their multifunctionality. [3] When configured as the core of a sandwich panel, they provide efficient structural load support during bending [4][5][6] while also enabling other functions such as cross flow heat exchange, [7][8][9] acoustic damping, [10,11] and impact energy absorption. [12][13][14] The earliest foams were made from easily cast alloys based upon aluminum and copper [15,16] but recent developments are leading to the emergence of materials made from steels and other higher strength alloys. [17][18][19] While foam structures with either open or closed cell topologies (and occasionally with both) are relatively easily made with a small (millimeter and even submillimeter) cell size, [20] they deform by strut bending and are therefore weak. [21] Periodic structures with lattice or honeycomb cores have been shown to offer much higher specific strengths because strut stretching dominates their response to stress. [22,23] Deshpande and Fleck [24] have shown that the specific strength of a stretch dominated lattice structure usually depends upon the specific strength of the material used to make it, the relative density and a geometric factor that measures the efficiency with which the lattice supports stress. Triangulated structures with the (tetrahedral) octet truss structure [25] (the pyramidal) lattice block arrangement of trusses, [26] and 3D kagome structures [27] are the most efficient topologies for load support. They can be fabricated by investment casting [28][29][30] and by sheet stamping/forming combined with either spot welding, [31] brazing, [32] or bonding. [33] However, it is difficult to fabricate low density versions of these structures with cell diameters below 10 mm.Small cell sizes are of interest for compact heat exchange and for impact mitigation where they then provide a more uniform deformation response. Small cell size periodic structures can be made from metal wires by laying up 2D weaves or 0/90 collinear wire arrays and brazing. [34] The mechanical response of structures made this way from stainless steels have been analyzed in compression, shear, and in bending [5] and shown to provide only slightly reduced strengths compared to optimal topologies. The best of these stainless steel structures give compressive strengths of 10-20 MPa at a density of 0.5 Mg m À3 .Here, we describe a diffusion bonding process that has been developed for making small cell size collinear lattices from Ti-6Al-4V wires of much higher specific strength than stainless steel. It is similar to a method recently proposed for the making of cellular materials from titanium coated SiC monofilaments. [35] We show that the compressive strength of these titanium structures is double that of equivalent steel structures making them well suited for situations whereTitanium sandwich panels with cellular cores of a uniform 1-5 mm diameter open c...

Lightweight Metal Cellular Structures Fabricated via 3D Printing of Sand Cast Molds

“…[8] Alternatively, they have been created by joining and bonding slotted metal sheets, [12] extrusion and electro-discharge machining, [9] and weaving and brazing metal filaments to form a periodic textile. [13,14] In the early 2000 s, Jamcorp Inc. explored the use of sand casting to process lattice block materials (LBMs). [15] The company used specially made preforms to create trussed structures.…”

“…[54] Cellular truss structures composed of repeated unit cells have been analytically studied by analyzing deformations of a unit cell, [54] and experimentally by testing cellular materials under shear or compressive loads. [8,12,14,17,19] …”

Deformation and fracture of impulsively loaded sandwich panels

“…Several methods have been proposed for sandwich panel fabrication using titanium [21,22,23,24] and other materials [25]. One approach well suited to the fabrication of low relative open cell cores with lattice truss topologies utilizes brazing methods to attach the core to the face sheets [26,27].…”

Dynamic compression of square tube cellular structures

“…By combining carbon fiber-reinforced polymer composite face sheets with lightweight Nomex and other polymeric cores, very high-flexural modulus structures have been developed for a variety of applications [Shahdin et al 2009]. Advances in fabrication methods have led to the emergence of sandwich panels whose faces and cellular cores are made from high-strength metallic alloys based upon aluminum [Kooistra et al 2004;], stainless steels [Ferri et al 2006;Radford et al 2007], and titanium [Queheillalt et al 2000;Elzey and Wadley 2001;Moongkhamklang and Wadley 2010]. These sandwich structures also have high flexural strengths and moduli, and offer significant advantages over monolithic plates of equivalent mass in a variety of dynamic loading scenarios [Xue and Hutchinson 2004;Deshpande and Fleck 2005;Dharmasena et al 2009;.…”