Abstract
With recent advances in manufacturing methods for metals with defined, complex shapes, the investigation of metallic lattice materials (metals containing significant porosity with a regular arrangement of the solid, frequently in the form of thin structural members or struts) has become more common. These materials show many interesting properties, and may have the capacity to be more highly engineered and optimized for a given application than the random structures of other microcellular metals, such as metallic foams and sponges, permit. However, the novel structure brings new structure-properties correlations to bear on the mechanical behavior of the materials. This paper examines one type of lattice, made from titanium alloy (Ti6Al4V) and fabricated by Electron Beam Melting (EBM), a material which typically shows only limited plasticity on deformation. The overall mechanical response is governed by the cooperative deformation of a very large number of individual struts that make up the lattice, and thus there is great potential for significant impact from damage arising due to defects in individual struts in the assembly. We explore the effect of simulated processing defects (missing struts) on the lattice properties, and how deformation and failure is distributed across the lattice after the onset of failure. To gain knowledge of how lattices deform, samples of various geometries, designed to probe compression, indentation-compression and tension (in the form of bending) are produced and tested under Digital Image Correlation (DIC) mapping. The understanding gained here will be of great use in designing new metallic lattice structures with greater damage tolerance and resistance to failure.
Highlights
Advances in novel manufacturing methods, such as Additive Manufacturing (AM) techniques (Murr et al, 2012; Frazier, 2014), have led to the ability to create porous metal structures with great control over the form the material takes
AM, with the ability to leave spaces or retain regions of unmelted powder that can be removed from the structure after processing, is well-adapted to the needs of porous metal production, especially those based on regular structures ( stochastic structures may be produced (Hernandez-Nava et al, 2015); while production of such lattices is possible without AM, or only using AM to assist with creating investment and molds used in processing (Chiras et al, 2002), it is much facilitated by the direct use of the technique
At even the lowest levels, this is likely to represent a much higher defect concentration that would occur in realistic processing of such lattices by additive manufacturing methods like Electron Beam Melting (EBM), but the high level will ensure that measureable effects are generated within a tractable number of test samples, and allow the overall trends to be identified
Summary
Advances in novel manufacturing methods, such as Additive Manufacturing (AM) techniques (Murr et al, 2012; Frazier, 2014), have led to the ability to create porous metal structures with great control over the form the material takes. Complex lattices with highly engineered designs have been produced (for example Amendola et al, 2015, 2016; Dumas et al, 2017), and relatively well-characterized forms such as the diamond structure (where the position of the struts replicates the tetrahedral orientations of the atomic bonds in the structure of the diamond form of carbon) are the more common This type of structure has been adapted to make more complex designs, such as density-graded lattices (Grunsven et al, 2014), and similar lattices can be designed to be elastically isotropic (Xu et al, 2016). As well as forming parts which can be exploited for their good weight-specific properties, AM manufactured lattices could serve in specialized applications, such as biomedical implants (Wally et al, 2015; Elahinia et al, 2016)
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