Abstract
In experimental work on the mechanical properties of stochastic metal foams, the consensus is that a minimum of six pores along each direction are required to give representative mechanical properties. This theory is tested for another porous metal, regular lattices, built using repeating unit cells of the diamond structure (a tetrahedral structure, in a cubic formation) by Electron Beam Melting (EBM) from grade 5 Ti6Al4V. Samples with different numbers of unit cells are made, using 3 different sets of EBM manufacturing conditions, and tested in compression. In all cases, a minimum of four unit cells are needed to ensure that size-independent mechanical properties are measured. Small changes in manufacture lead to large differences in properties.
Highlights
IntroductionThe inherent mechanical properties of materials are typically not size dependent
On a macroscopic scale, the inherent mechanical properties of materials are typically not size dependent
The number of unit cells is the number along the side length of the sample, which in this case of a cube, is an identical number in every direction; the behaviour of non-cubic sample shapes would be dictated by the direction containing the smallest number of unit cells
Summary
The inherent mechanical properties of materials are typically not size dependent. When mechanical properties of stochastic metal foams are investigated, the minimum number of pores required to ensure reliable results is widely accepted to be six pores [1,2] This derives from work where mechanical tests were performed on metal foam samples of different average numbers of pores across the shortest dimension, and a convergence of properties over increasing numbers of unit cells was observed [3,10]. In additive manufacturing methods using powder, extracting loose powder can be challenging if lattices with many unit cells are made This is especially the case where unit cell sizes are smaller, leading to a preference for samples with as few unit cells as possible for experimental testing. This work tests the compressive mechanical response of a series of lattices with different numbers of unit cells, to determine the correct minimum to use
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