The theory of low velocity impact between nano-sized, spherical particles and a rigid plane is developed by assuming fully plastic failure during approach and assuming the Johnson-Kandall-Roberts model of elasticity and adhesion applied during particle recoil. This model predicts initial particle acceleration on approach, followed by either deceleration and eventually instantaneous cessation of particle motion or extreme deformation and possible structural failure of the particle. If the approach motion ceases and the recoil begins, then either the particle is trapped on the surface or it separates. The typical frequency of oscillations of trapped particles is derived. Criteria for the occurrence of the various regimes are derived, together with conditions for when surface adhesion is important.

No abstract

No abstract

Additively manufactured cellular materials enable customized structural implants with superior osseointegration potential and mechanical properties better matched to bone. In this investigation, the compression response of Ti-6Al-4V alloy cellular materials comprising a simple cubic array of 2.00 mm diameter spherical voids with a 1.90 mm inter-void spacing are studied. Finite element analysis (FEA) shows that the lattice exhibited cubic symmetry with values for Young's modulus (E), Poisson's ratio, and shear modulus in the range of 28.5-29.5 GPa, 0.18-0.20, and 5.4-6.0 GPa, respectively. Compression tests carried out on cylinders with the same cellular structure fabricated by selective laser melting also show a strong dependence of elastic and plastic properties on orientation. Compression normal to the {100} plane of the simple cubic cell gives the highest E and strength, while compression normal to the {110} and {111} planes give lower values. The experimental E values for the {100} and {111} orientations show good agreement with the FEA results, but the {110} orientation shows lower values of E compared to the FEA predictions. Ultimate compressive failure of the cylinders occurred by gross slip along the {100} planes of the void array -coinciding with the slip planes for the simple cubic system.

Cellular Ti-6Al-4V materials with open-cell pore array structures have been fabricated by Electron Beam Melting (EBM) using an Arcam A2X system. The test samples were cylinders 20 mm diam. x 40 mm high, with pore diameters of 1.75 - 2.5 mm and porosities in the range of 61 - 83%. The structures were based on a simple cubic pore array.Sample stiffness and strength were both found to decrease with increasing porosity, exhibiting mean Young’s moduli of 3.5 – 15.6 GPa and mean yield stresses of 20.2 – 93.6 MPa. Finite element analysis (FEA) using ANSYS was performed to model the stress-strain curves for a representative volume, using measured bulk material properties. Stiffness and strength were significantly overestimated by this method, but better agreement with measured data was obtained when the representative volume was extended along the compression axis.