Variation of Impact Toughness of As-Built DMLS Ti6Al4V (ELI) Specimens with Temperature

Published ArticleThe response of direct metal laser sintering (DMLS) produced Ti6Al4V (ELI) to impact was investigated using an instrumented Charpy impact test machine and V-notch specimens. Impact toughness testing was conducted over the temperature range of -130oC to 250oC. The effect of the orientation of the V-notch, with reference to the base plate, was investigated. The results indicated that the samples that were produced with the V-notch facing the base plate (LO) had better values of impact toughness than those that were produced with the V-notch facing away from the base plate (UP) over most of the test temperatures. The study further established that as-built DMLS Ti6Al4V (ELI) retains appreciable notch toughness, even at extremely low temperatures

DYNAMIC BEHAVIOUR OF DIRECT METAL LASER SINTERED TI-6AL-4V (ELI) UNDER HIGH STRAIN RATES IN COMPRESSION LOADING

ArticleDeformation behaviour under dynamic compression of Ti-6Al-4V (ELI) produced through additive manufacturing in two different forms; as-built (AB) and stress relieved (SR), was investigated. Both AB and SR specimens were printed using the DMLS EOSINT M280 system. Compression tests were performed on the specimens at strain rate ranges lying between (300s-1-400s-1) and (600s-1-700s-1) using a Split Hopkinson Pressure Bar. This paper presents Scanning Electron Microscope (SEM) micrographs of the resulting fracture surfaces of the tested specimens, as well as scanned surfaces of through cuts, parallel and perpendicular to the load-direction of specimens that did not fracture, with a focus on the microstructural features peculiar to shear and adiabatic deformation

Numerical modelling of DMLS Ti6Al4V(ELI) polygon structures

Numerical modelling is particularly advantageous for analysing structures with complex behaviour. It is used to predict the mechanical properties of structures. Analytical modelling, on the contrary, has limited capacity for predicting the behaviour, particularly of structures, because it is based on mathematical equations that do not always exactly represent the geometry of the model. In such cases, numerical modelling is used for predicting structural bending, axial deformation, and buckling behaviour. This study documents numerical modelling of different types of polygon structures. To reduce computation costs, planar and extruded Ti6Al4V(ELI) hexagonal shell structures were used to predict stresses in the out-of-plane and in-plane directions. This was followed by numerical modelling of different types of planar polygon structures to predict their load-bearing capacity and stiffness. Thereafter, the hexagonal polygon was subjected to out-of-plane and in-plane uniaxial compression loads. This was done to compare the bending and buckling behaviour of finite element (FE) models to analytical models. The numerical and analytical results were then compared to determine how the ratio (t/L) of the wall thickness (t) and length of the polygon members (L) influenced the effective stiffness of the hexagonal polygon. The triangular polygon was seen to have the greatest load-bearing capacity and stiffness of all polygons that were modelled. The hexagonal model was observed to generate deformations due to compression, similar to those reported in literature. The critical buckling loads for the analytical honeycomb (HC) models were found to be below the yield stress for (1-, 1.125-, and 1.25-mm wall thicknesses) and above the yield stress for all FE HC models, respectively. The effective stiffness of the HC models were observed to increase with the increasing (t/L) ratio, for both the numerical and analytical models