An insight to the failure of FDM parts under tensile loading: finite element analysis and experimental study

Fused deposition modeling (FDM) is one of the widely adopted additive manufacturing techniques to fabricate complex three dimensional parts to a near-net shape. FDM parts are now-a-days not limited to prototype building for product realization but used as functional parts in widespread applications. The present work aimed at unveiling the deformation behavior of the FDM samples in general and individual rasters of different thicknesses (layer thickness), in particular, laid at different directions under uniaxial tension. Finite element (FE) analysis is carried for FDM tensile specimens to simulate elasto-plastic behavior and results are validated with the experimental observations. More realistic models for FE analysis are generated that include the layers of different thicknesses (0.178 mm, 0.254 mm, 0.330 mm) and rasters at different angles (0°, 90°, 0°/90°) maintaining the inter-layer and intra-layer bonded region (developed in the present work). FE analysis and experimental results indicate that developed stress, strain at yield, elongation and tensile strength first decreases with layer thickness and then increases. Number of layers along the loading direction is more in sample with 0.178 mm layer thickness thus more elongation and load bearing capacity whereas for 0.330 mm layer thickness, less number of air voids and higher intra-layer bonded region are the reasons for higher tensile strength of the specimen. FE results and fractographic analyses reveal that first failure and layer separation in 90° rasters occurs followed by brittle failure of 0° rasters where pulling and necking takes place. Results also show that 0° raster layers fail under pulling and rupture of fibers and numerous micro-hills indicating micro-pulling of each raster fiber within a layer of material are the reasons for the improved tensile strength for 0° raster specimen.