چكيده به لاتين
Additive manufacturing, also known as 3D Printing, is nowadays not only sought by researchers’ community but also by industries. AM provides rapid prototyping and production of complex designs. One of the limiting factors to use this manufacturing method in industry is insufficient investigation of its mechanical properties. In this thesis, tensile and three-point-bend (TPB) specimens were produced by a fused deposition modeling (FDM) printer in three different raster angle orientations, which were 0/90, 22/-68, and 45/-45 degrees. Then four different heat treatment cases were chosen to encompass the combination of two different unidirectional pressures and two furnace temperatures. One set of specimens was also considered as an As-built condition without any heat treatment. Then SCB specimens’ cracks were cut in three angles of 0, 20, and 40 degrees relative to the axis of loading, in order to cover mode I, mixed mode I/II, and pure mode II loading cases. Dogbone specimens underwent universal tensile testing with the aid of the DIC method to obtain accurate strain results. By extracting the data from these two tests, true stress-strain curves, engineering yield stress, elastic modulus, Poisson’s ratio, and fracture toughness were calculated and plotted for each of the investigated cases as well as its three initially-built raster angle conditions. Additionally, the Finite element method was implemented to achieve geometry fracture factors. Then with fracture loads obtained from TPB tests, stress intensity factors at break for experimental test were calculated. In order to predict fracture loads, three criteria were explained and utilized, MTS, GMTS, and GMTS with the use of equivalent material concept (EMC). Since the tests showed a ductile behavior, especially in heat-treated cases, GMTS with EMC exhibited the best fit to the experimental data. It was also concluded that with the right amount of temperature and pressure in a heat treatment process, one can increase the fracture toughness of additively manufactured ABS specimens up to 68%. Also, investigation of raster angles in as-built cases depicted that tensile properties, e.g. yield and ultimate tensile strengths, and also fracture toughness (in pure mode I loading) of 45/-45-degree raster angle printing condition had the best properties among other rasters. At last, the impact of heat treatment was overviewed and it was concluded that heat treatment increases plasticity of specimens as well as inter-raster bonds and strength.
