Browsing by Subject "thermal simulation"

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Effects of Design Parameters on Thermal History and Mechanical Behavior of Additively Manufactured 17-4 PH Stainless Steel
(University of Texas at Austin, 2018) Shrestha, Rakish; Nezhadfar, P. Dastranjy; Masoomi, Mohammad; Simisiriwong, Jutima; Phan, Nam; Shamsaei, Nima
In this study, the effects of part size on thermal history and mechanical properties of additively manufactured 17-4 PH stainless steel were investigated under monotonic tensile and strain-controlled fatigue loadings. Two sets of specimens were machined from square rods and oversized specimens, which were fabricated using a laser bed powder fusion (L-PBF) process, to introduce variation in specimen geometry and consequently thermal history. Monotonic tensile tests were conducted at a strain rate of 0.001 s-1 . Fully-reversed (Rε = -1), strain-controlled fatigue tests were performed at 0.003 and 0.0035 mm/mm, and varying test frequency to maintain a constant average strain rate in all tests. Experimental results indicated minimal effect of specimen geometry on the tensile properties of L-PBF 17-4 PH SS, which were also found to be comparable to the wrought material. On the other hand, some influence of specimen geometry on fatigue behavior was observed. Specimens machined from square rods exhibited slightly higher fatigue resistance as compared to specimens machined from oversized specimens. Furthermore, thermal simulations demonstrated higher bulk heating in specimens machined from oversized specimens as compared to those from square rods, which indicated the effect of part geometry on thermal history experienced by the fabricated part.
Thermal Simulation and Experiment Validation of Cooldown Phase of Selective Laser Sintering (SLS)
(University of Texas at Austin, 2017) Ji, Yi; Taylor, Samantha; Fish, Scott; Beaman, Joseph
Thermal stresses, induced by inhomogeneous temperature distribution inside a part during the cooldown phase of selective laser sintering, can be a major cause of part rejection for geometric deviation from its as-built specification. A validated cooldown simulation can provide predictions of temperature distribution in both parts and part cake which may enable alternative cooling profiles to reduce the likelihood of such rejections. This work describes experiments and comparative simulations developed to validate a sample tool for developing cool down control profiles in an SLS machine. In the experiments, thermocouples were inserted inside the part cake to monitor temperature at preselected locations during cooldown. The results from initial experiments and simulations were compared at these locations, to obtain improved estimates of uncertain powder conductivity and convective heat transfer parameters. The resulting simulation was then compared with independent experiments to evaluate the accuracy of such simulations. Though diffusion time in the part cake prevents active closed loop control in cooldown based on thermal measurements at the part, the simulation can be used to determine an open loop control profile for the build box heaters based on temperature gradient and resultant stresses inside the part.
THERMAL SIMULATION OF THE MATERIAL EXTRUSION PROCESS WITH DIFFERENT PRINT BED BOUNDARY CONDITIONS
(University of Texas at Austin, 2023) Huseynov, Orkhan; Al-Shaikh Ali, Mohammad; Fidan, Ismail
The temperature evolution in the material extrusion (MEX) process significantly affects the stability and bonding of 3D printed parts. Numerous studies have focused on developing models to capture the temperature history of the MEX process. However, there remains a need to explore the influence of different boundary conditions applied to the print bed. Additionally, the size of the bed relative to the 3D printed object has not been extensively investigated. This study aims to analyze the thermal behavior of the first layer in MEX by considering various boundary conditions and bed sizes. The obtained results will contribute to the development of faster yet reliable models for simulating the temperature variation in the MEX process.