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    Effects of Short-Term Thermal Aging on the Fracture Behavior of 3D-Printed Polymers
    (Springer, 2021) Daricik, Fatih; Delibas, Hulusi; Canbolat, Gokhan; Topcu, Alparslan
    3D printing technologies offer numerous advantages and have attracted the attention of researchers recently. Yet, the most commonly preferred additive manufacturing system is the extrusion-based process that is called fused deposition modeling (FDM) as it is simple, low cost, and prone to customization. In this paper, the effects of the short-term aging of the additively manufactured PLA and ABS specimens were investigated experimentally. The test specimens were aged by keeping them at ambient temperatures of - 80, - 20, 60, 100 degrees C for 10, 20, and 30 days. Thermally aged specimens and the pristine specimens were forced to fracture with bending load at room temperature. Thus, the permanent effects of thermal aging of the specimens were investigated utilizing the load-deflection curve, plane-strain fracture toughness, and the morphologies of fracture surfaces. It was concluded that the printed PLA materials are more susceptible to the thermal aging than the ABS printed materials. The contraction and expansion of the fused polymer filaments affect directly the bonding strength between the adjacent layers. Therefore, plane-strain fracture characteristics of the FDM polymer materials exposed to thermal aging differ according to the filament orientation and the aging time.
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    Investigation of a fiber reinforced polymer composite tube by two way coupling fluid-structure interaction
    (Techno-Press, 2022) Daricik, Fatih; Canbolat, Gokhan; Koru, Murat
    Fluid-Structure Interaction (FSI) modeling is highly effective to reveal deformations, fatigue failures, and stresses on a solid domain caused by the fluid flow. Mechanical properties of the solid structures and the thermophysical properties of fluids can change under different operating conditions. In this study, we investigated the interaction of [45/-45]2 wounded composite tubes with the fluid flows suddenly pressurized to 5 Bar, 10 Bar, and 15 Bar at the ambient temperatures of 24 degrees C, 66 degrees C, and 82 degrees C, respectively. Numerical analyzes were performed under each temperature and pressure condition and the results were compared depending on the time in a period and along the length of the tube. The main purpose of this study is to present the effects of the variations in fluid characteristics by temperature and pressure on the structural response. The variation of the thermophysical properties of the fluid directly affects the deformation and stress in the material due to the Wall Shear Stress (WSS) generated by the fluid flow. The increase or decrease in WSS directly affected the deformations. Results show that the increase in deformation is more than 50% between 5 Bar and 10 Bar for the same operating condition and it is more than 100% between 5 Bar and 15 Bar by the increase in pressure, as expected in terms of the solid mechanics. In the case of the increase in the temperature of fluid and ambient, the WSS and Von Mises stress decrease while the slight increases of deformations take place on the tube. On the other hand, two-way FSI modeling is needed to observe the effects of hydraulic shock and developing flow on the structural response of composite tubes.
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    Investigation of Rupture Risk of Thoracic Aortic Aneurysms via Fluid-Structure Interaction and Artificial Intelligence Method
    (Springer Heidelberg, 2024) Koru, Murat; Canbolat, Gokhan; Daricik, Fatih; Karahan, Oguz; Etli, Mustafa; Korkmaz, Ergun
    Patient-specific studies on vascular flows have significantly increased for hemodynamics due to the need for different observation techniques in clinical practice. In this study, we investigate aortic aneurysms in terms of deformation, stress, and rupture risk. The effect of Ascending Aortic Diameter (AAD) was investigated in different aortic arches (19.81 mm, 42.94 mm, and 48.01 mm) via Computational Fluid Dynamics (CFD), Two-way coupling Fluid-Structure Interactions (FSI) and deep learning. The non-newtonian Carreau viscosity model was utilized with patient-specific velocity waveform. Deformations, Wall Shear Stresses (WSSs), von Mises stress, and rupture risk were presented by safety factors. Results show that the WSS distribution is distinctly higher in rigid cases than the elastic cases. Although WSS values rise with the increase in AAD, aneurysm regions indicate low WSS values in both rigid and elastic artery solutions. For the given AADs, the deformations are 2.75 mm, 6. 82 mm, and 8.48 mm and Equivalent von Mises stresses are 0.16 MPa, 0.46 MPa, and 0.53 MPa. When the rupture risk was evaluated for the arteries, the results showed that the aneurysm with AAD of 48.01 mm poses a risk up to three times more than AAD of 19.81 mm. In addition, an Artificial neural network (ANN) method was developed to predict the rupture risk with a 98.6% accurate prediction by numerical data. As a result, FSI could indicate more accurately the level of rupture risk than the rigid artery assumptions to guide the clinical assessments and deep learning methods could decrease the computational costs according to CFD and FSI.
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    INVESTIGATION OF VASCULAR FLOW IN A THORACIC AORTA IN TERMS OF FLOW MODELS AND BLOOD RHEOLOGY VIA COMPUTATIONAL FLUID DYNAMICS (CFD)
    (World Scientific Publ Co Pte Ltd, 2024) Canbolat, Gokhan; Etli, Mustafa; Karahan, Oguz; Koru, Murat; Korkmaz, Ergun
    The studies on vascular flows have increased in the last decade. In this work; we have focused on the effects of flow model and blood rheology on hemodynamics for a real-subject scan using Computed Tomography Angiography (CTA) during numerical solutions. Various vascular flow studies using Newtonian or non-Newtonian blood models were presented in the literature with laminar or turbulent flow assumptions. In this study; six different turbulent models (Realizable k-epsilon, Standard k-epsilon, SST k-omega, Standard k-omega, Transition k-kl-omega, Transition SST) were compared to laminar flow to show whether turbulent flow solution is necessary. Blood rheology was investigated by using five different non-Newtonian models (Carreau, Herschel-Bulkley, Carreau-Yasuda, Casson, Power-Law) in addition to Newtonian model to indicate whether non-Newtonian blood assumptions is necessary. The In vivo boundary conditions were utilized by the UDF code which defines the real-patient cardiac cycle obtained by Echocardiography (ECHO) to present hemodynamics in the study. The results show that laminar flow well matched with the four turbulent models and two models shows by 4.8% and 19.5% differences in Wall Shear Stress (WSS) according to laminar flow. When the blood rheology was investigated, results revealed significant differences in WSS by 25.7%, 8.7%, 22.4%, 12.3%, and 32.5% for the non-Newtonian models in the given order, respectively, compared to Newtonian assumption. It concluded that laminar flow solution could be effective instead of solving turbulent flows in terms of computational cost, however, non-Newtonian blood effects could be considered to determine critical hemodynamics levels in a normal aortic arc.