Browsing by Author "Altas, Emre"

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Finite Element Simulation and Experimental Investigation on the Effect of Temperature on Pseudoelastic Behavior of Perforated Ni-Ti Shape Memory Alloy Strips
(Iop Publishing Ltd, 2022) Altas, Emre; Khosravi, Farshid; Gokkaya, Hasan; Arab Maleki, Vahid; Akinay, Yuksel; Ozdemir, Okan; Kandas, Halis
In the present study, the temperature-dependent pseudoelastic behavior of shape memory alloy (SMA) sheets is studied experimentally and by finite element (FE) modeling. For this purpose, temperature-dependent mechanical properties for Ni-Ti alloy materials are first obtained by using direct tensile and three-point bending experiments at 23 degrees C, 50 degrees C, and 80 degrees C temperatures, respectively. The structure of these materials is examined at different temperatures using SEM images and the XRD test. Furthermore, using the FE model, the pseudoelastic behavior and the effect of temperature on the residual deflection of the prose-shape memory strips with a circular hole under three-point bending loads are studied. After validating the results of the FE model with the results of experimental tests, the effects of various parameters such as the diameter and number of holes on residual deformation and residual strains are investigated. The results show that with increasing temperature, the mechanical properties including the tensile strength, Young's modulus, yield stress, and flexural strength of SMA strips increase significantly. For solid strips, although increasing the temperature increases the maximum flexural force, in contrast, it reduces the flexural stiffness. In solid strips, flexural stiffness decreases by 5.5% with increasing temperature from 23 degrees C to 80 degrees C.
Surface Integrity of Niti Shape Memory Alloy in Milling With Cryogenic Heat Treated Cutting Tools Under Different Cutting Conditions
(Springer, 2021) Altas, Emre; Altin Karatas, Meltem; Gokkaya, Hasan; Akinay, Yuksel
In this study, the surface integrity of nickel-titanium (NiTi) shape memory alloys (SMAs) was investigated after face milling processes with cryogenically treated/untreated cemented carbide cutting tools at the conditions of dry cutting and minimum quantity lubrication (MQL) of cutting fluids depending on the changing cutting parameters. The integrity of surface layer of the workpiece material was evaluated according to the mean surface roughness, microstructure and hardness, as well as according to the resultant cutting force and flank wear of inserts. Cutting tests were carried out at three different cutting speeds (20, 35 and 50 m/min), feed rates (0.03, 0.07 and 0.14 mm/tooth) and a constant axial cutting depth (0.7 mm). The influence of these parameters on the surface integrity was extensively investigated. The face milling tests of NiTi SMA at optimal cutting parameters show that the surface integrity enhanced at a cutting speed of 50 m/min and feed rate of 0.03 mm/tooth using boron-added cutting fluid (EG + %5BX) with deep cryogenic heat treated (- 196 degrees C) CVD coated S40T grade cutting tool. Under MQL conditions, the minimum mean surface roughness (0.278 mu m), resultant cutting force (268.2 N) and flank wear (0.18 mm) were obtained due to the high thermal conductivity and lubrication property of EG + %5BX cutting fluid. The highest hardness values (343 HV) were measured at the zone subjected to the highest deformation, while the lowest one (316 HV) was measured at the zone at the least deformation.