Contribution of functionally graded material modelling on finite element simulation of rod end parts in automotive steering system

One of the most important manufacturing steps of the rod end materials is the induction process by which the both hardness of the surfaces and the toughness of the part can be adjusted at the same time. In the study, rod end materials which are inducted and non-inducted are simulated in the view of the fatigue life properties. In the simulations, the rod end parts are defined as functionally graded materials where the mechanical properties of the materials are varying with the dimensions. Additionally, the noninducted material properties or fully strengthened material properties are defined for the geometry in order to comprehend the contribution of the definitions on the congruity of the finite element simulation results with the experiments. When the materials properties of the rod end part are defined as functional graded, the simulation results are found to be much more close to the experimental results.

     

Three dimensional stress analysis of solid oxide fuel cell anode micro structure

One of the most common problems in solid oxide fuel cells (SOFCs) is the delamination and thus the degradation of electrode/electrolyte interface which occurs in the consequences of the stresses generated within the different layers of the cell. Nowadays, the modeling of this problem under certain conditions is one of the main issues for the researchers. The structural and thermo-physical properties of the cell materials (i.e. porosity, density, Young's modulus etc.) are usually assumed to be homogenous in the mathematical modeling of solid oxide fuel cells at macro-scale. However, during the real operation, the stresses created in the multiphase porous layers might be very different than those at macro-scale. Therefore, micro-level modeling is required for an accurate estimation of the real stresses and the performance of SOFCs. This study presents a microstructural characterization and a finite element analysis of the delamination and the degradation of porous solid oxide fuel cell anode and electrode/electrolyte interface under various operating temperatures, compressing forces and material compositions by using the synthetically generated microstructures. A multi physics computational package (COMSOL) is employed to calculate the Von Misses stresses in the anode microstructures. The maximum thermal stress in the electrode/electrolyte interface and three phase boundaries is found to exceed the yield strength at 900 °C while 800 °C is estimated as a critical temperature for the delamination and micro cracks due to thermal stress generated. The thermal stress decreases in the grain boundaries with increasing content of one of the phases (either Ni or YSZ) and the porosity of the electrode. A clamping load higher than 5 kg cm⁻² is also found to exceed the shear stress limit.     

Tensile and Springback Behavior of DP600 Advanced High Strength Steel at Warm Temperatures

 In recent years, the use of advanced high strength steels in automotive industry has been increased remarkably. From advanced high strength steels, dual-phase (DP) steels have gained a great attention due to a combination of high strength and good formability. However, high strength usually increases springback behavior of material which creates problem for the parts during the assembly. In this study, uniaxial tensile deformation and springback behaviors of DP600 advanced high strength steel were investigated at rolling (0o), diagonal (45o), and transverse (90o) directions in the temperature range from room (RT) to 300 oC. All tests were performed at 25 mm/min deformation speed. A V-shape die (60o) was used for springback measurements. Results indicate that the formability and springback of the material were decreased with increasing the temperatures. The material showed complex behaviors at different directions and temperatures.     

Determination of formability characteristics of Crofer 22 APU sheets as interconnector for solid oxide fuel cells

In this study, the general formability characteristics of Crofer^® 22 APU sheets of different thicknesses (0.2 mm–1.0 mm) are experimentally investigated via tensile, out of plane, Erichsen, cupping and springback tests for a possible application for solid oxide fuel cells in sheet form unlike the conventional bulk form. Holloman equation is also used to fit the experimental stress-strain curves and the anisotropic behavior of the material is considered by determining Lankford parameters. The tensile test results show that the formability is about 0.29 mm/mm for 0.2 mm thick sheets, indicating the suitability of these sheets for the fabrication of interconnectors by a stamping process with desired channel geometry having dimensions similar to conventional channel dimensions. In addition, for a specific combination of process parameters such as blank holder force and lubrication, the formability can be enhanced as proven by Erichsen and cupping test results. Moreover, the formability is found to increase with increasing the sheet thickness and highly anisotropic behavior is observed. In three point bending tests, the negative springback behavior, namely spring-in, is surprisingly observed for a relatively narrow shoulder distance at all thicknesses and set angle values (θ = 90°–120°).     

Efficacy of Tissue Plasminogen Activator for Thrombolysis in Central Venous Dialysis Catheters

Background:  Low blood flow is a frequent complication of central‐vein (CV) dialysis catheters. Since thrombotic occlusion accounts for many cases of reduced blood flow, it is common practice to administer empiric thrombolytic therapy in an attempt to restore catheter patency and improve function.
Methods:  We prepared tissue plasminogen activator (tPA) from 50 mg lyophilized powder, which was diluted (1 mg/mL) in sterile water for injection. A volume of 1 mL was frozen in 3 cc polystyrene syringes at −20 °C and thawed at room temperature when needed. tPA was then administered into the arterial and venous ports of the central venous catheter in a volume equal to the manufacturer's stated luminal volume and was allowed to dwell for 30 minutes.
Results:  tPA was administered 62 times in 25 patients with 30 catheters (11 Tesio, 17 PermCath, 2 Shiley) for treatment of low blood flow (pump speed < 250 mL/min). Complete restoration of patency was achieved in 23 episodes (mean blood flow pre‐tPA 130 mL/min; post‐tPA 320 mL/min); partial restoration of patency was achieved in 20 episodes (mean blood flow pre‐tPA 69 mL/min; post‐tPA 233 mL/min). tPA was just as likely to be effective in patients with complete catheter occlusion (i.e., no blood flow) as it was when some initial blood flow was present. Nineteen episodes failed to respond to tPA. These episodes occurred in 13 catheters, 12 of which ultimately underwent radiologic evaluation; an extraluminal cause for low blood flow was found in all 12 catheters (6 malpositioned, 6 fibrin sheaths).
Conclusions:  tPA at a dose of 1 mg/mL is effective for restoring patency in CV dialysis catheters. Failure to respond to tPA strongly suggests an extraluminal cause of catheter malfunction.     

Effects of aging parameters on formability of 6061-O alloy

6XXX series aluminum–magnesium–silicon (Al–Mg–Si) alloys are medium strength alloys widely used as automotive body materials. The mechanical properties of these alloys are adjusted by performing age hardening heat treatments. In this research, the effect of aging time on formability of 6061-O alloy is investigated. The formability of the material is evaluated by tensile, Erichsen, and hole expansion tests. Results reveal that formability decreases with increasing aging time. The evolution of the anisotropy, r, with the aging time depends on the direction of probing relative to the texture direction. Yield surfaces predicted using the Hill-90 and Barlat-89 models are plotted using experimental r values for several aging times. Since r changes, these surfaces deform slightly and expand with increasing aging time.     

Microstructure based modelling of stress–strain relationship on dual phase steels

The deformation in microstructures of DP600, DP800 and DP1000 commercial advanced high strength steels have been researched through using the representative volume element method. For this purpose, deformation analyses have been carried out by transferring geometrical models and mechanical properties of phases of each material to the finite element software. Deformation relation between ferrite and martensite phases was determined. According to the loading direction, Shear bands have been observed to occur in the range of approximately 40°–45°. It has been understood that the failure mode is shear for DP600, DP800 and DP1000 steels. Crack propagation has been observed to occur in the ferrite phase trapped at the martensite grain boundary.     

Warm deformation and fracture behaviour of DP1000 advanced high strength steel

The effect of temperature has been investigated on the mechanical properties and fracture behaviour of DP1000 advanced high-strength steel. The variation of the mechanical properties depending on temperature has been determined by performing uniaxial tensile tests at the temperatures of 25, 100, 200, 300°C at the rolling directions of 0° (rolling), 45° (diagonal), and 90° (transverse) at the strain rate of 0.0083?s^?1. The yield strength and tensile strength have showed a slight decrease tendency between 25 and 200°C, but the highest value has been reached by showing an increase at 300°C temperature. The amount of elongation has not been affected significantly with the increase of the temperature. While hardening coefficient has increased due to the rising temperature, no effect has been observed on strength coefficient between 25 and 100°C, but an increase has occurred at higher temperature values.     

Determination of optimum ejector operating pressures for anodic recirculation in SOFC systems

In this study, a numerical analysis of an ejector for micro combined heat and power system based on 18 kW Solid Oxide Fuel Cell (SOFC) using methane as fuel is presented. An ejector design, which reflects the real system conditions in the view of the flow characteristics, is provided and the ejector performance is numerically investigated for various methane pressure to exhaust pressure ratios and methane inlet temperatures. The results show that the fuel inlet temperature and the pressure ratio of the methane to exhaust significantly affect the steam to carbon ratio (STCR) and entrainment ratio. The higher pressure ratio and methane temperature allow a high entrainment ratio and STCR, but as pressure ratio and methane temperature increase, STCR and entrainment ratio remain unchanged after a specific value. 1140 different scenarios related with the inlet and outlet pressures of the ejector and methane temperature are created to determine the optimum operating conditions. The simulations show that the optimum methane inlet pressure is 7 bar and exhaust pressure is 1.159 bar for the ejector geometry of the interest. The entrainment ratio and STCR are determined as 2.05 and 0.92, respectively at this optimum scenario.     

Numerical optimization of channel to land width ratio for PEM fuel cell

Flow field plays a vital role in proton exchange membrane (PEM) fuel cell where channel geometry being the primary factor. Most of the channel geometry analyses were limited to few number of case studies, whereas in this study total 73 case studies were analyzed for the optimization of channel and land width. A three dimensional isothermal single phase flow mathematical model is developed and further validated with experimental study to optimize the channel and land width through parametric sweep function for a staggering 73 number of case studies. The optimization analyses are carried out for a straight channel geometry considering a fixed operating voltage of 0.4 V and channel depth of 1.0 mm. Due to the large number of case studies, the analyzed performance parameters i.e. current density and pressure drop are easily understandable for the change in different channel and land width. The numerical results predicted that the pressure drop is more dependent on channel width compare to the land width and anode pressure drop is less significant than cathode pressure drop. However, both channel and land width have an equal importance on the cell current density. Considering channel pressure drop and current density, the optimization analyses showed that the channel to land width of 1.0 mm/1.0 mm would be best suitable for PEMFC channel geometry.