Volume 63, Issue 6

The predictive quality of numerical simulations for mechanical joining processes depends on the implemented material model, especially regarding the plasticity of the joining parts. Therefore, experimental material characterization processes are conducted to determine the material properties of sheet metal and generate flow curves. In this regard, there are a number of procedures which are accompanied by varying experimental efforts. This paper presents various methods of determining flow curves for HCT590X as well as EN AW-6014, including varying specimen geometries and diverse hardening laws for extrapolation procedures. The flow curves thus generated are compared considering the variety of plastic strains occurring in mechanical joining processes. The material data generated are implemented in simulation models for the joining technologies, clinching and self-piercing riveting. The influence of the varied methods on the predictive accuracy of the simulation model is analysed. The evaluation of the differing flow curves is achieved by comparing the geometric formation of the joints and the required joining forces of the processes with experimentally investigated joints.

Since the bonding strength of Babbit alloys to their steel support cannot be measured with Chalmers specimens according to DIN ISO 4386, part 2, if the layer is too thin, an alternative specimen constellation was developed which enables the measurement of the bonding strength of layers as thin as 0.5 mm. The new specimen geometry consists of two coaxially aligned steel cylinders of equal diameter which leave a gap between opposite faces. After pretreatment in a metallic immersion bath of tin or an alloy of tin with 50 wt.-% zinc, the Babbit alloy is poured into the gap. Then the bonded steel cylinders are tensile tested. The force at fracture is divided by the cylinder cross-section yielding the bonding strength. This configuration is termed the face tensile specimen and was successfully tested on three different Babbit alloys. Up to a layer thickness of 1.5 mm the face tensile specimen delivers bonding strength quite comparable to those achieved with Chalmers specimens. Face tensile specimens require less Babbit alloy and are less costly to manufacture.

A new duplex 25Cr-3Ni-7Mn-0.66 N alloy was prepared in a vacuum arc re-melting furnace and characterized by metallographic and EPMA methods. Its corrosion behavior was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and a Mott-Schottky (M-S) analysis in artificial seawater at room temperature and compared with those of super and normal commercial duplex stainless steel (SDSS and DSS). No significant difference in the open circuit potentials and pitting potentials was observed. Its passive film current density lies between those of SDSS and DSS. This was confirmed by EIS analysis. A pit attack was observed on the δ -phase for all duplex samples, because the PREN16 of the δ -phase was lower than that of the γ -phase. From the Mott-Schottky analysis, the passive films were found to be composed of bi-layer structures, a p-type semiconductor inner layer, and a n-type semiconductor outer layer. The degree of defect as well as the effect of nitrogen in passive film layer are discussed with respect to the point defect model.

In this study, ballistic performances of x wt.-% B4C (x = 5, 10, and 20) reinforced Al5Cu matrix composite samples were investigated as a monolithic and laminated composite armor component. Composite armor plates were produced by the powder metallurgy method. The prepared powders were pressed under 400 MPa pressing pressure. Green compacts were pre-sintered at 400 °C for 30 minutes in order to blow the lubricant. Subsequently, liquid phase sintering was performed at 610 °C for 210 minutes. In ballistic tests, 7.62 mm caliber armor-piercing bullets were used as the ballistic threat. In the ballistic tests of monolithic armors, only 10 mm thick powder metal composite plates were tested. In the ballistic tests of laminated composite armors, these powdered metal plates were layered with 10 mm thick alumina ceramic plate front layers and 10 mm thick AA5083 plates. Although all of the monolithic powder metal composite armors were penetrated, they showed multi-hit capability. All of the laminated composite armors provided full ballistic protection. It was determined that with the increase in B4C reinforcement rate, the ballistic resistance also increased due to the improvement in strength, hardness, and abrasive feature.

This paper presents the performance assessments for the traction motor of an electric racing kart, considering the different core materials. Firstly, the appropriate traction motor type is determined as a brushless direct current motor (BLDC) due to the superior features such as torque, efficiency, cooling performance and reliability. Thereafter the BLDC traction motor is optimized in Ansys RMXprt by using Taguchi’s design of experiment (DoE) method in order to meet the vehicle requirements. The BH curves are created for steel sheet (M19_24G), amorphous (2605SA1) and soft magnetic composite (SMC) (Somaloy 1000 3P) in Ansys Maxwell Environment, which are widely used as core materials in the literature. Then, the motor models are analyzed by the finite element method in Ansys Maxwell, and the core materials that can meet the minimum requirements in terms of magnetic flux density and saturation are verified. Finally, the dynamic vehicle model is set up in Ansys Simplorer in order to evaluate the motor performances. For that purpose, a reference speed profile is created by using the measured speed from the Gothenburg carting ring, and the battery consumption characteristic and reference speed tracking performance of the motor models with different cores are evaluated in the driving cycle.

Additive manufacturing techniques enable the fabrication of new lightweight components with tailored mechanical properties. Considering current application fields, components are often over-dimensioned since a lack of data regarding the mechanical properties under compression or tensile loading at high strain rates is present. In this work, the influence of various strain rates on the mechanical properties of electron beam powder bed fusion Ti6Al4V lattice structures was investigated. In order to capture the damage mechanisms that occurred, a single unit cell plane was considered. In terms of mechanical characterization, high-speed tensile tests at nominal strain rates from 0.025 to 250 s-1 were carried out. By the additional use of a high-speed camera system and subsequent digital image correlation, an investigation of material reactions during shortest test times was enabled. Based on the results, a positive strain rate dependency was identified for yield and ultimate tensile strength for both investigated lattice types. In detail, an increase in ultimate tensile strength of 16 % for BCC- and 20 % for F2CCZ-specimens could be detected.

The strcutral, electronic and thermodynamic proerties of Ag2GdSi, Ag2GdSn and Ag2GdPb Heusler alloys are investigated using first-principles calculations of density functional theory (DFT) through linearized augmented plane waves (FP-LAPW) implemented within Wien2k software package. Structural, electronic and thermodynamic investigations of Ag2GdSi, Ag2GdSn and Ag2GdPb Heusler alloys are performed. Moreover, details regarding the lattice parameters, bulk modulus and its pressure derivative, band structure and density of states are elaborated upon.

In frontal crashes, the most important parts that absorb the kinetic energy of the vehicle by plastic deformation are impact absorbers. Efforts are underway to develop innovative impact absorbers to keep the impact of the accident on drivers and passengers to a minimum. The TRIZ (theory of inventive problem solving) approach was used in the product development process of an impact absorber. TRIZ is a creative and systematic problem-solving method that can be used for the development of the next generation of products and systems. TRIZ tools such as ideality, technical contradictions formulation, inventive principles, s-field analysis, and scientific effects were used to achieve ideal final results (IFR). The solutions obtained are evaluated in terms of applicability/ manufacturing, cost, lightweight and patentability. This study generated a new standardized solution in Turkey.

The Lévy flight distribution optimization algorithm is a recently developed meta-heuristic. In this study, the Lévy flight distribution optimization algorithm and the Taguchi method are hybridized to solve the shape optimization problem, which is the final step in developing optimum structural components. The new method is termed the hybrid Lévy flight distribution and Taguchi (HLFD-T) algorithm. Geometric dimensions are used as design variables in the optimization, and the problem is aimed at mass minimization. The constraint in the problem is the maximum stress value. The well-known Kriging meta-modeling approach and a specifically developed hybrid approach have been coupled in this paper to find the component’s optimal geometry. The results show that the proposed hybrid algorithm (HLFD-T) has more robust features than the ant lion algorithm, the whale algorithm, and the Lévy flight distribution optimization algorithm for obtaining an optimal component geometry.

In this work, the optimization of structural and mechanical problems is carried out using the equilibrium optimizer (EO), which is a recent physical-based algorithm.The the ten-bar planar truss structure, planetary gearbox, hydrostatic thrust bearing, and robot gripper mechanism problems are solved using the EO algorithm. The results achieved using the EO in solving these problems are compared with those of recent algorithms. The computational results show that EO yields better outcomes and competitive results that can also be applied for the other problems studied.

In this work, a new hybrid optimization algorithm (HWW-NM), which combines the Nelder-Mead local search algorithm with the water wave algorithm, is introduced to solve real-world engineering optimization problems. This paper is one of the first studies in which both the water wave algorithm and the HWW-NM are applied to processing parameters optimization for manufacturing processes. HWW-NM performance is measured using the cantilever beam problem. Additionally, a problem for milling manufacturing optimization is posed and solved to evaluate HWW-NM performance in real-world applications. The results reveal that HWW-NM is an attractive optimization approach for optimizing real-life problems.

The aim of this work is to identify failure modes of double pinned sandwich composite plates by using artificial neural networks learning algorithms and then analyze their accuracies for identification. Mechanically pinned specimens with two serial pins/bolts for sandwich composite plates were used for recognition of failure modes which were obtained in previous experimental studies. In addition, the empirical data of the preceding work was determined with various geometric parameters for various applied preload moments. In this study, these geometric parameters and fastened/bolted joint forms were used for training by artificial neural networks. Consequently, ten different backpropagation training algorithms of artificial neural network were applied for classification by using one hundred data values containing three geometrical parameters. According to obtained results, it was seen that the Levenberg-Marquardt backpropagation training algorithm was the most successful algorithm with 93 % accuracy rate and it was appropriate for modeling of this problem. Additionally, performances of all backpropagation training algorithms were discussed taking into account accuracy and error ratios.

This work’s main objective is to determine the optimum process parameters in the electrohydraulic forming (EHF) of austenitic stainless steel AISI 304 of 0.25 mm thickness for macro and micro shape. A truncated cone with grooves in the apex is considered as macro-micro shape. The response surface methodology (RSM) was developed for process variables such as voltage and standoff distance to determine the optimum parameters. To validate the model, confirmation experiments have been conducted, i. e. for the optimum value of voltage (V) = 8.935 kV and standoff distance (SOD) = 40.60 mm, and from the experiments the forming depth predicted is 9.221 mm and depth from the experiments is 9.5 mm. The percentage deviation from the predicted and experimental forming depth is 3.025 %, an acceptable range of less than 5 % for the surface roughness, the predicted value is 0.2598 microns, and the experimentally measured value is 0.268. The percentage deviation is 3.156 % between the predicted and experimental values, an acceptable range of less than 5 %. This shows that the model is suitable for predicting both responses. The validation experiments also found that the sheet fills one of the grooves and partially fills the other, which shows the capability of the electrohydraulic forming process. Confirmation experiments have been conducted.

Although advances have been made in manufacturing technology, a number of problems still exist in the drilling process due to the chip formation which occurs in a closed area. This situation results in unpredictable force, torque and temperature generation. This study investigated the machining parameters in the drilling process using a finite element method (FEM). In the numerical analysis, thrust force, torque and temperature were calculated by three-dimensional simulation. Drilling processes were carried out with twist drill bits at three different cutting speeds and three different feed rates. The numerical analysis results were verified by experimental studies. The results show that FEM is a good candidate for obtaining cutting forces and temperature generation in drilling process.