Prediction of the optimal FSW process parameters for joints using machine learning techniques

In this work, a couple of dissimilar AA2024/AA7075 plates were experimentally welded for the purpose of considering the effect of friction-stir welding (FSW) parameters on mechanical properties. First, the main mechanical properties such as ultimate tensile strength (UTS) and hardness of welded joints were determined experimentally. Secondly, these data were evaluated through modeling and the optimization of the FSW process as well as an optimal parametric combination to affirm tensile strength and hardness using a support vector machine (SVM) and an artificial neural network (ANN). In this study, a new ANN model, including the Nelder-Mead algorithm, was first used and compared with the SVM model in the FSW process. It was concluded that the ANN approach works better than SVM techniques. The validity and accuracy of the proposed method were proved by simulation studies.

Determination of plastic deformation rate after solid particle erosion in ductile materials

AA6082-T6 aluminium alloy is a candidate material, specifically in aviation applications, which could be exposed to solid particle erosion. Solid particle erosion occurs due to repetitive high-speed impact of erodent particles on a target material. Every individual impingement of the erodent particle results in elastic/plastic deformations and material removal from the target material. In this study, solid particle erosion investigations were carried out under 1.5 and 3 bar with 60 and 120 mesh alumina particles. Both erosion rates and worn volumes of the samples were calculated and measured. Also, the authors present the plastic deformation rate in this study as a proportion of the actual (measured) worn volume to the equivalent volume of the mass loss. In addition, the average surface roughness of the samples were investigated, which is another parameter for understanding the effect of plastic deformation on surface properties during particle erosion.

Effect of steel forming on vehicle side impact behavior

Despite the seemingly daily development of high-strength new generation steel sheets, steel sheets still remain the most important engineering material used in a vehicle body. These steel parts in a vehicle body, meant to absorb energy during impact, are generally produced by steel forming methods. These steel forming operations may contain processes such as deep drawing, bending, cutting, spring back, spinning. According to the production conditions and type of processes used during the production of sheet metal parts, thinning, thickening, plastic deformation, folding, tearing and wrinkling may occur. In order to achieve more reliable impact simulations, these effects in the forming process should be conferred on impact analysis. Within the scope of this study, an analysis of the critical parts in steel forming that absorb the most energy during the side impact was conducted – first for vehicles. In a subsequent impact analysis, the effects of changes (thickness distribution, residual stress, plastic deformation, etc.) during steel forming were examined.

Effect of friction time on tensile strength and metallurgical properties of friction welded dissimilar aluminum alloy joints

Dissimilar (AA6061 & AA7075-T6) friction welded aluminum joints were taken into the investigation to correlate the influences of friction time on tensile and metallurgical properties. The dissimilar metals were welded by varying the friction time from 2 s to 6 s with the following constant parameters: a rotating speed of 1200 rpm, friction pressure of 35 MPa, upset pressure of 35 MPa, and upset time of 3 s. The higher friction time during joint fabrication needs to be selected to attain good metallurgical bonding between rubbing surfaces. The highest tensile strength of 228 MPa was attained when the friction time was given as 4 s. Furthermore, the increase in friction time widened the width and reduced the hardness of the heat affected zone on the AA6061 side where joint failure occurred. Finally, the metallurgical features of the dissimilar specimens were characterized using optical microscopy, scanning electron microscopy, and X-ray diffraction. Other details related to the characterization and results of the testing were recounted.

Potentiodynamic corrosion behavior and microstructural features of gas tungsten constricted arc (GTCA)-welded superalloy 718 joints

The gas tungsten constricted arc welding (GTCAW) process was used to join thin Su-718 alloy sheets to minimize alloying segregation and Laves phase precipitation in the fusion zone (FZ). The potentiodynamic corrosion behavior of GTCAW Su-718 alloy joints was studied and correlated to the microstructural features of welds. The potentiodynamic corrosion test was done in a 3.56 wt.-% NaCl solution to determine the corrosion rate of Su-718 alloy joints. The optical microscopy (OM) technique was used to analyze the microstructure of corroded weldments. The scanning electron microscopy (SEM) technique was used to study the Laves phase development in FZ. The SEM X-ray energy dispersive spectroscopy (EDS) technique was used to for elemental mapping of FZ. The corrosion resistance of Su-718 joints is inversely proportional to the precipitation of Laves phase in FZ. The GTCA welded Su-718 alloy joints disclosed superior corrosion resistance for the joints with lower Laves phase precipitation. It is correlated to the refining of FZ microstructure, which aids in minimizing the Laves phase precipitation. The joints with higher Laves phase precipitation revealed inferior corrosion resistance. It is attributed to coarsening of FZ microstructure, which raises the alloying segregation and leads to depletion of alloying elements in FZ. The dendritic core regions showed severe corrosion compared to the interdendritic regions. The corrosion resistance of GTCA welded Su-718 joints is better than that of CC-GTAW and PC-GTGAW joints and comparable to that of EBW and LBW joints. It refers to the arc constriction and high frequency current pulsation.

Corrosion behavior of particle reinforced aluminum composites

In the study, the corrosion behavior of aluminum matrix composites reinforced with boron carbide (B4C), silicon carbide (SiC) and alumina (Al2O3) were investigated in saltwater (3.5 % NaCl). Composite materials were produced by powder metallurgy. For composite materials production, various reinforcement and aluminum powders were mixed by mechanical alloying for 4 and 10 hours. After mechanical alloying, mixed powders were compacted under 700 MPa pressure and sintered at 600 °C. Electrochemical corrosion tests were applied on specimens in the saltwater solution using potentiodynamic methods. According to the results of the investigation, the best corrosion resistance was obtained by aluminum/B4C and the lowest by aluminum/Al2O3 composites.

Dynamic mechanical behavior of composite materials reinforced by graphene and huntite minerals

The aim of this study is to investigate the dynamic mechanical properties of composite materials reinforced by mineral experimentally. Graphene and huntite minerals were added to epoxy resin at different weight ratios (wt.-%) as 0.5 weight percent, 1 weight percent and 3 weight percent, to examine the effect of mineral types and percentages on the resulting dynamic mechanical properties. In addition, the effect of non-layered huntite unlike graphene, with a nano-sized grain structure, was investigated. Thus, glass transition temperature (Tg), storage modulus (E’), loss modulus (E”) and damping ratio (tan δ) values were determined and compared. Moreover, a tensile test was performed in order to explain the relation between stress and strain. It was seen that adding different minerals caused different results according to types and proportions. In general, adding minerals to the pure resin increased the storage modulus and loss modulus, whereas the damping ratio (tan δ) decreased compared to the pure resin.

Improvement of the mechanical and damping behavior of nylon by integration of nanoclay platelets

Nylon is used as a gear material thanks to its beneficial characteristics, such as self-lubrication, noiseless and fail-safe operation. Poor resistance to heat, dimensional stability, shock and impact loads are major drawbacks of nylon when used in engineering applications. The addition of a nanofiller to a nylon matrix can enhance its mechanical and vibrational properties. Montmorillonite nanoclay (Cloisite 15 A, Cloisite 20 A and Cloisite 30B) modified with ammonium salt was incorporated into the Nylon 6 matrix by solution mixing and melt mixing. Nanoclay with 1, 2 and 3 wt.-% were added to the nylon matrix and the resulting mechanical and free vibration characteristics were determined. The experimental results of the mechanical and free vibration behavior were compared with the ANSYS results. Tensile strength, modulus of elasticity, specific strength, specific stiffness, natural frequency and damping factor were found to increase as the weight percentage of the nanoclay in the nylon matrix increased. Cloisite 30B nanocomposite shows better mechanical and free vibration characteristics when compared with pure Nylon 6, Cloisite 15 A and Cloisite 20 A nanocomposites. The Cloisite 30B nano-composite was prepared with 2 wt.-% shows maximum mechanical and free vibration performance.

Concrete anisotropy estimated from ultrasonic signal amplitudes

The anisotropy of concrete is an essential issue in the construction industry. In this study, for the first time, ultrasonic compression and shear wave signals have been investigated for the orthogonal directions of unreinforced concrete by means of fast Fourier transformation (FFT). For this purpose, cubic concrete samples were prepared in 12 designs of different strengths for ultrasound transmission measurements. The characteristic amplitudes at dominant frequencies were determined by the FFT of these signals. The FFT amplitude differences in the compression and the shear wave signals on the orthogonally oriented surfaces provide essential information about the presence and degree of anisotropy. According to linear regression analysis, the FFT amplitude anisotropies and the amplitude ratios of the compression and shear waves decreased significantly according to increasing concrete strength. In addition, it was found that the anisotropy and the ratio of the FFT amplitudes increased proportionally to the water/cement ratio, the porosity and the water content of the various concrete designs.

Comparison of reduced graphene oxides synthesized chemically with different reducing agents for supercapacitors

The chemical reduction of graphene oxide is an effective method for the synthesis of reduced graphene oxide, having the obvious advantages of low cost and large scale applicability. Our work produced reduced graphene oxide through a simple water bath reduction approach using various reducing agents of N2H4 × H2O, NaBH4, Na2S2O3, HI, and a reference sample without reducing agent at the same reduction temperature and duration time, by which reduced graphene oxides represented as N-RGO, B-RGO, S-RGO, I-RGO, and RGO0 were fabricated. Subsequently, unbonded flexible electrodes based on carbon cloth were fabricated with the reduced graphene oxides mentioned above, whereupon the structure, morphology and electrochemical performance were characterized. The electrochemical results indicate that the order of specific capacitances is N-RGO > B-RGO > S-RGO > RGO0 > I-RGO, while I-RGO’s potential window is wider than that of the others. As a result, N-RGO displays the best electrochemical performance among all reduced graphene oxides, with a specific capacitance as high as 176.0 F × g-1 and 77.8 % of the initial specific capacitance maintained at a high current density of 20 A × g-1.