Band 63, Heft 8

This research work studied and evaluated the effects of reheat treatment conditions, which consisted of solution treatment at a temperature of 1448 K for 14.4 ks, followed by air cooling and precipitate aging at a temperature of 1118 K for 86.4 ks, on the microstructural rejuvenation or refurbishment of various modified alloys based on the cast nickel base superalloy, GTD-111 with aluminum, nickel and/or cobalt additions after long term heating at temperatures of 1173 K and 1273 K for 1440 ks. From the results obtained, it was found that the reheat treatment conditions applied are more suitable for microstructures after long term heating at a temperature of 1173 K. However, such reheat treatment conditions could not fully return reheat treated microstructures to microstructures similar to those of previous research work. It seems that the selected solutioning temperatures and/or times were not sufficient to completely dissolve all coarse gamma prime particles after long term heating for all samples with alloying additions. Typical size and area fractions of the gamma prime particles of the reheat treated microstructures are very similar to those of the original alloyed ones but with lower values, especially those related to the size of the gamma prime particles.

AISI 410 martensitic stainless-steel specimens were austenitized at 1253 K then oil quenched and tempered at 573, 673, 773 and 923 K for 3600 s. The impact energy of the specimens was tested at 298, 253, 223, 213 K and measured using ASTM E23 standard. After austenitizing and tempering, the microstructure of the specimens showed carbide precipitation. Tempering at 773 K resulted in the highest hardness due to secondary hardening, while tempering at 923 K resulted in the lowest hardness due to brittle carbide precipitation at the grain boundary which caused softening of the matrix by decreasing the solute carbon content. By contrast, the change in impact energy is inversely proportional to the hardness values. The impact surface of specimens tempered at 573, 673 and 773 K revealed transgranular fracture; on the other hand, the impact surface of the specimen tempered at 923 K revealed intergranular fracture. From our experimental results, the appropriate hardening and tempering procedure of AISI 410 for low temperatures applications is selectable.

In recent years, different short-time procedures have been developed that significantly reduce the experimental effort required to generate S-N curves and thus S-N databases. Methods like StressLife, StrainLife, and SteBLife are some of those which have shown enormous potential in this respect. In this contribution, the practicability of the SteBLife method is shown. Two S-N curve evaluation strategies based on temperature and magnetic field measurements are presented. These take statistical evaluation into account, describing a material’s scatter in terms of fatigue life. In order to demonstrate the versatility of the approach and to underline the advantages in terms of effort saved when compared to conventional procedures, the process on how to get the required information obtained is shown for three unalloyed and low-alloyed steels under different heat treatment conditions.

The statistical evaluation of fatigue tests can be carried out using the maximum likelihood method. With this method, the influence of run-outs on the S-N curve can be statistically considered. Typically, a bilinear S-N curve (Wöhler curve) in double-logarithmic representation is used. The logarithmic normal distribution is the basis for describing the scatter, which is assumed here to be independent of the number of cycles. For parameter determination via the maximum likelihood method, reliability is examined and compared with the evaluation methods proposed in DIN 50100. While a defined test procedure is required for the application of DIN 50100, any test data can be evaluated according to the maximum likelihood method. In comparison with the methods proposed in DIN 50100, it could be shown through some examples that the maximum likelihood method yields very reliable results for all S-N curve parameters.

The laser braze-welding technique was aimed to join a low alloyed zinc coated steel used in automotive industry, with a deformable, aging hardenable aluminum alloy from the 6xxx series using as filler material a AlSi12 wire. The heterogeneous joint was obtained by welding of aluminum alloy with the filler wire and by brazing of molten aluminum alloy together with the filler wire on the surface of a zinc coated steel which remained in solid state. The results showed that by using a proper heat input, the zinc coated steel was brazed without a melting process by the aluminum alloy which was in liquid state. On the interface between the zinc coated steel and the welded seam, a thin layer (the thickness was 6 to 8 μ m) formed consisting of star (Al-Fe-Si) or needle shape (Mg-Al-Fe-Mn) intermetallic phases.

Magnesium alloys on the surface of billets might be refined by chilled casting process, but the grains of the center of billets are coarse, and there are a lot of void defects in the center of billets. These defects can be eliminated by hot extrusion, while fibrous microstructures and strong basal textures might be formed. This paper presents a new short process technology which includes chilled casting and extrusion-shear (CCES). It is crucial to understand the effects of die structures on the deformation behaviors, strain distribution and load requirements. Three selections of processes and die structures were done by simulations and experiments which include CCES process with 4 times consecutive shearings plastic deformation, CCES process by lateral extrusion with 90° shearing angle, and combined CCES process mode. The research results show the third selection is recommended. Three-dimensional (3D) geometric models with different channel angles (30°, 45°) for the third selection CCES dies were designed. The heterogeneities of plastic deformation by CCES dies with different channel angles were analyzed from the simulation results. The simulation results show strains decrease with rising of channel angles. The lower channel angles improve the deformation heterogeneity of magnesium alloy billets. Smaller channel angles obtain higher strains and produce tinier sub-grains. The forces of the CCES process decrease with rising of channel angles. The analysis results showed that finer and uniform microstructures can be obtained if channel angles in the CCES dies are appropriate.

As a high-efficiency and high-quality welding process, hybrid laser-MAG welding (HLMW) has significant potential of application in welding thick plates. In the present study, based on thermal elastic–plastic theory, a three-dimensional finite element model is developed to predict the weld shape characteristics, residual stress and distortion in HLMW for a butt joint of 12-mm-thick high strength steel plate. Metal active gas arc welding (MAG) heat input and laser energy are modeled as one double-ellipsoid body heat source and one cone body heat source with enhanced peak density along the central axis, respectively. The comparison between calculated molten pool shapes and those obtained by the experiment shows a good agreement. Then weld shape characteristic, residual stresses and distortions are calculated in four different welding process parameters. The results show that the increase of laser power and current can effectively increase the weld penetration width when the welding speed is fixed. At the top surfaces of weldment, the peak stress of high laser beam power is more significant than that of low laser beam power. A high compressive transverse stress of low laser beam power can be found at the welding zone and the surrounding heat affected zone. However, at the bottom surfaces of weldment, the peak stress of low laser beam power is larger than that of high laser beam power. The peak stress of low laser beam power is much larger than that of high laser beam power. A high compressive transverse stress of low laser beam power can be found at the welding zone. The vertical deformation in low laser beam power and low arc current welding has the lowest value.

The main objective of the present study is to experimentally investigate and figure out the effect of deep cryogenic treatment in improving dynamic behaviors in terms of damping of a rotating shaft supported by rolling element bearings. An AISI 4140 steel for rotating shafts was selected for the experiments because it is the most widely used material in most industries for a wide range of applications such as machinery components, crankshafts, motor shafts, axle shafts, and railway locomotive traction motor shafts. Untreated, conventionally heat treated, deep cryogenic treated, and deep cryogenic treated and tempered shafts were used for the experiments to observe damping behavior changes of the shafts. Deep cryogenic treated and deep cryogenic treated and tempered shafts were cooled from pre-tempering temperature to -140 °C and held for tempering hold times of 12, 24, 36, and 48 hours. So, ten sets of shafts were employed for the experiment. The vibration data was captured for each of the shafts for five different shaft running speeds 600, 1200, 1800, 2400 and 3000 rpm. The results showed that damping ability of the deep cryogenic treated shaft at a hold time of 36 hours was superior to that of the others shafts.

For limited weight reduction and avoidance of composite damage caused by the press mounting of the traditional metal teeth press-fit joint, a novel teeth connection joint technique of the fiber wound composite transmission shaft was investigated by theoretical analysis, finite element simulation, and experiment verification. Based on the mechanics of composite materials, the expressions of equilibrium torsional stiffness and static torsional strength were derived. According to the three-dimensional Chang-Chang failure criterion, its finite element model of progressive damage analysis was established through the user material subroutine. Applying the fast curing resin system, a typical sample of the structure was prepared through co-curing for the static torsional strength test, and its failure details of the fracture surface were observed by using a scanning electron microscope, which confirmed the validity of theoretical and numerical results. Based on this, the influence of the ply method and geometric characteristics on the failure strength was studied, and the optimal design of the joint was realized by the genetic algorithm. Compared with the press-fit joint, this structure reduces weight by 70 % under the same joint strength, which provides a new way for the connection of the composite transmission shaft.

Heat treatment is a promising approach to advance the mechanical properties of AA 7075 aluminum alloy for aerospace structural applications. Quenching is commonly performed after solutionizing of AA 7075 aluminum alloy to impart supersaturated solid solution condition. It involves rapid cooling of the previously solutionized part to room temperature with water as a quenching medium. It leads to severe distortion of the structural part and deteriorates its surface integrity due to the high thermal residual stresses. This paper reports the distortion behavior of heat-treated AA 7075 aluminum alloy by implementing the standard Navy C-ring test. For precise measurements, the coordinate measuring machine (CMM) was used. Deep cryogenic treatment (DCT) was executed after conventional heat treatment (CHT) to reduce the tensile residual stresses and mitigate the distortion potential of AA 7075 aluminum alloy. Results showed significant improvement in surface finish and hardness of deep cryogenically treated AA 7075 aluminum alloy. It is attributed to the precipitation of fine spherical second phase particles distributed uniformly in the matrix. The distortion potential of heat-treated AA 7075 aluminum alloy is minimized by 30.7 % by deep cryogenic processing. It is correlated to the counterbalancing of tensile residual stresses in the heat treated part by compressive residual stresses ensued by deep cryogenic quenching.

Structural performance and lightweight design are a significant challenge in the automotive industry. Optimization methods are essential tools to overcome this challenge. Recently, nature-inspired optimization methods have been widely used to find optimum design variables for the weight reduction process. The objective of this study is to investigate the best differential mount design using nature-based optimum design techniques for weight reduction. The performances of the nature-based algorithms are tested using convergence speed, solution quality, and robustness to find the best design outlines. In order to examine the structural performance of the differential mount, static analyses are performed using the finite element method. In the first step of the optimization study, a sampling space is generated by the Latin hypercube sampling method. Then the radial basis function metamodeling technique is used to create the surrogate models. Finally, differential mount optimization is performed by using genetic algorithms (GA), particle swarm optimization (PSO), grey wolf optimizer (GWO), moth-flame optimization (MFO), ant lion optimizer (ALO) and dragonfly algorithm (DA), and the results are compared. All methods except PSO gave good and close results. Considering solution quality, robustness and convergence speed data, the best optimization methods were found to be MFO and ALO. As a result of the optimization, the differential mount weight is reduced by 14.6 wt.-% compared to the initial design.

In this paper, a single cylinder crankshaft manufactured with C45 steel was used to investigate variation in stress, deformation, and fatigue life and safety factor at critical locations of the crankshaft. For this purpose, numerical analyses using ANSYS/Workbench software were performed under different operating conditions. Additionally, low cycle fatigue analyses were conducted experimentally for the validation of the numerical results in terms of the failure characteristics of the crankshaft. It was concluded that chamfers at sharp corners of the crankshaft on the flywheel side showed critical regions, indicating that the experimental and numerical results were consistent. These results suggested that critical regions of the crankshaft could be optimized for the improvement of sustainability in long life service.

In this study, undoped semiconductor ZnO thin film and Bi-doped ZnO thin films were produced using the sol-gel spin coating method. By changing each parameter of the spin coating method, the best conditions for the formation of the film were determined via the trial and error method. When the appropriate parameter was found, the specified parameter was applied for each film. The structural, superficial, and optical properties of the films produced were characterized via atomic force microscope (AFM), UV-visible spectroscopy, and Fourier transform infrared (FTIR), and the effects of Bi dopant on these properties were investigated. When the morphological properties of the undoped and Bi-doped ZnO films were examined, it was observed that they had a structure in a micro-fiber shape consisting of nanoparticles. When the surface roughness was examined, it was observed that the surface roughness values became larger as the rate of Bi dopant increased. By examining the optical properties of the films, it was determined that they were direct band transition materials and Bi-doped thin films were involved in the semiconductor range. In addition, optical properties changed positively with Bi dopant. Since Bi-doped ZnO thin film has a wide bandgap and good optical properties, it is a material that can be used in optoelectronic applications.

White rice kernels are produced in the rice milling process with the help of rubber rollers. Husks are removed from paddy due to friction between the surface of rubber rollers and the paddy layer when the paddy passes between the two rubber rollers [1, 2, 3, 4, 5, 6]. Improved physico-mechanical properties of rubber compounds are needed for husk removal. Based on this review, it was found that small scale rice processing mills in Tamil Nadu, India face the problem of the poor service life of rubber rollers. Rubber compounds with a greater hardness are better for husking rice but breakage in the rice is high. Rice breakage can be minimized when soft rubber is used but the wear rate for soft rubber is high [6, 7, 8, 9, 10, 11, 12]. This study discusses the production of new rubber compounds produced by substituting the proportions of carboxylated nitrile butadiene rubber (XNBR) and epoxidized natural rubber (ENR) with two different carbon blacks. Physico-mechanical properties and lab scale rice-husk separation studies are conducted for these rubber compounds developed. The conclusion is that XNBR- ENR blends with ISAF N231 variety of carbon black prove to be suitable materials for husk removal applications.