Volume 61, Issue 11

Metallic components in nuclear engineering are exposed to extensive loads such as pressurization and temperature changes which can affect the properties of the material significantly depending on the load spectrum applied. In view of developing a procedure to evaluate the residual service life of metallic components in nuclear power plants aged during service, metastable austenitic steel AISI 347 (German designation: X6CrNiNb18−10) has been considered as an example. To this purpose, total strain-controlled fatigue tests were carried out under different environmental conditions and monitored by continuously measuring thermometric, resistometric, electromagnetic and electrochemical parameters. These parameters provide an information gain in terms of material characterization when compared to conventional strain measurements. Based on these parameters, the short time evaluation procedure StrainLife has been developed, which allows the determination of local S-N curves with a significantly reduced effort as compared with traditional procedures. This method has been implemented into the structural simulation program PROST for the integrity assessment of the components while considering local fatigue properties. This very effective method allows for the determination of local fatigue properties including the strain-specific local scatter of the metallic microstructure properties of the material which has not been possible by traditional means.

Biodegradable stents made of magnesium alloys have become revolutionary in the cardiovascular area. However, rapid corrosion in a body fluid environment is harmful to the mechanical properties and stability. In this study, untreated and cryogenically treated samples of AZ91 and AM60 alloy were employed at −196 °C for 48 h. Afterwards, the corrosion performance of the AZ91 and AM60 samples was tested in an isotonic solution containing 0.9 wt.-% NaCl. Electrochemical methods such as open-circuit potential measurement (OCP), potentiodynamic polarization, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion performance. In general, the results obtained for the electrochemical studies show that the cryogenically treated AZ91 and AM60 samples maintain superior corrosion resistance when compared to the former sample. The OCP results indicated that the cryogenically treated AZ91 and AM60 outperformed untreated samples after 1 h. The potentiodynamic studies confirmed that cryogenically treated AZ91 and AM60 had superior anodic pitting potential (E pit ) and that the passivation zone is higher than AZ91 and AM60 when untreated. The EIS confirmed the lower corrosion kinetics for AZ91 and AM60 treated in the former sample.

The rotors of electric machines are made of thin steel sheets, called electrical steel. Under service conditions, local strain may exceed the elastic limit i. e. for a lifetime assessment local strain might be of great significance. The main challenge for a reliable determination of the cyclic material properties of 0.3 mm thin electrical steel is to avoid buckling in the area of compression of fully reversed strain-controlled tests. Two approaches have been investigated. First, the test setup was improved and adapted to thin electrical steel specimens for which four different linear supported anti-buckling devices were developed and tested for fully reversed strain-controlled loading with the result that the best solution was a new approach using DLC coating instead of a polytetrafluoroethylene strip for reducing the friction between the specimen and the anti-buckling device. Secondly, the influence of increasing the specimen thickness by stacking single specimens through adhesive bonding is presented here.

The fatigue behavior of reinforcing bars is mainly influenced by their surface properties. Massive ribs and sharp notches provoke failure in fatigue. For the current research, it was necessary to develop a measurement system in order to allow for the highly precise measurement of the surface of fair sized fatigue specimens. The paper presents the boundary conditions at the beginning of the research project and gives a short overview of the measuring techniques currently used. It presents the development of a laser-based line scan (LLS) measuring system which applies the principle of laser-triangulation. The high accuracy and precision of the system of measurement was quantified in several investigations.

TiO 2 nanoparticles were directly added to molten steel. The corresponding analyses of inclusion and microstructure were carried out through scanning electron microscopy (SEM) and an energy-dispersive X-ray spectrometer (EDS). On the one hand, a large number of micrometer scale Ti-bearing inclusions were observed. Besides Ti, other elements, such as Al, Mn, Si and S, were present in these inclusions. These phenomena not only confirmed the validity of adding TiO 2 nanoparticles but likewise their growth and reactivity. This can be explained by the interaction between TiO 2 and a Fe matrix, the decomposition reaction of TiO 2 and a higher Gibbs free energy for the nanoparticles. On the other hand, these Ti-bearing inclusions can induce the nucleation of intragranular acicular ferrite. This is similar in appearance to a Ti-bearing inclusion originating through internal precipitation and may be explained by the theory of a Mn-depletion zone.

Manufacturers in the automotive and aviation industries strive to implement advanced high-strength steel (AHSS) since components have to merge low mass with great strength. Due to the potential sensitivity of AHSS to hydrogen embrittlement (HE), it is very important that test methods be selected with a view to the application. This paper is based on the mechanical test methods for HE reported in scientific publications and may serve as a guide for the selection of appropriate test methods. The aggregation of sample geometries and testing procedures documented is aligned with the overriding issues regarding hydrogen susceptibility, formability, securement of manufacturing processes, and in-service conditions.

In this study, the effects of adding particles to composite pipes were examined. For the study, composite pipes reinforced with particles were produced by using structural epoxy adhesive and mica as the particle. Composite pipes oriented at [-45 °/+45 °] were manufactured by the hand lay-up method. The composite pipes were loaded axially for measuring bending and compressive strength. When bending and compression loads are applied in the experiments it was seen that the particle reinforced methods indicated in the literature have a great effect of on the strength of the bending and compressive behaviour. The results show that addition of particles enhances compressive and bending strength.

One of the major challenges in the resistance spot welding of thin materials is deformation during the welding process. In this study, the resistance spot welding of two different thin aluminum materials (AA1050−O with a thickness of 0.5 mm and AA5754−H111 with a thickness of 1 mm) was investigated. The effects of welding current and welding time parameters on the mechanical properties (including tensile shear strength and hardness), the nugget formation and the fracture type were analyzed and evaluated. Microstructure evolutions of the deformation process were performed via SEM. As a result, it was seen that increasing welding current leads to an increase in strength and hardness of the joints due to button pull out failure. The best mechanical properties within the parameters were observed when the welding current was at 19 kA, with 5 cycles.

Electrolytic hard chrome plating is applied to improve the surface properties of metals and add a decorative look. In this study, hard chrome plating was applied to low carbon steel in various parameters by means of an electrolytic method. The plating and metal surface of the specimen were analysed using a scanning electron microscope (SEM). Following SEM analyses, microhardness measurements from the plating to the base metal in the samples were conducted at 100 g. The wear resistance in the plated samples was determined by the pin-on-disc method. Moreover, the surface morphology was examined by SEM and optic profilometer subsequent to the wear experiment. The results showed that the hard chrome plating, which was applied at 0.4 A × m -2 current density, 100 mm anode-cathode distance and 60 °C bath temperature, yielded the highest wear resistance and hardness.

In the present article the results of a microstructure study of dual phase, multiphase (with transformation induced plasticity effect) and manganese-boron steel have been presented in the as-delivered state and after laser fusion by means of color metallography, which, up to now, has not been applied in those types of joints. In order to reveal the components of the microstructure of the steel types studied, five reagents were applied: nital, pikral, Klemm, LePera and sodium metabisulfite, in different combinations. Various phases were revealed in the material in the as-delivered state and after fusion, and this would not have been possible using standard procedures by means of a light microscope. In the as-delivered state all basic phases were observed. In the state after laser remelting, the observed microstructures were completely different than in the received state giving bainite and martensite an advantage. Measurements of the hardness of the as-received material and the welds of the tested steels were performed, showing a significant increase in weld hardness.

There has been an increasing interest among researchers on natural/synthetic hybrid fiber reinforced composites due to their extensive advantages such as enhanced mechanical properties as compared to natural fiber reinforced composites. The balance between environmental friendliness and mechanical strength can be achieved through hybrid composite materials. This study aims to investigate the effects of stacking sequences on the mechanical properties of woven kenaf/glass hybrid composites. Woven kenaf/glass hybrid composites with two different stacking sequences were fabricated in the hot compression process. Non-hybrid glass and kenaf fiber reinforced polypropylene composites were also prepared for comparison. Tensile, flexural and Charpy impact tests were conducted in accordance with ASTM D 3039, ASTM D 790 and ASTM D 6110, respectively. The results showed that the tensile strength of glass/kenaf/glass hybrid laminates was only 3.4 % lower than that of non-hybrid glass fiber reinforced composites. The flexural strength of hybrid glass/kenaf/glass laminates was 32.5 % higher than non-hybrid glass fiber reinforced composites. In terms of impact strength in edgewise and flatwise orientations, hybrid glass/kenaf/glass laminates showed 8.6 % and 51.9 % improvement, respectively, as compared to non-hybrid glass fiber reinforced composites. This showed that the hybrid laminates exhibited superior mechanical properties as compared to non-hybrid glass fiber reinforced composites.

In this study, surface roughness tests were performed on AISI O2 cold work tool steel using coated and uncoated carbide cutting tools applying deep cryogenic treatment. Cutting parameters with optimum surface roughness for turning cold work tool steel were determined by the Taguchi method Turning experiments were made according to the Taguchi L 16 (43) orthogonal array. The evaluation of the experimental results was based on the signal/noise (S/N) ratio. Cutting parameters were selected for four different cutting tools, cutting speeds (150, 200, 250, 300 m × min -1 ) and feed rates (0.08, 0.16, 0.24, 0.32 mm × rev -1 ). The effect levels on the surface roughness of the cutting parameters by analysis of variance (ANOVA) were performed using the experimental results. Multiple regression analyses (linear) was conducted for the experimental results. The correlation coefficient (R 2 ) was obtained via the linear regression model which showed a value of 0.914 for Ra. Finally, confirmation tests were performed and showed that optimization was successfully implemented.

The surface roughness of a part produced plays a critical role in influencing functional properties such as corrosion behavior, fatigue strength, and wear resistance. Therefore, it is very important to improve the surface roughness of Al 7075−T6 material, which is frequently used in the aerospace industry. For this reason, the finishing process, used to improve the surface quality of the parts in an easy, inexpensive and chipless manner, has recently become an interesting research topic. In this study, a ball burnishing apparatus was designed and experiments were carried out at different parameters (force, feed rate and number of passes) for the purpose of improving the surface quality of the parts. For the design of the experiments, the Taguchi method was used, thus saving time and cost savings and reducing the number of experiments required. Variance analysis (ANOVA) was performed and the effect contribution of the parameters on surface quality were obtained. As a result of the experiments, it was found that force, feed rate and the number of passes were important factors.

Carbon Fibers Reinforced Plastics (CFRP) composite material bars were machined on the lathe. In experiments −15°, 0°, 15°, 30°, and 45° approach angles, 0.1 mm × rev -1 , 0.15 mm × rev -1 , and 0.2 mm × rev -1 feed rates and 560 rpm, 800 rpm, and 1120 rpm spindle speeds were selected. At −15° and 0° approach angles, the deformation influence was dominant on surface roughness and chip morphology, while the cutting effect taking place at the cutting edge was dominant at 30° and 45° approach angles. Primarily at 45°, the most significant roughness values and the shortest cut fibers were achieved due to the occurrence of maximum shear stress according to Tresca. However, fibers were removed from samples on the whole form as bundles, without any cutting, at −15° and 0° approach angles, by the effect of deformation. According to ANOVA, regression and variance analysis results were obtained with p-values and probability results of surface roughness smaller than 0.05 and 5 %, respectively. These results showed that the feed rate was the most influential parameter for turning of CFRP material, followed by the approach angle and spindle speed, respectively. However, the least influential parameter in the processes was spindle speed.