Volume 59, Issue 10

The microstructural features of three different materials have been quantified by means of 2D image analysis and X-ray micro-computer tomography (CT) and the results were compared to determine the reliability of the 2D analysis in the material characterization. The 3D quantification of shrinkage pores and Fe-rich inclusions of an Al-Si-Cu alloy by X-ray tomography was compared with the statistical analysis of the 2D metallographic pictures and a significant difference in the results was found due to the complex morphology of shrinkage pores and Fe-rich particles. Furthermore, wood particles of a wood-plastic composite were measured by dynamic image analysis and X-ray tomography. Similar results were obtained for the maximum length of the particles, although the results of width differ considerably, which leads to a miscalculation of the particles aspect ratio. Finally, air voids of a foam concrete were investigated by the analysis of the 2D pictures in ImageJ and the results of the 2D circularity were compared with the values of the 3D elongation obtained by micro-computed tomography. The 3D analysis of the air voids in the foam concrete showed a more precise description of the morphology, although the 2D result are in good agreement with the results obtained by X-ray micro-tomography.

The process of laser cladding has become more important during recent years because of its broad application for cladding, repair or additive manufacturing. In the field of mechanical engineering, one use is the repair of turbine blades. For high quality and reliability of the repaired components, it is necessary to adjust the weld bead geometry to the specific repair task. The bead geometry influences the metallurgical bonding and the degree of dilution as well as the formation of defects like pores or cracks. Therefore, it is important to know the effects of the different parameters on the welding bead. A valuable tool to meet this industrial challenge is the design of experiments (DoE). In this context, the user can choose between a huge number of test plans. Greater profit of information is expected by a larger test range. In order to confirm the acceptance, a five-step full factorial test plan is compared to a central composite design in this paper. Moreover, the limits of the experimental range are indicated and restrictions can be derived. As the results show, the essential effects are detected with a full factorial test plan as well as with a central composite design. Merely the effect strength could not always be specified unambiguously. On this account and in consideration of cost efficiency, the use of central compound design is recommended in industrial applications.

The present work reports the fabrication of A357 alloy matrix nanocomposites reinforced with 0.5, 1.0 and 2.0 wt.-% TiB 2 nanoparticles (20–30 nm) by a novel method which is the combination of semi-solid mechanical mixing and ultrasonic dispersion of nanoparticles in liquid state. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicated that reasonably effective deagglomeration and uniform distribution of TiB 2 nanoparticles into the matrix were achieved. Transmission electron microscopy studies also confirmed that the nanoparticles were embedded into the matrix and a good bonding was obtained between the matrix and the reinforcement. Increasing nanoparticle content led to grain refinement and significant enhancement in the mechanical properties of nanocomposites. The addition of 0.5, 1.0, and 2.0 wt.-% TiB 2 nanoparticles increased the 0.2 % proof stress of matrix alloy by approximately 31, 48 and 61 %, respectively. The contribution of different mechanisms to the strength enhancement is discussed. It is proposed that the strengthening is mainly due to Orowan mechanism and dislocation generation effect by the coefficient of thermal expansion mismatch between the TiB 2 nanoparticles and the matrix.

The aim of this study is to experimentally investigate fiber reinforced polymeric composite leaf springs which could be used in a light commercial vehicle instead of a double steel leaf spring. E-glass/epoxy, carbon/epoxy and E-glass-carbon/epoxy flat leaf springs were produced by vacuum assisted resin transfer molding (VARTM) method with specially designed mold. Experimental results show that spring rates were 91.4, 98.4 and 97.1 N × mm −1 for carbon/epoxy, E-glass/epoxy and E-glass-carbon/epoxy leaf springs, respectively. Fatigue tests indicate that the carbon/epoxy leaf springs have the longest average usage life with approximately 89 % weight reduction, although E-glass/epoxy ones satisfy the minimum usage life requirements with higher load carrying capacity with 82 % weight reduction.

Kurzfassung Im Rahmen eines Forschungsprojektes der Fraunhofer-Einrichtung für Großstrukturen in der Produktionstechnik (Fraunhofer IGP) und des Institutes für Korrosionsschutz Dresden GmbH (IKS Dresden) erfolgten Untersuchungen zur Entwicklung eines Untersuchungskonzeptes mit dem Ziel einer praxisnahen Abschätzung des Korrosionsverhaltens von Schließringbolzenverbindungen (SRB-Verbindungen). Die Untersuchungen basieren auf einer statistischen Versuchsplanung in Kombination mit Korrosionsprüfverfahren im Labor und in der Freibewitterung. Im ersten Schritt wird die Schließringbolzenverbindung genauer betrachtet und Einflussfaktoren auf das Korrosionsverhalten der Verbindungen aufgezeigt. Auf Basis dieser Faktoren wird ein Versuchsplan vorgestellt, der zum einen die Anzahl und Konfiguration der Probekörper vorgibt und zum anderen zur Auswertung der Einflussfaktoren auf das Korrosionsverhalten der Probekörper dient. Aufbauend auf dem Versuchsplan wird ein Prüfablauf für die Laboruntersuchung und die Freibewitterung an drei Standorten unterschiedlicher medialer Belastung für Schließringbolzenverbindungen erläutert. Die Darstellung von Versuchsergebnissen und die kritische Auseinandersetzung erfolgt exemplarisch für die Laboruntersuchung.

To address the problem of poor accuracy associated with using instrumented indentation tests to determine Vickers hardness, and the problem of selection of the most appropriate instrumented indentation approach, the finite element method was adopted to determine theoretical Vickers hardness values of different materials. On the basis of these theoretical values, a theoretical accuracy analysis of three representative methods was conducted for determining Vickers hardness via instrumented indentation: ISO method, Kang method and Ma method. Moreover, the results of the analysis were experimentally verified. The results show that with increasing ratio between the unloading work W e and total unloading work W t (i. e., W e /W t ), the theoretical error of Vickers hardness determined using each of the investigated instrumented indentation methods initially decreases and then increases. Compared to the other two instrumented indentation methods, the Ma method gave the lowest theoretical error of Vickers hardness. When the W e /W t ratio ranged from 0.01 to 0.3, with different values of the plane strain elastic modulus ratio η and strain-hardening ratio n, the errors of Vickers hardness determined using each of the investigated methods were all discrete. By contrast, when W e /W t ranged from 0.3 to 0.81, the errors were relatively concentrated. This work provides a theoretical basis for the further study of new methods for determining Vickers hardness via instrumented indentation testing.

The effect of isothermal quenching on microstructure and properties of forged and unforged Fe-B cast alloy were investigated in this paper. The prepared samples were analyzed using scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that, after isothermal quenching, the matrix transforms into lower bainite, but the morphology of boride remains nearly unchanged compared with its as-cast condition. Compared with water quenching, the hardness of forged and unforged samples after isothermal quenching is lower than the hardness of that after water quenching. The impact toughness of forged and unforged samples after isothermal quenching is higher than after water quenching. In two-body abrasion test, the wear resistance of forged and unforged samples after isothermal quenching is lower than that of forged and unforged samples after water quenching. In three-body abrasion test, the wear resistance of forged and unforged samples after isothermal quenching shows opposite behavior and is higher than that of forged and unforged samples after water quenching.

In the present study, abrasive wear and frictional behaviors of polyoxymethylene were investigated experimentally. To realize this, a test apparatus was designed and fabricated. Wear tests were carried out under dry conditions at room temperature. A central composite design was used to describe response and to estimate the parameters in the model. An empirical model had been developed to predict wear loss as a function of applied load and sliding distance. Friction coefficient decreases with increase in applied load. On the other hand, it is also found that friction coefficient increases with the increase in sliding velocity.

Lanthanum (La)-modified lead zirconate titanate (PLZT) thin films with doping concentration from 0 to 5 at.-% have been fabricated by sol-gel methods to investigate the effects of La doping on crystalline orientation, microstructure and dielectric properties of the modified films. The characterization of PLZT thin films were performed by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and precision impedance analysis. XRD analysis showed that PLZT films with La doping concentration below 4 at.-% exhibited (100) preferred orientation. SEM results indicated that PLZT films presented dense and columnar microstructures when La doping concentration was less than 3 at.-%, while the others showed columnar microstructures only at the bottom of the cross section. The maximum dielectric constant (1502.59 at 100 Hz) was obtained in a 2 at.-% La-doped film, which increased by 53.9 % compared with undoped film. Without introducing a seed layer, (100) oriented PLZT thin films were prepared by using conventional heat treatment process and adjusting La doping concentration.

This work aimed at investigating the adhesion behavior of high strength steels (dual phase steel of grade DP 600 and microalloyed steel of grade ZStE340) which were glued with epoxy and polyurethane adhesives. To improve the adhesion strength of the steel surfaces, the surfaces were treated with three different methods: grit blasting with corundum or duroplast, self-indicating pretreatment (SIP) adhesion mediator, or a combination of grit blasting and SIP. The samples were aged in hot climate for 25 days. SEM investigations showed that the surface roughness values were significantly increased after grit blasting. Using EDX analysis, the surface of DP 600 steel after grit blasting indicated that the zinc concentration on the surface was clearly decreased, obviously in case of duroplast blasting. Whereas, the surface of ZStE340 steel after grit blasting showed that the carbon concentration was decreased. Adhesion strength of the samples in their fresh condition is dependent on adhesive type, steel grade and pretreatment method. SIP treatment was found to have a positive impact on the adhesion strength of the DP 600 steel regardless the type of adhesive. The effect of grit blasting on adhesion strength was more pronounced in case of ZStE340 steel. Generally, the adhesion strength of the aged DP 600 or ZStE340 samples was slightly decreased, with some exceptions confined to ZStE340 glued with EP 3 which showed an increase in the aging strength. The fracture surfaces of all samples were also examined in this work by naked eye and SEM.

In this study, a turning operation was applied to DIN 1.2344 hot work tool steel under dry machining conditions. The optimum machining conditions were determined by investigating the surface roughness (Ra) and the flank wear (Vb) depending on the machining parameters. Experiments were performed according to the Taguchi L 9 orthogonal array and signal/noise (S/N) ratios were used in the evaluation of the test results. Optimum Ra and Vb values were determined by Taguchi optimization. The effects of the machining parameters on Ra and Vb were found with the help of analysis of variance (ANOVA). According to the ANOVA results, the most important parameter affecting Ra and Vb was feed rate. Two different multiple regression analyses (linear and quadratic) were conducted for the experimental results. A higher correlation coefficient (R 2 ) was obtained with the quadratic regression model, which showed a value of 0.99 for both Ra and Vb. Finally, confirmation tests were performed and showed that the optimization has been successfully implemented. By the Taguchi analysis the optimum results for both surface roughness and flank wear were found to be a cutting speed of 120 m × min −1 , a feed rate of 0.15 mm × rev −1 and a depth of cut of 0.5 mm. The results of the calculations and the confirmation tests for Ra were 0.84 μm and 0.80 μm, and for Vb, 0.0892 mm and 0.0824 mm, respectively.

In order to study the effect of water cement ratio on the damage degree of concrete at different stress levels, the acoustic and acousto-ultrasonic characteristics of concrete with different water cement ratio under multi-stage loading were analyzed. It was concluded that with the increase of the damage degree of concrete, the damage variable and the third harmonic ratio increased, while the acousto-ultrasonic velocity and acousto-ultrasonic energy decreased. Among them, the third harmonic ratio was the most sensitive parameter affecting the damage degree. The compressive strength of concrete decreased with the increase of water cement ratio, and they were linearly related. Furthermore, with the increase of the stress level or the increase of the water cement ratio, the damage of concrete occurred during the holding period increased.

This contribution presents an approach for the modeling and prediction of surface roughness in the turning of AZ91D magnesium alloys using an artificial neural network. The experiments were conducted with CCGT, DCGT and VCGT cutting tools under minimum quantity lubrication and dry machining conditions. AZ91D alloys were machined at different cutting speeds and feed rates, and the depth of cut was kept constant. 15 out of 18 experimental data points were used for the training of the artificial neural network model and the remaining 3 were used for the testing process. The average percentage error was calculated as 0.000815 % and 0.663 % for training and testing, respectively. The model and target results were found to have extremely low error rates.

The surface of AISI 1045 steel was coated using the flame spray technique. Iron-based superalloy (Fe16Mo2C0.25Mn) powders were used as matrix material and a mixture of mechanically alloyed 10 wt.-% Fe16Mo2C0.25Mn and 90 wt.-% Al 2 O 3 –3TiO 2 powders was used as reinforcing material. The mechanical alloying process was performed by milling with an attritor for 60 hours. The coating material comprised of a mixture of the matrix (Fe16Mo2C0.25Mn) powder and mechanically alloyed reinforcing powders at varying rates of 5, 10 and 15 %, respectively. The microstructure, microhardness, adhesive wear behaviors and the coefficients of friction of the coated specimens were examined. It was observed that defects increased and cracks formed on the interface, depending on the increase in the reinforcing ratio. It was determined that the coefficient of friction and wear loss increased by the increasing load in all specimens. The minimum wear loss was observed for the specimen with 10 % reinforcement and the maximum wear loss was observed for the specimen with 15 % reinforcement. The highest average coefficient of friction by the applied load was obtained for the coating with 10 % reinforcement and the lowest average coefficient of friction was obtained for the specimen with 5 % reinforcement.

Blast-furnace slag, a remnant of the old iron production, was used for a preparation of a clay-slag geopolymer which was applied to old concrete surface. An interface investigation by scan electron microscopy (SEM) confirmed the hypothesis that a clay-slag geopolymer can be used for repairing concrete. Based on the laboratory experiments, a highly damaged and contaminated old concrete floor with potholes ranging from 2 mm to 20 cm, located in metal manufacturing industrial plant, has been repaired overnight by a clay-slag geopolymer matrix (ratio of 1 : 0.5) filled with sand and pebbles (the total content of 70 wt.-%). This industrial-scale experiment has proven that geopolymers are suitable for damaged concrete repair and the daily rush in heavy industrial conditions has confirmed the resistance and surface hardness of the geopolymer mixture used. The article documents the original state of the floor, its state after eight hours and also two and four years later.