Volume 54, Issue 3

Several metallic heat shields of the combustion chamber of a large industrial gas turbine were affected by thermo-mechanical cracking after long service exposure. The base metal Alloy 617 is coated with a thermal barrier system. While microstructural evidence allowed the exclusion of creep damage as the metallurgical cause of failure, other microstructural features led to the conclusion that the affected components were massively overheated and experienced service temperatures of up to 1100 °C. There are several possible reasons for such overheating, ranging from burner failure and lack of cooling to abuse in service. A discussion of these factors is not the subject of this case study.

Apart from erosion of leading edges, erosion of the rotor blades trailing edges often occurs in condensing steam turbines, due to the impact of wet steam water droplets. Considerable erosion of the rotor blades trailing edges may be more dangerous for a reliable turbine operation than the leading edges erosion. During several years of research many results concerning erosion damage to the trailing edges of 66 MW condensing reduction steam turbine final stage rotor blades at the Thermo-electric power plant – heating plant (TE-TO) Zagreb have been gathered and are presented in this paper. Correlation between the erosion process behavior of the last stage turbine rotor blades trailing edges and the number of operating hours has been established.

The influence of welding parameters, i. e. the welding current, root gap and the shielding gas flow rate, on the tensile strength of AISI 304 austenitic stainless steel welded with gas tungsten arc welding was investigated. To determine the optimum levels of the parameters, the Taguchi approach was used to increase the tensile strength. The results were analysed by investigating the variance by which welding parameters significantly affect the response. Mathematical models were developed to describe the influence of the selected parameters on the tensile strength. The results were confirmed by experiments.

In this study, the impact behavior of a composite material made from Kevlar29 – Al 2 O 3 / epoxy for hard body armor is considered. The present experimental method focused on the behavior of the ballistic limit, energy absorption, and final velocity of flat cylindrical and conical projectiles. The results indicated that the maximum ballistic limit at impact velocity is 400 ±7 m/s for an 18 mm target thickness. Experimental results showed that the best ballistic performance was achieved with composite materials made of Kevlar29 – Al 2 O 3 /epoxy. The results concerning the initial and final velocities showed good agreement compared with the Ipson and Recht equation.

Aluminium and its alloys have recently become an important metal whose area and amount of usage increase more and more, due to their mechanical properties, recycling ability, and penetrability. If it is considered that the bauxite, which is the raw material of aluminium is rare on earth, and also the area and amount of aluminium usage increases over time, the importance of aluminium recycling goes up. aluminium recycling has become crucial by means of both, the potential of the scrap's dependant increase on usage and the primary aluminium production, as it is providing energy and cost savings. 7xxx grades of scrap are collected with other scrap of aluminium alloys in one turn and recycled all together. As the regain of these alloys is not done by isolation oft he various grades, the finally recycled ingots result in lower grades. High value aluminium scrap is regrettably not recovered, as it was anticipated. This study is dealing with 7075 aluminium alloys originated from discharged blow molding tools and the rest piece cuttings of blocks and plates. The material has been subjected to an induction furnace, and has been remelted into small ingots and hardened according to 7075 aluminium alloy parameters (hardening aluminium tooling).

High speed tool steels, widely used for tools, are characterized of excellent hardness, wear resistance, and high temperature properties. These steels are used not only for metal cutting but also in wood, textile, and leather industries. As in cast and wrought materials, high speed tool steels show a broader application range compared to tool materials which are produced by powder metallurgy. However, the production from bulk material requires high machining costs in the case of specially formed tools. Here is discussed that a new alloying design with niobium differing from known high speed steel chemical alloying designs is created and the production of high speed tool steels in as cast condition without hot working. The microstructure is modified by adding niobium and applying proper heat treatment to get blocky type small monocarbides ending up with providing high toughness and preventing the eutectic carbides which are situated in the interdendritic areas and which increase brittleness between dendrites in the as-cast structure.

In order to meet today's vehicle design requirements and to improve the cost and fuel efficiency, there is an increasing interest to design light-weight and cost-effective vehicle components. In this research, a new optimization algorithm, called the Cuckoo Search Algorithm (CS) algorithm, is introduced for solving structural design optimization problems. This research is the first application of the CS to the shape design optimization problems in the literature. The CS algorithm is applied to the structural design optimization of a vehicle component to illustrate how the present approach can be applied for solving structural design problems. Results show the ability of the CS to find better optimal structural design.

Aluminum matrix composites have a long history and they are still in the focus of interest. Molten metal processes are basic and the most common techniques of these kind of materials. Using lost foam casting process (LFCP) for aluminum matrix composite production is a new approach. LFCP is a special casting method, and it has flexibilities and advantages under complexity, material, and production aspects. It was considered that, reinforcement materials (SiC particles, etc) can be added to molten aluminum within the expanded polystyrene (EPS) foam patterns. Successful experiments were performed; SiC particles and molten aluminum were mixed with lost foam casting (LFC) technique. And this current study was carried out to determine the mechanical properties of A6063/SiC cast composites. The microstructures of the castings were investigated with optical and scanning electron microscopy (SEM). Archimedes density test, tensile, impact, and Brinell hardness tests were performed, and the results are consistent to those generally observed for metal matrix composites. Hardness, especially yield strength of matrix was increased with reinforcement addition, however ductility and toughness were decreased. Also, the respective production technique has a significant effect on the mechanical properties.

In automotive industry, rubber mounts are widely used to cushion the loads and isolate vibration in passenger vehicle compartments. In this study an engine rubber mount and strut bushing are analysed. The static and dynamic characteristics of the rubber specimen as well as the viscoelastic and hyperelastic properties are obtained by static and dynamic testing. The material properties coefficients in the finite element analysis have been implemented accordingly to the test data. The dynamic and static characteristics of the strut bushing and the engine mount are predicted with finite element analysis. The solutions show satisfactory agreement between predicted and experimental results. According to the authors, this work on the development of vibration isolation mounts using physical tests and simulations for verification of the final product, and providing the static and dynamic design factors represents pioneer work in open literature.

Kurzfassung Wie erkennt man Risse oder Einschlüsse in Stabstahl, bevor daraus beispielsweise eine Automobil-Antriebswelle entsteht? Halbzeug­produkte werden vor der Weiterverarbeitung zerstörungsfrei auf Fehlerfreiheit geprüft, denn nicht erkannte Schäden können teure Rückrufaktionen zur Folge haben. Dieser Beitrag stellt ein Verfahren vor, mit dem die bisherige konventionelle Ultraschallprüfung durch die Gruppenstrahlertechnik ersetzt wird und die Prüfqualität bei gleichzeitiger Beschleunigung des Prüfvorgangs signifikant erhöht werden kann.