Volume 59, Issue 4

Disc springs are very common and important machine elements used in almost all fields of mechanical engineering. They are applied when high spring forces are required and only a small mounting space is available, for example, in clutches or rolling bearings. Residual stresses induced by shot peening improve the performance significantly, at the same time shot peening increases the production time and cost. This paper investigates an incremental forming process that allows forming of the spring geometry and generation of residual stresses in a single setup. Accurate measurements of the spring performance are needed to control the product properties, especially when new processes are introduced. The possibility to apply magnetic measurements to control the spring properties is evaluated. A relation between spring characteristics and magnetic Barkhausen noise envelope is established. The findings are supported by residual stress measurements and light optical microscopy, showing martensite islands caused by incremental forming.

In this work, different dual phase microstructures were produced in 15CrNiMo7 steel, in order to study the effect of martensite volume fraction, martensite morphology, and epitaxial ferrite on tensile strength and fatigue behavior. Mechanical properties of five different dual phase steels have been investigated by carrying out tensile, hardness and fatigue tests. By increasing the martensite content, both tensile and yield strengths increased. The presence of new ferrite caused a decrease in strength and an increase in ductility. It was observed that the fatigue strength increased with increasing martensite content and decreasing martensite size (fiber). The new ferrite caused a small amount of decrease in fatigue strength. Fractographic analysis after fatigue test was performed by using SEM. It was observed that the striation spacing decreased with increasing martensite content.

A thermo-metallurgical procedure based on the SYSWELD code was developed to predict welding temperature field, microstructure and residual stress in butt-welded Ti-6Al-4V plate taking into account phase transformation. The formation of martensite was confirmed by the CCT diagram and microstructure in the weld joint, which significantly affects the magnitude of residual stress. The hole drilling procedure was utilized to measure the values of residual stress at the top surface of the specimen, which are in well agreement with the numerical results. Both simulated and test results show that the magnitude and distribution of residual stress on the surface of the plate present a large gradient feature from the weld joint to the base metal. Moreover, the distribution law of residual stresses in the plate thickness was further analyzed for better understanding of its generation and evolution.

This paper presents a novel diffusion bonding process of commercially pure aluminum to Ti-6Al-4V alloy at 520, 560, 600 and 640 °C for 30, 45 and 60 minutes under argon gas shielding without the use of interlayer. The approach is to overcome the difficulties in fusion welding of dissimilar alloys. Diffusion bonding is a dissimilar metal welding process which can be applied to the materials without causing any physical deformations. Processed samples were metallographically prepared, optically examined followed by Vickers microhardness test and subjected to tensile test in order to determine joint strength. Scanning electron microscopy and energy dispersive spectroscopy were used in this work to investigate the compositional changes across the joint region. Elemental composition of the region has been successfully defined between titanium alloy and aluminum. The maximum tensile strength was obtained from the samples bonded at the highest temperatures of 600 and 640 °C.

Aluminum based metal matrix composites are one of the advanced engineering materials that have been developed for low weight and high strength applications in automotive industries due to high specific strength and good wear resistance. In this context, aluminum alloy boron carbide and garnet composites were fabricated by the stir casting process. The microstructural examination was done by using a scanning electron microscope to assess the distribution of particulates in the aluminum matrix. The composites were characterized by hardness and tensile tests. The wear behavior of the composites was analyzed with the help of a pin-on-disc wear test. By increasing the amount of garnet in the composite, it has been observed that the tensile strength and hardness increase. The wear test analysis proved that the addition of reinforcements reduces the wear rate behavior of composite.

For the determination of phase transformation temperatures in metallic materials, dilatometric analysis (DA) is one of the most commonly applied thermoanalytical methods. Since it depends on elaborate sample preparation, in-situ methods are likely to support the application of welding process investigations. In this study, several gas metal arc (GMA) welded all-weld metal samples were examined regarding their solid state phase transformation temperature during cooling by means of dilatometry and single-sensor differential thermal analysis (SS DTA). The results show the applicability of the SS DTA method during GMA welding and good agreement with dilatometric values.

In this work, the CO 2 corrosion behavior of pipeline steel welds was systematically investigated. This was done by weight loss experiments in which welded samples were immersed in simulated produced water with different CO 2 partial pressures. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM) were used to effectively characterize the morphology, composition and phase of the corrosion products. The results showed that the corrosion rate of welded joints decreased as the immersion time increased. The corrosion rate of welded joints and the type of corrosion products formed also depend on the CO 2 partial pressure. The layers of corrosion products had inhomogeneous distributions of iron, carbon, oxygen and calcium, with a higher concentration of iron in the internal corrosion film than that in the external corrosion film.

In the past decades the study of nanocomposites has held the interest of researchers due to their better mechanical properties by the addition of small amounts of filler material called nanoclay. In this study, high-density polyethylene (HDPE) was chosen as matrix material and nanoclay as reinforcement material, i. e., Cloisite 30B. HDPE grafted with maleic anhydride (HDPE-g-MA) with 3 wt.-% compatibilizer was used to provide better adhesion between the high-density polyethylene and nanoclay. The nanocomposite materials were prepared by melt compounding in a twin screw extruder with a spindle speed of 50 rpm with zone temperatures. The addition of nanoclay to HDPE was in the range of 0 to 4 wt.-%. The specimens were prepared according to ASTM standard for various mechanical tests like flexural, tensile, hardness, and impact tests using respective dies in the injection molding machine. The scanning electron microscope analysis was used to characterize the ditribution of particles in the nanocomposites. In addition, the effect of five different amounts of nanoclay (0 to 4 wt.-%) on the mechanical properties of HDPE was examined to identify the most effective amount of nanoclay for improving the strength of nanocomposites.

The paper addresses findings regarding the influence of electrolytic plasma treatment on the mechanical properties as well as structural and phase states of × 12 CrNi 18 10 Ti steel. Electrolytic plasma treatment is based on carburizing of stainless steel heated in electrolytes. Treatment of steel samples has been performed as follows: the samples were heated up to a temperature between 850 and 950 °C and then they were cured for 7 minutes in an electrolyte of an aqueous solution containing 10 % glycerol (C 3 H 8 O 3 ) and 15 % sodium carbonate (Na 2 CO 3 ). It is found that, after plasma electrolytic treatment, the surface of × 12 CrNi 18 10 Ti steel had a modified structure and high hardness. Increasing wear resistance of × 12 CrNi 18 10 Ti steel has been observed after carburizing and the coefficient of friction has been reduced. X-ray analysis showed that retained austenite γ-Fe is a main phase, and there are some diffraction lines of orthorhombic Fe 3 C phase as well as Fe 3 O 4 cubic phase. It has been determined, that, after plasma electrolytic treatment, a carbide phase in the modified surface layer, irrespective of the location in the steel structure has the chemical composition Fe 3 C. High concentration of carbon atoms in a solid solution based on γ- and α-iron, a large dislocation density, presence of particles of carbide phase and retained austenite layers have been found.

Fiber reinforced polymer (FRP) composites have significant potential for applications in many engineering fields in place of metallic materials, due to their low density, high strength to weight ratio, high stiffness, better corrosion resistance and durability. The fabrication of these composites requires careful design and appropriate process developments to improve the mechanical properties. This study aims to investigate the effect of the post-cure heat treatment on the tensile and impact toughness of FRP composites. FRP composites were fabricated by using woven carbon and glass fiber fabric plies and their respective hybrid laminates. Hand lay-up using vacuum bagging method was used for manufacturing the laminated composites. After curing, the specimens were subjected to the post-curing process at temperatures of 25, 62.5 and 100 °C for 1 hour. Impact toughness and tensile strength of post-cured FRP composite specimens were investigated by the Charpy impact test and tensile test, respectively. Statistical analyses were also performed to compare the effect of both, the post-curing temperature and the FRP type, on the mechanical properties of composite specimens by using two-way ANOVA analysis. The results showed that post-curing has a favorable effect on energy absorption capacity and tensile properties of FRP.

Fiber optic sensing technology is increasingly becoming a superior nondestructive means for the stress monitoring of civil engineering structures. To understand the mechanical properties of superlarge diameter rock-socketed piles under complicated geological conditions, field tests were performed by distributed fiber optic sensors. The feasibility of Brillouin fiber optic sensing technology in testing the compressive stress of piles had been tested by indoor model tests and its correlation coefficient had been acquired. The in-situ installation of the fiber optic sensors is carried out on the super large diameter rock-socketed piles of the Hezhang Bridge, Guizhou province, China. Based on the test data collection during construction, the data treatment and analysis, the bearing behaviors and load transfer mechanism were explored. The feasibility of the fiber optic sensing technology in monitoring pile stress was verified and its application was proposed. The results have reference value to pile theory and the application of fiber optic sensing technology on similar projects.

Kurzfassung Der Einfluss der Maschinensteifigkeit auf die Versuchsführung ist ein seit langem untersuchtes Thema. Von den in den Kraftfluss einbezogenen Komponenten hat das Maschinengestell wesentlichen Anteil an der Eigenfederung. Diese lässt sich an ausgeführten Prüfmaschinen durch Belastungsversuche messtechnisch ermitteln. Aus der Steigung typbezogener Federkennlinien geht außer der Größe der Formänderung die gespeicherte elastische Formänderungsenergie hervor. Um den dadurch bedingten Maschineneinfluss zu minimieren, ist das Merkmal „harte” Prüfmaschine eine unabdingbare Forderung jeder konstruktiven Auslegung. Der Schwerpunkt vorliegender Abhandlung liegt daher auf der voraussagenden Steifigkeitsermittlung. Hierfür lassen sich Bemessungsregeln anhand des Stabwerkmodells „Rahmentragwerk” angeben. Variable Bemessungsparameter werden nach ihrem Einfluss auf die Steifigkeit in der Prüfachse abgestimmt.

Kurzfassung Um die elastischen Eigenschaften der Prüfmaschine und deren Einfluss auf die Dehngeschwindigkeit im Zugversuch zu bestimmen, wird die Systemstruktur anhand von Verhaltensmodellen untersucht. Für den quasistatischen Versuchsablauf kann die Wechselwirkung beteiligter Komponenten durch das Netzwerk in Reihe geschalteter Federn abgebildet werden. Zur Identifikation des Maschineneinflusses lassen sich Kopplungsbeziehungen zwischen Antrieb und Probe herleiten. Mit der ideal-steifen Maschine, verwirklicht durch erläuterte Zusatzeinrichtungen, kann eine unkontrollierte Verformung der Probe im elastisch-plastischen Übergangsbereich vermieden werden. Die Kompensation der Störeinwirkung nicht nur konstruktiv, sondern signalseitig herbeizuführen, ist Aufgabe des geregelten Antriebs. Aus der Signalverknüpfung konzentrierter Funktionsblöcke, abgebildet im Signalflussplan, werden Übertragungsbeziehungen des geschlossenen Regelkreises hergeleitet. Neben der Positionsregelung wird die aktuelle Regelungsart der Dehngeschwindigkeitsregelung aufgegriffen. Auf Stabilisierungsmaßnahmen durch adaptive Regelung wird hingewiesen.

Grinding is an important operation with various industrial applications. Literature studies indicate that grinding has an immense economic effect on the industry due to its high energy consumption, where approximately 5 to 6 % of the world electricity is consumed in mineral processing plants by using 80 % of this energy for crushing and grinding of raw materials. In this study, the grinding energy consumption was estimated using the Bond's work index by consideration of the effect of some additives on the grinding operations. The results show that the saved quartz grinding energy increases up to 30 % when using 0.04 % ethylene glycol ether as an organic grinding additive at a pH value of 7.

Among the nontraditional machining process, electrical discharge machining (EDM) is one of the significant processes for machining complicated and complex shapes. An experimental investigation was made with the help of electrical discharge machine on Inconel 718 using brass electrode tool to study the vibration behavior in the titanium carbide nanoparticles mixed dielectric fluid environment. Titanium carbide nanoparticles mixed with dielectric fluid possess a high strength, have good electrical and thermal properties and require lesser machining time than pure dielectric fluid. In this experiment, the central composite second order rotatable design and response surface methodology were used to develop an experimental model. Based on the developed models, analyses on machining characteristics of titanium carbide nanoparticles mixed EDM have been carried out. The current, pulse on time and pulse off time were considered as input process parameters and the output process parameters such as material removal rate and surface roughness were evaluated. Analysis of variance has been conducted to check the ability of the developed regression models. The investigations revealed that best surface finish could be obtained by setting the EDM machine parameters at low current and short pulse on time.