Band 27, Heft 3-4

The purpose of this paper was to consider an edge dislocation near a circular hole within the isotropic theory of gradient elasticity. The stress field is derived with the help of a stress function method. The gradient stresses possess no singularity at the dislocation line. As a result, the image force exerted on the dislocation due to the presence of the hole remains finite when the dislocation approaches the interface. The gradient solution demonstrates a non-classical size effect.

This article investigates the differences between the Aifantis and Gurtin-Anand strain gradient plasticity. The fact that Gurtin-Anand strain gradient plasticity is richer than the Aifantis strain gradient plasticity provides a basis for which we could derive equivalent Aifantis flow rule and extend it to accommodate scalar dissipative hardening. It was found that the major difference between the Gurtin-Anand and Aifantis theories lies on the use of the codirectionality hypothesis and constraint imposed on the gradient of the flow direction.

The microstructure characteristics and wear behavior of a spray-deposited (SD) and the hot compressed Al-28Si alloys were investigated and the results were compared with corresponding SD and as-cast alloys. The microstructure, hardness and wear properties of the spray-deposited alloy was studied using X-ray diffraction, optical microscopy, scanning electron microscopy (SEM), microhardness measurement and wear tests. The microstructures of the SD alloy were composed of refined and uniformly distributed primary silicon (Si) and the formation a fine eutectic phase at the inter particle boundaries of an equiaxed grain morphology of the aluminum (Al) matrix. The decrease in the porosity level and further refinement of primary Si and eutectic Si phases in the hot pressed alloy. The wear tests indicate that the hot pressed spray formed alloy showed good wear resistance compared to both the SD and as-cast alloys. The improvement in the wear behavior is discussed in the light of microstructure evolution by the spray-deposition process. The worn surfaces were characterized by SEM-energy dispersive X-ray spectroscopy (EDS).

In this experimental investigation, the mechanical characterization and microstructure study of chicken feather fiber (CFF) and crumb rubber filled epoxy resin hybrid composite has been done. The surface of the fibers was treated with sodium hydroxide to improve the interphase bonding. Chicken feathers were taken in different weight percentages of 1, 3, 5 and 7. A composite was fabricated with epoxy resin using the hand lay-up technique. After conducting various mechanical tests in accordance with the ASTM standards, it was observed that 5 wt% of CFF recorded the optimum results. Hybrid composites were then fabricated with 5 wt% CFF and varying weight percentages of crumb rubber, i.e. 0, 0.5, 1, 1.5, 2 and 2.5. On the basis of mechanical testing conducted on hybrid composite, tensile strength, flexural strength and impact strength showed a significant improvement. The justification of trend was given through the microstructural tests, which were a scanning electron microscopy (SEM) and X-ray diffraction analysis. It was concluded that 1 wt% of crumb rubber with 5 wt% CFF hybrid composites showed the optimum results amongst various combinations. Thus, properties showed significant improvement in the case of hybrid composite as compared to pure fiber-based composite.

New thermally sprayed amorphous metallic coatings have been developed recently that may provide a viable coating option for fluid handling equipment such as propellers, impellers and pumps. They possess the inherent risk of flow-dependent erosion-corrosion problems. In this investigation, iron based (Fe) amorphous coatings were deposited on AISI 316 stainless steel substrate by the high velocity oxy-fuel (HVOF) spraying process, and the coating microstructure was characterised using an optical microscope and scanning electron microscopy. The Fe-based amorphous coating consisted of an amorphous phase, an absence of dislocations, a nanocrystalline phase, less porosity and high hardness. The corrosion behaviour of the substrate and Fe-based amorphous coatings were evaluated by means of electrochemical tests in 3.5 wt.% NaCl solution. Three kinds of electrochemical tests were employed to identify the corrosion resistance of the coating and substrate. The results showed that the Fe 30 Cr 25 Mn 5 Mo 20 W 10 B 5 C 3 Si 2 amorphous metallic coating had a superior corrosion resistance than 316 stainless steel. It was attributed to the amorphous structure and the presence of the corrosion resistant element chromium (Cr).

Here, the corrosion properties of chromium (Cr) added to a copper-aluminum-nickel (Cu-Al-Ni) alloy were studied. Primarily, the alloy samples were prepared by increasing the percentages of Cr composition in the following series of 4%, 8% and 12% by keeping other alloying elements as constants. The alloy was made using the powder metallurgical technique. Consequently, hot forging was done on the sintered specimen. Both hypothetical and authentic densities were found for the hot forged samples which showed that the densities kept on increasing with the addition of Cr. The Cr embellishments were exposed using optical microscopy of varying magnifications. The corrosion properties achieved from the potentiostat showed that the corrosion resistance upsurges more than the other commercially available nickel-aluminum-bronze (NAB) alloys due to the Cr embellishments. The corroded surface was then investigated using scanning electron microscopy (SEM) which disclosed the formation of different κ phases along with an α matrix and other intermetallic phases in the present alloy. Furthermore, hardness tests were taken and these established that the hardness increases with Cr accompaniments. Thus, the present alloy can be endorsed as a novel material (Cu-Al-Ni-Cr) in the propellers of ships in which both hardness and corrosion resistant are obligatory.

Porous corundum ceramic samples were sintered at various temperatures in the range of 1350–1550°C. The effect of the sintering temperature on the porosity rate and compressive strength of corundum samples were investigated. The porosity rates were of the order of 3.3–38% and the high-density sample was obtained at a relatively high temperature. However, an increase of compressive strength by more than 6 times was observed with the sintering temperature rise. The Young’s modulus increased remarkably from 40.49 to 302.15 GPa, which is related to the corresponding decrease of porosity rate.

Geopolymer concrete is a booming technology in the construction industry. Much research is occurring in geopolymer concrete, as it emits low carbon dioxide into the atmosphere, is eco-friendly material and is an alternative for cement. This research mainly focuses on the use of fly ash based geopolymer concrete in ambient curing conditions and the use of manufactured sand due to the scarcity of natural sand. Mainly studies have evolved on the workability, setting time and compressive strength by the effect of ground granulated blast furnace slag (GGBFS), manufactured sand (M-sand), alkaline activator solutions to binder ratio and the proportions of sodium silicate to sodium hydroxide (SS/SH) in geopolymer concrete and mortar. The experimental studies were carried out using nine geopolymer concrete mixes and the comparisons were made. The workability of concrete decreases by increasing the percentage of GGBFS, M-sand and the proportions of SS/SH whereas workability of concrete increases when increasing the alkaline liquid to binder ratio. The compressive strength of geopolymer mortar and concrete increases when the percentage of GGBFS and M-sand is increased, and it decreases by increasing the alkaline liquid content. There is no change in strength by decreasing the proportions of SS/SH.

The aim of this study was to analyze the flow behavior of materials in friction stir welding (FSW) of magnesium (Mg) alloy to aluminum (Al) alloy materials at a low rotational speed of 300 rpm and at a low welding speed of 50 mm/min. It was observed that during the dissimilar welding at 300 rpm, some of the material of the advancing side (AS) rotated almost 360° and transferred to the position just behind the previous position, i.e. initial AS position and some of the material of leading edge region transferred to the trailing edge region and such a change continued. Material transfer takes place layer by layer from front to back portions of the FSW tool; a thin layer of material adhered to the tool in the front portion for every half rotation and transferred to the back portion of the tool and this repeated in subsequent rotations. Wrinkle formation began at the front side of the forward moving tool and as the material transferred to backside they became an onion ring pattern, and this was inevitable because the formation of onion rings instantly in the backside region of the tool was clearly impossible.

Rotating bending fatigue test results vary from specimen to specimen even if materials are tested in a standard laboratory set up because rotating bending fatigue life or fatigue strength depends upon various factors due to its dynamic action. One method of testing may be machine scatter (offset and angular misalignment). Angular misalignments are unavoidable in dynamic machines due to continuous operation leading to transverse vibrations in specimens. The magnitude of transverse vibrations was measured manually by dial gauge arrangement. Experiments were carried out until fracture either with smooth running conditions or with the effects of offset and angular misalignment. The enhanced effect of misalignments on fatigue life was done through the histogram normal distribution technique. There was a clear distinction between the appearances of the fracture surfaces between the specimens subjected to smooth running conditions and specimen vibration, which reveals general fatigue fracture phenomena and intergranular fatigue cracks, larger decohesion of graphite nodules and isolated cleavage facets. The manual technique used without any resistance strain gauges, as they were not efficiently sustainable under repetitive loads, helped in understanding the dynamic machine scatter on fatigue life in an economical way where there were lesser concentrations in these areas.

Topology optimization is a mathematical approach that optimizes the layout for the given design constraints such as loading and boundary conditions so that the optimum design obtained performs its function. In different types of loading conditions such as single load or multiple load topological optimization result in the best use of a material for a body in given volume constraints. In topological optimization the structural compliance is minimized while satisfying a constraint on the volume of the structure. This paper represents the topological optimization of the fork-end (double eye) of a knuckle joint with the objective to reduce the mass of an existing fork-end of a knuckle joint of an automobile or locomotive by applying the optimization technique. Reducing the weight of an automobile part will result in the overall weight reduction of a vehicle, thus, its energy consumption demands decrease thereby improving its fuel efficiency. The topological optimization was done using a finite element solver, ANSYS. The ANSYS Parametric Design Language was employed for utilizing the topological optimization capabilities of the commonly used finite element solver ANSYS. Solid92 elements were used to model and mesh the fork end of the knuckle joint in ANSYS. The optimality criteria method was used for topological optimizing the fork end of a knuckle joint.

The mechanical response of the restored “connections” of the epistyles of the Parthenon Temple on the Acropolis of Athens is studied assuming that the interconnected epistyles are under shear loading mode. The study is implemented by taking advantage of a numerical model, properly validated on the basis of the data of a recent relative experimental protocol. The main difficulty while studying the specific problem is the co-existence of three materials of completely different mechanical behaviors, i.e. the brittle marble of the epistyles, the ductile titanium of the connector and the cement-based material filling the grooves of the marble in which the connector is placed. The interfaces of this three-material-complex are simulated as simple contact with friction, the coefficient of which is, also, experimentally determined. Taking advantage of the data provided by the numerical model the stress field developed in the connector and the surrounding marble volume is described. Moreover, the forces imposed by the connector on the surface of the groove are quantitatively determined. Furthermore, the model permits a quantitative comparison between the mechanical response of the interconnected epistyles in the presence or in the absence of the “relieving space”. It is definitely concluded that the alternative design of the “connections”, according to which a small portion of the connector’s web is left uncovered by the filling material (relieving space), offers serious advantages against the traditional design, in the direction of reducing the intensity of the stress field developed in the marble volume surrounding the connector, thus, contributing to the protection of the authentic building material of the monument in the case of overloading of the epistyles.