Band 107, Heft 9

This paper presents a finite element study on the contact parameters of a soft hemispherical finger tip pressed against curved surface. The variation in magnitudes of contact radius, contact pressure and vertical displacement are estimated using two-dimensional finite element models. The special effects of geometry using a wide range of normal force on soft finger tips are presented with the aid of a dimensionless parameter, curve factor ( R / a ). It addresses the effects of the load–contact relationship for ten different fingertip combinations. From close observations it can be concluded that a higher magnitude of contact radius can be obtained with a lower curve factor and vice-versa. Also, it is evident that the radius of contact is higher for a curved object when compared with a flat one for a particular combination. However, there is a significant reduction in the magnitudes of vertical depression and contact pressure.

In the present work, the in-plane dynamic crushing behavior of functionally graded honeycomb structures with missing-wall defects is investigated. To study the influences of the functionally graded properties on dynamic crushing, a density gradient is introduced by changing the cell wall thicknesses along the impact direction. Results show that both the deformation mode and energy absorption are sensitive to the density gradient. However, the deformation mode displays less dependence on the density gradient when the honeycomb is impacted at a high velocity. Furthermore, the effects of defect ratios and defect locations are discussed. Results reveal that the larger defect ratio is responsible for the lower energy absorption. For the case of 70 m s −1 impact velocity, defects in the middle of the structure should be avoided, as they lead to inferior energy absorption.

A mathematical model of the continuous casting process for multi-crystalline silicon billet has been developed to predict the stress evolution in the billet using the commercial finite element package, ProCAST. The calculated temperature was validated by the measured data, and the good agreement shows the reliability of the present model. The effects of casting parameters on the stress of a billet were investigated and the simulation results were validated by the analytical calculation data. The results indicated that the stress slightly decreased with the increasing of the pouring temperature. With increasing the cooling intensity in the secondary cooling zone and decreasing the casting speed, the billet stress increased. In the present work, it was found that at a pouring temperature of 1560°C, with air cooling in the secondary cooling zone and a casting speed of 1 mm s –1 , a billet with low stress could be continuously cast.

In this study, the shape recovery and mechanical properties of Ni 54 Mn 16 Fe 9 Ga 21 high-temperature shape memory alloy are improved simultaneously. This results from the low, about 4.4%, volume fraction of γ phase being almost completely distributed along grain boundaries. The recovery strain gradually increases with the increase in residual strain with a shape recovery rate of above 68%, up to a maximum value of 5.3%. The compressive fracture strain of Ni 54 Mn 16 Fe 9 Ga 21 alloy is about 35%. The results further reveal that when applying a high compression deformation two types of cracks form and propagate either within martensite grains (type I) or along the boundaries between martensite phase and γ phase (type II) in the present two-phase alloy.

Ductile iron, popularly known as spherodized graphite iron (SGI), is a special variety of cast iron having carbon content more than 3 wt.% and has graphite present in compact, spherical shapes. These compact spheroids hamper the continuity of the matrix much less than graphite flakes, which results in higher strength and toughness with a structure that resembles gray cast iron, thus imparting superior mechanical properties. The high ratio of performance to cost which they offer to the designer and end user makes them used extensively for industrial applications. The basic chemical elements such as carbon, silicon, manganese, magnesium, copper etc. play an important role in the SGI casting process. The behavior of these elements in molten metal of the ductile iron varies because of their different mechanical and chemical properties. However, to extend the consistency and range of properties of SGI castings beyond its properties in the as-cast condition, heat treatment is a necessary operation. In this research specimens are prepared with different combinations of alloying elements. On these specimens studies are performed with various tests to understand the effect of heat treatment operations such as tempering and austempering to transform the brittle behavior to ductile behavior.

The abrasion behaviour of heat-treated 2.8C21Cr1Mo cast iron was studied. The specimens were destabilised at two temperatures, 980 and 1050°C, for 4 h, air hardened, and then tempered at five temperatures, 220, 320, 400, 500, and 620°C, for 2 h followed by air cooling. Using a pin-on-plate abrasion apparatus, the specimens were abraded on four types of bonded abrasives (silicon carbide, corundum, flint, and glass). The effect of work hardening on the abrasion resistance was investigated. It was found that the increase in alloy hardness produced by heat treatment had little effect on the abrasion resistance against silicon carbide or corundum; the inverse was true against flint or glass. The as-hardened structure containing 40% retained austenite gave the best abrasion resistance, whereas the hardened and tempered at 620°C showed the worst. Both bulk hardness and matrix hardness before wear correlated poorly with the abrasion resistance. Therefore, a general model “equivalent hardness” was developed, in which the hardness of the abraded matrix was considered. With this model, the abrasion behaviour can be clearly analysed.

La–Mg–Ni–Mn-based AB 2 -type La 1– x Ce x MgNi 3.5 Mn 0.5 ( x = 0, 0.1, 0.2, 0.3, 0.4) alloys were fabricated by melt spinning. X-ray diffraction and scanning electron microscopy revealed that the experimental alloys consisted of a major phase LaMgNi 4 and a secondary phase LaNi 5 . The Ce substitution for La and melt spinning refined the grains of the alloys clearly. Electrochemical tests showed that the as-cast and as-spun alloys exhibited excellent activation capability. With the increase in the spinning rate and Ce content, the discharge capacities of the alloys initially increased and then decreased, whereas their cycle stabilities always increased. Moreover, the electrochemical kinetics of the alloys initially increased and then decreased with the growth of Ce content and spinning rate. The major reason leading to the capacity degradation of the alloy electrodes was determined to be the pulverisation of the alloy particles and the corrosion and oxidation of the alloy surface.

Bronze matrix composites reinforced with Ni 3 Al particles were produced by means of a classical powder metallurgy (PM) technique. The Ni 3 Al particles used as reinforcement were produced by ball milling of cast alloy. The powders of the constituents of the bronze and Ni 3 Al powder were blended, compressed axially and sintered. The microstructures of the composites were characterized using optical microscopy and scanning electron microscopy. The compression strength and hardness of the composites were investigated. The tribological properties of composites and unreinforced bronze were determined using pin-on-disk geometry and results were compared with conventional phenolic resin bonded brake lining. The results showed that the PM bronze had higher strength than the composites while the hardness of the composites was higher than the PM bronze. According to dry sliding friction and wear tests, the composites have higher wear resistance and coefficient of friction than the conventional brake lining.

This research investigated the effects of Er addition (0–1 wt.%), cooling rate and hot extrusion on the microstructure, hardness and tensile properties of Al-15 wt.% Mg 2 Si in-situ composite. The results show that addition of Er with high concentrations changes primary Mg 2 Si particles from irregularly shaped to polygonal shaped and also transforms needle-shaped Al 5 FeSi compounds into a short rod morphology. Microstructural studies revealed that water-cooling is more beneficial to acquire polygon shaped primary Mg 2 Si and fish-bone Al 3 Er. Through hot extrusion, the networks of eutectic Mg 2 Si phase and fish-bone Al 3 Er compound are broken. In addition, the results of tensile testing show that both Er addition and water-cooling improve the ultimate tensile strength and elongation. The optimum tensile behavior was achieved by adding 0.6 wt.% Er to the water-cooled Al–Mg 2 Si composite after hot extrusion.

Composites of the ZrO 2 –CaO–Al 2 O 3 system exhibit high corrosion resistance and high chemical stability, these being suitable properties for enhanced performance as refractories. In this work composites based on ZrO 2 –CaAl 4 O 7 (CA 2 ) were developed by reaction sintering of two pure ZrO 2 powders with different particle size ( d 50 = 0.44 μm and d 50 = 8 μm) mixed with high-alumina cement. The effects of CaO to ZrO 2 molar ratio, particle size of ZrO 2 and sintering temperature on densification, c-ZrO 2 formation, microstructure and mechanical properties (Vickers hardness, dynamic Young's modulus and compressive strength) were determined. Porosity and mean pore size of composites reduced with decreasing both particle size of ZrO 2 and CaO content. The highest compression strength of ∼350 MPa and hardness of 6 GPa corresponded to dense ZrO 2 -based composite with 15 vol.% CA 2 sintered at 1400°C.

In this work, 6061–Al alloy–graphite (Al–Gr) composites were fabricated via the squeeze casting method. Al/Al–Gr joints were formed by direct active soldering with Sn3.5Ag4Ti0.5Cu active filler. The joint microstructures were examined using optical microscopy and scanning electron microscopy coupled with energy dispersive spectrometry. The Sn3.5Ag4Ti0.5Cu active filler can successfully join Al–Gr composite to 6061–Al alloy at a temperature of 250°C. During direct active soldering, Al dissolves into the active filler zone to form a coarse Al–Ag–Sn solid solution around the active filler. The shear-tested bonding strengths were 14.30 ± 1.57 MPa for Al/Al, 8.45 ± 1.37 MPa for Al–Gr/Al, and 8.15 ± 1.43 MPa for Al–Gr/Al–Gr joints. In the Al/Al–Gr joints, the fractures occurred through the active filler/Al–Gr interface.

Results of the first study on hot differential speed rolling (DSR) of Fe 3 Al-based intermetallic alloy are given in the present paper. The material was subjected to hot rolling at 1100°C with equal and non-equal (the DSR) speed of working rolls. The results of structural examinations indicate that the additional shear strain imposed to the material upon the DSR processing facilitates the activation of dynamic recrystallization. As opposed to the material hot deformed with equal speed of both rolls, the DSRed Fe 3 Al alloy was characterized by a fully transformed, close to equiaxed grain structure (average grain size of ∼120 μm). The observed structural evolution leads to a higher mechanical strength in DSRed samples as compared to the undeformed counterparts, however it does not result in a substantial improvement of the material's ductility.