Advanced Materials Research Vols. 83-86

Abstract: The high carbon chromium bearing steel, as a kind of special steel, entails high quality. The work aims to simulate the solidification process of continuous casting of high carbon chromium bearing steel, to find the cause for defect, and to optimize the secondary cooling parameters steel. A finite element model is developed to compute heat transfer and solidification in bearing continuous casting. By comparing the calculated data with the metallurgical constraints, the key factor caused the cracks on the strand can be found out. Then based on the subproblem approximation method, an optimization program is developed to search out the optimum cooling parameters. Those optimum parameters can meet all specified requirements but with a minimum expense of the operational and the design constraints and can make it possible to run the caster at its maximum productivity, minimum cost and to reduce the defects. Now, online verifying has been obtained with the cracks decreasing and the water consumption of secondary cooling zone saving.

Abstract: In this paper, the effects of nanotube diameter, waviness ratio and wavelength ratio on the tensile elastic modulus (TEM) of the carbon nanotube (CNT) reinforced polymer composites is investigated using a 3-D nanoscale representative volume element (RVE) based on continuum mechanics and using the finite element method (FEM). Formula to extract the effective material constant from solutions for the RVE under axial loading is derived based on the elasticity theory. Both long and short CNT embedded in the matrix are considered for investigating the effect of fiber diameter variation whereas only long wavy CNT is considered for investigating the effect of waviness and wavelength ratio variation, all at a volume fraction of 5%. First, the effects of CNT diameter on the TEM of the composite are investigated. Numerical results show that TEM of the polymer composite is influenced by tube diameter variation for both long and short CNT. Then the effects of waviness ratio and wavelength ratio on the TEM of polymer composite are investigated. Results show that both the waviness and wavelength ratio variation of CNT significantly influence the TEM of the polymer composite.

Abstract: In this investigation the role of alloying elements on austemperability of heavy section ductile irons was studied. Four different chemical compositions were chosen in a way to specify an optimal chemical composition with suitable austemperability. Austempering was carried out at 315 and 350oC for 1 hour on specimens prepared from cast Y-blocks with 75 mm thickness. Metallographic examinations and hardness tests indicated that thickness of bainitic layer was positively dependant on the amount of the alloying elements which deferred pearlitic transformation in TTT diagram to the longer time. In addition, by increasing the amount of alloying elements, the morphologies of ferrite in bainitic structure changed from featherlike to acicular. According to the results of this study, in order to achieve a full bainitic structure (in the specimens whit 75mm thickness), the optimal amounts of alloying elements were: 0.35 % Mn, 0.22 % Mo, 1.1-1.4% Ni and 0.6% Cu. In addition, regarding to the thick sections of Y-blocks, graphite degeneration defect was also studied, and it was noticed that this defect could be completely eliminated by adding 50ppm of antimony.

Abstract: This paper describes the results of four thermochemical surface treatments of austenitic stainless steels carried out at 450oC in a fluidised bed furnace and they are nitriding, carburizing and the newly developed hybrid process involving the simultaneous and sequential incorporation of nitrogen and carbon to form a dual layer structure in order to achieve much enhanced surface hardness and wear resistance without compromising the corrosion resistance of the steel. In all these treatments there formed alloyed layers with a common feature of being precipitation-free and supersaturated with nitrogen, or carbon or both in the austenite lattice which is known as S Phase or expanded austenite. However the layer thickness was not uniform in any of these treatments and an effective layer was produced after 8h treatment duration. The nitriding treatment produced thicker and harder layer compared to other treatments; the maximum hardness was over 1500 Hv for nitriding and the minimum hardness of 500 Hv for carburizing treatment. The nitriding treatment sample gave high wear resistance which corresponded to high hardness values.

Abstract: Cantilever plate structure deposited metal layer is widely used MEMS. Due to mismatch of thermal expansion coefficients between structure and metal layers, residual gradient stress would be induced and deform structure as devices cooling down from process high temperature to room temperature. In this work, constraints effect is investigated. There are three constraints discussed and could be fabricated by back etching, isotropic wet etching, and anisotropic dry etching. For detail analysis, finite element method is used to analyze. Different width and length of structure sizes are used to discuss constraint effect. From the results, it is found different constraint would affect deformation. Under the same structure sizes, flat surface constraint has the largest deformation. And ICP etching constraint has the smallest deformation. Due to mechanics behavior of plate being much different comparing to beam, deformation of plate is no long parabolic shape in length direction. There are complex deformations in width direction. It is also found the deformation is determined by mechanics behavior on constraints. Width and constraint types have no significant on deformation when length is large at free end and middle section. And length has no significant effect on deformation for ICP and backside etching at clamped end. Temperature would induce increasing deformation linearly at free end and middle section.

Abstract: In this paper the results of structural changes in ultra high molecular polyethylene (UHMWPE) upon gamma irradiation and storage in nitrogen environment are reported. Based on differential scanning calorimetry (DSC), wide angle x-ray scattering (WAXS), gel content, fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM), we show that upon gamma irradiation crystallinity percentage increases by 20% at high doses due to aging, at low doses up to 50 kGy there is no significant changes. Lamellar thickness increases with the dose, possibly due to chain scission and the addition of new molecular segments to the lamellae. Upon storage in nitrogen DSC data confirmed the appearance of new smaller lamellae. Crosslinking was achieved by irradiation but the ratio of scission to crosslinking is higher after aging. This was confirmed by the increase in the oxidation index and the high brittle behavior of the polymer after aging where fibrous surface was noticed.

Abstract: Thin films of a blend of 90, 75, 50 (wt/wt%) percentage of polyethylene oxide and polyvinyl alcohol were synthesized and irradiated with 5, 25, 50, 100 and 200 kGy. The presence of PVA leads to diffusion controlled mechanism where it decreases the crystallinity of PEO as restricted crystallization occurs.Low doses of 5 kGy cause crosslinking of the blends and increase the thermal stability. Higher doses up to 100 kGy cause the PEO crystallite boundaries to be erased and to blur spherulites structure; it also leads to an increase in the crystallinity. Higher doses of 200 kGy cause an increase in the hydrogen bonding where the material is more crystalline in structure and broken down which made more segments available for the hydrogen bonding. Degradation and oxidation of the blends due to the presence of free radicals in the polymer irradiated in air is noticed for blends with very high doses. Never the less, PVA in these blends protects the PEO composite from the effect of radiation.

Abstract: Carbon fiber reinforced plastics (CFRP) have high strength in comparison with dimensional stability, invariability of material property, high strength and rigidity, corrosion resistance. Therefore, CFRP is widely used in various fields including space and aviation industries, sports and leisure industries, and general structural members and parts. To achieve structural members of CFRP with high strength and rigidity, theoretical approaches is limited to isotropic material, and empirical studies have been conducted. As with other composite materials, CFRP shows different rigidity and strength due to difference in properties in fiber and matrix material. In this study, CFRP specimen with changing stack orientation angle was manufactured as general structural application, and bending strength and rigidity of the corresponding composite was measured. In addition, square aluminium tube reinforcement is applied to prevent the shortcoming of CFRP. Vacuum compressed CFRP via autoclave with square aluminium tube reinforcement material (Hybrid) was evaluated by changing of orientation angle.

Abstract: Degradation of tensile properties resulting from geometrical discontinuities due to localized pitting is usually evaluated in terms of the reduced section thickness associated with pit geometry which lowers the load carrying capacity of the structure. However, the effects of finer parameters associated with pit distributions such as pit area percent (PAP) are not usually taken into account. In this research, the effects of spacing, depth and PAP on tensile properties of a structural steel are investigated. Simulated pit distributions were produced on the gage sections of flat tensile specimens using mechanical drilling. It is found that final elongation is more adversely affected than tensile strength with increasing PAP, pith depth and pith spacing. However, the reduction in final elongation tends to be largely recovered at higher PAP values due to increasing uniformity of strain distribution. It is noted that increasing pit spacing at a constant PAP leads to greater reductions in tensile properties, especially at higher pit depths, due to the increased stress concentration and strain localization. It is further clarifies that the introduction of first few pits and their growth to larger depths could be very detrimental to the mechanical properties of structural alloys.

Abstract: The abrasive wear behaviors of different types of steels were evaluated using the abrasive wheel as a new technique in the pin on disc method. It is shown that the abrasive studies using this test method is acceptable for high wear resistance metals such as Hadfield steels, while it is not proper for soft materials such as mild steel. The test results on the different materials also show that initial hardness of materials cannot merely determine the wear resistance. However, microstructural changes during the sliding have significant effect on the wear behavior and must be included.