Expansion and reduction are the two common end forming processes for tubes. In the tube end expansion process using a square punch, it is difficult to obtain a small corner radii due to the stretching of the tube around the punch corners. The wall thickness around the corners is small when compared to the side wall. Hence, a tube having a poor square look is formed. In this study, a 2-stage end expansion of a round tube end into a square section having an improved square look i.e. small corner radii and increase in wall thickness around corners is developed. In the 1st stage, the tube end is flared into a cone shape using a 30° conical die by axial compression. In the 2nd stage, the conical end of the tube is drawn through a taper square die using a conical bottom square punch, and a near square section is formed. A 15% ironing ratio is applied during the drawing process to flatten the side wall of the square. Experimental and FEM simulation were performed to evaluate and to verify the forming process. Although the height of the square section increases when the punch stroke at the 1st stage is increased. However, this increase is limited by the buckling of the pipe at the circular section of the thick blank tube. Since the conical end is drawn into a square section having different radial lengths, the bottom of the square section is uneven. The uneven bottom end is trimmed off in the later process. A square section having a maximum height of 32 mm after trimming is successfully obtained from the experiment for the punch stroke, S = 44 mm using an API 5 L tube.

The objective of this study is to investigate the behavior of Aluminum shells AA5083-H116 under low energy impact and the effects of curvature and thickness were assessed under different impact velocities (5.6, 7.5, 9.5, 11.5 m/s). LS-DYNA software was used to evaluate the amount of absorbed energy by the Aluminum shell during impact under different curvature parameter c. The results showed that the amount of absorbed energy incereases with increasing curvature in a linear relationship which make it possible to predict the amount of absorbed energy for this aluminum alloy under different impact energy. Aslo, the amount of absorbed energy has a direct linear relation with the rise of impact energy. The slopes of curves for absorbed energy with respect to the imapct energy are similar for all curvatures. Shell thickness has inverse effect on the amount of absorbed energy and the relation shows similar ternds with diffrent curvatures. However thick shells show significant increase in maximum force and better stability in the dynamic behavior with less fluctuations in the impact force as the cuvature increases.

Compacted powders of titanium (Ti) and carbon (C) in form of pellets were exposed to a massive amount of heat generated from the thermite reaction of Fe2O3 and Al in a graphite–steel tube mounted in a developed centrifugal accelerator machine. The centrifugal force facilitated the formation of multi-component products during the process. Titanium carbide (TiC) product is joined to an Al2O3–Fe layer, which are the products of the thermite reaction. The existence of centrifugal acceleration had a significant effect on both metallurgical alloying and mechanical interlocking between different layers of the sample to form a functional material. A mathematical model developed for this experiment to describe the speed rate of iron infiltration inside the TiC product as well as viscosity rate variation was presented. The composition, microstructure and mechanical properties confirmed the model.

Hydroxyapatite (HA) has been extensively studied for its exceptional ability in promoting osseointegration as in bone graft substitute and biomimetic coating of prosthetic implants. However poor mechanical properties of HA, in particular its low fracture toughness, has made its widespread adaption in a number of biomedical applications challenging. Here we employ an optimized wet precipitation method to synthesize nanocrystalline HA with significantly improved mechanical properties. In addition doping by MgO is found to effectively suppress grain growth and enhance fracture toughness by nearly 50% while good densification and phase stability in all samples regardless of concentration of dopant are fully maintained. Microstructural analysis further suggests that the exceptionally superior mechanical properties can be explained by migration of MgO to grain boundaries where they transform the more common transgranular fracture into an intergranular mode. Our biodegradation tests also confirm that MgO-doped HA is indeed a suitable candidate for load bearing implants.

Series connection of power cells in asymmetrical cascaded configurations helps to cancel redundant output levels and maximise the number of different levels generated by the inverter. A new configuration of three-phase multilevel asymmetrical cascaded voltage source inverter is presented. This structure consists of series-connected sub-multilevel inverters blocks. The number of utilised switches, insulated gate driver circuits, voltage standing on switches, installation area and cost are considerably reduced. Cascaded-cell DC voltages in each inverter leg form an arithmetic sequence with common difference of E. With the selected inverter DC sources, high-frequency pulse-width modulation (PWM) control methods can be effectively applied without loss of modularity. Low-frequency and sinusoidal PWM techniques were successfully applied. Hence, high flexibility in the modulation of the proposed inverter is demonstrated. The prototype of the suggested inverter was manufactured and the obtained simulation and hardware results ensured the feasibility of the configuration, and the compatibility of both modulation techniques was accurately noted. Lastly, the semiconductor losses in the converter were calculated using simulation models. Based on the analysis of the total power losses, the proposed inverter provided high efficiency at different operating conditions.

The influence of small additions of MnO2 (up to 1 wt. %) on the sintering behaviour of yttria-stabilized zirconia sintered over the temperature range from 1250°C to 1500°C was investigated. It was found that the mechanical properties of Y-TZP were dependent on the dopant amount and sintering temperature. The results revealed that relative densities above 97.5 % of theoretical (i.e. > 5.95 Mg m-3) could be obtained in Y-TZPs sintered at low temperatures, 1250°C and 1300°C, with the additions of ≥ 0.3 wt. % MnO2. In comparison to the undoped samples, the additions of up to 1 wt. % MnO2 and for sintering up to 1350°C was found to be beneficial in enhancing the Vickers hardness of the ceramic. The fracture toughness of Y-TZP however, was found to increase only in the 1 wt. % MnO2-doped samples when sintered above 1400°C. The relation between the measured mechanical properties is discussed with the emphasis on the role of the manganese oxide.