Low pressure die casting (LPDC) is defined as a net shape casting technology in which the molten metal is injected at high speeds and pressure into a metallic die. The LPDC process is playing an increasingly important role in the foundry industry as a low-cost and high-efficiency precision forming technique. The LPDC process is that the permanent die and filling systems are placed over the furnace containing the molten alloy. The filling of the cavity is obtained by forcing the molten metal by means of a pressurized gas in order to rise into a ceramic tube, which connects the die to the furnace. The ceramics tube called stalk has high temperature resistance and high corrosion resistance. However, attention should be paid to the thermal stress when the stalk is dipped into the molten aluminum. It is important to develop the design of the stalk to reduce the risk of fracture because of low fracture toughness of ceramics. In this paper, therefore, the finite element method is applied to calculate the thermal stresses when the stalk is dipped into the crucible by varying the dipping speeds and dipping directions. It is found that the thermal stress can be reduced by dipping slowly if the stalk is dipped into the crucible vertically, while the thermal stress can be reduced by dipping fast if it is dipped horizontally.

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Fatigue crack growth tests of two ferrite-pearlite and two ferrite-bainite steels with different size and spacing of particle, where pearlite/bainite (hard) particles were uniformly distributed in the ferrite matrix, were carried out to investigate effect of second phase particle on fatigue crack growth behavior in Paris regime. The fatigue crack growth curves for the four materials did not coincide each other, even when the crack growth curves were arranged by the effective stress intensity factor range. From the in-situ observations, crack tip stress shielding phenomena, such as interlocking, branching, etc were found on the crack wake, which enhanced fatigue crack growth resistance. Small size and spacing of pearlite/bainite particle seemed to induce small but frequent crack deflections, which resulted in crack closure phenomena. On the other hand, large size of pearlite/bainite particle seemed to induce stress shielding phenomena and then contribute to high crack growth resistance, which was the main reason for lower fatigue crack growth rate of the large size and spacing of hard particle compared the small size of hard particle.

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In order to provide J-integral solutions for assessing the structural integrity of cracked pipes of nuclear power plants, finite element analyses were performed for circumferential surface cracks of uniform depth in pipes under bending load. Elastic and fully plastic solutions were obtained for a wide range of geometrical and material conditions. Based on the solutions obtained, a procedure for estimating J-integrals of Ramberg-Osgood materials was proposed. Through analyses under various conditions, it was shown that the estimation procedure gives reasonable solutions regardless of material and geometrical conditions and the magnitude of load. The average error in the estimated J-integrals was almost zero.

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The authors have developed a method of improving the thermal cyclic resistance of the thermal barrier coating system that is deposited on gas turbine components. A conventional thermal barrier coating consists of a duplex system: a top coating and a bond coating. The developed system has a protective intermediate layer of MoSi₂ which prevents oxidation of the bond coating. The conventional duplex plasma -sprayed coating was delaminated after 20 thermal cycles. On the other hand, the developed triple-layered coating system was not delaminated after 60 cycles. The reason for the enhanced resistance to thermal cycles of the developed triple-layered coating system is that the MoSi₂ layer between the top coating and the bond coating has a self-repairing property. MoSi₂ oxidizes to form SiO₂, which seals the cracks and pores formed between the top coating and the bond coating. Thus, the formation of a thermally grown oxide(TGO), which causes the delamination of the coating, is prevented and the thermal cyclic resistance is improved.

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