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A model describing nanoindentation as plastic deformation resulting from a strain gradient is investigated. Using a simplified axisymmetric nanoindentation, the effective strain gradient for indentation depth is derived. The proposed indentation model is a modification of Nix and Gao’s model (1998) . To validate this approach for nanoindentation, solutions for depth-dependent hardness of single various materials such as Cu, Al, Ni are compared with experiments. Results show that the proposed model agrees well with the hardness experiments.

This paper will discuss two different techniques to measure mechanical properties of thin film, bulge test and nano-indentation test. In the bulge test, uniform pressure applies to one side of thin film. Measurement of the membrane deflection as a function of the applied pressure allows one to determine the mechanical properties such as the elastic modulus and the residual stress. Nano-indentation measurements are accomplished by pushing the indenter tip into a sample and then withdrawing it, recording the force required as a function of position. . In this study, modified King’s model can be used to estimate the mechanical properties of the thin film in order to avoid the effect of substrates. Both techniques can be used to determine Young’s modulus or Poisson’s ratio, but in both cases knowledge of the other variables is needed. However, the mathematical relationship between the modulus and Poisson's ratio is different for the two experimental techniques. Hence, achieving agreement between the techniques means that the modulus and Poisson’s ratio and Young’s modulus of thin films can be determined with no a priori knowledge of either.

This paper is on the improvement of the oil pump assembly for preventing low oil pressure symptoms of the K9 Self-Propelled howitzer engine. Although the TBO(Time Between Overhauls) of K9 self-propelled howitzer engine is 1,500 engine operating hours, 13.37 % of K9 Self-Propelled howitzer engines which were operated for only hundreds of hours suffered low oil pressure symptoms and failed to operate normally. Detailed investigation into the engine was conducted to establish the cause and generation mechanism of the symptoms and it was found that oil leakage due to abrasive wear of pressure relief valve piston housing occurred in the oil pump assembly. To prevent abrasive wear of piston housing, new design concept and design parameters of pressure relief valve have been proposed. Performance, durability and system installation test on the prototype based on the proposed design were followed and results validated the proposed design. Oil pump assembly based on this study is applied to mass production.

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