In this study, fracture strength of WC-12Co thermal sprayed coating is investigated experimentally and analytically. In experiments, one pair of butt cylindrical specimen with coating is subjected to combined tension with torsion stresses. Stresses at the singular point on fracture surface are analyzed by Finite-Element-Method and is approximated by the expression σ=KR^<-λ where R means normalized thickness coordinate. It is found that principal stress distributions are common to all cases of testing stress conditions and so fracture condition of a brittle coating is represented as K≧Kcr in the principal stress distribution even under mixed fracture mode l with III.

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In order to clarify the mechanism of flaking which is generated on the race and bearing of the ceramics, rolling fatigue tests under lubricated ball-plate contact were carried out on the smooth HIP-Si_3N_4 race and the pre-cracked HIP-Si_3N_4 race, and the stress in the race were calculated using the expressions in terms of elementary function of spherical Hertzian contact by M. T. Hanson. As a result, it was found that the crack was initiated at the knoop indentation, and progressed by the maximum shear steres for the knoop race. Also, it was seen that the main crack that made the maximum principal stress to be driving force of the progress progressed along the trajectory of the minimum principal stress for the smooth and ring crack race.

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In recent years, the necessity of biomaterials has been increased more and more with an ageing society. Biomaterials mean the materials specially designed for the repair, reconstruction, and replacement of diseased or damaged part of human-body. Alumina is considered as a candidate material for bio-ceramics, because of its superior strength characteristics, corrosion resistance and bio-inert properties. In this study, the effects of human body environment upon contact fatigue behavior of alumina have been investigated by electro hydraulic control fatigue testing. Test specimens were polycrystalline aluminas that were used for artificial joint and so on. As the specimen aluminas was used, which have two different purity, that is , 99.7% and 99.9%, and sintered at 1600℃. Contact impression damaged morphologies and fracture surfaces of alumina specimens were mainly examined in detail by FE-SEM. As a result, the dimension of polycrystalline alumina contact impression trace was found to be larger in quasi-human body liquid solution (lactated ringer's solution) compared with that in air.

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Notched compact tension specimens of SUS304 stainless steel (notch tip radius of 1mm and 4mm, thickness of 6mm) were low-cycle-fatigued at RT. Fatigue crack initiated on the notch root surface near the midthickness and propagated to outer surfaces. The recrystallization-thermal etching technique revealed that the fatigue damage accumulate more near the midthickness of the notch tip than near the surface. It is shown that crack initiation near the midthickness is due to the faster and more fatigue damage accumulation near the midthickness than near the surface.

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In the extremely low cycle fatigue, a transition of the fracture mode occurs from the surface to internal fracture with an increase in the plastic strain range. Such a transition is caused by an increase in the paerlite cracking inside the material. The pearlite cracking is affected by the stress distribution, and is greatly dependent on the own direction of lamellae. However, Work Hardening seldom affects an increase in the paearlite cracking.

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The fretting fatigue life of airplane engine dovetail was investigated using stress singularity theory. The crack initiation of fretting fatigue occurs at the contact edge of blade dovetail between blade dovetail and wheel dovetail. The parameters of stress singularity obtained from maximum principal stress distribution by finite element method analysis is effective to evaluate the fretting fatigue with the cyclic load having a constant angle against the contact surface under a variable contact pressure in case of titanium alloy as well as in case of steel. The ratio ΔHl/ΔHc between intensity range of stress singularity and critical intensity range of stress singularity is an useful parameter to predict the fretting fatigue life.

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