In this report, it is described how the bending fatigue strength will be influenced by the form of cross-section of specimens. As the experimental results, it is cleared that the bending fatigue strength becomes small with the increasing of the area subjected to the highest stress. The results was explained by considering fatigue and stress distribution.

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This investigation was made in order to compare the diagram of torsional endurance limit of solid specimen with that of thin-walled hollow specimen. And it was clarified that the stress amplitude at the endurance limit is scarcely affected by the mean stress in the solid specimen as well-known and it decreases fairly with the increasing of the mean stress in the hollow specimen. This dissimilarity of the diagram of endurance limit due to the form of specimen was explained from variation of the distribution of mean stress during the fatigue test in the solid specimen.

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The authors have reported in the previous paper that the brittle coatings may break when the maximum principal strain exceeds a critical value and the cracks may spread perpendicularly to the principal strain.
The elastic constant and Poisson's ratio of coating are different from those of the base material; therefore, the stresses in the coating and those of the surface of specimen are different even when subjected to the same deformation. Standing on such a point of view, the law governing the fracture of coating is necessary to be strictly investigated. The relations of the stress and strain of coating to those of the base material are considered. Utilizing this relation, it has been explained by the experiments of the specimens with a uniaxial and a biaxial stress distribution whether of a few general laws of fracture should be applied.
By this experiment, the authors have found that the law of fracture based on the maximum principal strain can be applied with enough accuracy.

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In this report mechanical properties of phenol resin gears-such as the strength of teeth due to statical and impact tests, abraision resistance and noise absorbing properties, etc.-were studied.
Laminate of improved No. 11 base showed the most suitable properties for gear materials for the sizes of these models.
The superiority of phenolresin gears to the cast iron gears in bad lubricating conditions, and also the suitable lubricating conditions for phenol resin gears were made clear.

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