We have reported, in the shearing fatigue of rubber vibration isolator, that the radius of the fillet and the form factor of the specimen have a great influence upon the fatigue life and the appearance of the fatigue cracks. In this paper, we report on the shape effect on the tensile fatigue, and consider the results from a viewpoint of deformation. The test was performed under a constant repeating strain of 0-15% with a frequency of about 500rpm, and using the specimens with a thickness of 15mm, diameters of 30, 24, 18mm and radii of the fillet of 0, 2, 4, 6 and 7.5mm.
The results may be summarized as follows:
(1) Excepting the specimens which had either very small or large fillet, either of the radius of the fillet and the form factor have little influence on the tensile fatigue life, in the case the life defined by the number of strain repetitions up to the time when fatigue crack appears on the surface of the specimen.
(2) Fatigue cracks appeared in the following manner irrespective of the form factor. The specimen without the fillet ruptured in the bonded plane. In the specimen which had R=2mm, the fatigue crack appeared in the fillet. In the specimens which had R=4, 6, and 7.5mm, the fatigue cracks appeared in the middle (cylindrical) part.
(3) By calculating the apparent strain on the surface of the specimen, we could well explain the above experimental results.
(4) From our experiments, it seems to be more desirable that the radius of the fillet is made about 4mm.