抄録
It is pointed out first what favorable effect the small quantity of glass fiber ingredient in the reinforced Nylon 6 will have on the material to arrest the propagation of fatigue crack in it, and then the problem what is to account for the said favorable effect is carefully examined, from the standpoint of fractography, by performing repeatedly the test of low cycle fatigue, which is due to the tensile loads, by the use of an apparatus for the test of constant load. The results obtained are as follows.
(1) The fatigue crack in this case propagates itself slowly in match with the increasing ratio of glass fiber ingredient in the reinforced Nylon 6, no matter what sort of strain is repeated, unlike the crack propagation in the test of low cycle fatigue in the repeated bending by the use of the apparatus for the test of constant deflection.
(2) The relationship between the rate of propagation of crack in these specimens and the factor for the stress intensity at the crack tip follows Paris's formula, and it is found in the light of this relationship that the glass fibers will have power to arrest the propagation of fatigue crack.
(3) It is made clear by observation through the optical microscope that there are four typical patterns of fatigue fractured surface. These patterns of fatigue fractures together go to point to the condition that the glass fiber ingredient in the matrix functions to arrest the propagation of fatigue crack.
