On the Low Cycle Fatigue Strength of Glass Fiber Reinforced Plastics

Abstract

Static tensile tests and low cycle fatigue tests up to 10000 stress cycles under pulsating tension were carried out on plate specimens of glass fiber reinforced plastics. The test plates (340× 280×3.12∼4.13mm) were made by laying up with hand 16ply plain woven cloth of glass fiber. The test pieces were cut off with a hand saw from these plates at first in line with the warp and then at its angle of 45°. The following results were obtained from these tests. (1) In the case of the test pieces loaded in line with the warp, the tensile strength does not vary if the breadth of the test pieces is more than 4mm, but in the test specimens loaded at the angle of 45° of the warp, the tensile strength increases linearly with the breadth up to 12mm, and is constant when the breadth is more than 12mm. (2) The S-N curves under low cycle faigue up to 10000 stress cycles can be represented by straight lines, and the fatigue strength at any cycles of N loaded in line with the warp is expressed in the following empirical formulas: for the plain specimen
σ=σ_B-3.3log₁₀N
for the notched specimen
σ=σ_BK-2.0log₁₀N
where, σ_B: tensile strength of plain specimens, σ_BK: tensile strength of notched specimens. (3) The fatigue notch factor considered for the fatigue strength at N cycles increases when the stress cycles decreases, and the fatigue notch factor at one cycle, i, e. at tensile strength reaches its maximum. (4) The fatigue notch factor for the specimens loaded in line with the warp reaches its maximum when the notched specimen has the radius of 6mm. (5) The fatigue notch factor for the specimens loaded at the angle of 45° of the warp is less than the unit.