円孔を有する平織りガラス布強化ＧＦＲＰの疲労特性に及ぼす環境温度の影響

Abstract

The influence of environmental temperature on fatigue property of center hole notched GFRP reinforced by plain woven glass cloth was studied. In this paper, first, the fracture surface of GFRP after fatigue failure was observed by SEM photograph, and the difference of microscopic fracture style caused by the difference of environmental temperature was investigated. The matrix crack density produced in the fatigue process was measured, and the relation between crack density and modulus decay was confirmed. Then, the static and fatigue notch factors defined as the ratio of strength of the unnotched specimen to that of the hole notched specimen at a certain number of cycles were measured at various test temperatures. The temperature dependence of macroscopic fatigue process for the hole notched specimens with different hole diameters was considered.As the result, the following conclusions were obtained. When the environmental temperature rose, the microscopic fracture style shifted to the interface fracture from the cohesive fracture. Lower the environmental temperature, lower the stiffness modulus of the unnotched specimen under the fatigue process. Especially it was remarkable in the middle stage of the fatigue process, because the matrix is brittle and many matrix cracks are produced at low temperatures.For the hole notched specimen, the notch factor decreased with an increase of number of loading cycles for the whole range of hole diameter, because the stress concentration is relaxed by local modulus decay. However, at a low temperature and for small notched diameter, the fatigue notch factor increased with number of cycles, because of brittleness of matrix and remarkable propagation of matrix cracks from the vicinity of hole to its periphery. At high temperatures, it also increased because stress relaxation with local modulus decay does not progress so much comparatively.