Effect of temperature and after-cure on fatigue fracture behavior of a glass/phenol composite

This paper presents effect of temperature and after-cure on fatigue fracture behavior in a glass fibre reinforced phenolic resin composite. Firstly, monotonic tensile tests were conducted to measure the stress–strain curves and acoustic emission (AE) behavior. Secondly, fatigue tests at room temperature were performed for the virgin and two kinds of after-cured specimens. Thirdly, S–N curves are measured for the specimens with and without a hole at various temperatures. Fourthly, fatigue crack propagation (FCP) tests and in situ microscopic observation under tensile loading were conducted using notched specimens to investigate crack propagation behavior. Finally, fracture surfaces after the tests were observed by means of scanning electron microscopy (SEM). It is found that final failure abruptly takes place for the monotonic and fatigue tests without showing visible damage on the surface of the specimens while permanent strain and cumulative AE events increase just before fracture. The short-term after-cure process increases fatigue strength as well as static strength while the long-term after-cure process degrades the static strength and fatigue life. Fatigue strength decreases with increasing temperature for the virgin specimens without a hole. Fatigue life of open-holed specimens slightly decreases with increasing ambient temperature up to 200 °C. The FCP tests and in situ observation under loading revealed that fracture takes place in a brittle manner although stable crack propagation is observed in a few specimens. The SEM fractography indicates that pull-out of fibres was observed in all the specimens and that small resin particles were generated on the fibre surfaces of the specimens after the fatigue tests.