The effect of long‐time moisture exposure and low temperatures on mechanical behavior of open‐hole Cfrp laminate

Carbon fiber composite laminates (CFRP) used in aerospace are operating under various environmental conditions. Parts are often exposed to moisture which slowly diffuses into the laminate and forms internal stresses. During the flight, the aircraft is also exposed to low or elevated temperatures. The result is negative impact on composite performance due to formation of hygrothermal stresses. Understanding this phenomenon helps with prediction of the damage development which is vital for increasing the components service life. The open‐hole CFRP laminates were conditioned in humid air at 70°C/85% RH for 33,800 h and the effect of low temperatures on quasi‐cyclic tension properties and fracture behavior was investigated. The mechanical tests on two types of CFRP laminate with different number and orientation of plies were performed under − 55°C. The material behavior during the testing was monitored by acoustic emission technique. The light optical microscopy and scanning electron microscopy were used for the identification of failure mechanisms. The study showed that the hygrothermal effect has significant impact on materials toughness reduction. The damage mechanisms and characteristic morphologic features are changing due to the matrix degradation and weakened fiber/matrix interface.