Alternating salt‐fog spray aging of stitched woven composites: Mode I interlaminar fracture toughness

Abstract

The experimental investigation was focused on the effect of salt-fog corrosion on the interlaminar facture behavior of stitched woven composites with various stitching patterns. To this aim, four kinds of stitched woven composites were exposed to alternating salt-fog and hot-air environmental conditions according to GJB 150.11A-2009 standard, for 2 and 4 cycles. In particular, an un-stitched woven composite was used as a control. Double cantilever beam (DCB) tests were carried out in order to evaluate the interlaminar fracture toughness of woven composites during the aging process, and a scanning electron microscope (SEM) was employed to reveal the interlaminar damage mechanisms. The results provide evidence that the stitching method can significantly improve the interlaminar fracture toughness of woven composites. The decrease of Mode I interlaminar fracture toughness for stitched woven composites is more serious as the salt-fog spray aging cycles are increased. The stitching density has a significant effect on Mode I interlaminar fracture properties of the stitched woven composite both before and after the salt-fog spray aging treatment. The effect of salt-fog spray aging became more significant with an increase of the stitching density, while the interlaminar fracture toughness of the composites increased significantly.

Effect of salt–fog spray environment on bending fatigue properties of 3D woven composites

“…The water ingress due to the capillary phenomenon significantly accelerated the progress of crack initiation and propagation of composites under bending fatigue load, 11 And the salt-fog spray has promoted the formation of cracks in the resin-rich area and the interfacial debonding of the fiber and resin. 26 Thus, Initial cracks and the reduction of interface performance may have adverse effects on the lifespan of 3D woven composites under the bending fatigue load. In a salt–fog spray environment, the crack initiation occurred earlier, the number of cracks increased, and water molecules caused swelling and deformation of the matrix, which facilitated the expansion of microcracks at the interface under the bending fatigue load.…”

“…The salt–fog spray test was conducted according to the standard GJB 150.11A-2009 and reference 26, and the alternating steps of 24 h salt–fog spray and 24 h drying were adopted, with a test cycle of 48 h. In the salt-fog spray stage, the salt-fog had a chemical composition of 5% NaCl solution with the pH value of between 6.5 and 7.2, and the test temperature was set at 35°C. In the drying stage, the drying temperature was set to 35°C and the relative humidity was set to 40% in the oven.…”

“…[23][24][25] Differences were observed between the seawater immersion and salt-fog spray environments. 26 Salt spray corrosion environment is the environment that 3D woven composites may face when applied to military and marine equipment. 3D woven composites may subject to salt-fog spray corrosion environment and bending fatigue load in marine environment.…”

Mode I and II interlaminar fracture toughness of glass/carbon inter‐ply hybrid FRP composites: Effects of stacking sequence and testing temperature

“…Further, moisture, [61] temperature and loading speed [62][63][64][65][66][67][68] also have an influence. [27,69,70] The glass transition temperature (T g ) of the thermoset polymer matrices ideally used in FRP composites is a limiting factor that restricts their usage in high temperature environments. [71] The main focus of this work is to assess the elevated temperature delamination behavior (mode I and mode II ILFT) of carbon fiber/glass fiber epoxy interply epoxy hybrid composites.…”

“…Further, moisture, [ 61 ] temperature and loading speed [ 62–68 ] also have an influence. [ 27,69,70 ] The glass transition temperature (T g ) of the thermoset polymer matrices ideally used in FRP composites is a limiting factor that restricts their usage in high temperature environments. [ 71 ]…”