Effect of hygrothermal aging on moisture diffusion and tensile behavior of CFRP composite laminates

Carbon Fiber Reinforced Polymer(CFRP)composites are widely used in aircraft structures,because of their superior mechanical and lightweight properties.CFRP composites are often exposed to hygrothermal environments in service.Temperature and moisture can affect the material properties of composites.In order to make clear the moisture diffusion behavior and the properties degradation of composites,the TG800/E207 composite laminates with four stacking sequences[0]16,[90]16,[±45]4s,and[(+45/0/0/-45)s]sare designed and manufactured.Moisture absorption tests are carried out at 80℃,90%RH.It is shown that the moisture absorption curves of composite laminates present a three-stage.A modified Fickian model was proposed to capture the diffusion behavior of TG800/E207 composite laminates.The relationships among the non-Fickian parameters,the environmental parameters and the stacking sequences of CFRP were correlated and compared.Results showed that the modified Fickian curve is sensitive to the diffusivity of Stage Ⅰ and Stage Ⅱ.Compared with unaged specimens,the maximum tensile stress for[0]16,[90]16,[±45]4s,and[(+45/0/0/-45)s]sdecreased by 14.94%,28.15%,11.96%,and 26.36%,respectively.The strains at failure for[0]16,[90]16,[±45]4s,and[(+45/0/0/-45)s]sdecreased by 55.38%,62.65%,46.41%,and31.71%,respectively.The elastic modulus for[0]16,[90]16,[±45]4s,and[(+45/0/0/-45)s]sincreased by 90.93%,94.57%,49.22%,and 8.22%,respectively.[90]16sample has the minimum saturated moisture content and the maximum strength degeneration.

Hygrothermal effect on high-velocity impact resistance of woven composites

The woven glass fiber reinforced composites(GFRP)subjected to high-speed impact is investigated to identify the hygrothermal aging effect on the impact resistance.Both the hygrothermal aged and unaged glass/epoxy laminates are subjected to different impact velocities,which is confirmed as a sensitive factor for the failure modes and mechanisms.The results show the hygrothermal aging effect decreases the ballistic limit by 14.9%,but the influence on ballistic performance is limited within the impact velocity closed to the ballistic limit.The failure modes and energy dissipation mechanisms are confirmed to be slightly influenced by the hygrothermal aging effect.The hygrothermal aging effect induced localization of structural deformation and degradation of mechanical properties are the main reasons for the composite undergoing the same failure modes at smaller impact velocities.Based on the energy absorption mechanisms,analytical expressions predict the ballistic limit and energy absorption to reasonable accuracy,the underestimated total energy absorption results in a relatively poor agreement between the measured and predicted energy absorption efficiency.

Micromechanical Study on Moisture Induced Tensile Strength Reduction of GFRP

The main focus of this paper is to investigate the influence of hygrothermal aging on tensile strength of epoxy resin matrix composites.Firstly,tests of water absorption and moisture induced tensile strength degradation of glass fiber reinforced polymer(GFRP)are conducted.Results show that the moisture absorption behavior of the GFRP follows the Fick’s law,and its tensile strength retention decreases notably in the early hygrothermal aging stage and then gradually approaches a constant.Then,microscale longitudinal and transverse strength prediction models for unidirectional fiber reinforced composites are proposed.They are moisture concentration dependent and reflect the inherent probability of failures of fiber and matrix(or fiber/matrix interface).The moisture diffusing analysis demostrates that the proposed models can predict degradation of tensile strength of epoxy resin matrix composites undergoing different hygrothermal durations.The proposed models are validated by the experiments of hygrothermal residual strength of the GFRP mentioned above.