Hygrothermal Aging Study Of Carbon Fibre Reinforced Polyamide 6 Composites

Carbon fibre reinforced polyamide 6 composites are expected to be recyclable and high strength-to-weight.However,the characteristics of strong water absorption limits polyamide6's pervasive application.Therefore,in this paper,we focus on this disadvantage of polyamide6 and study the hygrothermal aging properties of short carbon fibre reinforced polyamide 6 and continuous carbon fibre reinforced polyamide 6 composites.The main contents of the paper are as follows:1.The short carbon fibre reinforced polyamide 6 composites were manufactured by using twin-screw extruder and continuous carbon fibre reinforced polyamide 6 laminates were manufactured by hot-pressing method.Then we optimized the preparation technology,got the high performance composites and finally set up rigorous hygrothermal aging tests program.2.Hygrothermal aging behavior of short carbon fibre reinforced polyamide 6 composites was studied.The study found that the moisture diffusion of CF/PA6 composites accorded with the Fick diffusion law.It is found that the CF/PA6 composites absorb less water than the PA resin,and shorter saturation time is observed under water immersion.The finite element(FE)approach is adopted to compare with the experimental results to simulate the moisture diffusion and predict the saturation time of aged specimens.The outcome shows good agreements between experimental,Fickian model and FEA results.The tensile and impact strengths of CF/PA6 and PA6 materials were compared and the fracture morphology was observed by electron microscopy.It was found that the matrix broken made by weakening of fibre-matrix interface was the main reason for the decline in mechanical properties.A predictive mathematical model based on Arrhenius methodology has been adopted to estimate the retention tensile strength by introducing environmental factors accounting the effects of different exposure temperatures.3.Hygrothermal aging behavior of continuous carbon fibre reinforced polyamide 6composites was studied.By gravimetric experiments,the moisture diffusion in CF/PA6laminates with three different sizes were characterized by gravimetric experiments in three environment ageing conditions for 50 days.Then the collected experimental data were assessed by using 1D,3D Fick's and equivalent diffusion coefficient moisture diffusion theories,and thereby the diffusion coefficients were fitted and determined.Subsequently,finite element models were further adopted,which validated the analytically obtained diffusion coefficients.The FE analysis,indicated that,the 3D moisture diffusion theory was essential agreement with the experimental and the equivalent diffusion coefficient method was unreliable for CF/PA6laminates.The mechanical properties of CF/PA6_w were been studied.It was found in 20,40and 60?conditions,the flexural strength is 68.03%,63.16%and 66.52%respectively.Furthermore,micromechanism of CF/PA6 specimens before and after immersion in water was observed by optical microscope.It was found that the evident matrix microcracks and severe moisture diffusion in the inner core of tested specimens was the main reason for the decline in mechanical properties.It is provided effective experimental data support and theoretical analysis for carbon fiber reinforced polyamide 6 composites in-depth research and application by this study.