Experimental Study On The Impact Damage And Fracture Mechanisms Of Carbon Fiber Reinforced Polymer Composites Under Hygrothermal Environment

Carbon fiber reinforced polymer(CFRP)has been widely used in navigation,marine and underwater fields because of its excellent comprehensive properties,such as high specific strength and high specific stiffness.Hygrothermal environment and external loads are the environmental factors which are often encountered in the underwater and navigation fields.The present research on hygrothermal properties of CFRP has been gradually matured,while there are few studies on the impact damage and of CFRP under hygrothermal environment.Therefore,it is a great significance to study the effects of hygrothermal environment on the impact damage and failure of carbon fiber composites laminates.The carbon/epoxy composite laminates were immersed in water at 50??60??70? for 10 days? 20 days? 30 days,respectively.The impact processes of three different speeds on CFRP laminates were investigated,and the results were analyzed by orthogonal experiment.The impact damages of composite specimens under different environments were tested by using ultrasonic C-scan,digital microscope system,scanning electron microscope(SEM)and visual inspection,in order to investigate the effect of hygrothermal environment on the microstructure and the mechanism of impact damage of CFRP laminates.Three kinds of different shapes of projectile with three different velocities were used to investigate the damage and failure of CFRP laminates,which specimens were moisture saturated samples at 70? and the drying state samples at room temperature.The results show that,the moisture absorption process of the composite material can be divided into two stages: there is a linear relationship between the moisture absorption and the square root of moisture absorption time at the first stage;at the second stage,the moisture absorption rate becomes slow,and the water absorption process of some hydrophilic groups occurs.In the orthogonal test of three levels of impact velocity,temperature,moisture absorption time of the three factors,when the ambient temperature is 70?,moisture absorption for 20 days with impact velocity of 90m/s,the energy absorption value and the area of damage hole of CFRP laminates reach maximum.The damage areas of laminates under both states increase,with the increase of the impact velocity of projectile with same shape.At low velocity state,the most serious damage of laminates is caused by the conical projectile,while the most serious damage of laminates is caused by the blunt projectile when laminates are penetrated.According to the energy absorption of laminates,heat-moisture treatment increases the plasticity of matrix,enhances the energy absorbing ability of the composite and the impact resistance.