Research On Low-velocity Impact And Post-impact Compression Properties Of Stitched Carbon Fiber Foam Sandwich Composites

The reinforcement of the carbon fiber foam sandwich composite material is carbon fiber,the matrix is resin,and the intermediate layer is foam.The three as a whole exert excellent performance such as light weight and high strength.However,in real life,carbon fiber foam sandwich composite materials are often impacted by various foreign objects,such as sand and gravel,hail and so on.These visible or invisible impact damage will cause the mechanical properties of the carbon fiber foam sandwich composite to be greatly reduced,and stitching can enhance the impact resistance of the composite.Therefore,it is necessary to stitch the carbon fiber foam sandwich composite material.This paper carried out the following research work:First,the improved lock stitching method was used to stitch the carbon fiber foam sandwich composite material,and the VARTM molding process was used to prepare[±45⁰/0⁰/90⁰],[±45⁰]₂,[0⁰/90⁰]₂Three lay-up methods of stitched/unstitched carbon fiber foam sandwich panels.To explore the effect of stitching on the mechanical properties of carbon fiber foam sandwich composites,low-speed impact experiments under various impact energies were carried out on the stitched/unstitched carbon fiber foam sandwich panels of[±45⁰/0⁰/90⁰]layup.Ultrasonic C-scan was used to detect the internal damage size of the carbon fiber foam sandwich.The depth of the pits on the impact surface was measured with a depth measuring instrument,and the pit depth-impact energy curve was fitted to characterize the damage resistance performance of stitched/unstitched carbon fiber foam sandwich panels with origin software.Finally,post-impact compression experiments were carried out on the stitched/unstitched carbon fiber foam sandwich panels,and the residual compressive strength CAI-pit depth curve,which characterizes the damage tolerance performance of the stitched/unstitched carbon fiber foam sandwich panels,was fitted with origin software.The results show that stitching can enhance the impact resistance and compression performance of carbon fiber foam sandwich composites.There is an inflection point on the curve that characterizes the damage impedance performance:the unstitched inflection point is at the impact energy of 7.6J and the pit depth is 1.582mm;the stitched inflection point is at 8.8J and the pit depth is 1.396mm.There is also an inflection point on the curve that characterizes the damage tolerance performance:the unstitched inflection point is at the pit depth of 1.5mm,and the stitched inflection point is at the pit depth of 1.38mm.The inflection point on the characteristic curve of damage impedance performance and the inflection point on the characteristic curve of damage tolerance performance are consistent.To explore the influence of fiber layup methods on the mechanical behavior of carbon fiber foam sandwich composites,the three layup methods of[±45⁰/0⁰/90⁰],[±45⁰]₂,[0⁰/90⁰]₂are stitched/unstitched carbon fiber foam sandwich composite material was suffered from low-speed impact experiment,and the internal damage of the carbon fiber foam sandwich was detected by ultrasonic C-scan.Finally,the three lay-up methods of the stitched/unstitched carbon fiber foam sandwich composite materials were compressed after impact experiment.The results show that the experimental conclusions of stitched/unstitched carbon fiber foam sandwich composites are consistent.[±45⁰]₂The impact resistance and compression performance of carbon fiber foam sandwich composites with layup method are the best,[±45⁰/0⁰/90⁰]layup method is in the middle,and[0⁰/90⁰]₂layup method is the best difference.The（±45⁰）layup angle can enhance the impact resistance and compression performance of the carbon fiber foam sandwich panel compared to the（0⁰/90⁰）layup angle.