Theoretical And Experimental Study On Low Velocity Impact And Compression After Impact Of Stitched Foam Core Composites

Carbon fiber reinforced composite materials get the characteristics of light weight and high strength.Due to their high specific strength and specific modulus,they are widely used in aerospace,transportation,construction and chemical industries,etc.Adding a foam core can effectively improve the impact resistance of the composite material.The use of stitching technology to add sutures to the foam core structure composite material can further improve the mechanical properties of the layers and avoid excessive layer delamination.This paper studies the low-velocity impact and post-impact compression properties of stitched/unstitched foam sandwich structure composites and perforated carbon fiber reinforced composite laminates.At the same time,Abaqus finite element analysis software is used to establish a corresponding model to assist in analyzing the internal damage of the material.The specific work is as follows:First,impact and post-impact compression test samples of stitched/unstitched foam sandwich structure composite materials were prepared by vacuum assisted resin transfer molding(VARTM)process,and impact with the energy of 5J and ultrasonic c-scan test were performed.Compressive performance test after impact was carried out on the samples without impact and after impact.Then based on the Abaqus finite element analysis software,the impact model corresponding to the experiment was established and the post-impact compression model was built by the method of softening inclusions.The reliability of the model is verified by response curves of impact and compression,and the damage inside and between layers of the composite panel is characterized by outputting variables such as HSNMCCRT,HSNFCCRT and CSDMG.Comparing the experimental results,it is found that the stitched structure has more uniform damage in all directions,while the unstitched structure is significantly more prominent and directional.Compared with the unstitched structure,the addition of sutures increases the peak impact load under5 J impact energy by 11.52% and reduces the depth of the pit by 26.47%.The compressive strength of the un-impacted and 5J-impacted specimens with stitched structure were respectively increased by 42.92% and 65.03%,which significantly improves the remaining compressive strength of the composite.In addition,In order to explore the impact of openings on the impact resistance and residual strength of laminates,specimens with the distances L between the impact center and the center of the hole of 5,10,15,20,25 mm and non-porous were prepared.The drop hammer impact test,post-impact compression test and ultrasonic C test were conducted.The finite element analytical software Abaqus was used to simulate impact and compression after impact of lanminates with a hole,which have several different distances L from the impactor to hole’s centre.Comparing the experimental and simulated results,it was found that the maximum impact force increase with the the increase of L,but the maximum displacement shows to decrease for 20 J impact energy.When L=5mm,the peak impact load is 12.0% lower than that of the non-porous laminate.Compared with the non-porous laminate,when L is 5mm,10 mm,15mm,20 mm and 25 mm,the remaining compressive strength of the laminate is reduced by 32.02%,23.85%,17.18%,11.32% and 2.44% respectively.