Preparation Of Epoxy-based CFRP And Research On Low-Velocity Impact Properties

Carbon Fibre Reinforced Plastics(CFRP)are widely used in aerospace,marine transportation,weapons and equipment,construction,wind power and other fields.Due to its own structural characteristics,CFRP laminates are at risk of being damaged by impact during preparation,service,and subsequent testing and maintenance.The surface of the impacted material is generally less damaged,but the internal damage is serious,especially at low speeds,damage generated under low-energy impact conditions,invisible internal damage will continue to expand into larger damage under stress,especially in alternating stress,vibration fatigue and other working conditions,the crack will expand rapidly,resulting in its service life,accelerated decay and eventual failure pose a threat to the safety of CFRP components.Therefore,it is of great significance to study the mechanical response and damage mechanism of CFRP laminates during low-speed impact,energy absorption and conversion,residual properties,and hybrid fiber composite materials,and provide references for theoretical research and practical applications.The main research contents of this paper are as follows:(1)The mechanics and damage theory of fiber composite materials are studied,and a low-velocity impact damage model of CFRP laminates including an intralaminar damage model and an interlaminar damage model is established;it introduces the in-plane damage initiation criterion(three-dimensional Hashin failure criterion)and progressive stiffness degradation model,and the interlayer damage initiation criterion(Quads Damage)and damage evolution model(BK criterion),and write the VUMAT of the model based on FORTRON language to determine the ABAQUS dynamic impact damage analysis process.(2)Adopt hot-pressing molding process,design and build hot-pressing test bench,and prepare epoxy resin-based CFRP laminate specimens for testing;conduct basic mechanical property experiments on laminates to obtain constitutive model parameters;use finite element simulation and test combined method,establish a finite element simulation model of CFRP laminate,including:solid element to simulate CFRP laminate and punch model,and cohesive element to simulate interlayer contact,continuous iterative calculation based on the damage analysis process,and based on the simulation results to analyze the different failure modes within and between layers during low-velocity impact,lays the groundwork for subsequent impact testing studies.(3)The low-velocity impact test of CFRP laminates was carried out,based on the low-velocity impact test results of CFRP laminates under different impact energies,the damage mode,damage mechanism,energy response and impact damage morphology of CFRP laminates were analyzed,the delamination threshold was 6000N,and the impact threshold was 20J,the penetration threshold is 25J,when the impact energy is from 10J to 25J,the delamination area increases from 294.3mm~2 to 842.4mm~2;based on the distribution of strain energy density in the impact pit area of CFRP laminates,the energy carried by the characteristic element of the impact pit is used to analyze the energy absorption and transformation of the damage area,the maximum strain energy density in the deepest pit is 0.06J/mm~3;finally,the simulation results are compared with the experimental results,and the errors are all within the acceptable range of 10%,which verifies the accuracy of the impact damage model.(4)The post-impact compression test was carried out to analyze the relationship between the residual compressive strength(CAI)of the CFRP laminate and the impact energy,and the reason for the decrease of the residual strength was analyzed based on the compressive damage morphology,the CAI strength decreased from 330MPa to 208MPa,and the amplitude is 37%,and the strength retention rate is only 63.0%;the impact resistance of CFRP laminates is evaluated from the perspective of damage resistance performance and damage tolerance performance,and the inflection point is 0.95mm;the impact rebound behavior of CFRP laminates is studied,and the final impact is analyzed,the cause of the pits,the viscoelastic properties of polymer matrix composites under low-speed impact were studied,including the impact of impact energy on the viscoelastic behavior of laminates and the energy absorption and transformation during the impact process,the inflection point was 12h;the fiber hybrid method was used to Hybrid design of CFRP laminates,design hybrid fiber laminates with different combinations of aramid fiber composites and CFRP,quantify and analyze the optimal hybrid structure and hybrid ratio of hybrid laminates,the optimal hybrid structure is aramid-carbon-aramid,the optimal hybrid ratio is 1/3,the peak load is reduced by 1.6%,the maximum displacement of the punch is increased by 8.7%,the peak load time is prolonged by 116.7%,the failure area of the hybrid laminate is reduced by 43.6%,and the crack size is reduced by 7-9 times.