Mechanics Analysis On Composite Sandwich Structure Under Repaired

Because composite material has the great mechanics properties of high specific strength,high specific stiffness,and endurance to complicated environment,composite sandwich structure,with much smaller mass but decent load bearing,is now comprehensively used in some key structures of aircraft.While during the process of manufacture,assembly and service,composite sandwich structure may easily meet with pinch,impact and other damage.Repairing these sandwich structures may keep them at service,and can either save the cost.Now academic circles still do not have taken enough research on the shape of damage and prediction of the strength in the repairing composite sandwich structures.So it does be a key problem to resist the development of the repairing technique.In this paper,the research on the honeycomb sandwich structure and foam sandwich structure and their under-repaired structure,through the way combined experiment of mechanics property and simulation of calculating,is taken into the study of the mechanics properties and predict the strength of the repaired sandwich structure.For studying the damage of repaired composite sandwich structure,a finite element model(FEA)is established for progressive damage analysis based on the damage of composite panel,core and cohesive element.First,the simulation is taken to calculate the damage of matrix and fibre based on the two-dimension or three-dimension modified Hashin criterion.Then,based on the Sandwich core theory,the honeycomb core's equivalent material properties can be get.Based on the Third Strength theory,the damage of the core can be studied.At last,to study the damage of cohesive element,based on adhesive CZM model,B-K criterion,the method to judge whether the cohesive element is failure and the degeneration of stiffness.To study the mechanics properties of the complete and repaired sandwich structure,a huge mass of mechanics experiments is taken.From the experiments,the strength,strain and stiffness of these specimens can be obtained and analyzed.By observing these failure structures,it can be found that the core does not get any damage in the tensile and shear test,but it can be found in the specimens from the compressive test.All the statics can be conducted to summarize the repaired specimens' tensile strength and stiffness reduce a bit to those complete ones,with the compressive and shear properties nearly be the same.The location of the patch have lower stiffness than any other location in the repaired specimens.By observing every kind of specimens,repaired sandwich specimens' damage usually happens on the location of the patch.At last,for predicting the strength and verifying the effectiveness of repairing structure,a three-dimension FEM is established to calculated the damage and strength of the repairing sandwich structure.From the simulation of tensile load and shear load,as the core doesn't have any damage,the strength gets a recovery.While calculating the compressive strength,the core's damage should take into consideration.Finite element analysis calculates a good result of strength,the distribution of strain and the expansion of damage,and the results conform with the results of the experiments.