Research On Damage And Energy Absorption Of Composite Honeycomb Sandwich Structure Under Low-velocity Oblique Impact

The composite honeycomb sandwich structure is widely used in lightweight transportation,aerospace,construction,military and other fields due to its excellent properties such as light weight,high specific strength,strong fatigue resistance,and good heat and sound insulation.One of the main drawbacks of this structure is that its performance can be reduced a lot when subjected to low-velocity impact,and the damage is difficult to detect with the naked eye,which greatly increases its safety risk in the actual engineering field.The impact in reality is usually not a normal impact,but an oblique impact whose impact direction does not coincide with the direction of the common normal line.The current research is mostly limited to the normal impact due to many limitations such as experiment and theory.The research on low-velocity oblique impact lacks systemicity and pertinence.There are still many deficiencies to be solved.To this end,this dissertation adopts the composite honeycomb sandwich structure with carbon fiber reinforced plastics(CFRP)laminate as the skin and aluminum alloy as the honeycomb core as the research object.Through a combination of finite element simulation and experimental exploration,the damage and energy absorption characteristics of CFRP,honeycomb sandwich structure with aluminum skin and honeycomb sandwich structure with CFRP skin under oblique impact,and the influence of structural parameters on damage and energy absorption of honeycomb sandwich structure with CFRP skin under low velocity oblique impact are analyzed.An orthogonal experimental design is carried out to determine the optimal combination of parameters for the structure to resist low-velocity oblique impact.Firstly,for CFRP laminate,the low-velocity oblique impact test platform is built based on the designed and processed oblique impact clamp.The impact test with impact angle of 0°and 10°under different impact energy is completed.Based on the progressive damage theory,cohesive damage model and three-dimensional Hashin criterion,the simulation model is established in ABAQUS,and the correctness of the model is verified by comparing with the experimental results.Based on the model,the influence of impact angle is analyzed.The results show that:the damage morphology of CFRP laminate under normal impact and oblique impact is different.The normal impact mainly leads to pits on the front of CFRP laminate,while the oblique impact mainly results in scratches on the front of CFRP laminate.The damage on the back of CFRP laminate is mainly matrix cracking.Under the same impact energy,the damage caused by oblique impact is always less than that caused by normal impact.it is found that the peak value of the contact force and residual kinetic energy of the impactor are negatively correlated with impact angle,while the contact time and the frictional energy loss due to the slippage of the impactor are positively correlated with impact angle.There is a big difference between the process of normal impact and the process of oblique impact due to the existence of friction.Secondly,for the honeycomb sandwich structure with aluminum skin,a simulation model based on the failure model of aluminum is established in ABAQUS,and the correctness of the model is verified by comparing with the test results in literature,Based on the model,the influence of impact angle on damage deformation and energy absorption of aluminum honeycomb sandwich structure with aluminum skin is analyzed.The results show that:The maximum damage depth and the deformation of top skin are negatively correlated with the impact angle.Compared with the normal impact,when the impactor slips under the condition of low-velocity oblique impact,it will change the action position on the sandwich structure and force the new honeycomb core element to buckle,which leads to the expansion of the damage area,but the overall damage is lighter,and the deformation of the bottom skin under low-energy impact can be almost ignored.With the increase of impact angle,the total energy absorption and the energy absorption of each part of the structure decrease due to the increase of the frictional energy loss due to the slippage of the impactor.Then,for the honeycomb sandwich structure with CFRP skin,using the CFRP laminate as skin and aluminum alloy as honeycomb core,the honeycomb sandwich structure with CFRP skin was made.The impact tests with impact angles of 0°and10°under different side lengths of honeycomb core unit are completed on the low-velocity oblique impact test platform.The simulation model is created in ABAQUS by using the previously verified modeling parameters and methods of the CFRP laminate as well as aluminum skin aluminum honeycomb core,plus the ductile failure model to simulate the failure of the adhesive layer between the skin and the honeycomb core.The reliability of the model is known by comparing the simulation results with the test results.The results show that:the main damage forms under low-velocity impact are the debonding between top skin and honeycomb core and the buckling deformation of the aluminum honeycomb core unit.The impact angle has an important influence on the damage and energy distribution of the honeycomb sandwich structure with CFRP skin.Under the condition of low-velocity oblique impact,the structural parameters have some effects on the peak contact force,contact time,damage and energy absorption of aluminum honeycomb sandwich structure with CFRP skin,which are different from those under normal impact.Finally,in order to find out the optimal parameter combination with a smaller peak contact force and more energy absorption under the condition of low-velocity oblique impact,the orthogonal experimental design method is used to select the thickness of the top skin,the side length of the honeycomb core unit,the thickness of the honeycomb core aluminum foil and the height of the honeycomb core.Each factor corresponds to three levels,and the simulation calculation is carried out according to the orthogonal table L9(3~4).In order to ensure the minimum comprehensive evaluation index constructed by multiplication and division method,that is,the peak value of contact force is as small as possible and the absorbed energy is as much as possible,the thickness of top skin is 1.2 mm,the side length of honeycomb core unit is 7 mm,the thickness of aluminum foil of honeycomb core is 0.04 mm,and the height of honeycomb core is 5 mm.