Analysis On Compression Deformation Modes And Structural Performance Of Foam-cored Spherical Sandwich Shells Under Cryogenic Loading

Foam-cored sandwich structure is usually made of metal face sheet and foam core layer,with high strength,specific stiffness and high modulus.It can provide insulation and noise reduction function according to the demands.In addition,the spherical shell structure has large internal space and good load carrying performance.It is widely used in rockets,missiles,aircraft fairing,fuel tanks,pressure vessels and deep-sea exploration equipment,both with load performance and special functional requirements of the parts.The load carrying capacity,deformation characteristics and energy absorption characteristics of the structure are the limiting factors of the high reliability of the actual components in the complex environment.The thermal properties and mechanical properties of heterogeneous multilayers in foam-cored spherical sandwich shells are very different.Structural load carrying capacities are very sensitive to size,manufacturing defects and load conditions.Especially in the low temperature environment of deep sea and aerospace,thermal deformation between layers is not coordinated which leads to load carrying capacity decreased significantly.In addition,such components are usually with large size,need more processing steps,also the cost of manufacturing and testing is high.So it is very urgent to accurately predict the load carrying capacity and deformation modes under low temperature in the design and trial stage.In this paper,the effect of compression load carrying performance of the foam-cored spherical sandwich shell is analyzed from three aspects: design,manufacture and service conditions.For the design,according to the geometrical sensitivity of the instability of the sandwich structure,the discriminant criterion of compression deformation mode is proposed,which provides the theoretical basis for the design of the foam-cored spherical sandwich shell.For the low temperature environment,the influence of low temperature load on the compression deformation mode and load carrying capacity is obtained by numerical simulation.For the manufacturing,the numerical method is put forward to simulate the compression and deformation behavior of foam-cored spherical sandwich shell under low temperature considering the defects of manufacturing,and the manufacturing control target is put forward to meet the working requirements.The main contents of this paper are as follows:(1)Criterion of compression deformation mode of foam-cored spherical sandwich shellThrough the compression test and simulation of single-layer spherical shell and foam-cored spherical sandwich shell,the deformation behavior of the structure is observed to analyze the load carrying capacity and the characteristics of compression deformation modes.Based on the analysis of the compressive deformation of single-layer spherical shells,the theoretical model of the whole process of foam compacting,sequential loading and collaborative effect during the compression deformation of foam-cored spherical sandwich shell is established.Based on the comparative analysis of the load carrying capacity of the inner and out face sheets,the physical mechanism of the two kinds of compression deformation modes of the foam-cored spherical sandwich shells is revealed.The theoretical analysis model and discriminant criterion of the compression deformation modes are established.Based on this criterion,the critical thickness ratios of the inner and out face sheets for the two kinds of compression deformation modes are obtained.The critical thickness ratio calculation model of the compression deformation modes related to the material mechanical properties and geometrical parameters of the structures is established.The rapid judgment of the compression deformation modes of the foam-cored spherical sandwich shell provides a theoretical basis for structural optimization design and lightweight.(2)Study on the influence of low temperature environment on compression deformation behavior of foam-cored spherical sandwich shellThe low temperature mechanical properties of face sheet and core materials are obtained by the test in low temperature environment.The thermo-mechanical coupling numerical simulation model of compression deformation process of foam-cored spherical sandwich shell at low temperature is established and compared with the experimental results.By studying the compression performance of foam-cored spherical sandwich shell structure under normal temperature and low temperature the effect of different low temperature environment on the deformation behavior of foam-cored spherical sandwich shell is studied.The influence of thermal deformation on the critical thickness ratio of the face sheets is analyzed by the criterion of compression deformation mode of foam-cored spherical sandwich shells.By comparing the compressive load and deformation of the structure under different deformation modes,the influence of the temperature on the load carrying capacity and deformation mode of the ideal structure is revealed.(3)Numerical method for foam-cored sandwich structure compression process with initial debonding defectsFor the initial debonding defects in the actual structure from the manufacturing process,the single and random initial defect generation method is proposed.By extracting and re-editing the face sheet/core contact node set,the single initial debonding defects in different sizes and distributions are set,or according to the different initial whole debonding area ratio,the bonding surface containing the initial debonding defects are randomly formed.The sensitivity of the load carrying capacity to the single initial debonding defect and the whole debonding area ratio are analyzed by numerical simulation.A more reliable and efficient numerical simulation method is established for the analysis of actual parts containing initial debonding defects.(4)Analysis of load carrying capacity and initial defect sensitivity of actual part at low temperatureBased on the thermo-mechanical coupling simulation technology and the debonding area generation method,the load carrying capacity of the foam-cored sandwich bulkhead under normal temperature and ultra-low temperature is analyzed.The initial debonding defects and the face sheet/core assembly gap are further introduced to observe the critical debonding expansion time,the expansion load and the expansion process of the initial debonding defects during the loading process.The region distribution and the critical size of the single debonding area,the critical value of the whole debonding area ratio are obtained,to guide the quality control of the adhesive process.At the same time,the area is obtained where the face sheet/core assembly gap has the greatest influence on the load carrying capacity of the structure.It is fed back to the processing quality control of the single part of the face sheet and core,so as to achieve the guidance of the foam-cored sandwich bulkhead manufacturing process.In view of the above,this paper aims at the problem of the compression load carrying performance of the foam-cored spherical sandwich shell under the low temperature environment.The influence of low temperature environment on the load carrying capacity and deformation mode of this kind of structure is analyzed.The main reason to affect the deformation mode of the structure is revealed.The numerical method considering the low temperature and the initial debonding defect is established and applied to the performance evaluation and design of the actual component to realize the prediction of the load limit,failure time and dangerous area of such structures,also guide the processing quality control.