Research On Mechanical Response And Residual Flexure Characteristics Of Braided Composite Tube Under Transverse Load

Textile composite materials have been widely used in aerospace,marine,construction,and automotive industries owing to their high specific strength,corrosion resistance and energy absorption compared to conventional materials.Circular braiding is a textile forming technology.Fiber bundles are interlaced and deposited on a specific mandrel to form braided preform with interlacing structure in braiding process.The braided composite is reinforced by stack-up plies,which increases damage tolerance and impact resistance.Additionally,manufacturing process of the braided reinforcement has high briaiding efficiency and forming velocity,which can be produced in large quantities to meet the demand of manufacturing industry.Recently,tubular braided composite was adopted in commercial airplane fuselage frame or auto-body.In the service life cycle of composite parts,transverse loads are caused from accidental tool dropping,resulting in complex damage modes such as resin cracking,indentation and delamination.These damages are invisible,which usually cause significant reduction of residual performance.It is very important to investigate the mechanical response of composite tube under transverse load for product safety design.In this study,the mechanical response and residual flexure characteristics of the braided composite tube with ply configuration under transverse low-velocity impact and quasi-static bending loads were explored.The damage development process of the composite tube with gradient structure under the transverse three-point bending load was studied by the method of experiment and simulation.Firstly,four kinds of composite tubes with different ply configurations(uniform structure:[~I40/~O40],[~I60/~O60];gradient structure:[~I40/~O60]and[~I60/~O40])were fabricated.The four kinds of tubes were subjected to transverse low-velocity impact tests on the drop hammer test-bench.Combined with infrared thermal imaging technology,the transverse three-point bending tests were carried out on the universal test machine.A macroscopic finite element model of composite tube with gradient structure was established to simulate the three-point bending process.In order to explore the residual flexure characteristics of composite tube,four-point bending tests were carried out for intact and impacted gradient structure tube with acoustic emission technology.Finally,the mechanical response of the tube and the development of damage were analyzed and discussed.Firstly,the research background and practical application significance of composite tube are mainly introduced in this paper.Via reading a lot of literature and combining with the research results at inland and abroad,the research status of the transverse load response and residual mechanical properties of composite tube were analyzed.Combined with own research,the direction and content of this paper were determined.On this basis,the preparation process of the braided composite tube and design of the transverse load tests are mainly introduced.Firstly,several preparation methods of composite tubes were introduced,and then the molding methods selected in this study was introduced in detail.The principle of circular braiding machine was illustrated.Braided composite tubes were got via vacuum assisted resin transfer molding method.Finally,four kinds of tubes with different ply configurations were obtained.As for the transverse low-velocity impact,the test device and data acquisition were introduced.The whole impact process was recorded by high-speed camera.In addition,the infrared camera was used to carry out the transverse three-point bending test of tubes with gradient structure.In the test of the residual bending performance of braided composite tube,the transverse four-point bending tests were mainly carried out with acoustic emission technology.Three point bending finite element simulation of composite tubes with gradient structure([~I40/~O60]and[~I60/~O40])is also carried out in this paper.Macrocosm modeling method was adopted and shell elements were used for layup design.Intra-layer damage behavior follows the Hashin criterion embedded in ABAQUS.A bilinear cohesive zone model(CZM)was used to simulate inter-layer damage behavior.In terms of discussion of results,the curvilinear response and damage morphology of the four tubes were analyzed analy in the low-velocity impact test results.It is found that the braided composite tubes with the same outer braiding angle has similar impact mechanical response and damage characteristics.Therefore,[~I40/~O60]and[~I60/~O40]tubes were selected to explore the influence of gradient structure on the transverse load of composite tube.In the tests of quasi-static three-point bending,the bending mechanical response,failure morphology and infrared thermal imaging characteristics of the tubes with gradient structure were analyzed.The results of simulation and test were compared and verified,and the deformation and damage development process of tubes in the bending process was observed,and the reason of damage of tubes with gradient structure was explored.Finally,the residual flexural properties of braided composite tubes with gradient structure are evaluated.The mechanical response and internal damage morphology of four point bending of braided composite tubes with gradient structure were analyzed.Via observing the bending damage characteristics of intact and impacted tubes and calculating the bending stiffness,peak force,crushing force efficiency and specific energy absorption,it is found that the impact damage will reduce the residual mechanical properties of tubes.