Toughening Mechanism And Damage Repair Of Cross-laminated Multi-stage Structure Of 3D Printing Imitating Strombus Gigas Shell

Lightweight and high-strength composites are of great significance for energy saving,emission reduction and cost reduction,and are the current research hotspots in aerospace,military and national defense and other cutting-edge fields.In recent years,inspired by the natural biological structure,scientists have designed and obtained a series of lightweight biomimetic structural materials by imitating the fine hierarchical structure in the biological structure,which provides a new way for the design and manufacture of high-performance composites.For example,researchers have obtained biomimetic structural materials with both high strength and high toughness by imitating the “brick-mud” staggered hierarchical structure of the shell pearl layer.In a recent study,scientists found a creature known as the queen Strombus gigas shell in the ocean,which has to resist the huge tidal forces in the ocean and the influence of predators.It makes the shellfish extraordinarily resilient while maintaining medium strength,about ten times higher than ordinary shells.This excellent mechanical property depends on its internal fine micro-hierarchical structure,which will provide a useful reference for the design and preparation of composites in some high-tech fields.In this paper,the failure mode of bionic Strombus gigas shell cross-laminated structure with different interlayer angle under tensile load were studied by mechanical experiment,finite element analysis and mechanical theory.The bionic structure with both strength and toughness were obtained.In the study,firstly,discontinuous fiber reinforced nylon onyx wire was used to obtain the representative bionic Strombus gigas shell structure unit with adjustable internal structure parameters by using programmable 3D printing technology.The quasi-static tensile test of the biomimetic cross-laminated structure with different interlayer angles was carried out on the Instron3343 tensile testing machine.The results show that with the increase of the interlayer angle,the strength of the material decreases gradually,and the energy absorption decreases at first and then increases,and then decreases continuously.Through the microscopic characterization of the failure section,it is found that there is a significant difference in the failure section of the samples with different interlayer angles.Further mechanical mechanism analysis shows that the interlayer angle is the key factor affecting the in-layer failure mode and mechanical properties of the bionic Strombus gigas shell cross-laminated structure,but has almost no effect on the interlayer behavior.Therefore,in this paper,through the optimization design of the interlayer angle,the biomimetic cross-laminated structure can greatly improve the toughness and give full play to the mechanical properties of the material on the basis of maintaining the strength,so that it can be applied to more complex working conditions.Based on the study of the toughening mechanism of 3D printing imitation Strombus gigas shell cross-laminated multistage structure,the internal damage repair function of 3D printed short carbon fiber reinforced bionic cross-laminated structure was studied.The damage repair of composites reinforced by long carbon fibers was also explored.According to the experimental standard,the corresponding standard specimens in accordance with the three-point bending test were made,and the tested short / long carbon fiber reinforced composite specimens were repaired by heat treatment and microwave treatment,respectively.the bending properties of the repaired specimens were tested again.It is found that the thermal repair method is more effective than microwave repair in repairing short carbon fiber reinforced bionic cross-laminated structures,and the thermal repair of specimens after repeated damage has the same effect,but the plasticity of the material decreases and the brittleness increases with the increase of repair times.Relatively speaking,microwave repair has the advantages of short time,high efficiency and selective repair of cracks.The effects of microwave repair and thermal repair on laminated structures with different long carbon fiber contents are similar,compared with the thermal field distribution of short carbon fiber reinforced cross-laminated structures repaired by microwave,due to the focusing effect of microwave,the thermal field distribution of long carbon fiber reinforced materials is more concentrated,and mainly distributed in the damaged parts,which further shows that microwave repair is targeted.Based on the study of the toughening mechanism of 3D printing imitation Strombus gigas shell cross-laminated multistage structure,the internal damage repair of 3D printed short carbon fiber reinforced bionic cross-laminated structure was studied.Furthermore,the damage repair of composites reinforced by long carbon fibers was also studied.According to the experimental standard,the corresponding specimens in accordance with the three-point bending test standard were made,and the tested short / long carbon fiber reinforced composite specimens were repaired by thermal repair and microwave repair,respectively.The repaired specimens were tested again by three-point bending test.The experimental results show that the thermal repair method is more effective than microwave repair in repairing short carbon fiber reinforced bionic cross-laminated structures,and the thermal repair of specimens after repeated damage has the same effect.However,with the increase of repair times,the plasticity of the material decreases and the brittleness increases,and the thermal field distribution in the repair process shows that microwave repair is more targeted.The effects of microwave repair and thermal repair on laminated structures with different long carbon fiber contents are similar,compared with the thermal field distribution of short carbon fiber reinforced cross-laminated structures repaired by microwave,the thermal field distribution of long carbon fiber reinforced materials is more concentrated,and the heat is mainly distributed in the parts of damage,which further shows that microwave repair is targeted.To sum up,the cross-laminated multi-stage structure samples of Strombus gigas shell with different interlayer angles were prepared by 3D printing method,and the toughening mechanism and optimization strategy were revealed by mechanical test,finite element numerical simulation and theoretical analysis.The damage repair behavior of carbon fiber reinforced biomimetic cross-laminated structure materials was studied.These results will provide useful guidance for the design and structure-function integration of lightweight and high-strength materials.