Topography Optimization And Layout Design Of Thin-walled Structures With Manufacturing Process Constraints

Thin-walled structures are important forms in lightweight design and property promotion of engineering structures since they have high specific strength,specific stiffness and energy absorption properties.The development of exclusive equipment sets an even higher demand on structure optimization,so it's an urgent requirement to find and design superior thin-walled structures.However,the properties of the thin-walled structures are highly depend on their geometrical topography.Therefore,efficient method of structure design should be developed to obtain superior structures with geometrical topography based on requirements.In addition,the manufacturing process and cost are highly related to the complexity of the structures,and structures produced by different manufacturing process have different geometry characteristics.Therefore,designing method considering manufacturing process should be put forward to obtain manufacturable structures.Superplastic Forming is an important forming process of thin-walled structures.For these structures,the fatigue failure is often occurred in the stress concentration areas with sharp comers.Studying the design of the geometrical topography of the structures to reduce the stress concentration is of great importance.Considering the promotion of energy absorption property,we established a topography optimization method with topography constraints for thin-walled structures,and proposed several structure designs considering structure characteristics of Tailor-Welding and Flexible Rolling/V ariable Gauge Rolling process,and put forward two designing schemes for energy absorption tubes based on the geometry characteristics along axial direction.To reduce the stress concentration of the thin-walled structures,we also proposed a geometrical topography designing method for titanium thin-walled structures through preset holes.The study content and achievements are as follows.(1)The proposal of topography optimization method for energy absorption thin-walled structures with topography characteristics oonstramts.The arrangement of thickness and topography of thin-walled structures can affect the defonnation mode of the structure,thus leading to the promotion of the energy absorption property.However,because of the cost and the constraints of the manufacture process,the variable thickness plate should have specific topography characteristics to reduce the complexity of manufacturing.In order to consider the topography characteristics constraints,we proposed a structure optimization method with constraints based on HCA method.In this method the structure characteristic constraints is considered,so the structures during the iteration meet the structure characteristics.In order to verify the effectiveness of this method,we take the plate structure as example to apply this method.The structure characteristics of the optimal structures is discussed,and we found out that they all meet the proposed structure characteristics.Then we evaluated the performance increment of the design schemes,and the results show the effectiveness of this design method.(2)The variable thickness design of crashworthiness structures considering manufacture characteristics.The variable thickness design can promote the properties of thin-walled structures,while advanced manufacturing techniques provide assurances of manufacturability.Therefore obtaining variable thickness design considering manufacturability based on specific manufacturing process is very important.In this thesis we optimized the plate structure based on the proposed topography optimization method considering topography characteristic constraints of tailor welded blanks and tailor rolled blanks.The effectiveness of the optimal scheme is proved by the performance comparison between the original designs and the optimal designs.The optimal designs show that they meet the requirement of manufacturing characteristics.Therefore,the topography optimization method proposed is suitable to design the crashworthiness thin-walled structures considering manufacturing features of plates.(3)The energy absorption design of thin-walled tubes based on the geometry characteristics along axial direction.Improving the energy absorption of thin-walled tubes is a main goal of crashworthiness thin-walled structure designing.Therefore,a better structure by structure design should have more plastic hinges and global progressive deformation mode.Based on this idea,we proposed two corresponding design schemes of thin-walled tubes.The first one is thin-walled tubes with bulkheads enhanced.As Euler buckling is a common phenomenon in thin-walled tubes under axial compression,we proposed the design of tubes with bulkheads inside,which could restrain the deformation mode.Square tubes and non-convex tubes are taken into consideration to study the energy absorption performance of different tubes.After the comparison among different tubes with variable thickness and bulkheads,we discovered that this design is an effective way to improve the energy absorption performance.In the end,we get the structure with the best performance through parameter optimization.The second design scheme to improve the performance is the shape optimization of the axial trace of curved tubes.As for the curved tubes,the deformation mode is significantly affected by the axial trace,and it can be observed that the plastic deformation is mainly concentrated at local folds.We believed that expanding the plastic deformation zone can help improving the energy absorption,and shape optimization of axial trace can change the deformation mode.The numerical analysis shows that shape optimization can improve the energy absorption significantly.Shape optimization with different load directions is also studied.The results show that tubes with optimal shape of the axial trace has relatively high performance with different direction loads.(4)Stress concentration reduction of titanium thin-walled structure with preset holes concerning SPF_DB manufacturing process.Superplastic Forming-Diffusion Bonding(SPF-DB)is an important manufacture technique of thin-walled structures,and the fatigue failure of the structures by SPF commonly occurs in the stress concentration zones with sharp comers.In order to improve the fatigue life of the thin-walled structure,the stress concentration should be reduced.We discovered that preset holes in the structure can affect the forming process and the formed shape of the structure.Therefore,we take the curvature of the surface of the structure as the optimization target and the parameters of the holes as the optimization variables in order to build a structure optimization model dealing with the stress concentration reduction problem.At last,we optimize the geometry parameters of the preset unbonded areas,thus the optimal stress concentration reduction design is obtained.