Optimization On Geometric Model And Research On Mechanic Characteristics Of Stranded Wire Helical Spring

Stranded wire helical spring(SWHS)is a kind of cylindrical spring wound by a wire rope strand.Compared with the single wire cylindrical helical springs,the stranded wire helical springs feature higher reliability,longer fatigue life and better vibration reduction ability because of the unique structure.Therefore,the stranded wire helical springs are widely used as key repositioning and vibration reduction components of military equipment and heavy machineries,etc.The stranded wire helical springs were only used in military equipment.In recent years,with the development of the high precision machine tools for stranded wire helical springs,conventional single wire cylindrical helical springs in many civilian products are replaced by stranded wire helical springs gradually for better performance and stability.However,there are still many shortcomings and deficiencies in current theoretical studies.The interwire contact interactions in the stranded wire helical springs are not considered in the existing geometric models,which introduces non-negligible error in geometric model and further theoretical and finite element method analysis.That the interwire frictional contact is not considered in the existing static response models limits the accuracy of the restoring force predicted by these models.The model parameters of the existing dynamic models have to be identified by using experimental data,which means that the existing dynamic models can not be used when designing the stranded wire helical springs.Furthermore,the theory of springback analysis for manufacturing the stranded wire helical springs is not researched yet,leading to the processing parameters of the stranded wire helical springs can not be set with sufficient theoretical support.In order to solve the key problems to improve the accuracy of the theoretical and finite element method analysis and the design and manufacturing efficiency,the present work focus on geometric model,static response modelling,dynamic response predicting and manufacturing springback of the spring.The main contents of this thesis will be introduced in detail:(1)A deformation-based geometric model of stranded wire helical spring is established because the existing geometric model is unable to analyze the interwire contact interactions and can not be used in finite element analysis of spring with small outside wire pitch because of the low accuracy and the interwire geometric interference.This model proposes a key parameter characterizing the outside wire centerline deformation caused by the contact between the adjacent outside wires.The new geometric model can analyze the periodical variation of the local helix angle of outside wire centerline and the contact zone between the adjacent outside wires.This model has higher precision than the existing geometric model and provides foundations for the following theoretical studies and finite element analysis;(2)A novel static response model of the spring with consideration of interwire frictional contact is proposed because the existing model is unable to analyze the gradual stiffness and hysteretic damping of the spring and predict the restoring force in the unloading branch accurately when the spring is used as a reset spring.And a new analytical model characterizing the pitch of the outside wire in the loaded spring is proposed because there is no existing model describing the change of the outside wire pitch when the spring is loaded.Base on the outside wire pitch and the deformation-based geometric model,the novel static response model analyzes the interwire frictional contact in the loaded spring,hence the precision of the predicted restoring force in the loading and unloading branch is much higher than that predicted by the existing model.This model provides theoretical foundations for the following theoretical studies on the dynamic response and manufacturing springback of the spring;(3)A novel dynamic response prediction model is proposed because the existing model is a phenomenological model and is unable to predict the dynamic response at the design stage of the spring.Based on deformation-based geometric model and the static response model of the spring with consideration of interwire frictional contact,the present model considers the interwire fretting when loading and unloading branch of the spring switches and predict the dynamic response curve of the spring.Different from the existing model,the present model is not based on experimental data,hence,it is able to predict the dynamic response.Based on the dynamic response curve of the spring predicted by the present theoretical model,the parameters of the modified Bouc-Wen model are identified,and the dynamic response prediction model is established.The harmonic response of a mass-spring system is predicted based on the dynamic response prediction model of the spring.Incorporating the advantage of the theoretical model and the phenomenological model,the present model can both predict the dynamic response at the design stage of the spring and be used to analyze the harmonic response of a mass-spring system;(4)A theoretical manufacturing springback model is proposed because no theoretical model was reported before and the process parameters was chosen without theoretical support when manufacturing the spring.The model can significantly improve the efficiency of developing new springs.The mathematical springback analysis of wires is carried out.The springback of outside wires when cold forming and prestressing of spring is analyzed.And the theoretical springback model of the spring is established base on the springback of outside wires.This model has high computation efficiency and acceptable accuracy for engineering application.