Research On Reliability Optimization Design Method Of Variable Stiffness Composite Spring

As the core component of the suspension,the performance of the spring will affect the driving condition of the vehicle.Compared with the traditional metal spring,variable stiffness composite helical spring has significant lightweight and better damping performance.At the same time,the variable stiffness characteristics matched with the vehicle performance can achieve better comfort and bearing capacity.Yet,the service condition of the spring is harsh,and its reliability will affect the driving safety.Therefore,the reliability of the variable stiffness composite helical spring will be the most critical performance index of the whole suspension.In this paper,the variable stiffness structure suitable for vehicles is selected from the aspects of manufacturability,design,and replaceability,and the reliability layer design is carried out based on the structure.Through a large number of simulation and experimental studies,the failure modes of springs under different materials and different layers are analyzed.It provides a reliability design idea for a new composite helical spring.The main research contents are as follows:(1)Aiming at the special variable diameter structure of 45 ° variable stiffness composite helical spring implanted with polyurethane mandrel,two ply schemes suitable for the spring in this paper are designed from the layer scheme of variable thickness laminates.Parametric modeling of different spring layer schemes is carried out.(2)The strength and fatigue theoretical models suitable for composite materials are summarized,the UMAT secondary development subroutine is written.and the complex spiral spring structure is reasonably simplified.The torsion condition of the spring wire is taken as the main research object in this paper,combining with ABAQUS software and secondary development subroutine,and the finite element models of different ply schemes are established.A prediction model of the spring strength and the fatigue reliability suitable for different ply schemes is proposed.(3)Taking genetic algorithm as the optimization method,starting from improving the ply parameters,and combining with Tsai-Wu strength theory,the stiffness theory and the mass calculation,the performance indexes above the spring are significantly improved through multi-objective optimization.(4)Samples of different materials and different layer schemes are prepared by the improving process.Through the strength test and the fatigue test,the failure types and damage mechanisms of the four springs are obtained,and the best ply scheme is obtained.Comparing the test results with the simulation results,it is verified that the strength and fatigue failure model can accurately predict the reliability of variable stiffness composite helical spring.(5)Compared the fatigue reliability of the spring before and after optimization,the optimized spring has better damage suppression ability under the premise of 62.5 %increase in life expectancy,which verifies the rationality of the laminates optimization.