Mechanics Research And Optimal Design Of A Vehicle Suspension Jounce Bumper With Negative Poisson's Ratio Structure

Suspension jounce bumper manufactured from microcellular Polyurethane(PU)has excellent performance of energy absorbing.Combine with coil spring and shock absorber,the suspension can achieve a progressive elasticity,which would significantly improve vehicle harshness performance.However,the load-displacement curve of PU jounce bumper sometimes cannot reach ideal zone result from the limitation of its structure.Therefore the harshness performance still can be improved.In this dissertation,a novel Negative Poisson's Ratio(NPR)structure was applied in jounce bumper.The mechanical performances of traditional jounce bumper and NPR jounce bumper were compared using numerical and experimental methods.Then the influences of structure parameters on the mechanical performance were also researched.Moreover,suspension and vehicle virtual prototypes were employed to evaluated jounce bumpers,and the NPR jounce bumpers were optimized where maximum acceleration of driving through bump was minimized.This dissertation mainly consisted of several aspects listed below:(1)A finite element stratification method was proposed to simulate intergral-skin PU materials.Foam model was employed to model the core area of PU.The skin and transition layers were respectively assumed to have 6 times and 3 times stress-strain curves as core area.The implicit calculation results showed high reliability of the proposed stratification method under moderate strain.(2)Analytical model of 2D double-arrows NPR structure cell was established.The mathematic relation between equivalent Young's modulus,equivalent Poisson's ratio and cell parameters were obtained.Conditions of elastic buckling and plasctic collapse were also researched.Based on the 2D double-arrow NPR structure,a novel NPR jounce bumper was designed.(3)A parametric modeling and anlysis method applying Matlab and Abaqus was proposed to improve calculation efficiency.Explicit numerical calculation was conducted on a NPR jounce bumper case.Linear stiffness was observed at small displacements.However,at moderate displacements,NPR jounce bumper started expanding instead of shrinking.Thus the gradient of load-displacement curve massively increased.NPR jounce bumper prototypes were manufactured,and uniaxial compression tests were conducted.The test results showed good agreement with the numerical results.From the aspect of viscoelasticity,the NPR jounce bumper prototype absorbed 49.3%of the impact energy thoughout the compression travel.Compared with traditional jounce bumper,the load-displacement curve of NPR jounce bumper had linearer stiffness at small displacement and smoother transition area at moderate displacement.In addition,the transition area moved towards large displacement for 3mm,which is beneficial to the vehicle NVH performance.(4)The influences of numbers of cells and layers,layer heights,layer thicknesses and material Young's modulus on the load-displacement curve of NPR jounce bumper were researched.An optimization method of NPR jounce bumper was proposed where ideal curve was targeted.Numbers of cells and layers were optimized to fulfill the ideal trasition area.Then layer height,layer thickness and material Young's modulus were tuned to adjust the stiffness of NPR jounce bumper.(5)A jounce bumper evaluation method was proposed using harshness criterion under impact loads.Suspension and vehicle virtual prototypes were established based on Adams/Car.The NPR jounce bumper can achieve better suspension stiffness curve even if the total height of jounce bumper was limited according to design requirments.The harshness analyses of driving through bump or pothole were conducted using vehicle virtual prototype.The results showed that the peak accelerations of driving through bump or pothole under all speeds were decreased after applying NPR jounce bumper.Therefore the harshness performance was improved.(6)A parametric optimization method of NPR jounce bumpe was proposed which targeted minimum peak accelerations of driving through bump.Gaussin process metamodel of peak acceleration was established.GA-SQP hybrid algorithm was employed for parametric optimization.The GA-SQP hybrid algorithm dragged the optimization iteration process out of the local optimum and close to the global optimum after a certain number of steps.The peak acceleration was decreased 13.3%after optimization.The Gaussin process metamodel had a deviation of 5.5%at optimum point.Therefore the established metamodel was reliable.And the application of Gaussin process metamodel can significantly improve optimization efficiency.