Research And Simulating Application Of Mechanical Properties Of Automotive Rigid Polyurethane Foams

In automotive structures,rigid polyurethane foams are often used as buffer part in interiors and bumpers to cushion impact and absorb energy in a car crash,which has a positive effect on the safety of occupants and pedestrians.Therefore,it is of great significance to study the mechanical properties of automotive rigid polyurethane foams for designing foams fillers and automotive safety.The mechanical properties of rigid polyurethane foams are complex and are affected by many factors.We firstly determined through the literature that the relative density,matrix material properties,cell body characteristics,and mechanical test data should be the key to study the mechanical properties of foams.LS-DYNA is a finite element analysis software that is widely used in the field of automotive crash safety.The conclusions we obtained will eventually be applied in simulation.Therefore,the relevant foams material models in the software are summarized and analyzed,and the process of creating a material model,the test data required for determining the parameters,as well as the application range and calculation characteristics of these material models are finally concluded.Then,we test the mechanical properties of the rigid polyurethane foams.The test samples are from the buffer part in the door trim panel.The triaxial compression tester is used to perform the unconsolidated undrained test,of 50 kg/m~3 and 70 kg/m~3 density samples under different pressures,and the test curves are obtained.Then according to the ASTM D1623-09 standard,we conduct a tensile test of 50kg/m~3 and 110kg/m~3 density samples at a strain rate of 1~100/s.The relationship between tensile elastic modulus/breaking strength of the rigid polyurethane foams and strain rate were found.These two sets of tests belong to the series of experiments of our group's research on rigid polyurethane foams.We also summarizes the existing test data including uniaxial tension and compression,hydrostatic pressure,unconsolidated undrained test data,etc.These constitute the complete uniaxial and triaxial mechanical properties test data.Based on the test data,and mainly according to Gibson and Ashby theory,we canculate the material constants of this type of rigid polyurethane foams,including the results of constitutive relationship of uniaxial tensile curves,compressive curves,and multiaxial compressive mechanical properties.In view of above conclusion,we predicting different mechanical properties of the rigid foams with different density or different strain rate.At last,our research conclusions are validated and applicated in LS-DYNA.Firstly,a theoretically closed-cell finite element model is built to verify the reasonable validity of the assumption of cell body deformation.Then the lower legform to bumper test of pedestrian safety protection regulations is simulated.We caculate the theoretical data and curves of 60 kg/m~3 foams.The detailed influence of the foams density and material model selection on the simulation results are estimated.