Thermo-Viscoelastic Constitutive Relations And Thermal Molding Simulation Of Flexible Polyurethane Foam

Flexible polyurethane(PU)foam is the largest amount of PU material used in a wide range of industries,such as light industry,textiles,transportation,and many other industries.Due to its extensive use and variability of the environment,materials are inevitably at high temperatures and are affected by temperature.With the change of temperature,the mechanical properties of flexible PU foam change,affecting the performance of the material;When using the material to shape,temperature is a key factor in its formation Therefore,it is necessary to obtain the mechanical properties of flexible PU foam at high temperatures.However,there is no report on the constitutive model under high temperature at present,and the corresponding numerical simulation of the molding is also in the research gap.Based on this,in this paper,the thermal viscoelastic constitutive model of flexible PU foam under high temperature is studied in depth,and a numerical simulation is performed on the thermal compression molding of the material in combination with the model.The aim is to understand the thermal viscoelastic mechanism of the flexible PU foam in depth.The main contents of this paper are as follows.(1)The compression experiments of flexible PU foam at different constant temperatures were carried out using DMA.The stress time and strain time data were obtained,with which the glass transition interval of flexible PU foam was determined.(2)Based on the viscoelastic constitutive model of flexible PU foam at room temperature and the principle of elastic recovery response,a nonlinear thermal-viscoelastic constitutive model of the material is proposed according to the structure of flexible PU foam.Then,the corresponding parameters of each model are obtained by fitting with the experimental data.And the correctness of the established model are verified by comparing model prediction with experimental data.(3)Utilizing the commercial software ABAQUS custom material interface to develop VUMAT and UMAT material subroutines for flexible PU foam.VUMAT and UMAT were verified based on experimental data.(4)Using the established material subroutine,a uniaxial thermal compression molding of flexible PU foam is simulated in ABAQUS for the first time.According to the experimental data,the constitutive characteristics of the material after unloading are modified,and the final shape and springback of the material after molding are predicted well.Using the modified constitutive model,a preliminary simulation of the hemispherical molding of bra cups is performed for the first time.A numerical simulation method is provided for the research of polyurethane thermal molding process.