Thermo-Formability Study Of Automotive Needlepunched Carpet Composites

Studies of material formability, which comes from pressing demand of practical forming processes, have gained more attentions during the past years. As a relatively newly emerging manufacturing technology in modern carpet industry, automotive needlepunched carpet composites usually happen to be tearing, wrinkling and crushing during their practical thermoforming processes. By far the globe automotive carpet manufacturers have applied their engineers'experiences and trial and error method to solve these problems. This leads to postponement of new products and quality fluctuation of current products. In China, current production capability of automotive carpets has still remained far behind that of domestic automotives, which results in numerous automotive carpets import every year. So with the financial support of national science fund (project item: 50305020), we firstly focus on thermo formability of automotive needlepunched carpet composites, have a systemic and in-depth study.By parameters ascertainment of extensile experiment in high temperature and execution of many test schemes, basic mechanical data of automotive needlepunched carpet composites have been accumulated. With a large number of extensile experiments of automotive needlepunched carpets under different heat transferring conditions (isothermal condition, natural heat convection condition), the common mechanical characters of automotive needlepunched carpets in high temperature have been summarized. With the application of viscoelastic principle about polymer materials, the deformative mechanisms under different temperature conditions about two typical automotive needlepunched carpets (1. a needlepunched fabric layer plus a latex layer, 2. a needlepunched fabric layer, a polypropylene (PP) thermo figuration layer plus a mat layer. ), have been analyzed, respectively.With the viewpoint of composite macroscopic mechanics, a nonlinear viscoelastic constitutive framework, including temperature effect, for automotive needlepunched carpets has been proposed from thermodynamics of irreversible processes. In order to characterize the difference of temperature effect with different heat transferring conditions, the description on temperature effect in our model is based on the definition of temperature in thermodynamics of irreversible process.According to the specific heat transferring modes corresponding to the different thermoforming process stages in practice, a single side cooling model and a natural convection model of spaceless plate have been introduced our proposed model framework, respectively. Then with a method of Laplace transform and Laplace inverse transform, the specific expressions of viscoelastic constitutive equations for automotive needlepunched carpet composites for the three heat transferring cases (isothermal, heat convectional, and heat conductive), have been archived. Model parameters among these obtained constitutive equations can be characterized just by basic mechanical experiment and thermal test, which makes our proposed model convenient for industrial applications.Applying the user-defined subroutine interface VUMAT of general purposed nonlinear finite element analysis software ABAQUS/Explicit to code our proposed model for automotive needlepunched carpets, numerical simulations of uniaxial extensile deformation and stamping deformation with a hemisphere punch are implemented, respectively for the different heat transferring cases. Verification of our proposed model is proved by the comparison between the numerical results and the experimental data. To gain a relatively objective evaluation on the proposed model, the Marlow model, which is a built-in material model in ABAQUS, is selected to implement the similar numerical simulations for comparison. Comparisons between these numerical results and the actual experimental data have further proved verification and efficiency of our proposed model.Finally, depending on the deformation characteristic of automotive needlepunched carpets in high temperature, three formability indexes are proposed based on our built model. By comparisons with corresponding experimental data, these indexes verifications are proved. Each of them evaluates the thermo formability of automotive needlepunched carpets from different aspects, which are ultimate strength, deformation ability and temperature sensitivity, respectively. By the applications of them, helpful references to a steady and robust thermal forming operation for automotive needlepunched carpet composites in practice are able to be archived.