Development of the temperature-dependent constitutive model of glass fiber reinforced polypropylene composites

Plain-woven glass fiber-reinforced polypropylene (PW-GFRPP), as the typical advanced CoFRTP, has been rapidly emerged in aerospace, civil and automobile fields, thanks to its low cost and excellent performances. The fiber yarns of PW-GFRPP will undergo large rotations and shear deformations with immersions of molten polypropylene resin during the hot mold pressing process. The shear deformations of fiber yarns not only directly affect the formability quality of the preformed structures but also make an impact on the mechanical performances of cured products. Thus, the scope of this study is to construct the temperature-dependent material constitutive model of PW-GFRPP and investigate the influences of temperature and blank holding force (BHF) on the formability of PW-GFRPP prepregs. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were first implemented to determine the melting and degradation temperatures of polypropylene. Next, the bias-extension tests for PW-GFRPP prepregs were carried out accounting for three temperature values (190°C, 220°C and 250°C). Then the temperature-dependent constitutive model was developed and validated. Finally, the validated constitutive model was used to explore the influences of temperature and blank holding force on the formability of PW-GFRPP composites on a double dome benchmark.