Experimental investigation into stamping of woven CF/PP laminates: Influences of molding temperature on thermal, mesoscopic and macroscopic properties

Abstract

This study aimed to investigate the influences of stamping temperature (or molding temperature) on thermal properties of matrix, mesoscopic structures of fabric and effective macroscopic mechanical properties of composite materials through experimental characterization. The plain woven carbon fiber/polypropylene composite laminates were prepared by hot stamping at 190 °C, 220 °C and 250 °C, respectively. Thermal study was performed using differential scanning calorimeter and thermogravimetric analysis. The mesoscopic properties were characterized through microscope and scanning electron microscope (SEM). Tensile test and short beam shear test were conducted to evaluate macroscopic properties of the material. Effects of fabric structure on the crack initiation and propagation as well as local strain concentration of thermoplastic composite were investigated in detail using digital image correlation (DIC) technique. Relationships of process parameters, thermal characteristics, mesoscopic fabric structures and macroscopic mechanical properties of the carbon fiber reinforced polypropylene (CF/PP) materials were explored under different stamping temperatures. The experimental results revealed that with increase in processing temperature, the crystallinity of polypropylene (PP) matrix increased, and the interfacial adhesion between fiber and resin became strong, leading to increase in tensile modulus. Due to the change of resin viscosity, the aspect ratio, crimp angle and gap size of the fiber bundles also vary. The interfacial debonding was a main failure mode in CF/PP composites. This study is anticipated to provide fundamental understanding in how to tailor effective properties of composites through manufacturing process.