Mechanical properties evaluation of glass fiber reinforced thermoplastic composite plate under combined bending loading and water immersion

Fiber reinforced thermoplastic composites have many advantages, such as repeated molding, high toughness, durability and recyclability, which made them a potential substitute as engineering strengthening materials for thermosetting composites. However, their long-term performances under complex service environments are not well understood, hindering its durability design. In the present paper, glass fiber reinforced polypropylene (GFRPP) plate was studied on its mechanical property evaluation subjected to water immersion (distilled water) and bending (bending strains of 0.54 % and 1.04 %) at elevated temperatures (40 degrees C, 60 degrees C and 80 degrees C) up to 180 days. Water uptake, mechanical properties, thermal properties and microstructure tests were further carried out to reveal the effects of water uptake content, immersed temperature and bending loading level on the properties. The results showed the water absorption curve at three temperatures presents a two-stage diffusion behavior. After the longest immersion time of 180 days, the strength retention of plate at 40 degrees C, 60 degrees C and 80 degrees C were 88.2 %, 58.3 % and 31.8 % for tensile strength, 83.6 %, 67.8 % and 47.9 % for flexural strength and 70.6 %, 61.7 % and 41.4 % for in-plane shear strength. Higher immersion temperature accelerated the swelling effects of polypropylene. Higher bending loading levels accelerated the crack or defects formation and propagation in the resin as well as at the interface. When the strength retention rates were 50 %, the longest service life of plate exposed in service environment of Da Lian (T=9.2 degrees C) were 23.9 years (tensile strength), 12.8 years (flexural strength) and 3.0 years (in-plane shear strength) without the bending strain. Through comparing with thermosetting composites, glass fiber reinforced polypropylene has almost close or higher tensile strength retention rate and service life for certain service conditions.