Fatigue behavior of fiber reinforced composite materials based on recycled pet

Abstract

Utilization of recycled polyethylene terephthalate (PET) based resins for manufacturing composites is an environment-friendly and cost-effective solution. With an aim to increase the acceptability of recycled PET based resins, the fatigue performance of glass fiber reinforced composite materials (GFR-rPET-1) based on unsaturated polyester resin derived from recycled PET (rPET-UPR) has been evaluated. Fatigue performance has been evaluated in terms of S-N Data, area of hysteresis loops during fatigue loading, fatigue life distributions, self generated temperature during fatigue loading and stiffness degradation. Composite laminates of stacking sequence [0/(±45)2/0]T have been fabricated using vacuum infusion process. Fatigue tests were performed at the stress ratio of 0.1, where the stress level varied from 40-80% of the ultimate tensile strength (UTS) (S=0.4–0.8). The results of fatigue tests show that the fatigue lives of composites based on rPET-UPR were lower as compared to virgin polyester matrix composites. Due to higher degradation of rPET-UPR matrix as well as weak interfacial properties, 13% higher self-generated temperature was observed during fatigue loading in comparison to virgin resin based composite materials. A three-phase stiffness degradation curve has been observed for these composite materials indicating stiffness loss in the range of 20-35 % till the time of failure, which correlates well with the experimental damage observations. A nonuniform and rapid damage growth was observed at high-stress levels, whereas a more uniform damage zone was observed at the low-stress levels. Improvement in mechanical properties of rPET-UPR have been obtained in past by addition of Carbon Nano Tubes, fumed silica, nano clay etc. In the present investigation, effect of graphene nano platelets (GPnP) incorporation on fatigue performance of rPET UPR based glass fiber reinforced composites (GFR-rPET-2) has also been evaluated. The addition of graphene nano platelets enhanced the fatigue life and fatigue strength of the composites. The development of damage in GFR-rPET-2 composites was less due to the presence of graphene which resulted in decelerating stiffness degradation rate and cyclic creep of modified composite. Transmission light photographs and lower self-generated temperature during fatigue loading also pointed toward lower damage in GFR-rPET-2 composite. It was observed that incorporation of graphene nanoplatelets in rPET-UPR based composites brings their fatigue performance at par with virgin polyester resin-based composites. Fatigue life distributions of GFR-rPET-1 as well as GFR-rPET-2 composites was modelled using two parameter Weibull distribution with co-relation coefficients exceeding 0.9. Statistical analysis of the fatigue life data established that there is no deleterious effect on the scatter observed in fatigue lives of these composites, as compared to composites based on virgin polyester resin, though a marginal increase in dispersion of fatigue lives was observed in GFR-rPET-2 composites due to incorporation of graphene nanoplatelets. Further probability of failure has been incorporated into S-N relationships for these composites for the benefit of designers.