Durability and notch sensitivity analysis of environmental ageing induced glass fibre mat and kenaf fibre mat-reinforced composites

Abstract

The durability of the notch and un-notch composites is mainly affected by environmental ageing, the condition of mechanical loading and mechanical ageing. Due to the dissimilarity of two components of fibre mat-reinforced thermosetting composites (e.g. fibre and resin), thermal stress and strain can be generated and raised by moisture, temperature variation, thermal ageing and mechanical ageing in any working environment. This study aims at investigating the effect of thermal ageing fatigue and mechanical ageing fatigue on the mechanical durability and notch sensitivity properties of glass fibre mat unsaturated polyester resin composites and kenaf fibre mat/unsaturated polyester composites. Tensile tests of smooth and notched specimens, low cycle tensile fatigue tests, dynamic mechanical analysis, stress distribution by point-stress failure criteria and notch sensitivity analysis were performed to both types of the specimens. Both composites were previously taken under up to 100 number of freeze-thaw ageing cycles (from −25 to + 58℃). It is found that the tensile modulus and un-notched strength of kenaf fibre mat/unsaturated polyester were decreased by 30 and 27%, respectively, which was more severe than that of glass fibre mat/unsaturated polyester composites. After the thermal ageing, notch (open hole) did not diminish the strength property of kenaf fibre mat/unsaturated polyester, and there was an absolute increase of characteristic distance (d0) which indicates the lower notch sensitivity of kenaf fibre mat/unsaturated polyester. Although glass fibre mat/unsaturated polyester had superior mechanical properties, after thermal ageing, while kenaf fibre mat/unsaturated polyester presented stable low cycle fatigue property, better energy absorption and notch sensitivity properties.

Time-temperature-dependent mechanical durability analysis of short (glass) fiber-reinforced polyethylene terephthalate injection molding composites with weld line

“…The tan (d) changed in a higher frequency due to the short period for polymer relaxation. As in the case of N30, the tan (d) peak moved upward at a higher frequency, indicating the higher damping intensity, [3][4][5]42 that referred to higher internal molecular motion and energy dissipation of the glass fiber-PET resin interface.…”

“…28,39 Besides this, due to the large difference in thermal expansion coefficient between PET resin and glass fiber in GF/PETs and the high temperature of the resin, the molecular arrangement of the polymer changed with temperature, resulting in the fiber bonding effect being reduced, and the macroscopic tensile strength was relatively reduced. 3,4,13 By repeating the experiment to eliminate the interference of accidental factors, looked up the data and analyzed the stress-displacement curve of the PET resin. It was found that the PET resin had a glass transition at about 80 C, reached the peak of cooling crystallization at around 136 C, and continued to heat up to 257 C, the PET material has undergone melt crystallization.…”

“…In recent years, as fiber-reinforced composites are being widely used in engineering tensile structure purposes replacing conventional materials with high specific strength, stiffness, and durability, 1–4 thermoplastic composites are practically recommended over counterparts for their indispensable chemical stability, damage tolerance, fast manufacturing, and recyclability. 1–3,5 The most popular thermoplastic molding method is known to be injection molding, 2,5 which has different variations, such as co-injection, fluid assisted, in-mold decoration injection molding, besides microcellular injection molding of filled polymers, and long or short fiber-reinforced injection molding, etc. 1,2 Short fiber-reinforced thermoplastics (SFRTs) have a vast range of applications with satisfactory mechanical properties including automobile, medical, aerospace, and electronic applications.…”

Kenaf fibers reinforced unsaturated polyester composites: A review

“…Apart from chemical treatment, moisture, temperature variation, and thermal aging might generate thermal stress and strain on fiber reinforced thermosetting composites. 116 In a study reported by Ariawan et al, 117 heat treated kenaf fibers were prepared by heating fibers for 2.5, 5, 7.5, 10, and 12.5 h at 140°C in an air-circulating oven. It was found that the heat treatment increases both the crystallinity index and fiber strength of kenaf fiber.…”

“…The optimum heat treatment temperature was reported to be 120°C, and as the temperature reached about 170°C flexural properties were reported to decrease. In a study reported by Miah et al, 116 the effect of thermal and mechanical aging fatigue on mechanical durability of kenaf fiber mat/UPE composites were reported. For this purpose, kenaf/UPE composites were exposed to up to 100 freeze-thaw aging cycles (from −25°C to +58°C).…”