Effect of Thermal Ageing on the Mechanical Strength of Carbon Fibre Reinforced Epoxy Composites

Abstract

Applications of Carbon Fibre Reinforced Polymers (CFRP) at temperatures over 150–200 °C are becoming common in aerospace and automotive applications. Exposure of CFRP to these temperatures can lead to permanent changes in their mechanical properties. In this work, we investigated the effect of thermal ageing in air on the strength of carbon fabric/epoxy composites. To this end, accelerated artificial ageing at different temperatures was performed on carbon fabric/epoxy specimens. The flexural and interlaminar shear strengths of the aged specimens were assessed by three-point bending and short beam shear tests, respectively, and compared to those of unaged samples. For ageing at temperatures below the glass transition temperature of the resin, Tg, a moderate reduction of strength was found, with a maximum decrease of 25% for 2160 h at 75% Tg. On the other hand, a rapid strength decrease was observed for ageing temperatures above Tg. This was attributed to degradation of the epoxy matrix and of the fibre/epoxy interface. In particular, a 30% strength decrease was found for less than 6 h at 145% Tg. Therefore, it was concluded that even a short exposure to operating temperatures above Tg could substantially impair the load-carrying capability of CFRP components.

Effect of Thermal Exposure on Residual Properties of Wet Layup Carbon Fiber Reinforced Epoxy Composites

“…As with all other tests, the maximum degradation was seen after exposure to the 260 °C temperature regime with decreases occurring within three distinct regimes of 4–8 h, 8–24 h, and 24–72 h with the rates of decrease of 11.4% per hour, 4% per hour, and 1.1% per hour, respectively. The trend of an initial increase in SBS strength followed by a decrease over longer periods of exposure follows results reported by Zavatta et al [ 42 ] where there was insignificant deterioration up to 198 °C and then very steep decreases at 260 °C, which was noted as being 145% of the T g of 71% and 89% at the 24 h and 72 h levels of exposure, respectively. Their results are very similar to those from the current study of 76% at 24 h and 89% at 72 h. It is seen that interlaminar failure is the dominant mode initially, transitioning through greater matrix degradation and failure to one of fiber-matrix debonding and interlayer separation as shown in Figure 9 for specimens representative of thermal aging at 232 °C for 48 h and above and at 260 °C at 8 h and above.…”

“…This study focuses on a range of temperatures between 23 °C and 260 °C, with exposure periods up to 72 h at temperature prior to testing for residual properties. The temperature range corresponds to that likely to be seen in the field, especially for cases where the composite is not in contact with the flame but could be exposed to levels of elevated temperature for extended periods of time and matches that used by Zavatta et al at the higher level [ 42 ], and near, but below, the resin decomposition temperature [ 43 ]. It is also within the range likely to be felt by the composite that was protected by a layer of insulation that separated it from the fire.…”

Preparation Optimization of CFRP and EPDM Composite by the Co-Curing Method

“…As the heating temperature was increased and the heating time was extended, the ILSS of CFRP composites reduced. The result may be explained by the fact that high-temperature heating over long periods of time leads to the degradation of the CFRP composite [ 45 ], and the uneven heating of the CFRP composite is due to the good thermal insulation of EPDM rubber and the thermal gradient propagation in the EPDM rubber. Nevertheless, the high-temperature preparation process for a short period of time does not have a negative impact on the mechanical properties of CFRP composites, but rather has a facilitating effect, since the high temperature for a short period of time facilitates the release of residual thermal stresses within the composite, which is consistent with the previous conclusions.…”

Evaluation of the viscoelastic behavior, thermal transitions, and self‐healing efficiency of microcapsules‐based composites with and without a catalyst using dynamic mechanical analysis technique

“…Repeating DMA multiple times for the same samples of microcapsule‐based epoxy composites without a catalyst necessary for self‐healing leads to aging and decreased mechanical properties 37 . However, DMA for the same samples with a catalyst allows self‐healing to occur, counteracting the aging‐induced deterioration in mechanical properties, emphasizing the importance of evaluating self‐healing efficiency.…”