Effects of sulphuric acid concentrations during solvolysis process of carbon fiber reinforced epoxy composite

Developing a cost-effective technique of reclaiming carbon fibers without significantly deteriorating their quality has gained much importance. This paper reports on reclaiming carbon fibers from the carbon fiber reinforced polymer (CFRP) by solvolysis technique using sulphuric acid. The main objective of this work was to determine the lowest sulphuric acid concentration which can remove the epoxy resin from the composites, at room temperature and atmospheric pressure. The sulphuric acid concentrations used ranged from 11 to 18 mol L-1 with 30 min reaction time and 50 mL volume. Thermogravimetric analysis (TGA) showed that the fiber content of the composites is 68% by weight. From the solvolysis process, mass of decomposed epoxy resin decreased with decreasing acid concentrations. SEM images show that the residual epoxy adhering to the fibers after solvolysis increased with decreasing molarity. Acid concentrations lower than 15 M were found to be not effective in removing the epoxy resin from the carbon fibers. The tensile strength and Young’s modulus of all the reclaimed fibers is marginally lower than the untreated carbon fibers. The tensile strength was found to increase as the acid concentration decreases with fibers in 15 M acid showed the highest tensile strength of 3.43 GPa (99.1% strength retention). Similar trend was also observed for Young’s modulus. The study shows the potential of sulphuric acid to reclaim carbon fiber from the CFRP with 15 M giving the optimum properties in terms of tensile properties retention and epoxy resin decomposition

Effects of sulphuric acid concentrations during solvolysis process of carbon fiber reinforced epoxy composite

Developing a cost-effective technique of reclaiming carbon fibers without significantly deteriorating their quality has gained much importance. This paper reports on reclaiming carbon fibers from the carbon fiber reinforced polymer (CFRP) by solvolysis technique using sulphuric acid. The main objective of this work was to determine the lowest sulphuric acid concentration which can remove the epoxy resin from the composites, at room temperature and atmospheric pressure. The sulphuric acid concentrations used ranged from 11 to 18 mol L-1 with 30 min reaction time and 50 mL volume. Thermogravimetric analysis (TGA) showed that the fiber content of the composites is 68% by weight. From the solvolysis process, mass of decomposed epoxy resin decreased with decreasing acid concentrations. SEM images show that the residual epoxy adhering to the fibers after solvolysis increased with decreasing molarity. Acid concentrations lower than 15 M were found to be not effective in removing the epoxy resin from the carbon fibers. The tensile strength and Young’s modulus of all the reclaimed fibers is marginally lower than the untreated carbon fibers. The tensile strength was found to increase as the acid concentration decreases with fibers in 15 M acid showed the highest tensile strength of 3.43 GPa (99.1% strength retention). Similar trend was also observed for Young’s modulus. The study shows the potential of sulphuric acid to reclaim carbon fiber from the CFRP with 15 M giving the optimum properties in terms of tensile properties retention and epoxy resin decomposition

Displacement rate effects on the mode II shear delamination behavior of carbon fiber/epoxy composites

This paper studies the influence of displacement rate on mode II delamination of unidirectional carbon/epoxy composites. End-notched flexure test is performed at displacement rates of 1, 10, 100 and 500 mm/min. Experimental results reveal that the mode II fracture toughness GIIC increases with the displacement, with a maximum increment of 45% at 100 mm/min. In addition, scanning electron micrographs depict that fiber/matrix interface debonding is the major damage mechanism at 1 mm/min. At higher speeds, significant matrix-dominated shear cusps are observed contributing to higher GIIC . Besides, it is demonstrated that the proposed rate-dependent model is able to fit the experimental data from the current study and the open literature generally well. The mode II fracture toughness measured from the experiment or deduced from the proposed model can be used in the cohesive element model to predict failure. Good agreement is found between the experimental and numerical results, with a maximum difference of 10%. The numerical analyses indicate crack jump occurs suddenly after the peak load is attained, which leads to the unstable crack propagation seen in the experiment

Experimental investigation of tensile properties of eco-composite laminates

Natural fiber composites are green composites that are renewable and sustainable towards the environment. It has low density which results in a good specific strength. With the current trending to lower the dependency on petroleum-based products, it leads to investigation on the environmental friendly materials to replace the conventional fibers. Therefore, natural fibers are hybridized with conventional fibers to form eco-composite laminates. Eco-composites have ecological and environmental advantages compared to synthetic composites while its strengths are comparable to the synthetic composites. However, not many studies have been done on the mechanical properties of this type of eco-composites. This paper presents the tensile properties of eco-composites consisting of flax-carbon/epoxy laminates in sandwich-like and intercalation configurations. From the tensile tests, the eco-composites strengths are comparable to the synthetic composite laminates. For eco-composite laminates, sandwich-like configurations are found to have better properties compared to the intercalation counterpart

A simple nonlinear constitutive model based on non-associative plasticity for UD composites: development and calibration using a Modified Arcan Fixture

A simple nonlinear constitutive model based on non-associative plasticity for unidirectional (UD) composites is developed and calibrated using a Modified Arcan Fixture (MAF) and Digital Image Correlation (DIC). The plasticity model accounts for the nonlinear response of unidirectional composites subjected to multiaxial loading, assuming transverse isotropy and negligible plasticity in the fibre direction. The different responses in transverse tension and compression are accounted for by a Drucker–Prager type yield function to include transverse pressure sensitivity. It is shown that using an associative flow rule leads to the prediction of non-physical plastic strain components, whilst the use of a non-associative flow rule resolves the deficiency of the associative model. The non-associative model is calibrated and verified against biaxial test data obtained from glass/epoxy specimens using the MAF, as well as against off-axis test data available in the literature for two additional composite material systems. The nonlinear stress-strain curves for unidirectional composites subjected to multiaxial stress states predicted by the model are in good agreement with all three sets of experimental data, thus demonstrating the predictive capabilities of the proposed model.</p