Cure conversion of structural epoxies by cure state analysis and in situ cure kinetics using nondestructive NIR spectroscopy

Influence of the Epoxy Resin Process Parameters on the Mechanical Properties of Produced Bidirectional [±45°] Carbon/Epoxy Woven Composites

“…Some of major attributes of these materials are as follows: (i) excellent chemical resistance, particularly to alkaline environments; (ii) outstanding adhesion to a broad variety of substrates; (iii) high tensile, compressive, flexural, and fatigue strengths; (iv) low shrinkage; (v) excellent electrical insulation properties; (vi) good corrosion resistance; and (vii) ability to cure over a wide range of temperatures [ 4 , 6 ]. To take advantage of epoxy resins properties, it is important to understand their curing kinetic process to improve composites’ processing time, energy consumption, costs, and product quality [ 7 , 8 ]. Therefore, the curing process of epoxy resin is the most crucial stage of the manufacturing process as it influences the final properties of fabricated parts.…”

“…Curing or cross-linking processes of epoxy resins take place through the oxirane functional monomers or hydroxyl groups to form a three-dimensional infusible network. The cross-linking process can occur mainly by two types of curing mechanisms: direct coupling of the resin molecules by a catalytic homopolymerization or coupling through an intermediate reactive known as curing agent, which are compounds containing active hydrogen (polyamines, polyacids, polymercaptans, and polyphenols, to name a few) [ 5 , 6 , 7 ]. Owing to the high reactivity of chemical species involved in the curing process, the reaction is highly exothermic; therefore, it is imperative that the polymerization process of epoxy resins must be carefully controlled in order to prevent that the released reaction heat can self-accelerate the process [ 2 , 4 ].…”

“…Owing to the high reactivity of chemical species involved in the curing process, the reaction is highly exothermic; therefore, it is imperative that the polymerization process of epoxy resins must be carefully controlled in order to prevent that the released reaction heat can self-accelerate the process [ 2 , 4 ]. Several analytic techniques have been demonstrated to monitor the extent of the reaction to determine the curing degree of epoxy resins [ 2 , 3 , 4 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. Among direct techniques, Fourier-transform infrared spectroscopy (FTIR) can be used to evaluate the concentration of one or more reactive groups as a function of time (during the curing process).…”

“…Some previous research works that study the curing process of epoxy resins using FTIR spectroscopy can be found in [ 2 , 7 , 9 , 15 , 16 , 17 , 18 , 19 ]. However, research works that focus on validating the epoxy resins processing parameters and their influence on the mechanical properties of parts fabricated for the aerospace sector are still scarce [ 3 ].…”

Internal Residual Strain Measurements in Carbon Fiber-Reinforced Polymer Laminates Curing Process Using Embedded Tilted Fiber Bragg Grating Sensor

“…Fiber deformation and internal delamination are difficult to observe by the naked eye and will form a potential hazard. There is an urgent need for a convenient and low-cost method for the on-line monitoring of residual strains generated in the curing process [ 4 , 5 , 6 , 7 ]. The measurement of curing parameters for composite prepregs can be accomplished using conventional analytical techniques, such as differential scanning calorimetry (DSC) [ 8 , 9 ], dielectric analysis (DEA) [ 10 ], dynamic mechanical analysis (DMA) [ 11 ], and so on.…”