The use of Carbon Fiber Reinforced Polymers (CFRPs) is widespread in high value manufacturing industries such as automotive and aerospace due to their mechanical properties and light weight. These mechanical properties depend on several factors such as the orientation of carbon fibers across the 3D volume and the manufacturing process (i. e. resin's degree of cure). For CFRP, an inadequate curing process can lead to suboptimal mechanical properties. Measuring the degree of cure in order to optimize the curing cycle is a challenging problem due to the need to validate results post production. Thus, a novel online, in-situ and non-intrusive technique to measure the degree of cure by applying a pattern recognition algorithm is presented. The technique is called vibration assisted cure for online identification (VACOI). VACOI makes use of a hot tool that, as it cures the uncured CFRP samples, vibrates sideways to produce a small oscillatory stress on the prepreg. This stress is measured in real time with a triaxial force sensor and processed with the pattern recognition method dynamic time warping (DTW). When the epoxy resin, within the prepreg, cures the resin's viscosity undergoes a change that is measured as a sudden increase then decrease of the stress' force amplitude. The degree of cure was validated with differential scanning calorimetry. VACOI was evaluated by curing prepreg samples at temperatures of 130 degrees C, 140 degrees C and 150 degrees C. The novel method is capable of real time curing recognition with success rates of: 71.40%-71.40% for 130 degrees C, 71.40-77.77% for 140 degrees C, and 77.77-81.81% for 150 degrees C.
