Cure Monitoring of Composite Carbon / Epoxy through Electrical Impedance Analysis
Composite materials are increasingly used in aeronautic; they offer many benefits such as mechanical strength, mass and consumption reduction. However, their process development needs to be known and controlled, in order to adjust the process parameters and optimize the characteristics of structures made from these materials. This paper is focused on impedance spectroscopy measurement and analysis technique to characterize material’s properties. In fact, the composites based on carbon fiber have electrical proprieties; therefore a three-dimensional modeling of the electrical conduction in the material is established by using a distributed allocation of an electrical resistance (RP) in parallel with a capacitance (CP). Then, thin electrodes (40 μm thick) are inserted inside the material and a specific impedance measurement bench is developed to perform real-time measurements of RP and CP on unidirectional (UD) mono-ply and multi-plies samples. During curing (in an oven) the change in values of both RP and CP in different stages of the curing cycle is showed. Then, problems that occur during the curing cycle (layup defect, loss of vacuum) were detected by a large gap of the measured electrical parameters in comparison with the ordinary case. Therefore, by this electrical measurement, we present a way to ensure an automated real-time monitoring of the composite curing
Smart Cure Monitoring Method of Carbon/Epoxy Laminates Using Electric Capacitance Change with Applied Alternating Current Frequency
Authors have developed an electric resistance change method for delamination monitoring of carbon/epoxy composite laminates. The method employs reinforcement fibers as sensors; electrodes are co-cured. Co-cured electrodes for delamination monitoring are adopted in the present study as sensors for monitoring the degree of cure. This study proposes a new method using electrical capacitance change for monitoring the degree of cure without using additional sensors. Applying alternating current between electrodes during the cure process provides dielectric properties of carbon/epoxy composites. As with the conventional cure monitoring method using extra dielectric sensors, the degree of cure of composites is monitored by measuring the dielectric constant of composites. The dielectric constant of epoxy resin changes concomitant with change of frequency of applied alternating current (AC). Using dependency of the applied AC frequency of the dielectric constant, the degree of cure is measured directly. The proposed method is applied to single and multi-ply carbon/epoxy composite laminates. The method demonstrates excellent estimations of the degree of cure without additional sensors.
Inhibition of Mild Steel Corrosion Using L-tryptophan and Synergistic Surfactant Additives
The corrosion inhibition characteristics of nitrogen containing amino acid L-tryptophan on mild steel in 0.1 M HCl solution, in the temperature range of 30-50 o C, was studied by weight loss and potentiodynamic polarization measurements. L-tryptophan significantly reduces the corrosion rates of mild steel; the maximum inhibition efficiency being 83% at 50 o C in presence of inhibitor concentration of 500 ppm. The effect of the addition of very small concentrations of anionic surfactant, sodium dodecyl sulfate (SDS), and of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), on the corrosion inhibition behavior of L-tryptophan was also studied. The inhibition efficiency (IE) of L-tryptophan significantly improved in presence of both surfactants. The effect of SDS and CTAB on the corrosion inhibition behavior of L-tryptophan appears to be synergistic in nature, the values of synergism parameter being greater than unity. The adsorption of inhibitors on mild steel surface obeyed Langmuir’s adsorption isotherm. The calculated thermodynamic parameters for adsorption reveal a strong interaction between the inhibitors and the mild steel surface. The results obtained by electrochemical studies are consistent with the results of the weight loss measurements. L-tryptophan acts more anodic than cathodic inhibitor.