Detecting Delamination in Carbon Fiber Composites Using Piezoresistive Nanocomposites

Carbon fiber prepreg composites are utilized successfully as structural materials for different lightweight aerospace applications. Delamination is a critical failure mode in these composite materials. As composite plies separate from each other, the composite loses some of its ability for supporting expected loads. Therefore, detection of delamination at right time is a foremost significance. This study presents a new way for detecting delamination in composite plates using piezoresistive nanocomposites. This new procedure is setup and studied through both experimental and computational investigations. In this research, nanocomposites with 5% coarse graphene platelets are fabricated for detecting delamination. 8-ply carbon fiber prepreg composite samples are fabricated by placing a Teflon film between layers of prepreg. Piezoresistive nanocomposites are attached on top of prepreg laminate samples using epoxy resin. The change in electrical resistivity of these nanocomposites due to the induced strain from flexural test (three point bend test) on delaminated and neat composite laminates are monitored to demonstrate the delamination detection and neat composite laminates are monitored to demonstrate the delamination detection method. A non-linear finite element model is developed using Abaqus software suite to compliment the mechanical testing. Virtual Crack Closure Technique (VCCT) is used to model a delamination in the composite sample. Experimental results and the simulations in this study indicate that piezoresistive nanocomposites can be used for detecting delamination in carbon fiber composite materials

Kinematics of Inter-Ply Interfaces In Composite Manufacturing

The ubiquitous usage of polymer matrix composites in many applications demands a comprehensive understanding of composite interfaces and processing induced residual stresses, which critically affect both the manufacturing processes and the deformation mechanisms. Processing induced residual stresses are often responsible for causing warping, delamination, and dimensional instability in composite structures. This research includes new in-situ experimental approaches, cure cycle design, interface modification, and thermomechanical modeling for developing a fundamental understanding of the cure kinetics during composite manufacturing. Strains, ply-movement, and formation of defects are observed in-situ using digital image correlation (DIC) during the autoclave cure cycle for the first time. The processing-induced defects in the composite are further characterized by X-ray micro-computed tomography (micro-CT). A non-destructive method is developed to calculate residual stresses using DIC Strains in combination with temperature-dependent moduli obtained from Dynamic Mechanical Analysis (DMA) and Classical Laminate Theory (CLT). Cure cycle design with interrupted cure and interface modification with ZnO nanorods experiments are developed to reduce these processing- induced residual stresses and thereby increase laminate strength. The experimental results are validated through thermomechanical modeling of the composite cure process

COMPARISION OF EFFICACYAND SAFETY OF ORAL LABETALOL AND NIFEDIPINE IN PREECLAMPSIA: A PROSPECTIVE OBSERVATIONAL STUDY

Objective: To compare the efficacy and safety of oral Labetalol and Nifedipine in preeclampsia patients and to aid professionals in making appropriate therapeutic decisions in the management of preeclampsia.Methods: A Prospective observational study with the total of 152 pregnant women with preeclampsia is conducted in a Tertiary Care Hospital in India. Pregnant women with preeclampsia prescribed with either oral labetalol or oral nifedipine were selected. Main outcome measures include monitoring of adverse effects of labetalol and nifedipine and efficacy of both drugs. Blood pressures were measured every 4 hrs using sphygmomanometer and average of three consecutive readings is recorded. The two groups were followed until delivery and are interviewed for any adverse reactions.Results: The duration of days required for labetalol to normalize the high blood pressure is 5 days (5±2.63 d), and that of nifedipine is 7.5 days (7.5±3.83 d) with P value of 0.0015. Common adverse Drug reactions (ADR's) of the both drugs are pedal edema (50%, 47.36%), headache (44.7%, 26.31%), and orthostatic hypotension (9%, 7%) etc are compared.Conclusion: Oral Labetalol is more efficacious than Oral Nifedipine, with an exception of more adverse effects and high cost.Â