Nondestructive evaluation of helicopter rotor blades using guided Lamb modes

This paper presents an application for turning and direct modes in a complex composite laminate structure. The propagation and interaction of turning modes and fundamental Lamb modes are investigated in the skin, spar and web sections of a helicopter rotor blade. Finite element models were used to understand the various mode conversions at geometric discontinuities such as web-spar joints. Experimental investigation was carried out with the help of air coupled ultrasonic transducers. The turning and direct modes were confirmed with the help of particle displacements and velocities. Experimental B-Scans were performed on damaged and undamaged samples for qualitative and quantitative assessment of the structure. A strong correlation between the numerical and experimental results was observed and reported.     

Synthesis and Characterization of Cardo Polysulfonates of 1,1′-Bis(4-Hydroxy Phenyl)Cyclohexane with 1,3-Benzene and 2,4-Toluene Disulfonyl Chlorides

Abstract

Cardo polysulfonates (PSBCB and PSBCT) of 1,1′-bis(4-hydroxy phenyl)cyclohexane with benzene-1,3 and toluene-2,4-disulfonyl chlorides have been synthesized by interfacial polycondensation of 1,1′-bis(4-hydroxy phenyl)cyclohexane (0.005 mol) with benzene-1,3/toluene-2,4-disulfonyl chlorides (0.005 mol) using water-chloroform (4:1, v/v) as interphase, alkali (0.015 mol) as acid acceptor, and cetyl trimethyl ammonium bromide (0.125 g) as emulsifier at 0°C for 3 hours. The structures of the polymers were supported by IR and NMR spectral data. The PSBCT was fractionated into several fractions by using 1,2-dichloroethane as solvent and n-butanol as precipitant. The fractions were characterized by GPC and viscometry in different solvents at four different temperatures. Viscosity studies showed that the PSBCT is flexible in solutions and has a specific solvent effect. PSBCB and PSBCT have good biological activity against E. coli and S. citrus organisms, and they possess excellent hydrolytic stability toward acids and alkalis.