Near-plane-wave acoustic propagation measurements in thin layers of adhesive polymer

Abstract

This paper presents a novel wide bandwidth pulse transmission technique for the study of the interactions between near-plane-wave ultrasound and thin films (down to 50 pm) of adhesive polymer set between glass substrates. Acoustically thick transducers are clamped in coaxial alignment on either side of.the glass substrates and short (less than 10 ns) acoustic transients are made to reverberate to and fro in the test bond. The signal received consists of time-resolvable and successively dispersed reverberations from the bond layer. It is digitized at 1 GHz and approximately corrected for the effects of transducer insertion and transient radiation coupling between the transducers. Frequency domain methods are then applied to estimate absorption coefficient, propagation velocity and the real and imaginary parts of the plane-wave elastic modulus, all as functions of frequency. Prelimary data obtained by this technique indicate that a number of adhesives display plane-wave velocity dispersion and absorption as a function of frequency that can be modelled by a relaxation process with a single time constant. A simple spring-dashpot model lor an anelastic Solid provides a mechanistic equivalent to the observed relaxation.

Determination of Shrinkage and Modulus Development of Thermosetting Resins

“…Ultrasonic techniques have been used to monitor the development of modulus. In 1991, Challis et al [10] used ultrasonics to measure the modulus of an adhesive polymer layer as a function of frequency. They placed the adhesive layer between two glass blocks and coupled the ultrasonic transducers (UT's) to the surface of the glass blocks using compressed aluminium foil.…”

Epoxy Cure Observed by Ultrasound, NMR and WAXS

“…However Figure 2 shows at 4 MHz the CW absorption, the SW absorption, the SW propagation velocity, and the CW propagation velocity as functions of time during cure for a similar adhesive. For comparison with W AXS and NMR measurements we have so far used an earlier technique [2] to measure CW propagation velocity during cure, and this result is shown in Figure If Figure 2 shows that CW absorption rises in the early stages of cure and then falls just before shear waves are observable; the CW velocity profile is similar to that shown on Figure If. We now relate these observations to the cure process.…”

“…The rationale was that ultrasonic compression wave (CW) measurements on curing epoxy were relatively easy [1,2], and that increases in CW propagation velocity during cure corresponded to the development of mechanical moduli, given only small changes in the density of the adhesive during cure. Of interest was the way in which CW measurements relate to the evolving chemistry and structure in the adhesive, how they relate to the development of shear strength, and whether CW absorption measurements could be useful in tracking the cure cycle.…”

Ultrasonic Measurement of Cylindrical Roller Bearing Lubrication Using High Pulse Repletion Rates

“…Based on isothermal line contact elastohydrodynamic lubrication theory, the minimum film thickness between the roller and the outer ring can be given by Dowson's equation [18] h min ¼ 2:65a 0:54 g 0 u ð Þ 0:7 E 0À0:03 R 0:43 x ðQ=lÞ À0:13 (6) where a is the viscosity-pressure coefficient, u is the entrainment velocity, g 0 is the ambient viscosity, E 0 is the reduced elastic modulus, and R x is equivalent curvature radius of the outer raceway.…”

“…Optical methods need translucent materials so they are rarely used outside the laboratory [4,5]. Compared with the methods mentioned above, the ultrasound method [6][7][8] removes the requirement of electrical isolation and transparency. The reflection coefficient of longitudinal ultrasonic waves has been shown to be highly sensitive to the lubricant-film thickness [9].…”