Ultrasonic measurements related to evolution of structure in curing epoxy resins

Abstract

The tracking of the cure of epoxy adhesives and the assessment of the cure state of adhesive bondlines joining engineering components are important for quality assurance during manufacture and for the safe functioning of manufactured assemblies in the field. Ultrasound can be used to give estimates of the compression modulus of curing and cured materials and thereby provide a means to assess non-destructively the cure state of adhered joints during manufacture and in service. These techniques are at present difficult to apply and are predominantly empirical in that little is known about the relationships between the measured ultrasound data and the evolving molecular structure of the adhesive as it cures. The present paper describes the application of a group of physical techniques that can be used to characterise the polymer structure during cure, with the aim of relating these to phenomena measurable by ultrasound. Wide angle X-ray scattering (WAXS) provides a basic measure of polymer chain formation, which is seen to correlate closely with the compression modulus as it develops during cure. Low resolution nuclear magnetic resonance (NMR) provides a means to observe the mobility of bound hydrogen nuclei and thereby to track the change in state of a resinhardener system from a viscous liquid to a crosslinked solid. The NMR data obtained during cure correlated well with compression modulus development. Ultrasonic shear wave spectrometry indicates when a curing material can first support shear motions and this agrees well with NMR data and with specifications of gel point given by manufacturers. Ultrasonic compression wave absorption data provide frequency dependent patterns that change during the cure cycle and that can be explained on the basis of the results of the WAXS, NMR, and shear wave experiments. These changing patterns have potential for tracking cure using low cost ultrasonic techniques, the results of which can be related to phenomena taking place on a molecular scale.PRC/1575

Non-destructive evaluation (NDE) of composites: using ultrasound to monitor the curing of composites

“…Krautkraemer and Krautkraemer [11]), including the study of the curing process [12]. Fundamental work was undertaken by Alig and coworkers [13][14][15][16][17][18][19], and Challis et al [20][21][22][23][24]. A good overview on methods for cure monitoring including ultrasound is given in Lodeiro and Mulligan [25].…”

Ultrasonic broadband characterization of a viscous liquid: Methods and perturbation factors

“…The measurements of velocity and attenuation dispersions are the most important factors in the monitoring of several properties such as ageing of a structure [1], viscoelastic behavior [2], polymer cure [3][4][5][6][7][8][9][10] and porosity characterization [11]. Reproducibility at normal incidence and temperature sensitivity has an important effect on dispersion acoustic parameters.…”

Ultrasonic Assessment of Thermoset Cure: Variations in the Macromolecular Structure Due to Variations in Thickness

“…Currently a number of techniques can be used to study the cure reaction within a laboratory environment. Differential scanning calorimetry (DSC) [1], dielectric spectroscopy [2], nuclear magnetic resonance (NMR) [3], wide angle X-ray scattering (WAXS) [4] and ultrasonic spectroscopy [5] have all been used. However, arguably only the ultrasonic and dielectric techniques have the potential to be developed for cure monitoring in an industrial environment.…”