Acoustic Monitoring of Cold-Setting Adhesive Curing in Wood Laminates: Effect of Clamping Pressure and Detection of Defective Bonds

Authors

  • Jacek M. Biernacki
  • Frank C. Beall

Keywords:

Ultrasonics, acousto-ultrasonics, adhesion, adhesives, laminates, glulam

Abstract

Many variables affecting adhesive bonding of wood, including moisture content, temperature, surface roughness and contamination, and wood density, are difficult to control and/or measure in industrial conditions. However, the combined effect of these factors may be compensated by controlling process variables, such as clamping pressure and time, and adhesive viscosity, concentration, and spread. This research project investigated an ultrasonic method as a nondestructive means of monitoring bonding processes and assessing the quality of the cured bonds in wood laminates. Monitoring was performed simultaneously at normal and angular (5° nominal) incidence to the bond plane, using pairs of clear Douglas-fir laminates with a single bond line. It was previously reported that ultrasonic transmission is sensitive to curing phases, such as spreading, penetration, curing, and bond thickness. This paper reports the effect of bond defects (uncured, underspread, and uneven spread) and clamping pressure on ultrasonic transmission. The results showed that defective bonds can be detected using patterns of relative attenuation changes during curing and an "unloading effect," measured as the relative transmission reduction after the clamping load is released. Also, transmission through uncured bond lines was strongly affected by pressure, an observation that can be utilized to select optimum clamping pressure.

References

Beall, F. C., and J. M. Biernacki. 1993. Monitoring the adhesive curing process for parallel wood laminates. Proc. Second International Conference on Acousto-Ul-trasonics. Atlanta, GA. The American Society for Nondestructive Testing, Inc. Pp. 163-169.nBiernacki, J. M., and F. C. Beall. 1993. Evaluation of the quality of adhesive bonding in parallel wood laminates. Proc. Second International Conference on Acous-to-Ultrasonics. Atlanta, GA. The American Society for Nondestructive Testing, Inc. Pp. 171-179.nBiernacki, J. M., and F. C. Beall. 1996. Acoustic monitoring of coldsetting adhesive curing in wood laminates. Int. J. Adhesion Adhesives (In press).nHouwink, R., and G. Salomon, (eds). 1965. Adhesion and adhesives. Vol 1. Adhesives. Elsevier Publishing Company, Amsterdam, Netherlands. 548 pp.nNagy, P. B. 1992. Ultrasonic classification of imperfect interfaces. J. Nondestr. Eval. 7:127-139.nReis, H. L. M. 1989. Non-destructive evaluation of adhesive bond strength in laminated wood beams. Brit. J. Non-Destr. Test. 31(12):675-679.nReis, H. L. M., F. C. Beall, J. V. Carnahan, M. J. Chica, K. A. Miller, and V. M. Klick. 1990. Nondestructive evaluation/characterization of adhesive bonded connections in wood structures. Pages 197-207 in H. L. M. dos Reis, ed. Nondestructive testing and evaluation for manufacturing and construction. Hemisphere Publishing Co., NY.n

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Published

2007-06-19

Issue

Number 1 / January 1996

Section

Research Contributions

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