Monitoring of adhesive-layer curing in wood-based material using microwaves
2002
Soma, T. (Tokyo Univ. (Japan)) | Shida, S. | Arima, T.
Wood-based materials like plywood, LVL and glulam are jointed together with wood adhesives. Adhesive failures not only decrease the strength of the material, but also compromise the safety of structures where wood-based materials are used as load-bearing members. In this study, microwave attenuation was measured using a free space method as a nondestructive and non-contact method to evaluate adhesive strength and to detect adhesive failure or adhesive unevenness during adhesive curing. The points examined in this report were as follows : (1) the influence of microwave propagation direction in the adhesive layer of wood based materials on microwave attenuation, (2) the relationship between microwave attenuation and adhesive strength during adhesive curing, (3) a determination of the factors which influence microwave attenuation during generation of adhesive strength, and (4) attenuation distribution during adhesive-layer curing. The experimental results were as follows : (1) attenuation during curing changed more when the adhesive layer was parallel to the direction of microwave propagation and the longitudinal direction of wood was parallel to the direction of the electric field of the microwave, (2) a positive correlation between changes of microwave attenuation and adhesive strength was confirmed, (3) microwave attenuation was influenced by the evaporation of volatile components from the adhesive and microwave attenuation indicated adhesive curing indirectly, and (4) in the initial stage of adhesive curing, detection of unevenness in the adhesive-layer would be possible by microwave attenuation measurements, and at each curing time, adhesive strength distribution could be estimated by attenuation changes.
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