In this paper, the effects of various properties of adherend on the impact shear strength are investigated.
The correlation between the impact shear strength and specific gravity, pH value or wettability was determined. Also the correlation between wettability measured by three methods and specific gravity or pH value was determined.
As experimental materials, 15 species from the temperate zone and 11 speceis from the tropical zone were used. These woods were glued with urea-formaldehyde resin adhesive and the glued woods were tested for the impact shear according to ASTM D 950-54. The wettability for each wood was determined by the method of capillary rise, inclined plate and droplet.
The coefficient of correlations for each case was calculated from experimental results. Then the regression line was yielded by regression analysis only when the significant correlation at the five percent level or better was recognized. If the correlation was not significant, it was either not present or a horizontal line was drawn through the mean value. The results analysis were presented in Figures 1-5.
The following conclusions may be drawn from the results of analysis :
(1) The impact shear strength increased along with the increasing of specific gravity or the decreasing of pH value in the temperate woods. In the tropical woods, the correlation between the impact shear strength and specific gravity or pH value was not significant.
(2) In the tropical woods, the correlation between the impact shear strength and wettability was significant in the case of the inclined plate method, therefore, the impact shear strength increased along with the increasing of cosine of contact angle.
(3) In the impact shear test of glued wood, the impact shear strength affects mainly the properties (thickness, brittleness, degree of cure etc.) of glue line, while the effects of adherend are slight.
(4) In many cases, the wettability decreased along with the increasing of specific gravity. For the temperate woods, the wettability when determined by method of capillary rise and droplet decreased along with the dereasing of pH value.