Abstract:

Abstract: Combining diametrical planks and strain gauge method,the radial distribution of ILRS (internal longitudinal residual strain) of Eucalyptus urophylla×E. grandis plantation logs was measured. Results showed that radial distribution of ILRS was symmetrical across the diameter. From the bark to pith,the largest tensile strain was near the bark,to the pith direction,tensile strain absolute value declined and turned zero at certain radius,after that tensile strain changed into compressive strain which presented obvious increasing tendency to the pith direction. The regression equation of radial distribution of ILRS was y=-21.075x²+4.529 7x+890.75,significantly correlated below 0.01 level (correlation coefficient was 0.87). Tree radius of crossover point from tensile strain to compressive strain was 0.618R. Radial distribution pattern of ILRS at different heights was similar,regression curve was significantly correlated below 0.01 level,but the correlation coefficient decreased with log height increasing. Radial distribution changing gradient of ILRS was greatly affected by log diameter; the curve of the smaller tree was much steeper. A new viewpoint was advanced in this study,namely there was a critical value for log stem diameter which had relation to radial distribution changing gradient of ILRS. When log stem diameter is less than the critical value,the gradient of ILRS will augment evidently with log stem diameter decreasing. The critical value is 19.9 cm for Eucalyptus urophylla × E. grandis plantation wood in this study.

Key words: Key words:Eucalyptus urophylla ×, E. grandis plantation;radial distribution of internal longitudinal residual strain;diametrical planks;strain gauge method