Comparative study on knot characteristics and physical and mechanical properties of Chinese fir wood of different strains and ages

To explore the difference of knot characteristics and physical and mechanical properties of Chinese fir wood in different strains and ages, so as to provide scientific basis for screening out non-saving strains of Chinese fir wood suitable for production promotion.

6-year-old and 30-year-old Luotian Chinese fir and yellow Chinese fir plantations of different strains and ages were examined. The average standard wood method was employed for felling and biomass determination. The fallen wood segments were processed into plates, and the joint characteristics as well as the physical and mechanical properties of the wood were ascertained. The disparities of knot characteristics and the physical and mechanical properties of the wood among different strains of Chinese fir plantations were compared.

There were differences in the knot characteristics of different strains of Chinese fir at the same age. The knot volume of Luotian Chinese fir is significantly smaller than that of yellow Chinese fir, and the proportion of no knot is significantly larger than that of yellow Chinese fir. The knot characteristics of Chinese fir at different ages of the same strain were different. The knot volume of 6-year-old Luotian Chinese fir and yellow Chinese fir was significantly lower than that of 30-year-old Chinese fir, and the proportion of no-knot wood was significantly higher than that of 30-year-old Chinese fir. There are differences in physical and mechanical properties of different strains of Chinese fir wood at the same age. The wood density, compressive strength and tensile strength of Luotian fir were significantly higher than those of yellow fir. There are differences in physical and mechanical properties of Chinese fir wood at different ages of the same strain. The total dry density, longitudinal tensile strength, flexure strength and flexure elastic modulus of 6-year old Luotian Chinese fir were significantly lower than those of 30-year old Luotian Chinese fir. There is a correlation between the knot characteristics of Chinese fir and the physical and mechanical properties of wood. The knot radius and knot volume of Chinese fir at the same age are significantly negatively correlated with wood density, compressive strength, tensile strength and bending strength. In Chinese fir wood of the same age stage, knot radius and knot volume exhibited highly significant or significant negative correlations with wood air-dry density, oven-dry density, compressive strength parallel to grain, tensile strength parallel to grain, and bending strength. The Kontfree proportion showed highly significant or significant positive correlations with air-dry density, oven-dry density, and compressive strength parallel to grain.

The knot characteristics and physical and mechanical properties of Chinese fir were different in different strains and ages, and the knot characteristics of Chinese fir were correlated with the physical and mechanical properties of wood.