The mixed mode fracture failure of eastern red spruce (Picea rubens) was investigated by means of single edge notch and center crack specimens with various crack inclinations in the tangential-longitudinal plane with prop agation in the longitudinal direction (i.e., TL system of crack propagation). These results demonstrate there is a definite interaction between failure stress inten sity factors KI and KII during the mixed mode fracture of wood. These mixed mode data were supplemented by the fracture toughness (KIC) and pure mode II critical stress intensity factor (KIIC). Several mixed mode fracture failure cri teria were compared. The criterion that could not be rejected is KI/KIC + (K 2 II/ KIIC) = 1.

The phenomenon of tack has been studied in urethan—urea elastomers prepared from polyether or polyester prepolymers and 4,4′-methylenebis(2-chloroaniline). It is shown that tack at zero elongation is attained only in polymers in which the flexible chains, i.e., polyesters or polyethers, contain 50 chain links or more. This coincides with the requirements for the Gaussian vector function in elastomers. The results suggest that, in the absence of flexible chain ends in these polymers, tack is solely contributed by the flexible segments along the polymer chains, while the rigid blocks in the chains do not participate in the formation of tack.

Red spruce (Picearubens Sarg.) near Princeton, Maine, U.S.A. fertilized with 168 kg N/h in 1970 increased in volume growth by nearly 50% over pretreatment rates during the 8-year posttreatment period; specific gravity was not affected. Average pulp yield per unit weight of posttreatment wood from fertilized trees was 1.9% greater than average yield from pretreatment wood, but rejects increased by 2.2% and kappa number by 17.7 mL. Average pulp yield per unit weight of posttreatment wood from unfertilized trees was 1.2% less than from pretreatment wood; rejects were 0.4% less and kappa number 2.6 mL higher. Fertilization increased the lignin content of posttreatment wood by about 3% and the resin content by 2%. Ash content also increased after fertilization.

synopsisThe phenomenon of tack has been studied in urethane-urea elastomers prepared from polyether or polyester prepolymers and 4,4'-methylenebis( 2-chloroaniline). It is shown that tack at zero elongation is attained only in polymers in which the flexible chains, i.e., polyesters or polyethers, contain 50 chain links or more. This coincides with the requirements for the Gaussian vector function in elastomers. The results suggest that, in the absence of flexible chain ends in these polymers, tack is solely contributed by the flexible segments along the polymer chains, while the rigid blocks in the chains do not participate in the formation of tack.