Лако-красочные материалы — производство

Lei and Wilson [35,67] developed a model for the fracture toughness (KIc) of flakeboards bonded with PF resin adhesive. The model is based on the initial crack length (a) in the specimen, the average size of the inherent flaw (O) in the solid wood, the expected increase in crack length resulting from nonbonded interflake cracks and voids (Aa), and the K1c value of the wood used to make the flakes:

K = K, y°-™———— ^(a/W)—————

(a + 8af5 Y [(a + A a)/W

Other factors are the compliance (Y) for the specimen geometry, the board width (W), and the average length of the cracks or voids in the flakeboard (1/m). The experiment revealed that the KIc value of the flakeboard was the same as the KIc value of solid wood when the average crack length was equal to 2.5 mm, the same value as determined by Schniewind and Lyon [32] for solid Douglas-fir. Another study [35] showed that the solid wood density and the compaction ratio of the flakeboard also affect the average crack length and thus the fracture toughness of the flakeboard. The lengths of nonbonded voids and interflake crack decreased as the compaction ratio increased up to a board density of 780 kg/m3. Mechanical damage to the flakes at a higher compaction ratio lowered fracture toughness.