Crack formation in unfinished siding of aspen ( Populus tremula L.) and Norway spruce ( Picea abies (L.) Karst.) during accelerated weathering

Abstract

Crack formation is a serious defect that may reduce the lifetime of un®nished wood in service. An accelerated weathering test was carried out to study crack formation of solid wood board specimens of aspen (Populus tremula L.) and Norway spruce (Picea abies (L.) Karst.). The in¯uence of the boards' distance from the pith was also studied. The aspen specimens developed a higher number of cracks than the spruce specimens. However, these cracks were shorter and less injurious than those propagating in spruce wood. It is concluded that a solid wood siding of aspen will show at least as good a performance as spruce regarding crack injuries. For both aspen and spruce, boards taken from near the pith had a lower proportion of long cracks than boards taken further out. This supports the rule that boards with a high proportion of annual rings perpendicular to the surface (the boards near to the pith) have a higher resistance to crack formation than boards with a high proportion of horizontal annual rings.

The effects of incising on the checking of wood: A review

“…Despite these statements, the terms checks and cracks are still used synonymously and current dictionary definitions of cracks are that they are breaks or lines in the surface of a material that has not broken into pieces. This definition of a crack is similar to scientific definitions of a check, which state that a check is a ‘separation of the wood due to seasoning which appears on one surface only’ (Anon 1993), or a ‘crack which does not penetrate wood deeper than 75% of the board thickness’ (Flæte, Høibø, Fjærtoft and Nilsen 2000). The only point of difference between these scientific definitions of checks and popular definitions of cracks is that the former develop as a result of seasoning whereas other factors can presumably cause cracks.…”

Feasibility of Mass Production of Laminated Veneer Lumber (LVL) from Japanese Cedar (Cryptomeria japonica) in Taiwan

“…This resulted in many micro-cracks in the wood cell wall. Flaete et al (2000) indicate that the wood is hygroscopic. The atmospheric water molecules show the wood of shrink and swell, and then the generated stress accelerates the outdoor deterioration of wood.…”

Termiski modificētas lapkoku koksnes dekoratīvās īpašības un to stabilitātes uzlabošana pret vides faktoru iedarbību = Thermally modified hardwood decorative properties and improvement of their resistance to weathering

“…Plaisu veidošanās raksturs ir atkarīgs gan no koku sugas, gan kokmateriālu (dēļu u.c.) izcelsmes vietas koka stumbrā, jo tas lielā mērā ir saistīts ar koksnes anatomisko struktūru, briešanas īpatnībām (Flaete et al, 2000). Turklāt ūdens, uzbriedinot šūnu sieniņas, veicina starojuma iespiešanos apgabalos, kas citādi gaismai nav pieejami (Sudiyani et al, 1999).…”

“…Galvenais virsmas makroskopisko plaisu veidošanos veicinošais faktors ir mitruma maiņas, kuru rezultātā stiepes deformācijas ir lielākas par koksnes elastības robežām (Caba et al, 2007;Flaete et al, 2000). Plaisas koksnes virsmā var veidoties arī tikai ūdens iedarbības rezultātā, bet solārais starojums paātrina un paplašina plaisu veidošanos koksnes virskārtā.…”

“…;Pandey and Khali, 1998;Sudiyani et al, 1999;Temiz et al, 2007). Novecināšanas procesā reizēm tiek iekļauti arī citi faktori -sasaldēšana un atkausēšana, tumsas periodi, pazemināta temperatūra(Flaete et al, 2000;Mitsui and Tsuchikawa, 2005). Pētījumi par mākslīgās novecināšanas iespējamu tuvināšanu dabīgiem apstākļiem turpinās, bet līdz šim nav atrasti mākslīgās novecināšanas testu apstākļi un cikli, kas dotu pietiekoši augstu korelāciju ar dabīgo novecošanos(Tolvaj and Mitsui, 2005;Deflorian et al, 2007).…”