Effect of Compression Wood on the Mechanical Properties of White Spruce and Red Pine

Compression wood in Picea glauca (Moench) Voss and Pinus resinosa Ait. lowers the strength (compression parallel to grain, static bending, and toughness) per unit weight of wood. But because of higher density, compression wood is generally stronger than normal wood when density is not considered. Inferior structural organization increases seasoning degrade and reduces toughness. Specimens from seven trees of each species (six with compression wood, one normal) were classified as: Type A – Slight compression wood; Type B – Intermediate compression wood; Type C – Pronounced compression wood. Specimens were tested air dry and green. Specific gravity was determined for all test specimens and correlated with strength values. Mean maximum crushing strength values (psi) were higher for compression wood than for normal wood, disregarding density. When specific gravity was considered, however, compression wood was not superior to normal wood in crushing strength. Further, strength increases from drying are greater in normal wood. Static bending tests showed higher mean moduli of rupture in green specimens with compression wood. When density was considered, the specific strength values for compression wood were definitely lower than those for normal wood, contrasting with crushing strength relationships. Toughness values displayed extremely wide variation and coefficients were far higher than those for the tests above. This was not explained by differences in the specimens. For both species, mean toughness values for green compression wood were significantly higher than for normal wood. Comparisons between some types with normal wood, however were not. Unlike other properties, toughness decreased rather than increased with drying.

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