Wood As a Bimodular Material
Keywords:Young's modulus, moisture content, bimodular, mechanical properties, failure mechanisms, modulus of elasticity, tension, compression, fibers
AbstractWood is usually considered to be a material with equal stiffness in tension and compression, but this supposition is not uniformly supported by experimental evidence. On the basis of data in the literature, the authors believe that there is sufficient evidence to conclude that some woods, particularly hardwoods, exhibit bimodular behavior. For the hardwood data analyzed here, the ratio of Young's modulus in tension to Young's modulus in compression (Et/Ec) averaged 1.08 and ranged as high as 1.28. Comparisons with composite materials with known bimodular behavior suggest that fiber displacement around rays (and the resulting fiber curvature) might be one cause of this behavior. Some data also indicate that the equality of the tension and compression moduli may be affected by the moisture content. There are similarities with synthetic fibers which suggest that wood fibers might also be bimodular, but the question of whether bimodular behavior can be ascribed to both undelignified fibers and solid wood remains unanswered.
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