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Why don’t branches snap? The mechanics of bending failure in three temperate angiosperm trees

Trees volume 26, pages 789–797 (2012)Cite this article

Abstract

Living tree branches are almost impossible to snap. Some show “greenstick fracture”, breaking halfway across before splitting along their length, while others simply buckle. In this study we investigated the bending failure of coppice branches of three temperate angiosperm trees: ash, Fraxinus excelsior; hazel, Corylus avellana; and white willow, Salix alba. We carried out bending tests, and made a series of observations on the structure, density and tensile and compressive strength of their wood to understand the pattern of failure. The three species showed contrasting behaviour; willow buckled whereas ash showed clean greenstick fracture and hazel a more diffuse greenstick fracture. These differences could be related to their wood properties. Willow buckled because its light wood had very low transverse compressive strength, particularly tangentially and was crushed by transverse stresses. Though the other species yielded in longitudinal compression on the concave side, they ultimately failed in tension on the convex side when bent because their higher density wood resisted transverse compression better. However, the crack was diverted down the midline because of the low tangential tensile strength of their wood. Differences in fracture between ash and hazel are related to fine-scale differences in their wood anatomy and mechanics.

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Acknowledgments

This study was supported by the NERC grant NE/F003730/1. We would like to thank Dr Richard Cutting and Dr John Waters of the School of Earth, Atmospheric and Environmental Sciences University of Manchester for use and assistance of the scanning electron microscopes.

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Authors and Affiliations

  1. Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT, UK

    A. van Casteren, W. I. Sellers & A. R. Ennos

  2. School of Biosciences, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

    S. K. S. Thorpe & S. Coward

  3. Musculoskeletal Science Research Group, Institute of Aging and Chronic Disease, Sherrington Buildings, The University of Liverpool, Liverpool, L69 3GE, UK

    R. H. Crompton

Authors
  1. A. van Casteren
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  2. W. I. Sellers
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  3. S. K. S. Thorpe
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  4. S. Coward
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  5. R. H. Crompton
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  6. A. R. Ennos
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Corresponding author

Correspondence to A. R. Ennos.

Additional information

Communicated by R. Matyssek.

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van Casteren, A., Sellers, W.I., Thorpe, S.K.S. et al. Why don’t branches snap? The mechanics of bending failure in three temperate angiosperm trees. Trees 26, 789–797 (2012). https://doi.org/10.1007/s00468-011-0650-y

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  • DOI: https://doi.org/10.1007/s00468-011-0650-y

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