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Effects of thermal modification on the flexure properties, fracture energy, and hardness of western hemlock

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Abstract

This study investigates the effect of thermal modification on the flexural properties, transverse fracture energy, and hardness of western hemlock, a material which is finding increasing applications in construction. Flexure tests on specimens featuring longitudinal and transverse grains showed that thermal modification at 167 °C leads to less statistical variability compared to unmodified samples. Additionally, thermal modification leads to a decrease in the transverse flexural strength. On the other hand, the fracture and Janka hardness tests revealed a more pronounced brittleness of the thermally modified samples. In fact, the total mode I fracture energy of modified single-edge notch bending samples was about 47% lower for radial–longitudinal systems and 60% lower for tangential–longitudinal systems. Similarly, the average Janka hardness in the tangential and transverse planes was 8.5% and 9.4% lower in the modified specimens, respectively. The results presented in this work show that thermal modification can have a significant effect on the fracturing behavior of western hemlock and its energy dissipation capabilities. For design, this must be taken into serious consideration as these properties significantly influence the damage tolerance of this wood in the presence of stress concentrations such as those induced in bolted joints and cut outs. Fracture energy and hardness are also strongly correlated to ballistic performance.

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Acknowledgements

This material is based upon work supported by the US Army Engineer Research and Development Center (ERDC) under contract W9132T22C0008. The tests described and the resulting data presented herein, unless otherwise noted, are supported under PE 0603119A, Project BO3 ‘Military Engineering Technology Demonstration (CA),’ Task 'Program Increase—Cross-Laminated Timber and Recycled Carbon Fiber Materials’.

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Authors and Affiliations

  1. William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Guggenheim Hall, Seattle, WA, 98195-2400, USA

    T. Nakagawa, Z. Chen & M. Salviato

  2. Composites Recycling Technology Center (CRTC), 2220 W 18th St, Port Angeles, WA, 98363-1521, USA

    E. Poulin, M. O’Brien, G. Houser & G. Wood

  3. Engineering Research and Development Center (ERDC) Construction and Engineering Research Laboratory (CERL), 2902 Newmark Drive, Champaign, IL, 61822, USA

    T. Rueppel, J. Swinea & P. Stynoski

  4. Department of Civil and Environmental Engineering, Washington State University, 405 Spokane St, Sloan 101, Pullman, WA, 99164-2910, USA

    P. Bahmani

  5. Chickadee Forestry LLC, 2023 E Sims Way #147, Port Townsend, WA, 98368-6905, USA

    M. Weinheimer

Authors
  1. T. Nakagawa
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  2. E. Poulin
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  3. T. Rueppel
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  4. Z. Chen
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  5. J. Swinea
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  6. M. O’Brien
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  7. G. Houser
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  8. G. Wood
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  9. M. Weinheimer
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  10. P. Bahmani
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  11. P. Stynoski
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  12. M. Salviato
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Contributions

TN, ZC, EP, TR, GW, PS, and MS conceived and planned the experiments. TN, ZC, EP, TR, MO, GH, and MW contributed to sample preparation. TN, ZC, EP, and TR carried out the experiments. TN, ZC, EP, TR, and MS performed the analysis of the results. TN, EP, TR, and MS took the lead in writing the manuscript. All authors provided critical feedback and helped shape the research, analysis, and manuscript.

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Correspondence to M. Salviato.

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Nakagawa, T., Poulin, E., Rueppel, T. et al. Effects of thermal modification on the flexure properties, fracture energy, and hardness of western hemlock. Wood Sci Technol 58, 109–133 (2024). https://doi.org/10.1007/s00226-023-01511-4

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