Compression characteristics of birch wood over wide ranges of strain, strain-rate and temperature

The objective of this study is to examine the material behaviour of birch wood (Betula pendula) under high strain- or loading-rates over a wide temperature range with a view to its use in structural- and crash-absorbing components in automotive applications. Birch wood was tested in the longitudinal, radial, and tangential directions under compression using a custom-made Split Hopkinson bar (SHB). Tests on the SHB covered strain rates from 380 s⁻¹ to 1,020 s⁻¹. Results were compared with quasi-static tests at 0.0045 s⁻¹. Temperature levels considered ranged from -40 °C over +20 °C up to +80 °C. The study shows that wood exhibits a significant strain-rate dependent strength increase across all anatomical directions and temperatures tested. The compressive strength exhibited an increase between 19 % and 154 % from quasi-static to high dynamic strain rates (approximately 900 - 1,000 s⁻¹), varying with direction and temperature. The highest strain-rate sensitivity occurred at +80 °C, the lowest at -40 °C. Energy absorption capacity also increased with strain-rate, indicating the potential for lightweight crash-absorbing components across a wide range of temperatures.