  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 167C slightly improves the flexural modulus and
strength and leads to less statistical variability compared to unmodified
samples. 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 (SENB)
samples was about 47% lower for radial-longitudinal systems and 60% lower for
tangential-longitudinal systems. Similarly, the average Janka hardness in the
tangential, radial, and transverse planes was 8.5%, 3.9%, 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 e.g., those induced in bolted joints and cut outs.
Fracture energy and hardness are also strongly correlated to ballistic
performance.
