Mechanical Behavior of Separated Earlywood and Latewood of Douglas–Fir Using Digital Image Correlation Method

To clarify the mechanical behaviour differences between earlywood and latewood, separated the early- wood and the latewood specimens loaded to the rupture with tensile load parallel to the grain. The separated test specimens for tensile test were prepared from douglas fir (Pseudotsuga menziesii) and stress-strain relation was evaluated by optical measurement system using the Digital Image Correlation (DIC), which can visualize strain during the tensile test. The results are summarized as follows: The estimated strain data by universal testing machine show good accordance with that estimated by DIC. There was a difference in the fracture pattern of the earlywood and the latewood of douglas fir that the surface of ruptured earlywood typically simple while that of was somewhat complicate. The longitudinal tensile strength of earlywood specimens of douglas fir at wood height from ground 12.8 m, 9.8 m, 6.7 m and 0.9 m were 51 MPa, 69 MPa, 110 MPa and 114 MPa, while those of latewood were 208 MPa, 234 MPa, 247 MPa and 198 MPa. Elastic modulus in the longitudinal tensile of earlywood speci- mens of douglas fir at wood height from ground 12.8 m, 9.8 m, 6.7 m and 0.9 m were 5458 MPa, 7202 MPa, 9705 MPa and 8761 MPa, while those of latewood were 13747 MPa, 19405 MPa, 17365 MPa and 14044 MPa.