Application of a laser measurement method in measuring the modulus of elasticity in tension parallel to grain of Cryptomeria japonica D.Don structural lumber

The objective of this paper is to introduce a laser measurement method to obtain the modulus of elasticity(MOE) in tension parallel to grain of structural lumber.Fifty-six pieces of Cryptomeria japonica D.Don plantation lumber(110 mm×55 mm×2 500 mm),dried at 90℃ temperature in kiln for 120 days,were selected as the testing specimens.After adjusting the moisture content to 15%,the dynamic MOE(E_fr) of all pieces was measured based on longitudinal vibration in fundamental frequency(FFT).A laser measurement system consisting of laser meter for tensile deformation,data logger and computer analyzer was then applied to measure tension MOE(σ_t) of lumber.Meanwhile,tension strength(σ_t) of lumber was obtained when pieces were in failure at maximum load.The results indicated that the average σ_t was 7.8%(0.63 GPa) less than E_fr.Statistical linear regression analyses revealed that useful relationship was evident among σ_t,E_fr and σ_t(P<0.001).The correlation coefficient was 0.971 between σ_t and E_fr,and 0.727 between σ_t and σ_t.The tensile testing results demonstrated that the laser measurement method could be used to obtain precise tensile deformation for reliable MOE in tension parallel to grain of structural lumber.