Partial compression strength of sugi (Japanese cedar, Cryptomeria japonica) wood near the pith perpendicular to the grain

It was reported that sugi (Japanese cedar, Cryptomeria japonica) boards with pith had a greater partial compression strength perpendicular to the grain (sigma(e)) than sugi boards without pith. However, the reason for the superior strength of sugi boards with pith remains unclear. In this study, as the first step to elucidate the reason, we report the effects of loading direction (tangential and radial), density, microfibril angle (MFA) of earlywood and latewood tracheids, latewood tracheid length and cross-sectional parameters of earlywood tracheids (CE) on sigma(e) in sugi wood. There was no significant effect of loading direction on sigma(e), and the specimens with pith had significantly larger sigma(e) values than the specimens without pith. A larger density, larger MFA, and smaller cross-sectional dimensions with a square shape in earlywood tracheids significantly increased sigma(e) in the radial loading direction. By multiple linear regression, it was recognized that density and MFA was the effective parameters, and MFA had a larger effect than did density in the predictor equation for sigma(e). This is the first study that reported the positive effects of MFA on sigma(e) in sugi wood.